An ultra-high spatiotemporal resolution imaging method and imaging system based on a carbon nanotube electron source

Abstract

The application discloses a kind of ultra-high space-time resolution imaging method and imaging system based on carbon nanotube electron source, it is related to ultrafast optics and atomic level imaging technical field.Carbon nanotube is assembled to tungsten needle tip tip end to construct carbon nanotube electron source;Design ultrafast pulsed laser pumping-detection system, pumping light will sample from ground state to excited state, probe light is formed on carbon nanotube electron source to form ultrafast photoelectron pulse, and two beams of light keep certain optical path difference;Electron pulse is projected to screen by point projection imaging system to project the ultrafast transient information of sample.The application can effectively avoid the broadening caused by vacuum dispersion effect and space charge effect when carrying out high spatial resolution imaging, to a certain extent, retain the narrow pulse width characteristics of electron source induced by ultrafast laser when emitting and the characteristics of extremely high spatial coherence of carbon nanotube electron source.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of ultrafast optics and atomic-scale imaging technology, and more particularly to an ultra-high spatiotemporal resolution imaging method and imaging system based on a carbon nanotube electron source. BACKGROUND

[0002] With the rapid development of nanotechnology, chip technology, new materials and biomedicine, the academic and industrial communities have an increasing demand for understanding the underlying physical and chemical phenomena at the microscopic scale. This requires microscopic imaging technology to provide higher spatial and temporal resolution to reveal the ultrafast processes and mechanisms of micro-nano materials and biomolecules. Traditional optical microscopes are limited by the diffraction limit, and the limit of spatial resolution can only approach half of the wavelength of light. In order to break this limit, various super-resolution microscopic techniques have been further developed and studied, such as stimulated emission depletion (STED), stochastic optical reconstruction microscopy (STORM), photoactivated localization microscopy (PALM), structured illumination microscopy (SIM), etc. These techniques achieve imaging beyond the diffraction limit through different physical mechanisms. However, due to the limitations of optical imaging principles, the spatial resolution of these super-resolution microscopic techniques is mostly limited to tens of nanometers, and the applicable systems are mainly biological samples, so they are powerless for real-space imaging of conventional materials at the molecular and atomic level. Compared with imaging using visible light, electrons have a much smaller de Broglie wavelength than light, and in theory can achieve atomic or even subatomic scale microscopic observation. Various electron microscopes have proven the feasibility of ultra-high spatial resolution in practice. With the continuous iteration of electron microscopes, atomic imaging observation is no longer a problem for the industry.

[0003] At atomic and molecular scales, almost all movements and changes are transient. In order to explore scientific phenomena and laws at such extremely small space-time scales, ultra-high space-time resolution microscopic imaging technology emerges as the times require. It combines spatial high-resolution microscopic imaging technology and femtosecond laser ultrafast time-resolved detection technology. The most representative ultra-high space-time resolution microscopic imaging technology is ultrafast scanning / transmission electron microscope. The existing ultrafast electron microscope generally integrates a femtosecond laser as the main pump-probe system and a supporting optical system on the basis of a mature commercial electron microscope, and the electron source is mainly single-crystal tungsten and LaB6. In theory, the ultrafast electron microscope can simultaneously realize nanoscale resolution and femtosecond-level relaxation time process observation, but due to the complex multi-level structure of the commercial electron microscope, it is difficult to ensure the time synchronization between the electron beam pulse and the ultrafast laser pulse, which undoubtedly further increases the complexity and maintenance difficulty of the system. The time resolution capability of the ultrafast electron microscope depends on the pulse width of the electron beam. The narrower the pulse width, the stronger the time resolution capability. Due to the long electron optical column structure of the electron microscope, even the initial femtosecond-level electron pulse width will be broadened in the vacuum with the increase of the propagation distance, and it is difficult to realize the detection of the real short femtosecond time scale process. At the same time, the ultrafast electron microscope usually uses a high-energy electron beam for imaging. When continuous imaging is performed under the requirement of ultra-high time resolution, some sensitive samples may be damaged.

[0004] Therefore, how to propose a new type of ultra-high space-time resolution imaging method and imaging system, which can effectively avoid the broadening caused by the vacuum dispersion effect and the space charge effect when high spatial resolution imaging is performed, to a certain extent, retain the narrow pulse width characteristics of the electron source when it is induced to exit by the ultrafast laser, and realize higher spatial and temporal resolution is a problem that those skilled in the art need to solve. SUMMARY

[0005] In view of this, the application provides an ultra-high space-time resolution imaging method and imaging system based on a carbon nanotube electron source, aiming at the short board of the existing ultrafast electron microscope in ultra-high space-time resolution imaging, a new type of carbon nanotube electron source and point projection microscopic imaging technology are developed to develop an ultra-high space-time resolution microscope and carry out preliminary verification. Compared with traditional materials, carbon nanotubes have smaller tip curvature radius and energy dispersion, and through the holographic imaging of the high-coherent electron beam generated thereby, higher spatial resolution can be achieved, and the technology has more potential in realizing dynamic observation at the atomic resolution in the future. The point projection microscopic imaging technology has a simple structure, and the entire device usually mainly includes three parts: a point electron source (carbon nanotube), a sample to be observed, and a fluorescent screen. When high spatial resolution imaging is performed, the distance between the point electron source and the sample to be observed needs to be kept at the order of tens of nanometers, and due to the natural ultra-close distance advantage, the electron beam propagates a short distance, which can effectively avoid the broadening caused by the vacuum dispersion effect and the space charge effect, and to a certain extent, the narrow pulse width characteristics of the electron source induced by the ultrafast laser are retained. Since the carbon nanotube as the electron source has a narrower pulse width than traditional materials, the technical solution has unique advantages in spatial and temporal resolution.

[0006] In order to achieve the above-mentioned purpose, the application adopts the following technical scheme: an ultra-high space-time resolution imaging method based on a carbon nanotube electron source, comprising:

[0007] The carbon nanotube is adsorbed on the tungsten needle tip to form a carbon tube electron source;

[0008] The laser beam is divided into two beams, the optical path difference of the two beams is adjusted through a delay module, and the two beams respectively reach the respective excitation medium at different times;

[0009] After the adjusted two beams are combined, they are again divided into two beams; after the division, one beam is a pump light, and the other beam is a probe light; the pump light serves as an energy source for exciting the sample to undergo an ultrafast dynamic process, and the probe light serves as an energy source for emitting electrons from the carbon tube electron source;

[0010] According to the optical path difference, the pump light acts on the sample from the ground state to the excited state, and after a certain time interval, the probe light excites the carbon nanotube to form an electron pulse, and after the electron pulse interacts with the sample in the excited state, sample imaging information is obtained.

