Porous silicon has been prepared using a vapor-etching based technique on a commercial silicon powder. Strong visible emission was observed in all samples. Obtained silicon powder with a thin porous layer at the surface was subjected to a photo-thermal annealing at different temperatures under oxygen atmosphere followed by a chemical treatment. Inductively coupled plasma atomic emission spectrometry results indicate that silicon purity is improved from 99.1% to 99.994% after annealing at 900°C.

In this work, we use a two-step metal-assisted chemical etching method to produce films of silicon nanowires shaped in micrograins from metallurgical-grade polycrystalline silicon powder. The first step is an electroless plating process where the powder was dipped for few minutes in an aqueous solution of silver nitrite and hydrofluoric acid to permit Ag plating of the Si micrograins. During the second step, corresponding to silicon dissolution, we add a small quantity of hydrogen peroxide to the plating solution and we leave the samples to be etched for three various duration (30, 60, and 90 min). We try elucidating the mechanisms leading to the formation of silver clusters and silicon nanowires obtained at the end of the silver plating step and the silver-assisted silicon dissolution step, respectively. Scanning electron microscopy (SEM) micrographs revealed that the processed Si micrograins were covered with densely packed films of self-organized silicon nanowires. Some of these nanowires stand vertically, and some others tilt to the silicon micrograin facets. The thickness of the nanowire films increases from 0.2 to 10 μm with increasing etching time. Based on SEM characterizations, laser scattering estimations, X-ray diffraction (XRD) patterns, and Raman spectroscopy, we present a correlative study dealing with the effect of the silver-assisted etching process on the morphological and structural properties of the processed silicon nanowire films.

The aim of this work was to investigate a simple and effective method to produce porous silicon from a powder of silicon. The preparation of porous silicon (PS) was realized by exposing silicon powders to acid vapor attack issued from acid solutions containing a 48% of HF and 65% of HNO3. The bond configuration of powder silicon before and after attack with acid vapor was monitored by Fourier transmission infrared spectroscopy (FTIR) and it was found that the PS was produced due to the newly formed Si-H bond during acid vapor attack. From the photoluminescence spectroscopy, it was shown that powder silicon attacked with acid vapor can lead to an increase of photoluminescence (PL) intensity when they are excited by light compared to untreated powder silicon and can provide blue shifts in the PL spectrum by increasing exposing time. This behavior may be attributed to the reduction in the size of the silicon, indicating consequently the formation of PS powder. The experimental results suggest a possibility that the chemical attack with acid vapor of the powder silicon provides a relatively easy way to produce porous silicon.

This work reports on correlation between structural and morphological properties of ZnTiO₃/porous silicon (PS). The PS was elaborated by electrochemical anodization from the single- crystal p-type silicon wafer. Nanocrystalline ZnTiO₃thinfilms have been prepared on PS using sol-gels pin coating technique. The deposited films were annealed in air at 800 °C for 2 h. The structural and morphological properties of the films were studied for different number of layers. X-ray diffraction spectra confirms that ZnTiO₃films were hexagonal phase and the crystallite size of ZnTiO₃films increased from 111 to 125 nm when the number of layers increase from 4 to 8 layers. SEM image shows approximate semi-spherical particles with a little agglomeration for all samples. The morphologies changed and the average grain size changed and increases from 81nm to 131nm.