WO2022125469A1 - Détecteur à résolution spatiale ultrarapide pour photons et particules chargées et ses applications - Google Patents

Détecteur à résolution spatiale ultrarapide pour photons et particules chargées et ses applications Download PDF

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Publication number
WO2022125469A1
WO2022125469A1 PCT/US2021/062067 US2021062067W WO2022125469A1 WO 2022125469 A1 WO2022125469 A1 WO 2022125469A1 US 2021062067 W US2021062067 W US 2021062067W WO 2022125469 A1 WO2022125469 A1 WO 2022125469A1
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Prior art keywords
electron
electrons
energy
time
amplifier
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PCT/US2021/062067
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English (en)
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Bernhard Wener ADAMS
Christoph Rose-Petruck
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Research Institute Corporation
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J31/00—Cathode ray tubes; Electron beam tubes
    • H01J31/08—Cathode ray tubes; Electron beam tubes having a screen on or from which an image or pattern is formed, picked up, converted, or stored
    • H01J31/26—Image pick-up tubes having an input of visible light and electric output
    • H01J31/48—Tubes with amplification of output effected by electron multiplier arrangements within the vacuum space
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J37/00—Discharge tubes with provision for introducing objects or material to be exposed to the discharge, e.g. for the purpose of examination or processing thereof
    • H01J37/02—Details
    • H01J37/244—Detectors; Associated components or circuits therefor
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J37/00—Discharge tubes with provision for introducing objects or material to be exposed to the discharge, e.g. for the purpose of examination or processing thereof
    • H01J37/26—Electron or ion microscopes; Electron or ion diffraction tubes
    • H01J37/261—Details
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J2237/00—Discharge tubes exposing object to beam, e.g. for analysis treatment, etching, imaging
    • H01J2237/04—Means for controlling the discharge
    • H01J2237/047—Changing particle velocity
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J2237/00—Discharge tubes exposing object to beam, e.g. for analysis treatment, etching, imaging
    • H01J2237/245—Detection characterised by the variable being measured
    • H01J2237/24571—Measurements of non-electric or non-magnetic variables
    • H01J2237/24585—Other variables, e.g. energy, mass, velocity, time, temperature

Definitions

  • the present invention relates generally to detection of individual photons or charged particles with spatial and ultrafast timing accuracy, and applications thereof.
  • the invention also relates to the use of time-energy-domain electron optics for mapping electron energies onto the time domain, and for scaling the time coordinate, such as for magnifying time differences.
  • the invention also relates to combining such time-energy electron optics with an ultrafast-timing electron detector with or without spatial resolution.
  • Ultrafast imaging capability is required in many application fields, such as imaging and spectroscopy of dynamic processes, time-of-flight (TOF) imaging including light detection and ranging (LIDAR) and indirect imaging of objects hidden from direct view, suppression of scattered light, quantum optics, or optical computing.
  • TOF time-of-flight
  • LIDAR light detection and ranging
  • indirect imaging of objects hidden from direct view suppression of scattered light
  • quantum optics or optical computing.
  • a key capability is to resolve the photon occupation of each individual mode of the electromagnetic field both transversely through two-dimensional spatial resolution matched to diffraction-limited optics, and longitudinally with a time resolution matched to the coherence time of spectrally filtered light. Detection of charged particles with spatial and ultrafast time resolution is also necessary for obtaining information on molecular breakup triggered by, for example, laser pulses.
  • Ultrafast picosecond-scale scale dynamics occur, for example, in charge transfer during photoexcitation of molecules.
  • signatures of the chargetransfer processes are measured mostly based on the timing between two pulses of electromagnetic radiation, such as laser-pump/laser-probe or laser-pump/x-ray probe spectroscopy.
  • a valuable addition to the researcher’s toolset would be an ultrafast photon detector, which can provide information on the timing between a single pulse of electromagnetic radiation and a detection event. This is especially the case for an ultrafasttiming and spatially resolving detector, which captures accurately timed photons originating from the sample into a wide solid angle.
  • the timing between emission and detection contains information on its path. This is the basis of the so-called TOF techniques, such as LIDAR, indirect imaging by analyzing spatial -temporal patterns of light originating from the object of interest, and scattered from walls or other objects, or the suppression of signals due to scattered light based on the slightly longer path compared to a direct path.
  • TOF techniques such as LIDAR, indirect imaging by analyzing spatial -temporal patterns of light originating from the object of interest, and scattered from walls or other objects, or the suppression of signals due to scattered light based on the slightly longer path compared to a direct path.
  • the scattersuppression capability will be important for medical imaging both with x-rays and with visible light.
  • phase space comprises two transverse coordinates and their two associated transverse momenta, given by the angles relative to the beam axis, as well as time and photon energy.
  • the latter two are also known as longitudinal coordinates because time is related to propagation distance along the beam axis.
  • an optical computer processes information in units contained in electromagnetic-field modes.
  • Transmission electron microscopy is capable of resolving very small structures down to the atomic scale.
  • the technique makes use of the small quantum mechanical wavelength of electrons, which scales roughly with the square root of the kinetic energy of the electrons, where relativistic corrections, especially at higher energies, lead to a deviation from square root scaling. Due to the limited angular acceptance of electron-beam optics, the electron wavelengths need to be considerably smaller than the feature size to be resolved, and atomic resolution requires, typically, electron energies of a few hundred kilo-electron-Volts (keV).
  • keV kilo-electron-Volts
  • these electrons will be called “inelastically scattered electrons,” and those that have not will be called “prompt electrons.”
  • imaging and sample electrons are valid only well before and well after any interactions within the sample, but that is where the electron optics and other means of manipulating the imaging electrons have their effect.
  • Interactions with the valence structure of the sample cause losses of the order of one to a few hundred electronvolts (eVs), and for interactions with inner-shell electrons, they are of the order of tens to thousands of eVs.
  • eVs electronvolts
  • chromatic aberrations in analogy to visible-light optics.
  • magnetic electron-energy filters are being used to reject the inelastically scattered electrons.
  • At the core of the invention is an ultrafast electron-detection scheme based upon timing-jitter reduction in an avalanche-gain signal amplifier.
  • the avalanche behavior provides the high amplification necessary to bring signals from single electrons to levels that can be processed by fast electronics.
  • inherent to the avalanche gain is unstable behavior subject to timing jitter, also known as the transit-time spread (TTS).
  • TTS transit-time spread
  • That first avalanche occurs at the leading edge of ts individual-avalanche timingjitter distribution, cutting all subsequent ones off before they even develop. If one primary electron incident on the first-stage amplifier generates N secondary ones emitted from it, then each of them can trigger the avalanche that develops first. Therefore, the timing jitter of the avalanche amplifier is reduced roughly by a factor of N.
  • This approach combines the strengths of two signal-conversion processes: the prompt generation of secondaries to preserve the timing accuracy, and the large gain of an avalanche process, which leads to a signal that can be picked up by electronics.
  • Disclosed embodiments are to provide a detector for individual photons, electrons, or other charged particles with a time resolution of the order of single-digit picoseconds or better, hence, “picosecond resolution.”
  • Disclosed embodiments are to accelerate photoelectrons from a photocathode, or electrons or other charged particles entering the detector, to a high energy, henceforth “energetic electron” or “energetic particle” so that each of them, in a volume of electrically conducting or semiconducting material, generates large numbers of so-called hot carriers, i.e., charge carriers at energies well above that of the conduction-band edge, and that these hot carriers, or secondary electrons resulting from them, each trigger an avalanche in a further avalanche amplification stage.
  • the low-jitter and avalanchegain stages may be integrated into a single unit, such as an avalanche photodiode.
  • Disclosed embodiments are to have each energetic electron from the photocathode, instead of striking an avalanche photodiode, rather strike a thin foil of conducting or semiconducting material by one of its surfaces and excite hot carriers within it, which then, upon reaching the opposite surface, are extracted by an electric field and accelerated towards an APD, an MCP or a stack of MCP’s, or arrays thereof, for further signal amplification, now from multiple simultaneously incident electrons.
  • EELS electron energy loss spectroscopy
  • a system for measuring electron arrival times at the location of the image sensor in an electron microscope for each image location, such as in each pixel.
