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Using Raman and infrared transmission spectroscopy, the vibrational properties of siloxene (SigOsHs) and its derivatives are investigated and interpreted in terms of various structural modifications of siloxene which have been proposed in the past. On the basis of experimental and theoretical investigations siloxene is found to be a mixture of Sis rings and/or linear Si chains interconnected by oxygen, and Si planes terminated by H and OH. The inBuence of thermal annealing, chemical treatment, and laser irradiation on the structure of siloxene is discussed in terms of the corresponding changes of the vibrational spectra and the x-ray-di8'raction patterns. The vibrational properties of siloxene are very similar to those of electrochemically anodized porous Si. Raman, infrared transmission, and photoluminescence measurements of the two classes of materials are compared and a possible mechanism for the efBcient luminescence in porous Si is discussed in light of the similarities between siloxene and porous Si.

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We demonstrate a technique to study self-diffusion in germanium, using isotope heterostructures ( Ge/ Ge). After interdiffusing the nominally undoped layers of Ge and Ge at temperatures between 543 and 690'C, the diffusion profiles are measured with secondary-ion-mass spectroscopy. The analysis of the experimental data allows an accurate determination of the self-diffusion enthalpy and the self-diffusion entropy. The isotope heterostructures are especially well suited for self-diffusion studies because the diffusion takes place at the interfaces inside the crystal. Thus, no surface effects or limited amounts of tracers complicate the measurements. We compare our results with those obtained with the standard techniques where the tracer self-diffusion coefficients are determined based on studying the redistribution of radioactive tracers, initially deposited on the specimen surface. Utilizing the stable isotopes in our experiment avoids complications due to decay of the radioactive tracers encountered in the traditional measurements.