Classifications

• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
  • H01J35/00—X-ray tubes
  • H01J35/02—Details
  • H01J35/04—Electrodes ; Mutual position thereof; Constructional adaptations therefor
  • H01J35/08—Anodes; Anti cathodes
  • H01J35/10—Rotary anodes; Arrangements for rotating anodes; Cooling rotary anodes
  • H01J35/105—Cooling of rotating anodes, e.g. heat emitting layers or structures
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
  • H01J2235/00—X-ray tubes
  • H01J2235/08—Targets (anodes) and X-ray converters
  • H01J2235/083—Bonding or fixing with the support or substrate
  • H01J2235/084—Target-substrate interlayers or structures, e.g. to control or prevent diffusion or improve adhesion
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
  • H01J2235/00—X-ray tubes
  • H01J2235/08—Targets (anodes) and X-ray converters
  • H01J2235/086—Target geometry

Definitions

• the embodiments disclosed herein relate to high-brightness sources of x-rays. Such high brightness sources may be useful for a variety of applications in which x-rays are employed, including manufacturing inspection, metrology, crystallography, structure and composition analysis and medical imaging and diagnostic systems. BACKGROUND
• FIG. 1 An example of the simplest x-ray source, a transmission x-ray source 08, is illustrated in FIG. 1
• the source comprises a vacuum environment (typically 10 "6 torr or better) commonly provided by a sealed vacuum tube 02 or active pumping, manufactured with sealed electrical leads 21 and 22 that pass from the negative and positive terminals of a high voltage source 10 outside the tube to the various elements inside the vacuum tube 02.
• the source 08 will typically comprise mounts 03 which secure the vacuum tube 02 in a housing 05, and the housing 05 may additionally comprise shielding material, such as lead, to prevent x-rays from being radiated by the source 08 in unwanted directions.
• an emitter 1 1 connected through the lead 21 to the high voltage source 10 serves as a cathode and generates a beam of electrons 1 1 1 , often by running a current through a filament.
• the target 01 is electrically connected to the opposite high voltage lead 22 to be at low voltage, thus serving as an anode.
• the emitted electrons 1 1 1 accelerate towards the target 01 and collide with it at high energy, with the energy of the electrons determined by the magnitude of the accelerating voltage.
• the collision of the electrons 1 1 1 into the solid target 01 induces several effects, including the emission of x-rays 888, some of which exit the vacuum tube 02 through a window 04 designed to transmit x-rays.
• the target 01 is deposited or mounted directly on the window 04 and the window 04 forms a portion of the wall of the vacuum chamber.
• the target may be formed as an integral part of the window 04 itself.
• FIG. 2 Another example of a common x-ray source design is the reflection x-ray source 80, is illustrated in FIG. 2.
• the source comprises a vacuum environment (typically 10 "6 torr or better) commonly maintained by a sealed vacuum tube 20 or active pumping, and manufactured with sealed electrical leads 21 and 22 that pass from the negative and positive terminals of a high voltage source 10 outside the tube to the various elements inside the vacuum tube 20.
• the source 80 will typically comprise mounts 30 which secure the vacuum rube 20 in a housing 50, and the housing 50 may additionally comprise shielding material, such as lead, to prevent x-rays from being radiated by the source 80 in unwanted directions.
• an emitter 1 1 connected through the lead 21 to the high voltage source 10 serves as a cathode and generates a beam of electrons 11 1 , often by running a current through a filament.
• a target 100 supported by a target substrate 1 10 is electrically connected to the opposite high voltage lead 22 and target support 32 to be at low voltage, thus serving as an anode.
• the electrons 1 1 1 accelerate towards the target 100 and collide with it at high energy, with the energy of the electrons determined by the magnitude of the accelerating voltage.
• the collision of the electrons 1 1 1 into the target 100 induces several effects, including the emission of x-rays, some of which exit the vacuum tube 20 and are transmitted through a window 40 that is transparent to x-rays.
• the target 100 and substrate 1 10 may be integrated or comprise a solid block of the same material, such as copper (Cu).
• electron optics electrostatic or electromagnetic lenses
• the path of the electrons may be forming a more concentrated, focused beam at the target.
• electron sources comprising multiple emitters may be provided to provide a larger, distributed source of electrons.
• the electrons collide with a target 100 they can interact in several ways. These are illustrated in FIG. 3.
• the electrons in the electron beam 1 1 1 collide with the target 100 at its surface 102, and the electrons that pass through the surface transfer their energy into the target 100 in an interaction volume 200, generally defined by the incident electron beam footprint (area) times the electron penetration depth.
• the interaction volume 200 is typically "pear" or “teardrop” shaped in three dimensions, and symmetric around the electron propagation direction.
• the interaction volume will be represented by the convolution of this "teardrop" shape with the lateral beam intensity profile.
• the penetration depth is much larger than for a material with greater density, such as most elements used for x-ray generation.
• electron energy may simply be converted into heat. Some absorbed energy may excite the generation of secondary electrons, typically detected from a region 221 located near the surface, while some electrons may also be backscattered, which, due to their higher energy, can be detected from a somewhat larger region 231.
• x-rays 888 are generated and radiated outward in all directions.
• the x-ray emission can have a complex energy spectrum. As the electrons penetrate the material, they decelerate and lose energy, and therefore different parts of the interaction volume 200 produce x-rays with different properties.
• the broad spectrum x-ray emission 388 arises from electrons that were diverted from their initial trajectory, depending on how close they pass to various nuclei and other electrons.
• the reduction in electron energy and the change momentum associated with the change in direction generate the radiation of x-rays.
• the change in energy is a continuum, and therefore, the energy of the generated x-rays also is a continuum.
• These continuum x-rays 388 are generated throughout the interaction volume, shown in FIG. 3 as the largest shaded portion 288 of the interaction volume 200.
• the bremsstrahlung x-rays 888 are typically emitted isotropically, i.e. with little variation in intensity with emission direction [see, for example, D. Gonzales, B. Cavness, and S. Williams, "Angular distribution of thick-target bremsstrahlung produced by electrons with initial energies ranging from 10 to 20 keV incident on Ag", Phys. Rev. A, vol. 84, 052726 (201 1)], higher energy excitation can have increased emission normal to the electron beam, i.e. at "0 degrees" for an incident beam at 90 degrees with respect to the target surface.
• the x-ray source 08 or 80 will typically have a window 04 or 40.
• This window 04 or 40 may additionally comprise a filter, such as a sheet or layer of aluminum, that attenuates the low energy x-rays, producing the modified energy spectrum 488 shown in FIG. 4.
• an electron of 100 keV may ionize a
• the x-ray photon has an energy equal to the energy difference between these two levels, or
• ⁇ ] 67.2 keV.
• Splittings can occur in the various levels, giving rise to slight variations in energy, e.g. ⁇ ⁇ 1 , ⁇ 2 , ⁇ 3 etc.
• the emission is generally called “characteristic lines", since they are a characteristic of the particular material.
• the sharp lines 988 in the example of an x-ray emission spectrum shown in FIG. 4 are “characteristic lines” for tungsten.
• Individual characteristic lines can be quite bright, and may be monochromatized with an appropriate filter or crystal monochromator where a monochromatic source is desired.
• the relative x-ray intensity (flux) ratio of the characteristic line(s) to the bremsstrahlung radiation depends on the element and the incident electron energy, and can vary substantially. In general, a maximum ratio for a given target material is obtained when the incident electron energy is
• these characteristic x-rays 388 are primarily generated in a fraction of the electron penetration depth, shown as the second largest shaded portion 248 of the interaction volume 200.
• the relative depth is influenced in part by the energy of the electrons 1 11, which typically falls off with increasing depth. If the electron energy does not exceed the binding energy for electrons within the target, no characteristic x-rays will be emitted at all. The greatest emission of characteristic lines may occur under bombardment with electrons having three to five times the energy of the emitted characteristic x-ray photons. Because these characteristic x-rays result from atomic emission between electron shells, the emission will generally be entirely isotropic.
• the actual dimensions of this interaction volume 200 may vary, depending on the energy and angle of incidence of the electrons, the surface topography and other properties (including local charge density), and the density and atomic composition of the target material.
• the composition of the target material is selected to provide x-ray spectra with ideal characteristics for a specific application, such as strong characteristic lines at particular wavelengths of interest, or bremsstrahlung radiation over a desired bandwidth.
• Control of the x-ray emission properties of a source may be governed by the selection of an electron energy (typically changed by varying the accelerating voltage), x-ray target material selection, and by the geometry of x-ray collection from the target.
• the x-rays may be emitted isotropically, as was illustrated in
• FIG. 3 only the x-ray emission 888 within a small solid angle in the direction of window 440 in the source, as shown in FIG. 5, will be collected.
• the x-ray brightness (also called “brilliance” by some), defined as the number of x-ray photons per second per solid angle in mrad 2 per area of the x-ray source in mm 2 (some measures may also include a bandwidth window of 0.1 % in the definition), is an important figure-of-merit for a source, as it relates to obtaining good signal-to- noise ratios for downstream applications.
• the brightness can be increased by adjusting the geometric factors to maximize the collected x-rays.
• the surface of the target 100 in a reflection x-ray source is generally mounted at an angle 0 (as was also shown in FIG. 2) and bombarded by a distributed electron beam 1 1 1.
• the five spots are more spread out and brightness is reduced, while for low angle ⁇ , the five source spots appear to be closer together, thus emitting more x-rays into the same solid angle and resulting in an increased brightness.
• the effective source area is the projected area viewed along the direction along which x-ray are collected for use, i.e. along the axis of the x-ray beam. Because of the limited electron penetration depth, the effective source area for an incident electron beam with a size comparable or larger than the electron penetration depth is dependent on the angle between the axis of the x-ray beam and the surface of the target, referred to as the "take-off angle".
• Another way to increase the brightness of the x-ray source for bremsstrahlung radiation is to use a target material with a higher atomic number Z, as efficiency of x-ray production for bremsstrahlung radiation scales with increasingly higher atomic number materials.
• the x-ray emitting material should ideally have good thermal properties, such as a high melting point and high thermal conductivity, in order to allow higher electron power loading on the source to increase x-ray production.
• FIG. 6A a cross-section is shown for a rotating anode x-ray source 580 comprising a target anode 500 that typically rotates between 3,300 and 10,000 rpm.
• the target anode 500 is connected by a shaft 530 to a rotor 520 supported by conducting bearings 524 that connect, through its mount 522, to the lead 22 and the positive terminal of the high voltage supply 10.
• the rotation of the rotor 520, shaft 530 and anode 500, all within the vacuum chamber 20, is typically driven inductively by stator windings 525 mounted outside the vacuum.
• the surface of the target anode 500 is shown in more detail in FIG. 6B.
• the edge 510 of the rotating target anode 500 is sometimes beveled at an angle, and the source of the electron beam 51 1 is in a position to direct the electron beam onto the beveled edge 510 of the target anode 500, generating x-rays 888 from a target spot 501.
• the target spot 501 generates x-rays, it heats up, but as the target anode 500 rotates, the heated spot moves away from the target spot 501, and the electron beam 51 1 now irradiates a cooler portion of the target anode 500.
• the hot spot has the time of one rotation to cool before becoming heated again when it passes through the hot spot 501.
• x-rays are generated from a fixed single spot, while the total area of the target illuminated by the electron beam is substantially larger than the electron beam spot, effectively spreading the electron energy deposition over a larger area (and volume).
• Another approach to mitigating heat is to use a target with a thin layer of target x-ray material deposited onto a substrate with high heat conduction. Because the interaction volume is thin, for electrons with energies up to 100 keV the target material itself need not be thicker than a few microns, and can be deposited onto a substrate, such as diamond, sapphire or graphite that conducts the heat away quickly.
• diamond is a very poor electrical conductor, so the design of any anode fabricated on a diamond substrate must still provide an electrical connection between the target material of the anode and the positive terminal of the high voltage.
• Diamond mounted anodes for x-ray sources have been described by, for example, K. Upadhya et al. US Patent 4,972,449;
• the substrate may also comprise channels for a coolant, for example liquids such as water or ethylene glycol, or a gas such as hydrogen or helium, that remove heat from the substrate [see, for example, Paul E. Larson, US Patent 5,602,899]
• a coolant for example liquids such as water or ethylene glycol, or a gas such as hydrogen or helium, that remove heat from the substrate
• a coolant for example liquids such as water or ethylene glycol, or a gas such as hydrogen or helium
• the substrate may in turn be mounted to a heat sink comprising copper or some other material chosen for its thermally conducting properties.
• the heat sink may also comprise channels for a coolant, to transport the heat away [See, for example, Edward J. Morton, US Patent 8,094,784].
• thermoelectric coolers or cryogenic systems have been used to provide further cooling to an x-ray target mounted onto a heat sink, again, all with the goal of achieving higher x-ray brightness without melting or damaging the target material through excessive heating.
• Jets of liquid metal require an elaborate plumbing system and consumables, are limited in the materials (and thus values of Z and their associated spectra) that may be used, and are difficult to scale to larger output powers.
• In the case of thin film targets of uniform solid material coated onto diamond substrates there is still a limitation in the amount of heat that can be tolerated before damage to the film may occur, even if used in a rotating anode configuration. Conduction of heat only occurs through the bottom of the film. In a lateral dimension, the same conduction problem exists as exists in the bulk material.
• This disclosure presents novel x-ray sources that have the potential of being up to several orders of magnitude brighter than existing commercial x-ray technologies.
• the higher brightness is achieved in part through the use of novel configurations for x-ray targets used in generating x-rays from electron beam bombardment.
• the x-ray target configurations may comprise a number of microstructures of one or more selected x-ray generating materials fabricated in close thermal contact with (such as embedded in or buried in) a substrate with high thermal conductivity, such that the heat is more efficiently drawn out of the x-ray generating material. This in turn allows bombardment of the x-ray generating material with higher electron density and/or higher energy electrons, which leads to greater x-ray brightness.
