A multifunctional ultrafast cathodoluminescence detection system and its application method

Abstract

This invention discloses a multifunctional ultrafast cathodoluminescence system and its application method. The system includes: a high-repetition-rate femtosecond laser system for emitting ultraviolet femtosecond lasers; a field emission scanning electron microscope (SEM) system for converting ultraviolet femtosecond lasers into cathodoluminescence; a cathodoluminescence collection system for collecting cathodoluminescence; a cathodoluminescence analysis system integrating multiple detection modules; and a spatial optical path system for guiding the selective transmission of optical signals. The multifunctional ultrafast cathodoluminescence system provided by this invention integrates multiple functional modules, enabling comprehensive analysis of the fluorescence signal based on the characteristics of the sample. It achieves multiple detection functions, including polarization analysis, intensity detection, angle-resolved spectral detection, full-spectrum information detection, and ultrafast time-resolved information detection of cathodoluminescence. The use of a Schottky field emission tungsten filament as the ultrafast photocathode enhances the spatiotemporal coherence of the electron pulses, resulting in high-resolution SEM images and a stable emission beam.

Description

Technical Field

[0001] This invention relates to the field of ultrafast cathodoluminescence detection, and more particularly to a multifunctional ultrafast cathodoluminescence detection system and its application method. Background Technology

[0002] With the development of nanotechnology and the increasing integration of semiconductor optoelectronic devices, researchers are building platforms for optoelectronic functional devices on various low-dimensional semiconductor nanomaterials, with sizes ranging from nanometers to atomic scales. For most low-dimensional semiconductor nanomaterials, the performance of their optoelectronic devices depends primarily on the dynamics of their charge carriers, such as excited-state charge carrier transport, defect-state capture of charge carriers, and charge carrier recombination luminescence. These dynamic processes mostly occur on nanosecond, picosecond, or even femtosecond timescales. Only with ultra-high spatiotemporal resolution energy carrier measurement and analysis techniques can the dynamics of excited-state charge carriers at different locations within a single nanostructure unit be detected. This allows for understanding the charge carrier dynamics of different nanostructures under interface, defect, and external field modulation, thus promoting the design and development of high-performance nano-optoelectronic functional materials and devices. Therefore, developing ultra-high spatiotemporal resolution energy carrier dynamics detection and analysis techniques is crucial for both advancing theoretical research in basic fields and developing various novel low-dimensional nanodevices and applications; it is also an extremely challenging task.

[0003] For the study of excited-state carrier dynamics in semiconductor nanomaterials, current research primarily employs time-resolved ultrafast spectroscopic analysis techniques based on picosecond and femtosecond lasers, such as time-resolved photoluminescence spectroscopy, time-resolved transient absorption spectroscopy, and time-resolved higher harmonic spectroscopy. However, in certain situations, these laser-based measurement techniques are significantly limited in their application to measuring the energy carrier dynamics of low-dimensional nanostructures due to the diffraction effect of light waves. Examples include semiconductor heterojunctions, defects, quantum wells, quantum dots, and metallic nanostructures, where only average dynamic information for large assemblies of nanostructures can be obtained. Given these limitations, cathodoluminescence technology, using electron probe microanalysis as the excitation source, plays an irreplaceable role in these applications. Compared to laser-based detection technologies, high-energy electron probes (HEEPs) offer two significant advantages: First, they are not limited by the excitation wavelength. The electron beam used to excite the fluorescence signal of the sample is very high-energy, easily exciting various wide-bandgap semiconductor materials, such as boron nitride, aluminum nitride, and zinc oxide. Second, they have extremely high spatial resolution. Lasers are limited by the diffraction limit, and the spot size can mostly only be focused to the micrometer scale, measuring average dynamic information over a large area. In contrast, after being focused by an electromagnetic lens, an HEEP can achieve sub-nanometer spatial resolution, enabling the detection of nanoscale materials.

[0004] Continuous electron beams can be obtained through filament emission from scanning electron microscopes (SEMs) or transmission electron microscopes (TEMs). However, achieving picosecond or even femtosecond timescale pulsed electron beams is extremely difficult, which limits the application of cathodoluminescence (CFD) in excited-state carrier dynamics research. To address this issue, ultrafast cathodoluminescence (CFD) technology based on pulsed electrons has emerged. Early ultrafast CFD techniques obtained pulsed electrons by adding a high-frequency deflection electric field to a conventional SEM. However, due to the limitation of the deflection electric field frequency, this method could only achieve time-resolved cathodoluminescence measurements at the nanosecond level. Picosecond-resolved ultrafast cathodoluminescence, a carrier luminescence dynamics detection technique with ultra-high spatiotemporal resolution, has been developed since 2005. In this technique, the pulsed electron beam used as the excitation source is generated by a femtosecond pulsed laser exciting the photocathode of the electron gun in the SEM. After acceleration and focusing by an electromagnetic lens, it is used to excite energy carriers in the sample to produce transient cathodoluminescence. The relationship between the transient fluorescence and time is then detected using streak cameras or time-correlated single-photon counting techniques. Because high-energy electrons have very short wavelengths and can be focused into very small areas, ultrafast cathodoluminescence technology can achieve high spatial resolution, making it a powerful tool for studying the energy carrier dynamics of semiconductor nanomaterials at high spatiotemporal resolution scales.

[0005] Traditional ultrafast cathodoluminescence technology suffers from limitations in modularity and integration. Furthermore, most mainstream time-resolved cathodoluminescence systems internationally employ planar photocathodes consisting of a tens-nanometer-thick gold film deposited on the surface of quartz glass. An ultraviolet femtosecond laser is focused from the back through the quartz glass onto a region of a few micrometers on the photocathode, generating ultrafast photoelectron pulses. Due to the laser's diffraction effect, the area where the femtosecond laser is focused on the photocathode is limited to the micrometer scale, severely impacting the coherence and temporal resolution of the generated photoelectron pulses. This significantly restricts the spatiotemporal resolution and performance of ultrafast cathodoluminescence. Summary of the Invention

[0006] To overcome the above technical problems, the present invention aims to provide a multifunctional ultrafast cathodoluminescence detection system and its application method, making up for the shortcomings of traditional ultrafast cathodoluminescence detection technology in terms of limited modularity and low integration. Furthermore, in some preferred embodiments, the detection system uses a tungsten filament capable of Schottky field emission as the ultrafast photocathode, which not only obtains high-resolution scanning electron microscope images and a stable emission beam, but also effectively improves the signal-to-noise ratio, resulting in a significant improvement in both spatial and temporal resolution.

