Transiente Lichtemission und Reaktionen an der MgO/Si Grenzfläche

This work discusses the investigation of silicon samples on magnesium oxide substrates under high vacuum and at high temperatures. For small samples (up to 100 μg) a characteristic, transient light emission effect was observed at temperatures of 1400 Kelvin and above. The sample loses brightness over a period of a few seconds, then lights up again within fractions of a second. The effect was observed and recorded with a video microscope. In initial experiments, small silicon splinters were used as samples. Later experiments were conducted with silicon cantilevers as used in atomic force microscopy in order to ensure a consistent sample geometry and smooth area of contact with the substrate. Placement of the highly fragile cantilevers on the substrate plates demanded for the development of a sample preparation method. The effect was investigated with a series of varied experiments, such as long term tempering or using different substrate materials. The reaction products were examined with electron microscopy and EDX spectroscopy. For some experiments a thin layer of reaction products, likely containing silicates, was found at the interface of sample and substrate. The emission effect is in all likelihood thermal and related to the formation and decay of a silicate layer and the endothermic formation of gaseous silicon monoxide. In order to quantify the temperature differences during the darkening and lightening of the sample brightness, a computer program was developed. The software allows for the temporal analysis of the sample brightness and the conversion of brightness values into absolute temperatures on the basis of the video microscopy recordings. A simple reaction model for the formation and decay of a reaction layer was developed. For the two main steps (layer formation and hole formation) the activation energies were estimated on the basis of the absolute sample temperatures and frequencies of the emission effect.