Methods for directional growth of rubrene nanowires, nanowires and their applications

Abstract

This invention provides a method for the directional growth of fluorene nanowires, along with the nanowires and their applications. The method involves annealing an M-plane sapphire substrate to form parallel horizontal nanochannels on its surface; then performing a surface hydrophobic treatment; and finally, using vapor deposition to directionally grow an array of fluorene nanowires on the sapphire substrate surface. This method allows for the simultaneous growth and orderly assembly of fluorene nanowires, enabling precise control over the growth orientation and position of the fluorene nanowires and facilitating subsequent integration of fluorene nanowire devices. The fluorene nanowire arrays obtained using this method exhibit advantages such as high length uniformity, good distribution uniformity, good orientation, good stability, and high crystal quality, making them suitable for application in micro / nano optoelectronic device products.

Description

Technical Field

[0001] This invention relates to the field of semiconductor nanomaterial growth, specifically to a method for the directional growth of red fluorene nanowire arrays, the nanowires, and their applications. Background Technology

[0002] Due to its highly delocalized conjugated large π bonds and anthracene rings, rubrene molecules are very stable and have a narrow band gap. These characteristics determine its unique photoelectric properties, providing it with broad development prospects in the fields of organic electronics and optoelectronic devices. Furthermore, rubrene molecules are also highly efficient fluorescent materials, exhibiting high single-crystal mobility and highly delocalized charge transport characteristics. Simultaneously, rubrene possesses ultra-high carrier mobility (up to 43 cm⁻¹). 2 v -1 s -1 Its micron-scale exciton diffusion length and unique photophysical properties have attracted widespread attention in the last decade or so.

[0003] Nanowires, as one-dimensional nanostructures, are becoming increasingly well-known for their unique electrical, optical, and thermal properties. Their extremely high aspect ratio, large specific surface area, and unique structure endow nanowire structures with efficient light absorption and special electron transport mechanisms.

[0004] A photodetector is a semiconductor device used to detect the presence of photons, converting optical signals into electrical signals. When applied to photodetectors, compared to bulk and thin-film materials, the small size effect of nanowires and the relatively small effective conductive channels shorten the time for charge carriers to pass through the channels, ultimately resulting in an increase in photoresponse rate and photoconductive gain.

[0005] Currently, the main methods for growing rubrene nanowires include anodic alumina template-assisted method, centrifugation-assisted organic nanowire growth technology, vacuum evaporation, eutectic melting crystallization method, and liquid phase exfoliation method.

[0006] (1) Anodized aluminum template-assisted method

[0007] The anodic aluminum oxide template-assisted method is a technique that uses a porous anodic aluminum oxide (AAO) film as a template to grow one-dimensional nanowires or nanotubes within the AAO pores through electrochemical deposition, sol-gel, hydrothermal methods, etc. Taking electrochemical deposition as an example, the general process is as follows: First, high-purity aluminum sheets are anodized in an acidic electrolyte to form a porous AAO film with a regular hexagonal arrangement. Then, the AAO film is used as a cathode, connected to the anode or insoluble anode of the metal or other material to be deposited, and placed in an electrolyte containing ions of the deposited species. A direct current or alternating current is passed through, causing the deposited species to be reduced and deposited within the AAO pores, forming nanowires or nanotubes. Finally, the AAO template is removed, yielding a free array of nanowires or nanotubes.

[0008] (2) Centrifugation-assisted method

[0009] Centrifugation-assisted method is a technique that uses centrifugal force to inject an organic solution into a porous anodic alumina membrane (AAO), thereby growing organic nanowires within the AAO pores. Its process is roughly similar to the anodic alumina template-assisted method described above.

[0010] Both the anodic aluminum oxide template-assisted method and the centrifugation-assisted method require porous anodic aluminum oxide film as a template. However, the preparation process of anodic aluminum oxide template is relatively complex, requiring multiple steps such as anodizing, etching, and removal of the underlying layer. This process is time-consuming and energy-intensive, and can easily lead to unevenness and defects in the template.

[0011] Secondly, steps such as anodizing, etching, and removing the substrate may damage or contaminate the nanowires, affecting their performance and stability. Furthermore, the pore size and depth of the template are limited, generally between 100 and 500 nm, making it difficult to fabricate nanowires of smaller or larger sizes. Additionally, the channels of the anodic aluminum oxide template are perpendicular to the substrate; therefore, when depositing small organic molecules within it, a high vacuum and temperature must be maintained to prevent molecular deflection or accumulation within the channels.

[0012] Furthermore, the anodic aluminum oxide template-assisted method can only prepare vertically aligned nanowire arrays, making it difficult to prepare nanowire arrays with other orientations or shapes. Finally, the template needs to be removed to obtain free nanowires.

[0013] (3) Vacuum evaporation method

[0014] Vacuum evaporation is a process in which a coating material (or film material) is evaporated and vaporized under vacuum conditions using a specific heating and evaporation method. The particles then condense on the surface of a substrate to form a film. Patent CN101476103A describes the preparation of micro-nanowires of the organic semiconductor material fluorene using vacuum evaporation. The general process is as follows:

[0015] The first step is to use high-purity red fluorene as a vapor deposition raw material and place it into a heating source (such as a tungsten wire or tungsten boat) in a vacuum vapor deposition device.

[0016] The second step involves placing a clean silicon wafer or a tetraphenylene single crystal grown using physical vapor transport methods as a substrate onto a sample holder in a vacuum evaporation apparatus, maintaining a certain distance from the heating source.

[0017] The third step is to extract the gas from the vacuum evaporation apparatus to achieve a high vacuum state (typically 10). -6 ~10 - 7 (pa) to reduce the scattering and contamination of gas molecules by evaporating particles.