[0007] This invention provides the following technical solution:

[0008] A multifunctional ultrafast cathodoluminescence system, comprising:

[0009] A high repetition rate femtosecond laser system (1) includes a femtosecond laser (1-1), a second frequency doubling device (1-2), and a fourth frequency doubling device (1-3) for generating a high repetition rate near-infrared femtosecond laser. The femtosecond laser (1-1) generates a near-infrared femtosecond laser. The near-infrared femtosecond laser is then multiplied by the second frequency doubling device (1-2) to generate green light, and then multiplied by the fourth frequency doubling device (1-3) to generate an ultraviolet femtosecond laser.

[0010] A field emission scanning electron microscope (2) is used to generate an electron beam from the ultraviolet femtosecond laser generated by the high repetition rate femtosecond laser system (1) through the photocathode of the field emission electron gun (2-2). The electron beam includes a continuous electron beam and a pulsed electron beam. The continuous electron beam is used to obtain the fluorescence properties of the sample under steady-state conditions, and the pulsed electron beam is used to obtain time-resolved carrier dynamics information and fluorescence lifetime information of the sample. The continuous electron beam is accelerated and focused to excite the sample to generate steady-state cathodoluminescence. The pulsed electron beam is composed of pulsed photoelectrons. The pulsed photoelectrons are accelerated and focused to excite the sample to generate transient cathodoluminescence. The pulsed electron beam is emitted by a tungsten filament of Schottky field emission through the photocathode of the field emission electron gun (2-2).

[0011] A cathodoluminescence collection system (3) is used to collect the fluorescence signal of the cathodoluminescence generated by the sample;

[0012] The cathodoluminescence analysis system (4) includes a selectively filtering polarization device (41) for selectively filtering and polarizing the fluorescence signal collected by the cathodoluminescence collection system (3); it also includes a first spectrometer (42), a first detection system (43), and a second detection system (44); wherein the first detection system (43) is used for intensity detection or angle-resolved spectral detection of the fluorescence signal; the second detection system (44) is used for full-spectrum information detection of static cathodoluminescence or ultrafast time-resolved information detection of the fluorescence signal; the first spectrometer (42) is used for selectively guiding the fluorescence signal, and the fluorescence signal selectively enters the first detection system (43) or the second detection system (44);

[0013] The second detection system (44) is electrically connected to the high repetition rate femtosecond laser system (1) and is synchronously excited and synchronously detected through the repetition rate electrical signal;

[0014] The spatial optical path system is used to guide the optical signal to be converted and selectively transmitted between the high repetition rate femtosecond laser system (1), the field emission scanning electron microscope system (2), the cathodoluminescence collection system (3), and the cathodoluminescence analysis system (4).

[0015] Furthermore, the field emission scanning electron microscope system (2) includes a first optical window (2-1), a field emission electron gun (2-2), an electromagnetic lens (2-3), a parabolic mirror (2-5), a low-temperature sample stage (2-4), and a second optical window (2-6), all disposed within a sealed cavity. The first optical window (2-1) is located on one side wall of the sealed cavity and directly opposite the photocathode tip of the field emission electron gun (2-2), allowing the ultraviolet femtosecond laser generated by the high repetition rate femtosecond laser system (1) to pass through the first optical window (2-1) and converge to the photocathode tip of the field emission electron gun (2-2). The field emission electron gun (2-2) excites the received ultraviolet femtosecond laser through the photocathode of the field emission electron gun (2-2) to form a... A continuous electron beam or pulsed electron beam of a certain intensity is further focused by the electromagnetic lens (2-3); the parabolic mirror (2-5) is provided with a through hole for the continuous electron beam or pulsed electron beam to pass through; the low-temperature sample stage (2-4) is used to place the sample to be tested and to allow the sample to be moved in three dimensions to the focal point of the parabolic mirror (2-5); the continuous electron beam or pulsed electron beam excites the sample to generate cathodoluminescence; the parabolic reflective surface of the parabolic mirror (2-5) reflects the cathodoluminescence generated by the sample excitation into parallel cathodoluminescence; the parallel cathodoluminescence is transmitted to the cathodoluminescence collection system (3) through a second optical window (2-6) provided on one side wall of the sealed cavity next to the low-temperature sample stage (2-4).

[0016] Furthermore, the first optical window (2-1) is made of leaded glass with high transmittance in the visible to ultraviolet bands.

[0017] Furthermore, the temperature control range of the low-temperature sample stage (2-4) is 10-300K.

[0018] Furthermore, the first detection system (43) includes a second beam splitter (43-1), a photomultiplier tube (43-2), and an angle-resolved fluorescence detection camera (43-3). The second beam splitter (43-1) is used to selectively guide the received fluorescence signal to selectively enter the photomultiplier tube (43-2) or the angle-resolved fluorescence detection camera (43-3).

[0019] Furthermore, the second detection system (44) includes a spectrometer (44-1), a third spectrometer (44-2), a static cathodoluminescence detector (44-3), and a time-resolved detector (44-4). The spectrometer (44-1) divides the polychromatic fluorescence signal into spectral lines through a grating. The third spectrometer (44-2) is used to selectively guide the spectral signal, which selectively enters the static cathodoluminescence detector (44-3) or the time-resolved detector (44-4).

[0020] Furthermore, the static cathodoluminescence detection device (44-3) is a spectral detection camera; the time-resolved detection device (44-4) includes a streak camera or a time-correlated single-photon detector.

[0021] Furthermore, it includes three air-float devices: a first optical platform (5), a scanning electron microscope air-float platform (6), and a second optical platform (7). The first optical platform (5) is used to support the high repetition rate femtosecond laser system (1) and reduce vibration; the scanning electron microscope air-float platform (6) is used to support the field emission scanning electron microscope system (2) and reduce vibration; the second optical platform (7) is used to support the cathodoluminescence collection system (3) and the cathodoluminescence analysis system (4) and reduce vibration. The first optical platform (5) and the second optical platform (7) are rigidly connected to the scanning electron microscope air-float platform (6) to achieve synchronous air-float connection.

[0022] Furthermore, the photocathode of the field emission scanning electron microscope system (2) is a tungsten filament with Schottky field emission and its surface is coated with zirconium oxide.

