An ultralong graphene nanoribbon semiconductor based on a nonmetallic substrate surface and a preparation method thereof
Patent Information
- Application Number
- CN202611523004.7
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2026-09-29
- Publication Date
- 2026-11-03
AI Technical Summary
The existing technology synthesizes graphene nanostrips on non-metallic substrates with excessively short lengths, which leads to increased carrier scattering, high end-boundary resistance, and requires complex transfer processes and introduces defects at the splicing interface, affecting device performance and yield.
Using non-metallic two-dimensional materials as substrates, and depositing metal atoms on their surface as catalysts, a stepwise annealing strategy is employed to carry out a Ullman coupling reaction under ultra-high vacuum conditions to prepare ultra-long graphene nanostrips. This avoids the shielding effect and strong coupling of the metal substrate, and allows for in-situ synthesis directly on the non-metallic surface.
The growth of micron-scale ultralong graphene nanostrips was achieved, which reduced the end-bound resistance, improved the carrier mobility, simplified the device fabrication process, avoided impurities and defects introduced by the transfer process, and directly constructed a continuous conductive channel.
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Figure CN123035868A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of low-dimensional semiconductor material preparation technology, and in particular to an ultralong graphene nanostrip semiconductor based on a non-metallic substrate surface and its preparation method. Background Technology
[0002] Semiconductor graphene nanostrips, due to their unique electronic structure and tunable band gap, have enormous application potential in fields such as field-effect transistors, spintronics, and optoelectronics. Traditional methods for preparing graphene nanostrips mainly include "top-down" photolithography / etching and "bottom-up" surface synthesis. Among them, the surface synthesis method utilizes halogenated precursor molecules on metal surfaces (such as Au(111) and Ag(111)) via Ullman coupling reactions, which can obtain atomically precise edges and widths.
[0003] However, most existing surface synthesis methods are limited to metal substrates. The high density of delocalized free electrons on the surface of metal substrates can lead to a shielding effect when characterizing the electronic states of samples. Furthermore, the strong interactions (hybridization) between organic molecules and the metal substrate often alter the electronic structure of graphene nanostrips, even causing band gap closure (metallization), severely affecting their semiconductor properties. Although nanostrips can be transferred to insulating or semiconductor substrates via transfer processes, these processes are complex and prone to introducing impurities and defects.
[0004] On the other hand, the graphene nanostrips synthesized on non-metallic substrates by existing methods are too short, which brings two core problems that directly affect device performance: First, the end boundaries of the nanostrips become the main scattering source of charge carriers, significantly increasing the end boundary resistance, resulting in the measured charge carrier mobility being far lower than theoretically expected; Second, short strips cannot directly cross the source-drain electrode spacing and must be spliced to form a conductive path. The splicing interface introduces additional contact resistance and structural defects, which severely limits the device's on / off ratio and yield.
[0005] Therefore, developing a method for directly synthesizing ultralong graphene nanostrips on non-metallic substrates (such as HOPG) is of great significance for preserving their intrinsic electronic properties, simplifying device fabrication processes, and reducing the requirements for micro- and nano-device processing technology. Summary of the Invention
[0006] To address the above-mentioned technical problems, this invention discloses an ultralong graphene nanostrip semiconductor based on a non-metallic substrate and its preparation method. The ultralong graphene nanostrips refer to those with a length exceeding 1 μm.
[0007] The technical solution adopted by this invention is as follows:
[0008] A method for preparing ultralong graphene nanoribbon semiconductors based on a non-metallic substrate surface includes the following steps:
[0009] Step S1 involves cleaning the non-metallic two-dimensional material substrate to remove the surface contamination layer; subsequently, annealing is performed under ultra-high vacuum conditions to obtain a clean and atomically flat step surface; wherein the vacuum level of the ultra-high vacuum conditions is 1×10⁻⁶. -4 ~1×10 -11 mbar; the annealing temperature is 100~700℃;
[0010] Step S2: Deposit precursor molecules on the non-metallic two-dimensional material substrate after step S1 to obtain a precursor molecule layer. The precursor molecules are halogen-containing organic molecules.
[0011] Step S3: Deposit metal atoms onto the precursor molecular layer;
[0012] Step S4 involves stepwise annealing of the sample to induce a Ullman coupling reaction in the precursor molecules, forming conjugated, ultra-long-chain semiconductor graphene nanoribbons. Steps S2 through S4 are all performed under ultra-high vacuum conditions.
