http://www.hindawi.com The latest articles from Hindawi Publishing Corporation © 2013 , Hindawi Publishing Corporation . All rights reserved. Mon, 20 May 2013 18:33:03 +0000 http://www.hindawi.com/isrn/cmp/2013/843702/ Using tight-binding model with nearest neighbour interactions, the optical properties of carbon nanotubes under the influence of an external magnetic field are analyzed. First, dipole matrix elements for two cases of light polarized parallel as well as perpendicular to the nanotube axis are analyzed. A close form analytic expression for dipole matrix is obtained for carbon nanotubes with arbitrary chirality in the case of light polarized parallel to the nanotube axis. Then the diagonal and off-diagonal elements of the frequency-dependent susceptibility in the presence of an axial magnetic field are investigated. The off-diagonal elements are applied to calculate the interband Faraday rotation and the Verdet constant. These effects should be clearly detectable under realistic conditions using weak magnetic fields. Abbas Zarifi Copyright © 2013 Abbas Zarifi. All rights reserved. Tue, 07 May 2013 09:00:39 +0000 http://www.hindawi.com/isrn/cmp/2013/327913/ The graphite structure is self-consistently calculated by use of the all electron Modified Augmented Plane Wave (MAPW) scheme with lattice constants considerably enlarged above the experimental value of graphite. Overall, the band structures of the series are found to be quite similar: the energy levels of the highly symmetric states K and H almost coincide, essentially fixing the Fermi level of the semimetallic solid. The dispersion along lines parallel to the atomic planes, already small in graphite at the experimental value of , continues to flatten with increasing value of . The structure with an interlayer distance enlarged by the factor 3 over the experimental value provides a good approximation of the behaviour of a monoatomic sheet. In this context, the unusual behaviour of graphene appears in a new light. Helmut Bross Copyright © 2013 Helmut Bross. All rights reserved. Wed, 27 Mar 2013 10:43:42 +0000 http://www.hindawi.com/isrn/cmp/2013/198710/ We review the progress in the last 20–30 years, during which we discovered that there are many new phases of matter that are beyond the traditional Landau symmetry breaking theory. We discuss new “topological” phenomena, such as topological degeneracy that reveals the existence of those new phases—topologically ordered phases. Just like zero viscosity defines the superfluid order, the new “topological” phenomena define the topological order at macroscopic level. More recently, we found that at the microscopical level, topological order is due to long-range quantum entanglements. Long-range quantum entanglements lead to many amazing emergent phenomena, such as fractional charges and fractional statistics. Long-range quantum entanglements can even provide a unified origin of light and electrons; light is a fluctuation of long-range entanglements, and electrons are defects in long-range entanglements. Xiao-Gang Wen Copyright © 2013 Xiao-Gang Wen. All rights reserved. Mon, 11 Feb 2013 14:38:41 +0000 http://www.hindawi.com/isrn/cmp/2013/568191/ Pure, single-phase and layered materials with good cation ordering are not easy to synthesize. In this work, solid solutions of (x = 0, 0.1, …, 0.9) are synthesized using a self-propagating combustion route and characterized. All the materials are observed to be phase pure giving materials of hexagonal crystal system with R-3m space group. The RIR and R factor values of stoichiometries of (x = 0.1, 0.2, 0.3, 0.4, and 0.5) show good cation ordering. Their electrochemical properties are investigated by a series of charge-discharge cycling in the voltage range of 3.0 to 4.3 V. It is found that some of the stoichiometries exhibit specific capacities comparable or better than those of LiCoO2, but the voltage plateau is slightly more slopping than that for the LiCoO2 reference material. Kelimah Elong, Norlida Kamarulzaman, Roshidah Rusdi, Nurhanna Badar, and Mohd Hilmi Jaafar Copyright © 2013 Kelimah Elong et al. All rights reserved. Thu, 07 Feb 2013 09:57:04 +0000 http://www.hindawi.com/isrn/cmp/2013/497073/ Hexagonal manganites belong to an exciting class of materials exhibiting strong interactions between a highly frustrated magnetic system, the ferroelectric polarization, and the lattice. The existence and mutual interaction of different magnetic ions (Mn and rare earth) results in complex magnetic phase diagrams and novel physical phenomena. A summary and discussion of the various properties, underlying physical mechanisms, the role of the rare earth ions, and the complex interactions in multiferroic