Depth distribution of zinc adsorbed on silicon surfaces out of alkaline aqueous solutions

In the mass production of advanced microelectronic devices (chips), contamination by transition metals is known as a major risk for device yield and reliability. Although zinc belongs to the most frequent contaminants, not many efforts have been made to understand the chemistry of the interactions between this element and silicon surfaces during wet chemical treatments. This paper deals with the interactions of oxide-free and chemically oxidized silicon(100) surfaces with aqueous zinc solutions of pH=9. TXRF (total-reflection X-ray fluorescence spectrometry), XPS (X-ray photoemission spectroscopy) and ISS (ion scattering spectroscopy) were applied in combination with chemical desorption experiments to characterize the silicon surfaces and the concentration and depth distribution of zinc. These studies show that zinc is partially incorporated in the native oxide which is growing under these conditions on an oxide-free silicon surface. In the case of a chemically oxidized surface, only a small part of the adsorbed zinc is incorporated in the oxide in a region close to the oxide surface due to ion exchange reactions during the contamination process

Removing coordinated metal ions from proteins: a fast and mild method in aequeous solution

Thermodynamic and kinetic studies of metal binding to proteins require the investigation of metal-free proteins, which are often difficult to obtain. We have developed a very fast and mild method to eliminate metal ions from proteins by column chromatography using a commercially available Ni-NTA-type stationary phase. This material, initially designed for protein purification purposes in biotechnology, acts as a strong cation chelator when Ni2+ ions are removed. We have tested this new method with Ca-ATPase, an integral membrane protein exhibiting a strong affinity for Ca2+. By eluting the protein over the Ni2+-free NTA gel, we could remove 95% of the total Ca2+ and obtain an essentially Ca2+-free protein. This method is efficient with only a small amount of NTA gel, and we suggest that it can be applied in general for removal of metal ions from proteins. Moreover, as this procedure can be carried out under mild conditions, the chosen protein kept its enzymatic activity

Kristallfehler in integrierten Schaltkreisen aus Silizium, insbesondere in Hinblick auf Groesstintegration (VLSI)

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