[0013] This technical solution uses a non-metallic two-dimensional material as the substrate, avoiding the shielding effect and strong coupling of electronic states by the metal substrate, thus preserving the intrinsic semiconductor properties of the prepared graphene nanoribbons. By depositing metal atoms on the non-metallic surface, the energy barrier of the Ullman coupling reaction is lowered using the metal atoms as catalysts, solving the problem of low reactivity on the non-metallic surface. Through a stepwise annealing strategy, linear polymer chains are first constructed, followed by the construction of flat aromatic graphene nanoribbons, effectively inducing molecular growth along a specific direction and achieving the synthesis of ultralong nanoribbons. No complex transfer process is required, allowing for direct in-situ characterization or device fabrication on the prepared sample.
[0014] As a further improvement of the present invention, in step S1, the non-metallic two-dimensional material substrate is mechanically peeled off to remove the surface contamination layer; further, the mechanical peeling is to use adhesive tape to stick to the surface of the non-metallic two-dimensional material substrate and peel off the surface contamination layer of the non-metallic two-dimensional material.
[0015] As a further improvement of the present invention, in step S1, the annealing temperature is 450~520℃ and the annealing time is 1~1.5h.
[0016] As a further improvement of the present invention, in step S2, thermal deposition of precursor molecules is used; when heating the molecular source to deposit molecules, the temperature of the non-metallic two-dimensional material substrate is room temperature, the temperature of the molecular source is 50~500℃, and the heating time is 10~30min.
[0017] As a further improvement of the present invention, in step S3, the metal atom is Ag, Fe, Cu or Au atom, used to assist in the catalytic Ullman coupling reaction.
[0018] As a further improvement of the present invention, in step S3, when depositing metal atoms, the temperature of the non-metallic two-dimensional material substrate is room temperature, the temperature of the metal source is 500~1000℃, and the deposition time is 1~300min.
[0019] As a further improvement of the present invention, in step S4, the stepwise annealing involves first annealing at 50~200℃ for 10~30 min, and then annealing at 250~350℃ for 10~30 min. Further, the stepwise annealing involves first annealing at 150~220℃ for 15~20 min, and then annealing at 320~350℃ for 15~20 min.
[0020] As a further improvement of the present invention, in step S1, the non-metallic two-dimensional material substrate is HOPG, TMDs, h-BN or MoS2.
[0021] As a further improvement of the present invention, in step S2, the precursor molecule is 2,7-dibromofluorene.
[0022] This invention discloses an ultralong graphene nanostrip semiconductor based on a non-metallic substrate surface, which is prepared by the preparation method of the ultralong graphene nanostrip semiconductor based on a non-metallic substrate surface as described above.
[0023] This invention discloses the application of the ultralong graphene nanostrip semiconductor based on the surface of a non-metallic substrate as described above, for the fabrication of electronic / optoelectronic devices.
[0024] Compared with the prior art, the beneficial effects of the present invention are as follows:
[0025] The technical solution of this invention uses a non-metallic substrate, which avoids the shielding effect of the metal substrate on the electronic state of the graphene nanostrips. The semiconductor graphene nanostrips obtained by this preparation method have a length of micrometers, breaking through the limitation of existing synthesis technology which is less than 0.1 μm. The obtained graphene strips do not require subsequent transfer and can be directly used to make electronic / optoelectronic devices. Attached Figure Description
[0026] Figure 1 This is a schematic diagram of the synthesis reaction pathway of precursor molecules and graphene nanoribbons in Example 1 of the present invention.
[0027] Figure 2 This is a surface morphology diagram of the HOPG substrate after treatment in Embodiment 1 of the present invention.
[0028] Figure 3This is an atomic force microscope image of the HOPG substrate surface after the deposition of precursor molecules and metal atoms in Example 1 of the present invention.
[0029] Figure 4 The images show atomic force microscopy (AFM) images and length histograms of the ultra-long graphene nanostrips formed after the second annealing step in Example 1 of this invention; where (a) is an AFM image and (b) is a length histogram.
[0030] Figure 5 This is an atomic force microscope image and length statistical histogram of the ultra-long graphene nanostrips formed after the second annealing step in Example 1 of the present invention.
[0031] Figure 6 This is a partial STM image of the ultralong graphene nanostrips obtained in Example 1 of the present invention. Detailed Implementation
[0032] The preferred embodiments of the present invention will be described in further detail below.
[0033] A method for synthesizing ultralong graphene nanostrips based on a non-metallic substrate surface includes the following steps:
[0034] Step S1: Mechanically peel off the HOPG substrate and anneal it under ultra-high vacuum.
[0035] Step S2: Deposit precursor molecules on the HOPG substrate.
[0036] Step S3: Redeposit metal atoms on the HOPG substrate.
