A plasmon-enhanced carbon nanotube field emission device, its fabrication method, and its application.

Abstract

This invention discloses a plasmon-enhanced carbon nanotube field emission device, its fabrication method, and its applications. The device includes an insulating substrate, a concentric circular metal grating on the substrate, anode and cathode electrodes located in the central region of the grating, and carbon nanotubes bridging the electrodes and forming nanoscale gaps. By designing the grating period to match the incident laser wavelength, surface plasmons can be excited, generating a localized electric field enhancement at the center, thereby significantly reducing the electron tunneling barrier at the carbon nanotube tip and increasing the field emission current. This invention also provides a corresponding fabrication method, including the patterning of the grating and electrodes, the deposition and patterning of the carbon nanotube thin film, and the formation of the nanoscale gaps. This device has a simple structure, effectively avoids thermal damage caused by direct laser radiation, and has application potential in fields such as field emission enhancement, optical signal detection, and optoelectronic modulation.

Description

Technical Field

[0001] This invention belongs to the field of vacuum nanoelectronic device technology, specifically relating to a carbon nanotube field emission device enhanced by plasmon resonance, its preparation method, and its application. Background Technology

[0002] Field emission electron sources have important applications in many key fields such as medical imaging, flat panel displays, X-ray sources, and communication devices. Carbon nanotubes, due to their unique physical properties, such as tunable Fermi level, small tip curvature radius, high emission current density, and low turn-on voltage, are considered highly promising field emission cathode materials. Although carbon nanotubes possess a high field enhancement factor, their high work function (approximately 5 eV) means that electrons still require a relatively high external electric field to escape from the material, which limits their application in low-power devices.

[0003] To reduce the electric field required for field emission, laser-assisted field emission technology has gradually attracted attention. This technology is mainly based on thermal field emission and optical field emission mechanisms. It uses laser energy to excite electrons to higher energy states, thereby reducing the tunneling barrier, increasing the electron tunneling probability, and ultimately increasing the emission current. However, directly irradiating a local area of ​​the emitter with a high-intensity laser can easily lead to overheating or even damage to the material, affecting the stability and lifespan of the device.

[0004] Recent research has further revealed that nanostructured metal surfaces can couple with incident light of specific wavelengths, exciting surface plasmon resonances and thus significantly enhancing the local electric field at the subwavelength scale. This plasmon enhancement effect has been confirmed in field emission experiments using traditional metal cathodes such as gold and copper, effectively increasing the emission current. This provides a new approach for developing low-power, high-sensitivity optoelectronic integrated field emission devices.

[0005] However, effectively combining plasmon resonance enhancement mechanisms with carbon nanotube field emission structures to achieve localized electric field enhancement while avoiding direct thermal damage to the emitter by the laser remains a challenge in current technology. Existing structures mostly employ one-dimensional gratings or nanoparticle arrays, whose electric field enhancement regions are relatively dispersed, making precise coupling with single or oriented carbon nanotube emitters difficult. Summary of the Invention

[0006] To address the shortcomings of existing technologies, this invention provides a plasmon-enhanced carbon nanotube field emission device, its fabrication method, and its applications. This structure, through the design of a ring-shaped metal grating matched with a laser wave vector, excites surface plasmons and causes them to coherently superimpose in the central region, forming a highly localized enhanced electric field. This significantly reduces the vacuum barrier near the tip of the carbon nanotube, increases the electron tunneling probability, and ultimately improves field emission performance while avoiding the thermal damage caused by direct laser irradiation of the emitter. The device structure is relatively simple, and the emission process can be controlled by optical signals, providing a feasible technical path for photoelectric detection and modulation.

[0007] This invention is achieved through the following technical solution:

[0008] A plasmonic-enhanced carbon nanotube field emission device, comprising:

[0009] Insulating substrate;

[0010] A concentric ring metal grating located on the insulating substrate, the concentric ring metal grating being composed of at least four ring metal structures with different radii;

[0011] Anode and cathode located on the insulating substrate and in the central region of the concentric circular metal grating;

[0012] A carbon nanotube film is located in the substrate region where the concentric ring metal grating and the anode and cathode are located, and the carbon nanotube film forms an emission gap of 1~100 nm between the anode and cathode.

[0013] The period and duty cycle of the concentric ring metal grating are matched with the wavelength of the laser source to excite surface plasmons and generate a local electric field enhancement in the central region.

