Method for preparing graphene

Abstract

The invention belongs to the technical field of inorganic compounds, and particularly, relates to a method for directly preparing graphene by taking CBr.sub.4 as a source material and using methods such as molecular-beam epitaxy (MBE) or chemical vapor deposition (CVD). A method for preparing graphene comprises the following steps: selecting a proper material as a substrate; directly depositing a catalyst and CBr.sub.4 on a surface of the substrate; and performing annealing treatment on the sample obtained through deposition. Compared with other technologies, an innovative point of the method in the invention is that the catalyst and CBr.sub.4 source can be quantitatively and controllably deposited on any substrate, and the catalyst and CBr.sub.4 source react on the surface of the substrate to form the graphene, so that the dependence of the graphene growth on a substrate material can be reduced to a great extent, and different substrate materials can be selected according to different application backgrounds.

Claims

1. A method for preparing graphene, comprising the following steps: (1) selecting a proper material as a substrate; (2) directly depositing CBr.sub.4 and catalys on a surface of the substrate, the catalyst is Ga, the deposition manner for CBr.sub.4 and catalyst is alternatively deposition in any order more than once, in each deposition manner, the total deposition of CBr.sub.4 is 3.8E7-3.8E9 molecules/μm.sup.2, the total deposition of catalyst is 1.7E7-1.7E9 atoms/m.sup.2, and a deposition temperature for the CBr.sub.4 and catalyst is between 10° C. and 490° C.; (3) performing annealing treatment on the sample obtained by step 2 to obtain the graphene.

2. The method for preparing graphene according to claim 1, characterized in that, the method for depositing the CBr.sub.4 and catalyst is molecular-beam epitaxy or chemical vapor deposition.

3. The method for preparing graphene according to claim 1, characterized in that, the substrate material is selected from metal, semiconductor, or insulator.

4. The method for preparing graphene according to claim 3, characterized in that, the substrate material is selected from silicon, germanium, silicon oxide, and sapphire.

5. The method for preparing graphene according to claim 1, characterized in that, the method for annealing treatment is that: the substrate is raised to 650-720° C., and the annealing time is 5-180 minutes; when completed, the temperature of the substrate is decreased to room temperature.

6. The method for preparing graphene according to claim 1, characterized in that, before step (1), the substrate further requires for a deoxygenation treatment and a pre-annealing treatment.

7. The method for preparing graphene according to claim 6, characterized in that, deoxidize temperature of the substrate material in the deoxygenation treatment is 400-700° C., temperature of the annealing treatment of the substrate material is 600-750° C.

8. A method for preparing graphene according to claim 1, characterized in that, in step (2) the deposition temperature for the CBr.sub.4 and catalyst is 450° C.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a roman spectrum of a sample before an annealing treatment, in which no obvious 2D peak can be observed.

(2) FIG. 2 is a roman spectrum of a sample 30 minutes after an annealing treatment at 800° C., in which 2D peak can be obviously observed, indicating the existence of graphene.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

(3) Embodiment 1

(4) The object of the present invention is to provide a convenient method for directly preparing graphene by taking CBr.sub.4 as a source material.

(5) In order to further elaborate the present method, herein, we illustrate a specific process for preparing graphene by taking semiconductor Ge as a substrate and using molecular beam epitaxial technique.

(6) In the experiment, Oxford Instruments V90 gas source molecular beam epitaxy (GSMBE) system is adopted, wherein the V90 may not only be used as the experimental instrument, but also be used as an equipment for small-scale production. It enables to epitaxial grow one piece of substrate of 4 inches, or one piece of substrate of 3 inches, or three pieces of substrate of 2 inches at one time, and in addition to manual operation, the automatic operation is allowable as well.

