Atomic Surface Structure of CH3-Ge(111) Characterized by Helium Atom Diffraction and Density Functional Theory

Zachary M. Hund, Kevin J. Nihill, Davide Campi, Keith T. Wong, Nathan S. Lewis, M. Bernasconi, G. Benedek, S. J. Sibener

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5 Citations (Scopus)


The atomic-scale surface structure of methyl-terminated germanium (111) has been characterized by using a combination of helium atom scattering and density functional theory. High-resolution helium diffraction patterns taken along both the "1I¯21I¯" and the "011I¯" azimuthal directions reveal a hexagonal packing arrangement with a 4.00 ± 0.02 Å lattice constant, indicating a commensurate (1 × 1) methyl termination of the primitive Ge(111) surface. Taking advantage of Bragg and anti-Bragg diffraction conditions, a step height of 3.28 ± 0.02 Å at the surface has been extracted using variable de Broglie wavelength specular scattering; this measurement agrees well with bulk values from CH3-Ge(111) electronic structure calculations reported herein. Density functional theory showed that methyl termination of the Ge(111) surface induces a mild inward relaxation of 1.66% and 0.60% from bulk values for the first and second Ge-Ge bilayer spacings, respectively. The DFT-calculated rotational activation barrier of a single methyl group about the Ge-C axis on a fixed methyl-terminated Ge(111) surface was found to be approximately 55 meV, as compared to 32 meV for a methyl group on the H-Ge(111) surface, sufficient to hinder the free rotation of the methyl groups on the Ge(111) surface at room temperature. However, accurate MD simulations demonstrate that cooperative motion of neighboring methyl groups allows a fraction of the methyl groups to fully rotate on the picosecond time scale. These experimental data in conjunction with theory provide a quantitative evaluation of the atomic-scale surface structure for this largely unexplored, yet technologically interesting, hybrid organic-semiconductor interface.

Original languageEnglish
Pages (from-to)18458-18466
Number of pages9
JournalJournal of Physical Chemistry C
Issue number32
Publication statusPublished - Jul 31 2015

ASJC Scopus subject areas

  • Electronic, Optical and Magnetic Materials
  • Energy(all)
  • Physical and Theoretical Chemistry
  • Surfaces, Coatings and Films

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