The Vapor - Liquid - Solid (VLS ) technique allows the growth of high aspect ratio Si wires. The Si nanowires formed by this technique can be thinned down by oxidation. This approach allows the formation of very thin Si cores which may be used to research the properties of Si nanostructures. In this work the growth and oxidation of these wires is characterized.In the growth a very thin layer of Au is deposited on a Si (111) surface, silane gas is introduced into the chamber as the Si source gas and the temperature is raised to 300 – 600°C. Initially a catalytically active Au surface phase leads to the growth of a defective epitaxial Si layer. As Au / Si molten alloy balls nucleate and grow in size to approach the threshold size for VLS wire growth, which is determined by the Gibbs - Thomson effect, the epitaxial layer growth rate decreases and a transition to Si nanowire growth occurs. The morphology and width of the wires is strongly dependent on the growth temperature and pressure. At low pressure and high temperature relatively thick well-formed wires grow straight up from the substrate surface along the [111] direction. As the temperature is decreased and the pressure is increased thinner wires (as thin as 10 nm ) grow which tend to exhibit growth defects. A light oxidation yields Si cores which are of the order of 5 nm in diameter.
A new Doppler-free optical-optical triple-resonance (DF~UI'R) spectmscopy is reported for the fist time. This high resolution technique is simply wried out using one single mode laser like Doppler-free two-photon speclroscopy, and can reach arbitrary levels in the high-lying p-parity states like fhe optical-optical double-resonance technique in atomic or molecular systems. It is an effective but simple meethod for the systematic study of atomic or molecular SVUC~UIW and their intra or internal dynamics.
Linear response theories based on the state specific multi-reference coupled electron-pair approximation-like methods (SS-MRCEPA) (Chattopadhyay and Mahapatra 2004 J. Phys. Chem. A 108 11664) (MRCEPA-LRT) have been amply utilized for computing excited-state potential energy surfaces (PES). Our MRCEPA-LRT methods provide energies in a size-intensive manner. As a pilot application, the effectiveness of the method is demonstrated by computing the PES of some low-lying excited states including the ground state of the BeH 2 molecule. This system is very effective and widely used to judge the potentiality of any state-specific theory since its ground state possesses degeneracy/quasidegeneracy and also faces intruders at different regions of the PES.
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