[0023] The application method of this multifunctional ultrafast cathodoluminescence system includes the following steps:

[0024] The first step is to place the sample to be tested in the field emission scanning electron microscope system (1), adjust the focus to align with the sample to be tested, and adjust the emission mode of the field emission electron gun (2-2) of the field emission scanning electron microscope system (2) to continuous electron beam mode or pulsed electron beam mode.

[0025] The second step is to turn on the high repetition rate femtosecond laser system (1). The high repetition rate femtosecond laser system (1) outputs ultraviolet femtosecond laser, which is guided by the spatial optical path system and converges from the side of the field emission electron gun (2-2) to the tip of the field emission photocathode, thereby exciting and generating an ultrafast photoelectron beam. The ultrafast photoelectron beam excites the sample to generate cathodoluminescence, and the fluorescence signal is collected by the cathodoluminescence collection system (3). Then the fluorescence signal enters the cathodoluminescence analysis system (4).

[0026] The third step involves selectively filtering and polarizing the fluorescence signal using a filtering and polarization device (41); then the fluorescence signal enters the first spectrometer (42), and selectively enters the first detection system (43) or the second detection system (44); the first detection system (43) selectively performs fluorescence intensity detection or angle-resolved spectral detection; the second detection system (44) selectively performs full-spectrum detection or ultrafast time-resolved detection of static cathodoluminescence.

[0027] Through the above steps, the fluorescence properties of the sample under steady-state conditions are obtained in continuous electron beam mode; and the time-resolved carrier dynamics and fluorescence lifetime information of the sample are obtained in pulsed electron beam mode.

[0028] Compared with the prior art, the present invention has the following beneficial effects:

[0029] (1) The multifunctional ultrafast cathodoluminescence system provided by the present invention incorporates multiple functional modules, which can comprehensively analyze the fluorescence signal of the sample according to its characteristics, and realize polarization analysis, intensity detection, angle-resolved spectral detection, full-spectrum information detection or ultrafast time-resolved information detection of cathodoluminescence. Among them, the ultrafast fluorescence spectrum obtained by the time-resolved detection device gives the luminescence dynamics information of the charge carrier.

[0030] In practical applications, this cathodoluminescence system serves as an analytical tool for studying the ultrafast carrier dynamics of semiconductor nanomaterials. It boasts ultra-high spatiotemporal resolution, achieving nanometer-level spatial resolution and picosecond-level temporal resolution. Utilizing functional modules such as polarization, angular resolution, and filtering, it can acquire rich optical property information from samples. Furthermore, in time-resolved mode, it can analyze the dynamics of exciton and electron-hole pair recombination luminescence in semiconductor nanomaterials, as well as the influence of impurities, defects, and structures on carrier dynamics. Its multifunctional, omnidirectional, and high spatiotemporal resolution characteristics overcome the shortcomings of traditional ultrafast cathodoluminescence technologies, such as limited modularity and low integration.

[0031] (2) The multifunctional ultrafast cathode fluorescence system and its application method provided by the present invention use a Schottky field emission tungsten filament as an ultrafast photocathode for the field emission electron gun, which improves the spatiotemporal coherence of the electron pulse, can obtain high-definition scanning electron microscope images and stable emission beams, and can effectively improve the signal-to-noise ratio, thereby greatly improving the spatial resolution and temporal resolution.

[0032] (3) The multifunctional ultrafast cathodoluminescence system and its application method provided by the present invention improve the overall stability and spatiotemporal resolution of the multifunctional ultrafast cathodoluminescence system by rigidly connecting the three air flotation devices.

[0033] (4) The multifunctional ultrafast cathode fluorescence system and its application method provided by the present invention can select and guide the propagation of light through a spatial optical path system between various functional modules, with smooth coupling and convenient switching. It can conveniently perform multidimensional detection of nanoscale semiconductor materials, and meet people's research on high spatiotemporal resolution carrier luminescence dynamics of emerging materials such as semiconductor nanowires, quantum dots, and nanosheets. Attached Figure Description

[0034] Figure 1This is a schematic diagram of the overall structure of an embodiment of the present invention.

[0035] Figure 2 A partial schematic diagram of the photocathode of a field emission electron gun according to an embodiment of the present invention.

[0036] Figure 3 This is a partial schematic diagram of a low-temperature sample stage according to an embodiment of the present invention.

[0037] Figure 4 This is a schematic diagram of three air flotation devices according to an embodiment of the present invention.

[0038] Figure 5 A diagram showing the pulsed electron beam current test results of an embodiment of the present invention.

[0039] Figure 6 An imaging effect diagram in pulsed electron mode according to an embodiment of the present invention.

[0040] Figure 7 The image shows the test results of the fluorescence properties of diamond microcrystals according to an embodiment of the present invention.

[0041] Figure 8 A graph showing the carrier dynamics test results of a bent zinc oxide microwire according to an embodiment of the present invention.

[0042] Figure 9 A schematic diagram illustrating the working principle of an embodiment of the present invention.

[0043] The numbers in the attached diagram are:

[0044] 1. High repetition rate femtosecond laser system; 1-1. Femtosecond laser; 1-2. Secondary frequency doubling device; 1-3. Fourthary frequency doubling device; 2. Field emission scanning electron microscope system; 2-1. First optical window; 2-2. Field emission electron gun; 2-3. Electromagnetic lens; 2-4. Low temperature sample stage; 2-5. Parabolic mirror; 2-6. Second optical window; 3. Cathodoluminescence collection system; 4. Cathodoluminescence analysis system; 41. Filtering and polarization device; 41-1. Filter 41-2 Polarizer; 42 First spectral dispersive device; 43 First detection system; 43-1 Second spectral dispersive device; 43-2 Photomultiplier tube; 43-3 Angle-resolved fluorescence detection camera; 44 Second detection system; 44-1 Spectrometer; 44-2 Third spectral dispersive device; 44-3 Static cathodoluminescence detection device; 44-4 Time-resolved detection device; 5 First optical platform; 6 Scanning electron microscope air-bearing platform; 7 Second optical platform. Detailed Implementation

[0045] The present invention will now be described in detail with reference to embodiments and accompanying drawings. However, it should be understood that the embodiments and drawings are for illustrative purposes only and do not constitute any limitation on the scope of protection of the present invention. All reasonable modifications and combinations included within the inventive spirit of the present invention fall within the scope of protection of the present invention.

[0046] The present invention will be further described below with reference to the accompanying drawings.