[0018] The fourth step involves heating the raw material to sublimate and vaporize it. Under controlled deposition rate and deposition time, red fluorene micro-nanowires with specific dimensions are deposited on the substrate.

[0019] This method requires high temperature, high vacuum, and complex equipment, resulting in high costs and operational difficulties. Furthermore, it is challenging to control the morphology, size, and distribution of nanowires, leading to poor uniformity and repeatability. In addition, the mechanism and kinetics of vacuum evaporation growth of nanowires are not fully understood, making it difficult to optimize process parameters and improve growth efficiency. The structure and properties of vacuum-evaporated nanowires can be affected by residual gases, impurities, grain boundaries, and defects, leading to unstable or non-uniform performance. Finally, post-processing and characterization of vacuum-evaporated nanowires also present challenges, such as how to remove excess substrate material, how to separate and collect individual nanowires, and how to measure their electrical, optical, and mechanical properties.

[0020] (4) Eutectic melt crystallization method

[0021] Eutectic melt crystallization is a technique that utilizes a mixture of two different chemical substances or elements in a specific ratio, which are then heated and fused at a temperature lower than their individual melting points to form a homogeneous mixture. This technique can be used to prepare organic nanowires with single-crystal structures and specific dimensions. Taking the growth of rubrene nanowires as an example, the general process is as follows:

[0022] First, rubrene and a volatile crystallizable additive (VCA), such as benzoic acid (BA), salicylic acid (SA), or 1,3,5-trichlorobenzene (TCB), are mixed in a certain proportion and then pulverized to form a eutectic mixture. These additives can form a eutectic system with rubrene, lowering its melting point and affecting its crystal structure and growth direction.

[0023] The eutectic mixture is then placed on a substrate and heated to slightly above the eutectic temperature until it is completely melted. During this process, the saturated vapor pressure of the additives must be maintained to prevent changes in the composition of the mixture. The temperature is then reduced to 100°C at a controlled cooling rate, and then cooled to room temperature. During cooling, the additives and fluorene crystallize simultaneously, forming fluorene micro-nanowires on the substrate.

[0024] Finally, the sample containing rubrene micro-nanowires was placed in a vacuum and the additives were evaporated at a low temperature (50°C) and pressure (1 torr) to obtain a pure rubrene micro-nanowire array.

[0025] This method requires precise control of temperature and cooling rate to ensure the eutectic reaction proceeds and nanowire formation. Temperatures that are too high or too low, or cooling rates that are too fast or too slow, can affect the quality and yield of the nanowires. Furthermore, suitable volatile crystalline additives need to be selected to form a stable eutectic system with the organic semiconductor and to volatilize at low temperatures. Impurities or residual volatile crystalline additives can also affect the purity and uniformity of the nanowires.

[0026] (5) Liquid phase stripping method

[0027] Liquid-phase exfoliation is a method that uses solvents or surfactants to disperse bulk materials and then uses ultrasonic methods to peel off single-layer or multi-layer nanosheets from the material surface. The resulting nanosheet dispersion is then obtained through centrifugation, and finally, nanowires can be deposited on different substrates. Taking the growth of rubrene nanowires as an example, the general process is as follows:

[0028] The first step is to disperse the red fluorene crystals in an organic solvent or a specific surfactant to form a homogeneous mixture.

[0029] The second step involves placing the mixture into an ultrasonic device, where the cavitation effect and mechanical vibration of the ultrasonic waves are used to peel off single or multiple layers of fluorene from the crystal surface, forming fluorene nanosheets.

[0030] The third step involves centrifuging the mixture containing rubrene nanosheets to separate them. Based on different relative centrifugal forces (RCF) and times, rubrene nanosheets of different sizes and morphologies are collected in fractions.

[0031] The fourth step involves redispersing the collected fluorene nanosheets of different grades in fresh solvents or surfactants to form stable dispersions. These dispersions can then be deposited on various substrates to obtain fluorene nanowire arrays.

[0032] Liquid-phase exfoliation requires the use of suitable solvents or surfactants to stabilize the dispersion of nanowires, which may increase costs, pollute the environment, or affect the performance of the nanowires. Secondly, using strong ultrasonic or shearing methods to exfoliate layered materials such as graphite can cause breakage, defects, or oxidation of the nanowires, making it difficult to control their morphology, size, and distribution, resulting in poor uniformity and repeatability. Furthermore, the influence of residual solvents, surfactants, and impurities can reduce the purity and uniformity of the nanowires.

[0033] It can be seen that the existing preparation methods all have various problems, such as the need for templates, complex processes, impurities introduced by solvent residues, or poor uniformity and repeatability. Moreover, the rubrene nanowires prepared by these methods are mainly arranged in quasi-vertical disorder and small-area in-plane disorder. For example, the rubrene micro-nanowires grown in patent CN101476103A are arranged in a cone shape with random vertical distribution, which is not conducive to the integration of devices in the later stage. In addition, there are very few reports on the horizontal array of rubrene nanowires grown in a directional manner. Summary of the Invention

[0034] The present invention aims to solve at least one of the technical problems existing in the prior art. To this end, the present invention proposes a method for the directional growth of rubrene nanowires, which can not only precisely control the growth orientation and growth position of rubrene nanowires, but also facilitate the subsequent integration of rubrene nanowire devices.

[0035] One aspect of the present invention provides a method for the directional growth of rubiginene nanowires, comprising the following steps:

[0036] Step S1: Anneal the M-plane sapphire substrate to form parallel horizontal nanochannels on its surface;

[0037] Step S2: Perform surface hydrophobic treatment on the sapphire substrate after step S1;

[0038] Step S3: Grow rubrene nanowires over a large area on the sapphire substrate surface treated in step S2 using vapor deposition, or cover the sapphire substrate surface treated in step S2 with a mask, and then grow rubrene nanowires on the sapphire substrate surface covered with the mask using vapor deposition.