[0011] Preferably, the carbon nanotube is adsorbed on the tungsten needle tip, comprising:

[0012] After the tip of the tungsten wire is etched, it is installed in the slot of the heating structure as a cathode, and the vertically arranged and densely packed carbon nanotube film on the silicon wafer is adhered to the anode plate with conductive adhesive, and is installed in the matching vacuum cavity for vacuum treatment;

[0013] The upright carbon nanotube is attracted to the top of the tungsten needle tip from the silicon wafer by the combined action of the thermal induced force and the electric field force.

[0014] The upright carbon nanotube is attracted to the top of the tungsten needle tip from the silicon wafer by the combined action of the thermal induced force and the electric field force.

[0015] The pressure difference is applied to one side of the tungsten needle tip and one side of the carbon nanotube film, and the tungsten needle tip is heated by a heating structure;

[0016] The distance between the carbon nanotube film and the heated tungsten needle tip is shortened by adjusting the differential head until they just contact, and the differential head is withdrawn after a period of time, completing the adsorption process.

[0017] Preferably, the delay module includes a delay mirror and a delay line displacement table;

[0018] When the delay mirror is located at the middle stroke of the delay line displacement table, the optical path difference of the two beams of light is zero;

[0019] When the delay mirror is located at the front limit of the delay line displacement table, the maximum positive optical path difference of the two beams of light is reached;

[0020] When the delay mirror is located at the rear limit of the delay line displacement table, the maximum negative optical path difference of the two beams of light is reached.

[0021] Preferably, a point projection imaging microscope is constructed according to the carbon nanotube electron source, the sample and the fluorescent screen;

[0022] The distance between the carbon nanotube electron source and the sample is d, and the distance between the carbon nanotube electron source and the fluorescent screen is D;

[0023] The magnification of the sample imaged by the point projection microscope is M=D / d;

[0024] As d decreases, the distance between the carbon nanotube electron source and the sample gradually approaches, and the magnification changes from low to high.

[0025] Preferably, by adjusting the delay difference of the pump light and the probe light reaching the sample, the intrinsic signal of the required imaging sample is compared with the signal after pumping, and the change process of the sample is obtained.

[0026] Preferably, it also includes: using a 50 times long focus microscope lens to focus the pump light, so that the center of the focal spot is focused on the carbon nanotube;

[0027] The probe light is focused by a convex lens, so that the diameter of the light spot focused on the sample is smaller than the substrate size.

[0028] Preferably, an ultrahigh space-time resolution imaging system based on a carbon nanotube electron source includes:

[0029] An adsorption device is used for adsorbing carbon nanotubes on a tungsten needle tip to construct a carbon tube electron source;

[0030] A laser is used for emitting a laser beam;

[0031] A first beam splitter is used for splitting the laser beam into two beams;

[0032] A time delay module is used for adjusting an optical path difference of the two beams;

[0033] A second beam splitter is used for combining the two beams after adjustment;

[0034] A third beam splitter is used for splitting the combined laser beam again, and one of the split beams is a pump beam and the other is a probe beam; the pump beam is used as an energy source for exciting a sample to generate an ultrafast dynamic process, and the probe beam is used as an energy source for emitting electrons from the carbon tube electron source;

[0035] A point projection microscope is used for obtaining dynamic imaging information of the sample according to the optical path difference; the pump beam excites the sample from a ground state to an excited state; after a certain time interval, the probe beam excites the carbon nanotube to form an electron pulse; and after the electron pulse interacts with the sample in the excited state, the imaging information of the sample can be obtained.

[0036] Compared with the prior art, the technical scheme has the following beneficial effects:

[0037] 1. Compared with the prior art, the scheme of the present application has a simple structure, no definite limitation on suitable material systems, low cost of components, and is more conducive to popularization and dissemination; 2. The present application has achieved an ultra-high spatial resolution which is not inferior to the prior art, and has multiple imaging modes, which can be used for real-space characterization of the sample by contrast imaging and holographic imaging at low and high magnifications, respectively. On this basis, the present application uses carbon nanotubes as an ultrafast electron source, which has a more excellent virtual source radius, energy dispersion, current density, and lower working temperature requirement than the conventional materials commonly used in the prior art, and can achieve further breakthrough in spatial resolution. 3. The special structure design of the point projection imaging microscope of the present application realizes an adjustable spatial distance between the ultrafast electron source and the sample to be imaged from far to near. The distance between the electron source and the sample is farther at low magnification, and the distance between the electron source and the sample is closer at higher magnification. When the distance between the electron source and the sample is tens of nanometers or even a few nanometers, the highest spatial resolution can be achieved. At the same time, through the three-dimensional controller, not only the imaging of each region of the sample can be achieved, but also the high displacement accuracy (the displacement resolution of the piezoelectric ceramic is in the nanometer level) is ensured. Therefore, on the basis of the precise adjustment of the imaging magnification of the sample, the distance between the electron source and the sample in the high magnification mode is extremely close. The distance between the ultrafast electron source and the sample in the prior art is much larger than that in the present application (basically more than cm), and the difference is as much as 7 orders of magnitude. The ultrafast electron source excited by the ultrafast laser in the prior art has an ultra-high time resolution at the initial time (usually in the fs level), but due to the long-distance propagation in the vacuum, it is inevitably affected by the vacuum dispersion effect and the space charge effect, and the original ultra-high time resolution is destroyed. Compared with the prior art, the present application uses this special structure design to cleverly avoid this problem, so that the ultra-high time resolution at the excitation time is preserved. Therefore, the present application uses carbon nanotubes as an ultrafast electron source for the first time, and achieves an ultra-high spatial resolution which is not inferior to the conventional materials, successfully verifies the imaging ability of the carbon nanotube ultrafast electron pulse, and builds a pump-probe system based on femtosecond laser which is matched with the point projection microscope, providing valuable experience and technical reference for developing a new type of point projection microscope with ultra-high time and space resolution. BRIEF DESCRIPTION OF DRAWINGS

[0038] In order to make the technical solutions in the embodiments of the present application or the prior art clearer, the accompanying drawings needed in the embodiments or prior art description will be briefly introduced. Obviously, the accompanying drawings in the following description only aim at the embodiments of the present application, and for those skilled in the art, other drawings can be obtained without creative effort based on the provided drawings.

