Ultrahigh spatial-temporal resolution imaging method and system based on carbon nanotube electron source

Abstract

The invention discloses an ultrahigh spatial-temporal resolution imaging method and system based on a carbon nanotube electron source, and relates to the technical field of ultrafast optical and atomic-scale imaging. Assembling a carbon nanotube to the tip of the tungsten needle tip to construct a carbon nanotube electron source; an ultrafast pulse laser pumping-detection system is designed, pumping light acts a sample from a ground state to an excited state, detection light acts on a carbon nanotube electron source to form an ultrafast photoelectron pulse, and two beams of light keep a certain optical path difference; and the electronic pulse projects ultrafast transient information of the sample onto a screen through a point projection imaging system. When high-spatial-resolution imaging is carried out, the flying distance of electrons from an electron source to a needle point is only tens of nanometers, and broadening caused by the vacuum dispersion effect and the space charge effect can be effectively avoided; the narrow pulse width characteristic of the electron source when the electron source is induced by ultrafast laser and the characteristic of extremely high spatial coherence of the carbon nanotube electron source are reserved to a certain extent.

Description

Technical Field

[0001] The present invention relates to the field of ultrafast optics and atomic-level imaging technology, and more specifically to an ultrahigh temporal and spatial resolution imaging method and imaging system based on a carbon nanotube electron source. Background Art

[0002] With the rapid development of nanotechnology, chip technology, new materials, and biomedicine, the academic and industrial communities have an increasing demand for a deeper understanding of physical and chemical phenomena at the microscopic scale. This requires microscopic imaging technology to provide higher spatial and temporal resolution to reveal 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 is usually only close to half the wavelength of light. In order to break through this limitation, a variety of super-resolution microscopy 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 microscopy 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 levels. Compared with imaging with visible light, electrons have a wavelength much smaller than the de Broglie wavelength of light, which theoretically enables microscopic observation of atoms and even subatomic scales. Various electron microscopes have also demonstrated the feasibility of ultra-high spatial resolution in practice. With the continuous iteration of electron microscopes, the observation of atomic imaging is no longer a problem that plagues the industry.

[0003] At the atomic and molecular scales, almost all movements and changes are transient. In order to explore the scientific phenomena and laws at these extremely small spatial and temporal scales, ultrahigh spatial and temporal resolution microscopy technology has emerged. It combines spatial high-resolution microscopy technology with femtosecond laser ultrafast time-resolution detection technology. Among them, the most representative ultrahigh spatial and temporal resolution microscopy technology is the ultrafast scanning / transmission electron microscope. Existing ultrafast electron microscopes generally integrate a pump-detection system based on a mature commercial electron microscope, which is mainly composed of a femtosecond laser and a supporting optical path system. The electron source is mainly single crystal tungsten and LaB6. In theory, ultrafast electron microscopes can simultaneously achieve nanometer-level resolution and observation of femtosecond relaxation time processes. However, due to the complicated multi-level structure of commercial electron microscopes, it is difficult to ensure the time synchronization between electron beam pulses and ultrafast laser pulses, which undoubtedly further increases the complexity and maintenance difficulty of the system. The time resolution capability of ultrafast electron microscopes depends on the pulse width of the electron beam. The narrower the pulse width, the stronger its time resolution capability. Due to the long electron optical tube structure of the electron microscope, even the femtosecond electron pulse width generated initially will widen in a vacuum as the propagation distance increases, making it difficult to detect processes on a true short femtosecond time scale. At the same time, ultrafast electron microscopes usually use high-energy electron beams for imaging, which may cause damage to certain sensitive samples when performing continuous imaging at ultra-high time resolution.

[0004] Therefore, how to propose a new type of ultra-high spatiotemporal resolution imaging method and imaging system that can effectively avoid the broadening caused by vacuum dispersion effect and space charge effect when performing high spatial resolution imaging, retain the narrow pulse width characteristics of the electron source when it is induced by ultrafast laser to a certain extent, and achieve higher spatial and temporal resolution is a problem that technical personnel in this field urgently need to solve. Summary of the invention

[0005] In view of this, the present invention provides an ultra-high spatiotemporal resolution imaging method and imaging system based on a carbon nanotube electron source. Aiming at the unavoidable shortcomings of existing ultrafast electron microscopes in ultra-high spatiotemporal resolution imaging, an ultra-high spatiotemporal resolution microscope based on a new carbon nanotube electron source and point projection microscopy imaging technology is developed and preliminarily verified. Compared with traditional materials, carbon nanotubes have a smaller tip curvature radius and energy divergence. Holographic imaging can achieve higher spatial resolution through the high coherence electron beam generated by them, and at the same time, it has more potential in realizing dynamic observation of atomic-level resolution in the future. Point projection microscopy 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 performing high spatial resolution imaging, the distance between the point electron source and the sample to be measured needs to be maintained at the order of tens of nanometers. Due to its natural ultra-close distance advantage, the electron beam propagation distance is short, which can effectively avoid the broadening caused by vacuum dispersion effect and space charge effect, and to a certain extent retains the narrow pulse width characteristics of the electron source when it is induced by ultrafast laser. Since the electron pulse width of carbon nanotubes as electron sources is narrower than that of traditional materials, this technical solution has unique advantages in both spatial and temporal resolution.

[0006] In order to achieve the above object, the present invention adopts the following technical solution: an ultra-high temporal and spatial resolution imaging method based on a carbon nanotube electron source, comprising:

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

[0008] Split the laser beam into two beams, and adjust the optical path difference between the two beams through the delay module so that the two beams reach their respective excitation media at different times;

[0009] After combining the two adjusted light beams, they are split again; after the splitting, one light beam is the pump light and the other light beam is the detection light; the pump light is used as the energy source to excite the sample to undergo ultrafast dynamics, and the detection light is used as the energy source for the carbon tube electron source to emit electrons;

[0010] According to the optical path difference, the pump light acts on the sample from the ground state to the excited state. After a certain time interval, the detection light excites the carbon nanotubes to form electron pulses. After the electron pulses act on the excited state sample, sample imaging information is obtained.