[0039] Through experiments, the inventors discovered that the surface of an annealed M-plane sapphire substrate can spontaneously form parallel horizontal channels with a "V"-shaped cross-section, eliminating potential defects on the substrate surface. These nanoscale channels, arranged in a parallel and orderly manner, provide directional constraints for the guided growth of rubrene nanowires, enabling the large-area growth of horizontally guided rubrene nanowire arrays with precise positioning and orientation.

[0040] In some embodiments of the present invention, the depth of the nanochannel is 5-15 nm, at which point the resulting rubrene nanowires exhibit better crystal quality and uniformity. Within the nanoscale range, the deeper the nanochannel, the better the growth of the rubrene nanowires is confined to the channel direction, resulting in fewer branches, longer lengths, and a morphology more akin to unbranched single nanowires, with a more ordered arrangement.

[0041] In some embodiments of the present invention, the temperature control procedure for the annealing process in step S1 is as follows: the temperature is increased from 25°C to 300°C over 60 minutes at a rate of 4.58°C / min, then increased from 300°C to 800°C over 60 minutes at a rate of 8.3°C / min, then increased from 800°C to 1600°C over 180 minutes at a rate of 4.44°C / min, then held at 1600°C for 600 minutes, and then allowed to cool naturally to room temperature. This results in more uniform and regular channels, which are more suitable for the growth of fluorescein nanowires.

[0042] In some embodiments of the present invention, the hydrophobic treatment in step S2 involves first hydrophilically treating the sapphire substrate to reduce its contact angle to less than or equal to 20°, and then performing a hydrophobic treatment to reduce its surface contact angle to greater than or equal to 110°. The hydrophobic treatment not only effectively reduces the surface energy of the M-plane sapphire channel substrate, lowering the barrier to rubrene nucleation and growth, thus facilitating the nucleation and growth of rubrene nanowires, but also increases the affinity between the M-plane sapphire surface and the rubrene organic molecular nanowires. This provides a crucial foundation for the preferential nucleation of rubrene organic molecules at the channel and their eventual orderly growth along the channel direction. The combination of hydrophilic treatment followed by hydrophobic treatment results in a more stable hydrophobic layer, which can maintain its hydrophobic properties during subsequent high-temperature nanowire growth, further promoting the growth of rubrene nanowires. The hydrophobic modification principle of OTMS involves the reaction of OTMS molecules with the -OH groups on the M-facet sapphire surface to form an octadecylsilane molecular layer. The hydrophobic properties of the OTMS framework change the sapphire substrate surface from hydrophilic to hydrophobic. Therefore, first cleaning the sapphire with plasma gas to fill the sapphire surface with -OH groups, making it hydrophilic, and then applying OTMS for hydrophobicity, yields better results and improves stability. Simultaneously, the plasma gas cleaning process further reduces impurities and cleans the sapphire surface more thoroughly.

[0043] Preferably, the hydrophilic treatment involves cleaning the sapphire substrate using a plasma gas cleaner; in some embodiments of the invention, a 70W plasma gas cleaner is used for 160 seconds. The hydrophobic treatment involves immersing the hydrophilic-treated sapphire substrate in an OTMS solution, resulting in a hydrophobic layer with better stability. In some embodiments of the invention, the sapphire substrate after plasma gas cleaning is immersed in an OTMS / hexane solution at a concentration of 1 μl / ml for surface modification treatment for 1-2 hours, yielding a monolayer adsorbed hydrophobic layer with superior performance.

[0044] In some embodiments of the present invention, in step S3, the large-area growth of rubrene nanowires is carried out in a dual-temperature zone tube furnace; 10 mg of rubrene powder is placed in a quartz boat and placed in the source temperature zone; a sapphire substrate is placed on an 8 mm high slot plate and together with it in a quartz boat with an inner diameter of 29 mm, placed in the growth temperature zone; the distance between the rubrene powder and the substrate is 31 cm; the source temperature zone temperature is 300 °C, the growth temperature zone temperature is 180 °C, the carrier gas is N2, the volumetric flow rate is 200 sccm, the pressure is 20 mbar, and the growth time is 30 min. The resulting nanowires have good uniformity and crystallinity.

[0045] In some embodiments of the present invention, in step S3, the directional growth of rubrene nanowires is carried out in a dual-temperature zone tube furnace. 10 mg of rubrene powder is placed in a quartz boat and placed in the source temperature zone; a sapphire substrate is placed on an 8 mm high slot plate and together with it in a quartz boat with an inner diameter of 29 mm, placed in the growth temperature zone; the distance between the rubrene powder and the substrate is 25 cm; the source temperature zone temperature is 295 °C, the growth temperature zone temperature is 180 °C, the carrier gas is N2 with a volumetric flow rate of 200 sccm, the pressure is 20 mbar, and the growth time is 30 min, resulting in better directional growth of the nanowires.

[0046] In some embodiments of the present invention, before growth, the rubrene powder is placed outside the growth temperature zone, heated to the set temperature, and then the rubrene powder is pushed into the position set at a distance from the substrate.

[0047] Another aspect of the present invention provides a method for preparing rubrene nanowires by the above-described method of directional growth of rubrene nanowires.

[0048] In some embodiments of the present invention, the width of the rubrene nanowires is 100-300 nm and the height is about 400 nm.

[0049] According to another aspect of the present invention, the application of the aforementioned rubrene nanowires in micro / nano optoelectronic device products is also provided.