  • a system is provided to perform the electron energy measurement in each image location based on the velocities of the electrons arriving at the sensor based on their time-of-flight (TOF) within the microscope.
  • means are provided for amplifying the TOF contrast of electrons.
  • a device in one embodiment, includes a first stage electron amplifier having a first gain, the first stage electron amplifier capable of receiving primary electrons, and for each of the primary electrons received emit a plurality of secondary electrons.
  • the device also includes a second stage electron amplifier having second gain, the second gain being greater than the first gain.
  • the second stage electron amplifier can be configured to receive the plurality of secondary electrons and emit tertiary electrons, the number of tertiary electrons being greater than the plurality of secondary electrons.
  • the timing jitter of the second stage electron amplifier can be reduced below its single electron value by simultaneous triggering of events from the plurality of secondary electrons.
  • the first stage electron amplifier includes a material configured to receive the primary electrons and generate a plurality of hot charge carriers.
  • the material can be a metal material or a semiconductor material.
  • the hot charge carriers can be emitted in the form of secondary electrons on a surface of the material.
  • the surface of the material is the surface facing the second stage electron amplifier.
  • the device may further include a grid or a foil adjacent the surface of the first stage electron amplifier facing the second stage electron amplifier.
  • the grid or foil can be biased at a positive voltage relative to the first stage electron amplifier to control emission of the plurality of secondary electrons from the first stage electron amplifier.
  • a device in one embodiment, includes an electron amplifier configured to be an image converter by receiving primary electrons and for each of the primary electrons generate a plurality of hot charge carriers, where the hot charge carriers can be emitted in the form of secondary electrons.
  • This embodiment further includes a readout for receiving signals generated from the plurality of secondary electrons and forming a time-resolved image therefrom.
  • the electron amplifier can be a first stage electron amplifier having first gain
  • the readout can be a first readout
  • the time-resolved image can be a first time-resolved image.
  • the device further includes a second stage electron amplifier downstream of the first readout, the second stage electron amplifier having second gain, the second gain being greater than the first gain.
  • the second stage electron amplifier can be configured to receive secondary electrons and emit tertiary electrons, with there being more tertiary electrons than secondary electrons.
  • This embodiment may further include a second readout for receiving signals generated from the tertiary electrons and forming a second time-resolved image therefrom.
  • the second stage electron amplifier can be an avalanche amplification semiconductor device (AASD), an avalanche photodiode (APD), a micro- channel plate (MCP), stacks of MCP’s, arrays of AASD’s, arrays of APD’s, arrays of MCP’s, arrays of stacks of MCP’s, or combinations thereof.
  • AASD avalanche amplification semiconductor device
  • APD avalanche photodiode
  • MCP micro- channel plate
  • the device may further include a readout downstream of the second stage electron amplifier for receiving signals generated from tertiary electrons and forming a time-resolved image therefrom.
  • the device may further include a photocathode upstream of the first stage electron amplifier, the photocathode can be biased at high-voltage potential relative to the first stage electron amplifier for converting photons to the primary electrons and accelerating each of the primary electrons to high energy.
  • the device may further include a spectral filter upstream of the photocathode, the spectral filter having a bandwidth and a corresponding coherence time comparable to a time resolution of the device.
  • the device may further include a converter cathode upstream of the first stage electron amplifier, whereby the converter cathode is capable of emitting primary electrons when struck by particles including molecular fragments having atoms, ions, molecules, sub-atomic particles or other massive particles.
  • an electron microscope system includes a sample configured to receive a plurality of electrons each having distinct arrival time and electron energy, a timeenergy electron optics for converting electron energy differences of the plurality of electrons into arrival time differences, and for converting arrival time differences of the plurality of electrons into electron energy differences, the time-energy electron optics having a device configured to convert between complementary variables of the arrival time and the electron energy, and a time-resolving detector for receiving the plurality of electrons from the timeenergy electron optics.
  • the device is a magnetic chicane configured to convert electron energy differences of the plurality of electrons into arrival time differences.
  • the device is a drift region configured to convert electron energy differences of the plurality of electrons into arrival time differences.
  • a part of the drift region is maintained at high-voltage potential, enclosed by grids for maintaining equipotential surfaces, for the reduction of electron velocity of each of the plurality of electrons.
  • the device is a radiofrequency accelerator cavity or an electrodynamic device configured to convert arrival time differences of the plurality of electrons into electron energy differences.
  • the grids include first grid and second grid at equal potential such that there is no electric field in the space in between, where the plurality of electrons includes first electron and second electron each having different electron velocity, and where each of the first electron and the second electron loses equal, absolute amount of their respective electron energy within the grids resulting in the electron velocity differences between the first electron and the second electron being amplified upon leaving the high-voltage potential drift region.
  • the electron microscope system may further include electron optics disposed in the drift region between the grids so as to operate the plurality of electrons therein at lower electron energy than the plurality of electrons outside the space enclosed by the grids.
  • the time-energy electron optics may include a plurality of converters to further increase time-of-flight contrast of electrons from the sample.
  • a method includes providing primary electrons, providing first stage electron amplifier operable to receive the primary electrons, the first stage electron amplifier having first gain, generating a plurality of secondary electrons from each of the primary electrons, providing second stage electron amplifier operable to receive the plurality of secondary electrons, the second stage electron amplifier having second gain, the second gain being greater than the first gain, and generating a plurality of tertiary electrons from each of the plurality of secondary electrons, where each of the plurality of secondary electrons is operable to trigger a plurality of avalanches of exponential gain such that a first fully developed avalanche of the plurality of avalanches dominates an overall timing of the second stage electron amplifier, and any subsequent avalanches of the plurality of avalanches are not developed as they are subsumed by the first fully developed avalanche of the plurality of avalanches.
  • the method further includes emitting the plurality of tertiary electrons, whereby the number of the plurality of tertiary electrons is greater than the number of the plurality of secondary electrons, and detecting the plurality of tertiary electrons with a detector.
  • a method of using an electron microscope includes the steps of: (a) providing a plurality of electrons, (b) providing a sample operable to receive the plurality of electrons, where each of the plurality of electrons has distinct arrival time and electron energy; (c) providing a time-energy electron optics operable to convert electron energy differences of the plurality of electrons into arrival time differences, and to convert arrival time differences of the plurality of electrons into electron energy differences, the time-energy electron optics having a device operable to convert between complementary variables of the arrival time and the electron energy, and (d) providing a time-resolving detector operable to receive the plurality of electrons from the time-energy electron optics.
  • the method further includes step (e) of providing a readout for receiving signals generated from the plurality of electrons and forming an image therefrom.
  • the providing step (c) of the method above may include providing the time-energy electron optics having the device, where the device is a magnetic chicane operable to convert electron energy differences of the plurality of electrons into arrival time differences.
  • the providing step (c) of the method above may include providing the time-energy electrons having the device, where the device is a radiofrequency accelerator cavity or an electrodynamic device operable to convert arrival time differences of the plurality of electrons into electron energy differences.
  • a method of using an electron microscope includes the steps of: (a) providing a plurality of electrons; (b) providing a sample operable to receive the plurality of electrons, where each of the plurality of electrons has distinct arrival time and electron energy; and (c) providing a time-energy electron optics operable to convert electron energy differences of the plurality of electrons into arrival time differences, and to convert arrival time differences of the plurality of electrons into electron energy differences, the time-energy electron optics having converters between the complementary variables of the electron energy and the arrival time, wherein one of the converters of energy -to-time being a magnetic chicane or a drift region such that first set of two electrons of the plurality of electrons entering the magnetic chicane or the drift region simultaneously and at different electron energies will emerge at different arrival times, and wherein one of the converters of time-to-energy being a radiofrequency cavity such that second set of two electrons of the plurality of electrons entering the radiofrequency cavity at the same electron energies but at different
  • the method of using the electron microscope may further include the steps of: (d) providing a time-resolving detector operable to receive the plurality of electrons from the time-energy electron optics; and (e) providing a readout for receiving signals generated from the plurality of electrons and forming a time-resolved image therefrom.
