A method for fabricating single-molecule devices based on all-vapor phase oxidative etching

Abstract

This invention relates to the field of single-molecule electronic device fabrication technology, and provides a method for fabricating single-molecule devices based on all-vapor phase oxidative etching. The method employs etching with oxidizing gases such as carbon dioxide, oxygen, water vapor, and air. Compared to solution oxidation methods, this eliminates the introduction of impurities such as oxidants and solvents, improving the cleanliness of the single-molecule device. Simultaneously, the highly chemically active electrode edges are oxidized during etching, enabling them to covalently connect with redox-effect terpyridine-metal complexes via amide bonds. This significantly improves the structure and stability of the single-molecule device based on all-vapor phase oxidative etching, exhibiting excellent testing and cycling stability.

Description

Technical Field

[0001] This invention relates to the field of single-molecule electronic device fabrication technology, and in particular to a method for fabricating single-molecule devices based on all-vapor phase oxidative etching. Background Technology

[0002] The core of single-molecule device fabrication technology lies in the preparation of electrodes with nanoscale gaps. Currently, the most widely used technologies include scanning probe microanalysis (SPI), mechanically controlled split junction fabrication (MCS), electromigration split junction fabrication (EMS), and nanoelectrode technology. SPI is a typical method for constructing single-molecule heterojunctions, but the geometric configuration of single-molecule devices limits their compatibility with traditional CMOS systems, hindering their integration and application. Similarly, mechanically controlled split junction fabrication remains only suitable for fundamental theoretical research, making it difficult to achieve mass production and high-density integration, and it cannot construct single-molecule devices with three or more terminals. The challenge of EMS lies in the thermal effect during electromigration, which can cause a localized increase in the temperature of the metal wire, leading to melting and making it difficult to control the spacing and configuration of the nanoelectrodes. Furthermore, the electromigration process may generate metal debris around the formed nanoelectrodes, hindering subsequent molecular connections and interfering with the measurement of the electrical properties of the molecular heterojunction. Therefore, new single-molecule device fabrication technologies are needed.

[0003] Graphene electrodes possess advantages such as stable properties, stable molecular-electrode connections, a single and controllable interface coupling mode, and ease of integration. Solution oxidation etching is currently a commonly used method for preparing graphene electrodes. However, the intense etching effect of oxygen plasma makes the etching process uncontrollable, making it difficult to control the gap and edge configuration of graphene electrode pairs. Furthermore, it can introduce oxidants or solvent impurities, resulting in insufficient cleanliness of single-molecule devices, thereby affecting their performance. Summary of the Invention

[0004] The present invention aims to at least solve one of the technical problems existing in related technologies. To this end, the present invention provides a method for fabricating single-molecule devices based on all-vapor phase oxidative etching, comprising the following steps:

[0005] S1: Fabrication of graphene layer electrodes on a substrate;

[0006] S2: Fabrication of graphene source electrode and graphene drain electrode on graphene layer electrode;

[0007] S3: Perform oxygen plasma pre-etching and hydrogen plasma forward etching on the graphene source electrode and graphene drain electrode to obtain triangular graphene electrode pairs.

[0008] S4: Etching the triangular graphene electrode pair with an oxidizing gas to obtain a triangular graphene electrode pair containing carboxyl functional groups;

[0009] S5: Construct single-molecule devices on triangular graphene electrode pairs containing carboxyl functional groups.

[0010] According to the present invention, a method for fabricating a single-molecule device based on all-vapor phase oxidative etching is provided, wherein step S1 includes the following steps:

[0011] S11: The substrate is immersed in a mixed solution of hydrogen peroxide and concentrated sulfuric acid to obtain a first film. After ultrasonic cleaning, a first marking pattern is made on the first film to obtain a second film. Photoresist is spin-coated on the second film, and a second marking pattern is prepared on an ultraviolet exposure machine. The first marking pattern and the second marking pattern are completely identical and correspondingly set.

[0012] The substrate includes one of silicon wafer, sapphire, silicon carbide, boron nitride, or mica;

[0013] S12: The second film is placed under the mask of the UV exposure machine for UV exposure to cure the photoresist into a film and obtain the third film. The third film is placed in the developing solution to immerse the photoresist film on the third film to reveal the third marking pattern. The third marking pattern is fixed and completely overlaps with the first marking pattern.

[0014] S13: The third marking pattern on the third film is deposited with gold in a thermal resistance evaporation coating instrument. After cooling, a fourth film is obtained. The fourth film is immersed in acetone solution and the photoresist film is peeled off to obtain a fifth film.

[0015] S14: Adhere the graphene sheet to Scotch transparent tape to obtain graphene tape. Tightly attach the fifth film and the graphene tape to the glass slide. After standing, remove the graphene tape to obtain the graphene layer electrode.

[0016] According to the present invention, a method for fabricating a single-molecule device based on all-vapor phase oxidative etching is provided, wherein step S2 includes the following steps:

[0017] S21: Spin-coat the graphene layer electrode with a double layer of photoresist and place the graphene electrode on a heating plate to obtain the first graphene electrode;

[0018] S22: Expose the first graphene electrode in an electron beam exposure system to obtain a second graphene electrode; develop the second graphene electrode in a developing solution; further, fix the second graphene electrode in a fixing solution to obtain a third graphene electrode.

[0019] S23: The third graphene electrode is placed on a thermal resistance evaporation coating instrument for gold deposition. After cooling, a fourth graphene electrode is obtained. The fourth graphene electrode is immersed in an acetone solution and the double-layer photoresist film is peeled off to obtain the graphene source electrode and the graphene drain electrode.