[0014] Preferably, the number of annular metal structures in the concentric annular metal grating is 4 to 50, and the grating area is 10 to 10,000 μm. 2 The concentric ring metal grating has an opening, or is electrically isolated from the anode and cathode through an insulating dielectric layer.

[0015] Preferably, the materials of the concentric ring metal grating and the anode and cathode are independently selected from one or a combination of two of Au, Pd, Al, Cu, Ni, Ti, Ag, Cr, Mo, W, and Fe; when there are two combinations, the mass ratio of the two is (0.01~100):1; the thickness of the metal layer of the concentric ring metal grating and the anode and cathode is 1~1000 nm.

[0016] Preferably, the anode and cathode electrodes are buried electrode structures;

[0017] The buried electrode structure includes: a lower electrode deposited on the insulating substrate, an insulating dielectric layer covering the lower electrode and part of the substrate, and a top electrode formed in the insulating dielectric layer and electrically connected to the lower electrode;

[0018] The concentric ring metal grating is disposed on the insulating dielectric layer, and its central region corresponds to the position of the top electrode;

[0019] The carbon nanotube film is bridged between the top electrodes and forms the emission gap.

[0020] The above-mentioned method for fabricating carbon nanotube field emission devices includes the following steps:

[0021] Step 1) Define a concentric ring grating pattern on an insulating substrate, deposit and pattern a metal layer to form a concentric ring metal grating;

[0022] Step 2) Define an electrode region on the insulating substrate, deposit and pattern a metal layer to form anode and cathode electrodes located in the central region of the concentric ring metal grating, and ensure that the concentric ring metal grating and the anode and cathode electrodes are electrically insulated.

[0023] Step 3) Deposit a carbon nanotube film on the substrate containing the concentric ring metal grating and the anode and cathode, define the active region pattern, and remove the carbon nanotube film outside the active region.

[0024] Step 4) Break the carbon nanotubes suspended between the anode and cathode to form carbon nanotube gaps.

[0025] Preferably, the order of step 1) and step 2) can be interchanged.

[0026] Preferably, the method for depositing carbon nanotube films in step 3) is selected from chemical vapor deposition on substrate growth, dispersion immersion deposition, spin coating, spray coating, wet transfer, dry transfer, inkjet printing, screen printing, or nano-transfer.

[0027] The method for removing the carbon nanotube film outside the active region is inductively coupled plasma etching, reactive ion etching, or oxygen plasma ashing.

[0028] Preferably, in steps 1), 2), and 3), the pattern definition technology employs ultraviolet exposure, deep ultraviolet exposure, electron beam writing, or nanoprinting.

[0029] Preferably, in step 4), the method for breaking the gaps formed by carbon nanotubes is Joule thermal ablation, focused ion beam bombardment, inductively coupled plasma etching, reactive ion etching, or oxygen plasma ashing.

[0030] The above-mentioned carbon nanotube field emission devices are used in field emission enhancement, optical signal detection, or optoelectronic modulation.

[0031] The beneficial effects of this invention are as follows:

[0032] (1) The concentric ring grating structure of the present invention can be efficiently coupled with incident laser of a specific wavelength, exciting surface plasmons and generating a highly localized electric field enhancement in the central region. This enhanced electric field acts directly on the carbon nanotube emitter located at the center of the grating, effectively reducing its surface barrier and increasing the electron tunneling probability, thereby significantly increasing the field emission current. Compared with direct laser irradiation, this method indirectly controls the emission process through near-field optical enhancement, avoiding the thermal damage that may be caused by high-energy laser directly acting on the tip of the carbon nanotube, and improving the reliability and service life of the device.

[0033] (2) The concentric ring structure of the present invention enables the excited surface plasmon waves to coherently superimpose during propagation toward the center, efficiently concentrating light energy in the central nanoscale region, thus greatly optimizing the conversion efficiency of light-field emission. Compared with other grating or nanoparticle structures, this design provides more precise and concentrated positioning of the electric field enhancement region and better spatial coupling with the carbon nanotube emitter, which is conducive to achieving stable and efficient performance improvement.

[0034] (3) By adjusting the period, duty cycle, number of rings, and metal material of the concentric ring grating, the present invention can flexibly control the surface plasmon resonance wavelength, thereby matching different laser sources and realizing active design of enhancement effect and working wavelength. At the same time, the structure is fully compatible with mainstream micro-nano fabrication processes (such as photolithography, evaporation, and etching), which is convenient for integration with existing semiconductor processes, providing a feasible technical path for the fabrication of high-performance, integrated optoelectronic emission devices.

