KCN solution treatment of amorphous hydrogenated silicon (a-Si:H) is a new technique for passivation of Si dangling bonds, capable to eliminate the interface states as well as a part of the bulk defects. It is based on the formation of Si-CN bonds by the cyanide treatment. The films were deposited on crystalline silicon (c-Si) and Coming glass substrates and subsequently chemically modified by KCN and HCN solutions. The latter solution was used as a passivation agent for the first time. Different cyanidization solutions in MeOH and water were tested. The X-ray diffraction and optical reflectance spectra of treated a-Si:H films were measured and analyzed. The optical thickness of intrinsic a-Si:H deposited on c-Si, obtained from the reflectance spectra, was apparently changed using HCN 0.1 M water solution. The X-ray measurements indicate a modification of the structure at the intrinsic a-Si:H/c-Si interfaces. The results were compared with those obtained on p-type of a-SiC:H/c-Si and a-SiC:H/glass, a-Si:H/c-Si structures. (C) 2004 Elsevier B.V. All rights reserved.