| Abstract Scope |
Graphene hydride, or better known now as graphane is as thermodynamically stable as comparable hydrocarbons, more stable than metal hydrides and more stable than graphene by ~0.15eV. . While bulk graphite has been observed to be chemically inert to most chemicals, graphene has demonstrated the ability to react with some atoms such as fluorine, and most importantly hydrogen. When hydrogen bonds with the π-bonds of graphene, the delocalized π-electron now becomes localized at the C-H bond, decreasing the conductivity, changing the bond hybridization from sp<SUP>2</SUP> to sp<SUP>3</SUP> and increasing the C-C bond length ~7% from 1.42A to 1.52A. The electron localization at the sp<SUP>3</SUP> bond leads to a decrease in conductivity, and opens up a bandgap varying from 0-3.5eV depending on the degree of hydrogenation.This enables new applications in bandgap engineered electronics using carbon-based materials. The difficulty with forming graphane is the need for atomic hydrogen. While other groups have formed graphane by in situ development of atomic hydrogen by hydrogen plasma or pumping explosive gases into the growth furnace, it was recently shown that graphane can also be formed ex situ electrochemically. In this paper, we demonstrate an enhanced electrochemical means to generate atomic hydrogen, by evaporated metal to improve hydrogen incorporation into graphene during the conversion process. On-axis, semi-insulating, 6H-SiC substrates were used to form epitaxial graphene at ~1400°C in vacuum as starting material for graphane production. All samples were chosen from the same wafer to maintain consistency in conversion. The ratio of the graphene Raman G-peak to the disorder D-peak was >10, showing the high quality of the starting material. Then 10Å-30Å of either Pt or Au were evaporated onto the graphene surface. Atomic hydrogen was generated using a home-built electrochemical setup with current applied though a 10% sulfuric acid solution, with a Pt wire and exposed graphene as the anode and cathode, respectively. Successful hydrogenation was confirmed by a marked increase in resistance, presence of C-H bond peak at ~2930 cm<SUP>-1</SUP> and peak shift, narrower than expected from damage and increase in D peak. It was observed that graphene samples with evaporated Pt were more reactive than Au evaporated samples and much more reactive than plain graphene according to Raman. The increase in resistance was also more substantial on the Pt converted samples ~10MΩ as compared to that of Au ~2kΩ, plain converted graphene ~1.7kΩ and unconverted graphene ~1kΩ. AFM images show interesting features in the unconverted and converted Au and Pt evaporated samples where before conversion evaporated metal looks conformal and after conversion the metal particles on both samples appear to clump together exposing the underlying graphene surface. After conversion graphene steps were present in the Pt and absent in the Au. |