[0035] (4) The device of the present invention not only significantly improves field emission performance, but its emission current also has high sensitivity to parameters such as incident light power and wavelength. This makes the device go beyond the traditional field emission electronic source function, and it can also serve as a highly efficient photoelectric signal conversion unit, showing important application prospects in fields such as high-speed optical signal detection, photoelectric modulation and optical control electronic sources. Attached Figure Description

[0036] Figure 1 These are SEM images of the overall device (A) and the local carbon nanotube area (B) in Example 1;

[0037] Figure 2 This is a schematic diagram of the device in Example 1;

[0038] Figure 3 This is a schematic diagram of the device fabrication process in Example 2;

[0039] Figure 4 This is a schematic diagram of the device fabrication process in Example 3;

[0040] Figure 5 The IV characteristic curve of the device in Test Example 1 is shown. Detailed Implementation

[0041] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments.

[0042] Unless otherwise specified, the technical means used in the following embodiments are all conventional means well known to those skilled in the art, and the experimental methods without specific conditions are all conventional methods in the art.

[0043] Unless otherwise specified, the equipment and materials used in the following embodiments are commercially available.

[0044] Example 1

[0045] This embodiment combines Figure 1 and Figure 2 The specific structure of the plasmon-enhanced carbon nanotube field emission device of the present invention will be described in detail.

[0046] like Figure 1 As shown in Figure A, the device is constructed on an insulating substrate, which is thermally oxidized silicon (SiO2 / Si), and its main function is to provide mechanical support and electrical isolation for subsequent structures.

[0047] like Figure 1 China A and Figure 2 As shown, a concentric ring metal grating is fabricated on the surface of an insulating substrate. This grating consists of multiple ring-shaped metal strips arranged around the same center with progressively increasing radii. Key structural parameters of the grating, including the period between rings and the width (duty cycle) of the metal strips, need to be precisely designed based on the target surface plasmon resonance mode to ensure wave vector matching with the incident laser of a specific wavelength, thereby efficiently exciting plasmon resonance. The number of rings in the grating can be selected between 4 and 50, and the overall grating area is typically between 10 and 10,000 μm. 2 Within the range. The metal material of the grating is selected from one or a combination of two of Au, Pd, Al, Cu, Ni, Ti, Ag, Cr, Mo, W, and Fe; when it is a combination of two, the mass ratio of the two is (0.01~100):1; the thickness of its metal layer is between 1 and 1000 nm.

[0048] like Figure 1As shown in Figure A, the anode and cathode of the device are disposed in the central region of the concentric ring metal grating. The electrodes are typically made of a combination of metals with good conductivity and adhesion, selected from one or a combination of two of the following metals: Au, Pd, Al, Cu, Ni, Ti, Ag, Cr, Mo, W, and Fe; when two metals are used, their mass ratio is (0.01~100):1; and the metal layer thickness is between 1~1000 nm. To ensure functional independence between the grating and the electrodes and to avoid short circuits, they must be electrically insulated from each other. This can be achieved in two main ways: one is to reserve an opening in the grating pattern design, allowing the electrode leads to pass through without contacting the grating ring (…). Figure 1 (A) Second, an insulating dielectric layer (not shown in the figure) is introduced between the grating and the electrode for physical isolation.

[0049] The core emitting structure of the device is a carbon nanotube thin film. This film is grown on a substrate containing the grating and electrodes using various methods such as chemical vapor deposition (CVD), deposition by immersion in a dispersion solution, spin coating, spray coating, wet transfer, dry transfer, inkjet printing, screen printing, or nano-transfer. Subsequently, the carbon nanotube thin film is precisely patterned using photolithography and etching processes (such as inductively coupled plasma etching, reactive ion etching, and oxygen plasma etching) (patterning techniques include ultraviolet exposure, deep ultraviolet exposure, electron beam writing, or nano-transfer), ensuring that it is primarily retained in the active region near the center of the grating. Figure 1 As shown in the partial SEM image of B, carbon nanotubes are randomly networked or oriented between the anode and cathode.