[0011] Preferably, adsorbing the carbon nanotubes on the tungsten needle tip comprises:

[0012] The tip of the tungsten wire is corroded and installed in the slot of the heating structure as a cathode, and the vertical close-packed carbon tube film on the silicon wafer is adhered to the anode plate with conductive glue and installed in a matching vacuum chamber for vacuum treatment;

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

[0014] Preferably, the upright 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, comprising:

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

[0016] The distance between the carbon tube film and the heated tungsten needle tip is shortened by adjusting the micrometer head until the two are just in contact. After a period of time, the micrometer head is withdrawn to complete the adsorption process.

[0017] Preferably, the delay module includes a delay reflector and a delay line displacement stage;

[0018] When the delay reflector is located at the middle stroke of the delay line stage, the optical path difference between the two beams is zero;

[0019] When the delay mirror is located at the front limit of the delay line stage, the maximum positive optical path difference between the two beams is achieved;

[0020] When the delay mirror is located at the rear end of the delay line stage, the maximum negative optical path difference between the two beams is reached.

[0021] Preferably, a point projection imaging microscope is constructed based on the carbon tube electron source, the sample and the fluorescent screen;

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

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

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

[0025] Preferably, by adjusting the time delay difference between the pump light and the detection light reaching the sample, the intrinsic signal of the sample to be imaged is compared with the signal after pumping to obtain the change process of the sample.

[0026] Preferably, the method further comprises: focusing the pump light using a 50x telephoto microscope lens so that the center of the focal spot is focused on the carbon nanotube;

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

[0028] Preferably, an ultra-high spatiotemporal resolution imaging system based on a carbon nanotube electron source comprises:

[0029] An adsorption device is used to adsorb carbon nanotubes on the tungsten needle tip to construct a carbon nanotube electron source;

[0030] Laser, for emitting laser beams;

[0031] A first beam splitter, used to split the laser beam into two beams;

[0032] Delay module, used to adjust the optical path difference between two beams of light;

[0033] A second beam splitter, used for combining the two adjusted light beams;

[0034] The third beam splitter is used to split the combined laser beams again. After the beam splitting, one beam of light is the pump light and the other beam of light is the detection light. The pump light is used as the energy source to excite the sample to undergo ultrafast dynamics, and the detection light is used as the energy source for the carbon tube electron source to emit electrons.

[0035] The point projection microscope is used to obtain dynamic imaging information of the sample based on the optical path difference. The pump light acts on the sample from the ground state to the excited state. After a certain time interval, the detection light excites the carbon nanotubes to form an electron pulse. The sample imaging information can be obtained after the electron pulse acts on the excited state sample.

[0036] It can be seen from the above technical solutions that, compared with the prior art, the present invention discloses an ultra-high spatiotemporal resolution imaging method and imaging system based on a carbon nanotube electron source, which has the following beneficial effects:

[0037] 1. Under the requirements of the same technical standards, the structure required by the existing technology is complex, and electron microscopes or other similar microscopic characterization technologies usually require a very high cost, and the research system targeted is also limited (the sample needs to have a certain conductivity and is usually not a magnetic sample). In comparison, the solution proposed by the present invention has a simple structure, no clear restrictions on the suitable material system, and the cost of each component is low, which is more conducive to promotion and popularization; 2. The present invention has achieved an ultra-high spatial resolution that is not inferior to the existing technology, and at the same time has a variety of imaging modes, which can characterize the real space morphology of the sample using contrast imaging and holographic imaging at low and high magnifications. On this basis, the present invention uses carbon nanotubes as ultrafast electron sources, which have better virtual source radius, energy dispersion, current density and lower operating temperature requirements than traditional materials commonly used in the prior art, and can also achieve further breakthroughs in spatial resolution. 3. The special structural design of the point projection imaging microscope developed by the present invention realizes that the ultrafast electron source and the sample to be imaged have an adjustable spatial spacing from far to near during imaging. Low-magnification imaging corresponds to a long distance between the electron source and the sample. The higher the magnification, the closer the distance between the electron source and the sample. 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 can the imaging of each area of ​​the sample be achieved, but also its extremely high displacement accuracy is guaranteed (the displacement resolution of piezoelectric ceramics is at the nanometer level). Therefore, on the basis of fine-tuning the imaging magnification of the sample, it can be ensured that the distance between the electron source and the sample in the high-magnification imaging mode is extremely close. In the existing technology, whether it is low-magnification or high-magnification imaging mode, the distance between the ultrafast electron source and the sample is much greater than that of the present invention (basically above the cm level), and the difference between the two is as much as 7 orders of magnitude. The ultrafast electron source excited by the ultrafast laser in the existing technology has an ultra-high time resolution (usually at the fs level) at the initial moment, but then due to the long-distance propagation in the vacuum, it is inevitably affected by the vacuum dispersion effect and the space charge effect and is significantly broadened, destroying the original ultra-high time resolution. In contrast, the present invention cleverly circumvents this problem by using this special structural design, so that the ultra-high temporal resolution during excitation can be retained. Therefore, the present invention uses carbon nanotubes as the ultrafast electron source of the point projection microscope for the first time, and achieves an ultra-high spatial resolution that is not inferior to that of traditional materials, successfully verifies the imaging capability of ultrafast electron pulses of carbon nanotubes, and builds a pump-detection system based on femtosecond lasers that is compatible with the point projection microscope, providing valuable experience and technical reference for the development of a new point projection microscope with ultra-high temporal and spatial resolution. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without paying creative work.

