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.

3D arrays of close-packed AgBiS 2 quantum dots (QDs) in thin film form were synthesized for the first time using novel, convenient sonochemical approach. Structural, optical, and photoelectrical properties of the synthesized material were investigated with an emphasis on their dependence on crystal size. The sonochemically synthesized AgBiS 2 colloidal crystals have an average QD radius of 4.2 nm, twice as small compared to the QD solid obtained without ultrasonic irradiation. The optical band gap energy of sonochemically synthesized AgBiS 2 QD thin films of 1.40 eV is strongly blue-shifted in comparison to that of the macrocrystal (0.90 eV) and that of nanostructured films synthesized by conventional chemical route (1.10 eV). Upon annealing, E g exhibits a red shift to 1.00 eV. Spectral dependence of stationary nonequilibrium conductivity of the 3D QD assemblies suggests that the thin films' photoconductivity is modulated by the intercrystalline barrier height decrease. E g of the films calculated on the basis of photoconduction spectral response in the low-absorption region is 1.18 eV. Thermal band gap energy of the films is 1.10 eV, whereas both the variable range hopping conduction and thermionic emission mechanisms are predominant in the overall intercrystalline charge carrier transport through 3D QD assemblies.

The transport properties of nonequilibrium (photoexcited) charge carriers in sonochemically synthesized threedimensional (3D) assemblies of AgBiS 2 quantum dots (QDs) deposited as thin films were studied. To characterize the photoconduction of quantum-confined nanocrystals close packed in thin film form, both stationary and time-resolved experiments were performed. Besides by interband electronic transitions in the bulklike part of the nanocrystals, the photoresponse of nanocrystalline films was found to be also affected to a greater extent by the crystal boundary barrier height modulation upon illumination. The surface and bulk recombination velocities were found to be comparable. Good agreement was obtained between the band gap energy determined by analysis of the photoconductivity data measured by the constant field and the constant photocurrent method (∼1.18 eV). This value is in agreement with the optical spectroscopy data. It is higher than the optical band gap of a bulk specimen of this semiconductor, due to 3D confinement effects on the charge carrier motions within individual QDs. The nonequilibrium conductivity was found to relax exponentially with a time constant of 1.67 ms, which corresponds to average lifetime of minority charge carriers (holes).