• a significant advantage to some embodiments is that the orientation of the microstructures allows the use of an on-axis collection angle, allowing the accumulation of x-rays from several microstructures to be aligned to appear to originate at a single origin, and can be used for alignments at "zero-angle" x-ray emission.
• x-rays from the multiple origins leads to greater x-ray brightness.
• Some embodiments of the invention additionally comprise x-ray optical elements that collect the x-rays emitted from one structure and re-focus them to overlap with the x-rays from a second structure. This relaying of x-rays can also lead to greater x-ray brightness.
• Some embodiments of the invention comprise an additional cooling system to transport the away from the anode or anodes. Some embodiments of the invention additionally comprise rotating the anode or anodes comprising targets with microstmctured patterns in order to further dissipate heat and increase the accumulated x-ray brightness.
• FIG. 1 illustrates a schematic cross-section diagram of a standard prior art transmission x-ray source.
• FIG. 2 illustrates a schematic cross-section diagram of a standard prior art reflection x-ray source.
• FIG. 3 illustrates a cross-section diagram the interaction of electrons with a surface of a material in a prior art x-ray source.
• FIG. 4 illustrates the typical emission spectrum for a tungsten target.
• FIG. 5 A illustrates emission from a prior art target for a target at a tilt angle
• FIG. 5B illustrates emission from a prior art target for a target at a tilt angle
• FIG. 5C illustrates emission from a prior art target for a target at a tilt angle
• FIG. 6A illustrates a schematic cross-section view of a prior art rotating anode
• FIG. 6B illustrates a top view of the anode for the rotating anode system of
• FIG. 6A is a diagrammatic representation of FIG. 6A.
• FIG. 7 illustrates a schematic cross-section view of an embodiment of an x-ray system according to the invention.
• FIG. 8 illustrates a perspective view of a target comprising a grid of embedded
• rectangular target microstructures on a larger substrate that may be used in some embodiments of the invention.
• FIG. 9 illustrates a perspective view of a variation of a target comprising a grid of embedded rectangular target microstructures on a larger substrate for use with focused electron beam that may be used in some embodiments of the invention.
• FIG. 10 illustrates a perspective view of a variation of a target comprising a grid of embedded rectangular target microstructures on a truncated substrate as may be used in some embodiments of the invention.
• FIG. 1 1 illustrates a perspective view of a variation of a target comprising a grid of embedded rectangular target microstructures on a substrate with a recessed shelf that may be used in some embodiments of the invention.
• FIG. 12 illustrates a cross-section view of electrons entering a target comprising target microstructures on a larger substrate that may be used in some embodiments of the invention.
• FIG. 13 illustrates a cross-section view of some of the x-rays emitted by the target of
• FIG. 14 illustrates a perspective view of a target comprising a single rectangular microstructure arranged on a substrate with a recessed region that may be used in some embodiments of the invention.
• FIG. 15 illustrates a perspective view of a target comprising a multiple rectangular microstructure arranged in a line on a substrate with a recessed region that may be used in some embodiments of the invention.
• FIG. 16A illustrates a perspective view of a target comprising a grid of embedded rectangular target microstructures that may be used in some embodiments of the invention..
• FIG. 16B illustrates a top view of the target of FIG. 16A.
• FIG. 16C illustrates a side/cross-section view of the target of FIGs. 16A and 16B.
• FIG. 17 illustrates a cross-section view of the target of FIG. 16, showing thermal transfer to a thermally conducting substrate under electron beam exposure.
• FIG. 18A illustrates a perspective view of a target comprising a checkerboard
• FIG. 18B illustrates a top view of the target of FIG. 18 A.
• FIG. 18C illustrates a side/cross-section view of the target of FIGs. 18A and 18B.
• FIG. 19A illustrates a perspective view of a target comprising a grid of embedded rectangular target microstructures arranged on a tiered substrate that may be used in some embodiments of the invention.
• FIG. 19B illustrates a top view of the target of FIG. 19A.
• FIG. 19C illustrates a side/cross-section view of the target of FIGs. 19A and 19B.
• FIG. 20 illustrates a cross-section view of the target of FIG. 19 radiating x-rays under electron bombardment.
• FIG. 21 illustrates a collection of x-ray emitters arranged in a linear array as may be used in some embodiments of the invention.
• FIG. 22 illustrates the 1/e attenuation length for several materials for x-rays having energies ranging from 1 keV to 400 keV.
• FIG. 23A illustrates a linear array of x-ray emitters being exposed to normal incidence electron beams as may be used in some embodiments of the invention.
• FIG. 23B illustrates a linear array of x-ray emitters being exposed to electron beams incident at an angle ⁇ as may be used in some embodiments of the invention.
• FIG. 23 C illustrates a linear array of x-ray emitters being exposed to a focused electron beam as may be used in some embodiments of the invention.
• FIG. 23D illustrates a linear array of x-ray emitters being exposed to electron beams incident at an angle 0 from multiple directions as may be used in some embodiments of the invention.
• FIG. 23E illustrates a linear array of x-ray emitters being exposed electron beams of various electron densities as may be used in some embodiments of the invention.
• FIG. 23 F illustrates a linear array of x-ray emitters being exposed to a uniform electron beam as may be used in some embodiments of the invention.
• FIG. 24 illustrates a schematic cross-section view of an embodiment of an x-ray system according to the invention comprising multiple electron emitters.
• FIG. 25 illustrates a collection of non-uniform x-ray emitters being exposed to electron beams of different electron densities as may be used in some embodiments of the invention.
• FIG. 26A illustrates a plot of the attenuation length and the CSDA (continuous slowing down approximation of electrons) for tungsten over a range of x-ray energies.
• FIG. 26B illustrates a plot of the ratio of attenuation length and CSDA for tungsten over a range of x-ray energies.
• FIG. 27 illustrates a plot of the ratio of attenuation length and CSDA for several
• FIG. 28C illustrates the collection of x-ray emitters
• FIG. 29A illustrates off-axis emission of x-rays from a collection of x-ray emitters arranged in a linear array as may be used in some embodiments of the invention.
• FIG. 29B illustrates off-axis emission of x-rays from a collection of x-ray emitters arranged in a widely spaced linear array as may be used in some embodiments of the invention.
• FIG. 30 illustrates a schematic cross-section view of an embodiment of an
• x-ray system comprising multiple electron emitters and a cooling system.
• FIG. 31 illustrates a cross-section of the target of the x-ray system of FIG. 30.
• FIG. 32 illustrates a schematic cross-section view of an embodiment of an
• x-ray system comprising a two-sided target.
• FIG. 33 illustrates a cross-section of the target of the x-ray system of FIG. 32.
• FIG. 34 illustrates a schematic cross-section view of an x-ray system according to an embodiment of the invention comprising multiple electron emitters bombarding opposite sides of a rotating anode.
• FIG. 35 illustrates a cross-section of multiple targets aligned for linear accumulation for use in a system according to the invention.
• FIG. 36 illustrates a cross-section of multiple targets comprising microstructures of x- ray generating material aligned for linear accumulation for use in a system according to the invention.
• FIG. 37A illustrates a side view of a target comprising an x-ray coating being bombarded using a distributed electron beam as may be used in some embodiments of the invention.
• FIG. 37B illustrates a perspective view of the target and distributed electron beam of
• FIG. 37A is a diagrammatic representation of FIG. 37A.
• FIG. 37C illustrates a front view of the target and distributed electron beam of FIG.
• FIG. 38A illustrates a side view of a target comprising microstructures being
• FIG. 38B illustrates a perspective view of the target and distributed electron beam of
• FIG. 38A is a diagrammatic representation of FIG. 38A.
• FIG. 38C illustrates a front view of the target and distributed electron beam of FIG.
• FIG. 39 illustrates a cross-section of multiple targets comprising microstructures of x- ray generating material in which reflecting optics are used to collect and focus x-rays for use in a system according to the invention.
• FIG. 40 illustrates a cross-section of multiple targets comprising microstructures of x- ray generating material of various orientations in which reflecting optics are used to collect and focus x-rays for use in a system according to the invention.
• Figure 41 illustrates a cross-section of multiple targets comprising microstructures of x-ray generating materials, in which an additional window and detector are used to monitor X-rays in the opposite direction of transmission
• FIG. 42 illustrates a cross-section of multiple targets comprising microstructures of x- ray generating material in which Wolter optics are used to collect and focus x-rays for use in a system according to the invention.
• FIG. 43 A illustrates a prior art embodiment of Wolter optics used for x-rays.
• FIG. 43B illustrates a prior art embodiment of Wolter optics with multiple cylindrical optical elements.
• FIG. 44 illustrates a cross-section of multiple targets comprising microstructures of x- ray generating material in which capillary optics are used to collect and focus x-rays for use in a system according to the invention.
• FIG. 7 illustrates an embodiment of a reflective x-ray system 80-A according to the invention.
• the source comprises a vacuum environment (typically 10 "6 torr or better) commonly maintained by a sealed vacuum chamber 20 or active pumping, and manufactured with sealed electrical leads 21 and 22 that pass from the negative and positive terminals of a high voltage source 10 outside the tube to the various elements inside the vacuum chamber 20.
• the source 80-A will typically comprise mounts 30 which secure the vacuum chamber 20 in a housing 50, and the housing 50 may additionally comprise shielding material, such as lead, to prevent x-rays from being radiated by the source 80-A in unwanted directions.
• an emitter 11 connected through the lead 21 to the high voltage source 10 serves as a cathode and generates a beam of electrons 111, often by running a current through a filament.
• Any number of prior art techniques for electron beam generation may be used for the embodiments of the invention disclosed herein. Additional known techniques used for electron beam generation include heating for thermionic emission, Schottky emission (a combination of heating and field emission), emitters comprising nanostructures such as carbon nanotubes), and by use of ferroelectric materials.
• a target 1 100 comprising a target substrate 1000 and regions 700 of x-ray generating material is electrically connected to the opposite high voltage lead 22 and target support 32 to be at low voltage, thus serving as an anode.
• the electrons 111 accelerate towards the target 1 100 and collide with it at high energy, with the energy of the electrons determined by the magnitude of the accelerating voltage.
• the collision of the electrons 11 1 into the target 1 100 induces several effects, including the emission of x-rays, some of which exit the vacuum tube 20 and are transmitted through a window 40 that is transparent to
• an electron control mechanism 70 such as an electrostatic lens system or other system of electron optics that is controlled and coordinated with the electron dose and voltage provided by the emitter 1 1 by a controller 10-1 through a lead 27.
• the electron beam 1 11 may therefore be scanned, focused, de- focused, or otherwise directed onto a target 1 100 comprising one or more microstructures 700 fabricated to be in close thermal contact with a substrate 1000.
• the alignment of the microstructures 700 may be arranged such that the bombardment of several of the microstructures 700 by the electron beam or beams 1 1 1 will excite emission in a direction orthogonal to the surface normal of the target in such a manner that the intensity in the direction of view will add or accumulate.
• the direction may also be selected by means of an aperture 840 in a screen 84 for the system to form the directional beam 888 that exits the system through a window 40.
• the aperture 840 may be positioned outside the vacuum chamber, or, more commonly, the window 40 itself may serve as the aperture.
• the aperture may be inside the vacuum chamber.
• Targets such as those to be used in x-ray sources according to the invention disclosed herein have been described in detail in the co-pending US Patent Application entitled STRUCTURED TARGETS FOR X-RAY GENERATION (US Patent Application 14/465,816, filed Aug. 21 , 2014), which is hereby incorporated by reference in its entirety and included as Appendix A. Any of the target designs and configurations disclosed in the above referenced copending Application may be considered for use as a component in any or all of the x-ray sources disclosed herein.
• FIG. 8 illustrates a target as may be used in some embodiments of the invention.
• a substrate 1000 has a region 1001 that comprises an array of microstructures 700 comprising x-ray generating material (typically a metallic material) that are arranged in a regular array of right rectangular prisms.
• x-ray generating material typically a metallic material
• electrons 1 11 bombard the target from above, and generate heat and x-rays in the microstructures 700.
• the material in the substrate 1000 is selected such that it has relatively low energy deposition rate for electrons in comparison to the x-ray generating micro structure material (typically by selecting a low Z material for the substrate), and therefore will not generate a significant amounts of heat and x- rays.
• the substrate 1000 material may also be chosen to have a high thermal conductivity, typically larger than 100 W/(m °C), and the microstructures are typically embedded within the substrate, i.e. if the microstructures are shaped as rectangular prisms, it is preferred that at least five of the six sides are in close thermal contact with the substrate 1000, so that heat generated in the microstructures 700 is effectively conducted away into the substrate 1000.
• targets used in other embodiments may have fewer direct contact surfaces.
• the term "embedded" is used in this disclosure, at least half of the surface area of the
• microstructure will be in close thermal contact with the substrate.
• a target 1 100 according to the invention may be inserted as a replacement for the target 01 for the transmission x-ray source 08 illustrated in FIG. 1, or for the target 100 illustrated in the reflecting x-ray source 80 of FIG. 2, or adapted for use as the target 500 used in the rotating anode x-ray source 580 of FIG. 6.
• microstructure when the word "microstructure” is used herein, it is specifically referring to microstructures comprising x-ray generating material. Other structures, such as the cavities used to form the x-ray microstructures, have dimensions of the same order of magnitude, and might also be considered “microstructures". As used herein, however, other words, such as “structures”, “cavities”, “holes”, “apertures”, etc. may be used for these structures when they are formed in materials, such as the substrate, that are not selected for their x-ray generating properties. The word “microstructure” will be reserved for structures comprising materials selected for their x-ray generating properties.
• microstructure x-ray generating structures with dimensions smaller than 1 micron, or even as small as nano- scale dimensions (i.e. greater than 10 nm) may also be described by the word “microstructures” as used herein.
• FIG. 9 illustrates another target as may be used in some embodiments of the invention in which the electron beam 1 1 1 -F is directed by electrostatic lenses to form a more concentrated, focused spot.
