The contribution deals with passivation of surfaces of c-Si and 6H-SiC by formation of very thin SiO2 films in boiling HNO3 solutions and by passivation of a-Si based double and triple layer structures deposited on Corning glass and c-Si by KCN solutions. The structures are investigated by spectroscopic ellipsometry, charge version of DLTS, C-V, FTIR-DRIFT, and by photoluminescence measuremets at 6 K. Newly developed 2nd generation of MOS structures prepared on c-Si with an approx. 3 nm SiO2 layer gives typical density of interface defect states of 5 x 10(10) eV(-1) cm(-2). Real part of complex refractive index of approx. 3 nm thick SiO2 layers is about 1.75. Application of HCN solutions to structure approx. 3 nm SiO2/Si (applied as the last technological step) leads to remarkable lowering of absorbance in wavelength region 4000 cm(-1)-2500 cm(-1). This result indicates a decrease of number of non-radiation transitions in the surface region of oxide/Si structures. Such structures have also the lowest density of interface defect states (observed by Q-DLTS). Application of boiling KCN solutions considerably increases amplitudes of photoluminescence signals coming from different double and triple a-Si based layers deposited on Corning glass. We relate this effect predominantly with reduction of non-radiation transitions in excited region of amorphous structures - with passivation of corresponding defect states in a-Si structures in boiling KCN solutions. (c) 2012 Elsevier B.V. All rights reserved.