TWO-DIMENSIONAL MATERIAL NANOSHEETS WITH LARGE AREA AND CONTROLLABLE THICKNESS AND GENERAL PREPARATION METHOD THEREFOR

Abstract

The present invention provides a two-dimensional material nanosheets with a large area and a controllable thickness and a general preparation method therefor. As an intralayer heat transfer coefficient of a two-dimensional material is much higher than an interlayer heat transfer coefficient thereof, the two-dimensional material is uniformly heated and sublimated layer by layer by controlling the energy of the laser pulses, a thinning thickness is controlled by adjusting the action time of the laser pulses, and finally, a two-dimensional material film with a controllable thickness is obtained. At the same time, a sample displacement stage moving freely in a two-dimensional plane space can realize preparation of the two-dimensional material film with a large area. Compared with traditional methods, the present invention can control a sample thickness of the two-dimensional material film, has a high generality, and is suitable for all kinds two-dimensional materials.

Claims

1. A general preparation method for a two-dimensional material nanosheets with a large area and a controllable thickness, comprising the following steps: 1) obtaining a multilayer two-dimensional material film on a SiO.sub.2 substrate, wherein each layer has a uniform and identical thickness; 2) coating a polymethyl methacrylate (PMMA) film on the surface of the two-dimensional material film by a spin-coating method; 3) heating and curing the PMMA film obtained by spin coating, with a heating condition being: 90° C.-110° C. for 1-3 minutes; 4) fixing a two-dimensional material sample coated with the PMMA film and adhered to the SiO.sub.2 substrate on a sample stage (5) of a high-energy nanosecond laser, wherein the sample stage (5) is connected with a displacement stage (6), the position of the sample stage (5) is adjusted by the displacement stage (6), the displacement stage can move in both directions of the XZ axis, the moving accuracy is on the order of 10 microns, and the maximum moving distances are: 10 cm and 10 cm; 5) using a high-energy nanosecond laser pulse device to provide Gaussian laser pulses with a laser wavelength of 532 nm and a spot diameter of 1 cm to heat and sublimate the sample on the sample stage (5); and controlling the displacement stage (6) to move in both directions of the XZ axis to make the action area of the laser gradually cover the whole substrate; different two-dimensional materials are heated and sublimated by adjusting pulse energy and pulse number, and the two-dimensional materials are sublimated and thinned layer by layer from the surface: by controlling laser pulse number, the number of layers being thinned is increased, and the thickness of the materials is reduced; and by adjusting the laser pulse number, the number of material layers being sublimated is controlled; the high-energy nanosecond laser pulse device comprises the high-energy nanosecond laser (1), a frequency doubler (2), an attenuator (3), a beam splitter (4), the sample stage (5) and the displacement stage (6); nanosecond laser pulses with a wavelength of 1064 nm are emitted by the high-energy nanosecond laser (1), the time of one pulse is 1 ns-10 ns, and the pulse number is 1-25; the wavelength of the nanosecond laser pulses is adjusted to 532 nm after passing through the frequency doubler (2), then the energy of the nanosecond laser pulses is attenuated to a required power range of 10 mJ-25 mJ after passing through the attenuator (3), and the nanosecond laser pulses are irradiated to the sample stage (5) by the beam splitter (4) used in conjunction with the attenuator; 6) immersing the sample treated by the laser in acetone to remove the PMMA on the surface and obtain a two-dimensional material film with a large area and a uniform thickness; the two-dimensional material is graphite, black phosphorus or molybdenum disulfide.

2. The general preparation method for a two-dimensional material nanosheets with a large area and a controllable thickness according to claim 1, wherein in step 1), the two-dimensional material film prepared by physical vapor deposition or chemical vapor deposition has a thickness uniformity of ±5%.

3. The general preparation method for a two-dimensional material nanosheets with a large area and a controllable thickness according to claim 1, wherein in step 2), the spin-coating process is: 400-800 RPM for 5-10 seconds and 3000-4000 RPM for 20-40 seconds, and the thickness of the PMMA layer obtained by spin coating is 200-400 nm.

4. The general preparation method for a two-dimensional material nanosheets with a large area and a controllable thickness according to claim 1, wherein in step 5), after laser heating treatment at one position, the position of the sample is continually adjusted by the displacement stage to continue laser treatment and obtain the two-dimensional material film with a size of 10 cm with a uniform and controllable thickness.

