The transition from single phonon to multiphonon energy transfer in atom–surface collisions

Abstract

A helium atom scattering study of the structure and phonon dynamics of the ice surface Energy and momentum transfer of He atoms scattered from a lithium fluoride crystal surfaceThe angular distributions and time-of-flight spectra of nearly monoenergetic He atoms with incident energies of 82 meV and 112 meV have been measured after scattering from a clean Cu͑001͒ surface over a large range of crystal temperatures from 100 K to 1000 K. With increasing temperatures the sharp diffraction and phonon peaks of the low temperature quantum regime become broad and featureless as expected for the multiphonon classical regime. The results are compared with a quantum mechanical theory which is able to explain the height, position, width, and area under the multiphonon maximum. In the classical regime, the temperature dependence of the inelastic intensity indicates that the He atoms are reflected by a smooth vibrating barrier presumably due to the surface electron density, and not by a lattice of discrete repulsive surface atomic cores.

Classical theory of molecule-surface scattering: Application to C2H2 scattering from LiF

“…The atomic smooth-surface model has been used successfully to explain a large number of experimental results for both measured angular distributions and energy resolved intensities for rare gases such as He, Ne, Ar, and Xe scattering from a variety of insulator, metal, and liquid metal surfaces. 26,34,36,41,42 The good agreement obtained for the angular distributions in this work shows that a similar model, extended to include rotational motion, appears to explain the multiple phonon energy exchange in classical moleculesurface scattering.…”

“…The Rayleigh velocity for LiF͑001͒ depends on crystal azimuth, but is approximately 4000 m/s. 40 In previous multiphonon studies of atomsurface scattering carried out for both insulator and metal substrates, v R has been fit to values less than the Rayleigh velocity, 41,42 but has also sometimes appeared to be dependent on the incident energy. 26,34 In this case the values of v R which allowed for the good fits with the data increased with energy, with v R ϭ130 m/s for the lowest energy E i T ϭ110 meV, v R ϭ520 m/s for E i T ϭ275 meV, and v R ϭ1050 m/s for E i T ϭ618 meV.…”

Helium diffraction on SiC grown graphene: Qualitative and quantitative descriptions with the hard-corrugated-wall model

“…When the range of the potential and the corrugation amplitude are limited i.e. much smaller than the lattice parameter, this surface is close to the corrugation functionZ(y), and the HCW is known to be qualitatively correct [35][36][37]. However, the accuracy of the HCW model can be limited and corrugation amplitudes with departures up to 30% from exact theoretical treatments have been reported [24].…”

Theory of Molecule-Surface Scattering at Thermal and Hyperthermal Energies

“…The effective surface phonon velocity y R was chosen to be 130 m͞s for the lowest energy E T i 110 meV, 520 m͞s for E T i 275 meV, and 1050 m͞s for E T i 618 meV. The value of y R is expected to be significantly smaller than the Rayleigh wave velocity [10], which is about 4000 m͞s for LiF [2,9], and previous treatments of atomic scattering have indicated that y R is energy dependent with values increasing with higher incident energy [8,13]. The value of v R is chosen to be 2 3 10 10 s 21 and the mass M C of the surface is taken to be 51.9 amu which is 2 times the mass of LiF.…”