[0039] Figure 1 The schematic structural diagram of the adsorption device of carbon nanotubes provided by the embodiment of the present application.

[0040] Figure 2 The schematic diagram of the optical path of the pump-probe system and the linkage scheme of the pump-probe system and the point projection microscope provided by the embodiment of the present application.

[0041] Fig. 3(a) is a schematic diagram of the carbon tube adsorbed for the first time at the tip position of the tungsten needle tip of the adsorption device independently built by the embodiment of the present application.

[0042] Fig. 3(b) is a schematic diagram of the single carbon tube protruding at the forefront of the carbon tube cluster adsorbed for the first time by the embodiment of the present application.

[0043] Fig. 3(c) is a schematic diagram of the carbon tube adsorbed for the second time at the tip position of the tungsten needle tip of the adsorption device independently built by the embodiment of the present application.

[0044] Fig. 3(d) is a schematic diagram of the single carbon tube protruding at the forefront of the carbon tube cluster adsorbed for the first time by the embodiment of the present application.

[0045] Fig. 4(a) is a schematic diagram of the outline of the carbon tube sample observed by the superfast electron source in the point projection microscope of the embodiment of the present application through the carbon tube sample.

[0046] Fig. 4(b) is a schematic diagram of the interference fringe distribution obtained when the magnification of the outline of the carbon tube sample is close to the limit by the embodiment of the present application.

[0047] Figure 5 The schematic diagram of the intensity distribution curve of the interference fringes presented by the carbon tube sample provided by the embodiment of the present application.

[0048] Wherein, 1-heating electrode, 2-heating filament, 3-tungsten needle tip, 4-silicon wafer, 5-anode plate, 6-current meter, 7-differential head, 8-objective lens, 9-convex lens, 10-1-first mirror, 10-2-second mirror, 10-3-third mirror, 10-4-fourth mirror, 10-5-fifth mirror, 11-sample to be observed, 12-fluorescent screen, 13-vacuum cavity, 14-laser, 15-frequency doubling crystal, 16-diaphragm, 17-1-first light splitter, 17-2-second light splitter, 17-3-third light splitter, 18-1-first half-wave plate, 18-2-second half-wave plate, 19-delay module, 20-carbon tube electron source. DETAILED DESCRIPTION

[0049] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative work fall within the scope of protection of the present application.

[0050] In the fields of physics, chemistry, material science and life science, the research on ultrafast time-resolved imaging technology at the level of single molecule and single atom is becoming a hot spot. In order to deeply explore electromagnetic dynamic phenomena of the microcosmic world at the spatial scale of atomic level and the time scale of femtosecond level, it is urgent to develop advanced probe technology with corresponding space-time resolution. Although the existing technology has made certain achievements in the field of ultrafast electron source, its limitations in spatial and temporal resolution have gradually appeared, and it is difficult to meet the accurate detection needs of molecular and even atomic scale dynamic process. The embodiments of the present application realize atomic level spatial resolution by adopting point projection imaging technology, and successfully verify the imaging ability of carbon nanotube ultrafast electron pulse by combining the self-built pump-probe system. This innovation provides valuable experience and technical reference for the development of new point projection microscope with ultra-high space-time resolution in the future.

[0051] The embodiments of the present application disclose an ultra-high space-time resolution imaging method based on a carbon nanotube electron source, comprising:

[0052] The carbon nanotube is adsorbed on the tungsten needle tip to form a carbon tube electron source;

[0053] The laser beam is divided into two beams, and the optical path difference of the two beams is adjusted by the delay module, so that the two beams respectively reach the respective excitation medium at different times;

[0054] The two beams of light after adjustment are combined, and then split again; after splitting, one beam of light is the pump light, and the other beam of light is the probe light; the pump light serves as an energy source for exciting the sample to undergo ultrafast dynamic processes, and the probe light serves as an energy source for the carbon nanotube electron source to emit electrons;

[0055] According to the optical path difference, the pump light acts on the sample from the ground state to the excited state, and after a certain time interval, the probe light excites the carbon nanotube to form an electron pulse, which interacts with the sample in the excited state to obtain sample imaging information. The sample imaging information is the excited state information of the sample which has not completely relaxed.

[0056] The present application is based on the fact that the energy dispersion of traditional materials as ultrafast electron sources is relatively large, and replacing them with carbon nanotubes can achieve smaller energy dispersion. Smaller energy dispersion not only makes the dispersion effect of the electron beam smaller during propagation, but also optimizes the problem of excessive electron beam divergence angle caused by the mutual repulsion between electrons (space charge effect), thereby helping to achieve higher time and spatial resolution.

[0057] Specifically, the carbon nanotubes are adsorbed on the tip of the tungsten needle, including:

[0058] After etching the tip of the tungsten wire, it is installed in the slot of the heating structure as the cathode, and the vertical and densely packed carbon nanotube film on the silicon wafer is adhered to the anode plate with conductive adhesive, and is installed in the matching vacuum chamber for vacuum treatment.

[0059] The vertical carbon nanotubes are attracted from the silicon wafer to the top of the tungsten needle tip by the combined action of thermal induction force and electric field force.

[0060] The present application uses carbon nanotubes as electron sources, which have nanoscale or even sub-nanoscale tip sizes, can provide small beam spot electron beams, and improve the spatial resolution of imaging, helping the scientific research and industrial communities to observe the microstructure in material science, biomedical science, and semiconductor devices with extremely high precision. Carbon nanotubes as electron sources have extremely high field enhancement factors, which means they can emit electrons at relatively low laser power, significantly improving electron emission efficiency and reducing power consumption compared to traditional materials.

[0061] Specifically, the tip of the tungsten wire is etched to several hundred nanometers by direct current etching method, and then installed in the slot of the heating filament; the vertical and densely packed carbon nanotube film grown on the silicon wafer by plasma enhanced chemical vapor deposition (PECVD) is adhered to the anode plate with conductive adhesive; the device is installed in the matching vacuum chamber, and the mechanical pump and molecular pump are respectively pumped for 10 minutes to ensure that the vacuum degree is below 1*10 -3 Pa level.

