Helium atom diffraction measurements of the surface structure and vibrational dynamics of CH(3)-Si(111) and CD(3)-Si(111) surfaces.

Abstract

The surface structure and vibrational dynamics of CH(3)-Si(111) and CD(3)-Si(111) surfaces were measured using helium atom scattering. The elastic diffraction patterns exhibited a lattice constant of 3.82 Å, in accordance with the spacing of the silicon underlayer. The excellent quality of the observed diffraction patterns, along with minimal diffuse background, indicated a high degree of long-range ordering and a low defect density for this interface. The vibrational dynamics were investigated by measurement of the Debye-Waller attenuation of the elastic diffraction peaks as the surface temperature was increased. The angular dependence of the specular (θ(i)=θ(f)) decay revealed perpendicular mean-square displacements of 1.0×10(-5) Å(2) K(-1) for the CH(3)-Si(111) surface and 1.2×10(-5) Å(2) K(-1) for the CD(3)-Si(111) surface, and a He-surface attractive well depth of ∼7 meV. The effective surface Debye temperatures were calculated to be 983 K for the CH(3)-Si(111) surface and 824 K for the CD(3)-Si(111) surface. These relatively large Debye temperatures suggest that collisional energy accommodation at the surface occurs primarily through the Si-C local molecular modes. The parallel mean-square displacements were 7.1×10(-4) and 7.2×10(-4) Å(2) K(-1) for the CH(3)-Si(111) and CD(3)-Si(111) surfaces, respectively. The observed increase in thermal motion is consistent with the interaction between the helium atoms and Si-CH(3) bending modes. These experiments have thus yielded detailed information on the dynamical properties of these robust and technologically interesting semiconductor interfaces.

DOI: 10.1063/1.3483465

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@article{Becker2010HeliumAD, title={Helium atom diffraction measurements of the surface structure and vibrational dynamics of CH(3)-Si(111) and CD(3)-Si(111) surfaces.}, author={James S Becker and Ryan D. Brown and Erik C. Johansson and Nathan S. Lewis and S J Sibener}, journal={The Journal of chemical physics}, year={2010}, volume={133 10}, pages={104705} }