• the target 1 100-F will still comprise a region 1001 - F comprising an array of microstructures 700-F comprising x-ray material, but the size and dimensions of this region 1001-F can be matched to regions where electron exposure will occur.
• the "tuning" of the source geometry and the x-ray generating material can be controlled such that the designs mostly limit the amount of heat generated to the microstructured region 1001-F, while also reducing the design and manufacturing complexity. This may be especially useful when used with electron beams focused to form a micro-spot, or by more intricate systems that form a more complex electron exposure pattern.
• FIG. 10 illustrates another target as may be used in some embodiments of the invention, in which the target 1100-E still has a region 1001-E with an array of microstructures 700-E comprising x-ray material that emit x-rays when exposed to electrons 111 , but the region 1001-E is positioned flush with or near the edge of the substrate 1000-E.
• This configuration may be useful in targets where the substrate comprises a material that absorbs x-rays, and so emission at near-zero angles would be significantly attenuated in a configuration, as was shown in FIG. 8.
• FIG. 8 is that a significant portion of the substrate on one side of the microstructures 700-E is gone. Heat therefore is not carried away from the microstructures symmetrically, and the local heating may increase, impairing heat flow.
• the target 1100-R comprises a substrate 1000-R with a recessed shelf 1002-R.
• FIG. 12 illustrates the relative interaction between a beam of electrons 11 1 and a target comprising a substrate 1000 and microstructures 700 of x-ray material. As illustrated, only three electron paths are shown, with two representative of electrons bombarding the two shown microstructures 700, and one interacting with the substrate.
• the depth of penetration can be estimated by Pott's Law. Using this formula, Table II illustrates some of the estimated penetration depths for some common x-ray target materials. Table II: Estimates of penetration depth for 60 keV electrons into some materials.
• the dimension marked as R to the left side of FIG. 12 corresponds to a reference dimension of 10 microns, and the depth D in the x-ray generating material, which, when set to be 2/3 (66%) of the electron penetration depth for copper, becomes D ⁇ 3.5 ⁇ .
• the majority of characteristic Cu K x-rays are generated within depth D.
• the electron interactions below that depth typically generate few characteristic K-line x-rays but will contribute to the heat generation, thus resulting in a low thermal gradient along the depth direction.
• One embodiment of the invention limits the depth of the microstructured x-ray generating material in the target to between one third and two thirds of the electron penetration depth at the incident electron energy.
• the lower mass density of the substrate leads to a lower energy deposition rate in the substrate material immediately below the x-ray generating material, which in turn leads to a lower temperature in the substrate material below. This results in a higher thermal gradient between the x-ray generating material and the substrate, enhancing heat transfer.
• the thermal gradient is further enhanced by the high thermal conductivity of the substrate material.
• selecting the depth D to be less than the electron penetration depth is also generally preferred for efficient generation of bremsstrahlung radiation, because the electrons below that depth have lower energy and thus lower x-ray production efficiency.
• the depth of the x-ray material may be selected to be 50% of the electron penetration depth. In other embodiments, the depth of the x-ray material may be selected to be 33% of the electron penetration depth. In other embodiments, the depth D for the microstructures may be selected related to the "continuous slowing down approximation" (CSDA) range for electrons in the material. Other depths may be specified depending on the x-ray spectrum desired and the properties of the selected x-ray material.
• CSDA continuous slowing down approximation
• the length L) of the x-ray generating material may also be specified.
• the depth D and lateral dimensions ⁇ and L may be defined relative to the axis of electron propagation, or defined with respect to the orientation of the surface of the x-ray generating material. For normal incidence electrons, these will be the same dimensions. For electrons incident at an angle, care must be taken to make sure the appropriate projections are used.
• FIG. 13 illustrates the relative x-ray generation from the various regions shown in FIG. 12.
• X-rays 888 comprise characteristic x-rays emitted from the region 248 where they are generated in the x-ray generating material, while the regions 1280 and 1080 where the electrons interact with the substrate generate characteristic x-rays of the substrate element(s), (but not characteristic x-rays of the element(s) of the x-ray generating material in the x-ray generating region 248).
• bremsstrahlung radiation x-rays emitted from the region 248 of the x- ray generating material are typically much stronger than in the regions 1280 and 1080 where electrons encounter only the low Z substrate, which emit weak continuum x-rays 1088 and 1228.
• FIG. 13 shows x-rays emitted only to the right, this is in anticipation of a window or collector being placed to the right, when this target is used in the low-angle high-brightness configuration discussed in FIG. 5.
• X-rays are in fact typically emitted in all directions from these regions.
• FIG. 13 illustrates an arrangement that allows the linear
• characteristic x-rays along the microstructures and therefore can produce a relatively strong characteristic x-ray signal.
• many lower energy x-rays will be attenuated by the target materials, which will effectively act as an x-ray filter.
• Other selections of materials and geometric parameters may be chosen (e.g. a non-linear scheme) if non- characteristic, continuum x-rays are desired, such as applications in which a bandpass of low energy x-rays are desired (e.g. for imaging or fluorescence analysis of low Z materials).
• targets that are arranged in planar configurations have been presented. These are generally easier to implement, since equipment and process recipes for deposition, etching and other planar processing steps are well known from processing devices for microelectromechanical systems (MEMS) applications using planar diamond, and from processing silicon wafers for the semiconductor industry.
• MEMS microelectromechanical systems
• a target with a surface with additional properties in three dimensions (3-D) may be desired.
• the apparent x-ray source size and area is at minimum (and brightness maximized) when viewed parallel to surface, i.e. at a zero degree (0°) take-off angle.
• the apparent brightest of x-ray emission occurs when viewed at 0° take-off angle.
• the emission from within the x-ray generating material will accumulate as it propagates at 0° through the material.
• the attenuation of x-rays between their points of origin inside the target as they propagate through the material to the surface increases with decreasing take-off angle, due to the longer distance traveled within the material, and often becomes largest at or near 0° take-off angle. Reabsorption may therefore counterbalance any increased brightness that viewing at near 0° achieves.
• the distance through which an x-ray beam will be reduced in intensity by 1/e is called the x-ray attenuation length, and therefore, a configuration in which the emitted x-rays pass through as little additional material as possible, with the distance selected to be related to the x-ray attenuation length, may be desired.
• FIG. 14 An illustration of a target as may be used in some embodiments of the invention is presented in FIG. 14.
• an x-ray generating region comprising a single
• microstructure 2700 is configured at or near a recessed edge 2003 of the substrate on a shelf 2002, similar to the situation illustrated in FIG. 1 1.
• the x-ray generating microstructure 2700 is in the shape of a rectangular bar of x-ray generating material, is embedded in a substrate 2000, and emits x-rays 2888 when bombarded with electrons 111.
• the thickness of the bar D (along the surface normal of the target) is selected to be between one third and two thirds of the electron penetration depth of the x-ray generating material at the incident electron energy for optimal thermal performance. It may also be selected to obtain a desired x-ray source size in the vertical direction.
• the width of the bar f ⁇ is selected to obtain a desired source size in the corresponding direction. As illustrated, W ⁇ 1.5D, but could be substantially smaller or larger, depending on the size of the source spot desired.
• the length of the bar L as illustrated is L ⁇ 4D , but may be any dimension, and may typically be determined to be between 1 ⁇ 4 to 3 times the x-ray attenuation length for the selected x-ray generating material.
• FIG. 15 An illustration of an alternative target as may be used in some embodiments of the invention is presented in FIG. 15.
• an x-ray generating region with six microstructures 2701, 2702, 2703, 2704, 2705, 2706 is configured at or near a recessed edge 2003 of the substrate on a shelf 2002, similar to the situation illustrated in FIG. 1 1 and FIG. 14.
• the x-ray generating microstructures 2701, 2702, 2703, 2704, 2705, 2706 are arranged in a linear array of x-ray generating right rectangular prisms embedded in a substrate 2000, and emit x-rays 2888-D when bombarded with electrons 1 11.
• the total volume of x-ray generating material is the same as in the previous illustration of FIG. 14.
• the thickness of the bar D (along the surface normal of the target) is selected to be between one third and two thirds of the electron penetration depth of the x-ray generating material at the incident electron energy for optimal thermal performance, as in the case shown in FIG. 14.
• the width of the bar W is selected to obtain a desired source size in the corresponding direction and as illustrated, W ⁇ 1.5 D, as in the case shown in FIG. 14. As discussed previously, it could also be substantially smaller or larger, depending on the size of the source spot desired.
• each sub-bar now has five faces transferring heat into the substrate, increasing the heat transfer away from the x-ray generating sub-bars 2701-2706 and into the substrate.
• the separation between the sub-bars is a distance d ⁇ 1, although larger or smaller dimensions may also be used, depending on the amount of x-rays absorbed by the substrate and the relative thermal gradients that may be achieved between the specific materials of the x-ray generating microstructures 2701-2706 and the substrate 2000.
• the total length of the x-ray generating sub-bars will commonly be about twice the linear attenuation length for x-rays in the x-ray generating material, but can be selected from half to more than 3 times that distance.
• the thickness of the bar (along the surface normal of the target) D was selected to be equal to one third to two thirds of the electron penetration depth of the x-ray generating material at the incident electron energy for optimal thermal performance, but it can be substantially larger. It may also be selected to obtain a desired x-ray source size in that direction which is
• FIG. 16 illustrates a region 1001 of a target as may be used in some embodiments of the invention that comprises an array of microstructures 700 in the form of right rectangular prisms comprising x-ray generating material arranged in a regular array.
• FIG. 16A presents a perspective view of the sixteen microstructures 700 for this target, while FIG. 16B illustrates a top down view of the same region, and FIG. 16C presents a side/cross-section view of the same region.
• the microstructures have been fabricated such that they are in close thermal contact on five of six sides with the substrate. As illustrated, the top of the microstructures 700 are flush with the surface of the substrate, but other targets in which the microstructure is recessed may be fabricated, and still other targets in which the microstructures present a topographical "bump" relative to the surface of the substrate may also be fabricated.
• An alternative target as may be used in some embodiments of the invention may have several microstructures of right rectangular prisms simply deposited upon the surface of the substrate. In this case, only the bottom base of the prism would be in thermal contact with the substrate.
• the ratio of the total surface area in contact with the substrate for the embedded microstructures vs. deposited microstructures is
• the ratio is essentially 1.
• the ratio may be increased to 6.
• the heat transfer is illustrated with representative arrows in FIG. 17, in which the heat generated in microstructures 700 embedded in a substrate 1000 is conducted out of the microstructures 700 through the bottom and sides (arrows for transfer through the sides out of the plane of the drawing are not shown).
• the amount of heat transferred per unit time (AQ) conducted through a material of area A and thickness d given by:
• FIG. 18 illustrates a region 1013 of a target according to an embodiment of invention that comprises a checkerboard array of microstructures 700 and 701 in the form of right rectangular prisms comprising x-ray generating material.
• the array as shown is arranged as an embedded array in the surface of the substrate.
• FIG. 18A presents a perspective view of the twenty- five embedded microstructures 700 and 701
• FIG. 18B illustrates a top down view of the same region
• FIG. 18C presents a side/cross-section view of the same region with recessed regions shown with dotted lines.
• FIG. 19 An illustration of another target as may be used in some embodiments of the invention is presented in FIG. 19, which shows a region 2001 of a target according to an embodiment of invention with an array of microstructures 2790 and 2791 comprising x-ray generating material having a thickness D.
• the array as shown is a modified checkerboard pattern of right rectangular prisms, but other configurations and arrays of microstructures may be used as well.
• these microstructures 2790 and 2791 are embedded in the surface of the substrate.
• the surface of the substrate comprises a predetermined non-planar topography, and in this particular case, a plurality of steps along the surface normal of the substrate 2000.
• the height of each step is h ⁇ D, but the step height may be selected to be between lx and 3x the thickness of the microstructures.
• the total height of all the steps may be selected to be equal or less than the desired x-ray source size along the vertical (thickness) direction.
• the total width of the microstructured region may be equal to the desired x-ray source size in the corresponding direction.
• the overall appearance resembles a staircase of x-ray sources.
• FIG. 19A presents a perspective view of the eighteen embedded microstructures 2790 and 2791
• FIG. 19B illustrates a top down view of the same region
• FIG. 19C presents a side/cross-section view of the same region.
• An electrically conductive layer may be coated on the top of the staircase structures when the substrate is beryllium, diamond, sapphire, silicon, or silicon carbide.
• FIG. 20 illustrates the x-ray emission 888-S from the staircase target of FIG. 19C when bombarded by electrons 1 1 1.
• the prisms of x-ray generating material heat up when electrons collide with them, and because each of the prisms of x-ray generating material has five sides in thermal contact with the substrate 2000, conduction of heat away from the x-ray material is still larger than a configuration in which the x-ray material is deposited on the surface.
• the emission is of x- rays unattenuated by absorption from other neighboring prisms and negligibly attenuated by neighboring substrate material.
• each prism will therefore be increased, especially when compared to the x-ray emission from the target of FIG. 18, which also illustrates a number of prisms 700 and 701 of x-ray generating material arranged in a checkerboard pattern.
• each prism is embedded in the substrate, therefore having five surfaces in thermal contact with the substrate 1000, but the emission to the side at 0° will be attenuated by both the prisms of the neighboring columns and the substrate material.
• Such an embodiment comprising a target with topography may be manufactured by first preparing a substrate with topography, and then embedding the prisms of x-ray material following the fabrication processes for the previously described planar substrates.