[0039] Figure 1 A schematic structural diagram of a carbon nanotube adsorption device provided in an embodiment of the present invention.

[0040] Figure 2 Schematic diagram of the optical path of the pump-detection system provided in an embodiment of the present invention and its linkage scheme with a point projection microscope.

[0041] FIG. 3( a ) is a schematic diagram of the carbon tube adsorbed for the first time at the tip of the tungsten needle tip by the adsorption device independently constructed according to an embodiment of the present invention.

[0042] FIG. 3( b ) is a schematic diagram of a single carbon tube protruding from the front end of a carbon tube cluster adsorbed for the first time according to an embodiment of the present invention.

[0043] FIG3( c ) is a schematic diagram of the carbon tube adsorbed for the second time at the tip of the tungsten needle tip by the adsorption device independently constructed according to an embodiment of the present invention.

[0044] FIG. 3( d ) is a schematic diagram showing a single carbon tube protruding from the front end of the carbon tube cluster adsorbed for the first time according to an embodiment of the present invention.

[0045] FIG. 4( a ) is a schematic diagram showing the outline of a carbon tube sample observed by an ultrafast electron source through the carbon tube sample in a point projection microscope according to an embodiment of the present invention.

[0046] FIG. 4( b ) is a schematic diagram of the interference fringe distribution obtained when the magnification of the carbon tube sample profile is close to the limit according to an embodiment of the present invention.

[0047] Figure 5 This is a graph showing the intensity distribution of interference fringes presented by the carbon tube sample provided in an embodiment of the present invention.

[0048] Among them, 1-heating electrode, 2-heating filament, 3-tungsten needle tip, 4-silicon wafer, 5-anode plate, 6-ammeter, 7-differentiator head, 8-objective lens, 9-convex lens, 10-1-first reflector, 10-2-second reflector, 10-3-third reflector, 10-4-fourth reflector, 10-5-fifth reflector, 11-sample to be observed, 12-fluorescent screen, 13-vacuum cavity, 14-laser, 15-frequency doubling crystal, 16-aperture, 17-1-first beam splitter, 17-2-second beam splitter, 17-3-third beam 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 following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0050] In today's physics, chemistry, materials science and life sciences, research on ultrafast time-resolved imaging technology at the single-molecule and single-atom level is becoming a hot topic. In order to deeply explore the electromagnetic dynamics phenomena in the microscopic world at the atomic spatial scale and the femtosecond time scale, it is urgent to develop advanced probe technologies with corresponding spatiotemporal resolution capabilities. Although existing technologies have made certain achievements in the field of ultrafast electron sources, their limitations in spatial and temporal resolution have gradually emerged, making it difficult to meet the needs of accurate detection of molecular and even atomic-scale dynamic processes. The embodiment of the present invention uses point projection imaging technology to achieve atomic-level spatial resolution, and combines a self-built pump-probe system to successfully verify the imaging capability of ultrafast electron pulses of carbon nanotubes. This innovation provides valuable experience and technical reference for the future development of new point projection microscopes with ultrahigh spatiotemporal resolution.

[0051] The embodiment of the present invention discloses an ultra-high temporal and spatial resolution imaging method based on a carbon nanotube electron source, comprising:

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

[0053] Split the laser beam into two beams, and adjust the optical path difference between the two beams through the delay module so that the two beams reach their respective excitation media at different times;

[0054] After combining the two adjusted light beams, they are split again; after the splitting, one light beam is the pump light and the other light beam is the detection light; the pump light is used as the energy source to excite the sample to undergo ultrafast dynamics, and the detection light is used as the energy source for the carbon tube 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 detection light excites the carbon nanotubes to form an electron pulse, and after the electron pulse acts on the excited state sample, the sample imaging information is obtained. The sample imaging information is the excited state information of the sample that is not completely relaxed.

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

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

[0058] The tip of the tungsten wire is corroded and installed in the slot of the heating structure as a cathode, and the vertical close-packed carbon tube film on the silicon wafer is adhered to the anode plate with conductive glue and installed in a matching vacuum chamber for vacuum treatment;

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

[0060] The embodiments of the present invention use carbon nanotubes as electron sources, which have nanometer-level or even sub-nanometer-level tip sizes, can provide electron beams with small beam spots, improve the spatial resolution of imaging, and help the scientific research community and industry to observe microstructures in materials science, biomedicine, and semiconductor devices with extremely high precision. Carbon nanotubes as electron sources have extremely high field enhancement factors, which means that they can emit electrons at relatively low laser power, which can significantly improve electron emission efficiency and reduce power consumption compared to traditional materials.

[0061] Specifically, the tip of the tungsten wire was etched to several hundred nanometers by direct current etching, and then installed on the slot of the heating filament; the vertical close-packed carbon tube film grown on the silicon wafer by plasma enhanced chemical vapor deposition (PECVD) was adhered to the anode plate with conductive glue; the device was installed in a matching vacuum chamber, and the mechanical pump and molecular pump were used to evacuate the vacuum for 10 minutes respectively to ensure that the vacuum degree was within 1*10 -3 Below the level of Pa.

[0062] Specifically, the upright 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, including:

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

[0064] The distance between the carbon tube film and the heated tungsten needle tip is shortened by adjusting the micrometer head until the two are just in contact. After a period of time, the micrometer head is withdrawn to complete the adsorption process.