5. The general preparation method for a two-dimensional material nanosheets with a large area and a controllable thickness according to claim 1, wherein in step 5), the displacement stage (6) comprises an x-axis displacement stage and a z-axis displacement stage, the x-axis displacement stage is provided with an x-axis guide rail (9) and an x-axis displacement knob (10), the z-axis displacement stage is provided with a z-axis guide rail (8), a z-axis displacement knob (7) and an object stage (11), the z-axis and x-axis displacement knobs are used to manually adjust the position of the sample stage in the vertical direction and the horizontal direction respectively, and the z-axis and x-axis guide rails play a role of assisting the sample stage to move electrically or manually; the object stage (11) can be controlled by the z-axis displacement knob (7) to move on the z-axis guide rail (8) along the vertical direction, and the sample stage (5) is installed on the object stage (11); the z-axis displacement stage can be controlled by the x-axis displacement knob (10) to move on the x-axis guide rail (9) along the horizontal direction; the displacement stage (6) is used in conjunction with the sample stage (5), the position of the sample stage (5) is adjusted electrically or manually by the displacement stage (6), and the maximum moving distances can reach 10 cm.

6. The general preparation method for a two-dimensional material nanosheets with a large area and a controllable thickness according to claim 1, wherein in step 6), the time for immersion in acetone is 1-2 hours.

Description

DESCRIPTION OF DRAWINGS

[0029] FIG. 1 is a structural schematic diagram of a high-energy nanosecond laser pulse device.

[0030] FIG. 2 is a structural schematic diagram of a displacement stage.

[0031] FIG. 3 is a schematic diagram of a principle for preparing a two-dimensional material nano film with a controllable thickness.

[0032] FIG. 4 shows optical micrographs of a graphene film before and after treatment with a 10 mJ high-energy nanosecond laser pulse device for 20 times in embodiment 1. (a) is an optical micrograph of a graphene sample before laser treatment, and (b) is an optical micrograph of the graphene sample after laser treatment.

[0033] FIG. 5 shows Raman spectrograms of a graphene film before and after treatment with a 10 mJ high-energy nanosecond laser pulse device for 20 times in embodiment 1. (a) is a Raman spectrogram of a graphene sample before laser treatment, and (b) is a Raman spectrogram of the graphene sample after laser treatment.

[0034] FIG. 6 shows optical micrographs of a molybdenum disulfide film before and after treatment with a 12 mJ high-energy nanosecond laser pulse device for 25 times in embodiment 2. (a) is an optical micrograph of a molybdenum disulfide sample before laser treatment, and (b) is an optical micrograph of the molybdenum disulfide sample after laser treatment.

[0035] FIG. 7 shows Raman spectrograms of a molybdenum disulfide film before and after treatment with a 12 mJ high-energy nanosecond laser pulse device for 25 times in embodiment 2. (a) is a Raman spectrogram of a molybdenum disulfide sample before laser treatment, and (b) is a Raman spectrogram of the molybdenum disulfide sample after laser treatment.

[0036] FIG. 8 shows optical micrographs of a black phosphorus nano sheet before and after treatment with a high-energy nanosecond laser pulse device in embodiment 3. In which, (a) is an optical micrograph of a black phosphorus sample before laser treatment, and (b) is an optical micrograph of the black phosphorus sample after laser treatment.

[0037] FIG. 9 shows Raman spectrograms of a black phosphorus nano sheet before and after treatment with a high-energy nanosecond laser pulse device in embodiment 3. In which, (a) is a Raman spectrogram of a black phosphorus sample before laser treatment, and (b) is a Raman spectrogram of the black phosphorus sample after laser treatment.

[0038] FIG. 10 is an AFM scanogram of a black phosphorus nano sheet prepared in embodiment 3.

[0039] In the figures: 1 high-energy laser; 2 frequency doubler; 3 attenuator; 4 beam splitter; 5 sample stage; 6 displacement stage; 7 z-axis displacement knob; 8 z-axis guide rail; 9 x-axis guide rail; 10 x-axis displacement knob; 11 object stage.

DETAILED DESCRIPTION

[0040] The present invention is further described below in combination with drawings and embodiments. However, the present invention is not limited to the following embodiments, and shall include all contents of the claims.