• the initial steps that create cavities to be filled with x-ray material may be enhanced to create the staircase topography structure in an initially flat substrate.
• additional alignment steps such as those known to those skilled in the art of planar processing, may be employed if overlay of the embedded prisms with a particular feature of topography is desired.
• Microstrutures may be embedded with some distance to the edges of the staircase, as illustrated in FIGs. 19 and 20, or flush with as edge (as was shown in FIG. 10).
• a determination of which configuration is appropriate for a specific application may depend on the exact properties of the x-ray generation material and substrate material, so that, for example, the additional brightness achieved with increased electron current enabled by the thermal transfer through five vs. four surfaces may be compared with the additional brightness achieved with free space emission vs. reabsorption through a section of substrate material.
• the additional costs associated with the alignment and overlay steps, as well as the multiple processing steps that may be needed to pattern multiple prisms on multiple layers, may need to be considered in comparison to the increased brightness achievable.
• microstructures comprising multiple x-ray generating materials, microstructures comprising alloys of x-ray generating materials, microstructures deposited with an anti-diffusion layer or an adhesion layer, microstructures with a thermally conducting overcoat, microstructures with a thermally conducting and electrically conducting overcoat, microstructured buried within a substrate and the like.
• x-ray target materials such as copper (Cu), and molybdenum (Mo) and tungsten (W)
• the microstructures may alternatively comprise unconventional x-ray target materials, such as tin (Sn), sulfur (S), titanium (Ti), antimony (Sb), etc. that have thus far been limited in their use due to poor thermal properties.
• target configurations that may be used in embodiments of the invention, as has been described in the above cited US Patent Application Ser. No. 14/465,816, are arrays of microstructures that take any number of geometric shapes, such as cubes, rectangular blocks, regular prisms, right rectangular prisms, trapezoidal prisms, spheres, ovoids, barrel shaped objects, cylinders, triangular prisms, pyramids, tetrahedra, or other particularly designed shapes, including those with surface textures or structures that enhance surface area, to best generate x- rays of high brightness and that also efficiently disperse heat.
• geometric shapes such as cubes, rectangular blocks, regular prisms, right rectangular prisms, trapezoidal prisms, spheres, ovoids, barrel shaped objects, cylinders, triangular prisms, pyramids, tetrahedra, or other particularly designed shapes, including those with surface textures or structures that enhance surface area, to best generate x- rays of high brightness and that also efficiently dispers
• target configurations that may be used in embodiments of the invention, as has been described in the above cited US Patent Application Ser. No. 14/465,816, are arrays of microstructures comprising various materials as the x-ray generating materials, including aluminum, titanium, vanadium, chromium, manganese, iron, cobalt, nickel, copper, gallium, zinc, yttrium, zirconium, molybdenum, niobium, ruthenium, rhenium, rhodium, palladium, silver, tin, iridium, tantalum, tungsten, indium, cesium, barium, gold, platinum, lead and combinations and alloys thereof.
• various materials as the x-ray generating materials including aluminum, titanium, vanadium, chromium, manganese, iron, cobalt, nickel, copper, gallium, zinc, yttrium, zirconium, molybdenum, niobium, ruthenium, rhenium, r
• x-ray configurations that comprise a plurality of microstructures comprising x-ray material that can be used as targets in x-ray sources to generate x-rays with increased brightness.
• These target configurations have been described as being bombarded with electrons and emitting x-rays, but may be used as the static x-ray target in an otherwise conventional source, replacing either the target 01 from the transmission x-ray source 08 of FIG. 1, or the target 100 from the reflective x- ray source 80 of FIG. 2 with a microstructured target to form an x-ray source in accord with some embodiments of the invention.
• the targets described above may be embodied in a moving x-ray target, replacing, for example, the target 500 from the rotating anode x-ray source 80 of FIG. 6 with a microstructured target as described above to create a source with a moving microstrucutred target in accord with other embodiments of the invention.
• FIG. 21 illustrates a collection of x-ray emitters arranged in a linear array.
• the long axis of the linear array runs from left to right in the figure, while the short axis would run in and out of the plane of the figure.
• Several x-ray generating elements 801 , 802, 803, 804... etc. comprising one or more x-ray generating materials are bombarded by beams electrons 1 1 1 1 , 1 1 12, 1 1 13, 1 1 14, ... etc. at high voltage (anywhere from 1 to 250 kcV), and form sub-sources that emit x-rays 818, 828, 838, 848, ... etc.
• the analysis here is for a view along the axis down the center of the linear array of sub-sources, where a screen 84 with an aperture 840 has been positioned.
• the aperture allows the accumulated zero-angle x-rays to emerge from the source, but in practice, an aperture which allows several degrees of emitted x-rays emitted at +3° or even at ⁇ 6° to the surface normal may be designed for use in some applications. It is generally preferred that the window be at normal or near normal incidence to the long axis of the linear array, but in some embodiments, a window tilted to an angle as large as 85° may be useful.
• the emission for the right-most emitter as illustrated simply propagates to the right through free space.
• the x-rays from the other emitters are attenuated through absorption, scattering, or other loss mechanisms encountered while passing through whatever material lies between emitters, and also by divergence from the propagation axis and by losses encountered by passage through the neighboring emitter(s) as well.
• Tj_o as the x-ray transmission factor for propagation to the right of the
• Ti j .j as the x-ray transmission factor for propagation from the th emitter 80/ to the /-7-th emitter 80(7-7);
• Tj as the x-ray transmission factor for propagation through the /th emitter 80/
• the x-ray attenuation may be different for x-rays of different energies, and that the product of Tj and T 2 may vary considerably for a given material over a range of wavelengths.
• FIG. 22 illustrates the 1/e attenuation length for x-rays having energies ranging from 1 keV to 400 keV for three x-ray generating materials: Molybdenum (Mo), Copper (Cu), Tungsten (W); and from 10 keV to 400 keV for three substrate materials: Graphite (C), Beryllium (Be) and water (H 2 0).
• the 1/e attenuation length Lj/ e for a material is related to the transmission factors above for a length L by
• a larger Lj /e means a larger Tj .
• the beam or beams of electrons 1 1 1 or 111 1, 1112, 1 113, etc. bombarding the x-ray generating elements 801, 802, 803... etc. may be shaped and directed using one or more electron control mechanisms 70 such as electron optics, electrostatic lenses or magnetic focusing elements.
• electron control mechanisms 70 such as electron optics, electrostatic lenses or magnetic focusing elements.
• electrostatic lenses are placed within the vacuum environment of the x-ray source, while the magnetic focusing elements can be placed outside the vacuum.
• Various other electron imaging techniques such as the reflective electron beam control system disclosed in the prior art REBL (Reflective Electron Beam Lithography system) as described in US Patent 6,870,172 "Maskless reflection electron beam projection lithography" may also be used to create a complex pattern of electron exposure.
• Electrons may bombard the elements at normal incidence, as illustrated in FIG. 21 and again illustrated in FIG. 23A; with electron beams 1 121 , 1 122, 1 123 etc. at an angle 0, as illustrated in FIG. 23B; with electron beams 1 131 , 1 132, 1 133 etc. at multiple angles (such as a focused electron beam), as illustrated in FIG. 23C; with electron beams 1 141, 1 142, 1 143 etc. bombarding the microstructures 700 from opposite sides and at an angle ⁇ , as illustrated in FIG. 23D; with electron beams 1 151 , 1 152, 1 153 etc. at with varying intensity or electron density, as illustrated in FIG. 23E; with a uniform large area beam of electrons 1 1 1 as illustrated in FIG. 23F, or any combination of the many arrangements of electron beams that may be devised by those skilled in the art.
• the actual design of the pattern for electron exposure may depend in part on the material properties of the x-ray generating material and/or the material filling the regions between the x-ray generating elements. If the x-ray generating material is highly absorbing, greater electron density may be used to bombard the regions that emit x-rays that have to travel the greatest distance through other x-ray generating elements, as illustrated in
• FIG. 23E Likewise, if the electron penetration depth is large, the x-ray generating material may be bombarded with electrons at an angle, as illustrated in FIG. 23B. If the electron penetration depth is larger than desired, thinner regions of x-ray generating material may be used, creating a source of smaller vertical dimension.
• the area of electron exposure can be adjusted so that the electron beam or beams primarily bombard the x-ray generating elements 1001, 1002, 1003, etc. and do not bombard the regions in between the elements.
• the space between x-ray generating elements can be filled not with vacuum but with a solid material that facilitates heat transfer away from the x-ray generating elements.
• Such source targets comprising arrays of multiple x-ray generating elements embedded or buried in a thermally conducting substrate such as diamond were disclosed in the co-pending U.S. Patent Application Ser. No. 14/465,816 as discussed above, which has been incorporated by reference in its entirety.
• the area between the x-ray generating elements comprises solid material and is also bombarded with electrons, it too will tend to heat up under electron exposure, which will reduce the thermal gradient with the x-ray generating elements and therefore reduce the heat flow out of the x-ray generating element.
• a source having multiple electron beams that are used to bombard distinct x-ray generating elements independently may also be configured to allow a different accelerating voltage to be used with the different electron beam sources.
• a source 80-B is illustrated in FIG. 24.
• the previous high voltage source 10 is again connected through a lead 21 -A to an electron emitter 11-A that emits electrons 1 1 1 -A towards a target 1 100-B.
• the target 1 100-B comprising the x-ray generating elements 801 , 802, 803, ...etc. will usually be uniformly set to the ground potential, the individual electron beam sources used to target the different x-ray generating elements may be set to different potentials, and electrons of varying energy may therefore be used to bombard the different x-ray generating elements 801, 802, 803,
• This may offer advantages for x-ray emission management, in that electrons of different energies may generate different x-ray emission spectra, depending on the materials used in the individual x-ray generating elements.
• the heat load generated may also be managed through the use of different electron energies.
• the design of the electron optics for such a multiple beam configuration to keep the various multiple beams from interfering with each other and providing electrons of the wrong energy to the wrong target element may be complex.
• the different x-ray generating elements may comprise different x-ray emitting materials, so that the on-axis view presents a diverse spectrum of characteristic x-rays from the different materials.
• Materials that are relatively transparent to x- rays may be used in the position closest to the output window 840 (e.g. the element furthest to the right in FIG. 21), while those that are more strongly absorbing may be used for elements on the other side of the array, so that they attenuate the other sources less.
• the distance between the x-ray generating elements may be varied, depending on the expected thermal load for different materials. For example, a larger space between elements may be used for elements that are expected to generate more heat under electron bombardment, while smaller gaps may be used if less heat is expected.
• the x-ray generating elements 1801 , 1802, 1803, ... etc. may have varying sizes and geometric shapes. This may be especially useful for situations where different materials are used, and the electron deceleration processes and x-ray absorption are different for the different materials.
• a useful figure of merit that may be considered in the design of the x-ray generating elements for linear accumulation x-ray sources is the ratio of the 1/e attenuation length for the x-rays within the material to one half of the "continuous slowing down approximation" (CSDA) range for the electrons.
• the CSDA range for the electrons is typically larger than the penetration depth, since an electron can lose energy through several collisions as it slows down.
• FIG. 26A illustrates a plot of these two functions for tungsten
• FIG. 26B illustrates a plot of the ratio.
• the x-ray data is from the previously cited source by Henke et al., while the CSDA range data is from the Physical Measurement Laboratory of NIST
• This ratio may be considered a figure-of-merit for the generation of x-rays for a material when used for the linear accumulation of x-rays, since its value is large when the x-ray transparency of the material is large (increasing Tj for that microstructure) but its value is also large when the CDSA range is small, (which means the electrons are absorbed quickly, and the x-rays appear to be emitted from a spot of smaller depth).
• FIG. 27 plots this ratio for a large range of x-ray energies for three materials (Cu, Mo and W). Once an x-ray material has been selected for the characteristic lines desired, this ratio may be used to suggest a particular energy range (such as -55 keV for tungsten) so that the system may be configured to operate in so that this figure-of-merit is relatively large.
• the thickness of the microstructures may be set to be 1 ⁇ 2 or less of CSDA as measured in the direction of e-beam propagation. For some selections of target materials, a thin foil coating of material may be sufficient to provide the x-ray emission needed, and more complex embedded or buried microstructures may not be required.
• the x-ray generating elements 801 , 802, 803, 804, ... etc. need not be continuously bombarded by electrons, but the electron beams 121 1, 1212, 1213, 1214, etc. ... may be switched on and off to distribute the heat load over time. This may be particularly effective when viewed on-axis, since all x-rays appear to be coming from the same origin.
• FIG. 28 A time-multiplexed embodiment is illustrated in FIG. 28.
• the electron beams 121 1 and 1214 for elements 801 and 804 respectively are on, while the others are off.
• the system may be switched between these configurations simply by blanking the various electron beams, or by blocking the beams with mechanical shutters or by repositioning the electron beams.
• electron beams may simply scan over target comprising the x-ray generating materials. In some embodiments, this may be a regular raster scan, while in other embodiments, the scan may be non-uniform, "dwelling" on or scanning over the x-ray generating region more slowly, while moving rapidly from one x-ray generating region to another. In other embodiments, an electron beam may be designed to bombard all x-ray generating regions simultaneously or multiple electron beams impinging the x- ray generating regions near simultaneously, but having the electron beam(s) turn on and off rapidly, creating a "pulsed" x-ray source. This may have some advantages for certain specific applications.
• Sources with variable timing for electron exposures may also be especially useful for embodiments that use different types of embedded microstructures bombarded with electrons at different potentials, as mentioned above, to excite a diverse spectrum of x-ray energies.
• a slightly off-axis configuration may be preferred.
• FIG. 29 Examples of such configurations are illustrated in FIG. 29.