hexagonal manganites, are presented in this paper. Bernd Lorenz Copyright © 2013 Bernd Lorenz. All rights reserved. Wed, 06 Feb 2013 09:16:24 +0000 http://www.hindawi.com/isrn/cmp/2013/210384/ We consider a two-dimensional fermion system on a square lattice described by a mean-field Hamiltonian involving the singlet id-density wave (DDW) order, assumed to correspond to the pseudo-gap (PG) state, favored by the electronic repulsion and the coexisting -wave superconductivity (DSC) driven by an assumed attractive interaction within the BCS framework. Whereas the single-particle excitation spectrum of the pure DDW state consists of the fermionic particles and holes over the reasonably conducting background, the coexisting states corresponds to Bogoliubov quasi-particles in the background of the delocalized Cooper pairs in the momentum space. We find that the two gaps in the single-particle excitation spectrum corresponding to PG and DSC, respectively, are distinct and do not merge into one “quadrature” gap if the nesting property of the normal state dispersion is absent. We show that the PG and DSC are representing two competing orders as the former brings about a depletion of the spectral weight available for pairing in the anti-nodal region of momentum space where the superconducting gap is supposed to be the largest. This indicates that the PG state perhaps could not be linked to a preformed pairing scenario. We also show the depletion of the spectral weight below at energies larger than the gap amplitude. This is an important hallmark of the strong coupling superconductivity. Partha Goswami Copyright © 2013 Partha Goswami. All rights reserved. Mon, 14 Jan 2013 10:34:24 +0000 http://www.hindawi.com/isrn/cmp/2013/646042/ The structural, elastic, electronic, thermal, and optical properties of superconducting nanolaminates Ti2InX (X = C, N) are investigated by density functional theory (DFT). The results obtained from the least studied nitride phase are discussed in comparison with those of carbide phase having value half as that of the former. The carbide phase is found to be brittle in nature, while the nitride phase is less brittle. Elastic anisotropy demonstrates that the c-axis is stiffer in Ti2InN than in Ti2InC. The band structure and density of states show that these phases are conductors, with contribution predominantly from the Ti 3d states. The bulk modulus, Debye temperature, specific heats, and thermal expansion coefficient are obtained as a function of temperature and pressure for the first time through the quasiharmonic Debye model with phononic effects. The estimated values of electron-phonon coupling constants imply that Ti2InC and Ti2InN are moderately coupled superconductors. The calculated thermal expansion coefficient is in fair agreement with the only available measured value for Ti2InC. Further the first time calculated optical functions reveal that the reflectivity is high in the IR-visible-UV region up to ~10 eV and 12.8 eV for Ti2InC and Ti2InN, respectively, showing these to be promising coating materials. M. Roknuzzaman and A. K. M. A. Islam Copyright © 2013 M. Roknuzzaman and A. K. M. A. Islam. All rights reserved. Thu, 20 Dec 2012 17:28:54 +0000 http://www.hindawi.com/isrn/cmp/2012/750497/ We report measurements of X-ray powder diffraction, vibrational study, the differential scanning calorimetry (DSC), and the electric properties of a made-up [C6H9N2]2CuCl4 sample. The alternative current (ac) conductivity of the compound [C6H9N2]2CuCl4 has been measured in the temperature range 356–398 K and the frequency range 209 Hz–5 MHz. The Cole-Cole (the imaginer part () versus real part () of impedance complex) plots are well fitted to an equivalent circuit model which consists of a parallel combination of a bulk resistance () and constant phase elements (CPE). The single semicircle indicates only one primary mechanism for the electrical conduction within [C6H9N2]2CuCl4. The variation of the value of these elements with temperatures confirmed the result detected by DSC and dielectric measurements. Thus the conduction in the material is probably due to a hopping or a small polaron tunneling process. M. Hamdi, A. Oueslati, I. Chaabane, and F. Hlel Copyright © 2012 M. Hamdi et al. All rights reserved. Tue, 20 Nov 2012 08:30:11 +0000 http://www.hindawi.com/isrn/cmp/2012/969830/ The temperature dependence of the dielectric constant is studied under some fixed electric fields for the smectic G- (tilted-) smectic A (orthogonal) transition of the ferroelectric liquid crystal of compound A6. For this study, a mean field model with the quadrupole-quadrupole interactions is introduced. By fitting the inverse dielectric susceptibility