Search

Manganese-doped zinc sulfide (MnxZn1-xS) nanorods were synthesized through solvothermal processes and were characterized by x-ray diffraction and scanning and transmission electron microscopy. Positron lifetime and Doppler broadening measure-ments were carried out on powdered samples with different dopant concentrations. A transformation from hexagonal to cubic structure was observed almost concomitantly with the filling of Zn2+ vacancies and/or substitution of Zn2+ ions by Mn2+ ions. The lifetime of positrons annihilating at the surfaces of nanorods decreased with increase in their diameter during increased doping by Mn2+ ions. At concentrations above 20%, pyramid-like coarse crystals of MnS were found coexisting with the ZnS nanostructures. The interior of the nanorods seemed to be free of vacancy-type defects unlike in the case of ZnS nanoparticles. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Single-layer ZnO–Al2O3 nanocomposite thin films with thickness approximately 119 nm, containing randomly dispersed nanocrystallites of ZnO in the Al2O3 matrix were prepared by sol gel technique. The relative molar concentration of ZnO was 20% in the matrix. The confined nanoparticles ZnO were investigated through ac impedance spectroscopy in the frequency range of 500 Hz to 5 MHz at 315 K, 325 K, 345 K, 355 K, 395 and 450 K. The dielectric relaxations in each case were found to be of Cole–Cole type. The thermally activated relaxation phenomenon was analysed with the help of an equivalent circuit which is proposed on the basis of the experimentally obtained complex capacitance and impedance spectral studies. The temperature dependent electrical conductivity was analysed on the basis of interstitial Zn ions and free electrons in the system. The defect concentration of the nanocomposite thin film was determined from the complex capacitance measurements. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Well-crystallized Mg x Zn 1-x O films were deposited on quartz substrates by sol-gel technique with a variation of x value from 0 to 0.15. The samples were annealed at different temperatures (500 °C to 700 °C) in air and oxygen atmosphere to study the effect of annealing atmosphere on the luminescence properties of the films. The optical, microstructural and photoluminescence properties of the films were studied. It was found that the band gap of the films increased with increasing Mg concentration (x value). A remarkable change in the photoluminescence spectra of the films for x = 0.05 was observed by varying the annealing atmosphere. Highly intense UV emission at room temperature could be obtained by annealing the Mg 0.05 Z 0.95 O film in static oxygen atmosphere, while the intensity of the visible defect related luminescence could be reduced, resulting in a high intensity ratio (∼100) of the two.

ZnO–SiO2 nanocomposite films with ZnO nanoparticles dispersed in a silica matrix (molar ratio of ZnO:SiO2 is 25:75) were deposited on quartz glass substrates by the sol-gel method. The optical, microstructural and photoluminescence properties of the films were studied. The films were annealed in air at different temperatures (373–773 K) to investigate the variation of grain size with annealing temperature. The photoluminescence (PL) spectra of the annealed films showed an excitonic emission in the range of 4.22 to 3.85 eV and two defect related emissions in the range of 2.736 to 2.514 eV and 2.45 to 2.32 eV. A linear shift of the peak positions with increasing particle radii (1.48 to 1.95 nm) of the ZnO nanoparticles was observed. The nature of transition of the defect related visible emissions has been discussed. The variation of defect content in the nanocomposites with the radii of the ZnO nanoparticles were examined from the Urbach tail width. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

CuInTe 2 films were synthesized by rapid thermal processing (RTP) of In/Cu/Te stacked elemental layers (SEL). The films were characterized by measuring optical, microstructural, electrical and galvanomagnetic properties. The optical band gap was found to vary within 0.95-0.97 eV with the variation of the Cu/In ratio within 0.72 to 0.92 while the grain size varied between 0.25 and 0.44 μm. Lattice constants were determined from the X-ray diffraction analysis. The films were polycrystalline in nature and oriented preferentially in (112) direction. It was found that grain boundary scattering played a dominant role in describing the electrical and galvanomagnetic properties.

Nanostructured CdS films are deposited by the high pressure magnetron sputtering technique onto glass and NaCl substrates at various substrate temperatures and at a fixed gas pressure. Electrical conductivity of these nano CdS films in dark and when illuminated is measured. It is observed that the conduction mechanism is dominated by the combined effects of thermionic emission, tunneling, and variable range hopping.

Explicit expressions for the absorption coefficient beyond the absorption edge are obtained by considering the Franz-Keldysh effect and mechanical stress to be operative simultaneously in the grain boundary regions of polycrystalline semiconductor films. The expressions are successfully utilized to explain the tail end of the absorption spectrum of ZnTe films.

Polycrystalline thin films of CdSxSe1−x (0 < x < 0.8) are prepared by co-evaporating CdS and CdSe from a two-zone evaporation source. The films are characterised by measuring optical and electrical properties. Information on the microstructures are obtained from XRD and TEM/SEM measurements. Raman shifts in the films with composition are also reported. Information on the scattering mechanism is derived from the thermoelectric power measurements. Grain boundary scattering effects in these films are also studied critically.

Optical transitions near the fundamental band edge are studied for CuInSe2 films having different Cu/In ratios by analysing the variations of the absorption coefficient (α) with incident photon energy. The results indicate allowed direct transitions at 0.986 to 1.075 eV depending upon the Cu/In ratio. The band gap shifts towards lower energy for increasing copper content in the films. There are indications of forbidden direct transitions at energies 0.81 to 0.89 eV. Fur CuInSe2-Schichten mit unterschiedlichem Cu/In-Verhaltnis werden die optischen Ubergange in dcr Nahe der Grundgitterkante durch die Analyse der Anderungen des Absorptionskoeffizienten (α) mit der einfallenden. Photonenenergie untersucht. Die Ergebnisse zeigen erlaubte direkte Ubergange bei 0,986 bis 1,175 eV, die vom Cu/In-Verhaltnis abhangen. Die Bandlucke verschiebt sich zu niedriger Energie fur wachsenden Kupfergehalt der Schichten. Es existieren Anzeichen fur verbotene direkte Ubergange bei Energien von 0,81 bis 0,89 eV.

Rapid production of single crystalline CdS nanoribbons with hexagonal wurtzite phase has been achieved by thermal evaporation of CdS powder on Si wafers. The flow rate of the carrier (Ar) gas along with the synthesis temperature plays an important role in defining the size and shape of the CdS nanoribbons. Scanning electron and transmission electron microscopic observations revealed the nanoribbons to have a flat end as well as side surfaces which will make it ideal for optoelectronic devices such as nanolasers and light emitting diodes based on individual nanoribbons. The nanoribbons have widths within 200-400 nm and lengths approximately a few hundred micrometers. Room-temperature photoluminescence measurements show green emission centered at approximately 525 nm which may be ascribed to the near band edge emission. The Raman spectra of the CdS nanoribbons show peaks around 304, 609, 915, and 1220 cm(-1) corresponding to the first-, second-, third-, and fourth-order longitudinal optical phonon modes, respectively.