Effects of Molecular Adsorption on the Electronic Structure of Single- Layer Graphene

摘要

The interaction of small molecules (CCl4, CS2, H2O, and acetone) with singlelayer graphene (SLG) has been studied under steady-state conditions using infrared multipleinternal- reflection spectroscopy. Adsorption results in a broad and intense absorption band spanning the 8764;200 to 500 meV range, which is attributed to electronic excitation. This effect which has not previously been reported for SLG, has been further investigated using dispersioncorrected density functional theory to model the adsorption of H2O on SLG supported on an SiO2 substrate. However, the ideal and defect-free model does not reproduce the observed adsorption-induced electronic transition. This and other observations suggest that the effect is extrinsic, possibly the result of an adsorption-induced change in the in-plane strain, with important differences arising between species that form liquid-like layers under steady- state conditions and those that do not. Furthermore, the C H stretching modes of CH2 groups, incorporated in the SLG as defects undergo nonadiabatic coupling to the electronic transition. This leads to pronounced antiresonance effects in the line shapes, which are analyzed quantitatively. These results are useful in understanding environmental effects on graphene electronic structure and in demonstrating the use of the vibrational spectroscopy of H-containing defects in characterizing SLG structure.