[0020] According to the present invention, a method for fabricating a single-molecule device based on all-vapor phase oxidative etching is provided, wherein step S3 includes the following steps:

[0021] S31: Process the graphene source electrode and the graphene drain electrode according to steps S21 and S22 respectively to obtain the first graphene electrode pair;

[0022] S32: The first graphene electrode pair is placed in an oxygen plasma etching system for pre-etching to obtain the second graphene electrode pair;

[0023] S33: Immerse the second graphene electrode pair in an acetone solution, peel off the photoresist film, and obtain the third graphene electrode pair;

[0024] S34: Process the third graphene electrode pair according to step S31 to obtain the fourth graphene electrode pair, and place the fourth graphene electrode pair in a hydrogen plasma etching system for positive etching to obtain the fifth graphene electrode pair.

[0025] S35: The fifth graphene electrode pair is processed according to step S33 to obtain a triangular electrode pair.

[0026] According to the present invention, a method for fabricating a single-molecule device based on all-vapor phase oxidative etching is provided, wherein step S5 includes the following steps:

[0027] The terpyridine-metal complex and dehydrating agent are added to the solvent and stirred to obtain a mixed solution. The triangular graphene electrode pair with carboxyl functional groups is placed in the mixed solution and allowed to stand in an inert gas for 24-48 hours to carry out the reaction and obtain a single-molecule device.

[0028] The dehydrating agent is at least one of N,N'-dicyclohexylcarbodiimide, N,N'-diisopropylcarbodiimide, or 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride;

[0029] The solvent is at least one of pyridine, trichlorobenzene, N,N-dimethylformamide or dimethyl sulfoxide;

[0030] The inert gas is argon or nitrogen.

[0031] According to the present invention, a method for fabricating a single-molecule device based on all-vapor phase oxidative etching is provided, wherein the triangular graphene electrode pair containing carboxyl functional groups includes a graphene source electrode with oxygen-containing functional groups and a graphene drain electrode with oxygen-containing functional groups.

[0032] According to the present invention, a method for fabricating a single-molecule device based on all-vapor phase oxidative etching is provided, wherein the terpyridine-metal complex is as shown in Formula 1:

[0033] H2N-R2-R1-R2-NH2

[0034] Formula 1

[0035] Among them, R1 includes

[0036] One of them;

[0037] R2 includes

[0038] According to the present invention, a method for fabricating a single-molecule device based on all-vapor phase oxidative etching is provided, wherein the terpyridine-metal complex comprises

[0039]

[0040]

[0041] One of them.

[0042] The above-described one or more technical solutions in the embodiments of the present invention have at least one of the following technical effects:

[0043] This invention provides a method for fabricating single-molecule devices based on all-vapor phase oxidative etching. Employing etching with oxidizing gases such as carbon dioxide, oxygen, water vapor, and air, this method eliminates the introduction of impurities like oxidants and solvents compared to solution oxidation methods, thus improving the cleanliness of the single-molecule device. Simultaneously oxidizing the chemically active electrode edges during etching allows them to covalently link with redox-effect terpyridine-metal complexes via amide bonds. This significantly enhances the structure and stability of the single-molecule device based on all-vapor phase oxidative etching, exhibiting excellent testing and cycling stability.

[0044] Additional aspects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Attached Figure Description

[0045] To more clearly illustrate the technical solutions in this invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0046] Figure 1 This is a scanning tunneling electron microscopy image of a triangular electrode pair after being etched by oxygen oxidation.

[0047] Figure 2 This is the Raman spectrum of the original graphene sample.

[0048] Figure 3 The image shows the Raman spectrum of the triangular electrode pair before it was etched by oxygen oxidation.

[0049] Figure 4 The X-ray photoelectron spectrum of the triangular electrode pair after being etched by oxygen oxidation.

[0050] Figure 5 The image shows the Raman spectrum of a triangular electrode pair after being oxidized and etched by carbon dioxide.

[0051] Figure 6 The X-ray photoelectron spectrum of the triangular electrode pair after being oxidized by carbon dioxide.

[0052] Figure 7 The image shows the Raman spectrum of the triangular electrode pair after being etched by water vapor oxidation.

[0053] Figure 8 The X-ray photoelectron spectrum of the triangular electrode pair after being oxidized by water vapor.

[0054] Figure 9 The curves showing the variation of IV properties with temperature after connecting target molecules between triangular graphene electrode pairs are presented. Detailed Implementation

[0055] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention. The following embodiments are used to illustrate this invention but should not be used to limit the scope of this invention.

[0056] In the description of the embodiments of the present invention, it should be noted that the terms "center," "longitudinal," "lateral," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing the embodiments of the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the embodiments of the present invention. In addition, the terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0057] In the description of the embodiments of the present invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "connected" and "linked" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium. Those skilled in the art can understand the specific meaning of the above terms in the embodiments of the present invention based on the specific circumstances.

[0058] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., refer to specific features, structures, materials, or characteristics described in connection with that embodiment or example, which are included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0059] The following is combined with Figures 1 to 9 The present invention describes a method for fabricating single-molecule devices based on all-vapor phase oxidative etching:

[0060] This invention provides a method for fabricating single-molecule devices based on all-vapor phase oxidative etching, comprising the following steps:

[0061] S1: Fabrication of graphene layer electrodes on a substrate;

[0062] S2: Fabrication of graphene source electrode and graphene drain electrode on graphene layer electrode;

[0063] S3: Perform oxygen plasma pre-etching and hydrogen plasma forward etching on the graphene source electrode and graphene drain electrode to obtain triangular graphene electrode pairs.