  • the providing step (c) of the method above may include providing the drift region at a high negative electric potential between two grids, the two grids having first grid and second grid at equal potential.
  • the providing step (c) of the method above may further include: generating no electric field in the space between the first grid and the second grid, where the plurality of electrons includes first electron and second electron each having different electron velocity, losing equal, absolute amount of their respective electron energy as each of the first electron and the second electron transits the grids, and amplifying the relative electron velocity differences between the first electron and the second electron within the drift region.
  • the providing step (a) of the method above may further include providing the plurality of electrons using a pulsed electron source.
  • a method includes: providing primary electrons, providing first stage electron amplifier operable to receive the primary electrons on first surface, generating secondary electrons from each of the primary electrons, where the number of secondary electrons is greater than the number of primary electrons, emitting the primary electrons and the secondary electrons from second surface of the first stage electron amplifier, the second surface opposite the first surface, where the energy of each of the secondary electrons is less than the energy of each of the primary electrons, providing second stage electron amplifier operable to receive the primary electrons and the secondary electrons on first surface of the second stage electron amplifier, where the first surface of the second stage electron amplifier faces the second surface of the first stage electron amplifier, and applying a magnetic field between the first surface of the second stage electron amplifier and the second surface of the first stage electron amplifier such that each of the primary electrons exhibits first deflection curvature and each of the secondary electrons exhibits second deflection curvature, where the second deflection curvature is greater than the first deflection curvature.
  • FIG. 1 A illustrates an exemplary photodetection with an avalanche photodiode (APD).
  • APD avalanche photodiode
  • FIG. IB is a schematic of a conducting or semiconducting material and an APD or a MCP (or stacks of MCP’s) according to another embodiment.
  • FIG. 1C is a schematic of FIG. IB with the addition of grids according to yet another embodiment.
  • FIG. ID illustrates a time-of-flight electron microscope (TOFEM).
  • FIG. 2 illustrates an exemplary of electrons traveling at different velocities.
  • FIG. 3 is a schematic of a magnetic chicane according to one embodiment.
  • FIG. 4 is a schematic of an electron optics according to one embodiment.
  • FIG. 5 is a schematic of a radiofrequency cavity according to one embodiment.
  • FIG. 6 is a schematic of a conducting or semiconducting material and an APD or a
  • MCP (or stacks of MCP’s) according to one embodiment.
  • FIG. 7 shows a cross-sectional view of an energy-filtered version of an ultrafast imaging electron detector according to an embodiment.
  • a photon For the detection of electromagnetic radiation, a photon first generates a photoelectron from a photocathode. That process is fast, typically well below the level of a picosecond.
  • the photocathode is kept at a negative bias of tens of kilovolt or more, so that the photoelectron is accelerated to a correspondingly high energy and strikes the surface of an avalanche-amplification diode, commonly known as an avalanche photodiode (APD), as shown in FIG. 1 A.
  • APD avalanche photodiode
  • the electron As it is scattered inelastically within the photodiode semiconductor material, the electron generates a ‘cloud’ of hot carriers, which then trigger simultaneous avalanches with a combined lower transit time spread (TTS) than a single avalanche would yield.
  • TTS transit time spread
  • the avalanche region of the APD can be designed for minimal TTS under the conditions of multiple simultaneous avalanche triggers.
  • the electron penetration depth and the size of the hot-carrier cloud can be controlled through the amount of acceleration that the electron undergoes before striking the APD. Both through the penetration depth, and because the size of the hot-carrier cloud determines the overlap between avalanches triggered out of it, the acceleration voltage gives control over the multiavalanche TTS.
  • the electron has, typically, a much shorter range in the semiconductor material than the photon would have if it were directly incident on the APD, and thus all avalanches triggered by the hot carriers start out from a much more tightly constrained depth. For this reason, the TTS from a photoelectron is lower than that from a photon directly absorbed in the APD.
  • FIG. 1 A illustrates picosecond photodetection with an APD, where a photoelectron emitted from a transmission or bulk photocathode as a consequence of photon absorption is accelerated to a high energy, penetrates into the APD, generates a cloud of hot carriers, which then trigger multiple avalanches.
  • light 101 incident on a photocathode 102 in transmission mode, or light 103 incident on a bulk photocathode 102 can generate a photoelectron 104, which can be accelerated 105 onto an APD 106, into which it penetrates and generates a hot-carrier cloud 107.
  • These hot carriers can then trigger many simultaneous avalanches 108.
  • the accelerated photoelectron can strike a foil, the ‘converter foil’ of conducting or semiconducting material that is sufficiently thin so as to not exceed the range of the incident electron in the material.
  • a typical foil thickness is in the range of microns.
  • the foil is biased negatively with respect to an avalanche-producing device, i.e., an APD or an MCP or MCP stack (henceforth simply as “MCP”).
  • An avalanche-producing device i.e., an APD or an MCP or MCP stack (henceforth simply as “MCP”).
  • MCP avalanche-producing device
  • MCP MCP or MCP stack
  • Intermediate metallic grids (“acceleration grids”) between the foil and the APD or MCP may be used for further control of the electric fields.
  • the energetic incident electron In transiting the foil material, the energetic incident electron generates a large number of so-called hot carriers, i.e., electrons or holes at energies well above (at the scale of a few electron- Volts) that of conduction electrons in the material.
  • the hot carriers are highly mobile and diffuse rapidly within the foil material, in particular, to the surface facing the APD or MCP or an acceleration grid. At that surface the hot carriers, with their comparatively high energy, can cause the emission of electrons into vacuum in the space between the foil and the APD/MCP/grid. These electrons are then accelerated and strike the APD or MCP as a simultaneous multi -electron signal that is amplified at a low TTS, as described herein.
  • the disclosed embodiments with the converter foil herein have the following advantages, among others.
  • the method of reducing TTS by accelerating a photoelectron and directly striking the avalanche amplifier works only with an APD, but not with an MCP, where the statistics of pore penetration depth remains unchanged. In order to make use of an MCP for the much larger area that it can offer in comparison to an APD, it is then necessary to use a foil for the first step of secondaryelectron generation through hot-carrier generation.
  • Detection of electrons and charged particles does not require an initial conversion to photoelectrons. However, to provide the energy necessary for producing enough prompt secondary carriers in the foil, the electrons or charged particles may need to be accelerated to accordingly high energies. It follows that the foil and the avalanche-amplifying device (e.g., APD or MCP) may be kept at a high positive potential, and the signal must be transmitted to other electronics near ground potential.
  • the avalanche-amplifying device e.g., APD or MCP
  • the signal produced by the avalanche-amplifying device e.g., APD or MCP
  • APD the avalanche-amplifying device
  • MCP the avalanche-amplifying device
  • the readout would typically consist of one electronics channel per APD.
  • the number of channels can be smaller than the number of effective pixels, and spatial resolution is refined by interpolation between channels.
  • One embodiment discloses an indirect scheme of picosecond photodetection with a foil and an APD or an MCP, where a photoelectron, emitted from a transmission or bulk photocathode as a consequence of photon absorption, is accelerated to a high energy, so as to produce a sufficient number of secondary electrons from the first stage amplifier for triggering multiple avalanches, and transits a thin foil where it generates a cloud of hot carriers. These are then extracted from the foil by an electric field between the foil and an APD or MCP, are accelerated, and trigger multiple simultaneous avalanches in the APD or MCP. An optional grid between the foil and the APD or MCP can be used to further control the extraction field strength.
  • FIG. IB shows light 111 incident on a photocathode 112 in transmission mode, or light 113 incident on a bulk photocathode 112, generating a photoelectron 114, which is accelerated 115 onto a foil 116, in which it generates hot carriers.
  • a photoelectron 114 which is accelerated 115 onto a foil 116, in which it generates hot carriers.
  • the primary electron that penetrates the foil 116 continues 121 on through the MCP 118, and can trigger an avalanche in it, but only in one pore.
  • the lateral spread of the secondary electrons 617 from the foil can be controlled to cover multiple pores and thus lead to a stronger signal that dominates over the single-pore signal from the primary electron that continues 121 its path through the foil 116 and MCP 118.
  • the electric field between foil 116 and grid 122 also lowers the work function for the emission of secondary electrons from foil 116.