[0062] Specifically, the upright carbon nanotube is attracted from the silicon wafer to the top of the tungsten needle tip by the combined action of the thermal induction force and the electric field force, including:

[0063] A pressure difference is applied to one side of the tungsten needle tip and one side of the carbon nanotube film, and the tungsten needle tip is heated by a heating structure;

[0064] The distance between the carbon nanotube film and the heated tungsten needle tip is shortened by adjusting the differential head until they just contact, and the differential head is withdrawn after a period of time, and the adsorption process is completed.

[0065] Specifically, a pressure difference of 20V is applied to one side of the tungsten needle tip (cathode) and one side of the carbon nanotube film (anode); then the voltage of the filament is gradually increased to make the tungsten needle tip slightly red (about 2V), and then the distance between the carbon nanotube film and the heated tungsten needle tip is gradually reduced by coarse and fine adjustment of the differential head until they just contact (the current meter reading increases sharply), and the upright carbon nanotube is attracted from the silicon wafer to the top of the tungsten needle tip by the combined action of the thermal induction force and the electric field force, and the differential head is withdrawn after 10s, and the adsorption process is completed.

[0066] Although the traditional material can be processed to a nanoscale curvature radius, compared with the sub-nanometer diameter one-dimensional material of the carbon nanotube, the field enhancement factor has a natural disadvantage, so that the carbon nanotube as an ultrafast electron source can realize a smaller electron beam spot, thereby improving the detail and clarity of imaging.

[0067] In one specific embodiment of the present application, one of the key materials of the present application is carbon nanotubes, and such carbon nanotubes need to ensure that they are stably present at the tip of the substrate and do not affect their excellent physical and chemical properties and high mechanical strength.

[0068] Specifically, the delay module includes a delay mirror and a delay line displacement table;

[0069] When the delay mirror is located at the middle stroke of the delay line displacement table, the optical path difference of the two beams is zero;

[0070] When the delay mirror is located at the front limit of the delay line displacement table, the maximum positive optical path difference of the two beams is reached;

[0071] When the delay mirror is located at the rear limit of the delay line displacement table, the maximum negative optical path difference of the two beams is reached.

[0072] Specifically, (1) the femtosecond laser outputs 800 nm of femtosecond laser, after the frequency doubling crystal, a part of the light is doubled to 400 nm, and a part remains 800 nm; (2) after the first light splitting piece, since the first light splitting piece transmits most of the 800 nm ultrafast light and reflects most of the 400 nm ultrafast light, better light splitting can be achieved; (3) after light splitting, low-pass / high-pass filters and half-wave plates need to be added to the light paths of the two lasers respectively, the former is to filter out the other laser (such as filtering out the 800 nm laser on the light path of the 400 nm light reflected by the light splitting piece), and the latter is to adjust the polarization direction for subsequent testing; (4) a delay module is added to the light path of 800 nm after light splitting, which basically ensures that the center position of the delay displacement table is equivalent to the optical path difference of the other light reaching the sample, so that the order of 800 nm ultrafast light and 400 nm ultrafast light reaching the sample position can be adjusted in a larger range; (5) subsequent beam combining and beam splitting, the purpose of beam combining is to ensure that the subsequent light path is basically the same (without additional optical path difference), and the purpose of beam splitting is to let 400 nm as pump light induce the sample from the ground state to the excited state, and 800 nm as probe light reaches after a femtosecond level time interval, and the excited state information of the sample which has not completely relaxed is observed under the benchmark of ultra-high spatial resolution and time resolution.

[0073] Specifically, a point projection imaging microscope is constructed according to a carbon nanotube electron source, a sample and a fluorescent screen.

[0074] The distance between the carbon nanotube electron source and the sample is d, and the distance between the carbon nanotube electron source and the fluorescent screen is D.

[0075] The magnification of the sample imaged by the point projection microscope is M=D / d.

[0076] As d decreases, the distance between the carbon nanotube electron source and the sample gradually approaches, and the magnification changes from low magnification to high magnification.

[0077] In the embodiment of the application, the carbon nanotube can emit femtosecond or even attosecond electron pulses under the excitation of femtosecond laser, and in combination with the structural characteristics of the point projection microscope, the electron pulse will not be significantly broadened when imaging the sample, which is extremely beneficial to the capture of ultrafast dynamic processes. Such ultra-high time resolution is particularly important for studying transient physical processes, chemical reactions and biological molecular motion. The carbon nanotube itself has strong chemical stability and mechanical strength, and can work for a long time as an electron source without loss or degradation, ensuring that the point projection microscope can operate stably and reliably in high-precision application scenarios for a long time, while the power consumption requirement of the device is low, the overall service life is long, the demand for frequent maintenance and replacement is reduced, and the operating cost is reduced.

[0078] Specifically, by adjusting the time delay difference of the pump light and the probe light reaching the sample, the intrinsic signal of the required imaging sample is compared with the signal after pumping to obtain the change process of the sample.

[0079] Specifically, it further comprises: focusing the pump light using a 50 times long-focus microscope lens, so that the center of the focal spot is focused on the carbon nanotube;

[0080] The probe light is focused using a convex lens, so that the spot diameter focused on the sample is smaller than the substrate size.

[0081] In summary, the embodiment of the present application discloses a method for constructing a carbon nanotube electron source, which assembles carbon nanotubes to the tip of a tungsten needle; an ultrafast pulsed laser pumping-probing system is designed, in which the pump light acts on the sample from the ground state to the excited state, the probe light acts on the carbon nanotube electron source to form an ultrafast photoelectron pulse, and the two beams of light maintain a certain optical path difference; the electron pulse projects the ultrafast transient information of the sample to the screen through a point projection imaging system. When performing high spatial resolution imaging, the flight distance of the electron from the electron source to the needle tip is only tens of nanometers, which can effectively avoid the broadening caused by the vacuum dispersion effect and the space charge effect, to a certain extent, the narrow pulse width characteristics of the electron source when it is induced to emit by the ultrafast laser and the extremely high spatial coherence characteristics of the carbon nanotube electron source are retained, and the spatial resolution can reach the single atom scale and the time resolution can reach below 100 fs.