[0064] S4: Etching the triangular graphene electrode pair with an oxidizing gas to obtain a triangular graphene electrode pair containing carboxyl functional groups;

[0065] S5: Construct single-molecule devices on triangular graphene electrode pairs containing carboxyl functional groups.

[0066] The oxidizing gas includes any one of carbon dioxide, oxygen, water vapor, or air.

[0067] According to the present invention, a method for fabricating a single-molecule device based on all-vapor phase oxidative etching is provided, wherein step S1 includes the following steps:

[0068] S11: The substrate is immersed in a mixed solution of hydrogen peroxide and concentrated sulfuric acid to obtain a first film. After ultrasonic cleaning, a first marking pattern is made on the first film to obtain a second film. Photoresist is spin-coated on the second film, and a second marking pattern is prepared on an ultraviolet exposure machine. The first marking pattern and the second marking pattern are completely identical and correspondingly set.

[0069] The substrate includes one of silicon wafer, sapphire, silicon carbide, boron nitride, or mica;

[0070] S12: The second film is placed under the mask of the UV exposure machine for UV exposure to cure the photoresist into a film and obtain the third film. The third film is placed in the developing solution to immerse the photoresist film on the third film to reveal the third marking pattern. The third marking pattern is fixed and completely overlaps with the first marking pattern.

[0071] S13: The third marking pattern on the third film is deposited with gold in a thermal resistance evaporation coating instrument. After cooling, a fourth film is obtained. The fourth film is immersed in acetone solution and the photoresist film is peeled off to obtain a fifth film.

[0072] S14: Adhere the graphene sheet to Scotch transparent tape to obtain graphene tape. Tightly attach the fifth film and the graphene tape to the glass slide. After standing, remove the graphene tape to obtain the graphene layer electrode.

[0073] In one embodiment, a silicon wafer (approximately 1cm × 1cm in size) with a 300nm silicon dioxide layer on its surface is immersed in a mixed solution of 30% hydrogen peroxide and concentrated sulfuric acid for 4 hours to remove the oxide layer on the surface of the silicon wafer. The volume ratio of 30% hydrogen peroxide to concentrated sulfuric acid is approximately 3:7. The immersed silicon wafer is then placed in deionized water for ultrasonic cleaning three times, 10 minutes each time. A cross mark is made on the cleaned silicon surface to facilitate the location of the loaded graphene in subsequent operations.

[0074] Further, a cross pattern was fabricated using a 365nm ultraviolet exposure machine. AR-P5350 ALLRESIST photoresist was spin-coated onto the silicon wafer surface at approximately 4000 rpm for about 45 seconds. To allow the photoresist to solidify, the silicon wafer was heated on a hot plate for 2 minutes. The silicon wafer was then placed under the mask with the cross pattern for ultraviolet exposure for 20 seconds. After exposure, the wafer was immersed in a developer solution (AR 300-36 solution mixed with deionized water at a ratio of approximately 7:1) for 20 seconds. The wafer was then fixed in deionized water for 10 seconds, resulting in the cross pattern on the photoresist film.

[0075] Furthermore, gold is deposited onto the cross pattern on the silicon wafer in a thermal resistance evaporation coating apparatus. Under the protection of the photoresist film, only the areas marked with the cross pattern on the silicon wafer are deposited with gold, while other areas on the silicon wafer are not deposited with gold. During the gold deposition, the gold penetrates the photoresist film, forming a firm gold cross mark on the silicon wafer.

[0076] Furthermore, firstly, 8nm of chromium is deposited on the silicon wafer to facilitate better adhesion of the gold. Then, the evaporation mode is switched to deposit 50nm of gold on the silicon wafer. After the deposition is complete, the wafer is cooled, removed, and then immersed in acetone solution to peel off the photoresist film from the wafer. At this point, only the firmly deposited gold "+" mark remains on the wafer. The silicon wafer with the gold mark is then cleaned sequentially with isopropanol solution, acetone solution, deionized water, and ethanol, each cleaning time being approximately 10 minutes. Afterward, the surface of the silicon wafer is dried with nitrogen gas for later use.

[0077] Further, select a Kish graphene sheet (commercially available) with a length of about 2-3 mm and stick it to the center of a Scotch transparent tape with a length of about 8 cm. Fold the tape in half repeatedly about 13 times in the center to distribute the Kish graphene sheet evenly on the tape. Then stick the tape onto the silicon wafer that has been treated above. Stretch the silicon wafer and the tape tightly onto the glass slide and let it stand for about 2-3 hours to allow the silicon dioxide substrate on the silicon wafer and the graphene to adhere tightly together through van der Waals forces. After that, remove the silicon wafer from the tape.

[0078] Furthermore, the silicon wafer with graphene attached was placed in an optical microscope to find graphene layer electrodes containing three graphene sheets of suitable size for subsequent experimental preparation, and the positions of the gold "+" marks corresponding to each graphene layer electrode were recorded for rapid positioning in the subsequent preparation process.

[0079] According to the present invention, a method for fabricating a single-molecule device based on all-vapor phase oxidative etching is provided, wherein step S2 includes the following steps:

[0080] S21: Spin-coat the graphene layer electrode with a double layer of photoresist and place the graphene electrode on a heating plate to obtain the first graphene electrode;

[0081] S22: Expose the first graphene electrode in an electron beam exposure system to obtain a second graphene electrode; develop the second graphene electrode in a developing solution; further, fix the second graphene electrode in a fixing solution to obtain a third graphene electrode.

[0082] S23: The third graphene electrode is placed on a thermal resistance evaporation coating instrument for gold deposition. After cooling, a fourth graphene electrode is obtained. The fourth graphene electrode is immersed in an acetone solution and the double-layer photoresist film is peeled off to obtain the graphene source electrode and the graphene drain electrode.