  • a device in one embodiment, includes a first stage electron amplifier such as a foil 116, the first stage electron amplifier having first gain.
  • the first stage electron amplifier can be configured to receive primary electrons, e.g., photoelectrons 114, and for each of the primary electrons emitting a plurality of secondary electrons, e.g., secondary electrons 117.
  • the device further includes a second stage amplifier such as an MCP 118, the second stage amplifier having second gain, where the second gain is greater than the first gain.
  • the second stage amplifier is configured to receive the plurality of secondary electrons and emit tertiary electrons, e.g., large number of electrons 119, the number of tertiary electrons being greater than the plurality of secondary electrons.
  • the timing jitter of the second stage electron amplifier can be reduced below its single electron value by simultaneous triggering of events from the plurality of secondary electrons, as disclosed herein.
  • the first stage electron amplifier may include a material such as a metal or semiconductor, or other conducting or semiconducting material.
  • the material may be configured to receive the primary electrons and generate a plurality of hot charge carriers, e.g., hot carriers disclosed earlier.
  • the plurality of hot charge carriers can be emitted in the form of the plurality of secondary electrons.
  • the plurality of secondary electrons can be emitted on the surface of the material, e.g., foil 116, facing the second stage electron amplifier, e.g., MCP 118.
  • an electric field can help to assist or control the emission of the secondary electrons similar to an acceleration field between the foil 116 and MCP 118 discussed above.
  • the second stage electron amplifier may be an APD, or an MCP, or stacks of MCP’ s.
  • the second stage electron amplifier may include an avalanche amplification semiconductor device (AASD), an avalanche photodiode (APD), a micro-channel plate (MCP), stacks of MCP’s, arrays of AASD’s, arrays of APD’s, arrays of MCP’s, arrays of stacks of MCP’s, or combinations thereof.
  • AASD avalanche amplification semiconductor device
  • APD avalanche photodiode
  • MCP micro-channel plate
  • the device may further include a readout, e.g., readout anode 120, downstream of the second stage electron amplifier, e.g., MCP 118, for receiving signals generated from the tertiary electrons, e.g., large number of electrons 119, and forming a time- resolved image therefrom.
  • a readout e.g., readout anode 120
  • MCP 118 the second stage electron amplifier
  • the device may further include a photocathode 112 upstream of the first stage electron amplifier, e.g., foil 116, where the photocathode can be biased at high- voltage potential relative to the first stage electron amplifier for converting photons, e.g., light 111, 113, to the primary electrons, e.g., photoelectrons 114, and accelerating 115 each of the primary electrons to high energy.
  • high voltage is any voltage that is high enough to generate a good number of secondary electrons in the foil, as will be understood by one skilled in the art.
  • Another embodiment discloses picosecond electron or charged-particle detection including an incident electron / charged particle coming from a field-free reaction region being accelerated to a high energy between two closely spaced grids, and then transits a thin foil where it generates a cloud of hot carriers. These are then extracted from the foil by an electric field between the foil and an APD or MCP, are accelerated, and trigger multiple simultaneous avalanches in the APD or MCP.
  • An optional grid between the foil and the APD or MCP can be used to further control the extraction field strength.
  • FIG. 1C shows an electron or charged particle 131 in a field-free reaction zone, or other type of region out of which electrons or charged particles are detected, incident on a grid 132 at the same potential as the reaction region. It then is accelerated by a high positive potential on another grid 133 and continues 134, at a high energy 135 at which it strikes a foil 136 to generate hot carriers within it.
  • the incident electron or charged particle 131 already has a sufficiently high energy, for example if coming out of the optics in an electron microscope, or if coming from a particle accelerator, acceleration by the pair of grid 132 and grid 133 may be unnecessary, and these components may thus be omitted.
  • the hot carriers in the foil then lead to the extraction of secondary electrons 137 by an electric field between the foil 136 and an MCP 138 (alternatively an APD), where multiple simultaneous avalanches are generated.
  • MCP 138 alternatively an APD
  • APD advanced avalanches
  • the primary electron that penetrates the foil 136 continues 141 on through the MCP 138, and can trigger an avalanche in it, but only in one pore.
  • the lateral spread of the secondary electrons 137 from the foil can be controlled to cover multiple pores and thus lead to a stronger signal that dominates over the single-pore signal from the primary electron that continues 141 its path through the foil 136 and MCP 138.
  • the electric field between foil 136 and grid 142 also lowers the work function for the emission of secondary electrons from foil 136.
  • a device similar to that disclosed above may further include a grid or a foil similar to the multiple grids 142 discussed above.
  • the grid or foil can be adjacent the surface of the first stage electron amplifier, e.g., foil 136, facing the second stage electron amplifier, e.g., MCP 138.
  • the grid or foil can be biased at a positive voltage relative to the first stage electron amplifier to control emission of the plurality of secondary electrons from the first stage electron amplifier.
  • a device includes an electron amplifier similar to those discussed above.
  • the electron amplifier can be configured to be an image converter by receiving primary electrons where for each of the primary electrons generate a plurality of hot carrier charges, whereby the plurality of hot carrier charges are emitted in the form of a plurality of secondary electron similar to that discussed above.
  • the device further includes a readout, e.g., readout anode 140, for receiving signals generated from the plurality of secondary electrons and forming a time-resolved image therefrom.
  • the electron amplifier of the device may be a first stage electron amplifier as discussed above having a first gain, the readout being a first readout, and the time-resolved image being a first time-resolved image.
  • the device further includes a second stage electron amplifier similar to that discussed above, the second stage electron amplifier downstream of the first stage electron amplifier.
  • the second stage electron amplifier has a second gain, where the second gain is greater than the first gain.
  • the second stage electron amplifier may be configured to receive the plurality of secondary electrons and emit tertiary electrons, where the number of tertiary electrons is greater than the plurality of secondary electrons.
  • the device may further include a second readout (similar to the first readout above), where the second readout is configured for receiving signals generated from the tertiary electrons and forming a second time- resolved image therefrom.
  • a method includes providing primary electrons, providing first stage electron amplifier operable to receive the primary electrons, the first stage electron amplifier having first gain. Next, generating a plurality of secondary electrons from each of the primary electrons followed by providing second stage electron amplifier operable to receive the plurality of secondary electrons, the second stage electron amplifier having second gain, the second gain being greater than the first gain.
  • each of the plurality of secondary electrons is operable to trigger a plurality of avalanches of exponential gain such that a first fully developed avalanche of the plurality of avalanches dominates an overall timing of the second stage electron amplifier, and any subsequent avalanches of the plurality of avalanches are not developed as they are subsumed by the first fully developed avalanche of the plurality of avalanches.
  • a method further includes emitting the plurality of tertiary electrons, where the number of the plurality of tertiary electrons is greater than the number of the plurality of secondary electrons and detecting the plurality of tertiary electrons with a detector.
  • a method of using an electron microscope includes (a) providing a plurality of electrons and (b) providing a sample operable to receive the plurality of electrons, each of the plurality of electrons has distinct arrival time and electron energy.
  • the method includes (c) providing a time-energy electron optics operable to convert electron energy differences of the plurality of electrons into arrival time differences, and to convert arrival time differences of the plurality of electrons into electron energy differences, the time-energy electron optics having a device operable to convert between complementary variables of the arrival time and the electron energy.
  • the method includes (d) providing a time-resolving detector operable to receive the plurality of electrons from the time-energy electron optics.
  • the method above may further include (e) providing a readout for receiving signals generated from the plurality of electrons and forming an image therefrom.
  • the providing step (c) above may include providing the timeenergy electron optics having the device, where the device is a magnetic chicane operable to convert electron energy differences of the plurality of electrons into arrival time differences.
  • the providing step (c) above may include providing the timeenergy electrons having the device, where the device is a radiofrequency accelerator cavity or an electrodynamic device operable to convert arrival time differences of the plurality of electrons into electron energy differences.
  • a method of using an electron microscope includes (a) providing a plurality of electrons, and (b) providing a sample operable to receive the plurality of electrons, where each of the plurality of electrons has distinct arrival time and electron energy.
