Surface functionality features of porous silicon prepared and treated in different conditions

Abstract

Hydrophilic layers of porous silicon are prepared by single-or two-step anodization and characterized by evaluating their surface hydrophilicity and contents of functional groups using IR spectroscopy and adsorption of acid-base indicators with different p-a values. The surface functional composition of the synthesized samples is shown to be adjustable depending on the anodization current density. The surface of samples obtained at anodization current density 30mA/cm2 is predominantly occupied with p-a 2.5 corresponding to =Si-OH groups. The increase of current density to 80 mA/cm2 results in the increase of surface functional nonuniformity with the formation of versatile centers, primarily Lewis acidic sites corresponding to Si atoms, as indicated by selective indicator adsorption in agreement with the disappearance of Si-H bonds in IR spectra and overall surface disordering according to SEM and AFM data.