Extended Huckel theory calculations are carried out for interstitial hydrogen atoms in silicon model crystals without and with vacancies. The energetically stable positions for the hydrogens appear to be the tetrahedral interstitial site in crystals without vacancies; in the case of vacancies the hydrogens favor positions in the dangling bonds of the vacancies 0.35 bond lengths away from the vacancy nearest neighbors. The vibrational frequencies for all defect types considered are in very close agreement with infrared bands observed after proton irradiation of silicon. The frequencies increase with the number of hydrogens in a vacancy. The hydrogen-related impurity levels are very close to the valence band edge, both above or below.

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Linear-combination-of-atomic-orbitals -molecular-orbitals cluster calculations using the extended Huckel theory are carried out for the interstitial carbon in the diamond lattice. The results suggest that the interstitial configuration is not the tetrahedral or hexagonal site, as has been previously assumed, but is instead an "interstitialcy" configuration, i.e. , either a split-(100) interstitial (which our results favor) or a bond-centered interstitial. The predicted minimum-energy configuration changes with charge state, suggesting that the interstitial in the diamond lattice is a possible example of the Bourgoin mechanism of athermal migration of a defect in the presence of ionizing radiation.

Deep etching of glass and glass ceramics is far more challenging than silicon etching. For thermally insensitive microelectromechanical and microoptical systems, zero‐expansion materials such as Zerodur or ultralow expansion (ULE) glass are intriguing. In contrast to Zerodur that exhibits a complex glass network composition, ULE glass consists of only two components, namely, TiO2 and SiO2. This fact is highly beneficial for plasma etching. Herein, a deep fluorine‐based etching process for ULE 7972 glass is shown for the first time that yields an etch rate of up to 425 nm min−1 while still achieving vertical sidewall angles of 87°. The process offers a selectivity of almost 20 with respect to a nickel hard mask and is overall comparable with fused silica. The chemical surface composition is additionally investigated to elucidate the etching process and the impact of the tool configuration in comparison with previously published etching results achieved in Zerodur. Therefore, deep and narrow trenches can be etched in ULE glass with high anisotropy, which supports a prospective implementation of ULE glass microstructures, for instance, in metrology and miniaturized precision applications.