[0082] The existing ultrafast electron microscope has a complex structure, and the total propagation distance of the electron beam in the electron gun, the lens barrel, the pole piece, the chamber and other components is relatively long. Originally, the narrow pulse when it is emitted is continuously broadened by the vacuum dispersion effect and the space charge effect during propagation, which causes the electron pulse to be broadened greatly when it reaches the sample, which is not conducive to realizing ultra-high time resolution. Compared with the existing ultrafast electron microscope, the ultrafast point projection microscope of the embodiment of the present application has a simple structure, which not only saves costs by omitting many redundant structures, but also can ensure that the electron beam only needs to propagate for tens of nanometers after being emitted to interact with the sample, which is more conducive to realizing ultra-high time resolution.

[0083] In one specific embodiment of the present application, an ultra-high time-space resolution imaging system based on a carbon nanotube electron source comprises:

[0084] The adsorption device is used for adsorbing the carbon nanotube on the tungsten needle tip (3) to construct a carbon nanotube electron source.

[0085] The laser (14) is used for emitting a laser beam.

[0086] The first light splitting plate (17-1) is used for splitting the laser beam into two beams.

[0087] a time delay module (19) for adjusting the optical path of one of the two beams of light to change the optical path difference between the two beams of light;

[0088] a second beam splitter (17-2) for combining the two beams of light after adjustment;

[0089] a third beam splitter (17-3) for splitting the combined laser light again, after which one beam of light is a pump light and the other beam of light is a probe light; the pump light serves as an energy source for exciting the sample to undergo ultrafast dynamics, and the probe light serves as an energy source for the carbon nanotube electron source to emit electrons;

[0090] a point projection microscope for obtaining dynamic imaging information of the sample according to the optical path difference; the pump light excites the sample from a ground state to an excited state, and after a certain time interval, the probe light excites the carbon nanotube to form an electron pulse, and the sample imaging information can be obtained after the electron pulse interacts with the sample in the excited state.

[0091] The purpose of adjusting the optical path difference between the two beams of light by the time delay module is to make the two beams of light reach the respective excitation medium at different times, one of which reaches the carbon nanotube electron source to excite electrons, and the electrons reach the sample (i.e., the position where the second beam of light acts). If the sample is not acted on by the second beam of light, the static signal of the sample is observed. If the sample is acted on by the second beam of light, the dynamic signal of the sample after excitation is observed. According to the time difference between the arrival of the second beam of light at the sample and the first beam of light, the dynamic signal presented will be different. For example, some physical processes are femtosecond-level, and some physical processes are picosecond-level, which can be observed by the embodiment of the present application.

[0092] Specifically, the structure of the adsorption device is as shown in Figure 1 The adsorption device comprises a heating electrode (1), a heating filament (2), a tungsten needle tip (3), a silicon wafer (4), an anode plate (5), an ammeter (6), and a differential head (7).

[0093] The heating electrode (1) is used to heat the heating filament (2).

[0094] The tungsten needle tip (3) has a pointed end facing outward and is installed on a slot of the heating filament (2).

[0095] One side of the silicon wafer (4) carries a carbon nanotube film with upright growth and close-packed distribution; the carbon nanotube film is composed of carbon nanotubes.

[0096] The other side of the silicon wafer (4) is adhered to the anode plate (5) by conductive adhesive.

[0097] The differential head (7) is used to adjust the position of the carbon nanotube film on the silicon wafer (4).

[0098] The ammeter (6) measures the current change when the tungsten needle tip (3) contacts the carbon nanotube film (4) on the silicon wafer;

[0099] Specifically, in order to realize carbon nanotubes as high-performance ultrafast electron sources, the embodiment of the present application mainly realizes the adsorption operation of carbon nanotubes (hereinafter referred to as carbon tubes) on the tungsten needle tip (3) through the following method, and completes the production of the electron source.

[0100] Step one, first prepare a carbon nanotube film of appropriate thickness grown by plasma enhanced chemical vapor deposition (PECVD), and adhere the heavily doped silicon wafer (4) carrying the carbon nanotube film to the conductive substrate through conductive adhesive. This conductive substrate is called an anode plate (5). One side of the anode plate (5) is connected to a micro differential head (7) that can adjust the transverse position of the carbon nanotube film. The initial position is where the micro differential head (7) has the maximum value.

[0101] Step two, then use the method of electrochemical etching to reduce the tip of a 0.5mm thick tungsten wire to a curvature radius of hundreds of nanometers, obtaining a tungsten needle tip (3). After etching, clean the tungsten needle tip (3) in the order of ethanol-water-ethanol to ensure that the surface is free of alkaline solution and contamination residues.

[0102] Step three, build a vacuum chamber (13) for adsorbing carbon nanotubes and a matching vacuum system. Then build a structure for heating the tungsten needle tip (3) in the vacuum chamber (13), place it at both ends of the electrode, and reserve a slot at the top of the heating structure to facilitate heating the tungsten needle tip (3) through heat conduction. After the heating structure is built, insert the tungsten needle tip into the slot. This side is called the cathode as a whole. At this time, the tip of the tungsten needle tip is within a few cm of the surface of the above-mentioned carbon nanotube film that has been installed.

[0103] Step four, seal the vacuum chamber (13). After sealing, use a mechanical pump and a molecular pump to extract a vacuum for 10 minutes respectively to ensure that the chamber vacuum is below 1*10 -3 Pa level.

[0104] Step five, install the current and voltage source for heating the tungsten needle tip (3) and providing a pressure difference for the cathode and anode during the gap time of vacuum extraction, and connect the high-precision ammeter (6) for testing.

[0105] Step six, wait for the chamber vacuum to reach 1*10 -3 Pa level, apply a 20V pressure difference to the cathode and anode, then slowly increase the current at both ends of the constant current source for heating the tungsten needle tip (3) until the reading reaches 10A2V. At this time, the temperature of the tungsten needle tip reaches above 1000K.

[0106] Step seven, rotate the micro differential head (7) so that the carbon nanotube film gradually approaches the heated tungsten needle tip (3), when the distance is far, the micro differential head (7) rotates a large amplitude, when the distance is close, the rotating amplitude is reduced, at this time, the observation of the ammeter, continue to slowly rotate the micro differential head (7) until the ammeter (6) appears mutation and stop rotating.

[0107] Step eight, stop rotating and maintain for 10s, through the combined action of thermal induction force and electric field force, a small amount of carbon nanotube on the carbon nanotube film is transferred to the tungsten needle tip (3), then slowly reverse rotate the micro differential head (7), move the carbon nanotube film to the rightmost side, complete the adsorption process, and facilitate the next adsorption.