[0050] The most crucial structural feature is the creation of a nanoscale gap on the carbon nanotube bridging the anode and cathode using controlled Joule ablation, focused plasma (FIB) bombardment, inductively coupled plasma etching, reactive ion etching, and oxygen plasma coating techniques. For example... Figure 1 In the middle B (230 nm is the distance between the metal electrodes; after the carbon nanotube is etched or burned off, it will be partially suspended; the actual field emission gap is the distance between the tips of the carbon nanotubes, which is generally less than 100 nm) and Figure 2 As shown, the width of this gap is typically 1–100 nm. This gap forms the vacuum tunneling barrier for field emission. When the concentric ring grating is irradiated by a laser of matched wavelength, the excited surface plasmons concentrate the light energy and localize it in the central region (i.e., the gap), generating an extremely strong local electric field. This enhanced electric field acts directly on both ends of the gap in the carbon nanotubes, significantly reducing the electron tunneling barrier and thus greatly increasing the field emission current.

[0051] In summary, the device of the present invention constructs a functional unit capable of realizing plasmon-enhanced field emission through a spatial combination of a concentric ring metal grating, anode and cathode electrodes at the center, and carbon nanotube thin films with specific gaps between the electrodes. Figure 1 The SEM images confirmed the structure, particularly the successful fabrication of the carbon nanotube gaps.

[0052] Example 2

[0053] This embodiment provides a method for fabricating a plasmonic-enhanced carbon nanotube field emission device, the process of which is as follows: Figure 3 As shown, the specific steps are as follows:

[0054] (1) Fabrication of concentric ring metal gratings

[0055] A clean insulating substrate (SiO2 / Si) is provided. A pre-defined concentric ring grating pattern is defined on the substrate using electron beam lithography. Subsequently, a titanium (Ti) adhesion layer with a thickness of approximately 20 nm and a gold (Au) layer with a thickness of approximately 200 nm are sequentially deposited using electron beam evaporation. Finally, the photoresist and excess metal are removed using a lift-off process, resulting in a Ti / Au concentric ring metal grating attached to the substrate surface. The period and linewidth of the concentric rings are designed according to the target laser wavelength to achieve surface plasmon resonance; the number of rings can be up to nine, with a total area of ​​approximately 700 μm. 2 .

[0056] (2) Electrode preparation

[0057] On the same substrate where the grating has already been fabricated, electron beam lithography is used again to define the cathode and anode patterns of the device in the central region and outside the concentric rings. Electron beam evaporation of Ti (20 nm) / Au (200 nm) and a lift-off process are then used to form metal electrodes electrically isolated from the grating structure. The leads of the electrodes can be designed to extend from the gaps between the grating rings or connected through pre-reserved grating openings.

[0058] (3) Depositing and patterning carbon nanotube films

[0059] The substrate containing the grating and electrodes was immersed entirely in a diluted dispersion of semiconducting carbon nanotubes (CNTs) and allowed to stand for 2 hours to allow the carbon nanotubes to adsorb onto the substrate surface, forming a random network film of suitable density. After removal, the substrate was cleaned with an organic solvent and dried. Then, using ultraviolet lithography, a photoresist was coated and patterned as a mask on the active region of the device (covering the center of the grating and part of the electrodes). An oxygen plasma descaling machine was used to thoroughly remove the carbon nanotubes exposed outside the mask. Finally, the photoresist mask was removed with acetone-ethanol to obtain a carbon nanotube film precisely confined to the target region.

[0060] (3) Formation of carbon nanotube emission gaps

[0061] The anode and cathode of the device were connected to a semiconductor parameter analyzer using a probe station. A DC voltage, starting from zero and gradually increasing, was applied between the electrodes. When the voltage reached a certain threshold, some of the carbon nanotubes bridging the electrodes were locally ablated and broken due to the Joule heating effect, forming gaps with widths ranging from a few nanometers to tens of nanometers. By monitoring the sudden changes in current and subsequent stability, the formation of nano-gap suitable for field emission was confirmed.

[0062] At this point, the device fabrication is complete. When a laser beam with a matching wavelength shines vertically onto the concentric circular grating from above, the plasmons excited on the grating surface concentrate energy in the central region, generating an extremely strong local electric field at the gaps between the carbon nanotubes, thereby significantly enhancing the field emission current.