Embodiment 1

[0041] A preparation method for a graphene film with a size of 10 cm and a controllable thickness of 1-100 layers, which is described in detail in accordance with a preferred embodiment:

[0042] 1) Preparing a 100-layer graphene film, comprising the following steps:

[0043] Growing graphene with a large area and a thickness of 100 layers by a CVD material growing process. A substrate material used is a nickel foil with a thickness of 300 nm, the nickel foil is placed in dilute nitric acid to be corroded for 15 minutes, washed, and blow-dried with nitrogen; then the nickel foil is immediately placed into a CVD chamber, and the chamber is vacuumed to 500 mTorr.

[0044] The growing temperature is 1000° C., the raw material is a mixture of methane and hydrogen with gas flows of 35 sccm and 2 sccm respectively, and graphene with a large area (10 cm*10 cm), a clean surface and a thickness of 100 layers is obtained by growing.

[0045] Preparing a 4-inch SiO.sub.2 substrate; ultrasonic cleaning the SiO.sub.2 substrate with acetone, isopropyl alcohol and deionized water for 15 minutes successively, and blow-drying the SiO.sub.2 substrate for later use; transferring the graphene to a SiO.sub.2 surface by a film wet transfer technology, and airing the graphene in a fume hood for two hours to make the graphene adhere tightly to the SiO.sub.2 surface; spin-coating PMMA onto the surface of the graphene material by a spin coater, with the spin-coating condition being: 400 RPM for 8 seconds and 3000 RPM for 20 seconds; heating and curing the PMMA film obtained by spin coating, with a heating condition being: 90° C. for 2 minutes, and forming a uniform PMMA thin layer with a thickness of 400 nm on the surface of a graphene sample.

[0046] 2) Preparing a graphene film with a controllable thickness by a heating and sublimating method using a high-energy nanosecond laser pulse device, comprising the following steps:

[0047] Clamping the graphene sample with a PMMA coating on a 4-inch SiO.sub.2 substrate onto a sample stage, and connecting the sample stage with a displacement stage; setting the wavelength of a nanosecond laser pulse laser to 532 nm, setting the pulse energy to 10 mJ, setting the duration of one laser pulse to 1 ns, and setting the action area of a laser spot on the graphene sample to be a circle with a diameter of 1 cm. When one pulse is applied, the number of layers of the graphene is reduced from 100 to 95; by increasing pulse number, the number of layers of the graphene is reduced linearly; and when the pulse number exceeds 20, only a single-layer graphene film is left on the SiO.sub.2 substrate. This is because the heat transfer coefficient of the SiO.sub.2 substrate is much higher than the interlayer heat transfer coefficient of the graphene material. Therefore, heat of laser pulses is transferred to the SiO.sub.2 substrate by a single layer of graphene, and the single layer of graphene will not be sublimated due to insufficient temperature.

[0048] 3) Preparing a graphene film with a size of tens of centimeters and a controllable thickness by a sample displacement stage, comprising the following steps:

[0049] Controlling the displacement stage to move in both directions of the XZ axis to make the action area of the laser gradually cover the whole 4-inch substrate; removing the treated sample, and immersing the sample in acetone for 1 hour to remove the PMMA on the surface and prepare a two-dimensional graphene film with a large area and a uniform thickness. The size of the two-dimensional graphene film prepared in the embodiment is 10 cm, and the number of layers is continually controllable from 1 to 100.

[0050] FIG. 4 shows optical micrographs of a graphene film before and after treatment with a high-energy nanosecond laser pulse device in the experiment. In which, FIG. 4(a) is an optical micrograph of a graphene film sample before laser treatment, and FIG. 4(b) is an optical micrograph of the graphene film sample after laser treatment.

[0051] FIG. 5 shows Raman spectrograms of a graphene film before and after treatment with a high-energy nanosecond laser pulse device in the experiment. In which, FIG. 5(a) is an Raman spectrogram of a graphene film sample before laser treatment, and FIG. 5(b) is an Raman spectrogram of the graphene film sample after laser treatment.

