Anisotropic etching of graphite and graphene in a remote hydrogen plasma

Abstract

We investigate the etching of a pure hydrogen plasma on graphite samples and graphene flakes on SiO2 and hexagonal Boron-Nitride (hBN) substrates. The pressure and distance dependence of the graphite exposure experiments reveals the existence of two distinct plasma regimes: the direct and the remote plasma regime. Graphite surfaces exposed directly to the hydrogen plasma exhibit numerous etch pits of various size and depth, indicating continuous defect creation throughout the etching process. In contrast, anisotropic etching forming regular and symmetric hexagons starting only from preexisting defects and edges is seen in the remote plasma regime, where the sample is located downstream, outside of the glowing plasma. This regime is possible in a narrow window of parameters where essentially all ions have already recombined, yet a flux of H-radicals performing anisotropic etching is still present. At the required process pressures, the radicals can recombine only on surfaces, not in the gas itself. Thus, the tube material needs to exhibit a sufficiently low H radical recombination coefficient, such a found for quartz or pyrex. In the remote regime, we investigate the etching of single layer and bilayer graphene on SiO2 and hBN substrates. We find isotropic etching for single layer graphene on SiO2, whereas we observe highly anisotropic etching for graphene on a hBN substrate. For bilayer graphene, anisotropic etching is observed on both substrates. Finally, we demonstrate the use of artificial defects to create well defined graphene nanostructures with clean crystallographic edges.

Oxidation of Suspended Graphene: Etch Dynamics and Stability Beyond 1000 °C

“…The anisotropically etched edges in our work are consistently armchair-oriented, in contrast to the zigzag-oriented edges or isotropic holes reported previously for oxidative graphene etching [19][20][21][22][23][24][25] and remote hydrogen plasma etching. 30,31 Vacuum annealing graphene at high temperatures in situ in the TEM has previously been reported to result in primarily armchair edges. 32,33 At lower pressures where we obtain more regular hexagons, the conditions are more similar to the high vacuum conditions of these reports, and carbon oxidation here might occur at a rate low enough to allow carbon atoms to re-arrange to form armchair edges.…”

Catalyst-Less and Transfer-Less Synthesis of Graphene on Si(100) Using Direct Microwave Plasma Enhanced Chemical Vapor Deposition and Protective Enclosures

“…It is because the increase in graphene nucleus density with decreased H 2 content due to the hydrogen etching resulted in a smaller graphene grain size [ 44 ]. Thus, the possible lowering of the hydrogen plasma-induced defect density with decreased hydrogen gas flow should be considered [ 57 ].…”

Hexagonal Nanopits with the Zigzag Edge State on Graphite Surfaces Synthesized by Hydrogen-Plasma Etching

“…In addition, there are conflicts among previous experimental results on monolayer graphene exfoliated on SiO 2 . Yang et al [39] reported successful creation of hexagonal nanopits of uniform size, while Diankov et al [40] and Hug et al [41] reported circular ones. For a zGNR unzipped from a carbon nanotube, no nanopit creation by H-plasma etching has been found [32].…”