The structure of the α-quartz (0 0 0 1) surface investigated using helium atom scattering and atomic force microscopy

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.