[0037] Step S4: By performing stepwise annealing on the sample, epitaxial growth is carried out along the surface to finally obtain ultra-long graphene nanoribbons.
[0038] Optionally, in step S1, mechanical peeling can be performed by the blue tape peeling method.
[0039] Optionally, in step S1, the vacuum level of the ultra-high vacuum is less than or equal to 1 × 10⁻⁶. -8 mbar.
[0040] Optionally, in step S1, the annealing temperature is 450~520℃.
[0041] Optionally, in step S1, the annealing time is 1 to 1.5 hours.
[0042] Optionally, in step S2, the substrate temperature is room temperature during molecule deposition.
[0043] Optionally, in step S2, the molecular source temperature is 80~150℃ during molecular deposition.
[0044] Optionally, in step S2, the deposition time of the deposited molecules is 10~30 min.
[0045] Optionally, in step S3, the substrate temperature is room temperature during molecule deposition.
[0046] Optionally, in step S3, the deposited metal atoms may be Au, Ag, Fe, or Cu.
[0047] Optionally, in step S3, the temperature of the metal source is 500~1000℃ when depositing metal atoms.
[0048] Optionally, in step S4, the step annealing is a two-step annealing, with the first annealing temperature being 150~220℃ and the second annealing temperature being 320~350℃, and the annealing time for both steps being 15~20min.
[0049] Traditionally, graphene materials possess high carrier mobility and zero bandgap characteristics. For device applications, it is generally desirable to have both high carrier mobility and a tunable bandgap to meet the high on / off ratio requirements of devices such as field-effect transistors and logic circuits. Considering this, two-dimensional graphene is cut into quasi-one-dimensional graphene nanostrips, utilizing quantum confinement and edge effects to open the bandgap. Furthermore, the fabrication of ultralong structures (micrometer-scale and above) of graphene nanostrips can meet the current requirements of ordinary semiconductor nodes for channels in devices larger than micrometers, making it a feasible channel material for high-performance nanoelectronic devices.
[0050] First, graphene nanostrips inherit the advantages of graphene in structure. Furthermore, the width and edge configuration of the strips can be precisely controlled by designing the precursor molecules. Nanostrips with different widths and edge types will exhibit different band gap characteristics than graphene, and the electrical properties of the material can be flexibly adjusted according to the needs of the device.
[0051] Secondly, previous research on the surface synthesis of graphene nanostrips has mostly been limited to metal substrates, which brings two prominent problems: First, the synthesized sample needs to be transferred from the metal substrate to the target substrate before device fabrication. The transfer process is prone to introducing impurities, wrinkles, and damage, which seriously affect device performance. Second, the high-density delocalized free electron gas on the surface of the metal substrate can have a shielding effect on the electronic states of the sample. Strong organic-metal coupling can also lead to the reconstruction or even metallization of the electronic bands of the nanostrips, changing their intrinsic conductivity, band gap, and optical response characteristics. More importantly, the graphene nanostrips obtained by existing methods on metal substrates are generally short in length. The strip end boundaries may become sources of carrier scattering, significantly increasing the end-bound resistance. At the same time, the short strips place high demands on advanced micro-nano device fabrication technologies. Ordinary fabrication techniques cannot directly construct complete devices across the electrode spacing; they need to be spliced to form a conductive path. The splicing interface introduces additional contact resistance and structural defects, severely limiting device performance and yield.
[0052] Therefore, a synthetic method capable of obtaining ultralong structures on non-metallic substrates is needed. Using the preparation method of this invention, after depositing metal atoms as a catalyst on the surface of a non-metallic two-dimensional material substrate, the dehalogenation polymerization reaction of precursor molecules can be directly completed on the non-metallic two-dimensional material substrate without subsequent transfer steps. This allows for the synthesis of longitudinally continuous ultralong graphene nanoribbons with lengths reaching the micrometer level, ranging from 1 to 8 μm. The advantages of the obtained ultralong structures are significant: on the one hand, they can effectively reduce the scattering effect of end boundaries on charge carriers, lower end-boundary resistance, and improve the intrinsic charge carrier mobility of the nanoribbons; on the other hand, they can directly realize the construction of continuous conductive channels across electrodes without the need for strip splicing, avoiding performance losses caused by splicing interfaces, and also providing a foundation for subsequent large-area, high-density device array arrangements.
