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.
ASJC Scopus subject areas
- Physics and Astronomy(all)
- Physical and Theoretical Chemistry