title: Oxygen absorption in free-standing porous silicon: a structural, optical and kinetic analysis.
abstract: Porous silicon (PSi) is a nanostructured material possessing a huge surface area per unit volume. In consequence, the adsorption and diffusion of oxygen in PSi are particularly important phenomena and frequently cause significant changes in its properties. In this paper, we study the thermal oxidation of p+-type free-standing PSi fabricated by anodic electrochemical etching. These free-standing samples were characterized by nitrogen adsorption, thermogravimetry, atomic force microscopy and powder X-ray diffraction. The results show a structural phase transition from crystalline silicon to a combination of cristobalite and quartz, passing through amorphous silicon and amorphous silicon-oxide structures, when the thermal oxidation temperature increases from 400 to 900 °C. Moreover, we observe some evidence of a sinterization at 400 °C and an optimal oxygen-absorption temperature about 700 °C. Finally, the UV/Visible spectrophotometry reveals a red and a blue shift of the optical transmittance spectra for samples with oxidation temperatures lower and higher than 700 °C, respectively.
authors.affiliation: Instituto de Investigaciones en Materiales, Universidad Nacional Autónoma de México, Circuito Exterior s/n, Ciudad Universitaria, Del, Coyoacán, Apartado Postal 70-360, 04510, Mexico D,F,, Mexico. chumin@servidor.unam.mx.
authors.forename: Rodolfo
authors.initials: R
authors.lastname: Cisneros
authors.forename: Heriberto
authors.initials: H
authors.lastname: Pfeiffer
authors.forename: Chumin
authors.initials: C
authors.lastname: Wang