Visible luminescence from porous silicon and siloxene

Infrared transmission and Raman spectra of siloxene (Si₆O₃H₆) and porous Si have been analyzed in terms of the structural composition. Siloxene consists of Si₆-rings interconnected by oxygen and terminated by hydrogen, and corrugated Si(111)-planes saturated by OH and H. The pronounced photoluminescence of siloxene is mainly related to the Si₆-rings. Porous Si shows similar luminescence and almost identical vibrational properties as siloxene, which makes this class of materials a possible candidate for the origin of the luminescence in p-Si. Annealing at temperatures below 300 °C and moderate illumination of siloxene induces the transformation from the Si-plane-like structure to the Si-ring-like structure. Anneal temperatures above 300 °C and intense illumination of both siloxene and p-Si leads to an effusion of hydrogen and an irreversible oxidation of the samples.