RU2426103C1 - Method of coherent x-ray phase microscopy - Google Patents

Abstract

FIELD: physics. ^ SUBSTANCE: solid object is irradiated by spatially coherent X-ray beam to detect diffraction 2D crosswise radiation intensity is far zone foe every discrete spatial position of object relative to sounding beam, 3D image is reconstructed by computer at spontaneous characteristics single-wave radiation to define mean contrast of 2D crosswise radiation spectrum field for every spatial position, coherence time äc of sounding radiation is decreased or radiation spectral line width övc is increased on changing from characteristic X-ray radiation to continuous decelerating X-ray radiation to magnitude corresponding to two-fold decrease in radiation spectrum filed contrast to define local phase lag äph from relation äph=äc=1/övc measured for every angle of object rotation so that 3D distribution of electron density and refractivity are reconstructed. ^ EFFECT: noninvasive measurement of 3D micro- and nano object images in using traditional X-ray tubes. ^ 2 cl, 2 dwg

Description

The invention relates to the field of semiconductor nano- and biomedical diagnostic technologies, in particular, to the creation of coherent X-ray tomographs that make it possible to contactlessly determine spatial inhomogeneities in nanolayers of semiconductor structures, as well as non-invasively determine the spatial distribution of electronic density of biological micro- and nanoscale intracellular structures.

A known method of x-ray tomography, including irradiating a three-dimensional object with an x-ray emitter equipped with an output slit, the emitter is located on a rotating ring. In the center of the ring is an irradiated three-dimensional object. X-ray radiation transmitted and scattered by the object is detected using a detector matrix located on the part of the ring opposite the emitter. To obtain a reconstructed computer three-dimensional image, a circular scan of the X-ray emitter and receiver relative to the axis of the ring is performed, along which the diagnosed object is scanned (see US patent No. 2007140410, IPC H05G 1/60; АВВ 6/00).

However, the minimum spatial resolution is of the order of a millimeter. This spatial resolution, typical of medical tomographs, is not enough for semiconductor nanotechnology or microbiology to diagnose intracellular structures.

A known method of x-ray structural analysis of crystal structures, including irradiating the surface of a bulk sample with a collimated beam of characteristic x-ray radiation, measuring the intensity of the reflected x-ray beam at a Bragg-Wulff angle when scanning the slip angle between the incident beam and the measured surface. The diffraction maximum of the reflected x-ray waves from the probed three-dimensional periodic structure satisfies the Bragg-Wulf relation

d _i sinφ _i = mλ,

where λ is the wavelength of the probe characteristic x-ray radiation; d _i - interplanar distance in the investigated crystal; φ _i is the slip angle, m is an integer (catalog of the company "Oxford Diffraction", 2009; sales@oxford-diffraction.com).

A known X-ray reflectometer using sounding on two X-ray lines with coaxial radiation of two beams from anticathodes from different materials of two X-ray tubes (see RF patent No. 2166184, IPC G01B 15/08, G01N 23/20). An X-ray reflectometer contains a polychromatic X-ray source, X-ray beam collimation means, a sample holder, a swivel bracket, on which a number of monochromators and radiation detection means are placed. The reflectometer further comprises a second radiation source, at least one translucent monochromator located along the x-ray beam between the radiation sources and the sample holder, and means for angular displacement of the second radiation source and the translucent monochromator. In this case, it is possible to install a translucent monochromator in a position in which the two indicated radiation sources are simultaneously irradiated on opposite sides of the translucent monochromator at different angles.

The use of x-ray radiation with coaxial beams with different wavelengths makes it possible to more accurately determine the lattice parameters of a crystal in difference diffraction angles.

However, this method does not allow to determine a three-dimensional image of the probed nano- or micro-object.

Closest to the claimed is a method of coherent x-ray diffraction microscopy. This method is used to obtain a three-dimensional phase-contrast image of disordered objects, that is, bodies that do not have periodicity properties in their internal structure (Phys. Rev. Lett. 102, 018101, 2009. Three-Dimensional Visualization of a Human Chromosome Using Coherent X- Ray Diffraction. Yoshinori Nishino, Yukio Takahashi, Naoko Imamoto, Tetsuya Ishikawa, Kazuhiro Maeshima).

