Atomic Surface Structure of CH3-Ge(111) Characterized by Helium Atom Diffraction and Density Functional Theory
详细信息 查看全文
- 作者：Zachary M. Hund ; Kevin J. Nihill ; Davide Campi ; Keith T. Wong ; Nathan S. Lewis ; M. Bernasconi ; G. Benedek ; S. J. Sibener
- 刊名：Journal of Physical Chemistry C
- 出版年：2015
- 出版时间：August 13, 2015
- 年：2015
- 卷：119
- 期：32
- 页码：18458-18466
- 全文大小：465K
- ISSN：1932-7455
文摘
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 鉄?虆21虆鉄?and the 鉄?11虆鉄?azimuthal directions reveal a hexagonal packing arrangement with a 4.00 卤 0.02 脜 lattice constant, indicating a commensurate (1 脳 1) methyl termination of the primitive Ge(111) surface. Taking advantage of Bragg and anti-Bragg diffraction conditions, a step height of 3.28 卤 0.02 脜 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鈥揋e bilayer spacings, respectively. The DFT-calculated rotational activation barrier of a single methyl group about the Ge鈥揅 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鈥搒emiconductor interface.