Quasi free-standing epitaxial graphene fabrication on 3C–SiC/Si(111)

Abstract

Growing graphene on SiC thin films on Si is a cheaper alternative to the growth on bulk SiC, and for this reason it has been recently intensively investigated. Here we study the effect of hydrogen intercalation on epitaxial graphene obtained by high temperature annealing on 3C-SiC/Si(111) in ultra-high vacuum. By using a combination of core-level photoelectron spectroscopy, low energy electron diffraction, and near-edge x-ray absorption fine structure (NEXAFS) we find that hydrogen saturates the Si atoms at the topmost layer of the substrate, leading to free-standing graphene on 3C-SiC/Si(111). The intercalated hydrogen fully desorbs after heating the sample at 850 °C and the buffer layer appears again, similar to what has been reported for bulk SiC. However, the NEXAFS analysis sheds new light on the effect of hydrogen intercalation, showing an improvement of graphene's flatness after annealing in atomic H at 600 °C. These results provide new insight into free-standing graphene fabrication on SiC/Si thin films.

Hydrogen intercalation of epitaxial graphene and buffer layer probed by mid-infrared absorption and Raman spectroscopy

“…We have measured resistances in the range 1-70 kΩ for fresh QFSMLG samples and the resistance is increased up to 0.2-2 MΩ range within one to two weeks of air exposure. Although our experiments are not in agreement with literature 16,19 we believe that the contradiction is due to different experimental techniques used to probe stability of hydrogen intercalation. For example, the Low energy electron diffraction (LEED) was used in Ref.…”

“…S2 in supplementary information of Ref. 19. Therefore we conclude that the temporal stability of hydrogenated graphene is an issue which needs to be addressed.…”

“…16,19 Hydrogen desorption from QFSMLG and QFSBLG has been reported to occur at about 700 • C in vacuum. 19 We confirm by our experiments that hydrogenated samples heated to ≈ 900 • C in high vacuum (10 5 mbar) for 30 minutes can be recovered nearly to the state before intercalation. However, in contrast do hydrogen desorption, we anneal buffer layer and SLG at 1000 mbar of hydrogen.…”

“…For example, the Low energy electron diffraction (LEED) was used in Ref. 19 to show unchanged LEED pattern after exposure to air for five days. We note, however, that no detailed analysis of diffraction spots' FWHM was performed.…”

“…[12][13][14] Therefore, the high mobility graphene with tunable Fermi level requires eliminating buffer 15 and thus reducing interaction between graphene and SiC. 16,17 This can be readily done by intercalation of the SiC/buffer interface by molecular 16 or atomic 18,19 hydrogen. Hydrogen saturates Si-C bonds, turns sp 3 carbon back into sp 2 bonded carbon and, as a result, so called buffer-free quasi free standing monolayer graphene (QFSMLG) is formed from buffer layer and quasi free standing bilayer graphene (QFSBLG) 16,20 is formed from SLG.…”