Understanding materials with dimensions down to few nanometers is of major importance for fundamental science as well as prospective applications. Structural transformation and phononconfinement effects in the nanodiamonds (NDs) have been theoretically predicted below 3 nm size. Here we investigate the effect of size on the surface chemistry, microscopic structure, and Raman scattering of high-pressure high-temperature (HPHT) and detonation nanodiamonds (DNDs) down to 2-3 nm. The surface and size of NDs are controlled by annealing in air and ultracentrifugation resulting in three ND fractions. Particle size distribution (PSD) of the fractions is analyzed by combining dynamic light scattering (DLS), analytical ultracentrifugation (AUC), small angle X-ray scattering (SAXS), X-ray diffraction (XRD), and transmission electron microscopy (TEM) as complementary techniques. Based on the obtained PSD we identify size-dependent and synthesis-dependent differences of NDs properties. In particular, interpretation of Raman scattering on NDs is revisited. Comprehensive comparison of detonation 3 and pure monocrystalline HPHT NDs reveals effects of diamond core size and defects, chemical and temperature (in)stability as well as limitations of current phonon confinement models. In addition, low-frequency Raman scattering in the 20 -200 cm -1 range is experimentally observed.The size dependence of this signal for both HPHT NDs and DNDs suggests that it may correspond to confined acoustic vibrational, "breathing-like" modes of NDs.

Silicon thin films grown near the boundary between the amorphous/microcrystalline growth offer superior properties for industrial applications. Series of silicon samples, in which crossing of this transition region was achieved by changing a single technological parameter (dilution of silane in hydrogen, deposition temperature, sample thickness) were used to test our model of transport, connecting the macroscopically observed transport properties and the crystallinity, hydrogen content, grain size and grain boundaries. Microscopic study by AFM led to the formulation of the geometrical model of growth of mixed phase Si. The demand for research of microcrystalline or polycrystalline silicon prepared at low substrate temperatures is stimulated by the use of cheap plastic substrates. In addition to a direct deposition an alternative technology, such as metal-induced crystallization supported by the electric field is discussed. Possible future application of thin silicon films, for example in a "nanolithography", is also shown.

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