[0050] Compared with existing technologies such as anodic alumina template-assisted growth, centrifugation-assisted organic nanowire growth, vacuum evaporation, eutectic melting crystallization, and liquid phase exfoliation, this invention achieves template-free growth of rubrene nanowires. Problems caused by templates are eliminated in this invention, and rubrene nanowire growth and horizontal ordered assembly can be achieved simultaneously. This provides a safe, simple, and economical horizontal array growth technology for rubrene nanowires. Furthermore, the use of a hydrophobic layer overcomes the strict limitations on the matching relationship between the substrate and the semiconductor crystal, enabling the growth of rubrene nanowires on M-plane sapphire substrates. In addition, the use of a mask for positioning growth and device integration reduces operational difficulty and ensures precise positioning. The horizontal array of rubrene nanowires grown using this method exhibits advantages such as high length uniformity, good distribution uniformity, ordered orientation, good stability, and high crystal quality. This provides an ideal material platform for the mass production and development of various micro / nano optoelectronic devices based on rubrene nanowires. Moreover, the horizontal array of rubrene nanowires grown using this method is compatible with existing micro / nano fabrication processes, which is beneficial for the large-scale production and on-chip integration of semiconductor micro / nano devices. Attached Figure Description

[0051] Figure 1 This is a schematic flowchart of the method for the directional growth of rubrene nanowires in Examples 1-2 of the present invention.

[0052] Figure 2 This is a schematic diagram of the vapor deposition apparatus in Embodiments 1-2 of the present invention;

[0053] Figure 3 These are SEM images of the M-plane sapphire substrate before and after heat treatment in Embodiment 1 of the present invention;

[0054] Figure 4 This is an AFM image of the M-plane sapphire substrate after heat treatment in Embodiment 1 of the present invention;

[0055] Figure 5 The images show the water contact angles of the sapphire substrate surface after hydrophilic / hydrophobic treatment and the surface water contact angles after nanowire growth in Example 1 of this invention.

[0056] Figure 6 Optical microscope image of rubrene nanowires grown on an unmodified sapphire substrate, for Comparative Example 1.

[0057] Figure 7 Optical microscope image of the fluorene nanowires obtained in Example 1;

[0058] Figure 8 The image shows a SEM image of the fluorene nanowires obtained in Example 1.

[0059] Figure 9The image shows an optical microscope image of the rubrene nanowires obtained in Example 2.

[0060] Figure 10 Fluorescence micrograph of the rubrene nanowires obtained in Example 1;

[0061] Figure 11 XRD patterns of horizontal arrays of rubrene nanowires with different growth times in Examples 1 and 3-4;

[0062] Figure 12 Figure 5 shows a physical image (Figure a) and an optical microscope image (Figure b) of the photodetector in Example 5.

[0063] Figure 13 The photodetector of Example 5 is used at a bias voltage of 20V, a wavelength of 405nm, and a power density of 4.15mW / cm². 2 It image under light source switching conditions;

[0064] Figure 14 Horizontal array optical microscope images of rubrene nanowires grown on different sapphire substrates in Comparative Example 2 and Example 1.

[0065] Figure 15 The image shows the AFM image of the rubrene nanowires obtained in Example 1. Detailed Implementation

[0066] In the description of this invention, unless otherwise explicitly defined, terms such as heating, cleaning, and weighing should be interpreted broadly. Those skilled in the art can reasonably determine the specific meaning of the above terms in this invention in conjunction with the specific content of the technical solution.

[0067] In the description of this invention, references to terms such as "some embodiments" and "examples" indicate that the specific methods or materials described in connection with that embodiment or example are included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiments or examples. Furthermore, the specific methods and materials described may be combined in any suitable manner in one or more embodiments or examples.

[0068] This invention provides a method for the directional growth of rubiginene nanowires, comprising the following steps:

[0069] Step S1: Anneal the M-plane sapphire substrate to form parallel horizontal nanochannels on its surface;

[0070] Step S2: Perform surface hydrophobic treatment on the sapphire substrate after step S1;

[0071] Step S3: Grow rubrene nanowires over a large area on the sapphire substrate surface after step S2 by vapor deposition, or cover the sapphire substrate surface after step S2 with a mask, and then grow rubrene nanowires in a specific location on the sapphire substrate surface covered with the mask by vapor deposition.

[0072] The nanochannels in step S1 are a prerequisite for the directional growth of nanowires. Through experiments, the inventors discovered that only the surface of the annealed M-side sapphire substrate can spontaneously form parallel horizontal channels with a "V"-shaped cross-section, thus eliminating any potential defects on the substrate surface. These nanoscale channels, arranged in a parallel and orderly manner, provide directional constraints for the guided growth of rubrene nanowires, enabling the large-area growth of horizontally guided rubrene nanowire arrays with precise positioning and orientation.

[0073] Preferably, the depth of the nanochannel is 5-15 nm, at which point the resulting rubrene nanowires exhibit better crystal quality and uniformity.

[0074] Preferably, the temperature control program for the annealing process in step S1 can be controlled as follows: the temperature is increased from 25°C to 300°C over 60 minutes at a rate of 4.58°C / min, then increased from 300°C to 800°C over 60 minutes at a rate of 8.3°C / min, then increased from 800°C to 1600°C over 180 minutes at a rate of 4.44°C / min, then held at 1600°C for 600 minutes, and then allowed to cool naturally to room temperature, resulting in more uniform and regular grooves.

[0075] The hydrophobic treatment in step S2 not only effectively reduces the surface energy of the M-plane sapphire channel substrate and lowers the barrier to rubrene nucleation and growth, thus facilitating the nucleation and growth of rubrene nanowires, but also increases the affinity between the M-plane sapphire surface and the rubrene organic molecule nanowires. This provides a crucial foundation for the preferential nucleation of rubrene organic molecules at the channel and their eventual orderly growth along the channel direction.

