Thermal and nonthermal kinetics of helium monolayers on Pt(111)

T. Niedermayer, H. Schlichting, D. Menzel, S. H. Payne, H. J. Kreuzer

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Abstract

Monolayers and submonolayers of helium-4 and helium-3 have been prepared on Pt(111) single-crystal surfaces using a specifically developed ultrahigh vacuum cryostat. Detailed data on thermal desorption and on desorption by absorption of far infrared photons and data on sticking have been obtained; evidence for collision-induced desorption has also been found. With a number of tests we prove that the photoinduced desorption is due to direct coupling of the incoming photons from the blackbody radiation of the environment to the dynamic dipole of the He adsorbate, and not to heating or to nonequilibrium phonon creation, and that this process proceeds independently of the thermal desorption. Theoretical treatments of both thermal and photodesorption are given. The results agree very well with the data in all important aspects; in particular, they reproduce the distinctly different isotope effects in both cases. From the thermal desorption data, we conclude that this system is governed by a two-dimensional gas at low to medium coverages and a compressed phase at high coverages. The thermal kinetics do not exhibit quantum effects, except that present in sticking. The observed photodesorption, however, is a clear quantum effect.

Original languageEnglish
Article number045427
JournalPhysical Review B - Condensed Matter and Materials Physics
Volume71
Issue number4
DOIs
StatePublished - Jan 2005

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