[0108] Step nine, observe the morphology of the adsorbed carbon nanotube on the tungsten needle tip (3) by a scanning electron microscope (SEM), ensure that the tungsten needle tip has a certain number of carbon nanotubes, and successfully make a carbon nanotube ultrafast electron source.

[0109] Figures 3(a)-3(d) The carbon nanotube is adsorbed at the tip position of the tungsten needle tip by the self-built adsorption device, and the sufficient number of carbon nanotubes is combined with the tungsten needle tip through the combined action of the thermal induction force and the electric field force, and the whole is oriented along the tip of the tungsten needle tip. Fig. 3(a) and Fig. 3(c) are the results of two adsorptions, respectively, and the combination of the carbon nanotube and the tungsten needle tip has more carbon nanotubes, and the combination mode is mainly bonding (the carbon nanotube is relatively firm on the metal needle tip, and does not fall off when being irradiated by a high-energy electron beam for a long time and characterization), which ensures the stability of the carbon nanotube on the tungsten needle tip. As can be seen from Fig. 3(b) and Fig. 3(d), the front end of the carbon nanotube cluster has a relatively prominent single carbon nanotube, and the diameter is less than 30nm and 20nm, respectively. The curvature radius of the tip of the single carbon nanotube is often smaller than the radius of the tube body, and is much smaller than the curvature radius of the traditional material as the electron source (usually in the order of hundreds of nanometers). Therefore, the adsorption method of the embodiment of the present application realizes that the front side of the electron source space position is an independent single carbon nanotube on the basis of ensuring that the carbon nanotube and the tungsten needle tip have sufficient combination capacity, ensures the uniqueness of the electron source emission site, and the curvature radius is in the order of tens of nanometers, which can realize the ultra-high spatial resolution superior to the traditional electron source.

[0110] The self-developed adsorption device of the embodiment of the present application not only ensures the stability of the carbon nanotube attached to the metal needle tip, but also makes the wall of the carbon nanotube face basically horizontal to the metal needle tip. On this basis, the most tip position does not appear multiple carbon nanotubes, but an independent single carbon nanotube with obvious position advantage, which undoubtedly provides favorable conditions for the carbon nanotube as an independent emission electron source.

[0111] The carbon tube adsorption device has simple structure, clear principle, low cost of each component development, and is convenient to popularize. The success rate of single adsorption is above 80%, the time cost is less except the time cost of vacuumizing, and the efficiency of adsorbing carbon tube is high.

[0112] In one specific embodiment of the present application, it can also be changed from single station to multi-station mode to adsorb carbon tubes on multiple tungsten needle tips at a time, further improving the sample preparation efficiency.

[0113] In one specific embodiment of the present application, another key device of the embodiment of the present application is a point projection imaging microscope and a matching optical path system. The point projection microscope is designed according to its principle based on the experience of building a vacuum system. In order to verify that the carbon tube as an ultrafast electron source can realize ultra-high space-time resolution in the point projection microscope, a pump-probe optical path system is designed and built, and the linkage scheme of the pump-probe optical path system and the point projection microscope is as shown in Figure 2 .

[0114] Specifically, the pump-probe optical path system includes a laser (14), a frequency doubling crystal (15), an aperture (16), a first beam splitter (17-1), a second beam splitter (17-2), a third beam splitter (17-3), a first half-wave plate (18-1), a second half-wave plate (18-2), a delay module (19), an objective lens (8), a convex lens (9), a first mirror (10-1), a second mirror (10-2), a third mirror (10-3), a fourth mirror (10-4), and a fifth mirror (10-5).

[0115] Among them, the laser (14) adopts an ultrafast laser with a repetition frequency of 80MHz and a pulse width of 140fs; the beam splitter includes the first beam splitter (17-1), the second beam splitter (17-2), and the third beam splitter (17-3); the beam splitter adopts a dichroic beam splitter; the delay module (19) includes a delay mirror and a delay line displacement table; the mirror includes the first mirror (10-1), the second mirror (10-2), the third mirror (10-3), the fourth mirror (10-4), and the fifth mirror (10-5).

[0116] Specifically, the specific optical path of sample imaging is as follows:

[0117] The 800nm single beam laser is emitted from the light outlet of the laser (14) using a femtosecond laser with a 80MHz repetition frequency and a 140fs pulse width, and a part of the 800nm laser is doubled to 400nm after the frequency doubling crystal (15) (focusing mirrors are needed before and after the frequency doubling crystal, which are not shown due to limited space). The light diaphragm (16) blocks a part of the uneven light spot outside. After the first light splitting plate (17-1), the 800nm and 400nm lasers are split (the selective reflection and transmission characteristics of the dichroic light splitting plate make it reflect most of the 400nm laser and transmit most of the 800nm laser). Then, short wave pass / long wave pass filters are added to the respective light paths of the two beams to ensure that only a single component is present in the light path (not shown in the light path diagram due to limited space). After splitting, the first half wave plate (18-1) and the second half wave plate (18-2) are added to the respective light paths of the two beams to adjust the polarization direction for subsequent testing.

[0118] The optical path difference needs to be artificially set after the two beams are split, which is to control the time difference of the two beams reaching the sample, that is, to adjust the order of the two beams reaching the sample within a certain range. The specific implementation means is to correct the optical path of the two beams. When the delay mirror is located at the middle stroke of the delay line displacement table, the optical path difference of the two beams is almost zero. When the delay mirror is located at the front limit and the rear limit of the delay line displacement table, the maximum positive optical path difference and the maximum negative optical path difference of the two beams are respectively reached (the positive optical path difference represents that the 400nm light reaches the sample first, and the negative optical path difference represents that the 800nm light reaches the sample first).

[0119] The two beams are combined after a certain distance through the second light splitting plate (17-2).

[0120] Specifically, one beam of laser passes through the first half wave plate (18-1) and the delay module in turn, and then enters the second light splitting plate (17-2).

[0121] The other beam of laser passes through the second half wave plate (18-1), the first mirror (10-1) and the second mirror (10-2) in turn, and then enters the second light splitting plate (17-2).

[0122] After the two beams are combined through the second light splitting plate (17-2), they pass through the third mirror (10-3) and enter the third light splitting plate (17-3) to be split again. After splitting, one of the beams acts as pump light and the other acts as probe light. The purpose of splitting and then combining is to ensure the spatial position synchronization of the two beams, and to facilitate the correction of the optical path difference. The purpose of the subsequent combination and splitting is that the two beams are excitation energy sources of different media, which need to be focused at different positions.