[0083] In one embodiment, the gold cross mark on the selected graphene electrode is photographed and saved under an optical microscope. The image may exhibit slight distortion during the photographing process, requiring correction of angles and other parameters. A self-developed program in MATLAB software corrects the displacement, rotation, and other parameters of the saved image. The corrected image is then imported into AutoCAD software to draw the cross mark pattern. The size of the drawn pattern matches the actual cross mark size on the exposure electrode. After the pattern design is complete, the etching process begins.

[0084] Furthermore, a double layer of photoresist, model 495K, was spin-coated onto a silicon wafer containing a three-layer graphene layer with a gold "+" mark. The silicon wafer was held in place on the spin coater tray using a vacuum method. During spin coating, a 3-second pre-rotation mode at approximately 650 rpm was first set, followed by a 45-second forward rotation mode at approximately 4000 rpm, to ensure more uniform photoresist distribution. The silicon wafer was then removed and placed on a heating plate to bake at 180°C for 2 minutes. After the photoresist had solidified, the spin coating process was repeated, but this time the second spin coating used a 950K photoresist.

[0085] Furthermore, the silicon wafer covered with double-layer adhesive was exposed using an electron beam exposure system. The electron beam exposure parameters were set as follows: beam voltage 25kV, beam current 1nA, and electron beam dose 600uC / cm. 2 Based on the drawn cross mark pattern, the cross mark on the silicon wafer is exposed in an electron beam exposure system. After exposure, the photoresist on the silicon wafer is developed for 40 seconds using a solution of isopropanol and methyl isobutyl ketone (Methyl isobutyl ketone), with a volume ratio of approximately 3:1:1. The silicon wafer is then fixed in an isopropanol solution for 20 seconds. Afterward, an appropriate amount of deionized water is used to rinse the surface of the silicon wafer several times to remove any remaining organic solution, and the silicon wafer is dried using a nitrogen stream.

[0086] Further, the dried silicon wafer is fixed in a thermal resistance evaporation coating apparatus. A chromium wire is heated to evaporate chromium metal onto the silicon wafer, with a thickness of approximately 8 nm. Then, the evaporation mode is switched, and a gold ingot is heated to evaporate gold metal onto the silicon wafer, with a thickness of approximately 50 nm. After evaporation and cooling, the silicon wafer is removed and immersed in acetone solution to peel off the photoresist film. At this point, a gold electrode layer appears on the electrode containing three graphene layers on the gold "+" mark, resulting in a stable graphene source electrode and a graphene drain electrode covered by the gold electrode layer.

[0087] According to the present invention, a method for fabricating a single-molecule device based on all-vapor phase oxidative etching is provided, wherein step S3 includes the following steps:

[0088] S31: Process the graphene source electrode and the graphene drain electrode according to steps S21 and S22 respectively to obtain the first graphene electrode pair;

[0089] S32: The first graphene electrode pair is placed in an oxygen plasma etching system for pre-etching to obtain the second graphene electrode pair;

[0090] S33: Immerse the second graphene electrode pair in an acetone solution, peel off the photoresist film, and obtain the third graphene electrode pair;

[0091] S34: Process the third graphene electrode pair according to step S31 to obtain the fourth graphene electrode pair, and place the fourth graphene electrode pair in a hydrogen plasma etching system for positive etching to obtain the fifth graphene electrode pair.

[0092] S35: The fifth graphene electrode pair is processed according to step S33 to obtain a triangular electrode pair.

[0093] Due to the difficulty in controlling the size and synthesis volume of graphene, constructing graphene devices with specific edge configurations is relatively challenging. Chemical etching methods for fabricating nanoscale graphene devices offer advantages such as mild reaction conditions and no byproducts. Furthermore, chemical etching of graphene exhibits good compatibility with micro / nano fabrication processes and is widely used. The fabrication of graphene electrodes primarily employs micro / nano fabrication methods such as optical exposure and electron beam exposure, combined with reactive gas etching. Depending on the properties of the gas, various etching schemes can be developed. This invention provides a gas-phase oxidative etching scheme for graphene.

[0094] The principle of graphene oxidative etching is based on the oxidation reaction of carbon atoms at high temperatures, which generates gases such as carbon monoxide and carbon dioxide. Simultaneously, the graphene lattice structure is disrupted, forming pores. The oxidative etching scheme for graphene provided by this invention can create regularly shaped hexagonal graphene etching pores at specific temperatures. As two adjacent etching pores gradually enlarge, triangular electrode pairs are formed. Further etching creates atomic-scale gaps between the triangular electrode pairs, providing further sites for molecular bonding reactions. However, to ensure precise alignment of the apexes of the triangular electrode pairs, the lattice orientation of the graphene etching needs to be known in advance. Using the known lattice orientation, artificial defects with the same lattice orientation are designed and fabricated within the graphene source / drain electrode channels. These introduced defect pores within the source / drain electrodes, after etching with oxidizing gas, can form perfectly aligned point-aligned electrode pairs within the channels.

[0095] In one embodiment, the process of obtaining the lattice orientation of the etched graphene in advance is called the pre-etching stage, and its specific process is as follows:

[0096] A clear "+" mark pattern on a selected three-layer graphene silicon wafer was photographed and saved under a high-magnification objective lens (100x) of an optical microscope. The image exhibited slight distortion during the photographing process, requiring correction of angles and other parameters. A self-developed program in MATLAB software was used to correct parameters such as displacement and rotation of the saved image. The corrected image was then imported into AutoCAD software to draw the "+" mark pattern. The size of the drawn pattern matched the actual "+" mark size on the exposure electrode. In the exposure software DY2000A, a circular array of holes containing pre-etched reaction defect sites was drawn, and the exposure area and sequence were selected sequentially. After the pattern design was completed, the etching process began.