from the mean field model to the experimental data from the literature, the observed behaviour of the dielectric constant is described satisfactorily for the smectic AG transition in A6. The transition temperature induced by an external electric field is also discussed for this ferroelectric compound. H. Yurtseven and E. Kilit Copyright © 2012 H. Yurtseven and E. Kilit. All rights reserved. Wed, 14 Nov 2012 10:04:51 +0000 http://www.hindawi.com/isrn/cmp/2012/382939/ A theoretical approach for the study of phonon dynamics and scattering properties of doped transpolyacetylene chain is presented. The coherent reflection and transmission scattering cross-sections for phonons incident on the doped unit cell boundary are calculated in accordance with the Landauer-Buttiker electron scattering description, using the matching procedure with the nearest and next nearest neighbor elastic force constants. This is done for two different dopants, namely, the potassium and sodium atoms. Our numerical results yield an understanding of the transpolyacetylene chain dynamical properties and the effects on phonon conductance due to phonon incident on the doped unit cell boundary. The coherent reflection and transmission coefficients show characteristic spectral features, depending on the cutoff frequencies for the propagating phonons and on the nature of the dopants. They illustrate the occurrence of Fano resonances in the scattering spectra that result from the interactions of propagating elastic waves of the undoped transpolyacetylene chain with the localized modes due to the breakdown of the translation symmetry in the x direction. M. Belhadi and S. Kheffache Copyright © 2012 M. Belhadi and S. Kheffache. All rights reserved. Wed, 14 Nov 2012 09:56:30 +0000 http://www.hindawi.com/isrn/cmp/2012/596357/ The high-pressure structural phase transition of semiconductor PbS has been investigated, using the three body potential (TBP) model. Phase transition pressures are associated with a sudden collapse in volume. The phase transition pressures and related volume collapses obtained from this model show a generally good agreement with available results. Moreover, the elastic properties of PbS are also investigated. Purvee Bhardwaj Copyright © 2012 Purvee Bhardwaj. All rights reserved. Mon, 05 Nov 2012 17:34:05 +0000 http://www.hindawi.com/isrn/cmp/2012/368634/ By using the first-principle methods, we have investigated the adsorption of the CO, CO2, NO, and NH3 molecules on an armchair graphene nanoribbon (AGNR). The optimal adsorption positions and orientations of these molecules on AGNR are determined. The adsorption energies, the charge transfer, and the density of states (DOS) are obtained. The NO, CO, and CO2 adsorbed molecules act as an acceptor, and the NH3 adsorbed molecule acts as a donor. The NO and CO molecules contributed with localized states in the center of the original band gap. But the system exhibits -type or -type semiconductor after NH3 or CO2 adsorption. Khadije Imani, Gholamhossein Jafari, and Mohammad Reza Abolhasani Copyright © 2012 Khadije Imani et al. All rights reserved. Sun, 21 Oct 2012 14:22:21 +0000 http://www.hindawi.com/isrn/cmp/2012/423650/ Phase transition temperatures of ferroelectric liquid crystals ((S)-(-)-2-methylbutyl 4′-(4″-n-alkanoyloxybenzoyloxy) biphenyl-4-carboxylates (where and 18)) are studied through two techniques of image analysis. One is a statistical method, applied to compute the statistical parameters from the textures of each sample and the other, computation of Legendre moments being applied as image moment analysis, both of which are considered as a function of temperature. The textures of the samples are recorded with the polarizing optical microscope (POM) attached to the hot stage and high resolution camera. The phase transition temperatures of samples are inferred by the abrupt changes in the computed parameter values. The results obtained from the present methodology are in good agreement with those published in earlier literature done by the different techniques, like differential scanning calorimetry (DSC). S. Sreehari Sastry, B. Gowri Sankara Rao, K. B. Mahalakshmi, K. Mallika, C. Nageswara Rao, and Ha Sie Tiong Copyright © 2012 S. Sreehari Sastry et al. All rights reserved. Thu, 18 Oct 2012 09:17:37 +0000 http://www.hindawi.com/isrn/cmp/2012/907257/ Polycrystalline ferrites, , (where and ), were prepared by using ceramic method. Single phase cubic structure was confirmed by X-ray diffractometer. The lattice parameter “a” was found to increase with increasing ion substitution. IR spectra of the samples were recorded from 200 to 1000 cm−1. The two primary bands corresponding to tetrahedral and octahedral