[0123] Embodiments of the present application use 400 nm laser (pump light) as the energy source to excite the sample to have ultrafast dynamic process, and use 800 nm laser (probe light) as the energy source to emit electrons from the carbon nanotube electron source.

[0124] The adsorbed carbon nanotube electron source usually has a size of several microns to ten microns, and thus has a high requirement on the spot diameter of the laser. Therefore, a 50 times objective lens (8) is used for focusing, so that the center of the focal spot is basically focused on the carbon nanotube. Although the imaged sample has a small size, the number of samples on the substrate is large. Therefore, the spot diameter on the sample only needs to be smaller than the substrate size. Considering the reliability of the optical path and the limitation of the focal length, a convex lens (9) is more suitable.

[0125] In one embodiment of the present application, the point projection imaging microscope generally includes three parts: a point electron source (carbon nanotube electron source (20)), a sample to be observed (11), a fluorescent screen (12), and a vacuum cavity (13). The distance between the carbon nanotube electron source (20) and the sample to be observed (11) is d, and the distance between the carbon nanotube electron source (20) and the fluorescent screen (12) is D. The magnification of the sample imaged by the point projection microscope is M=D / d. As d decreases, the distance between the point electron source and the sample to be observed (11) gradually approaches, and the magnification changes from low to high. When the distance between the carbon nanotube electron source (20) and the sample to be observed (11) approaches the limit of the imaging resolution of the point projection microscope, the distance is in the nanometer level. Therefore, it is necessary to ensure the feasibility of the two beams of light incident in different directions and acting on each other without obvious interference.

[0126] Specifically, the pump light sequentially passes through the fourth mirror (10-4), the fifth mirror (10-5), and the convex lens (9), and is focused on the sample to be observed (11), so as to act on the sample to be observed (11) from the ground state to the excited state.

[0127] The probe light is focused by the objective lens (8) and reaches the carbon nanotube. At this time, the carbon nanotube is adsorbed on the tungsten needle tip (3). The probe light excites the carbon nanotube to form an electron pulse. After the electron pulse interacts with the sample in the excited state, sample imaging information is obtained.

[0128] In a specific embodiment of the present application, after the point projection microscope and the pump-probe system are set up, the specific process of realizing ultra-high space-time resolution observation by using the carbon tube as an ultrafast electron source is as follows: the 400 nm laser first reaches the sample (11) to be observed, acts on the sample from the ground state to the excited state as the pump light, and part of the electrons are transferred from the low energy level to the high energy level; after a time interval of several femtoseconds to several hundred picoseconds, the 800 nm laser reaches the carbon tube electron source, and the ultrafast electron pulse of the carbon tube is excited as the probe light. After the interaction of the sample after the pump and the electron pulse, the information of the excited state of the sample can be obtained, including the dynamic process of the sample from the ground state to the excited state and the dynamic process of the sample from the excited state to the ground state (such as energy transfer, charge transfer, trap state, dark state, defect energy level, etc.). Due to the ultra-high spatial resolution of the carbon tube as an electron source, in theory, this scheme can observe the femtosecond to picosecond ultrafast dynamic process on the nanoscale. By adjusting the order of the 400 nm pump light and the 800 nm probe light reaching the respective media, the intrinsic signal of the imaging sample is compared with the signal after the pump, and various ultrafast physical and chemical processes concerned by the frontier science are analyzed and obtained.

[0129] The ultrafast point projection microscope of the embodiment of the present application uses a low-energy electron beam to image a dynamic process, and has little damage to the sample, and does not affect the smooth progress of the ultrafast process of the sample itself. Meanwhile, due to the pulse characteristics, the radiation dose is generally difficult to accumulate. This non-destructive imaging capability is particularly suitable for observation of fragile samples, and can well ensure the integrity of the sample, especially in the research of biological samples or organic materials. The traditional ultrafast electron microscope needs complex electron beam regulation to obtain an image, and needs to spend a long time. The ultrafast point projection microscope of the embodiment of the present application uses a transient electron beam to project a single imaging in a very short time, has a fast imaging speed, reduces the time of the sample exposed to the electron beam, improves the imaging efficiency, and is suitable for a dynamic process requiring rapid observation. The ultrafast point projection microscope of the embodiment of the present application relies on the geometric projection of the electron beam to image, and can be adjusted at different distances to obtain multi-level resolution imaging from the micron scale to the nanometer scale. Some traditional microscopes, such as atomic force microscopes (AFM), are often only suitable for small-scale high-resolution observation. The running mode of the ultrafast point projection microscope of the embodiment of the present application improves the flexibility of research, and is suitable for multi-scale structure analysis of complex samples. The ultrafast point projection microscope of the embodiment of the present application has a simple structure, does not need many complex structures of the traditional ultrafast electron microscope, can greatly save equipment costs, and the cost of the carbon nanotube as the electron source is also low compared with the process of traditional materials, so that the advanced imaging technology has more market competitiveness and popularization. The new point projection microscope based on the carbon nanotube of the embodiment of the present application has ultra-high space-time resolution, is a sharp tool for promoting cutting-edge scientific research, and can make achievements in the fields of material science, physics, chemistry, biology and other basic researches, and help researchers to more deeply understand the operation mechanism of the microcosmic world. The combination of high spatial resolution and ultrafast imaging capability can also provide an unprecedented tool for exploration of these disciplines, and accelerate the pace of scientific discovery.

[0130] The point projection microscope and the matching optical system of the embodiment of the present application successfully realize imaging of the carbon nanotube powder sample by the ultrafast electron source, and the imaging results are shown in FIGS. 4(a) and 4(b). As shown in FIG. 4(a), the system can obviously observe the outline of the carbon tube sample, and the diameter of the powder sample is mainly about 10 nm, so it has the imaging resolution of this order of magnitude. By further increasing the distance between the carbon tube electron source and the sample, the magnification is improved, and when the magnification approaches the limit, FIG. 4(b) is obtained. In FIG. 4(b), the clear interference fringe distribution can be obviously observed, and by measuring the overall size, the coherence length of the electron beam can be obtained. According to the formula r = λD / πξ, the virtual source radius r of the carbon tube electron source is obtained, wherein λ represents the wavelength of the electron beam, about 0.071 nm, D represents the distance from the carbon tube electron source to the fluorescent screen, 400 mm, and ξ is the coherence length, which is about 0.2 nm. Figure 5The measurement value is 9.43 mm (the measurement area is shown by the black dashed line in Fig. 4(b)). The calculated virtual source radius r of the carbon nanotube electron source is about 0.96 nm. Compared with conventional materials (usually tens of nanometers), the virtual source radius has obvious advantages, and the smaller virtual source radius can reduce the emission angle of the electron beam, thereby providing clearer images and higher detail resolution during imaging. At this time, only 800 nm femtosecond laser is introduced as the probe light, which preliminarily verifies the ultra-high spatial resolution of the carbon nanotube as an ultrafast electron source. At the same time, since the pump-probe light path system is designed and built in conjunction with the point projection microscope, the ultra-high time resolution can be realized on this basis.