  • one of the converters of energy-to-time is a magnetic chicane or a drift region such that first set of two electrons of the plurality of electrons entering the magnetic chicane or the drift region simultaneously and at different electron energies will emerge at different arrival times.
  • one of the converters of time-to-energy is a radiofrequency cavity such that second set of two electrons of the plurality of electrons entering the radiofrequency cavity at the same electron energies but at different arrival time will emerge at different electron energies.
  • the method as discussed above may include the providing step (c) having provided the drift region at a high negative electric potential between two grids, the two grids having first grid and second grid at equal potential.
  • the providing step (c) may further include: generating no electric field in the space between the first grid and the second grid, whereby the plurality of electrons includes first electron and second electron each having different electron velocity, losing equal, absolute amount of their respective electron energy as each of the first electron and the second electron transits the grids, and amplifying the relative electron velocity differences between the first electron and the second electron within the drift region.
  • the providing step (a) further includes providing the plurality of electrons using a pulsed electron source, as will be discussed in more detail below.
  • FIG. ID illustrates an overview of a time-of-flight electron microscope (TOFEM), where a pulsed laser emits electrons from a photocathode. The electrons are then accelerated and guided by electron lenses (not shown), transit through the sample, and are imaged onto a detector by further electron optics (not shown). On the way from the sample to the detector, the electrons pass through an energy -to-timing converter and arrive at the detector separated out longitudinally according to their energies. As shown, a photocathode 161, optionally with a tip 162 for facilitating localized emission, is kept at a negative high-voltage potential.
  • TOFEM time-of-flight electron microscope
  • a sub-picosecond pulsed laser 163 generates photoelectrons from the tip 162, which are then further extracted by beam -forming electrodes 164 and accelerated towards ground potential 165.
  • the electrons 166 are then guided by electron optics (not shown) to “illuminate” a sample 167, where they may lose some of their energy.
  • the electrons then arrive at an ultrafast imaging electron detector 170, where they are recorded by location and arrival time relative to the pulses from the subpicosecond pulsed laser 163.
  • TOF time-of-flight
  • This sensor is based on micro-channel plates (MCPs) and is read out by digitizing the waveforms of signals conveyed from the MCPs via gigahertz (GHz)-scale transmission lines, similar to the way it is done in another MCP-based detector known as large area picosecond photodetector (LAPPD). Mapping the electron energies into relative time can be done in several ways, two of which are described exemplarily, below.
  • MCPs micro-channel plates
  • LAPPD large area picosecond photodetector
  • the electrons are generated from a photocathode driven by a sub-picosecond pulsed laser and are accelerated in an electrostatic field to the nominal operating voltage of the electron microscope, typically about 300 kiloelectron volt (keV).
  • Laser-driven photocathodes can produce electrons with an energy spread of well below one electron volt (eV), and this small energy spread is strictly preserved in the electrostatic acceleration.
  • eV electron volt
  • the photocathode may optionally be structured to provide a well defined submicron, or even nanometer-scale emission location.
  • the charge in each pulse should be low, and the laser repetition rate should be correspondingly high to provide the operating current, ideally with time intervals between pulses not much larger than the longest expected time lag in electrons due to energy loss E/ in the sample.
  • an operating current of 1 nanoamp (nA) which is typical to high- end for a high-resolution transmission electron microscope (HRTEM), and with a laser repetition rate of about 1 gigahertz (GHz)
  • nA nanoamp
  • HRTEM high-resolution transmission electron microscope
  • GHz gigahertz
  • the electrons arrive at the sample at times and energies defined to the levels of subpicosecond and a few eV or even sub-eV, respectively. After traversing the sample, the electrons are still highly defined with respect to time, but some have lost energy E/ in amounts ranging, typically, from a few eV to a few hundred eV. This range of energy deficit can be mapped onto arrival time at the sensor relative to the arrival of the prompt electrons that are retaining their energy Eo. The mapping can be done in several ways, three of which are described exemplarily in more detail, below.
  • the long propagation path can be folded into loops using magnetic deflection.
  • the above-mentioned picosecond separation is given by the capabilities of a typical MCP-based multi-electron detector, as described below. If a sensor with a higher time resolution is used, the propagation distance can be reduced accordingly. Separation by velocity can also be used over a much shorter propagation distance as an element of an energy -time mapper in combination with, in particular, a radiofrequency accelerator. This and other embodiments will be described below.
  • FIG. 2 shows a straight electron-beam path which two electrons travel at different velocities. Initially, the electrons are both at the same longitudinal position along the beam, but as both propagate, the faster one increasingly gets ahead of the slower one. As shown, two electrons, first electron 201 and second electron 202, are traveling along the same beam path 203 with a given longitudinal coordinate 204, but at different velocities, where first electron 201 travels at a lesser velocity 205, while second electron 202 travels at a higher velocity 206 (as represented by the length of the arrows 205, 206).
  • Both electrons 201, 202 start out at approximately the same longitudinal coordinate position 204, but after propagating some distance, first electron 207 now lags behind second electron 208, while both maintain their respective unchanged velocities, first velocity 209 equal to velocity 205 and second velocity 210 equal to velocity 206. Thus, first electron 207 will arrive later at the sensor than second electron 208.
  • electron arrival time differences due to energy deficits can be achieved over shorter distances than with straight line propagation with the introduction of a magnetic chicane.
  • the magnetic chicane may be inserted into the imaging optics of the electron microscope similar to that of the energy -to-time converter 168 of FIG. ID.
  • FIG. 3 shows a schematic representation of a magnetic chicane that introduces an electron-energy-dependent geometric-path delay.
  • a magnetic chicane where a beam containing electrons at different energies enters a mirror symmetric sequence of four magnets. Due to the symmetry, all electrons join the same trajectory upon leaving the magnet assembly, but lower energy electrons are deflected more strongly than high energy ones, and therefore travel a longer geometric path.
  • the magnetic chicane includes a sequence of dipole magnets: Ml 302, M2 303, M3 304, and M4 305.
  • higher-order magnets may be included for focusing.
  • Electrons arriving at the entry to the chicane 301 then traverse the sequence of dipole magnets M1-M4 302-305 that bend the trajectories with electron- energy-dependent curvatures, so that the electrons travel on curved paths with energydependent geometric lengths.
  • the arrangement is symmetrical with respect to a plane 306 between magnets M2 303 and M3 304, so that the electrons are returned to their original trajectories 309 that they would take in the absence of these magnets.
  • Chicanes are standard components in the “toolbox” of particle-accelerator physics. The electron paths resemble those in an omega filter, but the chicane used here is tuned to maximize the effect of time-difference amplification. In operation, electrons with higher energies 307 are deflected less than electrons with lower energies 308. Hence, the former travel shorter paths through the chicane than the latter.
  • both the higher energy electrons 307 and lower energy electrons 308 join the original trajectory 309 that the electrons would have taken in the absence of magnets, or at zero magnetic fields.
  • the lower energy electrons 308 lag behind the higher energy electrons 307, to some extent due to their lower velocity, but mainly due to their longer geometric path through the chicane.
  • the lower-energy electrons 308 are deflected more strongly in each of the magnets 302, 303, 304, 305, they take a geometrically longer path through the chicane, and thus rejoin the original trajectory at a correspondingly later time in proportion to their velocity deficit.
  • an electron microscope system may include a sample configured to receive a plurality of electrons each having distinct arrival time and electron energy as disclosed herein.
  • the system may include a time-energy electron optics similar to those discussed herein, for converting electron energy differences of the plurality of electrons into arrival time differences, and vice versa, e.g., for converting arrival time differences of the plurality of electrons into electron energy differences.
  • the time-energy electron optics having a device (to be discussed below) configured to convert between complementary variables of the arrival time and the electron energy.
  • the system may further include a time-resolving detector for receiving the plurality of electrons from the time-energy electron optics.
  • the time-energy electron optics may include a plurality of converters to further increase time-of-flight contrast of electrons from the sample.
  • the device as discussed above for the electron microscope system may include a magnetic chicane similar to that described in FIG. 3, the magnetic chicane configured to convert electron energy differences of the plurality of electrons into arrival time differences.
