Highly efficient photoinduced desorption of N2O and CO from porous silicon.

Photoinduced desorption (PID) of N(2)O and CO from porous silicon (PSi) samples is reported. Both adsorbates exhibit unusually large cross sections for PID at 193 nm, up to 10(-15) cm(2), 2-3 orders of magnitude larger than the literature values for similar processes on flat Si. Under this UV irradiation, N(2)O molecules undergo photodissociation (a competing process leading to surface oxidation) with a cross section that is 2 orders of magnitude smaller than photodesorption. In the case of CO desorption is the exclusive photodepletion mechanism. PID efficiency decreases with increasing CO coverage suggesting PID hindrance by interactions among the desorbing CO molecules leading to re-adsorption at higher coverage. The wavelength and fluence dependence measurements exclude the possibility of laser induced thermal desorption for both adsorbates. The proposed mechanism for this phenomenon is desorption induced by hot electron transfer from the substrate to the adsorbate. Enhanced lifetime of transient negative adsorbate due to stabilization by localized holes on PSi nanotips can explain the observed abnormally large PID efficiency on top of porous silicon.

Effect of glass dissolution on the solution deposition of ZnO films and its exploitation for deposition of Zn silicates.

ZnO is probably the most studied material deposited as films by aqueous solution methods. Both neutral and alkaline solutions are commonly used, and deposition is often carried out in glass vessels. We show that for depositions carried out under alkaline conditions, slow dissolution of the glass by the solution often results in formation of zinc silicates together with the ZnO. While this silicate formation is most clearly seen after long deposition times (many hours), it can be detected already within 1 h, while often ZnO depositions proceed for substantially longer. We also describe conditions where the zinc silicate deposits without formation of ZnO providing a method of depositing such films. Finally, we note that the glass of a reaction vessel also can affect deposition of CdSe, pointing to a more general role of this normally neglected parameter.