[0131] The embodiment of the present application aims at the short board of the existing ultrafast electron microscope in ultra-high time-space resolution imaging, develops a new point projection microscope with ultra-high time-space resolution potential and preliminarily verifies it. By exciting the carbon nanotube to emit an ultrafast electron pulse through femtosecond laser, the ultra-high spatial resolution imaging of the sample at the nanoscale is realized, and the virtual source radius index better than conventional materials is calculated from the imaging result. In addition, the pump-probe light path system matched with the point projection imaging microscope is designed and built, and a mature scheme for observing the ultrafast dynamics process of the sample by the electron pulse is proposed, which provides valuable experience and technical reference for developing a new point projection microscope with ultra-high time-space resolution.

[0132] The embodiments in the specification are described in a progressive manner, and each embodiment focuses on the difference from other embodiments. The same or similar parts between the embodiments can be referred to each other. For the device disclosed in the embodiments, since it corresponds to the method disclosed in the embodiments, the description is relatively simple, and the related parts can be referred to the method part.

[0133] The above description of the disclosed embodiments enables a person skilled in the art to implement or use the present application. Various modifications to the embodiments will be apparent to those skilled in the art, and the general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present application. Therefore, the present application will not be limited to the embodiments shown herein, but will conform to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method of ultra-high spatio-temporal resolution imaging based on carbon nanotube electron source, characterized in that, include: Carbon nanotubes are adsorbed onto the tip of a tungsten needle to form a carbon nanotube electron source; The laser beam is split into two beams, and the optical path difference between the two beams is adjusted by a delay module so that the two beams arrive at their respective excitation media at different times. After the two adjusted beams are combined, they are split again. After splitting, one beam is the pump beam and the other is the probe beam. The pump beam serves as the energy source to excite the ultrafast kinetic process in the sample, and the probe beam serves as the energy source for the carbon nanotube electron source to emit electrons. Based on the optical path difference, the pump light moves the sample from the ground state to the excited state. After a certain time interval, the probe light excites the carbon nanotubes to form an electron pulse. The electron pulse interacts with the excited sample to obtain sample imaging information. Carbon nanotubes are adsorbed onto the tip of a tungsten needle, including: After etching the tip of the tungsten wire, it is installed in the slot of the heating structure as a cathode. The thin film of vertically packed carbon nanotubes on the silicon wafer is attached to the anode plate with conductive adhesive and then installed in the matching vacuum chamber for vacuuming. The upright carbon nanotubes are attracted from the silicon wafer to the tip of the tungsten needle by the combined action of thermal induction force and electric field force; The upright carbon nanotubes are attracted from the silicon wafer to the tip of the tungsten needle by the combined action of thermal induction force and electric field force, including: A pressure difference is applied between the tungsten needle tip and the carbon nanotube film, and the tungsten needle tip is heated by a heating structure. By adjusting the micro-head to shorten the distance between the carbon nanotube film and the heated tungsten needle tip until they just touch, and maintaining this position for a period of time, the micro-head is removed to complete the adsorption process.

2. The ultra-high spatio-temporal resolution imaging method based on carbon nanotube electron source according to claim 1, characterized in that, The delay module includes a delay mirror and a delay line displacement stage; When the delay mirror is located at the middle of the delay line displacement stage, the optical path difference between the two beams is zero; When the delay mirror is at the front limit of the delay line displacement stage, the maximum positive optical path difference between the two beams is reached. The maximum negative optical path difference between the two beams is reached when the delay mirror is at the rear limit of the delay line displacement stage.

3. The method according to claim 1, wherein the method is characterized by, A point projection imaging microscope was constructed based on a carbon nanotube electron source, a sample, and a fluorescent screen. The distance between the carbon nanotube electron source and the sample is d, and the distance between the electron source and the fluorescent screen is D; The magnification of a sample imaged using a point projection microscope is M = D / d; As d decreases, the distance between the carbon nanotube electron source and the sample gradually decreases, and the magnification changes from low to high.

4. The ultra-high spatio-temporal resolution imaging method based on carbon nanotube electron source according to claim 1, characterized in that, By adjusting the time difference between the pump light and the probe light reaching the sample, the intrinsic signal of the sample to be imaged is compared with the signal after pumping to obtain the sample's change process.

5. The method of claim 1, wherein the carbon nanotube electron source is a carbon nanotube field emission electron source. Also includes: The pump light was focused using a 50x telephoto microscope lens so that the center of the focal spot was focused on the carbon nanotube. A convex lens is used to focus the probe light so that the diameter of the light spot focused on the sample is smaller than the substrate size.

6. A carbon nanotube electron source based ultra-high spatiotemporal resolution imaging system, applying the carbon nanotube electron source based ultra-high spatiotemporal resolution imaging method of any one of claims 1-5, characterized in that, include: An adsorption device is used to adsorb carbon nanotubes onto a tungsten needle tip to construct a carbon nanotube electron source. A laser is used to emit a laser beam. The first beam splitter is used to split the laser beam into two beams; The delay module is used to adjust the optical path difference between the two beams of light; The second beam splitter is used to combine the two adjusted beams. A third beam splitter is used to split the combined laser beam again, and one of the split beams is used as pump light and the other as probe light. The pump light is used as the energy source for exciting the sample to undergo ultrafast dynamics, and the probe light is used as the energy source for exciting the carbon nanotube to emit electrons. A point projection microscope is used to obtain the dynamic imaging information of the sample according to the optical path difference. The pump light excites the sample from the ground state to the excited state. After a certain time interval, the probe light excites the carbon nanotube to form an electron pulse. The electron pulse interacts with the sample in the excited state, and the imaging information of the sample is obtained.

Images