In this paper, we present the first structural investigation of quartz using helium atom scattering (HAS). Studies were carried out on the α-quartz (0 0 0 1) surface (Z-cut). He-diffraction experiments reveal a complex hexagonal diffraction pattern. Prominent peaks are visible at positions corresponding to the periodicity of the bulk unit cell (4.90 ± 0.02 Å). In addition, weak (2 × 2) peaks and satellite peaks are observed. Two recent theoretical papers both propose a (1 × 1) reconstruction for α-quartz (0 0 0 1) with 120° symmetry for the surface unit cell: the so called dense structure. We propose a model where terraces with step heights of a multiple 1/3 of the unit cell height lead to domains rotated by ±60° relative to each other. This is supported by AFM images. The satellite peaks indicate an incommensurate super-lattice structure with a periodicity of the order of 57 Å, presumably related to strain relief mechanisms. The (2 × 2) peaks may stem from co-existing regions of a semi-dense structure, which is predicted to have a higher energy than the dense, (1 × 1) phase.
ASJC Scopus subject areas
- Physikalische und Theoretische Chemie
- Physik der kondensierten Materie
- Oberflächen und Grenzflächen