Browsing by Author "Denk, Matthias"

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Structural investigation of solid liquid interfaces : metal semiconductor interface
(2006) Denk, Matthias; Dosch, Helmut (Prof. Dr.)
This work presents a study of the structure of solid-liquid interfaces, more precisely studies of liquid metal-semiconductor interfaces, using high-energy x-ray diffraction. The semiconductor consisted of silicon single crystals in different orientation and doping and the liquid metal was either pure indium or lead. Altogether four interfaces were investigated: In(liq.)-Si(100), Pb(liq.)-Si(100), Pb(liq.)-Si(111), and Pb-PbO-Si(111). The experiments have been performed at the European Synchrotron Radiation Facility (ESRF) in Grenoble. The high-energy (70keV) technique developed recently allows in-situ measurements on deeply buried interfaces of all kinds. Solid-liquid interfaces are common in everyday life but up till now there is a lack of experimental knowledge about their structure on atomic length scales. With most experimental methods it is simply impossible to access deeply buried interfaces. High energy x-ray diffraction is the perfect tool for these systems. On the one hand side high energetic x-rays can penetrate into bulk material, on the other hand they are scattered at interfaces. To gain structural information parallel to the interface grazing incidence diffraction measurements were performed. The structure perpendicular to the interface was revealed with x-ray reflectivity measurements. For all liquid-metal semiconductor interfaces a huge density increase was found in the proximity region at the interface. The width of the increased density was in the range of 8 to 16 atomic diameters of the atoms of the liquid. The density increase was found to be in the range of 21% to 48% compared to the bulk liquid density. Conventional models are not able to explain this phenomenon. It can not be explained by a special packing of the atoms or the known pair correlation function of the liquid, which has a shorter correlation length. There must be some kind of charge transfer occuring at the interfaces from the liquid metal to the dangling bonds of the silicon surface. From the different interfaces influencing parameters of the density increase were identified. From three interfaces it was concluded that the surface density of the dangling bonds of the silicon, the doping of the silicon crystal and the free electron density of the bulk liquid metal are influencing parameters of the interfacial behaviour.