Silicon-rich silicon oxide thin films have been prepared by thermal evaporation of silicon monoxide in vacuum. The SiOx film composition (1.1⩽ x ⩽1.7) has been controlled by varying the deposition rate and residual pressure in the chamber. Long time stability of all films has been ensured by a postdeposition annealing at 523 K for 30 min in Ar atmosphere. Some films were further annealed at 973 K and some others at 1303 K. Raman scattering measurements have implied the formation of amorphous silicon nanoparticles in films annealed at 973 K and Si nanocrystals in films annealed at 1303 K. The latter conclusion is strongly supported by high resolution electron microscopy studies which show a high density of Si nanocrystals in these films. Photoluminescence has been observed from both amorphous and crystalline nanoparticles and interpreted in terms of band-to-band recombination in the nanoparticles having average size greater than 2.5 nm and carrier recombination through defect states in smaller nanoparticles.

The temperature-dependent optical absorption of 3D arrays of close-packed strongly quantized ZnSe QDs, deposited in thin film form, is studied in the interval from 11 to 340 K. Because of the particle size distribution and interdot coupling between proximal QDs within the QD arrays, the excitonic peaks are not visible at all, even at temperatures as low as 11 K. The temperature coefficient of the band-gap energy in the strongly quantized QD arrays was found to be twice larger than the value characteristic of a bulk ZnSe specimen. The Debye temperature, on the other hand, is shown to decrease by about 15% in comparison with the bulk value, which is attributed to the phonon confinement effects. It is shown that the sub-band-gap exponential absorption tails in the strongly quantized 3D QD arrays obey the Urbach−Martienssen rule. The temperature dependence of the Urbach energy and the relation between this quantity and the band-gap energy of the films could be excellently fitted to the predictions of the Cody’s model. However, in contrast to the macrocrystalline semiconductors, the temperature-dependent component of the Urbach energy accounts for less than 15% of the overall value, which is attributed to the very high degree of inherent structural disorder in the QD arrays. This is in line with the conclusions derived from analyses of the temperature dependence of the steepness parameter, σ, which imply a rather high energy of the phonons contributing to the Urbach−Martienssen tails in the optical absorption of the QD arrays.

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A series of ZnSe single layers having thickness between 30 nm and 1 µm was deposited on c-Si and glass substrates at room substrate temperature. Thermal evaporation of ZnSe powder in high vacuum has been applied. Moreover, SiO x /ZnSe periodic multilayers prepared by the same deposition technique and having ZnSe layer thickness of 2 and 4 nm have been studied. Raman spectra were measured at 295 K, using the 442 nm line of a He-Cd laser as well as different lines of the Ar + or Ar + /Kr + lasers. The observed Raman features have been related to multiple optical phonon (1LO to 4LO) light scattering and connected with the existence of randomly oriented crystalline ZnSe grains in both ZnSe single layers and ZnSe layers of the multilayers. Relatively large line width (≈ 15 cm −1 ) of the 1LO band has been observed and related to lattice distortion in the crystalline grains and existence of amorphous phase in the layers thinner than 100 nm. The Raman spectra measured on both ZnSe single layers and SiO x /ZnSe multilayers using the 488 nm line with a gradually increased laser beam power indicate an increased crystallinity at high irradiation levels.

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Template-free conventional chemical and sonochemical approaches to 3D assemblies of indium(III) sulfide quantum dots were developed that allow deposition of strongly quantized cubic α-In 2 S 3 nanocrystals close packed in thin film form. Our observation of metastable cubic structure at room temperature (instead of the thermodynamically most stable tetragonal β modification in the case of bulk material) was related to the very small crystal size. Because of heterogeneous sonochemical effects, the average crystal radius of the QD solids reduces from 2.5 to 2.0 nm upon sonification of the reaction system by continuous high-intensity ultrasound. Upon postdeposition annealing treatment, these values increase to 4.1 nm. Structural, optical and electrical properties of the synthesized QD solids were studied in details. The band gap energy value of 2.85 eV for the as-deposited QD solids in thin film form is strongly blue-shifted (by 0.85 eV) with respect to the value characteristic for a macrocrystalline specimen. In the case of as-deposited films by sonochemical approach, band gap value is 3.00 eV, indicating the possibility for further control of the optoelectronic properties of this material by sonochemical approach. Upon postdeposition thermal treatment at 150 and 200 °C, band gap energy red shifts to 2.20 and 2.00 eV were observed. Analysis of the size-quantization effects in the synthesized QD solids deposited in thin film form enabled us to estimate that the Bohr's excitonic radius in the studied semiconductor lies in the range from 2.5 to 4.1 nm. The absence of clearly defined excitonic peaks in the absorption spectra of the studied QD assemblies was attributed to the size-distribution of the nanoparticles and to the interdot electronic coupling effects. Analysis of the charge carrier transport properties in the QD assemblies within the Kazmerski's model indicated that the intercrystalline barrier height decreases by 0.04 eV upon thermal treatment of the films. Conductivity activation energy was found to be 0.82 eV, while the thermal band gap energy, calculated from the thermoelectrical measurements in the region where intrinsic conductivity mechanism is activated, was 2.22 eV. AFM measurements have shown that QD assemblies constituting the sonochemically deposited films show stronger tendency toward coagulation than those synthesized by conventional chemical approach.

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Continuous-wave heterogeneous sonochemical method was developed to synthesize 3D assemblies composed by QDs of metastable (cubic) modification of CdSe with sphalerite structural type. 3D QD assemblies were deposited in thin film form and as bulk precipitates. Structure, surface morphology, optical absorption as well as charge carriers' and phonon confinement effects were studied in details. The average nanocrystal radius, calculated by the Scherrer and Williamson-Hall methods, diminishes from 2.7 nm for samples synthesized by conventional colloidal chemical route to 2.0 nm for samples synthesized by sonochemical route. Upon post-deposition thermal annealing this value increases to 12.0 nm. QD size decrease is followed by increase of the uni-directional lattice strain and dislocation density (as defined by Hirsch), as well as by decrease of the lattice constant value. Previous findings were justified by analysis of X-ray diffraction peaks shape, which were found to be dominated by the particle size-distribution, instead of non-uniform strain. The energy of the fundamental direct C v 8 ! C c 6 interband electronic transition, computed from optical absorption data within parabolic approximation for the dispersion relation, shifts from 2.67 eV for sonochemically deposited samples and 2.08 eV for chemically deposited ones, to 1.77 eV upon post-deposition thermal treatment (close to the bulk value of 1.74 eV). The type of ''interband'' transitions does not change upon dimensionality reduce. Enhanced band gap energy blue shift upon average QD size decrease is followed by oscillator strength increase. Such trends were rationalized in terms of 3D confinement effects on charge carriers' motion. Experimentally observed band gap energies agree very well with the predictions of the effective mass model of Brus. The next direct interband electronic transition, from the spin-orbit split component of the valence band to the conduction band, has been detected and analyzed. The 1LO bands in the Raman spectra of chemically and sonochemically deposited samples appear at 206 and 204 cm -1 , as compared to the bulk value of 210 cm -1 . The extent of homogeneous broadening of the corresponding band is larger in sonochemically deposited samples, indicating enhanced frequency of phonon-phonon collisions in smaller QDs. The observed frequency shifts are dominated by phonon-dispersion terms, instead of lattice contraction.