Solid State Phenomena Vol. 155

Abstract: The reduction of size of the low dimensional materials leads to a dramatic increase of surface-to-volume ratio. The properties of a solid are essentially controlled by related surface/interface energies. Although such changes are believed to dominate behaviors of nanoscale structures, little experience or intuition for the expected phenomena, especially the size dependent properties and their practical implications, are modeled. In this contribution, the classic thermodynamics as a powerful traditional theoretical tool is used to model different bulk interface energies and the corresponding size dependences where emphasis on the size dependence of interface energy is given, which is induced by size dependence of coherent energy of atoms within nanocrystals. It is found that solid-vapor interface energy, liquid-vapor interface energy, solid-liquid interface energy, and solid-solid interface energy of nanoparticles and thin films fall as their diameters or thickness decrease to several nanometers while the solid-vapor interface energy ratio between different facets is size-independent and is equal to the corresponding bulk ratio. The predictions of the established analytic models without any free parameter, such as size and temperature dependences of these four kinds of interface energies, are in agreement with the experimental or other theoretical results of different kinds of low dimensional materials with different chemical bond natures.

Abstract: We study electron transport properties of some molecular wires and a unconventional disordered thin film within the tight-binding framework using Green's function technique. We show that electron transport is significantly affected by quantum interference of electronic wave functions, molecule-to-electrode coupling strengths, length of the molecular wire and disorder strength. Our model calculations provide a physical insight to the behavior of electron conduction across a bridge system.

Abstract: We explore the behavior of persistent current and low-field magnetic response in mesoscopic one-channel rings and multi-channel cylinders within the tight-binding framework. We show that the characteristic properties of persistent current strongly depend on total number of electrons , chemical potential μ, randomness and total number of channels. The study of low-field magnetic response reveals that only for one-channel rings with fixed , sign of the low-field currents can be predicted exactly, even in the presence of disorder. On the other hand, for multi-channel cylinders, sign of the low-field currents cannot be mentioned exactly, even in the perfect systems with fixed as it significantly depends on the choices of , μ, number of channels, disordered configurations, etc.

Abstract: The bombardment of energetic ions on polymer membranes will produce the loosely bound passage in the membrane structure due to the energy loss. The Swift Heavy Ions (SHI) creates the latent tracks of several nm surrounded by several tens of nm track halo. The tracks can be visualized under Atomic Force Microscope after wet chemical etching. In present study the polymeric membranes of 30 μm was prepared by solution cast method and irradiated by 60 MeV C+5 energetic ions. The electronic energy losses are predominant at high energies. The membranes were etched chemically to convert the tracks in to suitable pores. The Atomic Force Microscopy (AFM) gives the size and distribution of the pores. The pore size is observed in nano regime. The pore density was found to depend on the irradiation dose.

Abstract: Solid-state lighting (SSL) is emerging as a highly competent field and a possible alternative to existing lighting technologies. Development of a suitable phosphor is an important aspect of SSL. The aim of this review is to summarize status of Inorganic Phosphors towards SSL applications. Various examples have been taken from oxide, fluoride, nitride, sulfide and phosphate based host lattices. The important concepts like CIE coordinates and Color Correlated Temperature (CCT) will also be discussed. The sections encompasses of red, blue and green light emitting phosphors. The white light emitting phosphors will also be discussed in details.

Abstract: Study of Sr[(Mg0.32Co0.02) Nb0.66]O3 [SMCN] thin films prepared by Pulsed Laser Deposition Technique (PLD) were carried out in the temperature range of 150 to 450K and frequency range of 100KHz to 1.1MHz. X-ray diffraction of the thin film shows single phase formation with monoclinic symmetry. The dielectric properties show enhanced ε' values compared to bulk suggesting promising applications in alternative technologies. Due to simultaneous increase in dissipation factor with temperature the net ac conductivity is found to be decreasing. Technologically important two step activation energy is observed in the film. This property can be used in switching devices. In low temperature region the activation energy corresponds to shallow traps while the migration of oxygen vacancies contributes in high temperature region.

Abstract: ZnO thin-films were prepared from sol-gel precursors using electrospray method. The structure, morphology and optical property of ZnO thin-films deposited on glass substrates were investigated by X-ray diffraction (XRD), atomic force microscopy (AFM) and absorption spectrums (ABS). The surface images obtained directly from AFM showed the compact ZnO films were composed of wurtzite ZnO nanoparticles. The ZnO films presented high optical transmittance in the visible region and strong absorption in ultraviolet region.

Abstract: Magnetite and Co ferrite particles were synthesized with control of particle size distribution via non-aqueous route. The XRD pattern shows the formation of single phase spinel structure with the particle size of 96 Å and 80 Å respectively for magnetite and cobalt ferrite. TEM image of the same shows the particles are nearly spherical with the size matches with that obtained from X-ray and the size distribution is less than 5%. Magnetic measurement also shows the particles of uniform size with high value of saturation magnetization at room temperature compared to that obtained by other route. SANS study confirms our results of monodispersed particles with spherical shape.

Abstract: ZnO semiconductor doped with a few per cent of some transition metal ions can exhibit above room temperature ferromagnetism, transforming it into a very promising candidate for future spin-electronic applications. In the present article we have compared the electronic structure of two polycrystalline ZnMnO pellets doped with diluted Mn concentration (2% and 4%), carefully characterized by SQUID and XRD, including Rietveld refinement. The characterization measurements established that the samples have the ZnO lattice with ZnS type Wurtzite hexagonal symmetry and no detectable impurities. The samples exhibit distinctly different magnetic properties. The 2% sample displayed a clear FM ordering at 300 K while the 4% sample did not show any ordering down to 5K. The electronic structure of these two samples has been investigated using Mn L23 x-ray absorption spectroscopy, Zn 2p and 3p, Mn 3p and O 1s x-ray photoemission spectroscopy. Our aim was to find out how the changes in the electronic structure can correlate to the observed magnetic properties in such diluted magnetic semiconductor materials. The results show that most of the Mn ions of the ferromagnetic sample are in the divalent state. For the higher Mn percent nonmagnetic sample, a larger contribution of higher oxidation Mn states are dominant and the oxygen content also increases. The two factors can be correlated to the suppressed ferromagnetism, though it is hard to pinpoint that which of these two weighs more in the suppression mechanism.