• FIG. 29A the x-ray emission through an off-axis window 841 or aperture in a screen 84 or wall is illustrated. Because the x-ray emission is generally isotropic, emission from all microstructures bombarded with electrons will emit in this direction as well. However, the various rays of this emission 878 that pass through the aperture 841 will not propagate in the same direction and will diverge, giving the appearance of an extended source. If the appearance of an extended source is desired, however, using such an off-axis, small -angle collection configuration for the x-rays may be suitable.
• FIG. 29B illustrates the emission from multiple microstructures, this time in a direction away from the incident electron beams 1 1 1 1 , 1112, 11 13, etc.
• the spacing of the microstructures 801, 802, 803... is much larger relative to their size, so the off- axis angle that x-rays can be detected by a detector without attenuation from neighboring x-ray emitting elements is much smaller than for the situation illustrated in FIG. 29 A.
• FIG. 30 and FIG. 31 Illustrated in FIG. 30 and FIG. 31 (which shows more detail for the target) is a more general x-ray system 80-C, incorporating some of the above-discussed elements.
• the system comprises an electron system controller 10-V that directs various voltages through a number of leads 21-A, 21-B, and 21-C to a number of electron emitters 1 1 -A, 1 1-B, and 1 1-C that produce electron beams 1 1 1-A, 1 11-B, 1 11-C etc.
• Each of these electron beams 11 1 -A, 1 1 1- B, 1 1 1-C may be controlled by signals from the system controller 10-V through leads 27-A, 27- B, and 27-C that govern electron optics 70-A, 70-B, and 70-C.
• the system additionally comprises a cooling system, comprising a reservoir 90 filled with a cooling fluid 93, typically water, that is moved by means of a mechanism 1209 such as a pump through cooling channels 1200, including a cooling channel that passes through the substrate 1000 of the target 1 100-C.
• a cooling fluid 93 typically water
• a mechanism 1209 such as a pump
• cooling channels 1200 including a cooling channel that passes through the substrate 1000 of the target 1 100-C.
• FIG. 31 illustrates the target 1 100-C under bombardment by electrons in an extended version of this system in which two additional electron beams 1 1 1-D and 1 1 1-E have been added.
• both of the beams 1 1 1-D and 1 1 1-E have a higher current than the three electron beams to the right 1 1 1-A, 1 1 1-B, and 1 1 1-C
• the leftmost electron beam 11 1-E has a highest current density of all the beams, illustrating that the beams need not be of equal density.
• the leftmost x-ray generating elements 804 and 805 receiving the higher current are also illustrated as having larger gaps between them and their neighboring microstructures than is provided between the rightmost elements 801, 802, and 803, which receive lower electron current.
• 804 and 805 may be comprised of materials that are higher in atomic number than 801, 802, and 803.
• a conducting overcoat 770 that is both thermally conducting (to remove heat) and electrically conducting, providing a return path to ground 722 for the electrons. Also provided is a screen 84 with an aperture 840 to allow x-rays that are on- axis to radiate away from the target.
• the transmission of x-rays T for the substrate be near 1.
• a substrate material of length L and linear absorption coefficient a s For a substrate material of length L and linear absorption coefficient a s ,
• Ly e is the length at which the x-ray intensity has dropped by a factor of 1/e.
• FIG. 32 One embodiment of a source 80-D using a target with multiple x-ray generating elements arranged for linear accumulation is illustrated in FIG. 32, with the target 2200 shown in more detail in FIG. 33.
• a controller 10-2 provides high voltage to two emitters 1 1-D and 1 1 -E that emit electron beams 1221 and 1222 towards opposite sides of a target 2200.
• the properties of the electron beams 1221 and 1222, such as the position, direction, focusing etc. are controlled by electron optics 70-D and 70-E, respectively through leads 27-D and 27-E that coordinate the properties of the beam with the beam current and high voltage settings, all governed by the controller 10-2.
• the target 2200 comprises a substrate 2200 and two thin coatings 2221 and 2222 of x-ray generating material, one on each side of the substrate 2200.
• the electron beams 1221 and 1222 are directed by the electron optics 70-D and 70-E to bombard the thin coatings 2221 and 2222 on opposite sides of the target 2200 at locations such that the x-rays 821 and 822 that are generated from each location are aligned with an aperture 840 in a screen 84 that allows a beam of x-rays 2888 to by emitted from the source 80-D.
• the electron optics 70-D and 70-E may be used to focus the electron beams 1221 and 1222 to spots as small as 25 ⁇ or even smaller.
• the alignment of the two electron bombardment spots to produce superimposed x-ray emission patterns will be carried out by placing an x-ray detector beyond the aperture 840 and measuring the intensity of the x-ray beam 2888 as the position and focus of the electron beams 1221 and 1222 are changed using electron optics 70-D and 70-E.
• the two spots can be considered aligned when the simultaneous intensity from both spots is maximized on the detector.
• the target 2200 may be rigidly mounted to structures within the vacuum chamber, or may be mounted such that its position may be varied. In some embodiments, the target may be mounted as a rotating anode, to further dissipate heating.
• the thickness of the coatings 2221 and 2222 can be selected based on the anticipated electron energy and the penetration depth or the CSDA estimate for the material. If the bombardment occurs at an angle to the surface normal, as illustrated, the angle of incidence can also affect the selection of the coating thickness.
• the tilt of the target 2200 relative to the electron beams 1221 and 1222 is shown as -45°, any angle from 0° to 90° that allows x-rays to be emitted may be used.
• FIG. 34 A system 580-R comprising these features is illustrated in FIG. 34.
• a controller 10-3 provides high voltage through leads 21- G and 21-F to two emitters 1 1-F and 11-G that emit electron beams 2511-F and 251 1 -G respectively.
• a source 80-D as described above is not limited to a single target with two sides. Shown in FIG. 35 is a pair of targets 2203, 2204, each with two coatings 2231 and 2232, and 2241 and 2242 respectively of x-ray generating material on a substrate 2230 and 2240, respectively.
• the source will have a similar configuration to that illustrated in FIG. 32, except that there are now four electron beams 1231 , 1232, 1241 , 1242 that are controlled to bombard the respective coatings on two targets 2203, 2204 and generate x-rays 831 and 832, and 841 and 842 respectively.
• the four x-ray generating spots are aligned with an aperture 840 in a screen 84 to appear to originate from a single point of origin.
• An alignment procedure as discussed above for the case of a two-sided target, except that now the four electron beams 1231 , 1232, 1241, and 1242 are adjusted to maximize the total x-ray intensity at a detector placed beyond the aperture 840.
• the targets 2203 and 2204 may be rigidly mounted to structures within the vacuum chamber, or may be mounted such that their position may be varied. In some embodiments, the targets 2203 and 2204 may be mounted as rotating anodes, to further dissipate heating. The rotation of the targets 2203 and 2204 may be synchronized or independently controlled.
• the thickness of the coatings 2231 , 2232 and 2241, 2242 can be selected based on the anticipated electron energy and the penetration depth or the CSDA estimate for the material. If the bombardment occurs at an angle to the surface normal, as illustrated, the angle of incidence can also affect the selection of the coating thickness. Although the tilt of the targets 2203 and 2204 relative to the electron beams 1231, 1232 and 1222 is shown as -45°, any angle from 0° to 90° that allows x-rays to be emitted may be used.
• the coatings for the various targets may be selected to be different x-ray materials.
• the upstream coatings 2241 and 2242 may be selected to be a material such as silver (Ag) or palladium (Pd) while the downstream coatings 2231 and 2232 may be selected to be rhodium (Rh), which has a higher transmission for the characteristic x-rays generated by the upstream targets.
• This may provide a blended x-ray spectrum, comprising multiple characteristic lines from multiple elements.
• a tunable blend of x-rays may be achieved.
• the coatings themselves need not be uniform materials, but may be alloys of various x-ray generating substances, designed to produce a blend of characteristic x- rays.
• FIG. 36 illustrates another embodiment in which the target comprises microstructures of x-ray generating material embedded in the substrate instead of thin coatings.
• Two targets 2301 and 2302 are shown (although a single target, such as illustrated in FIGs. 32 and 33, may also be configured in this manner as well), each with four microstructures of x-ray generating material 231 1 , 2312, 2313, 2314, and 2321 , 2322, 2323, 2324, respectively embedded to on each side of a substrate 2310, 2320 respectively. Electron beams 1281, 1282, 1283, and 1284 are directed onto the targets 2301, 2302, and produce x-rays that form a beam 882 that appears to originate from the same source when aligned with an aperture 840-B in a screen 84-B.
• the embedded microstructures for this embodiment may comprise different x-ray generating materials, or an alloy or blend of x-ray generating materials to achieve a desired spectral output.
• FIG. 37 Another embodiment in which the target 2400 is aligned with a distributed electron beam 241 1 is illustrated in FIG. 37.
• the electron beam 241 1 is focused to several spots onto a coating 2408 of x-ray generating material formed on a substrate 2410.
• the electron beam 241 1 may be adjusted so that the multiple spots are formed in an aligned row, and their x-ray emission 2488 along the row (at zero-angle) will appear to originate from a single point of origin.
• FIG. 38 A variation of this embodiment is illustrated in FIG. 38.
• microstructures 2481, 2482, 2483 of x-ray generating material are embedded in the substrate 2410.
• the distributed electron beam 2411 bombards these microstructures, again generating x-rays 2488 that appear to originate from a single point of origin.
• Conventional optical elements for x- rays such as grazing angle mirrors, mirrors with multilayer coatings, or more complex Wolter optics or capillary optics may be used.
• the relation between the targets and the optics will be established at the time of fabrication.
• the optics may be secured in place, either with a particular mount or an epoxy designed for use in a vacuum, using an alignment procedure such as those well known by those skilled in the art of optical fabrication.
• the final alignment may be accomplished as described previously, by placing an x-ray detector at the output aperture and adjusting the focus and position for the various electron beams to achieve maximum x-ray intensity. Final adjustments may also be made for the alignment of the optical elements using x-rays.
• the detector may also be used to provide feedback to the electron beam controllers, providing, for example, a measure of spectral output, which may in turn be used to direct an electron beam generating a particular characteristic line to increase or decrease its power.
• targets need to be illuminated with electrons with the same angle of incidence.
• some materials may have different penetration depths, and therefore bombarding with electrons at a different angle of incidence may be more efficient at producing x-rays for that particular target.
• different electron densities, energies, angles, focus conditions, etc. may be used for different targets.
• FIG. 39 illustrates an embodiment using three aligned targets 2801 , 2802, 2803 each comprising a microstructure 2881, 2882, 2883 of x-ray generating material embedded in a substrate 281 1 , 2812, 2813.
• Each of the targets is bombarded by an electron beam 1 181 , 1182, 1 183 respectively to generate x-rays 2818, 2828, 2838 respectively.
• x-ray imaging mirror optics 2821, 2822, 2831, 2832 are positioned to collect x-rays emitted at wider angles and redirect them to a focus at a position corresponding to the x-ray generating spot another x-ray target.
• the focus is set to be the x-ray generating spot in the adjacent target, but in some embodiments, all the x-ray mirrors may be designed to focus x-rays to the same point, for example, at the final x-ray generating spot in the final (rightmost) x-ray target.
• imaging mirror optics 2821, 2822, 2831, 2832 may be any conventional x-ray imaging optical element, such as an ellipsoidal mirror with a reflecting surface typically fabricated from glass, or surface coated with a high mass density material, or an x-ray multilayer coated reflector (typically fabricated using layers of molybdenum (Mo) and silicon (Si)) or a crystal optic, or a combination thereof.
• x-ray imaging optical element such as an ellipsoidal mirror with a reflecting surface typically fabricated from glass, or surface coated with a high mass density material, or an x-ray multilayer coated reflector (typically fabricated using layers of molybdenum (Mo) and silicon (Si)) or a crystal optic, or a combination thereof.
• Mo molybdenum
• Si silicon
• FIG. 40 A variation of this embodiment is illustrated in FIG. 40.
• the first (upstream) x-ray target 2830 now comprises a substrate 2833 in which microstructures 2883 of x-ray generating material have been embedded, as has been described elsewhere.
• the intensity of the x-rays 2838-A emitted from this target 2830 will be increased due to the linear accumulation of the x-rays emitted from these several microstructures 2883, and may contribute to a brighter overall x-ray source in this embodiment, just as they do in the previously described embodiments.
• the electron beam 1183-A may be adjusted to have a different incidence angle (as illustrated), size, shape and focus from the embodiment of FIG. 39 in order to bombard the microstructures 2883 more effectively.
• FIG. 41 Another variation of this embodiment is illustrated in FIG. 41.
• the second x-ray beam 2988-L propagating to the left is also illustrated.
• This second x-ray beam propagates through a second aperture 840-L in a plate 84-L, and can be used as a second x-ray exposure source, or can be used in conjunction with a detector 4444 to serve as a monitor for x-ray beam properties such as brightness, brilliance, total intensity, flux, energy spectrum, beam profile, and divergence or convergence.
• x-ray beam properties such as brightness, brilliance, total intensity, flux, energy spectrum, beam profile, and divergence or convergence.
• FIG. 42 Another embodiment of the invention is illustrated in FIG. 42.
• the optical elements 2921 and 2931 collecting x-rays emitted from one target and focusing them downstream are now optical elements known as Wolter optics.
• Wolter optics are a well known system of nested mirrors to collect and focus x-rays, typically having parabolic and/or hyperbolic reflecting surfaces with each element typically used at grazing angle.
• the reflecting surface is a glass.
• the glass surface may be coated with a high mass density material or an x-ray multilayer (typically fabricated using layers of molybdenum (Mo) and silicon (Si)).
• FIG. 43 A and FIG. 43B illustrate a prior art embodiments of Wolter optics used for x-rays comprising a variety of cylindrical lenses oriented both horizontally and vertically. As described above, the material selection and coatings used for these optical elements may be selected to match the spectrum of x-rays anticipated to be emitted from the various x-ray origins.
• FIG. 44 Another embodiment of the invention is illustrated in FIG. 44.
• the optical elements 2941 and 2951 collecting x-rays emitted from one target and focusing them downstream are now optical elements known as polycapillary optics.
• Polycapillary optics are similar to fiber optics, in that x-rays are guided through a thin fiber to emerge at the other end in a desired position. However, unlike fiber optics, which comprise a solid fiber of glass that reflects using total internal reflection, polycapillary optics comprise a number of hollow tubes, and the x-rays are guided down the tubes by an external reflection from the material at grazing angles.