[0097] Furthermore, the sample area with graphene source and drain electrodes was spin-coated with 495K photoresist according to the operation steps of the above embodiment. After the 495K photoresist was fixed into a film, the sample area was placed in an electron beam exposure system for exposure. The electron beam exposure parameters were set as follows: beam voltage 30kV, beam current 0.12nA, and electron beam dose 400uC / cm. 2 .

[0098] Further, based on the drawn cross-shaped marking pattern, the corresponding pre-etched cross-shaped marking pattern and circular hole array are exposed on the photoresist. The photoresist on the sample area is developed for 30 seconds using a solution of isopropanol and methyl isobutyl ketone (mixing volume ratio approximately 3:1). The silicon wafer with the sample is then placed in the isopropanol solution for fixing for 10 seconds. Afterwards, an appropriate amount of deionized water is used to rinse the surface of the silicon wafer several times to remove any residual organic solution, and then it is dried using a nitrogen stream. At this point, the photoresist on the exposed cross-shaped marking pattern and circular hole areas has disappeared, but photoresist remains in other areas of the electrode. It is necessary to remove the graphene within these cross-shaped marking patterns and holes to provide reaction sites for artificially introduced defects.

[0099] Further, the dried graphene electrode pair was placed in an oxygen plasma etching system for initial etching of the reaction sites. The vacuum level for the initial etching was maintained below 3 Pa, and an appropriate amount of oxygen was introduced into the system to control the gas pressure at around 15 Pa. The etching power was set to 50 W, and the etching time was 25 s. Afterward, the pre-etched graphene electrode pair was immersed in an appropriate amount of acetone solution to peel the photoresist film off the graphene electrode pair. The organic solution on the surface of the graphene electrode pair was then repeatedly rinsed with deionized water to remove it for later use.

[0100] Furthermore, the graphene silicon wafer with circular hole defects initially fabricated using an oxygen plasma etching system is placed into a remote oxidizing vapor phase plasma etching system. By setting appropriate etching conditions, hexagonal patterns can be gradually etched onto the circular holes. When defects exist on the graphene surface, the etching reaction will preferentially etch hexagonal patterns at the edges of the defects; it is more difficult to form this etching phenomenon in areas without defects.

[0101] Taking pure oxygen etching as an example, different etching behaviors can occur with temperature: oxygen etching of pores in multilayer graphene usually occurs at temperatures above 600℃. When the etching temperature is between 600-745℃, the etching rate of the graphene armchair edge is relatively high, causing the pore edges of the graphene to exhibit a zigzag configuration, and the graphene pores gradually transform into regular hexagons. When the temperature is greater than 745℃, the competitive etching between the zigzag edge and the armchair edge configuration results in a higher etching rate for the zigzag edge, making the etched pores appear approximately circular.

[0102] The etching system employs a passive inductive coupling method, where a radio frequency power supply provides a high-frequency alternating electric field. This electric field can induce oxygen atoms to ionize, thus forming a mixed state of oxygen atoms, oxygen ions, and electrons within the reaction zone. Oxygen atoms are the active material in this etching reaction.

[0103] Furthermore, the etching temperature was set to approximately 700℃, and the etching distance was set to approximately 48cm (the distance between the center of the silicon wafer and the center of the glow discharge). Before etching, oxygen was repeatedly introduced into the cavity to clean it. The oxygen flow rate was set to 10 sccm, the etching power to 50W, and the etching was performed for 30 minutes. After that, the etching power was turned off, and the silicon wafer was removed when the cavity temperature dropped to room temperature.

[0104] The pre-etched hexagonal pattern is characterized in the SEM imaging system. The SEM image is then imported into AutoCAD software. The angle measurement tool in the software is selected to measure the angle of the hexagon multiple times and take the average angle value. The obtained average angle value is the lattice direction of the hexagonal hole.

[0105] In one embodiment, the specific steps of hydrogen plasma positive etching are as follows:

[0106] Based on the lattice orientation of the graphene hexagonal pores determined by pre-etching, the pre-etching step is repeated to etch several circular pores aligned with the lattice orientation of the graphene hexagonal pores in an oxygen plasma system. Then, the graphene silicon wafer with the circular pores is placed in a remote hydrogen plasma etching system, and the corresponding etching conditions are set: a temperature of approximately 700℃ and an etching distance of approximately 48 cm, to etch standard hexagonal patterns onto the circular pores.

[0107] However, since there will be an unavoidable error between the set hole size and the hole size after development, the specific hole size after development is uncertain. It is impossible to infer the precise size of the gap by the subsequent etching rate of graphene by hydrogen plasma. Multiple etching methods can be used to avoid the problem of the gap of the triangular electrode pair being too small or too large after etching.

[0108] Furthermore, during the first etching, circular holes can be etched into hexagonal holes, with a certain spacing between adjacent hexagonal vertices. During the second etching, the hexagonal vertices intersect, creating gaps, at which point the graphene electrode pair transforms into a triangular electrode pair. This process continues, with each etching process gradually increasing the gap size. By controlling the corresponding etching time, triangular electrode pairs with sizes corresponding to the molecular dimensions can be obtained.

[0109] The precise gap size can be obtained through theoretical calculations. Theoretically, the current through the electrodes can be estimated using Simmons fitting. This current is generated by applying a certain bias voltage, causing electrons on one electrode to tunnel to the other. The magnitude of this current is a function of the electrode spacing, satisfying the following equation:

[0110]

[0111] Where I is the current, d is the gap spacing, e is the electron charge, A is the electron tunneling area, and V is the bias voltage. The size of the vacuum barrier, Here, m is the reduced Planck constant, and m is the electron mass.