[0047] like Figure 1 and Figure 9 As shown, the entire system involves the following devices: a high-repetition-rate femtosecond laser system 1, a field emission scanning electron microscope system 2, a cathodoluminescence collection system 3, a cathodoluminescence analysis system 4, and a spatial optical path system. The high-repetition-rate femtosecond laser system 1 includes a femtosecond laser 1-1, a second-order frequency doubling device 1-2, and a fourth-order frequency doubling device 1-3 for generating high-repetition-rate near-infrared femtosecond lasers. Near-infrared femtosecond lasers are generated by the femtosecond laser 1-1, and after passing through the second-order frequency doubling device 1-2, green light is generated. This green light is then further multiplied by the fourth-order frequency doubling device 1-3 to generate ultraviolet femtosecond lasers. The field emission scanning electron microscope system 2 is used to generate ultraviolet femtosecond lasers from the ultraviolet femtosecond lasers generated by the high-repetition-rate femtosecond laser system 1 through the photocathode of the field emission electron gun 2-2. Electron beams include continuous electron beams and pulsed electron beams. Continuous electron beams are used to obtain the fluorescence properties of samples under steady-state conditions, while pulsed electron beams are used to obtain time-resolved carrier dynamics and fluorescence lifetime information of samples. Continuous electron beams, after acceleration and focusing, excite the sample to produce steady-state cathodoluminescence. Pulsed electron beams consist of pulsed photoelectrons, which, after acceleration and focusing, excite the sample to produce transient cathodoluminescence. The pulsed electron beam is emitted through a field emission electron gun 2-2, with the photocathode being a Schottky field emission tungsten filament. The cathodoluminescence collection system 3 collects the fluorescence signal of the cathodoluminescence generated by the sample; the cathodoluminescence analysis system 4 includes a filtering and polarization device 41 for selectively filtering and polarizing the fluorescence signal collected by the cathodoluminescence collection system 3; it also includes a first spectrometer 42, a first detection system 43, and a second detection system 44; wherein, the first detection system 43 is used for intensity detection or angle-resolved spectral detection of the fluorescence signal; the second detection system 44 is used for full-spectrum detection of static cathodoluminescence or ultrafast time-resolved information detection of the fluorescence signal; the first spectrometer 42 is used for selectively guiding the fluorescence signal, so that the fluorescence signal selectively enters the first detection system 43 or the second detection system 44; the second detection system 44 is electrically connected to the high repetition rate femtosecond laser system 1 and is synchronously excited and synchronously detected through the repetition rate electrical signal; the spatial optical path system is used to guide the optical signal to be converted and selectively transmitted between the high repetition rate femtosecond laser system 1, the field emission scanning electron microscope system 2, the cathodoluminescence collection system 3, and the cathodoluminescence analysis system 4.

[0048] Specifically, the high-repetition-rate femtosecond laser system 1 includes, for example, a femtosecond laser 1-1 for generating high-repetition-rate near-infrared femtosecond laser, a second-order frequency doubling device 1-2, and a fourth-order frequency doubling device 1-3. The second-order frequency doubling device 1-2 converts the near-infrared femtosecond laser into green light, and the fourth-order frequency doubling device 1-3 further converts the green light into ultraviolet femtosecond pulsed laser. In this structure, the high-repetition-rate near-infrared femtosecond laser generated by the femtosecond laser 1-1 is converted into green light after second-order frequency doubling by the second-order frequency doubling device 1-2, and then further converted into ultraviolet femtosecond pulses after fourth-order frequency doubling by the fourth-order frequency doubling device 1-3. These pulses are then guided into the field emission scanning electron microscope system 2 via a spatial optical path system. The second-order or fourth-order frequency doubling device 1-3 can specifically be a laser frequency multiplier. The high-repetition-rate femtosecond laser 1-1 has a repetition frequency of not less than 25 MHz and a pulse width of 250 femtoseconds.

[0049] The field emission scanning electron microscope system 2 includes, for example, a field emission electron gun 2-2, an electromagnetic lens 2-3, a parabolic mirror 2-5, a low-temperature sample stage 2-4, a first optical window 2-1, and a second optical window 2-6, all housed within a sealed cavity. The first optical window 2-1 is located on one side wall of the sealed cavity and directly opposite the photocathode tip of the field emission electron gun 2-2. Ultraviolet femtosecond laser light received from the first optical window 2-1 is focused at the photocathode tip of the field emission electron gun 2-2, exciting ultrafast photoelectrons. These photoelectrons are then focused by the electromagnetic lens 2-3 and pass through the parabolic mirror 2-5, exciting the sample to produce cathodoluminescence.

[0050] In the aforementioned system, the ultraviolet femtosecond laser generated by the high-repetition-rate femtosecond laser system 1 enters the field emission scanning electron microscope system 2, which excites the photocathode of its field emission electron gun 2-2. In pulsed electron beam mode, it generates a pulsed electron beam composed of pulsed photoelectrons. After acceleration and focusing by the electromagnetic lens 2-3, the pulsed photoelectrons can be used to excite the sample to produce transient cathodoluminescence. In continuous electron beam mode, it generates a steady-state field emission continuous electron beam. After acceleration and focusing by the electromagnetic lens 2-3, the continuous electron beam can be used to excite the sample to produce steady-state cathodoluminescence.

[0051] Furthermore, such as Figure 2As shown, the field emission scanning electron microscope system 2 also includes a lens support and a lens holder located outside the sealed cavity. Specifically, outside the first optical window 2-1 through which the ultraviolet femtosecond laser passes, there is a support for an adjustable-focusing optical lens. The lens holder is mounted on the support, and the adjustable-focusing optical lens is mounted on the lens holder. The support and lens holder work together to guide the ultraviolet femtosecond laser through the optical lens in a collimated direction into the first optical window 2-1. Preferably, the lens holder can be driven by a motor to move in three dimensions, causing the optical lens on it to move accordingly, thereby collimating the ultraviolet femtosecond laser towards the photocathode tip of the field emission electron gun 2-2. The lens holder is a conventional electrically controlled three-dimensional moving support.

[0052] In the field emission scanning electron microscope system 2 described above, the first optical window 2-1 is positioned directly opposite the photocathode tip of the field emission electron gun 2-2. By moving the optical lens, the ultraviolet femtosecond laser obtained from the high repetition rate femtosecond laser system 1 can excite the side of the photocathode tip of the field emission electron gun 2-2, generating an ultrafast photoelectron pulse.