[0065] Specifically, a voltage difference of 20V is applied between one side of the tungsten needle tip (cathode) and one side of the carbon tube 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 tube film and the heated tungsten needle tip is gradually reduced through coarse and fine adjustment of the differential head until the two are just in contact (the ammeter reading increases sharply), and the upright carbon tubes are attracted from the silicon wafer to the top of the tungsten needle tip through the combined action of thermal induced force and electric field force. After maintaining for 10 seconds, the differential head is withdrawn to complete the adsorption process.

[0066] Although traditional materials can be processed to nanometer-scale curvature radius, their field enhancement factor has a natural disadvantage compared to one-dimensional materials with sub-nanometer diameters such as carbon nanotubes. Therefore, using carbon nanotubes as an ultrafast electron source can achieve an electron beam with a smaller focal spot, thereby improving the details and clarity of imaging.

[0067] In a specific embodiment of the present invention, one of the key materials of the embodiment of the present invention is carbon nanotubes, and such carbon nanotubes need to ensure that they exist firmly on the tip of the substrate without affecting their excellent physical and chemical properties and high mechanical strength.

[0068] Specifically, the delay module includes a delay reflector and a delay line displacement stage;

[0069] When the delay reflector is located at the middle stroke of the delay line stage, the optical path difference between the two beams is zero;

[0070] When the delay mirror is located at the front limit of the delay line stage, the maximum positive optical path difference between the two beams is achieved;

[0071] When the delay mirror is located at the rear end of the delay line stage, the maximum negative optical path difference between the two beams is reached.

[0072] Specifically, (1) the femtosecond laser outputs 800nm ​​of hundred-femtosecond laser light. After passing through the frequency doubling crystal, the wavelength of part of the light is doubled to 400nm, and part of it remains at 800nm; (2) after passing through the first beam splitter, since the first beam splitter transmits most of the 800nm ​​ultrafast light and reflects most of the 400nm ultrafast light, it can achieve better beam splitting; (3) after beam splitting, it is necessary to add a low-pass / high-pass filter and a half-wave plate to the optical path of each of the two laser beams. The former is to filter out the other laser beam (for example, filter out the 800nm ​​laser on the 400nm optical path reflected by the beam splitter), and the latter is to adjust the polarization direction for subsequent measurement. (4) Add a delay module to the 800nm ​​optical path after splitting to basically ensure that the optical path difference between the center position of the delay stage and the other beam of light reaching the sample is equivalent, so that the order of the 800nm ​​ultrafast light and the 400nm ultrafast light arriving at the sample position can be adjusted in a large range; (5) Subsequently, beam combining and beam splitting are performed. The purpose of beam combining is to ensure that the subsequent optical paths are basically consistent (without additional optical path difference). Beam splitting allows 400nm to be used as pump light to induce the sample from the ground state to the excited state, and 800nm ​​to be used as detection light to arrive after an interval of femtosecond time scale, so as to observe the excited state information of the sample that has not been completely relaxed under the benchmark of ultra-high spatial resolution and time resolution.

[0073] Specifically, a point projection imaging microscope is constructed based on a carbon tube electron source, a sample and a fluorescent screen;

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

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

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

[0077] In the embodiment of the present invention, the carbon nanotubes can emit femtosecond or even attosecond electron pulses under the excitation of a femtosecond laser. Combined with the structural characteristics of the point projection microscope, the electron pulses will not be significantly broadened when imaging the sample, which is extremely beneficial for capturing ultrafast dynamic processes. Such ultra-high time resolution is particularly important for studying transient physical processes, chemical reactions, and biomolecular motion. The carbon nanotubes themselves have strong chemical stability and mechanical strength. As an electron source, they can work for a long time without loss or degradation, ensuring that the point projection microscope can operate long-term and stably in high-precision application scenarios. At the same time, the power consumption requirements for the equipment are low, and the overall service life is long, which reduces the need for frequent maintenance and replacement, and reduces operating costs.

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

[0079] Specifically, the method further includes: using a 50-fold telephoto microscope lens to focus the pump light so that the center of the focal spot is focused on the carbon nanotube;

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

[0081] In general, the embodiment of the present invention invents a method for constructing a carbon nanotube electron source, assembling carbon nanotubes to the tip of a tungsten needle tip; designing an ultrafast pulse laser pump-probe system, wherein the pump light acts on the sample from the ground state to the excited state, and 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 onto the screen through a point projection imaging system. When the embodiment of the present invention performs 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, and to a certain extent retains the narrow pulse width characteristics of the electron source when it is induced by the ultrafast laser and the extremely high spatial coherence characteristics of the carbon nanotube electron source, and its spatial resolution can reach the single-atom scale and the time resolution can reach below 100fs.

[0082] The existing ultrafast electron microscope has a complex structure, and the total propagation distance of the electron beam in the electron gun, lens barrel, pole shoe, chamber and other components is relatively long. The narrow pulse originally emitted at the time of propagation is continuously broadened by the vacuum dispersion effect and space charge effect during propagation, resulting in a large broadening of the electron pulse when it reaches the sample, which is not conducive to achieving ultra-high time resolution. In contrast, the ultrafast point projection microscope of the embodiment of the present invention has a simple structure, which not only saves many redundant structures and saves costs, but also ensures that the electron beam only needs to propagate tens of nanometers after emission to interact with the sample, which is more conducive to achieving ultra-high time resolution.

