Structural and optical properties of Zn₁₋xCoxO thin films prepared by RF reactive sputtering technique

We have reported the effect of Co doping on structural and optical properties of ZnO thin films prepared by the RF reactive sputtering technique. The composite targets were formed by mixing and pressing ZnO and CoO powders. The thin films were deposited on silica and glass substrates. The structures of samples have been studied by using X-ray diffraction (XRD) and atomic force microscopy (AFM). With the sensitivity of the XRD instruments, the structural analyses of Co-doped ZnO films reveal formation of predominant (002) reflection corresponding to the hexagonal wurtzite structure without any secondary phase. The AFM study showed that surface morphology of the Zn₁₋xCoxO films is composed of closely packed nanocrystallites with nanorod shape. The optical properties of the samples were studied using UV-vis absorption and PL spectra. The optical absorption spectra show a red shift of the band edge, which indicates that Co²⁺ ions substitute Zn²⁺ ions in ZnO lattice. In the room-temperature photoluminescence spectra, four main peaks were revealed in all the samples, which are attributed to ultraviolet, violet-blue, blue and green emission

Comparative studies of optical absorption, photoluminescence and EPR spectra of PbMnI₂ bulk layers and nanocrystals

We report a study of the layered diluted magnetic semiconductor (DMS) Pb₁₋xMnxI₂ in 3D bulk layers and nanocrystal form by using optical absorption, photoluminescence and electron paramagnetic resonance (EPR). The samples of the bulk Pb₁₋xMnxI₂ crystals with x lying within the range 0 to 0.15 were grown using the Bridgman-Stockbarger technique. The composite nanostructures containing DMS nanocrystals of Pb₁₋xMnxI₂ were prepared by cooling the boiling saturated aqueous solution to room temperature. The exciton structure of the absorption spectra of nanoparticles exhibits blue shift due to the quantum confinement effect. In photoluminescence spectra of nanocrystals, two main peaks were revealed, which are attributed to the band-edge transitions and defect states. The EPR spectra for bulk layers and nanocrystals consist of an intense broad line and several weak narrow lines that correspond to hyperfine spectra of Mn²⁺ ions

Statistical model analysis of local structure of quaternary sphalerite crystals

At the 2004 Ural International Winter School, we introduced the statistical strained tetrahedron model and discussed ternary tetrahedron structured crystals. The model allows one to interpret x-ray absorption fine structure (EXAFS) data and extract quantitative information on ion site occupation preferences and on the size and shape of each elemental constituent of the configuration tetrahedra. Here we extend the model to cover quaternary sphalerite crystal structures. We discuss the two topologically different quaternary sphalerite systems: the pseudo balanced A₁₋xBxYyZ₁₋y (2:2 cation:anion ratio), and the unbalanced AxBx C₁₋x₋x Z or AXyYy Z₁₋y₋y (3:1 or 1:3 cation:anion ratios) truly quaternary alloy systems. These structural differences cause preference values in pseudo quaternaries to vary with the relative contents, but to remain constant in truly quaternary compounds. We give equations to determine preference coefficient values from EXAFS or phonon spectra and to extract nearest-neighbour inter-ion distances by EXAFS spectroscopy. The procedure is illustrated and tested on CdMnSeTe, GaInAsSb, and ZnCdHgTe quaternary alloys

Influence of High Power Laser Beam on Physical Properties of Epitaxial Films of Hg1−x\text{}_{1-x}Cdx\text{}_{x}Te (x≈0.2)

Models have been proposed explaining differences in electrophysical and photoelectrical properties of epitaxial films of Hg$\text{}_{1-x}$Cd$\text{}_{x}$Te (x≈0.2) before and after treating by single pulses of Nd:YAG laser. These models were obtained on the basis of the calculated distributions of temperature, temperature gradient and concentration of interstitial mercury during and after exposing to the laser pulse. These calculations were done using the net method

Peculiarities of Composition and Temperature Dependence of Energy-Band Parameters of Znx\text{}_{x}Cdy\text{}_{y}Hg1−x−y\text{}_{1-x-y}Te

The influence of addition of Zn on band parameters of Zn$\text{}_{x}$Cd$\text{}_{y}$Hg$\text{}_{1-x-y}$Te solid solution at different temperatures (4.2-200 K) was investigated. The cyclotron resonance at 4.2 K and magnetophonon resonance at 77-200 K were used to determine band structure parameters. The temperature dependence of band structure parameters (energy gap, effective mass of electron) for the composition of series of epilayers (x varied in 0.08-0.20 range and y - 0.07-0.12) was obtained. It is found that band structure parameters for some compositions (for example x = 0.17, y = 0.08) are almost independent from temperature and equal: γ₁$\text{}^{L}$= 19.55, γ₂$\text{}^{L}$ = γ₃$\text{}^{L}$ = 8.5, K$\text{}^{L}$ = 6.48, F = -0.5, E$\text{}_{g}$ = 0.35 eV, E$\text{}_{p}$ = 17.9 eV. The effective mass of electrons was found to be greater with addition of Zn while the effective mass of heavy holes is left unchanged

Gold Nanoparticles Like A Matrix For Covalent Immobilization Of Cholesterol Oxidase – Application For Biosensing

Gold nanoparticles are emerging as promising agents for various areas of material science as well as nanotechnology, electronics and medicine. The interest in this material is provided due to its unique optical, electronic and molecular-recognition properties. This paper presents results of preparation, characterization and biofunctionalization of gold nanoparticles. Nanoparticles have been conjugated with the cholesterol oxidase enzyme in order to prepare the active element for biosensors. Cholesterol oxidase is one of the most important analytical enzyme, used for cholesterol assay in clinical diagnostics, and there is still a necessity in improvement of existing analytical techniques, including bio-nanotechnological approaches based on modern nanosystems. The prepared bio-nanosystem was characterized by the enzyme activity test. Obtained results showed a stable binding of the enzyme with nanoparticles and preserved the bioactivity approves which gives possibility to use the prepared bio-nanosystems for analytical purposes

Influence of long-term defect diffusion on HgCdTe electronic structure

The long-term diffusion processes of defects in HgxCd$_{1-x}$Te mixed crystals were investigated. Measurements of reflectivity and surface characterisation by means of scanning electron microscopy (SEM) were performed for samples with x = 0.4 and x = 0.62. The experiments were repeated after wet chemical etching. Optical results were compared with the reflectivity spectra obtained 20 years ago using the same samples of investigated material. We discuss the observed large changes in the optical spectra on the basis of comparative analysis and SEM results

Role of the Thermal Stress on the Magnetophonon Peak Structure in the Parallel Transport of the GaAs/AlGaAs Multiple Quantum Wells

The magnetophonon resonance in parallel transport of two types multiple quantum wells was studied. The transverse magnetoresistance was measured in pulsed magnetic fields up to 30 T (within temperature region from 77 to 340 K). A fine structure of magnetophonon resonance peaks which depends on temperature and does not depend on the type of multiple quantum wells, was observed. This effect could be attributed to two phenomena: contribution of barrier phonons and influence of thermostresses