• Polycapillary optics are a well known means of collecting and redirecting x- rays, and any of a number of conventional polycapillary optical elements may be used in the embodiments of the invention disclosed here. It is generally considered, however, that a polycapillary optic comprising multiple capillary fibers be used so that x-rays emitted at many angles can be collected and directed to a point of desired focus.
• a compact source for high brightness x-ray generation is achieved through electron beam bombardment of multiple regions aligned with each other to achieve a linear accumulation of x-rays. This is achieved by aligning discrete x-ray emitters, or through use of novel x-ray targets comprising a number of microstructures of x-ray generating materials fabricated in close thermal contact with a substrate with high thermal conductivity. This allows heat to be more efficiently drawn out of the x-ray generating material, and allows bombardment of this material with higher electron density and/or higher energy electrons, leading to greater x- ray brightness.
• the orientation of the micro structures allows the use of an on-axis collection angle, allowing accumulation of x-rays from several microstructures to be aligned, appearing to have a single origin, also known as "zero-angle" x-ray emission.
• An x-ray source comprising:
• At least one target comprising:
• a substrate comprising a first selected material
• the plurality of discrete structures are embedded into the surface of the substrate.
• the plurality of discrete structures are buried into the surface of the substrate within a depth of less than 100 microns.
• the means for directing an electron beam comprises electron optics.
• the means for directing an electron beam comprises electrostatic lenses.
• the means for directing an electron beam comprises magnetic lenses.
• the means for directing an electron beam allows for controlling the electron beam by an operation selected from the group consisting of:
• the means for directing an electron beam allows for
• the means for directing an electron beam allows for
• the means for directing an electron beam allows for
• the similar shapes are selected from the group consisting of
• the first selected material is selected from the group consisting of:
• the second material is selected from the group consisting of:
• the third material is selected from the group consisting of:
• the linear array is defined to have a long axis and a short axis
• microstructures of the target are aligned such that
• the target is aligned such that
• a cooling system comprising:
• the x-ray source of any of the preceding Concepts additionally comprising: a mechanism to rotate the target.
• An x-ray source comprising:
• a first window transparent to x-rays attached to the wall of the vacuum chamber; and, within the vacuum chamber,
• each target comprising a material selected for its x-ray generating properties, and in which at least one dimension of said material is less than 20 microns; and in which
• the material selected for its x-ray generating properties is selected from the group consisting of:
• At least one of the targets additionally comprises a substrate.
• the x-ray source of any one of Concepts 27-31 in which
• the substrate comprises a material selected from the group consisting of:
• the x-ray generating material is in the form of a thin film on the substrate.
• the target comprises a plurality of discrete structures embedded in a substrate comprising a material
• the x-ray source of Concept 34 additionally comprising:
• the means for directing an electron beam comprises electron optics.
• the x-ray source of Concept 39 additionally comprising
• the x-ray source of Concept 47 additionally comprising:
• the detector is aligned such that
• An x-ray source comprising:
• a first window transparent to x-rays attached to the wall of the vacuum chamber; and, within the vacuum chamber,
• a target comprising:
• the x-ray source of Concept 49 further comprising
• a plurality of targets comprising:
• the substrate comprises a material selected from the group consisting of:
• At least one of the structures is a thin film coating on the surface of the substrate.
• one or more microstructures is embedded
• the first electron emitter and the second electron emitter are aligned
• a method for generating x-rays comprising
• exposing at least one target comprising:
• a substrate comprising a first selected material
• each lateral dimensions of said at least one of the discrete structures is less than 50 microns
• a method for generating x-rays comprising
• FIG. 13 illustrates a region 1001 of a target according to an embodiment of the invention that comprises an array of microstructures 700 in the form of right rectangular prisms comprising x-ray generating material arranged in a regular array.
• FIG. 13A presents
• FIG. 13B illustrates a top down view of the same region
• FIG. 13C presents a side/cross-section view of the same region.
• side/cross-section view in this disclosure, the view meant is one as if a cross-section of the object had been made, and then viewed from the side towards the cross-sectioned surface. This shows both detail at the point of the cross-section as well as material deeper inside that might be seen from the side, assuming the substrate itself were transparent [which, in the case of diamond, is generally true for visible light].
• the microstructures have been fabricated such that they are in close thermal contact on five of six sides with the substrate. As illustrated, the top of the microstructures 700 are flush with the surface of the substrate, but other embodiments in which the microstructure is recessed may be fabricated, and still other embodiments in which the microstructures present a topographical "bump" relative to the surface of the substrate may also be fabricated.
• An alternative embodiment may have several microstructures of right rectangular prisms simply deposited upon the surface of the substrate. In this case, only the bottom base of the prism would be in thermal contact with the substrate.
• the ratio of the total surface area in contact with the substrate for the embedded microstructures vs. deposited microstructures is
• the ratio is essentially 1.
• FIG. 14A The heat transfer is illustrated with representative arrows in FIG. 14A, in which the heat generated in microstructures 700 embedded in a substrate 1000 is conducted out of the microstructures 700 through the bottom and sides (arrows for transfer through the sides out of the plane of the drawing are not shown).
• the amount of heat transferred per unit time ( ⁇ 0 conducted through a material of area A and thickness d given by:
• A is the thermal conductivity in W/(m °C) and AT is the temperature difference across thickness d in °C. Therefore, an increase in surface area A, a decrease in thickness d and an increase in A all lead to a proportional increase in heat transfer.
• FIG. 14B An alternative embodiment is illustrated in FIG. 14B, in which the substrate additionally comprises a cooling channel 1200.
• Such cooling channels may be a prior art cooling channel, as discussed above, using water or some other cooling fluid to conduct heat away from the substrate, or may be fabricated according to a design adapted to best remove heat from the regions near the embedded microstructures 700.
• the substrate may, for example, be bonded to a heat sink, such as a copper block, for improved thermal transfer.
• the copper block may in turn have cooling channels within it to assist in carrying heat away from the block.
• the substrate may be attached to a thermoelectric cooler, in which a voltage is applied to a specially constructed semiconductor device. In these devices, the flow of current causes one side to cool while the other heats up.
• Commercially available devices, such as Peltier coolers can produce a temperature difference of up to 70 °C across the device, but may be limited in their overall capacity to remove large amounts of heat from a heat source.
• the substrate can be attached to a cryogenic cooler, such as a block containing channels for the flow of liquid nitrogen, or be in thermal contact with a reservoir of liquid nitrogen or some other cryogenic substance, to provide more extreme cooling.
• a cryogenic cooler such as a block containing channels for the flow of liquid nitrogen
• thermal conductivity generally increases with decreasing temperature from room temperature.
• FIG. 15 illustrates an alternative embodiment in which the cavities formed in the substrate 1000 are first coated with an adhesion layer 715 (preferably of minimal thickness) before embedding the x-ray generating material that forms the microstructures 700.
• an adhesion layer may be appropriate in cases where the bond between the x-ray material and the substrate material is weak.
• the adhesion layer may also act as a buffer layer when the difference between thermal expansion coefficients for the two materials is large.
• the adhesion layer may be replaced or extended (by adding another layer) with a diffusion barrier layer to prevent the diffusion of material from the microstructures into the substrate material (or vice versa).
• the selection of materials and thicknesses should consider the thermal properties of the layer as well, such that heat flow from the microstructures 700 to the substrate 1000 is not significantly impeded or insulated by the presence of the adhesion layer 715.
• FIG. 16 illustrates an alternative embodiment in which an electrically conducting layer 725 has been added to the surface of the target.
• an electrically conducting layer 725 When bombarded by electrons, the excess charge needs a path to return to ground for the target to function effectively as an anode.
• the target as illustrated in FIG. 13 were to comprise only discrete, unconnected microstructures 700 within an electrically insulating substrate material (such as undoped diamond), under continued electron bombardment, significant charge would build up on the surface. The electrons from the cathode would then not collide with the target with the same energy, or might even be repelled, diminishing the generation of x-rays.
• a thin layer of conducting material that is preferably of relatively low atomic number, such as aluminum (Al), beryllium (Be), carbon (C), chromium (Cr) or titanium (Ti), that allows electrical conduction from the discrete microstructures 700 to an electrical path 722 that connects to a positive terminal relative to the high voltage supply.
• This terminal as a practical matter is typically the electrical ground of the system, while the cathode electron source is supplied with a negative high voltage.
• FIG. 17 illustrates another embodiment of the invention, in which the microstructures 702 are embedded deeper, or buried, into the substrate 1000.
• Such an embedded microstructure may be further covered by the deposition of an additional layer 1010, which may Appendix A be, for example, diamond, providing the same heat transfer properties as the substrate. This allows heat to be conducted away from all sides of the buried microstructure 702. For such a situation, however, it is advisable to provide a path 722 to ground for the electrons incident on the structure, which may be in the form of a embedded conducting layer 726 laid down before the deposition of the additional layer 1010.
• this conducting layer 726 will have a "via" 727, or a vertical connection, often in the form of a pillar or cylinder, that provides an electrically conducting structure to link the embedded conducting layer 726 to an additional conducting layer 728 on the surface of the target, which in turn is connected to the path 722 to ground.
• FIG. 18 illustrates another embodiment of the invention, in which the microstructures in turn comprise additional structures within them.
• the microstructure is shown having a bottom layer 731 , a middle layer 732, and a top layer 733. These layers may be selected to comprise different x-ray generating materials, such that the volume emits multiple characteristic lines.
• a microstructure comprising a number of materials arranged side-by-side may be used to achieve a desired x-ray emission spectrum.
• a microstructure comprising a uniform or non-uniform mixture or alloy of two or more materials may be used to achieve a desired x-ray emission spectrum.
• Another embodiment comprises having the middle layer 732 comprise the same material as that of the substrate, to provide high thermal dissipation for the top layer 733 and the bottom layer. Additionally, a conductive layer along the side wall (not shown) may be added to provide an electrical path to a conductive path, as was shown in FIGs. 16 and 17.
• FIG. 19 illustrates another embodiment of the invention, in which the microstructures 702 are again buried within the substrate.
• a single layer 770 is deposited, selected for a combination of electrical properties and thermally conducting properties.
• This single layer 770 may in turn be connected to a path 722 to ground to allow the target to serve as an anode in the x-ray Appendix A generation system.
• the material of the layer 770 may be selected to comprise aluminum (Al), beryllium (Be), chromium (Cr), or copper (Cu).
• the elements of these embodiments may be combined with each other, or combined with other commonly known target fabrication methods known in the art.
• the buried microstructures 702 of FIG. 19 may also comprise multiple materials, as was illustrated in FIG. 18.
• the adhesion layer 715 as illustrated in FIG. 15 may also be applied to fabrication of embedded microstructures 700 as shown in FIG. 16. The separation of these alternatives is for illustration only, and is not meant to be limiting for any particular process.
• microstructures illustrated in FIGs. 13-19 have been shown as regularly spaced patterns with uniform size and shape, an irregular or random pattern of uniform microstructures, or a regular pattern of microstructures having non-uniform size and shape, or an irregular pattern of microstructures having non-uniform size and shape can also be used in embodiments of the invention.
• microstructures in, for example, the shape of right rectangular prisms fabrication processes may create structures that have walls at angles other than 90°, or do not have corners that are exactly right angles, but may be rounded or beveled or undercut, depending on the artifacts of the specific process used.
• fabrication processes may create structures that have walls at angles other than 90°, or do not have corners that are exactly right angles, but may be rounded or beveled or undercut, depending on the artifacts of the specific process used.
• Embodiments in which the microstructures are essentially similar with the shapes described herein will be understood by those skilled in the art to be disclosed, even if process artifacts lead to some deviation from the shapes as illustrated or described.
• microstructures that have a distribution of sizes, with spacing between microstructures that can have a range of distances, may also be functional.
• FIG. 20 illustrates a region 101 1 of a target according to an embodiment of invention that comprises two regular arrays of microstructures 700 and 702 in the form of right rectangular prisms comprising x-ray generating material, typically a metal.
• the arrays are staggered laterally and at different depths such that, when under electron irradiation, each of the microstructure is surrounded by the "cooler" substrate material.
• the physical separation of the microstructures provides small hot spots in a sea of cooler material, thus generating many local thermal gradients that rapidly dissipate heat from the microstructures.
• FIG. 20A presents a perspective view of the sixteen embedded microstructures 700 and the nine buried
• FIG. 20B illustrates a top down view of the same region
• FIG. 20C presents a side/cross-section view of the same region.
• the buried microstructures 702 -A may be fabricated to be slightly larger than the embedded microstructures 700, such that electrical contact is established between the structures on different layers. If the buried microstructures 702-A have sufficient electrical conductivity, a single electrically conducting layer 725 providing a path 725 to ground may therefore be sufficient to prevent charging of both layers.
• the configuration illustrated in FIG. 21 A may, for some settings of electron energy and material composition, provide too small an area to provide effective heat transfer and electrical conduction.
• the buried microstructures 702-B may be fabricated to be buried deeper into the substrate 1000, and have their own conducting layer 726 connected by a via 727 to provide an additional electrical connection to the path 722 to ground for the buried microscructures 702-B.
