Helium atom diffraction measurements of the surface structure and vibrational dynamics of CH3 -Si (111) and CD3 -Si (111) surfaces

James S. Becker, Ryan D. Brown, Erik Johansson, Nathan S. Lewis, S. J. Sibener

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The surface structure and vibrational dynamics of CH3 -Si (111) and CD3 -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 (θi = θf) decay revealed perpendicular mean-square displacements of 1.0× 10-5 Å2 K-1 for the CH3 -Si (111) surface and 1.2× 10-5 Å2 K -1 for the CD3 -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 CH3 -Si (111) surface and 824 K for the CD3 -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 Å2 K-1 for the CH3 -Si (111) and CD3 -Si (111) surfaces, respectively. The observed increase in thermal motion is consistent with the interaction between the helium atoms and Si- CH3 bending modes. These experiments have thus yielded detailed information on the dynamical properties of these robust and technologically interesting semiconductor interfaces.

Original languageEnglish
Article number104705
JournalJournal of Chemical Physics
Issue number10
Publication statusPublished - Sep 14 2010


ASJC Scopus subject areas

  • Physics and Astronomy(all)
  • Physical and Theoretical Chemistry

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