In situ optical and structural studies of H2 chemisorption in C8K

Publisher Website
Google Scholar
Abstract
Results of in situ optical (reflectance, Raman scattering) and 00l x-ray diffraction studies of hydrogen chemisorption in Grafoil-based stage 1 C8K intercalation compounds are presented. Upon hydrogen uptake, stage 2 KC8H2/3 was found to coexist with C8K forming first in the optical skin depth. The intensities of the 00l x-ray diffraction peaks show quantitatively that the reaction C8K + 1/2xH2 ⇉ (1 − 3/2x)C8K + 3/2xC8KH2/3 occurs for x>0.4 in the bulk. The effects of the surface morphology of Grafoil on the near-normal incidence reflectance was investigated and found to be described by an energy (E) dependent function S(E) = exp[−aEn], such that the corrected spectrum Rc = SR, where R is the Grafoil reflectance. In this manner, reflectance spectra of C8K-Grafoil and C8KH2/3-Grafoil were quantitatively analyzed to determine the free carrier contribution. The free carrier lifetimes were found to be a factor of 2 shorter in Grafoil-based hosts, compared to highly oriented pyrolytic graphite-based hosts. The optical results for C8KH2/3 indicate the H(ls) band is full (or very nearly full).