  • Another way of increasing electron-energy-dependent time differences is to decelerate the electrons in an electrostatic field, both reducing the velocity-equalizing effect of relativistic corrections, and, more importantly by the direct arithmetic effect of increasing the differential travel time over a given distance, as traversing that distance takes a longer time at reduced electron energies.
  • the deceleration can be achieved within imaging electron optics between the sample and the sensor, for instance, at a position in the electron optical column where an intermediate image is formed, which is then imaged onto the sensor at the reduced electron energy.
  • other positions of the energy reduction stage are also possible, and its placement is determined in an overall optimization of the electron microscope. The energy reduction is done to a level that is still sufficient for generating a large number of secondary electrons in a thin foil, as described herein.
  • the electrons in order to keep the sample and the sensor at roughly the same electrostatic potential near ground, the electrons may be re-accelerated to their original energies after having acquired a strong time difference contrast by traveling through a section of electron beam path at reduced energy, and therefore reduced velocities.
  • the high-potential region should be kept within shield grids, so that both the deceleration, and the re-acceleration after a propagation distance, occur over very short distances using, for example, pairs of closely spaced wire meshes held at different electrical potentials. For example, in FIG.
  • an object 403 is imaged by electron optics 401 to form an image 402 at the entrance to the high-potential region between grids 407 and 410.
  • the pair of grids comprising grid 405 at ground potential 406 and grid 407 at high potential 414 decelerate the electrons. Then, there is a region of constant high potential 414 between grids 407 and 410, where electron optics 408 transmit the image 402 to another image 409 at the exit of the high-potential region.
  • the pair comprising grids 410 at high potential 414 and grid 411 at ground potential 412 re-accel erate the electrons.
  • the deceleration field 404 is maintained between grids 405 and 407, and the acceleration field is maintained between grids 410 and 411.
  • the electrons, having emerged from the high- potential region are imaged from 409 to the sensor 416 by electron optics 415.
  • an energy -to-time converter 168 such as that shown in FIG. ID can be realized by deceleration, propagation, and acceleration.
  • a sample can be imaged onto a decelerating closely spaced wire mesh pair, an intermediate image can be imaged again, at lower energy, onto an accelerating wire mesh pair, and finally, from there onto a sensor.
  • the outward facing meshes are at ground potential and the inward facing meshes are at the same negative potential, so that the energies of electrons within the space between them can be reduced.
  • FIG. 4 shows a schematic representation of the electron optics imaging from a sample onto an electron decelerator, from whence an image can be formed onto an electron accelerator, and finally onto the sensor (e.g., with decelerator and accelerator energy to time converter in the image forming section).
  • an electron lens 401 can magnify an image 402 of a sample 403 onto a decelerator 404 consisting of two closely spaced electrically conductive grids, where the sample-facing mesh 405 is at ground potential 406, and the inward-facing deceleration mesh 407 is at a high negative potential.
  • the electrons, now at reduced energy, are imaged further by an electron lens 408, which forms an image
  • the inward-facing deceleration mesh 407 and the inward-facing acceleration mesh 410 are electrically connected 414 to the perimeter of the region between the decelerator and accelerator, so that the electrons in there are in an electrically equipotential region.
  • An additional electron lens 415 can transmit the intermediate image as full-energy electrons onto the accelerator 413 to the sensor 416.
  • the energetic electrons traversing the decelerator-accelerator section may generate secondary electrons from the wire meshes. Those originating from sample facing mesh 405 will be rejected by the electric potential on the inward-facing deceleration mesh 407, while those originating from the inward-facing deceleration mesh 407 will be distinguished from the imaging electrons by their low energy and longer TOF through the reduced-energy section between the mesh pairs, and can also be cleared out by a weaker magnetic field that affects these few eV scale electrons, but only insignificantly the multi-keV imaging electrons in the reduced energy section. Secondary electrons from the inward-facing acceleration mesh
  • the device as discussed above for the electron microscope system may include a drift region similar to those described in FIG. 4.
  • the drift region is capable of converting electron energy differences of the plurality of electrons into arrival time differences.
  • a part of the drift region can be maintained at high-voltage potential, enclosed by grids for maintaining equipotential surfaces, for the reduction of electron velocity of each of the plurality of electrons, as discussed above.
  • the grids may include first grid and second grid at equal potential such that there is no electric field in the space in between.
  • the plurality of electrons may include first electron and second electron each having different electron velocity, whereby each of the first electron and the second electron loses equal, absolute amount of their respective electron energy within the grids resulting in the electron velocity differences between the first electron and the second electron being amplified upon leaving the high-voltage potential drift region.
  • system may further include electron optics placed within the drift region between the grids so as to operate the plurality of electrons therein at lower electron energy than the plurality of electrons outside the space enclosed by the grids.
  • a radiofrequency cavity structure for accelerating charged particles according to an embodiment.
  • two electrons can enter the cavity at the same energy, i.e., the same velocity, with one being a little earlier than the other.
  • Both electrons encounter an oscillating electric field inside the cavity, but at different phases due to their different longitudinal instantaneous positions along their common trajectory.
  • the phase of the oscillating electric field can be tuned to near zero-crossing of the electric field at the time of electron arrival, such that the earlier electron encounters only a very small, or zero electric field, while the latter electron runs up against a stronger electric field and is decelerated.
  • the electrons leave the cavity with almost the same relative delay, but due to the deceleration, the latter electron can have lower energy and lower velocity.
  • FIG. 5 shows a schematic representation of a radiofrequency accelerator structure 501 with its symmetry axis 502 indicated, and two electrons shown for purposes of this discussion.
  • First electron 503 and second electron 504 can enter the cavity structure 501, each having its own velocity: first velocity 505 and second velocity 506, which are, for purposes of this discussion, equal to each other.
  • An oscillating electromagnetic field is present in the cavity in a mode where the electric field lines are aligned along (or against) the symmetry axis 502, and the magnetic field is solenoidal around the symmetry axis 502.
  • the electrons enter the cavity 501 at different times, as indicated by their different positions along the symmetry axis 502 in a snapshot in time.
  • the phase of the electromagnetic oscillation is adjusted such that earlier first electron 503 is subjected to a small or vanishing electric field 507, i.e., is synchronized with a zero crossing of the electric field, while the latter second electron 504 encounters a stronger electric field 508 that decelerates it.
  • the electrons 503, 504 After passing through the accelerator structure 501, the electrons 503, 504 have only minimally changed their timing relationship, indicated as the distance between first electron 509 and second electron 510.
  • first velocity prime 511 the exit velocity of first electron 509
  • second velocity prime 512 the exit velocity of second electron 510
  • [Hl] Disclosed herein are ways of increasing time differences within a short distance by employing a sequence of mutually enhancing transformations from energy to time and time to energy. These are optical elements converting between physical complementary variables in the time-energy domain in direct analogy to conventional optical elements that convert between the complementary variables of transverse, relative to an optical axis, position and momentum (proportional to angle relative to the optical axis). They will therefore be called ‘time-energy electron optics’.
  • the electrons coming from the sample at a range of energy deficits relative to Eo separate out in time by propagation or in a chicane are then accelerated and/or decelerated selectively based on their arrival times in an electrodynamic device, and then separated further in time in another propagation section or chicane, but now with an increased spread of energies, and thus velocities.
  • This sequence can be deployed once, or be repeated multiple times, as necessary to build a time-energy electron optic.
  • the electrodynamic device is a radiofrequency accelerator cavity (RF cavity) of the type used in particle-accelerator physics.
  • the cavity is driven at, typically, a frequency of a few GHz, such that the arrival of electrons of energy Eo in it coincides with a zero crossing of the electric field, while electrons arriving later are decelerated by an energy proportional to their arrival-time lag. Electrons at energy Eo are then not affected by the electric field in the cavity, and those arriving later within a fraction of the RF cycle are accelerated or decelerated depending on their arrival time relative to the RF phase. There is also a solenoidal magnetic field associated with the time derivative of the electric field. This field is zero at the center line of the RF cavity, and thus does not affect electron beams properly aligned to the center of RF cavity.
