Anna Osherov

Tunability of the optical band edge in thin PbS films chemically deposited on GaAs(100)

The optical properties of chemical-solution-deposited thin films of lead sulfide (PbS) were investigated using infrared transmission and photoluminescence spectroscopies. The synthesized films are characterized by a wide range of microstructures, from 15 nm nanocrystals up to monocrystals. Energy bandgap values for bulk and nanostructured layers varied from 0.41 eV up to 0.48 eV, respectively. Blueshifts in both absorbance and emission peaks of the nanostructured layers were obtained due to quantum size effects. The optical properties of the films are shown to be size-dependent, with the band edge increasing with temperature.

Enhanced photoluminescence and photonic bandgap modification from composite photonic crystals of macroporous silicon and nanocrystalline PbS thin films

We report on the fabrication of composite photonic crystals (PCs) of macroporous silicon and PbS thin films and about their passive and active optical properties. We have measured a redshift in the composite PC photonic stopbands relative to those of the PC substrate. In addition, we have measured a high extraction efficiency of the photoluminescence from the embedded PbS films due to band-edge singularities and slow-light modes of a defect-free two-dimensional composite PC. The peak extraction efficiency has been found to be six times larger than that of planar unpatterned PbS films.

Luminescence and structure of nanosized inclusions formed in SiO2 layers under double implantation of silicon and carbon ions

Luminescent and structural characteristics of SiO2 layers exposed to double implantation by Si+ and C+ ions in order to synthesize nanosized silicon carbide inclusions have been investigated by the photoluminescence, electron spin resonance, transmission electron microscopy, and electron spectroscopy methods. It is shown that the irradiation of SiO2 layers containing preliminary synthesized silicon nanocrystals by carbon ions is accompanied by quenching the nanocrystal-related photoluminescence at 700–750 nm and by the enhancement of light emission from oxygen-deficient centers in oxide in the range of 350–700 nm. Subsequent annealing at 1000 or 1100°C results in the healing of defects and, correspondingly, in the weakening of the related photoluminescence peaks and also recovers in part the photoluminescence of silicon nanocrystals if the carbon dose is less than the silicon dose and results in the intensive white luminescence if the carbon and silicon doses are equal. This luminescence is characterized by three bands at ∼400, ∼500, and ∼625 nm, which are related to the SiC, C, and Si phase inclusions, respectively. The presence of these phases has been confirmed by electron spectroscopy, the carbon precipitates have the sp3 bond hybridization. The nanosized amorphous inclusions in the Si+ + C+ implanted and annealed SiO2 layer have been revealed by high-resolution transmission electron microscopy.

Studying of quantum-size effects origination in semiconducting lead sulfide nanocrystals

Lead sulfide (PbS) crystals with sizes from 20 to 500 nm were deposited in chemical bath from an alkaline solution (CBD method). The morphology of specimens was studied using high resolution scanning electron microscopy (HRSEM). Influence of crystallite sizes on the electronic structure was studied with X-ray photoelectron spectroscopy (XPS) and high resolution electrons energy losses spectroscopy (HREELS). The work function was measured with a Kelvin probe microscopy in air.The photoelectron doublet peaks at spectra of Pb 4f donor and S 2p acceptor were found to be shifted toward the higher binding energies comparing to the corresponding lines positions in the reference PbS compound. This shift increases with decreasing of the crystals size. The effect of size shift in lead sulfide could be noticed when size is smaller than 300 nm. HREELS showed that dispersion of nanoparticles causes smoothing of the PbS band gap in different directions of reciprocal lattice, and the minimal transition energy increases from 0.39 to 3.62 eV. The work function of the material is shown to be in inverse proportion to the semiconductor crystal size. This data correlates well with the electron spectroscopy results.