were observed at about 575 cm−1 and 370 cm−1, respectively. Elastic properties of these mixed ferrites were estimated as a function of composition. Young's modulus , rigidity modulus , bulk modulus , Debye temperature (), and mean sound velocity () were calculated from the transverse () and longitudinal () wave velocities. The variation of elastic moduli with composition was interpreted in terms of binding forces between the atoms of spinel lattice. AC conductivity and dielectric properties of the samples were measured at room temperature over 100 Hz–1 MHz. The electrical conduction mechanism could be explained with the electron hopping model. Frequency exponential factor was calculated and it was found between 0.4 and 0.8. S. A. Mazen and N. I. Abu-Elsaad Copyright © 2012 S. A. Mazen and N. I. Abu-Elsaad. All rights reserved. Wed, 17 Oct 2012 17:30:22 +0000 http://www.hindawi.com/isrn/cmp/2012/391813/ The multielectron wave function of an interacting electron system depends on the size of the system, that is, the number of electrons. Here the question investigated is how the wave function changes for a symmetric Friedel-Anderson impurity when the volume is doubled. It turns out that for sufficiently large volume (when the level spacing is smaller than the resonance width) the change in the wave function can be expressed in terms of a universal single-electron state centered at the Fermi level. This electron state is independent of the number of electrons and independent of the parameters of the Friedel-Anderson impurity. It is even the same universal state for a Kondo impurity and a symmetric Friedel impurity independent of any parameter. The only requirement is that the impurity has a resonance exactly at the Fermi level and that the level spacing is smaller than the resonance width. This result clarifies recent fidelity calculations. Gerd Bergmann Copyright © 2012 Gerd Bergmann. All rights reserved. Wed, 17 Oct 2012 10:17:17 +0000 http://www.hindawi.com/isrn/cmp/2012/313285/ Pentacene OFETs of bottom-gate/bottom-contact were fabricated with three types of pentacene organic semiconductors and cross linked Poly(4-vinylphenol) or polycarbonate as gate dielectric layer. Two different processes were used to prepare the pentacene active channel layers: (1) spin-coating on dielectric layer using two different soluble pentacene precursors of SAP and DMP; (2) vacuum evaporation on PC insulator. X-ray diffraction studies revealed coexistence of thin film and bulk phase of pentacene from SAP and thin film phase of pentacene from DMP precursors. The field effect mobility of 0.031 cm2/Vs and threshold voltage of −12.5 V was obtained from OFETs fabricated from SAP precursor, however, the pentacene OFETs from DMP under same preparation yielded high mobility of 0.09 cm2/Vs and threshold value decreased to −5 V. It reflects that the mixed phase films had carrier mobilities inferior to films consisting solely of single phase. For comparison, we have also fabricated pentacene OFETs by vacuum evaporation on polycarbonate as the gate dielectric and obtained charge carrier mobilities as large as 0.62 cm2/Vs and threshold voltage of −8.5 V. We demonstrated that the spin-coated pentacene using soluble pentacene precursors could be alternative process technology for low cost, large area and low temperature fabrication of OFETs. Shizuyasu Ochiai, Kumar Palanisamy, Santhakumar Kannappan, and Paik-Kyun Shin Copyright © 2012 Shizuyasu Ochiai et al. All rights reserved. Wed, 26 Sep 2012 16:13:07 +0000 http://www.hindawi.com/isrn/cmp/2012/140842/ Crystalline fullerene C60 nanotubes were prepared simply via liquid-liquid interfacial precipitation using the mixture of C60-saturated pyridine and isopropyl alcohol. C60-saturated pyridine solution was exposed to visible light to promote the growth of fullerene C60 nanotubes. The average diameters of the fullerene particles in C60-pyridine colloid solution after irradiation were characterized by dynamic light scattering. After light irradiation, an outer separated layer of pyridine surrounds the fullerene particles because of the charge transfer complexes formation. The mean ratios of inner diameter to outer diameter of fullerene C60 nanotubes fabricated at different irradiation time and wavelength were given in this paper for the first time. On the basis of the relationship between the average diameters of the fullerene particles in C60-pyridine colloid solution and the mean ratio of inner diameter to outer diameter of FNTs fabricated after irradiation, outer separated layer of pyridine surrounding the fullerene particles was supposed to play an important role in the formation process of fullerene C60 nanotubes. Yongtao