Strong quantum confinement effect in nanocrystalline cerium oxide

Highly uniform and well-dispersed cerium oxide quantum dots were successfully synthesized by simple precipitation method by using cerium ammonium nitrate and ammonium hydroxide as precursor materials with suitable conditions. The X-ray diffraction pattern indicates the formation of cubic phase CeO₂. The average particle size of cerium oxide from high resolution transmission electron microscopy (HRTEM) was found to be 3 nm. The X-ray photoelectron (XPS) spectrum confirms the presence of Ce³⁺ in CeO₂. Optical studies by UV–vis spectroscopy for the synthesized CeO₂ nanoparticles exhibit a blue shift (E_g = 3.78 eV) with respect to the bulk material (E_g = 3.15 eV) due to quantum confined exciton absorption.     

Influence of fluorine substitution on the morphology and structure of hydroxyapatite nanocrystals prepared by hydrothermal method

Hydroxyapatite (HAp) nanocrystals with different levels of fluorine substitution (P/F = 0, 6, 4 and 2) on the OH sites were produced via hydrothermal method. The fluorine substitution was found to alter the morphology of crystals appreciably. The aspect ratio and the crystallinity of HAp crystals increased with increasing fluorine substitution. The presence of broad ring and hallow ring patterns in electron diffraction suggests the low-crystalline nature of HAp crystals. With increasing fluorine substitution, the diffraction patterns exhibited discrete rings and numerous diffraction spots, implying the increased crystallinity. Raman spectra from the HAp nanoparticles also support the less-crystalline nature of the pristine HAp and the enhanced crystallization by fluorine substitution. In HAp crystals processed with no fluorine substitution, surface energy and planar Ca²⁺ density are less sensitive to the crystallographic orientation because of its low-crystalline nature, favoring equi-axed or slightly elongated particles. The addition of fluorine apparently increased the crystallinity, enhancing the orientation dependent growth and accordingly the aspect ratio. Osteoblast proliferation was observed to be enhanced by fluorine substitution in HAp. In vitro biological data support that the excellent osteoblastic cell viability and functional activity of the fluoridated apatite.     

D.c. conduction studies on thermally evaporated neodymium oxide thin films

Aluminium-neodymium oxide-aluminium thin film capacitors have been prepared by thermal evaporation and the d.c. conduction properties of these films have been studied. The thicknesses of the films have been determined by a multiple beam interferometer. The current-voltage power-law dependence showed that the conduction in these films is space-charge limited. The linear dependence of the current density on the square root of the applied field confirmed the exponential trap distribution. The trap density has been found to be of the order of 10²⁶ m^–3. It has also been observed that the Schottky type of conduction is predominant in the high-field region and the height of the Schottky barrier has been determined. It is seen that the conduction mechanism is an activated process with the activation energy decreasing with increasing field.     

Studies on polycrystalline Cd0.96Zn0.04Te thin films prepared by vacuum evaporation

Polycrystalline Cd_0.96Zn_0.04Te thin films are deposited onto glass substrates (Corning 7059) kept at room temperature by vacuum evaporation. The films exhibit zinc blende structure with predominant (1 1 1) orientation. The rms roughness of the films evaluated by atomic force microscope is 3.7 nm. The band gap energy of the films measured by optical transmittance measurement is 1.539 eV. The photoluminescence (PL) spectrum of the films shows intense emission due to free and bound exciton recombination and no emission associated with crystal imperfection and PL line shapes give indications of the high quality of the layers. These films have been implanted with properly mass analyzed Boron ions (¹⁰B⁺) and the effect of implantation has been analyzed by X-ray diffraction, Raman scattering and optical transmittance measurements and the results are explained on the basis of the implantation induced surface roughness and lattice disorder.     

Magnetron sputtered transparent conducting CdO thin films

Thin films of cadmium oxide have been produced by dc reactive magnetron sputtering in nitrogen and oxygen atmosphere. The structural, optical, and electrical characterization of these films are investigated. Structural analysis indicates that the films are polycrystalline and cubic. Composition analysis by Rutherford backscattering spectrometry has been made and it is found that the films contain excess cadmium and deficient oxygen. It is observed from the optical properties that the films possess a transmittance of about 85% in the visible and near infrared regions of the spectrum and direct bandgap values in the range 2.50 to 2.68 eV for films of thicknesses 146 to 177 nm. Electrical measurements point out that the films have resistivity, carrier concentration, and mobility in the range 2.65 to 6.64 × 10^-6 Ωm, 1.60 to 2.35 × 10²⁶ m^-3, and 57.65 to 100.48 × 10⁻⁴ m² v⁻¹ s⁻¹ respectively.