[0053] Furthermore, as a non-metallic substrate, the non-metallic two-dimensional material does not suffer from the electronic state shielding problem present in metallic substrates. The surface of the non-metallic two-dimensional material possesses a highly ordered atomic arrangement and van der Waals layered structure. The interaction between the non-metallic two-dimensional material and the graphene nanostrips is dominated by van der Waals forces, and it does not form strong chemical coupling with the organic structure on the surface. Therefore, it does not lead to electronic band reconstruction or metallization of the nanostrips, thus preserving the intrinsic electrical properties of the nanostrips. Finally, the synthesis method proposed in this invention has universal guiding significance for the synthesis of ultralong graphene nanostrips on non-metallic substrates and can provide a technical reference for the synthesis of low-dimensional carbon nanostructures on non-metallic substrates.
[0054] The following description uses specific examples to illustrate the point.
[0055] Example 1
[0056] Taking a method for synthesizing ultralong graphene nanostrips on a HOPG substrate as an example, the method includes the following steps:
[0057] Step S1: Mechanically peel the HOPG using blue adhesive tape to remove the surface contamination layer. Then, rapidly place the sample into an ultra-high vacuum system with a vacuum level better than 1×10⁻⁶. -8 Under mbar conditions, the substrate is heated to 500°C and annealed for 1 hour to obtain a clean and atomically flat step surface.
[0058] Step S2: The precursor molecule 2,7-dibromofluorene is loaded into a Knudsen furnace. The Knudsen furnace is heated to 100-120°C, and the precursor molecule is deposited onto the HOPG substrate treated in step S1. The deposition time is 5 minutes, and the substrate is kept at room temperature.
[0059] Step S3: At room temperature, heat the metal source to 800°C using an electron beam evaporation or thermal evaporation source to deposit Cu atoms onto a substrate covered with precursor molecules. The deposition time is 1 minute. The introduction of Cu atoms is intended to act as a catalyst to assist the subsequent coupling reaction.
[0060] Step S4: Perform a two-step stepwise annealing treatment on the sample: Step 1: Heat the sample to 170℃ and hold for 20 min. This step aims to induce the formation of linear polymer chains between precursor molecules, causing the molecules to align in a specific direction. Step 2: Further heat the sample to 350℃ and hold for 20 min. This step aims to transform the linear polymer chains into flat aromatic graphene nanoribbons, ultimately growing ultra-long graphene nanoribbons while simultaneously removing Cu atoms.
[0061] In this embodiment, 2,7-dibromofluorene is used as a precursor molecule, which is deposited on the surface of a HOPG substrate. Heating is used to induce a coupling reaction in the precursor molecule, allowing it to grow epitaxially along the substrate surface, ultimately yielding ultralong graphene nanostrips. Finally, annealing is performed to remove the metal atoms.
[0062] Furthermore, 2,7-dibromofluorene molecular source was selected as the precursor evaporation source. Before the evaporation source was deposited, it could be treated to remove impurities by slowly evaporating small molecule impurities at low evaporation temperatures for 1-2 days until a pure precursor molecular evaporation source was obtained.
[0063] Furthermore, in step S1, the aforementioned HOPG substrate can provide good support for the two-dimensional porous graphene while meeting the requirement for substrate conductivity for LT-STM testing, and will not generate strong coupling with the material, affecting the study of the electronic state of the graphene nanostrips.
[0064] In this embodiment, 2,7-dibromofluorene was selected as the precursor molecule. The structure of 2,7-dibromofluorene is shown in formula (1).
[0065] (1)
[0066] The synthesis reaction pathway diagram of precursor molecules and graphene nanoribbons is shown below. Figure 1 As shown. The 2,7-dibromofluorene molecular source was heated to 160°C for approximately two days (40-48 hours) to remove impurities, purify the precursor molecules, and obtain a stable molecular evaporation rate. Mechanical exfoliation and thermal annealing to 500°C for 1 hour on a HOPG substrate were then performed to obtain a clean and atomically flat step surface. The AFM image of the clean and flat HOPG substrate is shown below. Figure 2 As shown. Precursor molecules were deposited on a HOPG substrate by thermal evaporation at a temperature of 140°C for 5 minutes, with a deposition pressure of 1×10⁻⁶. -8 mbar; then Cu atoms are deposited on the HOPG substrate by electron beam evaporation or thermal evaporation at a temperature of 800℃ for 5 mins. The AFM image of the HOPG surface after deposition of precursor molecules and metal atoms is shown below. Figure 3 As shown. Finally, a two-step annealing process was performed under ultra-high vacuum: Ullmann polymerization occurred at 180–220 °C, where a copper catalyst induced the breakage of the C-Br bond, and the generated aryl radicals coupled to form C-C bonds between the precursor monomers, thereby constructing a linear polymer chain. The AFM image of the ultralong graphene nanostrips is shown below. Figure 4 As shown in (a) in the figure, Figure 4 As shown in (b), the lengths of the ultralong graphene nanostrips are concentrated in the range of 1.4–1.6 micrometers.