[0053] Preferably, the material of the first optical window 2-1 is leaded glass with high transmittance in the visible to ultraviolet band.

[0054] Preferably, in order to obtain pulsed photoelectrons with better coherence, the field emission electron gun 2-2 uses a tungsten filament that can realize Schottky field emission as its photocathode. The tungsten filament is a composite material and its surface is coated with zirconium oxide. The role of zirconium oxide is to reduce the work function of electrons. In this preferred embodiment, the photocathode can generate a stable and high-intensity pulsed electron beam after being excited.

[0055] Furthermore, the parabolic reflector 2-5 is positioned on the mounting axis of the electromagnetic lens 2-3, and the parabolic reflector 2-5 has a through-hole for the pulsed electron beam to pass through. This through-hole has a diameter of 1-2 mm, allowing either a pulsed or continuous electron beam to pass through, thereby enabling the excitation and imaging of the sample.

[0056] In the aforementioned field emission scanning electron microscope system 2, the cryogenic sample stage 2-4 is a device for cooling the sample within a thermally insulated, sealed cavity. It is located on the mounting axis of the electromagnetic lens 2-3, at the rear end of the through-hole of the parabolic mirror 2-5, and is used to place the sample to be observed. It has a thermally insulated, sealed cavity to maintain the sample's low temperature. The cooling device for the thermally insulated, sealed cavity is a liquid helium Dewar flask. The cryogenic sample stage 2-4 also has a temperature control unit connected to the liquid helium Dewar flask. By controlling the cooling of the liquid helium Dewar flask through the temperature control unit, the temperature within the sealed cavity containing the sample can be continuously controlled and adjusted from 10K to 300K. The cryogenic sample stage 2-4 also includes a three-dimensional movement mechanism for controlling three-dimensional movement. By adjusting the three-dimensional movement mechanism, the cryogenic sample stage 2-4 is moved in three dimensions, adjusting the sample's position to the focal point of the parabolic mirror 2-5. Light emitted from the focal point is reflected by the parabolic mirror to form parallel light and passes through the second optical window 2-6. The three-dimensional movement mechanism is the existing electrically adjustable three-dimensional movement mechanism, which will not be described in detail here.

[0057] The sample is aligned with the ETD detector of the field emission scanning electron microscope system 2 within the insulated and sealed cavity where the sample is located. The ETD detector is a component of the field emission scanning electron microscope system 2 and is used for secondary electron detection.

[0058] Preferably, the parabolic reflector 2-5 is a flat-insertion type. The flat-insertion type of parabolic reflector 2-5 is easy to insert and remove, convenient to replace, and more convenient to use.

[0059] In the field emission scanning electron microscope system 2 described above, the second optical window 2-6 is used to transmit parallel cathode fluorescence.

[0060] Preferably, the material of the second optical window 2-6 is leaded glass with high transmittance in the visible to ultraviolet band.

[0061] The cathodoluminescence collection system 3 includes, for example, a cathodoluminescence collection probe and a three-dimensional moving mechanism for fixing the cathodoluminescence collection probe.

[0062] The cathode fluorescence collection probe is located outside the second optical window 2-6 on the opposite side of the ETD detector electron microscope in the field emission scanning electron microscope system 2. A three-dimensional moving mechanism fixes the cathode fluorescence collection probe and can be adjusted in three dimensions to accurately collect the fluorescence signal. The cathode fluorescence collection probe is an existing type and will not be described in detail here.

[0063] The cathodoluminescence analysis system 4 includes a filtering and polarization device 41, a first spectrometer 42, a first detection system 43, and a second detection system 44. The filtering and polarization device 41 consists of a filter 41-1 and a polarizer 41-2 sequentially installed after the cathodoluminescence collection probe. The fluorescence signal selectively passes through the filter 41-1, allowing for band filtering as needed. The filter 41-1 is insertable; in full-spectrum acquisition mode, it can be conveniently omitted, meaning the fluorescence signal can directly enter the polarizer 41-2 or pass through the filter 41-1 and then the polarizer 41-2. The polarizer 41-2 is electrically controlled and rotatable, used to analyze the polarization characteristics of the fluorescence signal. The fluorescence signal then passes through the first spectrometer 42, which guides the fluorescence signal into either the first detection system 43 or the second detection system 44.

[0064] The first detection system 43 includes a second beam splitter 43-1, a photomultiplier tube 43-2, and an angle-resolved fluorescence detection camera 43-3. The second beam splitter 43-1 is used to selectively guide the transmitted fluorescence signal, allowing the fluorescence signal to selectively enter either the photomultiplier tube 43-2 or the angle-resolved fluorescence detection camera 43-3. The photomultiplier tube 43-2 obtains intensity imaging of the fluorescence signal; the angle-resolved fluorescence detection camera 43-3 obtains angle-resolved detection information of the fluorescence signal.

[0065] The second detection system 44 includes a spectrometer 44-1, a third spectrometer 44-2 for guiding fluorescence signals, a static cathodoluminescence detector 44-3, and a time-resolved detector 44-4. The fluorescence signal enters the spectrometer 44-1, which separates the polychromatic fluorescence signal into spectral line fluorescence signals through a grating. The third spectrometer 44-2 selectively guides the fluorescence signal from the spectrometer 44-1, and the fluorescence signal selectively enters either the static cathodoluminescence detector 44-3 or the time-resolved detector 44-4.

[0066] In the aforementioned cathodoluminescence analysis system 4, a three-component spectrometer is provided to control the direction of the fluorescence signal. The first spectrometer 42 can selectively guide the fluorescence signal into the second spectrometer 43-1 or the spectrometer 44-1 of the second detection system 44. If the fluorescence signal is introduced into the second spectrometer 43-1, the second spectrometer 43-1 can select whether the receiving end of the fluorescence signal is a photomultiplier tube 43-2 or an angle-resolved fluorescence detection camera 43-3 to obtain a fluorescence intensity image or an angle-resolved fluorescence image of the sample. If the fluorescence signal is introduced into the spectrometer 44-1, the fluorescence signal is focused by a lens into the spectrometer 44-1, which is capable of fine spectrometry, for spectroscopic processing. The spectrometer 44-1 specifically comprises a monochromator, a diffraction grating, and other wavelength dispersion devices. It has two fluorescence signal interfaces. A static cathodoluminescence detector 44-3 is coupled to one of these interfaces, and a time-resolved detector 44-4 is coupled to the other. A third spectrometer 44-2 controls the direction of the two fluorescence signals. One set of fluorescence signals can be selectively output to the static cathodoluminescence detector 44-3, and the other to the time-resolved detector 44-4. The static cathodoluminescence detector 44-3 is specifically a spectral detection camera (i.e., an optical CCD). This camera acquires the full spectrum of the received fluorescence signal and performs time integration on the cathodoluminescence. The time-resolved detector 44-4 can be an ultrafast fluorescence detection device such as a streak camera or a time-correlated single-photon counter to perform time-resolved cathodoluminescence detection, thereby obtaining dynamic information on carrier recombination luminescence in the sample. The streak camera or time-correlated single-photon counter is electrically connected to the femtosecond laser 1-1, and synchronous excitation and detection are performed through the repetition frequency electrical signal.