Qu, Wenwen Yu, Nana Niu, Shaocen Liang, Guibao Li, and Guangzhe Piao Copyright © 2012 Yongtao Qu et al. All rights reserved. Mon, 24 Sep 2012 10:57:26 +0000 http://www.hindawi.com/isrn/cmp/2012/732973/ The electrodynamic properties of the quasi-one-dimensional organic conductors (TMTSF)2X are discussed, with particular emphasis on important deviations from the simple Drude model, the transition from a Luttinger-liquid to a Fermi-liquid behavior at the dimensional crossover when pressure is applied or temperature reduced, indications of a pseudogap as well as a low-frequency collective mode. Superconductivity and spin-density-wave ground states breaking the symmetry and gaps should occur in the excitation spectra. The previous literature is summarized and the current status of our understanding presented. Novel THz experiments on (TMTSF)2PF6 and (TMTSF)2ClO4 not only shine light into some of the open questions, but also pose new ones. Martin Dressel Copyright © 2012 Martin Dressel. All rights reserved. Mon, 10 Sep 2012 12:01:43 +0000 http://www.hindawi.com/isrn/cmp/2012/293032/ Thin films of silver-copper-oxide were deposited on glass substrates by RF magnetron sputtering of Ag80Cu20 target under various oxygen partial pressures in the range 5×10−3–8×10−2 Pa. The effect of oxygen partial pressure on the crystallographic structure and surface morphology and electrical and optical properties was systematically studied and the results were reported. The oxygen content in the films was correlated with the oxygen partial pressure maintained during the growth of the films. The films which formed at low oxygen partial pressure of 5×10−3 Pa were mixed in phase of Ag2Cu2O3 and Ag while those deposited at 2×10−2 Pa were grown with Ag2Cu2O3 and Ag2Cu2O4 phases. The films which formed at oxygen partial pressure of 2×10−2 Pa showed electrical resistivity of 2.3 Ωcm and optical band gap of 1.47 eV. P. Narayana Reddy, A. Sreedhar, M. Hari Prasad Reddy, and S. Uthanna Copyright © 2012 P. Narayana Reddy et al. All rights reserved. Thu, 30 Aug 2012 16:23:59 +0000 http://www.hindawi.com/isrn/cmp/2012/184023/ It has been shown during the present study that the E-etching at elevated temperatures can be adopted for the dislocation etching in hydride vapor-phase epitaxy (HVPE) GaN layers. It has been found that the X-ray diffraction (XRD) evaluation of the dislocation density in the thicker than 6 𝜇m epilayers using conventional Williamson-Hall plots and Dunn-Koch equation is in an excellent agreement with the results of the elevated-temperature E-etching. The dislocation distribution measured for 2-inch GaN-on-sapphire substrate suggests strongly the influence of the inelastic thermal stresses on the formation of the final dislocation pattern in the epilayer. Vladimir Ivantsov and Anna Volkova Copyright © 2012 Vladimir Ivantsov and Anna Volkova. All rights reserved. Thu, 23 Aug 2012 11:24:34 +0000 http://www.hindawi.com/isrn/cmp/2012/387380/ We investigated spin transfer torque magnetization precession in a nanoscale pillar spin-valve under external magnetic fields using micromagnetic simulation. The phase diagram of the magnetization precession is calculated and categorized into four states according to their characteristics. Of the four states, the precessional state has two different modes: steady precession mode and substeady precession mode. The different modes originate from the dynamic balance between the spin transfer torque and the Gilbert damping torque. Furthermore, we reported the behavior of the temporal evolutions of magnetization components in steady precession mode at the condition of the applied magnetic field using the orbit projection method and explaining perfectly the magnetization components evolution behavior. In addition, a result of a nonuniform magnetization distribution is observed in the free layer due to the excitation of non-uniform mode. H. B. Huang, X. Q. Ma, Z. H. Liu, X. M. Shi, T. Yue, Z. H. Xiao, and L. Q. Chen Copyright © 2012 H. B. Huang et al. All rights reserved. Thu, 16 Aug 2012 16:19:41 +0000 http://www.hindawi.com/isrn/cmp/2012/410326/ We performed the structure optimization of Co2TiAl based on the generalized gradient approximation (GGA) and linearized augmented plane wave (LAPW) method. The calculation of electronic structure was based on the full-potential linear augmented plane wave (FP-LAPW) method and local spin density approximation exchange correlation LSDA+𝑈. We also studied the impact of the Hubbard potential or onsite Coulomb repulsion (𝑈) on electronic structure; the values are varied within reasonable limits to study the resulting effect on the physical properties of Co2TiAl system. The calculated density of states (DOS) shows that half-metallicity of Co2TiAl decreases with the increase in 𝑈 values. D. P. Rai and R. K. Thapa Copyright © 2012 D. P. Rai and R. K. Thapa. All rights reserved. Sun, 27 May 2012 16:17:04 +0000 http://www.hindawi.com/isrn/cmp/2012/208234/ First-principles total energy calculations of the structural and electronic properties of Ce-doped fullerene have been performed within the framework of the density functional theory at the generalized gradient approximation level. Among various locations, Ce atom was found to engage with the six-fold carbon ring. The total energy is found to significantly change as the Ce atom being shifted from the center of the cage toward the edge close to the six-membered ring where the total energy reaches its local minimum. Moreover, repulsive interaction between Ce atom and the cage components turns as the adatom directly interacts with the six C atoms of the ring. The lowest-energy CeC60 geometry is found to have a binding energy of approximately 5.34 eV, suggesting strong interaction of the dopant with the cage members. Furthermore, fundamental key structural parameters and the total density of states of the optimized structure have been determined and compared with the available data. A. Z. AlZahrani Copyright © 2012 A. Z. AlZahrani. All rights reserved. Mon, 07 May 2012 13:26:53 +0000 http://www.hindawi.com/isrn/cmp/2012/198590/ With the seemly limit of scaling on CMOS microelectronics fast approaching, spintronics has received enormous attention as it promises next-generation nanometric magnetoelectronic devices; particularly, the electric field control of ferromagnetic transition in dilute magnetic semiconductor (DMS) systems offers the magnetoelectronic devices a potential for low power consumption and low variability. Special attention has been given to technologically important group IV semiconductor based DMSs, with a prominent position for Mn doped Ge. In this paper, we will first review the current theoretical understanding on the ferromagnetism in MnxGe1−x DMS, pointing out the possible physics models underlying the complicated ferromagnetic behavior of MnxGe1−x. Then we carry out detailed analysis of MnxGe1−x thin films and nanostructures grown by molecular beam epitaxy. We show that with zero and one dimension quantum structures, superior magnetic properties of MnxGe1−x compared with bulk films can be obtained. More importantly, with MnxGe1−x nanostructures, such as quantum dots, we demonstrate a field controlled ferromagnetism up to 100 K. Finally we provide a prospective of the future development of ferromagnetic field effect transistors and magnetic tunneling junctions/memories using dilute and metallic MnxGe1−x dots, respectively. We also point out the bottleneck problems in these fields and rendering possible solutions to realize practical spintronic devices. Faxian Xiu Copyright © 2012 Faxian Xiu. All rights reserved. Thu, 26 Apr 2012 10:47:24 +0000 http://www.hindawi.com/isrn/cmp/2012/501686/ This review examines the properties of graphene from an experimental perspective. The intent is to review the most important experimental results at a level of detail appropriate for new graduate students who are interested in a general overview of the fascinating properties of graphene. While some introductory theoretical concepts are provided, including a discussion of the electronic band structure and phonon dispersion, the main emphasis is on describing relevant experiments and important results as well as some of the novel applications of graphene. In particular, this review covers graphene synthesis and characterization, field-effect behavior, electronic transport properties, magnetotransport, integer and fractional quantum Hall effects, mechanical properties, transistors, optoelectronics, graphene-based sensors, and biosensors. This approach attempts to highlight both the means by which the current understanding of graphene has come about and some tools for future contributions. Daniel R. Cooper, Benjamin D’Anjou, Nageswara Ghattamaneni, Benjamin Harack, Michael Hilke, Alexandre Horth, Norberto Majlis, Mathieu Massicotte, Leron Vandsburger, Eric Whiteway, and Victor Yu Copyright © 2012 Daniel R. Cooper et al. All rights reserved. Sun, 08 Apr 2012 15:19:38 +0000 http://www.hindawi.com/isrn/cmp/2012/950354/ The photoluminescence of zinc oxide nanowires was investigated via the thermal annealing treatment in oxygen-rich and oxygen-poor conditions. Dramatic changes in the relative intensity of the ultraviolet and the green visible luminescence were observed following different annealing treatments. The changes in photoluminescence bear little correlation to the changes in the oxygen-to-zinc