[0067] Based on Example 1, the temperature of the second annealing step was changed to 320°C as a control sample.
[0068] The statistical histograms of the lengths of graphene nanostrips obtained by annealing at different temperatures in the second step of Example 1 and the control sample are shown below. Figure 5 As shown, graphene nanostrips with significantly different lengths are formed at different annealing temperatures. In Example 1, after the second step of annealing, the sample was transferred to the chamber of a low-temperature high-resolution scanning tunneling microscope (LT-STM) for in-situ imaging characterization, as shown... Figure 6 As shown, the lattice structure of ultralong graphene nanostrips on the HOPG surface can be observed.
[0069] The above description, in conjunction with specific preferred embodiments, provides a further detailed explanation of the present invention. It should not be construed that the specific implementation of the present invention is limited to these descriptions. For those skilled in the art, various simple deductions or substitutions can be made without departing from the concept of the present invention, and all such modifications and substitutions should be considered within the scope of protection of the present invention.
Claims
1. A method for preparing ultralong graphene nanostrip semiconductors based on a non-metallic substrate surface, characterized in that: Includes the following steps: Step S1 involves cleaning the non-metallic two-dimensional material substrate to remove the surface contamination layer; subsequently, annealing is performed under ultra-high vacuum conditions to obtain a clean and atomically flat step surface; wherein the vacuum level of the ultra-high vacuum conditions is 1×10⁻⁶. -4 ~1×10 -11 mbar; the annealing temperature is 100~700℃; Step S2: Deposit precursor molecules on the non-metallic two-dimensional material substrate after step S1 to obtain a precursor molecule layer. The precursor molecules are halogen-containing organic molecules. Step S3: Deposit metal atoms onto the precursor molecular layer; the metal atoms are Ag, Fe, Cu, or Au atoms; Step S4: Perform stepwise annealing on the sample to induce the precursor molecules to undergo a Ullman coupling reaction and form long-chain graphene nanoribbons; wherein, the stepwise annealing is to first anneal at 50~200℃ for 10~30min, and then anneal at 250~350℃ for 10~30min.
2. The method for preparing ultralong graphene nanostrip semiconductors based on a non-metallic substrate surface according to claim 1, characterized in that: In step S1, the non-metallic two-dimensional material substrate is mechanically peeled off to remove the surface contamination layer; the mechanical peeling is performed by using adhesive tape to stick to the surface of the non-metallic two-dimensional material substrate and peeling off the surface contamination layer of the non-metallic two-dimensional material; in step S1, the annealing temperature is 450~520℃ and the annealing time is 1~1.5h.
3. The method for preparing ultralong graphene nanostrip semiconductors based on a non-metallic substrate surface according to claim 1, characterized in that: In step S2, thermal deposition of precursor molecules is used; when heating the molecular source to deposit molecules, the temperature of the non-metallic two-dimensional material substrate is room temperature, the molecular source temperature is 50~500℃, and the heating time is 10~30 min.
4. The method for preparing ultralong graphene nanostrip semiconductors based on a non-metallic substrate surface according to claim 3, characterized in that: In step S3, when depositing metal atoms, the temperature of the non-metallic two-dimensional material substrate is room temperature, the temperature of the metal source is 500~1000℃, and the deposition time is 1~300min.
5. The method for preparing ultralong graphene nanostrip semiconductors based on a non-metallic substrate surface according to claim 1, characterized in that: In step S4, the stepwise annealing involves first annealing at 150~220℃ for 15~20min, and then annealing at 320~350℃ for 15~20min.
6. The method for preparing ultralong graphene nanostrip semiconductors based on a non-metallic substrate surface according to claim 1, characterized in that: In step S1, the non-metallic two-dimensional material substrate is HOPG, TMDs, h-BN, or MoS2.
7. The method for preparing ultralong graphene nanostrip semiconductors based on a non-metallic substrate surface according to claim 1, characterized in that: In step S2, the precursor molecule is 2,7-dibromofluorene.
8. An ultralong graphene nanostrip semiconductor based on a non-metallic substrate surface, characterized in that: It was prepared using the method for preparing ultralong graphene nanostrip semiconductors based on non-metallic substrate surfaces as described in any one of claims 1 to 7.
9. The application of the ultralong graphene nanostrip semiconductor based on a non-metallic substrate surface as described in claim 8, characterized in that: Used in the fabrication of electronic / optoelectronic devices.