[0067] In some embodiments, the first beam splitter 42, the second beam splitter 43-1, and the third beam splitter 44-2 are all supported by a three-dimensional moving mechanism, which can be electrically controlled to move in three dimensions. A reflector is installed on the three-dimensional moving mechanism. The three-dimensional movement of the three-dimensional moving mechanism drives the reflector to move in three dimensions, guiding the light reflection. The three-dimensional moving mechanism is provided by an existing electrically controlled three-dimensional moving mechanism, and will not be described in detail.

[0068] In some embodiments, the multifunctional ultrafast cathode fluorescence system also includes three air flotation devices, such as Figure 4As shown, the three air-floating devices are a first optical platform 5, a scanning electron microscope (SEM) air-floating platform 6, and a second optical platform 7. The first optical platform 5 supports and dampens the high-repetition-rate femtosecond laser system 1; the SEM air-floating platform 6 supports and dampens the field emission scanning electron microscope (SEM) system 2; and the second optical platform 7 supports and dampens the cathodoluminescence (CAT) collection system 3 and the CAT analysis system 4. The first optical platform 5 and the second optical platform 6 are rigidly connected to the SEM air-floating platform 6 to achieve synchronous air-floating. The rigid connection can be made using stainless steel plates. The three air-floating devices also support equipment from adjacent space optical path systems to ensure the stability of the space optical path equipment and ensure unobstructed optical paths.

[0069] In the specific implementation of the above structure, high-strength stainless steel plates are used to rigidly connect the scanning electron microscope air-float platform 6 to the first optical platform 5 and the second optical platform 7 respectively, achieving a synchronized air-float state. When external disturbances occur, the three air-float systems can respond simultaneously without changing their relative positions, ensuring that the spatial and temporal resolutions of the field emission scanning electron microscope system 2 in the multifunctional ultrafast cathode fluorescence system are not affected by vibrations in the external environment.

[0070] Furthermore, the streak camera used for ultrafast cathodoluminescence spectroscopy detection is divided into synchronous scanning mode and slow scanning mode. In synchronous scanning mode, the repetition rate electrical signal output from the oscillator of femtosecond laser 1-1 is connected to the streak camera to achieve synchronous scanning, or a portion of the laser output from femtosecond laser 1-1 triggers an avalanche photodiode to obtain a pulse signal to trigger the streak camera to achieve synchronous scanning. In slow scanning mode, a portion of the light with lower power is split in the optical path to trigger the avalanche photodiode connected to the streak camera, thereby synchronizing the femtosecond laser with the slow scanning module of the streak camera. The above two methods can achieve synchronization between the streak camera (or time-correlated single-photon counter) and the femtosecond laser pulse.

[0071] The spatial optical path system is used to guide the convergence, conversion, selection, and transmission of optical signals among the high-repetition-rate femtosecond laser system 1, the field emission scanning electron microscope system 2, the cathodoluminescence collection system 3, and the cathodoluminescence analysis system 4. The spatial optical path system mainly consists of light guide pillars, lenses, mirrors, and prisms, guiding light rays in a designated direction for convergence, conversion, selection, and transmission within the optical path.

[0072] Example 1:

[0073] like Figure 5As shown, the figure presents filament images of the pulsed electron beam under different accelerating voltages. The filament image refers to the projection of the filament beam. The figure also shows the relationship between the pulsed photoelectron beam current and the accelerating voltage and beam size, all of which are nearly linear, unlike ordinary scanning electron microscopy (SEM). Furthermore, high spatial resolution SEM images can still be obtained in pulsed photoelectron mode. Figure a shows filament images under different accelerating voltages; as the accelerating voltage decreases, the photoelectron beam current weakens significantly. Figure b shows the relationship between the accelerating voltage and the filament beam current measured by an external picoammeter, demonstrating a near-linear dependence of the filament beam current on the accelerating voltage. Figure c shows the relationship between the beam size and the filament beam current measured by an external picoammeter, demonstrating a linear dependence of the filament beam current on the beam size. These findings demonstrate that in pulsed electron beam mode, filament beams of different sizes and intensities can still be obtained according to specific needs.

[0074] Example 2:

[0075] like Figure 6 As shown, the figure provides a scanning secondary electron image in pulsed electron beam mode, demonstrating extremely high spatial resolution and clarity. The spatial resolution reaches 50nm, which fully meets the user's high-resolution imaging requirements for the field emission scanning electron microscope system 2. Figure a is a scanning electron microscope image of a copper mesh under switched laser mode, indicating that the electrons used for imaging are all photoelectrons, and the number of thermionic electrons is negligible. Figure b is a high-resolution scanning electron microscope image of a tin ball obtained in integration mode, showing image clarity close to that of a conventional scanning electron microscope.

[0076] This invention provides a method for applying the above-mentioned multifunctional ultrafast cathodoluminescence system, which includes the following steps:

[0077] The first step is to place the sample to be tested in the field emission scanning electron microscope system 1, adjust the focus to align with the sample, and adjust the emission mode of the field emission electron gun 2-2 of the field emission scanning electron microscope system 2 to either continuous electron beam mode or pulsed electron beam mode.

[0078] More specifically, in the first step described above, the sample to be tested is placed on the low-temperature sample stage 2-4, and the sample position is adjusted to the focal point of the parabolic reflector 2-5; the temperature of the low-temperature sample stage 2-4 is adjusted to the required test temperature, and the magnification of the field emission scanning electron microscope system 2 is adjusted; the emission mode of the field emission electron gun 2-2 of the field emission scanning electron microscope system 2 is adjusted to continuous electron beam mode or pulsed electron beam mode.

