Becker, James S. and Brown, Ryan-D and Johansson, Erik and Lewis, Nathan S. and Sibener, S. J. (2010) Helium atom diffraction measurements of the surface structure and vibrational dynamics of CH_3-Si(111) and CD_3-Si(111) surfaces. Journal of Chemical Physics, 133 (10). Art. No. 104705. ISSN 0021-9606 http://resolver.caltech.edu/CaltechAUTHORS:20101029-074325400
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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 x 10^(−5) Å^2 K^(−1) for the CH_3–Si(111) surface and 1.2 x 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 x 10^(−4) and 7.2 x 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.
|Additional Information:||© 2010 American Institute of Physics. Received 13 July 2010; accepted 5 August 2010; published online 13 September 2010. This work was supported at the University of Chicago by the Air Force Office of Scientific Research and the UChicago NSF Materials Research Science and Engineering Center and at Caltech by NSF Grant No. CHE-0911682.|
|Subject Keywords:||Debye temperature, helium ions, lattice dynamics, long-range order, surface structure|
|Classification Code:||PACS: 68.35.B-; 68.47.-b; 63.70.+h|
|Usage Policy:||No commercial reproduction, distribution, display or performance rights in this work are provided.|
|Deposited By:||Ruth Sustaita|
|Deposited On:||29 Oct 2010 16:13|
|Last Modified:||26 Dec 2012 12:34|
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