[0083] In a specific embodiment of the present invention, an ultra-high temporal and spatial resolution imaging system based on a carbon nanotube electron source comprises:

[0084] An adsorption device is used to adsorb the carbon nanotubes onto the tungsten needle tip (3) to construct a carbon nanotube electron source;

[0085] A laser (14) for emitting a laser beam;

[0086] A first beam splitter (17-1), used for splitting the laser beam into two beams;

[0087] A delay module (19) is used to adjust the optical path length of one of the light beams, thereby changing the optical path length difference between the two light beams;

[0088] A second beam splitter (17-2) is used to combine the two adjusted light beams;

[0089] The third beam splitter (17-3) is used to split the combined laser beams again, and after the beam splitting, one beam of light is the pump light and the other beam of light is the detection light; the pump light is used as the energy source to excite the sample to undergo ultrafast dynamics, and the detection light is used as the energy source for the carbon tube electron source to emit electrons;

[0090] The point projection microscope is used to obtain dynamic imaging information of the sample based on the optical path difference. The pump light acts on the sample from the ground state to the excited state. After a certain time interval, the detection light excites the carbon nanotubes to form an electron pulse. The sample imaging information can be obtained after the electron pulse acts on the excited state sample.

[0091] Among them, the significance of adjusting the optical path difference of the two beams of light through the delay module is to allow the two beams of light to reach their respective excitation media at different times, one of which reaches the carbon tube electron source to excite electrons, and the electrons reach the sample (that is, the position where the second beam of light acts). If there is no other beam of light acting on the sample, what is seen is the static signal of the sample. If there is a second beam of light, what is seen is the dynamic signal after the sample is excited. According to the time when the second beam of light arrives at the sample later than the first beam, the dynamic signal presented will be different. For example, some physical processes are at the femtosecond level, and some physical processes are at the picosecond level. These can all be observed through the embodiments of the present invention.

[0092] Specifically, the structure of the adsorption device is as follows Figure 1 As shown, the adsorption device includes: 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 tip of the tungsten needle tip (3) faces outwards and is mounted on the slot of the heating filament (2);

[0095] One side of the silicon wafer (4) carries a carbon tube film that is vertically grown and densely distributed; the carbon tube film is composed of carbon nanotubes;

[0096] The other side of the silicon wafer (4) is adhered to the anode plate (5) using conductive glue;

[0097] The micrometer head (7) is used to adjust the position of the carbon tube film on the silicon wafer (4);

[0098] The ammeter (6) measures the change in current when the tungsten needle tip (3) contacts the carbon tube 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 invention mainly realizes the adsorption operation of carbon nanotubes (hereinafter referred to as carbon tubes) on the tungsten needle tip (3) through the following method to complete the production of the electron source.

[0100] Step 1: First, prepare a carbon tube film of appropriate thickness grown by plasma enhanced chemical vapor deposition (PECVD), adhere the heavily doped silicon wafer (4) carrying the carbon tube film to a 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 differential head (7) that can adjust the lateral position of the carbon tube film. The initial position is the point where the differential head (7) has the maximum value.

[0101] Step 2: Then, the tip of the 0.5 mm thick tungsten wire is corroded and reduced to a curvature radius of 100 nanometers by an electrochemical corrosion method to obtain a tungsten needle tip (3). After the corrosion is completed, the tungsten needle tip (3) is cleaned in the order of ethanol-water-ethanol to ensure that there is no alkaline solution and contaminant impurities remaining on the surface.

[0102] Step 3: Build a vacuum chamber (13) and a matching vacuum pumping system for adsorbing carbon tubes, then build a heating structure for the tungsten needle tip (3) in the vacuum chamber (13), place it at both ends of the electrode, and reserve a slot on the top of the heating structure to facilitate heat heating of the tungsten needle tip (3) by heat conduction. After the heating structure is built, insert the tungsten needle tip into the slot, and this side is called the cathode as a whole. At this time, the tip of the tungsten needle tip is less than a few centimeters away from the surface of the installed carbon tube film.

[0103] Step 4: Seal the vacuum chamber (13). After sealing, use a mechanical pump and a molecular pump to draw vacuum for 10 minutes respectively to ensure that the chamber vacuum is 1*10 -3 Below the level of Pa.

[0104] Step 5: During the interval between vacuuming, a current and voltage source is installed to heat the tungsten needle tip (3) and provide a voltage difference between the positive and negative electrodes, and a high-precision ammeter (6) for testing is connected.

[0105] Step 6: Wait for the chamber vacuum to reach 1*10 -3 Pa, a voltage difference of 20V is applied to the positive and negative electrodes, and then the current at both ends of the constant current source for heating the tungsten needle tip (3) is slowly increased until the reading reaches 10A2V, at which time the temperature of the tungsten needle tip reaches above 1000K.

[0106] Step 7: Rotate the differential head (7) so that the carbon tube film gradually approaches the heated tungsten needle tip (3). When the distance between the two is far, the rotation amplitude of the differential head (7) is large. When the distance is close, reduce the rotation amplitude. At this time, observe the reading of the ammeter. Continue to slowly rotate the differential head (7) until the reading of the ammeter (6) suddenly changes and then stop rotating.

[0107] Step 8: After stopping the rotation and maintaining it for 10 seconds, a small amount of carbon tubes on the carbon tube film are transferred to the tungsten needle tip (3) through the combined action of thermal induction force and electric field force, and then the micrometer head (7) is slowly rotated in the opposite direction to move the carbon tube film to the far right to complete the adsorption process and facilitate the next adsorption.

[0108] Step nine: Use a scanning electron microscope (SEM) to observe the morphology of the adsorbed carbon tubes on the tungsten needle tip (3) to ensure that there are a certain number of carbon tubes at the tip of the tungsten needle tip, and successfully manufacture a carbon tube ultrafast electron source.

