Methods of controllably forming bernal-stacked graphene layers
Methods of controllably forming Bernal-stacked graphene layers are disclosed. The methods comprise: (1) cleaning a surface of a catalyst; (2) annealing the surface of the catalyst; (3) applying a carbon source onto the cleaned and annealed surface of the catalyst in a reaction chamber; and (4) growing the Bernal-stacked graphene layers on the surface of the catalyst in the reaction chamber, where the number of formed Bernal-stacked graphene layers is controllable as a function of one or more growth parameters, such as a total pressure of the reaction chamber. Further embodiments of the present disclosure also include steps of: (5) terminating the growing step; and (6) transferring the formed Bernal-stacked graphene layers from the surface of the catalyst onto a substrate.
1. A method of controllably forming Bernal-stacked graphene layers, wherein the method comprises:
cleaning a surface of a catalyst;
annealing the surface of the catalyst;
applying a carbon source onto the cleaned and annealed surface of the catalyst in a reaction chamber; and
growing the Bernal-stacked graphene layers on the surface of the catalyst in the reaction chamber,
wherein the method further comprises controlling the number of formed Bernal-stacked graphene layers by controlling at least the following growth parameters:
(a) a total pressure of the reaction chamber,
wherein the controlling of the total pressure comprises adjusting the total pressure; and
(b) a ratio of reductive gas pressure to carbon source pressure in the reaction chamber,
wherein the controlling of the ratio comprises maintaining the ratio at a fixed number,
wherein an increase in the total pressure of the reaction chamber at the maintained ratio of reductive gas pressure to carbon source pressure in the reaction chamber increases the number of Bernal-stacked graphene layers, and
wherein a decrease in the total pressure of the reaction chamber at the maintained ratio of reductive gas pressure to carbon source pressure in the reaction chamber decreases the number of Bernal-stacked graphene layers.
2. The method of claim 1 , further comprising a step of placing the reaction chamber under a stream of a reductive gas.
3. The method of claim 2 , wherein the reductive gas is hydrogen.
4. The method of claim 2 , wherein the reductive gas has a pressure ranging from about 5 Torr to about 800 Torr.
5. The method of claim 2 , wherein the reaction chamber is placed under the stream of the reductive gas at least during the applying step and the growing step.
6. The method of claim 1 , wherein the catalyst is selected from the group consisting of Ni, Co, Fe, Pt, Au, Al, Cr, Cu, Mg, Mn, Mo, Rh, Si, Ta, Ti, W, U, V, Zr, and combinations thereof.
7. The method of claim 1 , wherein the catalyst is a copper foil.
8. The method of claim 1 , wherein the catalyst has a surface area ranging from about 1 cm 2 to about 10 m 2 .
9. The method of claim 1 , wherein cleaning the surface of the catalyst comprises electrochemical-polishing the surface of the catalyst.
10. The method of claim 1 , wherein annealing the surface of the catalyst comprises thermal annealing.
11. The method of claim 10 , wherein the thermal annealing comprises exposure of a catalyst surface to temperatures of at least about 1,000° C.
12. The method of claim 1 , wherein the applying of the carbon source occurs by chemical vapor deposition.
13. The method of claim 1 , wherein the carbon source is selected from the group consisting of hydrocarbons, polymers, non-polymeric carbon sources, small molecules, organic compounds, fullerenes, fluorenes, carbon nanotubes, phenylene, ethylenes, sucrose, sugars, polysaccharides, carbohydrates, proteins, and combinations thereof.
14. The method of claim 1 , wherein the carbon source is a hydrocarbon.
15. The method of claim 14 , wherein the hydrocarbon is methane.
16. The method of claim 1 , wherein the carbon source has a pressure ranging from about 0.2 Torr to about 30 Torr.
17. The method of claim 1 , wherein the growing occurs at temperatures of at least about 1,000° C.
18. The method of claim 1 , wherein the growing occurs while the reaction chamber has a total pressure ranging from about 5 Torr to about 800 Torr.
19. The method of claim 1 , wherein the growing occurs for less than about 15 minutes.
20. The method of claim 1 , further comprising a step of terminating the growing step by cooling the surface of the catalyst.
21. The method of claim 1 , further comprising a step of transferring the formed Bernal-stacked graphene layers from the surface of the catalyst onto a substrate.
22. The method of claim 1 , wherein the growing occurs from multiple growth centers,
wherein the growth centers comprise multilayer graphene seeds,
wherein the growth centers grow laterally and epitaxially, and
wherein the growth centers merge seamlessly to form Bernal-stacked graphene layers.
23. The method of claim 1 , wherein the Bernal-stacked graphene layers have from 2 to 10 Bernal-stacked graphene layers.
24. The method of claim 1 , wherein the Bernal-stacked graphene layers have more than 10 Bernal-stacked graphene layers.
25. The method of claim 1 , wherein the Bernal-stacked graphene layers are in polycrystalline form.
26. The method of claim 1 , wherein the Bernal-stacked graphene layers have domain sizes ranging from about 1 μm to about 5 μm.
27. The method of claim 1 , wherein the growth parameters further comprise one or more growth parameters selected from the group consisting of a reductive gas flow rate in the reaction chamber, growth temperature, growth time, a cooling rate of the surface of the catalyst after the growing step, and combinations thereof.
28. The method of claim 1 , wherein the controlling of the total pressure comprises adjusting the pressure of the carbon source in the reaction chamber,
wherein an increase in the pressure of the carbon source increases the number of Bernal-stacked graphene layers, and
wherein a decrease in the pressure of the carbon source decreases the number of Bernal-stacked graphene layers.
29. The method of claim 28 , wherein the pressure of the carbon source is controlled at a range from about 0.2 Torr to about 30 Torr.
30. The method of claim 1 , wherein the controlling of the total pressure comprises adjusting the pressure of a reductive gas in the reaction chamber,
wherein an increase in the pressure of the reductive gas increases the number of Bernal-stacked graphene layers, and
wherein a decrease in the pressure of the reductive gas decreases the number of Bernal-stacked graphene layers.
31. The method of claim 30 , wherein the pressure of the reductive gas is controlled at a range from about 5 Torr to about 750 Torr.
32. The method of claim 1 , wherein the total pressure of the reaction chamber is controlled at a range from about 5 Torr to about 800 Torr.
33. The method of claim 1 , wherein the ratio of the reductive gas pressure to the carbon source pressure is maintained at about 28.