Dynamic hexagonal spreading patterns of small silicon droplets on the basal plane (001) of quartz were observed by video microscopy. A detailed analysis of the hexagonal triple line demonstrates that the patterns show slight chiral distortions that can be attributed to the screw axis of the substrate crystal. This article reveals the detailed influence of crystal symmetry on the anisotropy of reactive wetting. In this context, a first discussion about the interplay of wetting and etching of a crystal is provided.

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Silicon monoxide is a complex material which tends to form atomic and nanoscale amorphous structures. The question is in which ways can the stability of SiO on suitable carriers or interfaces be enhanced. This was investigated by statistical thermodynamics based on density functional theory calculations on SiO layers on and in-between MgO(100) model surfaces. Furthermore, the stability of ordered close-packed SiO layers and their relaxation into amorphous structures were studied. Some selected SiO structures between thin MgO sheets were investigated and their interface energies are discussed. The results for the interface tensions can be understood by a strong lateral repulsion between atoms in ordered close-packed SiO layers on MgO(100). The SiO layer can thereby induce stress on the MgO sheets.

Small silicon samples were brought into contact with magnesium oxide substrate plates and heated under vacuum. At heating temperatures above 1400 K, a transient light emission effect in the Si/MgO interface was observed. The changes in sample brightness are likely caused by a thermal effect. Typically the sample temperature decreases gradually by 40-80 K and is followed by a very fast rise in temperature. The light emission effect may be correlated to the transient formation and decomposition of an inhibiting layer of magnesium silicate and the endothermic formation of gaseous silicon oxide. Tempering a silicon sample on a magnesium oxide plate for several hours produced an etch pit in the substrate material from which the silicon sample split off during the cooling phase. The etch pit was investigated via electron microscopy. EDXS analysis of the finely structured surface of the reaction zone reports a composition of 2/1/5 (Mg/Si/O). A crosssection of the same area reveals a thin layer of reaction products on top of the substrate material.

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Reactive wetting of quartz by silicon is an ideal model system for the understanding and control of reactive wetting effects. Very slow and well controlled reactive spreading of a small silicon droplet on quartz can be achieved and observed in a new type of chemical transport mini reactor equipped with a video microscope setup operating in the melting point vicinity of silicon at T

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