[0112] In the experiment, a certain bias voltage was applied to the gold electrodes at both ends of the graphene electrode pair, and the corresponding current value was measured. This current value was then compared with the fitted and estimated current value to deduce the corresponding gap size of the graphene electrode pair. Electrode pairs with different gap sizes can be designed using this equation.

[0113] In one embodiment, the specific steps of step S4 are as follows:

[0114] It should be noted that after constructing triangular electrode pairs with molecular sizes, carboxyl functional groups are oxidized and modified on the edges of the triangular electrode pairs by gas-phase oxidation to obtain triangular graphene electrode pairs containing carboxyl functional groups. Then, amide condensation reaction is used to connect the terpyridine-metal complex with amino-terminated molecules to the terminal sites of the triangular graphene electrode pairs containing carboxyl functional groups to form amide covalent bonds. This connection method is stable and strong.

[0115] Since graphene is composed of carbon, the carboxyl functional groups constructed at the edges of the triangular electrode pair can be modified by etching with an oxidizing gas, which can include any one of carbon dioxide, oxygen, water vapor or air.

[0116] Following the above operating steps, place the triangular electrode pair in the oxygen oxidizing etching system for etching: According to Figure 1 It can be seen that after oxygen oxidative etching, the oxygen etching rate at the edge of the armchair is more dominant, and the edge of the etched hole is formed by a zigzag configuration, thus ultimately producing a hexagonal etched hole. Figure 2 The Raman spectrum of the original graphene sample is compared. Figure 2 ,from Figure 3 It can be seen that after oxygen oxidative etching, the Raman spectrum of graphene is at 1350 cm⁻¹. -1 The presence of defect characteristic peaks at the location indicates that the graphene has been functionalized with carboxyl groups after oxygen oxidative etching; through Figure 4 It can be seen that the photoelectron spectrum of graphene after oxygen oxidative etching shows significant binding energy peaks corresponding to carboxyl chemical bonds, further proving that graphene has been functionalized by carboxyl groups.

[0117] In one embodiment, following the above operating steps, the triangular electrodes are placed in a carbon dioxide oxidizing etching system for etching: (Comparison) Figure 2 ,from Figure 5 It can be seen that after carbon dioxide oxidative etching, the Raman spectrum of graphene is at 1350 cm⁻¹. -1 The presence of defect characteristic peaks at the location indicates that the graphene has been functionalized with carboxyl groups after carbon dioxide oxidative etching; through Figure 6 It can be seen that the photoelectron spectrum of graphene after carbon dioxide oxidative etching shows significant binding energy peaks corresponding to carboxyl chemical bonds, which significantly proves that graphene has been functionalized by carboxyl groups.

[0118] In one embodiment, following the above operating steps, the triangular electrodes are placed in a water vapor oxidizing etching system for etching: (Comparison) Figure 2 ,from Figure 7 It can be seen that after water vapor oxidative etching, the Raman spectrum of graphene is at 1350 cm⁻¹. -1 The presence of defect characteristic peaks at the location indicates that the graphene has been functionalized with carboxyl groups after water vapor oxidative etching; through Figure 8 It can be seen that the photoelectron spectrum of graphene after water vapor oxidative etching shows significant binding energy peaks corresponding to carboxyl chemical bonds, which significantly proves that graphene has been functionalized by carboxyl groups.

[0119] According to the present invention, a method for fabricating a single-molecule device based on all-vapor phase oxidative etching is provided, wherein step S5 includes the following steps:

[0120] The terpyridine-metal complex and dehydrating agent are added to the solvent and stirred to obtain a mixed solution. The triangular graphene electrode pair with carboxyl functional groups is placed in the mixed solution and allowed to stand in an inert gas for 24-48 hours to carry out the reaction and obtain a single-molecule device.

[0121] The dehydrating agent is at least one of N,N'-dicyclohexylcarbodiimide, N,N'-diisopropylcarbodiimide, or 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride;

[0122] The solvent is at least one of pyridine, trichlorobenzene, N,N-dimethylformamide or dimethyl sulfoxide;

[0123] The inert gas is argon or nitrogen.

[0124] According to the present invention, a method for fabricating a single-molecule device based on all-vapor phase oxidative etching is provided, wherein the triangular graphene electrode pair containing carboxyl functional groups includes a graphene source electrode with oxygen-containing functional groups and a graphene drain electrode with oxygen-containing functional groups.

[0125] In one embodiment, the steps for constructing a single-molecule device are as follows:

[0126] Take out an iron stand and place it in a fume hood. Then take out a three-necked flask and fix it on the iron stand. Use a two-way exhaust pipe and a glass stopper to fix and seal the two ports of the three-necked flask. Then put the dry triangular graphene electrode pair containing carboxyl functional groups into the third port of the three-necked flask. Pour 1 mg of terpyridine-metal complex and 0.1 g of catalyst into the third port of the three-necked flask. Then seal the port with a soft stopper. After all ports are sealed, evacuate the three-necked flask for about 30 minutes. Close the vacuum valve to keep the sealed three-necked flask in a stable vacuum state.

[0127] Further, 10 mL of anhydrous pyridine was drawn up using a syringe, and injected into a three-necked flask through a puncture in the soft stopper at the third port. The balloon was removed and filled with an appropriate amount of nitrogen gas. The balloon inlet was then fixed to the end of the syringe furthest from the needle tip, sealed, and left to stand for 48 hours. The entire reaction was conducted under anhydrous and oxygen-free experimental conditions. In the sealed environment, pyridine gradually dissolved the terpyridine-metal complex, undergoing an amide condensation reaction. The terpyridine-metal complex with amino-terminated molecules reacted with the terminal sites of the triangular graphene electrode pair containing carboxyl functional groups to form amide covalent bonds, obtaining a single-molecule device. After 48 hours, the single-molecule device was removed. To remove residual organic solution from the single-molecule device, it was rinsed three times sequentially with an appropriate amount of acetone solution and deionized water.