• This configuration provides more distance between the sources of heat and x-rays, and for some applications may be preferred.
• the etching process can be tuned to provide an undercut.
• a process with an undercut is selected to etch the cavities in the substrate that are used to form the microstructures, and the Appendix A microstructures are formed using an isotropic process such as electroplating, which can fill all portions of the cavity, microstructures that are "secured” in place may be formed, as is illustrated in FIG. 22.
• FIG. 22 illustrates a region 1012 of a target according to an embodiment of invention that comprises an array of microstructures 704 that have been formed by filling cavities having an undercut in the substrate 1000.
• the microstructures 704 so formed are in the form of trapezoidal prisms comprising x-ray generating material.
• the array as shown is arranged as an embedded array in the surface of the substrate, and the "lip" or remaining substrate material around the top serves to better hold the microstructures 704 in place, preventing its detachment under stress or thermal overload.
• FIG. 22A presents a perspective view of the sixteen embedded trapezoidal microstructures 704 in this embodiment, while FIG. 22B illustrates a top down view of the same region, and FIG. 22C presents a side/cross-section view of the same region.
• FIG. 23 illustrates a region 1013 of a target according to an embodiment of invention that comprises a checkerboard array of microstructures 700 and 701 in the form of right rectangular prisms comprising x-ray generating material.
• the array as shown is arranged as an embedded array in the surface of the substrate.
• FIG. 23A presents a perspective view of the twenty- five embedded microstructures 700 and 701 in this embodiment, while FIG. 23B illustrates a top down view of the same region, and FIG. 23C presents a side/cross-section view of the same region with recessed regions shown with dotted lines.
• FIG. 24 illustrates a region 1014 of a target according to an embodiment of invention that comprises an array of microstructures 706 in the form of right regular cylinders comprising x-ray generating material.
• the array as shown is arranged as an array embedded in the substrate.
• FIG. 24A presents a perspective view of the sixteen embedded microstructures 706 in this embodiment, while FIG. 24B illustrates a top down view of the same region, and FIG. 24C presents a side/cross-section view of the same region across the center of a row of the microstructure 706.
• FIG. 25 also illustrates a region 1015 of a target according to an embodiment of invention that comprises a closely packed array of microstructures 708 and 709 in the form of right regular cylinders comprising x-ray generating material.
• the closely packed array as shown is also arranged as an embedded array in the surface of the substrate.
• Appendix A however, the arrangement is such that, when viewed from the side or end, there appear to be are no "gaps" in the source of the x-rays, as there would be for the arrangement of FIG. 24.
• FIG. 25A presents a perspective view of the eighteen embedded microstructures 708 and 709 in this embodiment
• FIG. 25B illustrates a top down view of the same region
• FIG. 25C presents a side/cross-section view of the same region with depth perception.
• FIG. 26 illustrates a region 1016 of a target according to an embodiment of invention that comprises a closely packed array of microstructures 711 and 712 in the form of right triangular prisms comprising x-ray generating material.
• the closely packed array as shown is arranged as an embedded array in the surface of the substrate.
• FIG. 26A presents a perspective view of the eighteen embedded microstructures 71 1 and 712 in this example, while FIG. 26B illustrates a top down view of the same region, and FIG. 26C presents a side/cross-section view of the same region with depth perception.
• FIG. 27 illustrates a region 1017 of a target according to an embodiment of invention that comprises a closely packed array of microstructures 713 and 714 in the form of tetrahedral prisms comprising x-ray generating material, in which a single face is approximately flush with the surface of the substrate 1000.
• the closely packed array as shown is arranged as an embedded array in the surface of the substrate.
• FIG. 27A presents a perspective view of the eighteen embedded microstructures 713 and 714 in this embodiment
• FIG. 27B illustrates a top down view of the same region
• FIG. 27C presents a side/cross-section view of the same region with depth perception.
• FIG. 28 illustrates a region 1018 of a target according to an embodiment of invention that comprises a combination of previously described microstructures 700, 701 and 702 in the form of right rectangular prisms comprising x-ray generating material.
• the layer of microstructures 700 and 701 embedded near the surface forms a checkerboard pattern, as was illustrated in FIG. 23, while the structure also comprises a buried layer of microstructures 702 that are placed below the "gaps" in the upper checkerboard pattern.
• FIG. 28A presents a perspective view of the forty-eight embedded microstructures 700, 701 , and 702 in this Appendix A embodiment, while FIG. 28B illustrates a top down view of the same region, and FIG. 28C presents a side/cross-section view of the same region with depth perception.
• FIG. 29 illustrates a region 1019 of a target according to an embodiment of invention that comprises both embedded microstructures 716 and buried microstructures 717 in the form of long right rectangular prisms comprising x-ray generating material.
• the long prisms are arranged to extend in directions orthogonal to each other, in a configuration that is often called a "stack-of-logs" configuration.
• the microstructures 717 in the buried layer may be in electrical contact with the microstructures 716 in the upper embedded layer, while in other embodiments, a distinct electrically conducting layer to carry charge away from the buried microstructures 717 may be fabricated to provide a path to ground.
• FIG. 29A presents a perspective view of the microstructures 716 and 717 in this embodiment
• FIG. 29B illustrates a top down view of the same region
• FIG. 29C presents a side/cross-section view of the same region with depth perception.
• FIG. 30 illustrates a region 1020 of a target according to an embodiment of invention that comprises an array of microstructures 718 in the form of spheres comprising x-ray generating material.
• the array as shown is arranged as an embedded array in the surface of the substrate.
• FIG. 30A presents a perspective view of the sixteen embedded microstructures 704 in this embodiment, while FIG. 30B illustrates a top down view of the same region, and FIG. 30C presents a side/cross-section view of the same region.
• Fabrication of a region of embedded spheres as illustrated in FIG. 30 may in some embodiments have a favorable mechanical rigidity or lower manufacturing cost, but the creation of a spherical cavity in the substrate into which material may be deposited may present process challenges. Therefore, in some embodiments, a hemispherical cavity may be created in the substrate, which is then filled with x-ray generating material, or pre-fabricated spheres may be deposited on the surface and encased with a deposited overcoat material.
• Microstmctures may be designated to be a predetermined thickness D within the target, where, as discussed before, D may be selected to be a certain fraction of the electron penetration depth for a electrons of a given energy in a given x-ray generating material (such as, for example, 30% or 50%) or may be a range of allowed depths.
• Microstructures may be specified such that their lateral dimensions L and Wdo not exceed D by more than a specific factor (e.g.
• microstmctures may be specified such that their lateral dimensions L and W do not exceed the x-ray attenuation length (the length at which the intensity of an x-ray beam of a specific energy falls off by a factor of 1/e), which will be different for different applications.
• the region comprising microstmctures may be specified by defining a volume fraction of the entire area to be exposed to electrons up to the thickness D that will comprise x-ray generating material.
• D x-ray generating material
• Such configurations may offer, for example, an advantage in terms of additional surface area for heat transfer.
• the volume fraction for the x-ray generating region may also be set to varying values, depending on the electron energy, the x-ray generating material properties, and the substrate reabsorption properties. For some applications requiring specific characteristic lines, configurations with a lower volume fraction may be preferred. For other variations on the emission spectmm, such as those with a range of wavelengths, a higher volume fraction that increases the bremsstrahlung may be preferred. In general, volume fractions in the first layer of thickness D may be set to be between 15% and 85% for various applications. Appendix A
• spherical microstructures of x-ray generating material may be prepared in advance, and then dispersed onto the surface of the substrate.
• a process that fixes the microstructures in place may be used, particularly if it is desired that the microstructures be positioned in a regular array (as was illustrated in
• FIG. 30 This may be followed by a deposition process that encases these spherical
• microstructures in a thermally conducting material may be a material chosen only for its thermally conducting properties, while in other cases, the deposited material may be selected as a mixture of materials selected so that both thermal conductivity and electrical conductivity are beneficial, and the encasing material also serves as the electrically conducting layer that provides a path to ground.
• the dispersal of microstructures comprising x-ray generating material need not be confined to uniform spheres, but may be a number or particles of various sizes and shapes. This is illustrated in FIG. 31, in which a region 1021 of a target according to the invention comprises non-uniform microstructures. Likewise, in a similar embodiment, a region 1022 of a target according to the invention may comprise microstructures not only of varying sizes and shapes, but microstructures of different material compositions as well, as illustrated in FIG. 32.
• a surface with additional properties in three dimensions may be desired.
• the apparent x-ray source size and area is at minimum (and brightness maximized) when viewed parallel to surface, i.e. at a zero degree (0°) take-off angle.
• the apparent brightest of x-ray emission occurs when viewed at 0° take-off angle.
• the emission from within the x-ray generating material will accumulate as it propagates at 0° through the material.
• the attenuation of x-rays between their points of origin inside the target as they propagate through Appendix A the material to the surface increases with decreasing take-off angle, due to the longer distance traveled within the material, and often becomes largest at or near 0° take-off angle. Reabsorption may therefore counterbalance any increased brightness that viewing at near 0° achieves.
• the distance through which an x-ray beam will be reduced in intensity by 1/e is called the x-ray attenuation length, and therefore, a configuration in which the emitted x-rays pass through as little additional material as possible, with the distance selected to be related to the x-ray attenuation length, may be desired.
• FIG. 33 An illustration of one embodiment of a target is presented in FIG. 33.
• an x-ray generating region comprising a single microstructure 2700 is configured at or near a recessed edge 2003 of the substrate on a shelf 2002, similar to the situation illustrated in FIG. 10.
• the x-ray generating microstructure 2700 is in the shape of a rectangular bar of x-ray generating material, is embedded in a substrate 2000, and emits
• the thickness of the bar D (along the surface normal of the target) is selected to be between one third and two thirds of the electron penetration depth of the x-ray generating material at the incident electron energy for optimal thermal performance. It may also be selected to obtain a desired x-ray source size in the vertical direction. The width of the bar Wis selected to obtain a desired source size in the corresponding direction. As illustrated, W ⁇ 1.5Z ) , but could be substantially smaller or larger, depending on the size of the source spot desired.
• the length of the bar L as illustrated is L ⁇ 4D , but may be any dimension, and may typically be determined to be between 1 ⁇ 4 to 3 times the x-ray attenuation length for the selected x-ray generating material.
• the distance between the edge of the shelf and the edge of the x-ray generating material p as illustrated ⁇ sp ⁇ W, but may be selected to be any value, from flush with the edge 2003 (p 0) to as much as 1 mm, depending on the x-ray reabsorption properties of the substrate material, the relative thermal properties, and the amount of heat expected to be generated when bombarded with electrons.
• FIG. 34 An illustration of an alternative embodiment of the invention is presented in FIG. 34.
• a target according to the invention comprising an x- ray generating region with six microstructures 2701 , 2702, 2703, 2704, 2705, 2706 is configured at or near a recessed edge 2003 of the substrate on a shelf 2002, similar to the situation illustrated in FIG. 10 and FIG. 33.
• 2706 are arranged in a linear array of x-ray generating right rectangular prisms embedded in a substrate 2000, and emit x-rays 2888-D when bombarded with electrons 1 1 1.
• the total volume of x-ray generating material is the same as in the previous illustration of FIG. 33.
• the thickness of the bar D (along the surface normal of the target) is selected to be between one third and two thirds of the electron penetration depth of the x-ray generating material at the incident electron energy for optimal thermal performance, as in the case shown in FIG. 33.
• the width of the bar Wis selected to obtain a desired source size in the corresponding direction and as illustrated, W ⁇ 1.5 D, as in the case shown in FIG. 33. As discussed previously, it could also be substantially smaller or larger, depending on the size of the source spot desired.
• each sub-bar now has five faces transferring heat into the substrate, increasing the heat transfer away from the x-ray generating sub-bars 2701-2706 and into the substrate.
• the separation between the sub-bars is a distance d ⁇ 1, although larger or smaller dimensions may also be used, depending on the amount of x-rays absorbed by the substrate and the relative thermal gradients that may be achieved between the specific materials of the x-ray generating microstructures 2701-2706 and the substrate 2000.
• the total length of the x-ray generating sub-bars will commonly be about twice the linear attenuation length for x-rays in the x-ray generating material, but can be selected from half to more than 3 times that distance.
• the thickness of the bar (along the surface normal of the target) D was selected to be equal to one third to two thirds of the electron penetration depth of the x-ray generating material at the incident electron energy for optimal thermal performance, but it can be substantially larger. Appendix A
• the bars as shown may be embedded in the substrate (as shown), but if the thermal load generated in the x-ray generating material is not too large, they may also be placed on top of the substrate.
• FIG. 35 which shows a region 2001 of a target according to an embodiment of invention with an array of microstructures 2790 and 2791 comprising x-ray generating material having a thickness D.
• the array as shown is a modified checkerboard pattern of right rectangular prisms, but other configurations and arrays of microstructures may be used as well.
• these microstructures 2790 and 2791 are embedded in the surface of the substrate.
• the surface of the substrate comprises a predetermined non-planar topography, and in this particular case, a plurality of steps along the surface normal of the substrate 2000.
• the height of each step is h ⁇ D, but the step height may be selected to be between lx and 3x the thickness of the microstructures.
• the total height of all the steps may be selected to be equal or less than the desired x-ray source size along the vertical (thickness) direction.
• the total width of the microstructured region may be equal to the desired x-ray source size in the corresponding direction.
