Lithium adsorption on the graphite (0001) surface

Initial exposure of single-crystal graphite samples to lithium vapor from a molecular beam source results in no long-range order in the lithium overlayer as observed by low-energy electron diffraction over the temperature range 80-500 K and coverage range 0.01-5 monolayers. A hexagonal close-packed incommensurate structure is observed only after annealing the surface to ~500 K. Auger electron spectroscopy measurements of the lithium $\mathrm{KVV}$ transition for a multilayer coating prior to annealing reveal an Auger electron energy of 51 eV (that of metallic lithium), whereas after annealing the Auger energy shifts to 42 eV. This energy shift is due to diffusion of lithium into the bulk graphite and formation of a lithiumgraphite submonolayer structure with resultant change of the lithium electronic configuration from that of metallic lithium to a configuration similar to that in lithium compounds such as ${\mathrm{LiB}}_2$, ${\mathrm{LiN}}_3$, and LiF. The hcp incommensurate two-dimensional structure is a lithium structure on the surface with no indication of lithium residing within the top surface layers. This phase shows no phase transitions over the temperature range 80-500 K.