Embodiment 2

[0052] A preparation method for a molybdenum disulfide film with a size of 10 cm and a controllable thickness of 1-50 layers, which is described in detail in accordance with a preferred embodiment:

[0053] 1) Preparing a 50-layer molybdenum disulfide film, comprising the following steps:

[0054] Growing a molybdenum disulfide film with a large area and a thickness of 50 layers by a PVD material growing process. A substrate material used is SiO.sub.2, the SiO.sub.2 is placed in acetone, isopropyl alcohol and deionized water in sequence for ultrasonic treatment, washed, and blow-dried with nitrogen; then the SiO.sub.2 is immediately placed into a PVD chamber, and the chamber is vacuumed to 500 mTorr.

[0055] The growing temperature is 800° C., the raw material is high-purity molybdenum disulfide powder, argon is used as a carrier with a gas flow of 100 sccm, and the molybdenum disulfide film with a large area (10 cm*10 cm), a clean surface and a thickness of 50 layers is obtained by growing.

[0056] Spin-coating PMMA onto the surface of the molybdenum disulfide film by a spin coater, with the spin-coating condition being: 500 RPM for 8 seconds and 3500 RPM for 30 seconds; heating and curing the PMMA film obtained by spin coating, with a heating condition being: 90° C. for 2 minutes, and forming a uniform PMMA thin layer with a thickness of 300 nm on the surface of the molybdenum disulfide film.

[0057] 2) Preparing a molybdenum disulfide film with a controllable thickness by a heating and sublimating method using a high-energy nanosecond laser pulse device, comprising the following steps:

[0058] Clamping a molybdenum disulfide sample with a PMMA coating on a 4-inch SiO.sub.2 substrate onto a sample stage, and connecting the sample stage with a displacement stage; setting the wavelength of a nanosecond laser pulse laser to 532 nm, setting the pulse energy to 15 mJ, setting the duration of one laser pulse to 1 ns, and setting the action area of a laser spot on the molybdenum disulfide sample to be a circle with a diameter of 1 cm. When one pulse is applied, the number of layers of molybdenum disulfide is reduced from 50 to 48; by increasing pulse number, the number of layers of the molybdenum disulfide is reduced linearly; and when the pulse number exceeds 25, only a single-layer molybdenum disulfide film is left on the SiO.sub.2 substrate. This is because the heat transfer coefficient of the SiO.sub.2 substrate is much higher than the interlayer heat transfer coefficient of the molybdenum disulfide material. Therefore, heat of laser pulses is transferred to the SiO.sub.2 substrate by a single layer of molybdenum disulfide, and the single layer of molybdenum disulfide will not be sublimated due to insufficient temperature.

[0059] 3) Preparing a molybdenum disulfide film with a size of tens of centimeters and a controllable thickness by a sample displacement stage, comprising the following steps:

[0060] Controlling the displacement stage to move in both directions of the XZ axis to make the action area of the laser gradually cover the whole 4-inch substrate; removing the treated sample, and immersing the sample in acetone for 1 hour to remove the PMMA on the surface and prepare a two-dimensional molybdenum disulfide film with a large area and a uniform thickness. The size of the two-dimensional molybdenum disulfide film prepared in the embodiment is 10 cm, and the number of layers is continually controllable from 1 to 50.

[0061] FIG. 6 shows optical micrographs of a molybdenum disulfide film before and after treatment with a high-energy nanosecond laser pulse device for 25 times in the experiment. In which, FIG. 6(a) is an optical micrograph of a molybdenum disulfide film sample before laser treatment, and FIG. 6(b) is an optical micrograph of the molybdenum disulfide film sample after laser treatment.

[0062] FIG. 7 shows Raman spectrograms of a molybdenum disulfide film before and after treatment with a high-energy nanosecond laser pulse device for 25 times in the experiment. In which, FIG. 7(a) is a Raman spectrogram of a molybdenum disulfide film sample before laser treatment, and FIG. 7(b) is a Raman spectrogram of the molybdenum disulfide film sample after laser treatment.

Embodiment 3

[0063] A preparation method for a black phosphorus film with a size of 10 cm and a controllable thickness of 10-100 layers, which is described in detail in accordance with a preferred embodiment:

[0064] 1) Preparing reactants, comprising the following steps:

[0065] Preparing a 4-inch SiO.sub.2 substrate; ultrasonic cleaning the SiO.sub.2 substrate with acetone, isopropyl alcohol and deionized water for 15 minutes successively, and blow-drying the SiO.sub.2 substrate for later use; placing 1 mg of single crystal black phosphorus sample on an adhesive tape, and performing mechanical exfoliation by repeating folding without overlapping for 10 times; transferring a black phosphorus nano sheet obtained by mechanical stripping to the cleaned SiO.sub.2 substrate; spin-coating PMMA onto the surface of the black phosphorus material by a spin coater, with the spin-coating condition being: 800 RPM for 10 seconds and 4000 RPM for 40 seconds; heating and curing the PMMA film obtained by spin coating, with a heating condition being: 90° C. for 2 minutes, and forming a uniform PMMA thin layer with a thickness of 200 nm on the surface of the black phosphorus sample.