[0063] Example 3

[0064] This embodiment provides a method for fabricating a device variant with a buried electrode structure, aiming to further optimize the electric field distribution and device integration. The process is as follows: Figure 4 As shown, the specific steps are as follows:

[0065] (1) Preparation of buried electrodes and insulating layers

[0066] Shallow trenches are formed on an insulating substrate (SiO2 / Si) using photolithography and inductively coupled plasma etching. Next, Ti / Au (thickness can be 20 / 200 nm) is deposited within the trenches using electron beam evaporation and lift-off processes to form the underlying buried electrodes. Then, a uniformly thick (220 nm) silicon oxide (SiO2) film is grown across the entire substrate surface using plasma-enhanced chemical vapor deposition (PECVD) as both an insulating protective layer and a planarization layer.

[0067] (2) Fabrication of concentric ring gratings

[0068] On the insulating layer, a concentric ring grating pattern is defined using electron beam lithography, and the grating structure is formed by electron beam evaporation of Ti / Au (20 / 200 nm) and a lift-off process. The center of the grating must be aligned with the buried electrode below.

[0069] (3) Prepare the top contact electrode and make a hole.

[0070] Electron beam lithography is used again to define the top electrode pattern in the grating center region. First, inductively coupled plasma etching is used to etch away the silicon oxide insulating layer above the electrode pattern region, exposing the buried electrode surface below. Then, Ti / Au (10 / 100 nm) is deposited by electron beam evaporation and a lift-off process to form the top anode and cathode electrodes that are in direct electrical contact with the buried electrode.

[0071] (4) Depositing and patterning carbon nanotube films

[0072] A carbon nanotube (CNT) film was deposited on the device surface using the same method as step (3) in Example 1 (dispersion immersion deposition). Subsequently, the carbon nanotube film was patterned by photolithography and oxygen plasma etching, defining the area covering the center of the grating and the top electrode.

[0073] (5) Formation of carbon nanotube emission gaps

[0074] Using the same Joule thermal ablation method as step (4) in Example 1, nano-gap was formed in the carbon nanotube film between the top anode and cathode.

[0075] The buried electrode structure in this embodiment is beneficial for creating a more concentrated electric field in the vertical direction, while also enabling higher planar integration of the device and more flexible electrode lead design.

[0076] Test Example 1

[0077] The device prepared in Example 2 above was subjected to photoelectric testing, and the testing method is as follows:

[0078] In a probe station and vacuum environment, a scanning voltage was applied between the anode and cathode of the device using a semiconductor parameter analyzer, and the field emission current was measured simultaneously. The current-voltage (IV) characteristic curves were measured under both no laser illumination (dark condition) and with vertical illumination of the grating region using a laser wavelength matched to the grating design (light condition). The IV characteristic test results of the device are as follows: Figure 5 As shown, the specific analysis is as follows:

[0079] (1) Plasmon effect significantly reduces field emission turn-on voltage

[0080] Under dark conditions, the field emission current of the device only begins to be detected at approximately 6 V (approximately 0.25 × 10⁻⁶). -4 A). Under laser-induced plasmon excitation (Light) conditions, measurable field emission currents appear at approximately 5 V (approximately 0.25 × 10⁻⁶). -4 A). This indicates that the plasmon enhancement effect reduces the effective field emission turn-on voltage of the device by approximately 1 V. This directly proves that the locally enhanced electric field excited by the concentric circular grating structure effectively reduces the external electrical threshold required for electron tunneling, achieving low-voltage start-up, which is of great significance for reducing device power consumption.

[0081] (2) Plasmon effect significantly increases field emission current

[0082] Comparing under the same 9 V operating voltage, the dark field current is 1.27 × 10⁻⁶. -4 A, while the emission current under illumination reaches 2.5 × 10⁻⁶. -4 A. Illumination conditions increased the device's output current to approximately twice that under dark conditions, quantitatively demonstrating the multiplication effect of plasmon enhancement on field emission current. Particularly noteworthy is the steeper upward slope of the current curve after 6 V under illumination conditions, indicating a synergistic effect between photo-induced plasmon enhancement and the applied electric field in the high electric field region, further amplifying the performance improvement.

[0083] (3) The device has excellent photoelectric control characteristics.

[0084] Significant and systematic differences exist in the IV curves under both illuminated and dark conditions across the entire test voltage range. The device's output current can be effectively modulated by the incident light, exhibiting a clear photoelectric response. Particularly in the 5 V to 7 V voltage range, the device exhibits "photo-activated" characteristics; while at higher voltages, it exhibits "photo-induced gain" characteristics. This characteristic makes the device not only a high-performance field emission electron source but also a highly sensitive photoelectric signal conversion unit with significant modulation depth.