[0076] Preferably, a hydrophilic treatment followed by a hydrophobic treatment results in a more stable hydrophobic layer that can maintain its hydrophobic properties during subsequent high-temperature nanowire growth, making it more suitable for the growth of rubrene nanowires. More preferably, the sapphire substrate is first hydrophilically treated to achieve a contact angle ≤20° (e.g., 18°, 16°, 14°, 12°, 10°, 8°, 6°), and then hydrophobically treated to achieve a surface contact angle greater than or equal to 110° (e.g., 114°, 116°, 118°, 120°, 130°). Preferably, the hydrophilic treatment involves cleaning the sapphire substrate using a plasma gas cleaner; in some embodiments of the invention, a 70W plasma gas cleaner is used for 160 seconds. The hydrophobic treatment involves immersing the hydrophilically treated sapphire substrate in an OTMS (octadecyltrimethoxysilane) solution, resulting in a more stable hydrophobic layer. In some embodiments of the present invention, the sapphire substrate, after being cleaned by plasma gas, is immersed in an OTMS n-hexane solution with a ratio of 1 μl / ml for surface modification treatment for 1-2 hours, which can obtain a single-layer adsorbed hydrophobic layer with better performance.

[0077] In some embodiments, before performing surface hydrophobic treatment on the sapphire substrate treated in step S1, a cleaning step is further included. The sapphire substrate treated in step S1 is ultrasonically cleaned sequentially with acetone, isopropanol, 95% ethanol, deionized water, and 95% ethanol solution, with each cleaning session lasting 10 minutes and an ultrasonic power of 135W, to remove impurities such as oil stains adhering to the surface of the sapphire substrate. After ultrasonic cleaning, the sapphire substrate is purged with nitrogen gas to remove organic solvents and other impurities from its surface. Cleaning allows for better hydrophobic modification, resulting in a tighter bond between the modified layer and the substrate, and a more stable hydrophobic layer.

[0078] Step S3: Large-area growth of rubrene nanowires is performed using vapor deposition or by positioning and growing rubrene nanowires on a substrate surface covered with a mask.

[0079] Typically, a dual-temperature zone tube furnace is chosen, which is divided into a source temperature zone and a growth temperature zone. The rubrene powder is placed in the source temperature zone, and the sapphire substrate is placed in the growth temperature zone. Before growth, the rubrene powder is placed outside the growth temperature zone. After the temperature is raised to the set temperature, the rubrene powder is pushed into the set position at the distance from the substrate.

[0080] Preferably, for large-area growth of fluorene nanowires, 10 mg of fluorene powder is placed in a quartz boat and placed in the source temperature zone; a sapphire substrate is placed on an 8 mm high slot plate and together in a quartz boat with an inner diameter of 29 mm, placed in the growth temperature zone; the distance between the fluorene powder and the substrate is 31 cm; the source temperature zone temperature is 300 °C, the growth temperature zone temperature is 180 °C, the carrier gas is N2 with a volumetric flow rate of 200 sccm, the pressure is 20 mbar, and the growth time is 30 min. The resulting nanowires have good uniformity and crystallinity.

[0081] Preferably, rubrene nanowires are grown on the surface of a substrate covered with a mask. 10 mg of rubrene powder is placed in a quartz boat and placed in the source temperature zone. The sapphire substrate is placed on an 8 mm high slotted plate and together with the substrate in a quartz boat with an inner diameter of 29 mm, placed in the growth temperature zone. The distance between the rubrene powder and the substrate is 25 cm. The source temperature zone temperature is 295 °C, the growth temperature zone temperature is 180 °C, the carrier gas is N2 with a volumetric flow rate of 200 sccm, the pressure is 20 mbar, and the growth time is 30 min. This method yields better directional growth of the nanowires.

[0082] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to specific embodiments and accompanying drawings, but this does not constitute a limitation on the scope of protection of the present invention.

[0083] Unless otherwise specified, all reagents used in the following examples are commercially available; and all methods used in the following examples are conventional methods.

[0084] The experimental instruments used in the following examples were: a TF1200-60 tube furnace from Shanghai Weixing Furnace Industry Co., Ltd.; quartz tubes with outer diameter, inner diameter, and length of 35 mm, 29 mm, and 1500 mm, respectively; a D08-4E flow display and a D07-19B mass flow controller from Beijing Qixing Huachuang Flowmeter Co., Ltd.; an ME103E / 02 electronic balance from Mettler Toledo Instruments (Shanghai) Co., Ltd.; a BILON6-180 ultrasonic cleaner from Shanghai Bilang Instrument Manufacturing Co., Ltd.; and a PT-5S plasma cleaner from Shenzhen Sanhe Boda Cleaning Machine Co., Ltd. SEM images were obtained using a ZEISS Gemini 500 field emission scanning electron microscope at an accelerating voltage of 2.00 kV. XRD images were measured using a D8 advancedaVinci X-ray polycrystalline diffractometer from Bruker Technologies.

[0085] Example 1

[0086] refer to Figure 1-2 A method for large-area, directional growth of horizontally guided red fluorene nanowire arrays includes the following steps:

[0087] 1) Using an M-plane sapphire substrate (i.e., a-Al2O3, with a crystal plane index of ), The sapphire substrate was placed in a box furnace for annealing. The annealing steps were as follows: the M-side sapphire substrate was rinsed with acetone and alcohol in sequence, then dried with a nitrogen gun and placed in a ceramic crucible. Finally, it was placed in a high-temperature annealing furnace, where the temperature was increased from 25°C to 300°C over 60 minutes at a rate of 4.58°C / min, then increased from 300°C to 800°C over 60 minutes at a rate of 8.3°C / min, and then increased from 800°C to 1600°C over 180 minutes at a rate of 4.44°C / min. It was then held at 1600°C for 600 minutes. The substrate was then removed after naturally cooling to room temperature.