The method includes irradiating a nanoobject (chromosome) with an X-ray laser beam having maximum spatial and temporal coherence. The beam is pre-diaphragmed using an absorbing screen with a micro-hole (20 microns in diameter) and two mutually perpendicular slots, transmitted and diffracted by a nanoobject, coherent X-ray radiation is detected using a detector array (CCD camera) for each fixed position of the rotation angle of the nanoobject around the axis perpendicular to the perpendicular . Computer reconstruction of the three-dimensional structure of a nano-object from the finite sequence of two-dimensional diffracted X-ray fields obtained for the corresponding rotation angles was performed using the algorithm (J. Miao, KOHodgson, T. Ishikawa, C. A. Larabell, MALe Gros, and Y. Nishino, Proc. Natl. Acad. Sci. USA. 100, 110, 2003).

However, this method does not allow us to identify phase delays associated with the interaction of X-ray radiation with a volumetric probed object having a different electron density, which is reflected in the characteristics of the speckle field contrast. In addition, this method for its implementation requires the use of an X-ray laser, which is very expensive ($ 1.3 billion was spent on the implementation of an X-ray laser in Japan), and this method is used only for basic fundamental research.

The objective of the invention is to enable not only the visualization of a three-dimensional image based on sensing by spontaneous x-ray radiation with controlled coherence, but also the possibility of determining the electron density of probed amorphous objects with nanoscale spatial resolution.

The technical result consists in the possibility of non-invasive measurement of 3D 3D images of micro- and nano-objects using traditional x-ray tubes with spontaneous x-ray characteristic and bremsstrahlung.

The problem is solved in that in a method of coherent X-ray phase microscopy, which includes irradiation with a spatially coherent X-ray beam, detecting the diffraction transverse distribution of the transmitted radiation intensity in the far zone for each discrete spatial position of the object relative to the probe X-ray beam, computer reconstruction of the three-dimensional image, according to the solution, is established spontaneous characteristic resonant radiation mode, you they use a monochromator to transmit one wavelength, use a focon to form an x-ray beam, and two adjustable slots located at the exit of the focon create a spatially coherent x-ray beam, emit one wavelength of characteristic radiation, not only transverse two-dimensional distribution is determined for each spatial position of the object intensity, but also calculate the average contrast of the two-dimensional distribution of transverse speckle field of transmitted radiation, reduce the coherence time τ _c probing present the x-ray radiation, or respectively increased spectral line width Δν _c radiation in the restructuring of the characteristic X-rays to a continuous bremsstrahlung X-ray radiation to a value corresponding halving the contrast of speckle radiation field, and determining the local phase delay τ _ph of the ratio τ _ph = τ _c = 1 / Δν _c, measured for each rotation angle of the test object, and the computer reconstruct three-dimensional distribution of electron density and relative dormancy refractive exponent.

In addition, the method of coherent X-ray phase microscopy, including irradiation with a coherent X-ray beam, detecting the diffraction transverse distribution of the transmitted radiation intensity in the far zone for each discrete spatial position of the object relative to the probe X-ray beam, computer reconstruction of a three-dimensional image, according to another embodiment, the frequency Δν _{L of the} stimulated x-ray radiation to a value corresponding to a halving the two-dimensional correlation coefficient of scattered speckle fields, and determine the local phase delay τ _ph from the relation τ _ph = 1 / Δν _L measured for each rotation angle of the probed object, the volume distribution of electron density and relative refractive index is computer-reconstructed.

The invention is illustrated by drawings, figure 1 shows a block diagram of a device for determining the volumetric image of micro- and nanostructured objects based on the measurement of x-ray coherent-phase microscopy with controlled temporal coherence, figure 2 shows a block diagram of a device for determining the volumetric image of micro- and nanostructured objects based on measurements of coherent X-ray microscopy with a controlled x-ray radiation frequency,

Where

1. voltage controlled x-ray tube;

2. power supply of an x-ray tube controlled by a personal computer;

3. an x-ray lens based on a focon, which is a hollow glass microtubule with a decreasing diameter;

4. dividing crystal;

5. two mutually perpendicular adjustable slots;

6. investigated micro- or nano-object;

7. matrix detector;

8. personal computer;

9. X-ray waveguide spectrometer;

10. a scanner that allows you to rotate the object and displace perpendicular to the probe beam;

11. X-ray laser.

The method is as follows.