[0079] The second step is to turn on the high repetition rate femtosecond laser system 1. The ultraviolet femtosecond laser output by the high repetition rate femtosecond laser system 1 is guided by the spatial optical path system and converged from the side of the field emission electron gun 2-2 to the tip of the field emission photocathode, thereby exciting the generation of an ultrafast photoelectron beam. The ultrafast photoelectron beam excites the sample to generate cathodoluminescence. The fluorescence signal is collected by the cathodoluminescence collection system 3, and then the fluorescence signal enters the cathodoluminescence analysis system 4.

[0080] The third step involves selectively filtering and polarizing the fluorescence signal using a filtering and polarization device 41. The fluorescence signal then enters the first spectrometer 42, selectively entering either the first detection system 43 or the second detection system 44. The first detection system 43 selectively performs fluorescence intensity detection or angle-resolved spectral detection; the second detection system 44 selectively performs full-spectrum detection or ultrafast time-resolved detection of static cathodoluminescence.

[0081] In the third step described above, the fluorescence signal is selectively filtered and polarized in the cathodoluminescence analysis system 4 using a filtering and polarization device 41. Then, the fluorescence signal enters the first spectrometer 42, and selectively enters either the first detection system 43 or the second detection system 44. The first detection system 43 selectively guides the obtained fluorescence signal through the second spectrometer 43-1 to selectively perform fluorescence intensity detection or angle-resolved spectral detection. The second detection system 44 selectively guides the obtained fluorescence signal through the third spectrometer 44-2 to selectively perform full-spectrum detection or ultrafast time-resolved detection of static cathodoluminescence.

[0082] Through the above three steps, the fluorescence properties of the sample under steady-state conditions are obtained in continuous electron beam mode; and the time-resolved carrier dynamics and fluorescence lifetime information of the sample are obtained in pulsed electron beam mode.

[0083] The following examples will further illustrate the application methods of the multifunctional ultrafast cathodoluminescence system.

[0084] Example 3:

[0085] like Figure 7 The diagram illustrates the use of Figure 1 The fluorescence characteristics of diamond microcrystals were tested in continuous electron beam mode using the provided ultrafast cathodoluminescence system. Images a and d are scanning electron microscope images at room temperature and low temperature, images b and e are cathodoluminescence spectra at room temperature and low temperature, and images c and f are cathodoluminescence images at room temperature and low temperature.

[0086] The specific operation is described below:

[0087] Place the sample to be tested into the cryogenic sample stage 2-4. At low magnification, use the three-dimensional movement mechanism of the field emission scanning electron microscope system 2 to locate the sample. After determining the sample position, increase the magnification of the electron microscope to capture an image of the sample's morphology. Figure 7 As shown in a and d in the figure. Adjusting the three-dimensionally movable low-temperature sample stage 2-4 to the focal point of the parabolic mirror optimizes signal collection efficiency. At this point, the temperature of the low-temperature sample stage 2-4 is adjusted to the required testing temperature. By adjusting the first spectrometer 42 and the third spectrometer 44-2, the fluorescence signal can be dispersed and reach the CCD, obtaining a static cathodoluminescence spectrum, as shown in the figure. Figure 7 As shown in b and e in the diagram. With the same sample, if the signal is fed into photomultiplier tube 43-2, a high spatial resolution fluorescence intensity distribution map of the sample can be obtained, as shown in the diagram. Figure 7 As shown in c and f in the figure. The above test results demonstrate that diamond has an extremely strong single-photon emission peak at low temperatures, and also provide a direct correlation between the surface morphology of diamond microcrystals and fluorescence intensity.

[0088] Example 4:

[0089] Figure 8 Describes the use Figure 1 The provided ultrafast cathodoluminescence system was used to test the carrier dynamics of a bent zinc oxide microwire in pulsed electron beam mode. Figure a shows the result from a streak camera, b shows the time-integrated cathodoluminescence spectrum, c shows the time-resolved cathodoluminescence spectrum at different times, and d shows the intensity decay curves of excitons at different energies.

[0090] The specific operation is described below:

[0091] The sample to be tested is placed in the low-temperature sample stage 2-4. A continuous electron beam is used to locate the sample and determine its detection position. At this point, the field emission scanning electron microscope (SEM) system 2 is switched to pulsed electron beam mode. In pulsed electron beam mode, the position of the sample to be tested is determined, and the spot scan mode of the SEM system 2 is used to precisely locate the sample. The sample is selected as the inner side of the curved zinc oxide micrometer wire for excitation. The obtained fluorescence signal is then introduced into a streak camera to obtain an ultrafast fluorescence spectrum, such as... Figure 8 As shown in Figure a, the figure illustrates the decay of the fluorescence signal after spectral dispersion with time delay. Alternatively, by adjusting the corresponding reflector, the signal can be fed into a spectral detection camera to obtain the time-integrated fluorescence spectrum, as shown below. Figure 8 As shown in b in the figure. Image processing programs such as Matlab can be used to... Figure 8The original data in section 'a' is processed to obtain fluorescence spectra at different time delays and the dynamics of cathodoluminescence decay over time at different wavelengths. By taking a column of pixel values ​​at a certain time as the ordinate and wavelength as the abscissa, fluorescence spectra at different times can be obtained, such as... Figure 8 As shown in c in the figure. Similarly, by taking a row of pixel values ​​at a certain wavelength as the ordinate and the time axis as the abscissa, the decay curves of excitons at different energies can be obtained, as shown in the figure. Figure 8 As shown in d, the decay curves show that excitons of different energies have different decay processes, illustrating the transfer process between excitons of different energies.

[0092] The above embodiments are merely preferred embodiments of the present invention, and the scope of protection of the present invention is not limited to the above embodiments. All technical solutions falling within the scope of the present invention's concept are within the scope of protection of the present invention. It should be noted that for those skilled in the art, improvements and modifications made without departing from the principles of the present invention should also be considered within the scope of protection of the present invention.