[0088] 2) Cut the annealed sapphire substrate into 1×1cm pieces. 2 Small square pieces of the substrate were placed in a beaker and ultrasonically cleaned sequentially with acetone, isopropanol, 95% ethanol, deionized water, and 95% ethanol solution. Each cleaning session lasted 10 minutes at an ultrasonic power of 135W to remove oil and other impurities adhering to the sapphire substrate surface. After ultrasonic cleaning, the sapphire substrate was purged with nitrogen gas to remove organic solvents and other impurities.

[0089] The sapphire substrate, after being purged with nitrogen, was placed in a plasma gas cleaner with a power of 70W for 160 seconds. The plasma-cleaned sapphire substrate was then immersed in an OTMS solution (a mixture of 10 ml n-hexane and 10 μl OTMS) for surface modification treatment for 1-2 hours.

[0090] 3) Using the sapphire substrate prepared in the above steps, physical vapor deposition (PVD) is used to grow rubrene nanowires. 10 mg of rubrene powder is placed in a quartz boat and placed in the source temperature zone of a dual-temperature tube furnace. The sapphire substrate is placed on an 8 mm high slot plate and placed together in a quartz boat with an inner diameter of 29 mm, placed in the growth zone of the quartz tube. The distance between the source powder and the substrate is 31 cm. The source temperature is set to 300 °C, the substrate growth temperature to 180 °C, the carrier gas to be N2 with a flow rate of 200 sccm and a pressure of 20 mbar, and the growth time to 30 min. After measuring the distance between the source powder and the substrate, the position is marked with a pen. Before growth, the quartz boat with the source powder is placed outside the tube furnace temperature zone. After heating to the programmed temperature, the rubrene powder is pushed into the desired distance from the substrate.

[0091] A large-area horizontally guided red fluorene nanowire array was obtained through the above steps.

[0092] Example 2

[0093] refer to Figure 1-2A method for positioning and directionally growing horizontally guided red fluorene nanowire arrays includes the following steps:

[0094] Steps 1) and 2) are the same as in Example 1;

[0095] 3) Cover the sapphire substrate with a 1.5cm × 1.5cm metal mask containing a 0.5mm × 0.5mm rectangular array of small holes, and begin physical vapor deposition (PVD) growth of rubrene nanowires. Place 10mg of rubrene powder in a quartz boat and position it in the source temperature zone of a dual-temperature tubular furnace. Place the sapphire substrate on an 8mm high slot plate and place it together in a quartz boat with an inner diameter of 29mm, positioned in the growth zone of the quartz tube. The distance between the source powder and the substrate should be 25cm. Set the source temperature to 295℃, the substrate growth temperature to 180℃, the carrier gas to N2 with a flow rate of 200sccm and a pressure of 20mbar, and the growth time to 30min. After measuring the distance between the source powder and the substrate, mark the position with a pen. Before growth, place the quartz boat with the source powder pusher outside the tube furnace temperature zone. After heating to the programmed temperature, push the rubrene powder into the desired distance from the substrate.

[0096] The above steps yield a horizontally guided red fluorene nanowire array with precise positioning and orientation.

[0097] Example 3

[0098] The difference from Example 1 is that in step 3), the nanowire growth time is 60 min.

[0099] Example 4

[0100] The difference from Example 1 is that in step 3), the nanowire growth time is 120 min.

[0101] Example 5

[0102] The large-area horizontally oriented rubrene nanowire array obtained in Example 1 was covered with a metal mask, interdigitated electrodes were deposited by vapor deposition, and assembled into a photodetector. The photodetector performance of the large-area horizontally oriented rubrene nanowire was then tested.

[0103] Comparative Example 1

[0104] The difference from the embodiment is that step 2) is missing, and the surface modification treatment of the annealed M-side sapphire substrate is not performed; otherwise, they are the same.

[0105] Comparative Example 2

[0106] Large-area red fluorene nanowire arrays were grown on CM 0.1° sapphire substrates, CM 0.2° sapphire substrates, CM 0.5° sapphire substrates, C-A2° sapphire substrates, and CA 6° sapphire substrates, respectively, with other steps the same as in Example 1.

[0107] Wherein, C-M0.1° sapphire substrate: refers to the sapphire crystal with its C-plane (0001) along the M-axis. A wafer with a 0.1° bevel cut in the direction of cutting;

[0108] CM 0.2° Sapphire substrate: refers to the C-plane (0001) of the sapphire crystal along the M-axis. A wafer with a 0.2° bevel cut in the direction of cutting;

[0109] CM 0.5° Sapphire substrate: refers to the C-plane (0001) of the sapphire crystal along the M-axis. A wafer with a 0.5° bevel cut in the direction of cutting;

[0110] CA 2° sapphire substrate: refers to the sapphire crystal with its C-plane (0001) along the A-axis. A wafer obliquely cut at 2°;

[0111] CA 6° sapphire substrate: refers to the sapphire crystal with its C-plane (0001) along the A-axis. A wafer with a 6° bevel cut.

[0112] Horizontal array optical microscope images of rubrene nanowires grown on different sapphire substrates in Comparative Example 1 and Example 1 are shown below. Figure 14 As shown, af represents C-M0.1° sapphire substrate, CM 0.2° sapphire substrate, C-M0.5° sapphire substrate, CA 2° sapphire substrate, CA 6° sapphire substrate, and M sapphire substrate, respectively.

[0113] Characterization and Discussion

[0114] Figure 3 The images shown are SEM images of the M-plane sapphire substrate before and after heat treatment in Example 1. Figure 3 a is an SEM image of the M-plane sapphire substrate before heat treatment. Figure 3 b is an SEM image of the M-plane sapphire substrate after heat treatment; Figure 4 This is an AFM image of the M-plane sapphire substrate after heat treatment in Example 1, where... Figure 4 a is the AFM image of the M-plane sapphire substrate after heat treatment. Figure 4 Figure b shows the height variation in diagram a. It can be seen that after heat treatment, the surface of the M-side sapphire substrate will spontaneously form parallel horizontal channels with a "V"-shaped cross-section. The depth of these nanochannels is 5-15 nm. (Comparison...) Figure 3 , Figure 4 It can be seen that after high-temperature annealing in a box furnace, a single-orientation "V"-shaped channel spontaneously forms on the surface of the M-plane sapphire substrate, with a crystal plane index of ± Furthermore, the width and height of the channel are uniform.