In the x-ray tube 1, by changing the voltage in the power supply 2, a spontaneous characteristic x-ray emission mode is set at a single resonant wavelength. Divergent x-ray radiation is introduced into the x-ray lens 3, which is a focon consisting of hollow glass microtubes, the diameter of which along the length of the tubes, which are tens of centimeters, is continuously reduced by several orders of magnitude, which makes it possible to obtain an x-ray beam diameter of not more than 10 microns at In this case, the radiation power density can increase by 8 orders of magnitude. A part of the x-ray beam generated by the focon is sent to a X-ray waveguide spectrometer 9 using a fission crystal 4. The use of two mutually perpendicular slots 5 makes it possible to reduce the beam size to hundreds of nanometers and obtain a spatially coherent X-ray beam. The investigated micro- or nano-object 6 is irradiated with such an X-ray beam. In this case, the micro- or nano-object 6 discretely rotates about the axis perpendicular to the X-ray beam using the scanner 10. If the size of the object 6 is larger than the size of the beam, then using the scanner 10 the object is perpendicular to the axis x-ray beam. For each spatial position of the investigated object, the intensity of transmitted and diffracted coherent X-ray radiation is detected using a matrix detector 7. Using a personal computer, 8 of the two-dimensional distribution of the transmitted x-ray characteristic radiation intensity obtained for a set of discrete angles of rotation of the object, a three-dimensional image of the object is computer-reconstructed, and the calculation phase delays in a bulk medium linearly related to electronically The power and relative refractive index allows reconstructing the distribution of electron density or relative refractive index (see RF patent No. 2308012, IPC G01M 11/02).

The matrix detector 7, which detects the intensity of x-ray radiation, is spatially located in the far diffraction zone at a distance L from the object. This distance is selected from the condition determined by the transverse size of the pixel in the matrix detector 7, which should be smaller or much smaller than the characteristic transverse size of the X-ray speckles associated with the transverse dimensions of the slits d from the relation r _s ≈λ · L / π · d. Estimates show that if L = 1 meter, λ = 0.1 nm, d = 1 micron, r _s ≈30 microns. By decreasing the voltage on the x-ray tube, the intensity of the resonant characteristic x-ray radiation having a coherence length L _c determined by the ratio L _c ≈λ ² / Δλ and reaching L _c ≈10 ³ -10 ⁴ · λ, where λ is the wavelength of the characteristic x-ray radiation line, is decreased. , Δλ is the width of the corresponding emission line. In this case, the relative contribution to the total intensity of the bremsstrahlung x-ray increases. In the limiting case of radiation of only continuous bremsstrahlung X-rays, the typical coherence length is L _c ≈ 2-3λ. Thus, by varying the voltage on the x-ray tube 1, it is possible to effectively control the temporal coherence of the x-ray radiation τ _c and, accordingly, the coherence length L _c = τ _c · s, which makes it possible to halve the speckle field contrast, and for this radiation setting of the x-ray tube 1, the x-ray the emission spectrum using an X-ray waveguide spectrometer 9 and determine the spectrum width Δν _c = Δλ · s / λ ² . From the known Khinchin-Wiener relation τ _c = 1 / Δν _c , the radiation spectrum width Δν _c is related to the emitter coherence time τ _c . The coherence time τ _c determines the phase delay τ _ph corresponding to halving the speckle field contrast, the phase delay determined in this way, measured for each angle of rotation of the object relative to the probe x-ray beam, allows the computer to reconstruct the spatial electron density and relative refractive index.

When using the radiation of an X-ray laser 11, for each radiation frequency, a two-dimensional speckle field intensity for the transmitted radiation object is measured and the laser radiation frequency corresponding to halving the two-dimensional speckle field correlation coefficient is recorded and the local phase delay is determined from the relation

τ _c = 1 / Δν _L ,

where Δν _L is the tuning range of the radiation frequency of the X-ray laser, corresponding to a halving of the two-dimensional correlation coefficient of speckle fields.

