JOURNAL OF THEORETICAL AND APPLIED PHYSICS (IRANIAN PHYSICAL JOURNAL)
Year:2012 | Volume:6 | Issue:6|Papers Count:11

Europium-doped gallium oxide (Ga2O3: Eu) thin films have successfully been grown using direct current magnetron sputtering by means of Eu concentration variation. Energy-dispersive X-ray spectroscopy spectra indicate gallium, oxygen, and europium elements as the growing films' chemical compositions. Based on scanning electron microscopy images, the morphology of Ga2O3: Eu thin film is seemingly like a granulated nano-size configuration. In this study, UV-visible spectrophotometer results show that the variation of Eu doping concentration inflicted no change toward the optical bandgap of the growing films. The optical bandgaps of undoped Ga2O3 film and Ga2O3: Eu film were seen to be relatively similar, i.e., approximately 3.4 eV. Yet, the presence of Eu doping in Ga2O3 configuration had led to blueshift phenomenon when the concentration was 2% and redshift phenomenon when it was 5%. Photoluminescence emissions of all samples were observed in the red area with the emission peak between 593 and 602 nm.

In the present paper, we have studied the effect of photo-illumination on electrical properties of nanocrystalline ZnSe thin films. The ZnSe thin films with different grain sizes (coherently diffracting domains) have been prepared. The semiconducting material with the composition Zn25Se75 has been prepared using melt-quenching technique. Thermal evaporation technique has been used to prepare nanocrystalline ZnSe thin films on highly cleaned glass substrates at different partial pressures of Ar gas. The grain size has been controlled by the partial pressure of inert gas. The grain size has been calculated using X-ray diffraction plots. Mobility activation has been studied from the photocurrent decay curves. The effective density of states (Neff), frequency factor (S), and trap depth (E) have been calculated for all the films having different grain sizes. Three different types of trap levels have been found in these films. There is a linear distribution of traps having different energies below the conduction band. The increase in photoconductivity is explained in terms of built in potential barriers (φb) at the grain boundaries.

Ground state geometry, energetics, and bonding of pure Lin (n=2 - 9) and impure LinSn (n=1 - 8) small clusters are investigated using the density functional theory. Introducing a single Sn impurity significantly changes the geometry of the host clusters forn>5. Although the Sn atom is not trapped inside the cluster, it has the greatest coordination number among other atoms in the cluster. The analyses showed that the nearest neighbor bond lengths in Sn are approximately 10% shorter than those in Li. The results elucidate that the binding energy per atom in impure clusters is greater than that in pure clusters. Finally, it is shown that for Li8 and Li4Sn clusters that each have with eight valence electrons, the greater gap in the highest occupied molecular orbital and the lowest unoccupied molecular orbital results in a more stable cluster.

The nature of electron pairing mechanism and physical properties leading to superconducting state and normal state resistivity in alkali metal (Rb) intercalated fullerenes are explored. Keeping in mind that free electrons in lowest molecular orbital are coupled with inter-molecular phonons, the coupling with inter-molecular phonon leads to transition temperature (Tc) of about 4.17 K. The electrons also couple with the intra-molecular phonons. Within the framework of strong coupling theory, Tc is estimated at 34 K. The carbon isotope effect exponent, the energy gap ratio, influence of pressure and volume on Tc, and thermodynamical parameters describing the superconducting state confer that Rb3C60 as s-wave superconductor. Estimated contribution to resistivity using scattering with interand intra-molecular phonon, when subtracted from single crystal data, infers quadratic temperature dependence over most of the temperature range and is attributed to electron–electron inelastic scattering. Both low frequency intermolecular and high frequency intra-molecular phonons have significant bearing in Rb3C60 superconductor.

In 2006, some authors determined that the triboluminescence (TL) of manganese-doped zinc sulfide (ZnS: Mn) increases with increasing impact velocity. In 2011, the authors discovered a method of synthesizing europium dibenzoylmethide triethylammonium (EuD4TEA) that produced TL 106% greater than ZnS: Mn. In fact, this material is bright enough to be seen in daylight. This paper investigates the effects of increasing impact energy on the TL of EuD4TEA and various grain sizes of ZnS: Mn using a drop tower. The low energy results indicate that increasing impact energy can increase the triboluminescent light yield for impact energies up to 1.4 J, the upper limit of the drop tower. The minimum activation energies required for each material are also explored. In addition, the effects of the increasing impact energy on the triboluminescent decay time are also investigated. The details of the experimental setup, synthesis of EuD4TEA, and results are discussed in this paper.