[0115] Figure 5 This is a water contact angle diagram of the M-plane sapphire substrate surface after hydrophilic / hydrophobic treatment and growth of rubrene nanowires in Example 1, where... Figure 5 (a) is a diagram showing the water contact angle on the M-side sapphire substrate surface after plasma gas cleaning. Figure 5 (b) shows the water contact angle diagram of the M-plane sapphire substrate surface after hydrophobic modification. Figure 5 (c) Surface water contact angle diagram of the M-side sapphire substrate after surface modification treatment and subsequent growth of rubrene nanowires; After hydrophilic treatment, the surface water contact angle of the sapphire substrate is 17.6°, after hydrophobic modification it is 115.4°, and after growth of rubrene nanowires it is 118.7°. This indicates that after OTMS surface modification treatment, the contact angle between the M-side sapphire substrate and water droplets is significantly increased, the hydrophobicity is enhanced, and the surface energy is reduced; moreover, after OTMS solution surface modification treatment, the hydrophobic layer on the sapphire substrate is well maintained after high-temperature nanowire growth.

[0116] Figure 7 The images shown are optical microscope images of the red fluorene nanowires obtained in Example 1, where image b is a magnified view of image a. Figure 8 The images shown are SEM images of the rubrene nanowires obtained in Example 1, where image b is a magnified view of image a. Figure 9 The images shown are optical microscope images of the rubrene nanowires obtained in Example 2, where image b is a magnified view of image a. Figure 15 The image shows the AFM image of the fluorene nanowires obtained in Example 1. Figure 15 a is the AFM image of the fluorene nanowires. Figure 15 b is a height variation diagram of figure a; it can be seen that the embodiments of the present invention can prepare uniformly grown and well-positioned rubrene nanowires. The width of the obtained rubrene nanowires is 100-300nm, the height is about 400nm, and the length can be customized according to the mask.

[0117] Figure 6 Optical microscopy images of rubrene nanowires grown on an unmodified sapphire substrate, as shown in Comparative Example 1; by and Figure 7 In comparison, it can be seen that without improved treatment, it is difficult to form an ordered and uniform array of rubrene nanowires on the surface of a sapphire substrate.

[0118] Figure 11The XRD patterns of horizontal arrays of fluorescein nanowires with different growth times in Examples 1 and 3-4 are shown. By comparing the peak positions and line shapes of the XRD curves of fluorescein nanowires with different growth times, it can be seen that the fluorescein grown in the embodiments of the present invention has high crystallinity and good crystal quality. The crystallinity of the samples with growth times of 30 min and 120 min is not significantly different; therefore, a growth time of 30 min is preferred. Furthermore, the comparison of XRD patterns of fluorescein powder and fluorescein nanowires shows that surface modification treatment solves the problem of lattice matching between nanowire growth and the substrate.

[0119] Figure 10 In Figures a and b, both are fluorescence micrographs of rubrene nanowires obtained in Example 1, obtained through... Figure 10 It is evident that the rubrene nanowire array grown using this method emits red fluorescence, with strong and uniform luminescence, which indirectly proves that the rubrene nanowire array grown using this method has few defects and high crystallinity.

[0120] Figure 14 The images shown are horizontal array optical microscope images of rubrene nanowires grown on different sapphire substrates in Comparative Example 2 and Example 1. The comparison shows that, using the method of this embodiment, only on M-plane sapphire substrates can ordered and uniform rubrene nanowires be obtained.

[0121] Figure 12 Figure 5 shows a physical image (Figure a) and an optical microscope image (Figure b) of the photodetector in Example 5. Figure 13 The photodetector of Example 5 is used at a bias voltage of 20V, a wavelength of 405nm, and a power density of 4.15mW / cm². 2 It image under light source switching conditions; by Figure 12 and Figure 13 It can be seen that the photodetector manufactured by the horizontally guided red fluorene nanowires grown by this scheme has obvious light response in the light source switching state, indicating that the red fluorene nanowires of the present invention can be used in optoelectronic devices.

[0122] Because rubrene contains anthracene rings in its structure, it has high electron affinity and hole mobility, making its synthesis highly sensitive to changes in temperature and pressure. Therefore, rubrene nanowires synthesized in existing technologies are mostly randomly arranged. However, the method of this invention…

[0123] (1) Experiments have shown that high-temperature annealing of M-facet sapphire causes spontaneous formation of ± directions on its surface. The horizontally ordered nanochannels eliminate potential defects on the substrate surface. These nanoscale channels provide directional constraints for the guided growth of rubrene nanowires, enabling better large-area growth of horizontally guided rubrene nanowire arrays with precise positioning and orientation. Furthermore, experiments have shown that rubrene can only be grown on M-plane sapphire substrates.

[0124] (2) The annealed M-side sapphire substrate with channels was immersed in OTMS solution for substrate surface modification treatment. OTMS molecules react with the -OH groups on the M-side sapphire surface to form an octadecylsilane molecular layer, which breaks through the strict limitation on the matching relationship between the substrate and the semiconductor crystal. Moreover, it remains stable after high-temperature growth of nanowires, which reduces the substrate surface energy, increases hydrophobicity, improves affinity with organic semiconductor nanowires, increases the adsorption rate of rubrene gas molecules on the substrate, and reduces the rubrene growth barrier. At the same time, the reduced surface energy of the M-side sapphire substrate also meets the minimum energy principle for nanowire growth. Rubrene molecules preferentially nucleate in the channels on the substrate surface and grow continuously along the channels.

