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<jats:title>Abstract</jats:title><jats:p>We investigate the etching of a pure hydrogen plasma on graphite samples and graphene flakes on SiO<jats:sub>2</jats:sub> and hexagonal boron-nitride substrates. The pressure and distance dependence of the graphite exposure experiments reveals the existence of two distinct plasma regimes: the <jats:italic>direct</jats:italic> and the <jats:italic>remote</jats:italic> plasma regime. Graphite surfaces exposed <jats:italic>directly</jats:italic> 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 <jats:italic>remote</jats:italic> 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 as found for quartz or pyrex. In the <jats:italic>remote</jats:italic> regime, we investigate the etching of single layer and bilayer graphene on SiO<jats:sub>2</jats:sub> and hexagonal boron-nitride substrates. We find <jats:italic>isotropic</jats:italic> etching for single layer graphene on SiO<jats:sub>2</jats:sub>, whereas we observe highly <jats:italic>anisotropic</jats:italic> etching for graphene on a hexagonal boron-nitride 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.</jats:p>
- 出版日期2017-7-5