ratios that were revealed using Raman scattering and other characterization techniques. The chemisorption of oxygen and the subsequent surface band bending, instead of the oxygen vacancy concentration, are shown to be the mechanism that determines the observed changes in photoluminescence. Dake Wang and Nicholas Reynolds Copyright © 2012 Dake Wang and Nicholas Reynolds. All rights reserved. Mon, 05 Mar 2012 09:28:38 +0000 http://www.hindawi.com/isrn/cmp/2012/738023/ Conducting and transparent optical ZnO thin films were deposited on glass substrates by a simple mini spray technique. Alternatively, some of the obtained films were doped with indium and ytterbium at the molar rates of: 1, 2, and 3% (In) and 100, 200, and 300 ppm (Yb). In addition to the classical structural investigations including XRD, microhardness vickers (Hv), and optothermal techniques, thorough optical measurements have been carried out for comparison purposes. The refractive indices and the extinction coefficients of the differently doped layers have been deduced from their transmission-reflection spectra over an extended wavelength range. Analysis of the refractive index data through Wemple-DiDomenico single oscillator model yielded quantum characteristics along with the values of long-wavelength dielectric constant, average oscillator wavelength, average oscillator strength, average oscillator energy and dispersion energy. Real and imaginary parts of dielectric constant have also been used to calculate free carrier plasma resonance frequency, optical relaxation time, and free carriers concentration-to-effective mass ratio. Finally, analysis of Urbach-Martienssen model parameters allowed proposing nanoscale explanations to the divergence about doping-related evolution of Urbach tails, this intriguing item having been intensively discussed in the literature in the last decades. A. Boukhachem, B. Ouni, A. Bouzidi, A. Amlouk, K. Boubaker, M. Bouhafs, and M. Amlouk Copyright © 2012 A. Boukhachem et al. All rights reserved. Mon, 06 Feb 2012 09:39:38 +0000 http://www.hindawi.com/isrn/cmp/2012/342642/ Cluster formation in a two-dimensional Lennard-Jones system under different conditions of temperature (𝑇) and particle concentration (𝑐) has been studied using the Monte-Carlo method with the introduction of real thermal motion of the constituent particles through a modification of the conventional Metropolis algorithm. The 𝑐-𝑇 phase diagram determined from the study of the root mean square displacement of the particles shows features characteristics of the 𝑃-𝑇 diagram for phase equilibrium in real systems. The solid-like to liquid-like transition takes place when the average nearest neighbour distance increases by ~1% of the equilibrium value in the low-temperature solid-like configuration. The Lindemann parameter (𝛿) is found to decrease with the increase of 𝑐 to reach a steady value of 𝛿=0.0106±0.0004 for 𝑐≥0.6 . Barnana Pal Copyright © 2012 Barnana Pal. All rights reserved. Thu, 19 Jan 2012 09:50:04 +0000 http://www.hindawi.com/isrn/cmp/2011/392917/ CaS:Eu and SrS:Eu phosphors were synthesized by solid-state reaction. The effects of doping concentrations on luminescent properties of phosphors are investigated. The samples are excited using electroluminescent blue light emitting diode (460 nm) to examine them as potential coating phosphors for white-light LEDs. The excitation and emission spectra of these phosphors are broadband which can be viewed as the typical emission of Eu2+ ascribed to the 4f–5d transitions. Because of their broadband absorption in the region 400–630 nm, these phosphors meet the application requirements for blue LED chips. A white-light LED was fabricated through the integration of a 460 nm chip. The results indicate that these phosphors can be considered as candidates for the application in blue LED chip-based white-light LEDs. K. Suresh, K. V. R. Murthy, Ch. Atchyutha Rao, and N. V. Poornachandra Rao Copyright © 2011 K. Suresh et al. All rights reserved. Thu, 05 Jan 2012 11:48:13 +0000 http://www.hindawi.com/isrn/cmp/2011/980192/ We have considered the 1D spin-(1/2) Heisenberg model with added Dzyaloshinskii-Moriya interaction. The effect of a uniform magnetic field on the ground state phase diagram of the model is studied. We have mapped the model to an effective model which is known as the 1D XXZ in both uniform and staggered magnetic fields. By selecting a block of two or three spins, we have solved the Hamiltonian exactly. Our results show that the quantum phase transitions can be obtained from the block of pair or three spins. M. R. Soltani, J. Vahedi, M. R. Abolhassani, and A. A. Masoudi Copyright © 2011 M. R. Soltani et al. All rights reserved.