[0125] (3) Further, by adjusting the growth parameters of PVD, the optimal parameters for the growth of rubrene nanowires were determined, and a directional horizontal array of rubrene nanowires was prepared.

[0126] (4) The solution of the present invention can control the growth position of fluorene nanowires through the designed mask template, thereby accurately realizing the positioning growth and device integration of horizontally guided fluorene nanowire arrays. The operation is simple and the positioning is accurate.

[0127] The red fluorene nanoarray obtained by the present invention is orderly arranged and compatible with existing micro-nano fabrication processes, which is beneficial to the large-scale production and on-chip integration of semiconductor micro-nano devices.

[0128] Compared with anodic alumina template-assisted methods, centrifugation-assisted organic nanowire growth technology, vacuum evaporation, eutectic melting crystallization, and liquid phase exfoliation, this invention achieves template-free growth of rubrene nanowires, eliminating the problems caused by templates. Furthermore, it allows for simultaneous growth and horizontally ordered assembly of rubrene nanowires, enabling precise control over their growth orientation and position, and facilitating subsequent integration into rubrene nanowire devices. This provides a safe, simple, and economical method for growing horizontal arrays of rubrene nanowires. The resulting horizontal arrays exhibit high length uniformity, good distribution uniformity, good orientation, good stability, and high crystal quality, providing an ideal material platform for the mass production and development of various micro / nano optoelectronic devices based on rubrene nanowires.

[0129] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be noted that the above descriptions are merely specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for the directional growth of rubrene nanowires, characterized in that, Includes the following steps, Step S1: Anneal the M-plane sapphire substrate to form parallel horizontal nanochannels on its surface; the temperature control program for the annealing process is as follows: increase from 25 ℃ to 300 ℃ at a rate of 4.58 ℃ / min over 60 min, then increase from 300 ℃ to 800 ℃ at a rate of 8.3 ℃ / min over 60 min, then increase from 800 ℃ to 1600 ℃ at a rate of 4.44 ℃ / min over 180 min, then hold at 1600 ℃ for 600 min, and then allow to cool naturally to room temperature; Step S2: Perform a surface hydrophobic treatment on the sapphire substrate after the treatment in Step S1; the hydrophobic treatment involves first performing a hydrophilic treatment on the sapphire substrate to make its contact angle less than or equal to 20°, and then performing a hydrophobic treatment to make its surface contact angle greater than or equal to 110°. Step S3: Large-area growth of rubrene nanowires is performed on the sapphire substrate treated in step S2 using vapor deposition. The large-area growth of rubrene nanowires is carried out in a dual-temperature zone tube furnace. 10 mg of rubrene powder is placed in a quartz boat and placed in the source temperature zone. The sapphire substrate is placed on an 8 mm high slot plate and placed together in a quartz boat with an inner diameter of 29 mm, placed in the growth temperature zone. The distance between the rubrene powder and the substrate is 31 cm. The source temperature is 300 ℃, the growth temperature is 180 ℃, the carrier gas is N2 with a volumetric flow rate of 200 sccm, the pressure is 20 mbar, and the growth time is 30 min.

2. A method for the directional growth of rubrene nanowires, characterized in that, Includes the following steps: Step S1: Anneal the M-plane sapphire substrate to form parallel horizontal nanochannels on its surface; the temperature control program for the annealing process is as follows: increase from 25°C to 300°C at a rate of 4.58°C / min over 60 minutes, then increase from 300°C to 800°C at a rate of 8.3°C / min over 60 minutes, then increase from 800°C to 1600°C at a rate of 4.44°C / min over 180 minutes, then hold at 1600°C for 600 minutes, and then allow it to cool naturally to room temperature; Step S2: Perform a surface hydrophobic treatment on the sapphire substrate after the treatment in step S1. The hydrophobic treatment is to first perform a hydrophilic treatment on the sapphire substrate so that its contact angle is less than or equal to 20°, and then perform a hydrophobic treatment so that its surface contact angle is greater than or equal to 110°. Step S3: Cover the sapphire substrate surface after the treatment in step S2 with a mask, and then use vapor deposition to grow red fluorene nanowires on the sapphire substrate surface covered with the mask. The positioning growth is carried out in a dual-temperature zone tube furnace. Take 10 mg of red fluorene powder and place it in a quartz boat and place it in the source temperature zone; place the sapphire substrate on an 8 mm high tank plate and place it together in a quartz boat with an inner diameter of 29 mm and place it in the growth temperature zone; the distance between the red fluorene powder and the substrate is 25 cm; the source temperature zone temperature is 295 °C, the growth temperature zone temperature is 180 °C, the carrier gas is N2, the volumetric flow rate is 200 sccm, the pressure is 20 mbar, and the growth time is 30 min.

3. The method for directional growth of rubrene nanowires according to claim 1 or 2, characterized in that, The depth of the nanochannel is 5-15 nm.

4. The method for directional growth of rubrene nanowires according to claim 1 or 2, characterized in that, The hydrophilic treatment involves cleaning the sapphire substrate using a plasma gas generator; the hydrophobic treatment involves immersing the hydrophilic sapphire substrate in an OTMS solution.

5. The method for directional growth of rubrene nanowires according to claim 1 or 2, characterized in that, Before growth, the red fluorene powder is placed outside the growth temperature zone. After the temperature is raised to the set temperature, the red fluorene powder is pushed into the position set at the distance from the substrate.

6. Red fluorene nanowires, characterized in that, The nanowires were prepared using the method described in any one of claims 1-5 for the directional growth of rubrene nanowires.

7. The application of the rubrene nanowires as described in claim 6 in micro / nano optoelectronic device products.

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