[0128] The single-molecule device prepared by this invention is an atomically precise single-molecule device. Furthermore, electrical tests were performed on the atomically precise single-molecule device:

[0129] The electrical characteristics of the single-molecule device were tested using an ST-500 probe station and an Agilent 4155C semiconductor parameter analyzer. The single-molecule device was fixed to the center of the probe station stage using conductive adhesive. Gold needles were then inserted into the gold electrodes at both ends of the single-molecule device, and its current-bias characteristic curve was measured. The relationship between the device's current-bias characteristic curve and temperature was tested using a comprehensive physical property testing system, such as... Figure 9 As shown, single-molecule devices exhibit a consistent trend in the range of 80K-300K, and are significantly modulated by temperature changes, indicating that single-molecule devices possess stable and efficient electrical control capabilities.

[0130] According to the present invention, a method for fabricating a single-molecule device based on all-vapor phase oxidative etching is provided, wherein the terpyridine-metal complex is as shown in Formula 1:

[0131] H2N-R2-R1-R2-NH2

[0132] Formula 1

[0133] Among them, R1 includes

[0134] One of them;

[0135] R2 includes

[0136] According to the present invention, a method for fabricating a single-molecule device based on all-vapor phase oxidative etching is provided, wherein the terpyridine-metal complex comprises

[0137]

[0138] One of them.

[0139] The preparation method of the terpyridine-metal complex is illustrated through the following four examples:

[0140] Example 1

[0141] 3-acetylpyridine and Add the first mixture to 40 mL of methanol and stir to obtain a first mixed solution. Add 36 mL of concentrated ammonia and 3.6 mL of 15% potassium hydroxide aqueous solution to the first mixed solution and stir at room temperature for 4 days to obtain a first reaction solution. Filter the first reaction solution to obtain a first solid product. Wash the first solid with water and dry it. Purify it by column chromatography to obtain a second solid product. Recrystallize the second solid product with ethanol to obtain...

[0142] Furthermore, FeCl2 was added to 20 mL of methanol and stirred at 0 °C for 10 min to obtain a second mixed solution. 20 mL of water was added to the second mixed solution, and rotary evaporation was performed to remove methanol, yielding a reactant solution. 20 mL of KPF6 solution was added to the reactant solution, and the mixture was stirred for 20 min to obtain a third mixed solution. The third mixed solution was filtered to obtain a third solid product. This third solid product was extracted with dichloromethane, dried with anhydrous sodium sulfate, and finally rotary evaporated to remove dichloromethane, yielding...

[0143]

[0144] Example 2

[0145] 3-acetylpyridine and Add the first mixture to 40 mL of methanol and stir to obtain a first mixed solution. Add 36 mL of concentrated ammonia and 3.6 mL of 15% potassium hydroxide aqueous solution to the first mixed solution and stir at room temperature for 4 days to obtain a first reaction solution. Filter the first reaction solution to obtain a first solid product. Wash the first solid with water and dry it. Purify it by column chromatography to obtain a second solid product. Recrystallize the second solid product with ethanol to obtain...

[0146] Furthermore, RuCl3 was added to 20 mL of methanol and stirred at 0 °C for 10 min to obtain a second mixed solution. 20 mL of water was added to the second mixed solution, and the methanol was removed by rotary evaporation to obtain a reactant solution. 20 mL of KPF6 solution was added to the reactant solution, and the mixture was stirred for 20 min to obtain a third mixed solution. The third mixed solution was filtered to obtain a third solid product. The third solid product was extracted with dichloromethane, dried with anhydrous sodium sulfate, and finally rotary evaporated to remove the dichloromethane to obtain the final product.

[0147]

[0148] Example 3

[0149] 3-acetylpyridine and Add the first mixture to 40 mL of methanol and stir to obtain a first mixed solution. Add 36 mL of concentrated ammonia and 3.6 mL of 15% potassium hydroxide aqueous solution to the first mixed solution and stir at room temperature for 4 days to obtain a first reaction solution. Filter the first reaction solution to obtain a first solid product. Wash the first solid with water and dry it. Purify it by column chromatography to obtain a second solid product. Recrystallize the second solid product with ethanol to obtain...

[0150] Furthermore, FeCl2 was added to 20 mL of methanol and stirred at 0 °C for 10 min to obtain a second mixed solution. 20 mL of water was added to the second mixed solution, and rotary evaporation was performed to remove methanol, yielding a reactant solution. 20 mL of KPF6 solution was added to the reactant solution, and the mixture was stirred for 20 min to obtain a third mixed solution. The third mixed solution was filtered to obtain a third solid product. This third solid product was extracted with dichloromethane, dried with anhydrous sodium sulfate, and finally rotary evaporated to remove dichloromethane, yielding...

[0151]

[0152] Example 4

[0153] 3-acetylpyridine and Add the first mixture to 40 mL of methanol and stir to obtain a first mixed solution. Add 36 mL of concentrated ammonia and 3.6 mL of 15% potassium hydroxide aqueous solution to the first mixed solution and stir at room temperature for 4 days to obtain a first reaction solution. Filter the first reaction solution to obtain a first solid product. Wash the first solid with water and dry it. Purify it by column chromatography to obtain a second solid product. Recrystallize the second solid product with ethanol to obtain...