Claims

1. A multifunctional ultrafast cathode fluorescence system, characterized in that: The system includes: A high-repetition-rate femtosecond laser system (1) includes a femtosecond laser (1-1), a second-order frequency doubling device (1-2), and a fourth-order frequency doubling device (1-3) for generating a high-repetition-rate near-infrared femtosecond laser. The femtosecond laser (1-1) generates a near-infrared femtosecond laser. After passing through the second-order frequency doubling device (1-2), the near-infrared femtosecond laser generates green light, and then passes through the fourth-order frequency doubling device (1-3) to generate an ultraviolet femtosecond laser. A field emission scanning electron microscope (2) system includes a first optical window (2-1), a field emission electron gun (2-2), an electromagnetic lens (2-3), a parabolic mirror (2-5), a low-temperature sample stage (2-4), and a second optical window (2-6), all disposed within a sealed cavity. The first optical window (2-1) is located on one side wall of the sealed cavity and directly opposite the photocathode tip of the field emission electron gun (2-2), allowing the ultraviolet femtosecond laser generated by the high repetition rate femtosecond laser system (1) to pass through the first optical window (2-1) and converge to the photocathode tip of the field emission electron gun (2-2). The field emission electron gun (2-2) excites the received ultraviolet femtosecond laser through the photocathode of the field emission electron gun (2-2) to form a... A continuous electron beam or pulsed electron beam of a certain intensity is further focused by the electromagnetic lens (2-3); the parabolic mirror (2-5) is provided with a through hole for the continuous electron beam or pulsed electron beam to pass through; the low-temperature sample stage (2-4) is used to place the sample to be tested and to allow the sample to be moved in three dimensions to the focal point of the parabolic mirror (2-5); the continuous electron beam or pulsed electron beam excites the sample to generate cathodoluminescence; the parabolic reflective surface of the parabolic mirror (2-5) reflects the cathodoluminescence generated by the sample excitation into parallel cathodoluminescence; the parallel cathodoluminescence is transmitted to the cathodoluminescence collection system (3) through the second optical window (2-6) provided on one side wall of the sealed cavity next to the low-temperature sample stage (2-4); A cathodoluminescence collection system (3) is used to collect the fluorescence signal of the cathodoluminescence generated by the sample; The cathodoluminescence analysis system (4) includes a selectively filtering polarization device (41) for selectively filtering and polarizing the fluorescence signal collected by the cathodoluminescence collection system (3); it also includes a first spectrometer (42), a first detection system (43), and a second detection system (44); wherein the first detection system (43) includes a second spectrometer (43-1), a photomultiplier tube (43-2), and an angle-resolved fluorescence detection camera (43-3), and the second spectrometer (43-1) is used to selectively guide the received fluorescence signal, guiding the fluorescence signal to selectively enter the photomultiplier tube (43-2) or the angle-resolved fluorescence detection camera (43-3); The second detection system (44) includes a spectrometer (44-1), a third spectrometer (44-2), a static cathodoluminescence detector (44-3), and a time-resolved detector (44-4). The spectrometer (44-1) divides the polychromatic fluorescence signal into spectral lines using a grating. The third spectrometer (44-2) is used to selectively guide the spectral signal, which selectively enters the static cathodoluminescence detector (44-3) or the time-resolved detector (44-4). The first spectrometer (42) is used to selectively guide the fluorescence signal, which selectively enters the first detection system (43) or the second detection system (44). The second detection system (44) is electrically connected to the high repetition rate femtosecond laser system (1) and is synchronously excited and synchronously detected through the repetition rate electrical signal; A spatial optical path system is used to guide the optical signal to be converted and selectively transmitted between the high repetition rate femtosecond laser system (1), the field emission scanning electron microscope system (2), the cathodoluminescence collection system (3), and the cathodoluminescence analysis system (4).

2. The multifunctional ultrafast cathode fluorescence system according to claim 1, characterized in that: The first optical window (2-1) is made of leaded glass with high transmittance in the visible to ultraviolet bands.

3. The multifunctional ultrafast cathode fluorescence system according to claim 2, characterized in that: The temperature control range of the low-temperature sample stage (2-4) is 10 to 300 K.

4. The multifunctional ultrafast cathodoluminescence system according to claim 1, characterized in that: The static cathodoluminescence detection device (44-3) is a spectral detection camera; the time-resolved detection device (44-4) includes a stripe camera or a time-correlated single-photon detector.

5. The multifunctional ultrafast cathode fluorescence system according to claim 1, characterized in that: It includes three air-bearing devices: a first optical platform (5), a scanning electron microscope air-bearing platform (6), and a second optical platform (7). The first optical platform (5) is used to support the high repetition rate femtosecond laser system (1) and reduce vibration; the scanning electron microscope air-bearing platform (6) is used to support the field emission scanning electron microscope system (2) and reduce vibration. The second optical platform (7) is used to support the cathodoluminescence collection system (3) and the cathodoluminescence analysis system (4) and to reduce vibration. The first optical platform (5) and the second optical platform (7) are respectively rigidly connected to the scanning electron microscope air flotation platform (6) to achieve synchronous air flotation connection.

6. The multifunctional ultrafast cathode fluorescence system according to any one of claims 1 to 5, characterized in that: The photocathode of the field emission scanning electron microscope system (2) is a tungsten filament with Schottky field emission and its surface is coated with zirconium oxide.

7. The application method of the multifunctional ultrafast cathodoluminescence system according to claim 1, comprising the following steps: The first step is to place the sample to be tested in the field emission scanning electron microscope system (1), adjust the focus to align with the sample to be tested, and adjust the emission mode of the field emission electron gun (2-2) of the field emission scanning electron microscope system (2) to continuous electron beam mode or pulsed electron beam mode. The second step is to turn on the high repetition rate femtosecond laser system (1). The high repetition rate femtosecond laser system (1) outputs ultraviolet femtosecond laser, which is guided by the spatial optical path system and converges from the side of the field emission electron gun (2-2) to the tip of the field emission photocathode, thereby exciting and generating an ultrafast photoelectron beam. The ultrafast photoelectron beam excites the sample to generate cathodoluminescence, and the fluorescence signal is collected by the cathodoluminescence collection system (3). Then the fluorescence signal enters the cathodoluminescence analysis system (4). The third step involves selectively filtering and polarizing the fluorescence signal using a filtering and polarization device (41); then the fluorescence signal enters the first spectrometer (42), and selectively enters the first detection system (43) or the second detection system (44); the first detection system (43) selectively performs fluorescence intensity detection or angle-resolved spectral detection; the second detection system (44) selectively performs full-spectrum detection or ultrafast time-resolved detection of static cathodoluminescence. Through the above steps, the fluorescence properties of the sample under steady-state conditions are obtained in continuous electron beam mode; and the time-resolved carrier dynamics and fluorescence lifetime information of the sample are obtained in pulsed electron beam mode.

Images