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).they have revealed a mechanism for low-temperature water adsorption on a graphite (0001) surface that is governed by a delicate balance between substrate-adsorbate geometry constraints, the strength of the graphite-water bond, and the strength of the intermolecular hydrogen bond. We hypothesise that the water molecules that initially strike the surface adsorb and diffuse until they bind to defect sites. On a partially covered surface, if the molecule strikes a patch of a clean surface, it will eventually diffuse to the nucleation centre (defect site) and form
hydrogen-bonded aggregates. If, however, a molecule impinges on an already formed cluster, it will adsorb and stay on top of the cluster. The first layer therefore spreads out parallel to the surface faster than the second and higher layers develop. The effect is particularly pronounced on a graphite surface with its low defect concentration that makes the average size of water clusters relatively large.
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).they have revealed a mechanism for low-temperature water adsorption on a graphite (0001) surface that is governed by a delicate balance between substrate-adsorbate geometry constraints, the strength of the graphite-water bond, and the strength of the intermolecular hydrogen bond. We hypothesise that the water molecules that initially strike the surface adsorb and diffuse until they bind to defect sites. On a partially covered surface, if the molecule strikes a patch of a clean surface, it will eventually diffuse to the nucleation centre (defect site) and form
hydrogen-bonded aggregates. If, however, a molecule impinges on an already formed cluster, it will adsorb and stay on top of the cluster. The first layer therefore spreads out parallel to the surface faster than the second and higher layers develop. The effect is particularly pronounced on a graphite surface with its low defect concentration that makes the average size of water clusters relatively large.
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