[0109] Figure 3(a)-Figure 3(d) The carbon tubes were adsorbed at the tip of the tungsten needle tip by an adsorption device built independently. It can be seen from the figure that a sufficient number of carbon tubes are combined with the tungsten needle tip through the combined action of thermal induction force and electric field force, and the overall orientation is along the tip of the tungsten needle tip. Figure 3 (a) and Figure 3 (c) are the results of two adsorptions, respectively. There are more carbon tubes at the junction of the carbon tube and the tungsten needle tip, and the bonding method is mainly bonding (the carbon tube is relatively firm on the metal needle tip, and it does not fall off when bombarded with high-energy electron beams during long-term placement and characterization), which ensures the stability of the carbon tube on the tungsten needle tip. Figure 3 (b) and Figure 3 (d) show that there is a relatively prominent single carbon tube at the front end of the carbon tube cluster, and the diameter is less than 30nm and 20nm respectively. The radius of curvature emitted by its tip is often smaller than the radius of the tube body, which is much smaller than the radius of curvature of traditional materials as electron sources (usually in the order of hundreds of nanometers). Therefore, the adsorption method of the embodiment of the present invention ensures that the front side of the electron source spatial position is an independent single carbon tube on the basis of ensuring that the carbon tube and the tungsten needle tip have sufficiently strong bonding ability, thereby ensuring the uniqueness of the electron source emission site, and its curvature radius is in the order of tens of nanometers, which can achieve ultra-high spatial resolution that is better than traditional electron sources.

[0110] The embodiment of the present invention can not only ensure the stability of the carbon tube attached to the metal needle tip through the independently developed adsorption device, but also make the tube wall of the carbon tube basically keep level with the metal needle tip. On this basis, there are no multiple carbon tubes at the tip position, but an independent single carbon tube with obvious position advantage, which undoubtedly provides favorable conditions for the carbon tube to be used as an independent emission electron source.

[0111] The carbon tube adsorption device of the embodiment of the present invention has a simple structure, a clear principle, and a low cost for developing each component, which is convenient for promotion. The success rate of single adsorption is above 80%, and except for the time spent on vacuuming, the remaining time is relatively short, and the efficiency of adsorbing carbon tubes is relatively high.

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

[0113] In a specific embodiment of the present invention, another key device of the present invention is a point projection imaging microscope and its supporting optical path construction. The point projection microscope is designed based on the experience of building a vacuum system and its principle. In order to verify that carbon tubes can achieve ultra-high temporal and spatial resolution in a point projection microscope as an ultrafast electron source, the present invention designs and builds a pump-detection optical path system, and links it with the point projection microscope as shown in the following example. Figure 2 shown.

[0114] Specifically, the pump-detection optical path system comprises 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 reflector (10-1), a second reflector (10-2), a third reflector (10-3), a fourth reflector (10-4), and a fifth reflector (10-5);

[0115] The laser (14) is an ultrafast laser with a repetition rate of 80 MHz and a pulse width of 140 fs; the beam splitters include a first beam splitter (17-1), a second beam splitter (17-2), and a third beam splitter (17-3); the beam splitters are dichroic beam splitters; the delay module (19) includes a delay reflector and a delay line displacement stage; the reflectors include a first reflector (10-1), a second reflector (10-2), a third reflector (10-3), a fourth reflector (10-4), and a fifth reflector (10-5);

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

[0117] A femtosecond laser with a repetition rate of 80MHz and a pulse width of 140fs is used. The light outlet of the laser (14) emits a single beam of 800nm ​​laser light. After passing through the frequency doubling crystal (15), a portion of the 800nm ​​laser light is frequency doubling to 400nm (focusing lenses are required before and after the frequency doubling crystal, which are not shown due to limited space). The aperture (16) blocks a portion of the uneven light spot on the outside. After passing through the first beam splitter (17-1), the 800nm ​​and 400nm laser light is split (the selective transmissive-reflective characteristics of the dichroic beam splitter make it reflect most of the 400nm laser light and transmit most of the 800nm ​​laser light). Subsequently, short-wave pass / long-wave pass filters are installed on the respective optical paths of the two laser beams to ensure that the optical path has only a single beam component (not shown in the optical path diagram due to limited space). After the splitting, a first half wave plate (18-1) / a second half wave plate (18-2) needs to be added to the optical paths of the two laser beams respectively. The first half wave plate (18-1) / the second half wave plate (18-2) is used to adjust the polarization direction for subsequent testing;

[0118] After the two beams of light are split, the optical path difference needs to be set manually in order to control the time difference between the two beams of light reaching the sample, that is, to adjust the order in which the two beams of light reach the sample within a certain range. The specific means of implementation is to correct the optical path of each of the two beams of light. When the delay mirror is located in the middle of the delay line stage, the optical path difference of the two beams of light is almost zero, and when the delay mirror is located at the front and rear limits of the delay line stage, the maximum positive optical path difference and the maximum negative optical path difference of the two beams of light are reached respectively (a positive optical path difference means that the 400nm light reaches the sample first, and a negative optical path difference means that the 800nm ​​light reaches the sample first).

[0119] After the two laser beams are split, they pass through a certain distance and then are combined through a second beam splitter (17-2);

[0120] Specifically, a laser beam passes through a first half-wave plate (18-1) and a delay module in sequence, and then enters a second beam splitter (17-2);

[0121] Another laser beam passes through the second half-wave plate (18-1), the first reflector (10-1), and the second reflector (10-2) in sequence, and then enters the second beam splitter (17-2);

[0122] After the two laser beams are combined through the second beam splitter (17-2), they pass through the third reflector (10-3) and enter the third beam splitter (17-3) for further beam splitting. After beam splitting, one beam is used as pump light and the other beam is used as detection light. The purpose of beam splitting and then combining is to ensure the synchronization of the spatial positions of the two beams and to facilitate the correction of the optical path difference; and the purpose of combining and then splitting is that the two beams are excitation energy sources of different media and need to be focused at different positions.

[0123] In the embodiment of the present invention, a 400 nm laser (pump light) is used as an energy source to excite the sample to undergo ultrafast dynamics, and an 800 nm laser (probe light) is used as an energy source for the carbon tube electron source to emit electrons.

