Quartz and Glass: Revealing the Atomic Surface Structures of Silica

The main aim of this project is to determine the atomic structure of some of the most widespread surfaces in nature: Quartz and some of the most industrially important surfaces: glass. This is done by investigating the surfaces with a very unique tool: A beam of neutral helium atoms. We have discovered a hitherto unknown surface reconstruction of quartz with a periodicty of about 5 nm. This is one of the largest period reconstructions that has ever been observed on a bare crystal surface.

Silica (SiO2) is one of the most common materials on earth. It exists in crystalline and amorphous forms. The applications range from glass windows and building materials over foam stabilisers, filters and fillers, to quartz oscillators and optical fibre s. Crystalline silica micro particles (quartz) are dangerous causing the illness silicosis upon inhaling. Amorphous silica particles of the same size are harmless. It is still not understood why. Despite the fact that silica is one of the most common m aterials on earth with an enormous range of applications, the atomic surface structures of crystalline and amorphous silica are still not known. The problem has been that while the bulk silica materials can be investigated using techniques such as X-ray a nd Neutron scattering, there is a lack of suitable characterisation techniques for the surfaces on the atomic/nano level due to the insulating nature of silica and the chemical composition. Here we propose to use Helium Atom Scattering in combination wi th Atomic Force Microscopy to determine the surface structure for the basic crystal planes of alpha quartz and for the melt surface of silica glass. Measurements will be done both on clean surfaces and on hydroxylated surfaces, which are prevalent in Natu re. The measurements on the alpha quartz surface structures will be compared to theoretical predictions and further theoretical work will be done to include the long range reconstructions, which we observed in preliminary measurements. Furthermore we will test the hypothesis, which was brought forward a few years back that the surface of silica glass contains di-membered and tri-membered rings of the tetrahedrally shaped basic silica units. Such rings are particularly prone to chemical attack, so this is a very important information for understanding and modelling fracturing and corrosion of glass.