[0085] The experimental results of this test example show that the plasmon-controlled carbon nanotube field emission device with concentric circular grating structure provided by the present invention can effectively excite plasmons through optical signals, thereby significantly reducing the turn-on voltage, multiplying the emission current, and exhibiting good optoelectronic modulation capabilities. It is expected to be applied in fields such as field emission enhancement, optical signal detection, and optoelectronic modulation.

[0086] The embodiments described above are only some, not all, of the embodiments of the present invention. The detailed description of the embodiments of the present invention is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments. The scope of protection of the present invention is determined by the scope claimed in the claims. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

Claims

1. A carbon nanotube field emission device enhanced by plasmon resonance, characterized in that, include: Insulating substrate; A concentric ring metal grating located on the insulating substrate, the concentric ring metal grating being composed of at least four ring metal structures with different radii; Anode and cathode located on the insulating substrate and in the central region of the concentric circular metal grating; A carbon nanotube film is located in the substrate region where the concentric ring metal grating and the anode and cathode are located, and the carbon nanotube film forms an emission gap of 1~100 nm between the anode and cathode. The period and duty cycle of the concentric ring metal grating are matched with the wavelength of the laser source to excite surface plasmons and generate a local electric field enhancement in the central region.

2. The plasmon-enhanced carbon nanotube field emission device according to claim 1, characterized in that, The number of concentric ring metal gratings is 4 to 50, and the grating area is 10 to 10,000 μm. 2 The concentric ring metal grating has an opening, or is electrically isolated from the anode and cathode through an insulating dielectric layer.

3. The plasmon-enhanced carbon nanotube field emission device according to claim 1, characterized in that, The materials of the concentric ring metal grating and the anode and cathode are independently selected from one or a combination of two of Au, Pd, Al, Cu, Ni, Ti, Ag, Cr, Mo, W, and Fe; when there are two combinations, the mass ratio of the two is (0.01~100):1; the thickness of the metal layer of the concentric ring metal grating and the anode and cathode is 1~1000 nm.

4. The plasmon-enhanced carbon nanotube field emission device according to claim 1, characterized in that, The positive and negative electrodes are buried electrode structures; The buried electrode structure includes: a lower electrode deposited on the insulating substrate, an insulating dielectric layer covering the lower electrode and part of the substrate, and a top electrode formed in the insulating dielectric layer and electrically connected to the lower electrode; The concentric ring metal grating is disposed on the insulating dielectric layer, and its central region corresponds to the position of the top electrode; The carbon nanotube film is bridged between the top electrodes and forms the emission gap.

5. A method for fabricating a carbon nanotube field emission device as described in any one of claims 1-4, characterized in that, Includes the following steps: Step 1) Define a concentric ring grating pattern on an insulating substrate, deposit and pattern a metal layer to form a concentric ring metal grating; Step 2) Define an electrode region on the insulating substrate, deposit and pattern a metal layer to form anode and cathode electrodes located in the central region of the concentric ring metal grating, and ensure that the concentric ring metal grating and the anode and cathode electrodes are electrically insulated. Step 3) Deposit a carbon nanotube film on the substrate containing the concentric ring metal grating and the anode and cathode, define the active region pattern, and remove the carbon nanotube film outside the active region. Step 4) Break the carbon nanotubes suspended between the anode and cathode to form carbon nanotube gaps.

6. The preparation method according to claim 5, characterized in that, The order of step 1) and step 2) can be interchanged.

7. The preparation method according to claim 5, characterized in that, Step 3) The method for depositing carbon nanotube thin films is selected from chemical vapor deposition on-sheet growth, dispersion immersion deposition, spin coating, spray coating, wet transfer, dry transfer, inkjet printing, screen printing or nano-transfer. The method for removing the carbon nanotube film outside the active region is inductively coupled plasma etching, reactive ion etching, or oxygen plasma ashing.

8. The preparation method according to claim 5, characterized in that, In steps 1), 2), and 3), the pattern definition technology employs ultraviolet exposure, deep ultraviolet exposure, electron beam writing, or nanoprinting.

9. The preparation method according to claim 5, characterized in that, In step 4), the method for breaking the gaps formed by carbon nanotubes is Joule thermal ablation, focused ion beam bombardment, inductively coupled plasma etching, reactive ion etching, or oxygen plasma ashing.

10. The application of the carbon nanotube field emission device as described in any one of claims 1-4 in field emission enhancement, optical signal detection, or photoelectric modulation.

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