• the overall appearance resembles a staircase of x-ray sources.
• FIG. 35A presents a perspective view of the eighteen embedded microstructures 2790 and 2791 in this embodiment, while FIG. 35B illustrates a top down view of the same region, and FIG. 35C presents a side/cross-section view of the same region.
• An electrically conductive layer may be coated on the top of the staircase structures when the substrate is beryllium, diamond, sapphire, silicon, or silicon carbide.
• FIG. 36 illustrates the x-ray emission 888-S from the staircase embodiment of FIG. 35C when bombarded by electrons 1 1 1.
• the prisms of x-ray generating material heat up when electrons collide with them, and because each of the prisms of x-ray generating material has five sides in thermal contact with the substrate 2000, conduction of heat away from the x-ray material is still larger than a configuration in which the x-ray material is deposited on the surface.
• the emission is of x-rays unattenuated by Appendix A absorption from other neighboring prisms and negligibly attenuated by neighboring substrate material.
• FIG. 23 which also illustrates a number of prisms 700 and 701 of x-ray generating material arranged in a checkerboard pattern.
• each prism is embedded in the substrate, therefore having five surfaces in thermal contact with the substrate 1000, but the emission to the side at 0° will be attenuated by both the prisms of the neighboring columns and the substrate material.
• Such an embodiment comprising a target with topography may be manufactured by first preparing a substrate with topography, and then embedding the prisms of x-ray material following the fabrication processes for the previously described planar substrates.
• the initial steps that create cavities to be filled with x-ray material may be enhanced to create the staircase topography structure in an initially flat substrate.
• additional alignment steps such as those known to those skilled in the art of planar processing, may be employed if overlay of the embedded prisms with a particular feature of topography is desired.
• Microstrutures may be embedded with some distance to the edges of the staircase, as illustrated in FIGs. 35 and 36, or flush with as edge (as was shown in FIG. 9).
• a determination of which configuration is appropriate for a specific application may depend on the exact properties of the x-ray generation material and substrate material, so that, for example, the additional brightness achieved with increased electron current enabled by the thermal transfer through five vs. four surfaces may be compared with the additional brightness achieved with free space emission vs. reabsorption through a section of substate material.
• the additional costs associated with the alignment and overlay steps, as well as the multiple processing steps that may be needed to pattern multiple prisms on multiple layers, may need to be considered in comparison to the increased brightness achievable.
• FIG. 37 illustrates an embodiment of the invention configured as a rotating anode 2500.
• a plurality of x-ray generating materials have been formed, and may be formed by any of the processes previously described.
• two distinct materials are illustrated, each with various microstructures in the form of either annular rings 2508 and 2509 or square structures 2518 and 2519.
• additional cooling channels may be provided in the rotating anode to further cool the anode, allowing bombardment with electrons at higher voltages or with higher current densities to make a brighter x-ray source.
• the target material in the rotating anode uses a plurality of microstructures according to the invention disclosed herein, the improved thermal properties may allow higher electron power loading. This enables an x-ray source of higher brightness, because the electron energy and current may be increased once the additional heat load can be accommodated.
• the thermal benefits may be used to enable a rotating anode source of the same brightness, but with components that are easier to engineer, such as lower voltage, lower current, or slower anode rotation speed. Appendix A
• the methods for fabricating the targets according to the invention involve a number of steps that are outlined in the flow chart of FIG. 38, and the cross-section diagrams of FIGs. 39 - 40.
• a substrate 3000 of a suitable material is selected.
• FIG. 39A this is denoted by the step designated "1)".
• this will typically be a material selected for various physical and thermal properties, and in particular, low mass density, low Z, and a high thermal conductivity.
• substrate materials are listed in Table I, several with high thermal conductivity (i.e. materials with thermal conductivity greater than 100 W/(m °C)).
• diamond stands out as a potential substrate.
• the thermal conductivity is -2200 W/(m °C), one of the highest values known for any material.
• approximately -120 °C this value can increase to be almost three times higher.
• Wafers of CVD grown diamond up to 120 mm in diameter and with diamond coatings up to 2 mm thick may be may be purchased from Diamond Materials GmbH of Freiburg, Germany.
• Substrates of silicon coated with diamond or diamond on insulator (DOI) may also be purchased from, for example, Advanced Diamond Technologies, Inc. of
• Diamond-like carbon (DLC) films such as those manufactured by Richter Precision, Inc. of East Louis, PA may also be useful as substrate materials.
• Beryllium may also be a candidate for a substrate material.
• Beryllium wafers may be commercially purchased from, for example, American Elements, Inc. of Los Angeles, CA, and Atomergic Chemetals Corporation of Farmingdale, New York. Appendix A
• substrates are graphite, silicon, boron nitride, gallium nitride, silicon carbide and sapphire. Other suitable materials may also be known to those skilled in the art.
• the next step 3100 is to pattern the substrate 3001, as shown in FIG. 39A.
• the next step 3100 is to pattern the substrate 3001, as shown in FIG. 39A.
• H. Masuda et al. "Fabrication of Through-Hole Diamond Membranes by Plasma Etching Using Anodic Porous Alumina Mask", Electrochemical and Solid-State Letters, vol. 4(1 1), pp. G101-G103 (2001); Y. Ando et al. "Smooth and high-rate reactive ion etching of diamond", Diamond and Related Materials vol. 11 (2002) pp. 824-827 (2002); X.D. Wang et al. "Precise patterning of diamond films for MEMS application", J. Material Processing
• a polished polycrystalline diamond film ⁇ 3 mm thick is patterned using a porous alumina mask.
• the mask is prepared in advance using a silicon carbide mold to texture an aluminum surface, which is subsequently oxidized through an anodization process.
• the alumina film so formed has pores with positions determined by the texture on the SiC mold.
• the film is then removed from its aluminum substrate and transferred to the diamond surface.
• the diamond is then subjected to an oxygen reactive ion etch process, in which the porous alumina film acts as a mask.
• step "a)" a mask 3060 is formed and patterned on a substrate 3050.
• the mask may be, for example, alumina patterned on an aluminum substrate.
• step “b) the mask is removed.
• step "2) the mask 3060 is attached to the substrate 3000.
• step "3) the mask and substrate undergo a pattern transfer step, such as an oxygen reactive ion etch (RIE), Appendix A creating the patterned substrate 3001 from the initial substrate 3000.
• step "4) the mask 3060 is removed, and leaving the patterned substrate 3001.
• RIE oxygen reactive ion etch
• the substrate may be patterned using conventional lithographic processes. These may include coating the substrate with a photoresist, such as HSQ, and exposing the resist using electron beams or ultraviolet photons in a pattern that represents the desired structure to be formed on the wafer. The resist is then developed to remove the exposed regions, laying the substrate bare. The substrate and patterned resist combination are then processed with a suitable etching process (such as a reactive ion etch (RIE) with oxygen gas) that transfers the pattern in the resist into the substrate. Once this is completed, the excess resist is removed, leaving a patterned substrate essentially the same as the patterned substrate 3001 designated by step "4)" in FIG. 39A and 39B.
• RIE reactive ion etch
• the substrate may be coated with a specially selected material that serves as a hard mask for patterning the substrate.
• the steps in this case are: coating of a hard mask onto the substrate, coating resist onto the hard mask, patterning the resist with either electron or optical exposure, developing the resist, transferring the pattern from the resist into the hard mask, and transferring the pattern from the hard mask into the substrate, leaving a patterned substrate essentially the same as the patterned substrate 3001 designated by step "4)" in
• FIGs. 39A and 39B Such lithographic processes and their variations may be well known to those skilled in the art.
• the substrate may also be directly ion milled using a machine such as a focused ion beam.
• Other techniques, such as laser etching, may also be used to pattern the substrate.
• the next step is the deposition of a material that can produce x-rays of desired characteristics into the patterned cavities 3300.
• This may be through any number of well-known deposition techniques, depending on the material, including chemical vapor deposition (CVD), sputtering, electroplating, mechanical stamping, or others that will be known to those skilled in the art.
• CVD chemical vapor deposition
• sputtering sputtering
• electroplating electroplating
• mechanical stamping or others that will be known to those skilled in the art.
• x-ray generating materials including aluminum, titanium, vanadium, chromium, manganese, iron, Appendix A cobalt, nickel, copper, gallium, zinc, yttrium, zirconium, molybdenum, niobium, ruthenium, rhenium, rhodium, palladium, silver, tin, iridium, tantalum, tungsten, indium, cesium, barium, gold, platinum, lead and combinations and alloys thereof.
• step of polishing 3500 with either a mechanical/abrasive polishing process, or a chemical-mechanical polishing (CMP) process, removes the excess material, leaving behind the cavities in the patterned substrate 3001 now filled with discrete microstructures 3401 of x-ray material, as illustrated with the corresponding step in FIG. 39B denoted by "6)".
• CMP chemical-mechanical polishing
• Some materials when used in combination with certain substrates, may form an interface layer that provides a good bond between the two.
• CVD deposition of tungsten material 3400 onto a patterned diamond substrate 3001 can be adequate to fill the cavities in the diamond, with the tungsten forming a strong carbide bond in the boundary between the tungsten and the carbon.
• an adhesive layer such as the deposition of a 10 nm thick layer of titanium (Ti) or chromium (Cr) between the copper and a diamond substrate may be preferred to improve the mechanical integrity of the anode, both by increasing the adhesion between the two materials, and also in some cases by preventing diffusion of material from one region into the other.
• step “5a)” illustrates the deposition of a suitable adhesion layer 3350 onto the patterned substrate 3001.
• Typical adhesion layers 3350 may be layers of chromium (Cr) or titanium (Ti) when used, for example, with copper (Cu) as the x-ray material.
• Other materials may include carbide alloys of the target material, such as copper carbide (CuC) for copper or aluminum carbide (AIC) for aluminum.
• CuC copper carbide
• AIC aluminum carbide
• other materials with good adhesion to both materials known to those skilled in the Appendix A art may be used.
• molybdenum is often used as a barrier layer for copper.
• adhesion layers multiple layers of materials, such as titanium carbide (TiC) bilayers or chromium carbide (CrC) bilayers may be used as adhesion layers.
• the thickness of the adhesion layer may vary with the selection of x-ray material and substrate material, but will typically be on the order of 10 nm thick.
• the deposition step may be followed by a carbonization step, to form a carbide compound with the substrate.
• a carbide material may be directly deposited to provide an adhesion layer.
• the next step is the deposition of a conducting layer, so that electrons impinging on the x-ray material will have a path to ground.
• the deposited material 3750 may be any one of a number of electrically conducting materials, such as beryllium (Be), aluminum (Al), chromium (Cr), titanium (Ti), silver (Ag), gold (Au), copper (Cu), or carbon materials such as graphite or carbon nanotubes.
• the material may be as thin as 5 nm or as thick as 100 nm, and in some circumstances, such as if there are larger topography variations in the substrate with filled cavities, the material may be as thick as 500 nm.
• the deposition techniques may be any number of a variety of deposition techniques, including but not limited to chemical vapor deposition (CVD), sputtering, electroplating, mechanical stamping, or others that will be known to those skilled in the art.
• CVD chemical vapor deposition
• sputtering sputtering
• electroplating electroplating
• mechanical stamping or others that will be known to those skilled in the art.
• a final protective overcoat, or cap layer may also be deposited.
• the deposited material 3950 may be any one of a number of materials, but may be typically selected to be the same material used for the substrate, such as diamond (C) diamond-like carbon (DLC), or beryllium (Be), or another materials, such as silicon carbide Appendix A
• the material may be as thin as 100 nm, or may be as thick as 50 ⁇ .
• the deposition techniques may be any number of a variety of deposition techniques, including but not limited to chemical vapor deposition (CVD), sputtering, electroplating, mechanical stamping, or others that will be known to those skilled in the art.
• CVD chemical vapor deposition
• sputtering sputtering
• electroplating electroplating
• mechanical stamping or others that will be known to those skilled in the art.
• the deposition of the cap layer may be preceded by the deposition of an adhesion layer, such as a titanium carbide (TiC) to form a seed layer for the growth of diamond.
• an adhesion layer such as a titanium carbide (TiC) to form a seed layer for the growth of diamond.
• TiC titanium carbide
• the deposition may be very thin, perhaps between 1 and 5 nm, to provide this seed layer.
• the final object comprises a substrate comprising a plurality of microstructures of x-ray generating material suitable for use as a target in an x-ray source.
• the electrically conducting layer has been described as occurring before the deposition of a cap layer, but a layer that combines these functions (i.e. an electrically conducting cap layer) such as that illustrated in FIG. 19. Likewise, some of the process steps may be repeated to deposit multiple layers of target materials, as was illustrated in FIG. 18.
• multiple layers of microstructures may be created by repeating process steps (or portions thereof) as described in this section.
• FIG. 13C Appendix A
• FIG. 14B Appendix A
• FIG. 16 Appendix A
• FIG. 18 Appendix A
• FIG. 19 Appendix A
• FIG.21A A first figure.
• FIG.21B Appendix A
• FIG. 22A is a diagrammatic representation of FIG. 22A
• FIG. 22C Appendix A 3
• FIG. 23C Appendix A
• FIG. 24C Appendix A
• FIG. 25A is a diagrammatic representation of FIG. 25A
• FIG. 25C Appendix A
• FIG. 26C Appendix A
• FIG. 27C Appendix A
• FIG. 28A is a diagrammatic representation of FIG. 28A
• FIG. 28C Appendix A
• FIG. 29C Appendix A
• FIG. 30A is a diagrammatic representation of FIG. 30A
• FIG. 30C Appendix A
• FIG. 32 Appendix A
• FIG. 33 Appendix A
• FIG. 34 Appendix A
• FIG. 35C Appendix A
• FIG. 37 Appendix A
• Substrate e.g. Diamond
• FIG. 39B Appendix A

Landscapes

• X-Ray Techniques (AREA)

Priority Applications (4)

Applications Claiming Priority (12)

Publications (2)

Family

ID=53274258

Family Applications (1)

Country Status (4)

Cited By (20)

Families Citing this family (13)

Citations (2)

Family Cites Families (22)

• 2014
  • 2014-09-19 CN CN201480051973.6A patent/CN105556637B/zh active Active
  • 2014-09-19 WO PCT/US2014/056688 patent/WO2015084466A2/en active Application Filing
  • 2014-09-19 EP EP16200793.4A patent/EP3168856B1/en active Active
  • 2014-09-19 JP JP2016544039A patent/JP2016537797A/ja active Pending
  • 2014-09-19 EP EP14868433.5A patent/EP3047501A4/en not_active Withdrawn
• 2018
  • 2018-09-26 JP JP2018179789A patent/JP6659025B2/ja active Active

Patent Citations (2)

Non-Patent Citations (1)

Also Published As

Similar Documents

Legal Events