title: 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.
authors.affiliation: Department of Chemistry and The James Franck Institute, The University of Chicago, 929 E. 57th Street, Chicago, Illinois 60637, USA.
authors.forename: James S
authors.initials: JS
authors.lastname: Becker
authors.forename: Ryan D
authors.initials: RD
authors.lastname: Brown
authors.forename: Erik
authors.initials: E
authors.lastname: Johansson
authors.forename: Nathan S
authors.initials: NS
authors.lastname: Lewis
authors.forename: S J
authors.initials: SJ
authors.lastname: Sibener
mesh_terms: D006371:Helium / Q000737:chemistry*; D056004:Molecular Dynamics Simulation; D015394:Molecular Structure; D017646:Organosilicon Compounds / Q000737:chemistry*; D046590:Spectroscopy, Electron Energy-Loss; D017550:Spectroscopy, Fourier Transform Infrared; D013499:Surface Properties; D014732:Vibration
chemical_list: D017646:Organosilicon Compounds; D006371:Helium