[0124] The adsorbed carbon tube electron source has a relatively high requirement on the diameter of the laser spot because its overall size is usually in the order of several microns to ten microns. Therefore, a 50x objective lens (8) is used for focusing so that the center of the focal spot is basically focused only on the carbon tube. Although the imaged samples are individually very small, there are a large number of them on the substrate. Therefore, the diameter of the light spot focused on the sample only needs to be smaller than the substrate size. Considering the reliability of the optical path construction and the limitation of the focal length, a convex lens (9) is more suitable.

[0125] In a specific embodiment of the present invention, the point projection imaging microscope generally comprises three parts: a point electron source (carbon tube electron source (20)), a sample to be observed (11), a fluorescent screen (12) and a vacuum chamber (13). The distance between the carbon tube electron source (20) and the sample to be observed (11) is d, and the distance between the carbon tube 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 magnification to high magnification. When approaching the limit of the imaging resolution of the point projection microscope, the distance between the carbon tube electron source (20) and the sample to be observed (11) is at the nanometer level, so it is necessary to inject the two beams of light along different directions to ensure the feasibility of each acting without obvious interference.

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

[0127] After being focused by the objective lens (8), the detection light reaches the carbon nanotube, at which time the carbon nanotube has been adsorbed on the tungsten needle tip (3); the detection light excites the carbon nanotube to form an electron pulse, and after the electron pulse acts on the excited sample, sample imaging information is obtained.

[0128] In a specific embodiment of the present invention, after the point projection microscope and the pump-probe system are built, the specific process of using the carbon tube as an ultrafast electron source to achieve ultrahigh spatiotemporal resolution observation is as follows: a 400nm laser first reaches the sample to be observed (11), and acts as a pump light to act on the sample from the ground state to the excited state, and some electrons transition from the low energy level to the high energy level; after a time interval as short as a few femtoseconds and as long as several hundred picoseconds, an 800nm ​​laser reaches the carbon tube electron source, and acts as a probe light to excite the carbon tube's ultrafast electron pulse, and after the electron pulse acts on the sample after being pumped, the excited state of the sample can be obtained. Information, including the dynamic process of the sample from the ground state to the excited state and the dynamic process of relaxation from the excited state back 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 carbon tubes as electron sources, theoretically this scheme can observe ultrafast dynamic processes in the order of femtosecond to picosecond levels at the nanoscale; by adjusting the order in which the 400nm pump light and the 800nm ​​detection light arrive at their respective media, the intrinsic signal of the desired imaging sample is compared with the signal after pumping, and the various ultrafast physical and chemical processes that are of concern to cutting-edge science are analyzed.

[0129] The ultrafast point projection microscope of the embodiment of the present invention uses a low-energy electron beam to image the dynamic process, which causes little damage to the sample and will not affect the smooth progress of the ultrafast process of the sample itself. At the same time, due to its pulse characteristics, the radiation dose is generally difficult to accumulate. This non-destructive imaging capability is particularly suitable for the observation of fragile samples, especially in the study of biological samples or organic materials, it can well ensure the integrity of the sample. Traditional ultrafast electron microscopes require complex electron beam regulation to obtain images, which takes a long time. The ultrafast point projection microscope of the embodiment of the present invention uses instantaneous electron beam projection to complete a single imaging in a very short time. Its imaging speed is fast, which reduces the time the sample is exposed to the electron beam, improves the imaging efficiency, and is suitable for dynamic processes that require rapid observation. The ultrafast point projection microscope of the embodiment of the present invention relies on the geometric projection of the electron beam for imaging, which can be adjusted at different distances to obtain multi-level resolution imaging from micrometer scale to nanometer scale. However, some traditional microscopes, such as atomic force microscopes (AFM), are often only suitable for high-resolution observations of smaller scales. The operation mode of the embodiment of the present invention enhances the flexibility of research and is suitable for multi-scale structural analysis of complex samples. The ultrafast point projection microscope of the embodiment of the present invention has a simple structure and does not require many complex structures of traditional ultrafast electron microscopes, which can greatly save equipment costs. At the same time, the cost of carbon nanotubes as electron sources is also low enough compared to the process of traditional materials, making this advanced imaging technology more competitive and popular in the market. The new point projection microscope with ultra-high spatiotemporal resolution based on carbon nanotubes in the embodiment of the present invention is a powerful tool for promoting cutting-edge scientific research results. It can make achievements in basic research fields such as materials science, physics, chemistry, and biology, and help researchers to have a deeper understanding of the operating mechanism of the microscopic world. The combination of high spatial resolution and ultrafast imaging capabilities can also provide unprecedented tools for the exploration of these disciplines and accelerate the pace of scientific discovery.

[0130] The embodiment of the present invention successfully realizes the imaging of carbon nanotube powder samples by ultrafast electron source through a point projection microscope and a matching optical path system, and the imaging results are shown in Figures 4(a) and 4(b). As can be seen from Figure 4(a), the system can clearly observe the outline of the carbon tube sample, and the diameter of the powder sample is mainly around 10nm, so it has an imaging resolution of this order of magnitude. The distance between the carbon tube electron source and the sample is further increased, and the magnification is improved. When the magnification is close to the limit, Figure 4(b) is obtained. In Figure 4(b), a clear interference fringe distribution can be clearly observed. By measuring its overall size, the coherence length of the electron beam can be obtained. Combined with the formula r=λD / πξ, the virtual source radius r of the carbon tube electron source is obtained, where λ represents the electron beam wavelength, which is about 0.071nm, D represents the distance from the carbon tube electron source to the fluorescent screen, which is 400mm, and ξ is the coherence length, which is obtained by Figure 5The measurement shows that its value is 9.43mm (the measured area is shown in the black dashed area of ​​Figure 4(b)). Calculation shows that the virtual source radius r of the carbon tube electron source is about 0.96nm. Compared with traditional materials (usually tens of nanometers), its virtual source radius has obvious advantages. 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 800nm ​​femtosecond laser was introduced as the detection light, which preliminarily verified the ultra-high spatial resolution of carbon tubes as ultrafast electron sources. At the same time, due to the design and construction of the pump-detection optical path system linked to the point projection microscope, ultra-high temporal resolution can be achieved on this basis.