[0066] 2) Preparing a black phosphorus nanosheet by a heating and sublimating method using a high-energy nanosecond laser pulse device, comprising the following steps:

[0067] Clamping the black phosphorus sample with a PMMA coating on a 4-inch SiO.sub.2 substrate onto a sample stage 5, and connecting the sample stage 5 with a displacement stage 6; setting the wavelength of a nanosecond laser pulse laser to 532 nm, setting the pulse energy to 25 mJ, setting the duration of one laser pulse to 1 ns, and setting the action area of a laser spot on the black phosphorus sample to be a circle with a diameter of 1 cm. When one pulse is applied, the number of layers of black phosphorus is reduced by 5; by increasing pulse number, the number of layers of the black phosphorus is reduced linearly; and when the pulse number exceeds 19, a 10-layer black phosphorus film with a thickness of 5 nm is left on the SiO.sub.2 substrate. This is because the heat transfer coefficient of the SiO.sub.2 substrate is higher than the interlayer heat transfer coefficient of the black phosphorus material. Therefore, heat of laser pulses is transferred to the SiO.sub.2 substrate by 10 layers of black phosphorus, and the 10 layers of black phosphorus will not be sublimated due to insufficient temperature.

[0068] 3) Preparing a black phosphorus film with a size of tens of centimeters and a controllable thickness by a sample displacement stage, comprising the following steps:

[0069] The z-axis and x-axis displacement knobs of the displacement stage 6 are used to manually adjust the position of the sample stage 5 in the vertical direction and the horizontal direction respectively, the z-axis displacement knob 7 and the x-axis displacement knob 10 are used to adjust the position of the sample stage in the vertical direction and the horizontal direction respectively, the z-axis guide rail 8 and the x-axis guide rail 9 play a role of assisting the sample stage to move, and the sample stand 5 is moved vertically and horizontally along the guide rails.

[0070] Controlling the displacement stage 6 to move in both directions of the XZ axis to make the action area of the laser gradually cover the whole 4-inch substrate; and immersing the sample in acetone for 1 hour to remove the PMMA on the surface and prepare a two-dimensional black phosphorus nanosheet with a large area and a uniform thickness. The two-dimensional black phosphorus film prepared in the embodiment has a structure of 10 layers, with a thickness of 0.5 nm for each layer, a total thickness of 5 nm and a size of 10 cm.

[0071] FIG. 8 shows optical micrographs of a black phosphorus film before and after treatment with a high-energy nanosecond laser pulse device in the experiment. It can be seen from the figure that the thickness of a black phosphorus sample before treatment is relatively thick, and the thickness of black phosphorus after laser treatment is significantly reduced.

[0072] FIG. 9 shows Raman spectrograms of a black phosphorus film before and after treatment with a high-energy nanosecond laser pulse device in the experiment. It can be seen from the figure that each Raman spectrogram has three purity characteristic peaks; in terms of position, the purity characteristic peaks are consistent with Raman characteristic peaks of black phosphorus, which indicates that the sample contains no oxide or other impurities, and the purity is high; in terms of amplitude, the Raman peaks of the black phosphorus sample before treatment are significantly higher than those after treatment, which indicates that the thickness is significantly reduced.

[0073] FIG. 10 is an AFM scanogram of a black phosphorus nano sheet prepared in the experiment. It can be seen from the figure that the thickness of a sample is about 5 nm.

[0074] The above embodiments 1, 2 and 3 are typical embodiments of the present invention and do not constitute any limitation of the present invention. For example, quantity of bulk materials, laser pulse energy, laser pulse number, etc. can be further adjusted. Therefore, according to the general idea of the present invention, the adjustments and modifications of the described process parameters made by those skilled in the art shall fall into the protection scope of the present invention without departing from the conception of the present invention or going beyond the scope defined in the claims.