Water adsorption on the clean graphite (0001) surface has been studied by high-resolution electron-energyloss
spectroscopy (HREELS) and temperature-programmed desorption (TPD). At 85 K H,O adsorbs nondissociative/
y forming hydrogen-bonded aggregates. The structure and the growth mode of water clusters
depend on the substrate temperature and the coverage. At all coverages, above a fewpercent of a monolayer
(ML), the desorption is characterized by zero-order kinetics, while the HREEL spectra reveal a threshold
coverage approximately 1 ML when the average co-ordination of the H,O molecules changes. Isothermal
measurements of the desorption rate and HREELS measurements at elevated temperatures suggest an
irreversible phase transition from amorphous to crystalline ice at approximately 735 K,