RESUMO
Reflectance anisotropy spectroscopy (RAS) equipment is applied to monitor dry-etch processes (here specifically reactive ion etching (RIE)) of monocrystalline multilayered III-V semiconductors in situ. The related accuracy of etch depth control is better than 16 nm. Comparison with results of secondary ion mass spectrometry (SIMS) reveals a deviation of only about 4 nm in optimal cases. To illustrate the applicability of the reported method in every day settings for the first time the highly etch depth sensitive lithographic process to form a film lens on the waveguide ridge of a broad area laser (BAL) is presented. This example elucidates the benefits of the method in semiconductor device fabrication and also suggests how to fulfill design requirements for the sample in order to make RAS control possible.
RESUMO
Reactions under single collision conditions with benzene C(6)H(6) and with benzene-d(6) C(6)D(6) of size selected cationic cobalt clusters Co(n)(+) and of anionic cobalt clusters Co(n)(-) in the cluster size range n = 3-28 revealed that dehydrogenation by cationic clusters is sparse, whereas it is ubiquitous in reactions by anionic clusters. Kinetic isotope effects (KIE) in total reaction rates are inverse and, in part, large. Dehydrogenation isotope effects (DIE) are normal. A multistep model of adsorption and stepwise dehydrogenation from the precursor adsorbate unravels a possible origin of the inverse KIE: Single step C-H bond activation is swift (no KIE in forward direction) and largely reversible (normal KIE backward) whereas H/D tunneling is likely to contribute (backward). DFT calculations of the structures and energetics along the reaction path in [Co(13)C(6)H(6)](+) lend support to the proposed multistep model. The observed effects on rates and KIEs of cluster charges and of cluster sizes are noted to elucidate further.