The methodological basis for measuring phase delays in three-dimensional structures when probing with X-ray radiation is interference phenomena arising from multiple scattering of electromagnetic waves, first tested in the optical range for emitters (superluminescent diodes) with a controlled coherence length (see RF patent No. 2308012, IPC G01M 11 / 02). When a two-dimensional object is irradiated with a spatially coherent beam of monochromatic electromagnetic waves (radio, optical and X-ray) with characteristic wavelengths from meters to nanometers, the so-called speckle field appears in the far diffraction zone due to interference of the scattered waves, and the contrast of the speckle fields will tend to unit. For a three-dimensional object, if the thickness of the probed object is greater than the wavelength, then during diffraction in such three-dimensional structures, phase delays of scattered waves occur, which will be reflected in the interference pattern in the far zone. When probing with x-ray laser radiation with a coherence time, much more than the time (phase) delays in the volume object under study, the speckle field contrast will be maximum. However, if the temporal coherence of the emitter is reduced and much smaller than the phase delays, the contrast of the speckle field will tend to zero.

The inventive method proposes to determine the phase delay while reducing the contrast of diffracted speckle fields by half. The measurement of the phase or time delays of the probed waves is unambiguously associated with a change in the relative refractive index of the medium (propagation velocity of electromagnetic waves) due to the interaction of the waves with the probed medium. In the case of X-ray sounding, a change in the refractive index or phase delays will be due to the local (within the size of the beam) spatial electron density of the sensed object.

Thus, using the distribution of the diffraction transverse distribution of the X-ray speckle field, taking into account phase delays, a three-dimensional image is restored using computer programs, and the use of local phase delay allows us to additionally determine the volume inhomogeneity of the electron density of the probed object.

The method uses sounding of a three-dimensional object using frequency-tunable laser x-ray radiation, which leads to a spatial change in the speckle field associated with a change in the phase conditions of interference of diffracted fields due to local inhomogeneities of electron density. This behavior of the speckle field is based on the effect discovered and tested by the author of the change in the speckle structure of the scattered field when the frequency of the probed optical radiation changes (see patent No. 2282228, IPC G03H 1/32; Akchurin G.G., Akchurin A.G. Speckle- correlation method for determining the dispersion of optical fibers and scattering parameters in optically inhomogeneous media by lasers with frequency deviation // Instruments and experimental equipment, 2006, No. 4, pp. 110-115).

Claims (2)

1. A method of coherent X-ray phase microscopy, including irradiation with a spatially coherent X-ray beam of a three-dimensional object, detecting a diffraction two-dimensional transverse distribution of the transmitted radiation intensity in the far zone for each discrete spatial position of the object relative to the probe X-ray beam, computer reconstruction of a three-dimensional image, characterized in that it is established spontaneous characteristic single-wave radiation regime and for of each spatial position of the object, the average contrast of the two-dimensional transverse distribution of the speckle field of the transmitted radiation is determined, the coherence time τ is reduced _{from the} probe x-ray radiation or, accordingly, the spectral line width Δν _{c of the} radiation is increased when tuning from characteristic x-ray radiation to continuous bremsstrahlung radiation to a value corresponding to a halving the contrast values of the speckle field of radiation and determine the local phase τ τ _ph из from the relation τ _ph = τ _c = 1 / Δν _c , measured for each rotation angle of the probed object, by which the volume distribution of electron density and relative refractive index is reconstructed. 2. A method of coherent X-ray phase microscopy, including irradiation with a coherent X-ray beam, detecting a diffraction two-dimensional transverse distribution of the transmitted radiation intensity in the far zone for each discrete spatial position of the object relative to the probe X-ray beam, computer reconstruction of a three-dimensional image, characterized in that the frequency Δν _{L of the} stimulated x-ray radiation to a value corresponding to a halving of two the measured correlation coefficient of the scattered speckle fields and determine the phase delay τ _ph from the relation τ _ph = 1 / Δν _L , measured for each rotation angle of the probed object, from which the volume distribution of electron density and relative refractive index is reconstructed.

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