Structural and optical properties of TiO2 ALD coated silicon nanostructures were investigated. The morphology and
chemical composition of TiO2 coated silicon nanopillars and porous silicon were studied by using methods of scanning
electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX). Optical characteristics were studied using
measurements of reflectance and luminescence spectra. Detailed analysis of morphological features and
photoluminescence mechanisms were provided. Peculiarities of reflectance spectra were discussed. It was shown the
possible application of these structures as antireflectance coatings.
Structural and optical properties of Al<sub>2</sub>O<sub>3</sub>/TiO<sub>2</sub> nanolaminates fabricated by atomic layer deposition (ALD) were
investigated. We performed Raman spectroscopy, transmission electron microscopy (TEM), X-Ray reflectivity (XRR),
UV-Vis spectroscopy, and photoluminescence (PL) spectroscopy to characterize the Al<sub>2</sub>O<sub>3</sub>/TiO<sub>2</sub> nanolaminates. The
main structural and optical parameters of Al<sub>2</sub>O<sub>3</sub>/TiO<sub>2</sub> nanolaminates were calculated. It was established that with
decreasing of the layer thickness, the value of band gap energy increases due to the quantum size effect related to the
reduction of the nanograins size. It was also shown that there is an interdiffusion layer at the Al<sub>2</sub>O<sub>3</sub>/TiO<sub>2</sub> interface which
plays a crucial role in explaining the optical properties of Al<sub>2</sub>O<sub>3</sub>/TiO<sub>2</sub> nanolaminates. Correlation between structural and
optical parameters was discussed.
In this work, we present a detailed experimental Raman investigation of nanostructured silicon films prepared by metalassisted chemical etching with different nanocrystal sizes and structures. Interpretation of observed one and two-phonon Raman peaks are presented. First-order Raman peak has a small redshift and broadening. This phenomenon is analyzed in the framework of the phonon confinement model. Second-order Raman peaks were found to be shifted and broadened in comparison to those in the bulk silicon. The peak shift and broadening of two-phonon Raman scattering relates to phonon confinement and disorder. A broad Raman peak between 900-1100 cm<sup>-1</sup> corresponds to superposition of three transverse optical phonons ~2TO (X), 2TO (W) and 2TO (L). Influence of excitation wavelength on intensity redistribution of two-phonon Raman scattering components (2TO) is demonstrated and preliminary theoretical explanation of this observation is presented.
An impact of morphology on reflectance of porous silicon was investigated. Depending on the metal-assisted chemical etching conditions the macro- micro structures could be formed. The reflectance properties of various porous silicon structures after ammonia adsorption were investigated. It was shown that increasing of ammonia concentration in the measurement camber leads to an increase of the reflectance. The most sensitive structures for ammonia detection are porous silicon having approximately size of pores - 10-15 μm. A fast response of porous silicon on the adsorption of ammonia molecules may be used for development of new sensors.