Extinction spectra of chiral silver nanostructures are calculated by means of Discrete Dipole Approximation (DDA).Dependence of Plasmonic peaks to both structural parameters of nanostructures and direction of the incident light are obtained. This dependence is investigated on variation of chiral dimensions, chiral shape and direction of incident light. We have observed a resonance peak of transverse mode (TM) for the extinction spectra of chiral structure at normal incidence. However, for oblique angle incident light, in addition to the TM mode, a longitudinal mode (LM) appears at longer wavelengths. The latter undergoes a shift to longer wavelengths with increasing the diameter of chirl arm. When the cross-section of chiral is changed to an oval this resonance peak disappears, while some other peaks appear at longer wavelengths that were not present for a chiral with circular cross-section.Extinction spectra of chiral nanostructure with different structural parameters and different rise angles (slanted chirals) showed dependence on the incident light direction.

Emission, absorption, and excitation spectra of 4f®5d transitions of Ce3+ions in yttrium aluminum borate (YAB) crystal are reviewed and successfully reproduced by theoretical investigations. The Ce3+energy level diagram has been compiled after a careful analysis of the optical spectra. Theoretical calculations based on free ion and crystal field Hamiltonians are used to interpret the observed transitions. The 4f and 5d crystal field parameter permits determination of the engine states of Ce3+ion in YAB and then calculating the absorption line intensities as well as the effective section and the decay times.

Gold nanoparticles were prepared via liquid arc discharge technique using a seed-mediated approach in solution and characterized by dynamic light scattering, UV–vis spectroscopy, X-ray diffraction, optical imaging, and atomic force microscopy. A surface plasmon resonance was observed around 520 nm based on optical absorption spectroscopy of as-prepared samples at 15 A arc current in HAuCl4 solution. It was found that sodium citrate acts as a stabilizer and surface capping agent of the colloidal nanoparticles. It was found that the intensity of the plasmonic peak of as-prepared gold nanoparticles in 1 min arc duration gradually increases due to seed mediation up to 6 h. The formation time of gold nanoparticles in higher seed concentrations is less than the lower seed concentrations.

Swanepoel method is employed for spectroscopic determination of optical properties of Cu3N thin film using transmittance data. Investigated films have been deposited using reactive magnetron sputtering system. Deposition time was 9 to 21 min. Refractive index, absorption coefficient, and bandgap energy of the samples are determined.Thickness of the films is calculated by Swanepoel method, and result is compared with the thickness of the films measured by profilmeter. It is shown that Swanepoel method is a reliable way to calculate the optical constants of thin films when the transmittance spectrum of the film is influenced by wavelike patterns due to reflection of the probe beam from different interfaces.

In the present work, the optical properties of a GaAs quantum wire with a parallelogram cross section are studied. In this regard, we have used the expressions for the optical properties obtained by the compact-density matrix formalism. Here, we have investigated the intersubband optical absorption coefficients and refractive index changes as a function of the structure parameter of the wire (side length) and the incident optical intensity. According to the obtained results, it is found that (1) the total refractive index changes increase and shift towards lower energies when the side length increases and that (2) the total absorption coefficient decreases as the side length increases. Also, the resonance peak shifts towards lower energies by increasing the side length.

Fast neutrons that are produced via compact neutron generators have been used for thermal and fast neutron radiographies. In order to investigate objects with different sizes and produce radiographs of variable qualities, the proposed facility has been considered with a wide range of values for the parameters characterizing the thermal and fast neutron radiographies. The proposed system is designed according to article 4 of the Restriction of Hazardous Substances Directive 2002/95/EC, hence, excluded the use of cadmium and lead, and has been simulated using the MCNP4B code. The Monte Carlo calculations were carried out using three different neutron sources: deuterium-deuterium, deuterium-tritium, and tritium-tritium neutron generators.