[0131] In view of the unavoidable shortcomings of existing ultrafast electron microscopes in ultrahigh spatial and temporal resolution imaging, the embodiments of the present invention have developed a new point projection microscope with the potential for ultrahigh spatial and temporal resolution and conducted preliminary verification. Ultrahigh spatial resolution imaging of samples at the nanoscale is achieved by exciting carbon nanotubes with femtosecond lasers to emit ultrafast electron pulses, and a virtual source radius index superior to that of traditional materials is calculated from the imaging results. In addition, the embodiments of the present invention also design and build a pump-probe optical path system that is compatible with the point projection imaging microscope, and propose a mature solution for realizing the observation of ultrafast dynamic processes of samples by electron pulses, which provides valuable experience and technical reference for the development of a new point projection microscope with ultrahigh spatial and temporal resolution.

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

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

Claims

1. An ultra-high temporal and spatial resolution imaging method based on a carbon nanotube electron source, characterized in that: include: The carbon nanotubes are adsorbed on the tungsten needle tip to form a carbon tube electron source; Split the laser beam into two beams, and adjust the optical path difference between the two beams through the delay module so that the two beams reach their respective excitation media at different times; After combining the two adjusted light beams, they are split again; after the splitting, one light beam is the pump light and the other light beam is the detection light; the pump light is used as the energy source to excite the sample to undergo ultrafast dynamics; the detection light is used as the energy source for the carbon tube electron source to emit electrons; According to the optical path difference, the pump light acts on the sample from the ground state to the excited state. After a certain time interval, the detection light excites the carbon nanotubes to form electron pulses. After the electron pulses act on the excited state sample, sample imaging information is obtained.

2. The ultra-high temporal and spatial resolution imaging method based on a carbon nanotube electron source according to claim 1, characterized in that: Adsorbing carbon nanotubes on the tungsten needle tip includes: The tip of the tungsten wire is corroded and installed in the slot of the heating structure as a cathode, and the vertical close-packed carbon tube film on the silicon wafer is adhered to the anode plate with conductive glue and installed in a matching vacuum chamber for vacuum treatment; The upright carbon nanotubes are attracted from the silicon wafer to the top of the tungsten needle tip through the combined action of thermal induced force and electric field force.

3. The ultra-high temporal and spatial resolution imaging method based on a carbon nanotube electron source according to claim 2, characterized in that: The upright carbon nanotubes are attracted from the silicon wafer to the top of the tungsten needle tip by the combined action of thermal induced force and electric field force, including: A pressure difference is applied between one side of the tungsten needle tip and one side of the carbon tube film, and the tungsten needle tip is heated by a heating structure; The distance between the carbon tube film and the heated tungsten needle tip is shortened by adjusting the micrometer head until the two are just in contact. After a period of time, the micrometer head is withdrawn to complete the adsorption process.

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

5. The ultra-high temporal and spatial resolution imaging method based on a carbon nanotube electron source according to claim 1, characterized in that: Construct a point projection imaging microscope based on a carbon tube electron source, a sample and a fluorescent screen; The distance between the carbon tube electron source and the sample is d, and the distance between the source and the fluorescent screen is D; The magnification of a sample imaged by a point projection microscope is M = D / d; As d decreases, the distance between the carbon tube electron source and the sample gradually gets closer, and the magnification changes from low to high.

6. The ultra-high temporal and spatial resolution imaging method based on a carbon nanotube electron source according to claim 1, characterized in that: By adjusting the time delay difference between the pump light and the detection light reaching the sample, the intrinsic signal of the desired imaging sample is compared with the signal after pumping to obtain the change process of the sample.

7. The ultra-high temporal and spatial resolution imaging method based on a carbon nanotube electron source according to claim 1, characterized in that: Also includes: Using a 50x telephoto microscope lens to focus the pump light so that the center of the focal spot is focused on the carbon nanotube; The detection light is focused by using a convex lens so that the diameter of the light spot focused on the sample is smaller than the size of the substrate.

8. An ultra-high spatiotemporal resolution imaging system based on a carbon nanotube electron source, using an ultra-high spatiotemporal resolution imaging method based on a carbon nanotube electron source as claimed in any one of claims 1 to 7, characterized in that: include: An adsorption device is used to adsorb carbon nanotubes on the tungsten needle tip to construct a carbon nanotube electron source; Laser, for emitting laser beams; A first beam splitter, used to split the laser beam into two beams; Delay module, used to adjust the optical path difference between two beams of light; A second beam splitter, used for combining the two adjusted light beams; The third beam splitter is used to split the combined laser beams again. After the beam splitting, one beam of light is the pump light and the other beam of light is the detection light. The pump light is used as the energy source to excite the sample to undergo ultrafast dynamics, and the detection light is used as the energy source for the carbon tube electron source to emit electrons. The point projection microscope is used to obtain dynamic imaging information of the sample based on the optical path difference. The pump light acts on the sample from the ground state to the excited state. After a certain time interval, the detection light excites the carbon nanotubes to form an electron pulse. The sample imaging information can be obtained after the electron pulse acts on the excited state sample.

Images