[0154] Furthermore, RuCl3 was added to 20 mL of methanol and stirred at 0 °C for 10 min to obtain a second mixed solution. 20 mL of water was added to the second mixed solution, and the methanol was removed by rotary evaporation to obtain a reactant solution. 20 mL of KPF6 solution was added to the reactant solution, and the mixture was stirred for 20 min to obtain a third mixed solution. The third mixed solution was filtered to obtain a third solid product. The third solid product was extracted with dichloromethane, dried with anhydrous sodium sulfate, and finally rotary evaporated to remove the dichloromethane to obtain the final product.

[0155]

[0156] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for fabricating single-molecule devices based on all-vapor phase oxidative etching, characterized in that, Includes the following steps: S1: Fabrication of graphene layer electrodes on a substrate; S2: Fabrication of graphene source electrode and graphene drain electrode on graphene layer electrode; S3: Perform oxygen plasma pre-etching and hydrogen plasma forward etching on the graphene source electrode and graphene drain electrode to obtain triangular graphene electrode pairs. S4: Etching the triangular graphene electrode pair with an oxidizing gas to obtain a triangular graphene electrode pair containing carboxyl functional groups; S5: Construct single-molecule devices on triangular graphene electrode pairs containing carboxyl functional groups.

2. The method for fabricating a single-molecule device based on all-vapor phase oxidative etching according to claim 1, characterized in that, S1 includes the following steps: S11: The substrate is immersed in a mixed solution of hydrogen peroxide and concentrated sulfuric acid to obtain a first film. After ultrasonic cleaning, a first marking pattern is made on the first film to obtain a second film. Photoresist is spin-coated on the second film, and a second marking pattern is prepared on an ultraviolet exposure machine. The first marking pattern and the second marking pattern are completely identical and correspondingly set. The substrate includes one of silicon wafer, sapphire, silicon carbide, boron nitride or mica; S12: The second film is placed under the mask of the UV exposure machine for UV exposure to cure the photoresist into a film and obtain the third film. The third film is placed in the developing solution to immerse the photoresist film on the third film to reveal the third marking pattern. The third marking pattern is fixed and completely overlaps with the first marking pattern. S13: The third marking pattern on the third film is deposited with gold in a thermal resistance evaporation coating instrument. After cooling, a fourth film is obtained. The fourth film is immersed in acetone solution and the photoresist film is peeled off to obtain a fifth film. S14: Adhere the graphene sheet to Scotch transparent tape to obtain graphene tape. Tightly attach the fifth film and the graphene tape to the glass slide. After standing, remove the graphene tape to obtain the graphene layer electrode.

3. The method for fabricating a single-molecule device based on all-vapor phase oxidative etching according to claim 1, characterized in that, S2 includes the following steps: S21: Spin-coat the graphene layer electrode with a double layer of photoresist and place the graphene electrode on a heating plate to obtain the first graphene electrode; S22: Expose the first graphene electrode in an electron beam exposure system to obtain a second graphene electrode; develop the second graphene electrode in a developing solution; further, fix the second graphene electrode in a fixing solution to obtain a third graphene electrode. S23: The third graphene electrode is placed on a thermal resistance evaporation coating instrument for gold deposition. After cooling, a fourth graphene electrode is obtained. The fourth graphene electrode is immersed in an acetone solution and the double-layer photoresist film is peeled off to obtain the graphene source electrode and the graphene drain electrode.

4. The method for fabricating a single-molecule device based on all-vapor phase oxidative etching according to claim 3, characterized in that, S3 includes the following steps: S31: Process the graphene source electrode and the graphene drain electrode according to steps S21 and S22 respectively to obtain the first graphene electrode pair; S32: The first graphene electrode pair is placed in an oxygen plasma etching system for pre-etching to obtain the second graphene electrode pair; S33: Immerse the second graphene electrode pair in an acetone solution, peel off the photoresist film, and obtain the third graphene electrode pair; S34: Process the third graphene electrode pair according to step S31 to obtain the fourth graphene electrode pair, and place the fourth graphene electrode pair in a hydrogen plasma etching system for positive etching to obtain the fifth graphene electrode pair. S35: The fifth graphene electrode pair is processed according to step S33 to obtain a triangular electrode pair.

5. The method for fabricating a single-molecule device based on all-vapor phase oxidative etching according to claim 4, characterized in that, S5 includes the following steps: A terpyridine-metal complex and a dehydrating agent are added to a solvent and stirred to obtain a mixed solution. The triangular graphene electrode pair with the carboxyl functional group is placed in the mixed solution and allowed to stand in an inert gas for 24-48 hours to carry out the reaction and obtain a single-molecule device. The dehydrating agent is at least one of N,N'-dicyclohexylcarbodiimide, N,N'-diisopropylcarbodiimide, or 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride; The solvent is at least one of pyridine, trichlorobenzene, N,N-dimethylformamide or dimethyl sulfoxide; The inert gas is argon or nitrogen.

6. The method for fabricating a single-molecule device based on all-vapor phase oxidative etching according to claim 5, characterized in that, The triangular graphene electrode pair containing carboxyl functional groups includes a graphene source electrode with oxygen-containing functional groups and a graphene drain electrode with oxygen-containing functional groups.

7. The method for fabricating a single-molecule device based on all-vapor phase oxidative etching according to claim 5, characterized in that, The molecular formula of the terpyridine-metal complex is shown in Formula 1: H2N-R2-R1-R2-NH2 Formula 1 Among them, R1 includes One of them; R2 includes 8. The method for fabricating a single-molecule device based on all-vapor phase oxidative etching according to claim 7, characterized in that, The terpyridine-metal complex includes One of them.

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