  • ETEM electrodynamic time-to-energy mapper
  • the phase of the electromagnetic fields driving the ETEM is adjusted relative to the timing of the photocathode laser, and thus the arrival times of electrons at the ETEM, such that the prompt electrons are left unaffected, and the inelastically scattered electrons are decelerated. The latter thus lose energy approximately in proportion to their arrival-time lag relative to the prompt electrons.
  • the sinusoidal time dependence of the electric field can be approximated by a linear time dependence, and the proportionality holds well.
  • more complex time-dependent amounts of deceleration can be realized.
  • the device as discussed above for the electron microscope system may include a radiofrequency accelerator cavity or an electrodynamic device as discussed in FIG. 5.
  • the radiofrequency accelerator cavity or the electrodynamic device is configured to convert arrival time differences of the plurality of electrons into electron energy differences.
  • a thin foil of conducting or semiconducting material is placed on top of an MCP or a stack of MCP’s and is kept at a high negative potential relative to the top of the MCP or MCP stack. Incident high-energy electrons generate showers of hot electrons from the foil, which are further amplified in the MCP or MCP’s.
  • FIG. 6 shows a cross-section of an electron-detection assembly consisting of a thin foil 601 (thickness exaggerated for graphical purposes) of conducting or semiconducting material for the first-step generation of secondary electrons from incident high-energy ones, an MCP 602 or stack of MCP’s 602 for further amplifying the resulting signal, and a readout anode 603 for capturing charge pulses and reading them with fast waveform-sampling electronics (not shown).
  • the term “MCP” shall also apply to an MCP stack.
  • an electron 604 with an energy of, say 100 to 500 keV strikes the thin foil 601 and passes through the entire assembly 605 while generating hot electrons within the foil 601.
  • These secondary electrons 606 leave the foil 601 and are accelerated towards the MCP 602, which is at a positive bias of a few kV relative to the foil.
  • the term “hot electrons” refers to their energies, which, at a few eV, are far above those of the conduction electrons, but well below the incident-electron energy. Hot electrons travel very rapidly in the conduction band of many materials.
  • Both the primary and the secondary electrons generate further secondary electrons 607 within the MCP 602. These generate electrical signals on the readout anode 603, which are then read out with waveform-sampling electronics. Because the secondary electrons 606 from the foil 601 hit several pores in the MCP 602, they generate a much stronger signal than the primary electron on the readout anode 603, and the two contributions can be separated in the sampled waveforms.
  • the electron sensor is based on MCP or a stack of MCP’s, augmented by a thin-foil transmission-electron multiplier placed in front of the MCP’s.
  • the foil made of a thin film, typically a few microns thick, of conductor or semiconductor material, is biased negatively at several 1000 V relative to the MCP or top MCP of a stack.
  • MCP may also refer to a stack of MCP’s.
  • the foil serves as a primary low-jitter electron multiplier where energetic electrons from the electron microscope generate large amounts of so-called hot charge carriers in the valence and conduction band of the material.
  • the electronmultiplication process in the foil by itself not producing as many electrons as the MCP’s, is however, subject to much less timing spread, and it contains a sufficient number of electrons to reduce the transit-time spread in the MCPs through the statistics of multiple-avalanche amplification.
  • the fast primary (prompt or inelastically scattered) electron from the electron microscope will penetrate the foil and will also trigger an avalanche in one pore of the MCP. Because the primary electron is still highly energetic, an avalanche triggered by it will occur earlier than any triggered by the secondary electrons from the foil, but its exact timing is subject to the statistics discussed above. In order to ensure that the signal from the one pore triggered by the fast primary electron remains insignificant, the distance of the foil to the MCP and the voltage bias between them are adjusted such that the secondary electrons leaving the foil spread by their transverse momentum over an area on the MCP that covers multiple pores. Then, the signal from those multiple pores will dominate over that from the one pore triggered by the primary electron, which can thus be separated out through processing of the signal waveform.
  • a filtering system which uses a transverse magnetic field similar to those often used in electron microscopy.
  • Other embodiments may use imaging with electrostatic focusing of the type used in generation-I night-vision tubes.
  • Common to all these filters is that they either outright reject the primary electrons, or they separate them spatially on the MCP, so that two pulses are generated from different locations. Which of these is to be attributed to the primary, and which to the secondary electrons, is clear from the relative timing and strengths of the pulses.
  • the thin foil of conducting or semiconducting material is kept separated from the MCP, and a wire mesh is used as an electrode to accelerate the electrons emerging from the foil. These electrons are then imaged onto the MCP using electron optics, and a magnetic energy filter spatially separates the higher-energy primary electrons from the secondaries emerging from the foil.
  • FIG.7 shows a cross-section of an electron-detection assembly consisting of a thin foil 701 (thickness exaggerated for graphical purposes) of conducting or semiconducting material for the first-step generation of secondary electrons from incident high-energy ones, an acceleration grid 702 for these secondaries, an MCP 703 for further amplifying the resulting signal, and a readout anode 704 for capturing charge pulses and reading them with fast waveform-sampling electronics (not shown).
  • an electron 705 with an energy of, typically, 100 to 500 keV strikes the thin foil 701 and passes 706 through it while generating hot electrons within it, which are emitted as secondary electrons 707 from the foil and accelerated by the acceleration grid 702.
  • Both the primary, and the secondary electrons are sent through imaging electron optics including a magnetic energy filter whose effect is indicated by the curved electron paths between the acceleration grid 702 and the MCP 703. Due to their different energies and thus different curvatures of their trajectories, the primary and the secondary electrons hit the MCP 703 in different locations and are read as separate pulses. The secondary electrons 707 hit several pores in the MCP 703 and generate a much stronger signal than the primary electron, making it is clear which is which.
  • a method includes providing primary electrons, providing first stage electron amplifier operable to receive the primary electrons on first surface, and generating secondary electrons from each of the primary electrons, where the number of secondary electrons is greater than the number of primary electrons.
  • the method includes emitting the primary electrons and the secondary electrons from second surface of the first stage electron amplifier, the second surface opposite the first surface, where the energy of each of the secondary electrons is less than the energy of each of the primary electrons.
  • providing second stage electron amplifier operable to receive the primary electrons and the secondary electrons on first surface of the second stage electron amplifier, where the first surface of the second stage electron amplifier faces the second surface of the first stage electron amplifier, and applying a magnetic field (similar to that discussed above in FIG.
  • LAPED large-area picosecond electron detector
  • the embodiments disclosed herein may be applied to provide applications with picosecondprecision photon and particle detection and much better time resolution technology than those that currently exist.
  • the LAPED concept may be an element in the design of time- of-flight electron microscopy (TOFEM), improving efficiency of high-resolution transmission electron microscopy (HRTEM), including cryo-electron microscopy, to reduce radiation exposure to samples in HRTEM or cryo-electron microscopy.
  • TOFEM can build upon a combination of an LAPED and time-energy-domain electron optics to allow for the acquisition of fully three-dimensional data (2d image and electron energy) for both the elimination of chromatic aberrations, and the acquisition of electron energy] loss spectra (EELS) without the use of an electron filter.
  • EELS electron energy] loss spectra
  • the LAPED may have to time the arrival of each electron to single-digit picosecond (ps) precision.
  • the LAPED while the LAPED can detect electrons directly, the LAPED may be used in combination with a photocathode (e.g., a converter for converting photons to photoelectrons).
  • a photon detector can be designed based on photoemission of electrons, accelerated to high energies, and detected by an LAPED.
  • the use of the LAPED concept may be implemented for the detection of electrons as well as any other particles or photons by converting them to electrons.
  • the LAPED can use multiple micro-channel plates (MCP’s) or stacks of MCP’s, it may also operate with only one MCP.
  • MCP micro-channel plates
  • the LAPED may include a first-stage low- jitter electron amplifier.
  • signals from the LAPED may be done with a microstrip line array or capacitive coupling.
  • the coherence time can be set in inverse proportion to the spectral bandwidth. Due to the picosecond-scale time resolution of the detector, one can reach coherence times comparable to the time resolution of the detector with interference filters, thus allowing the resolution of photon occupation in individual longitudinal modes of the electromagnetic field.
  • a device similar to that disclosed in FIG. IB can further include a spectral filter (not shown) upstream of the photocathode, e.g., photocathode 112, where the spectral filter can include a bandwidth and a corresponding coherence time comparable to a time resolution of the device.