(7) In the experiment, we choose semiconductor Ge (2° offset) as a substrate, the temperature of which is further raised from 150° C. to 680° C. at a rate of 0.5° C./s by a heater. Around 455° C., it is observed that the oxides on the substrate are rapidly removed. Keep the substrate at the temperature of 680° C. to perform annealing for 20 minutes, and once the annealing is completed, the temperature of the substrate is cooled down to 450° C. to perform the growth of graphene sample; for growth, the temperature of the Ga furnace is raised to 1015° C., while the pressure of CBr.sub.4 is adjusted to PCBr.sub.4=0.12 Torr. During the growth process, firstly, Ga is deposited for 80 seconds, with a deposition of 1.7E8 atoms/μm.sup.2; then turn on a CBr.sub.4 valve, with a deposition of 3.8E7 molecules/μm.sup.2, turn off the CBr.sub.4 valve after 20 minutes; the above process was repeated 10 times. After that, the temperature of the substrate is raised to 720° C. at a rate of 0.8° C./s to perform annealing, and the total time from the beginning of heating to the end of annealing so that start to cool, is 16 minutes. After annealing, the temperature of the substrate is cooled down to finish the growth.

(8) After the sample growth is completed, the sample is annealed. Then, the samples before and after annealing were detected by Raman spectra. Raman spectra is carried out by a DXR type Raman spectroscopy produced by Thermal Scientific Company, which adopts a laser of 532 nm to excite, a scanned range of 1000-3000 cm.sup.−1, and a wave number resolution of 1 cm.sup.−1.

(9) Raman spectra is a kind of scattering spectrum. Raman spectroscopy is based on the Raman scattering found by the Indian scientist Raman, and is an analytical method applied in the investigation of molecular structure by the analyze of scattering spectra that having different frequency with the incident light, so as to obtain the information of vibration and rotation of molecules. The application of Raman spectra for characterizing graphene allows the numbers of layers of the graphene to be determined more precisely. The shape of the Raman spectra (including peak position and peak stretch) is mainly determined by the number of layers and mass of the graphene, thus the number of layers and mass of the graphene can be nondestructive characterized with high efficiency by using Raman spectra. The shape, width and position of the Raman spectra are related to its numbers of layers, so that it provides a high efficiency, nondestructive characterization method to measure the numbers of layers of a graphene. Both G peak (˜1580 cm.sup.−1) and 2D peak (˜2700 cm.sup.−1) are characteristic peaks of graphene, such that the general number of layers of graphene may be determined by the intensity ratio of D peak and G peak. D peak (˜1350 cm.sup.−1) accompanies with a variety of defects.

(10) Raman spectral measurement of the unannealed graphene is shown in FIG. 1. As can be seen from FIG. 1, there are two obvious absorption peaks, i.e., an absorption peak (G peak) at 1586 cm.sup.−1 and an absorption peak (D peak) at 1373 cm.sup.−1, with low signal-to-noise ratio and weaker signal strength.

(11) The temperature of the grown sample is raised to 800° C. to perform annealing for 30 minutes, and the Raman spectra of the sample after annealing is shown in FIG. 2. As can be seen from FIG. 2, there are three obvious absorption peaks, i.e., an absorption peak (G peak) at 1565 cm.sup.−1, an absorption peak (D peak) at 1338 cm.sup.−1, and an absorption peak at 2678 cm.sup.−1. When compared to the sample before annealing, the sample after annealing shows a slight offset for both G peak and D peak, as well as an obvious better spectral characteristic, and a ten times increasing of intensity, and an appearance of 2D peak. The Raman peak at 2678 cm.sup.−1 ought to be the 2D peak of the epitaxial graphene, indicating that the inventors have successfully obtained graphene samples.

(12) The inventors have illustrated the experimental results that graphene has been successfully prepared by taking a semiconductor Ge as a substrate and using molecular beam epitaxy technique, which proves the feasibility of the method of the present invention; further optimize experimental parameters and post-treatment process are expected to achieve high-quality graphene films. Certainly, the method can be extended to other metal, semiconductor or insulator substrates, such as silicon, germanium, silicon oxide, sapphire and the like.