  • the core concept of the LAPED a combination of low-jitter primary electron amplifier with an avalanche-like amplification of an MCP to achieve singledigit picosecond time resolution, can be applied for precision-timed detection of massive sub-atomic, atomic as well as molecular particles such as velocity-mapping imaging (VMI) in atomic and molecular physics.
  • VMI is, essentially, time-of-flight mass spectrometry, and is typically used for the analysis of molecular fragments due to laser-induced molecular breakup or ionization.
  • IB can further include a converter cathode (not shown) upstream of the first stage electron amplifier, e.g., foil 116, where the converter cathode can emit primary electrons when struck by particles including molecular fragments having atoms, ions, molecules, subatomic particles or other massive particles.
  • a converter cathode (not shown) upstream of the first stage electron amplifier, e.g., foil 116, where the converter cathode can emit primary electrons when struck by particles including molecular fragments having atoms, ions, molecules, subatomic particles or other massive particles.
  • time-energy optics for conversion between electron arrival times and their energies and vice versa can be used to improve the TOF contrast of electrons with slightly different energies, such timing within the range of capabilities of the LAPED.
  • TEO could also be used to bring electron timing within range of other slower electron detectors.
  • the LAPED may also be referred to as an imaging picosecond photon detector (IPPD).
  • IPPD imaging picosecond photon detector
  • the advantages of the IPPD over existing technology is that IPPD separates low-jitter-gain and avalanche-gain stages, such separation allowing for more relaxed integration of the amplifier stages and therefore multiple design options.
  • the low-jitter-gain stage in the IPPD can be optimized independently of the avalanche-gain stage, in particular with respect to former’s material choice and thickness to match incidentelectron energies.
  • MCP can be much larger than economically viable APD arrays
  • MCP can, in principle, reach single-digit picosecond timing, such performance yet to be proven for APD’s (APD’s suffer from relatively slow charge transport in silicon (electrons saturation velocity of about 10 5 m/s) while electrons traveling down a pore of an MCP can reach much higher velocities (e.g., 1 % of the speed of light, e.g., 3x10 8 m/s)); and
  • MCP’s can be read out with far fewer electronics channels than there are effective pixels (systems with APD’s are typically read out on 50-60 channels and reach spatial resolution (at 50 ps timing) of about 200x200 pixels but when mega-pixels imaging is required, reducing the channel count will be critical).
  • a method of using an electron microscope with a pulsed electron source so that electrons arrive at a sample at fixed time points and fixed energy, and any energy loss of the electrons in the sample is mapped onto the time coordinate for electron arrival at the detector as a difference relative to the arrival of electrons that have not lost energy, such mapping being done by the time-energy-domain electron-optical system.
  • a method of using an electron microscope in a three- dimensional data acquisition mode where the energy of each electron transmitted through the sample is determined from its arrival time at the detector where energies are being mapped to the time coordinate by the time-energy-domain optical system.
  • the electron TOF from the electron source to the sample in the electron microscope is fixed, given by isochronous electron optics, and the total TOF from the source to the detector then indicates the TOF from the sample to the detector, and thus the electron energies after the sample.
  • the TOF provides a third data dimension over the two image dimensions, thus separating out the energy data, which a magnetic filter would entangle by mapping electron arrivals only with two image dimensions.
  • the TOF contrast of electron energies can be increased by magnifying time-energy-domain electron optics that convert electron times or energy differences into time differences.

Abstract

L'invention concerne des procédés de détection de photons individuels ou de particules chargées avec une précision temporelle picoseconde à un chiffre et spatiale bidimensionnelle. Les modes de réalisation sont applicables à des photons d'énergies capables de produire des photoélectrons, typiquement, mais pas nécessairement, d'environ un électron-volt à plusieurs kilo-électron-Volts, ainsi que des particules chargées atteignant le détecteur à des énergies arbitraires. Les modes de réalisation sont basés sur l'amplification du signal inhérent à une particule chargée primaire énergétique ou à un photoélectron par génération de porteurs chauds dans un matériau conducteur ou semi-conducteur en vrac, éventuellement combinée à une amplification supplémentaire dans une plaque à microcanaux. Des applications peuvent être trouvées dans des procédés basés sur des photons d'imagerie et autrement de résolution spatiale de la dynamique moléculaire ultra-rapide, de l'imagerie à temps de vol comprenant l'imagerie médicale, l'optique quantique et le calcul optique. D'autres applications peuvent être trouvées dans des procédés à base de particules chargées dans le mappage de vitesse de fragments moléculaires et d'électrons dans une fragmentation moléculaire déclenchée. D'autres applications peuvent être trouvées dans une imagerie à résolution temporelle en microscopie électronique, en particulier une analyse d'énergie électronique pleine image par temps de vol, à l'aide d'une optique électronique à domaine d'énergie-temps pour augmenter le contraste temps-vol.
PCT/US2021/062067 2020-12-07 2021-12-06 Détecteur à résolution spatiale ultrarapide pour photons et particules chargées et ses applications WO2022125469A1 (fr)

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Citations (10)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US20050006582A1 (en) * 2003-04-17 2005-01-13 Leo Elektronenmikroskopie Gmbh Electron microscopy system, electron microscopy method and focusing system for charged particles
US20090236521A1 (en) * 2004-04-02 2009-09-24 California Institute Of Technology Method and system for ultrafast photoelectron microscope
US20110276526A1 (en) * 2008-12-19 2011-11-10 Europhoton Gmbh, Gesellschaft Fur Optische Sensori position resolved measurement apparatus and a method for acquiring space coordinates of a quantum beam incident thereon
US20130026363A1 (en) * 2009-02-06 2013-01-31 Hitachi High-Technologies Corporation Charged particle radiation device
US20130234023A1 (en) * 2008-10-09 2013-09-12 California Institute Of Technology Characterization of nanoscale structures using an ultrafast electron microscope
US20160111267A1 (en) * 2010-12-17 2016-04-21 Thermo Fisher Scientific (Bremen) Gmbh Ion Detection System and Method
US20170301526A1 (en) * 2015-09-01 2017-10-19 Government Of The United States Of America, As Represented By The Secretary Of Commerce Imaging spectrometer
US20180156926A1 (en) * 2005-04-22 2018-06-07 Koninklijke Philips N.V. Digital silicon photomultiplier for tof-pet
US20180351023A1 (en) * 2016-09-20 2018-12-06 Llc "Dephan" Avalanche photodetector
US10190916B1 (en) * 2016-01-29 2019-01-29 U.S. Department Of Energy System for true thermal-light applications

Patent Citations (10)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US20050006582A1 (en) * 2003-04-17 2005-01-13 Leo Elektronenmikroskopie Gmbh Electron microscopy system, electron microscopy method and focusing system for charged particles
US20090236521A1 (en) * 2004-04-02 2009-09-24 California Institute Of Technology Method and system for ultrafast photoelectron microscope
US20180156926A1 (en) * 2005-04-22 2018-06-07 Koninklijke Philips N.V. Digital silicon photomultiplier for tof-pet
US20130234023A1 (en) * 2008-10-09 2013-09-12 California Institute Of Technology Characterization of nanoscale structures using an ultrafast electron microscope
US20110276526A1 (en) * 2008-12-19 2011-11-10 Europhoton Gmbh, Gesellschaft Fur Optische Sensori position resolved measurement apparatus and a method for acquiring space coordinates of a quantum beam incident thereon
US20130026363A1 (en) * 2009-02-06 2013-01-31 Hitachi High-Technologies Corporation Charged particle radiation device
US20160111267A1 (en) * 2010-12-17 2016-04-21 Thermo Fisher Scientific (Bremen) Gmbh Ion Detection System and Method
US20170301526A1 (en) * 2015-09-01 2017-10-19 Government Of The United States Of America, As Represented By The Secretary Of Commerce Imaging spectrometer
US10190916B1 (en) * 2016-01-29 2019-01-29 U.S. Department Of Energy System for true thermal-light applications
US20180351023A1 (en) * 2016-09-20 2018-12-06 Llc "Dephan" Avalanche photodetector

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