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YCrO 3 (YCO), BiFeO 3 (BFO), and YCrO 3 /BiFeO 3 (YCO-BFO) thin films were prepared on quartz substrates using spin coating by a sol-gel method. X-ray diffraction demonstrated that YCO and BFO thin films had a perovskite orthorhombic, and rhombohedral structure, respectively. The stronger and sharper diffraction intensity of YCO-BFO bilayered thin film indicated that the bottom YCO layer was able to promote the grain growth of BFO film, which was further verified by scanning electron microscope. The ferroelectric test demonstrated that the leakage current density of YCO-BFO bilayered film was reduced by one order of magnitude compared to that of BFO film, which had a better ferroelectric property. Optical absorption spectra indicated that the band gap of YCO-BFO thin film was lower than that of BFO film, suggesting their potential application as UV and blue-green-driven photocatalysts. The magnetic test verified that the ferromagnetic property of YCO-BFO film was obviously enhanced compared to those of BFO and YCO thin films. The results revealed that YCO layer played an important role for improving multiferroic properties of BFO thin film. The mechanisms of the effects of bottom YCO layer on optical and multiferroic properties of BFO thin film in the YCO-BFO bilayered film were discussed in detail. [ABSTRACT FROM AUTHOR]

A series of Eu doped α-Ca 3 (PO 4 ) 2 phosphors were synthesized by a high-temperature solid-state reaction in air atmosphere. The crystal structures, photoluminescence properties of the phosphors were systematically studied. The emission spectra showed a broad emission band centered at 492 nm attributed to the typical 4f 6 5d 1 →4f 7 transition of Eu 2+ ions, and several sharp peaks from 560 to 750 nm attributed to the 5D 0 →7F J ( J =0,1,2,3,4) transition of Eu 3+ ions. The results, combined with the X-ray photoelectron spectroscopy measurements, demonstrate self-reduction of Eu 3+ to Eu 2+ occurred in α-Ca 3 (PO 4 ) 2 matrix for the first time. This suggested that the Eu 2+ ions in α-Ca 3 (PO 4 ) 2 could serve as a spectroscopic probe to detect the content of α-Ca 3 (PO 4 ) 2 in phase transition process. [ABSTRACT FROM AUTHOR]

Abstract: The temperature dependent band gap energy of Cu2ZnSnS4 thin film was studied in the temperature range of 77–410K. Various relevant parameters, which explain the temperature variation of the fundamental band gap, have been calculated using empirical and semi-empirical models. Amongst the models evaluated, the Varshni and Pässler models show the best agreement with experimental data in the middle temperature range. However, the Bose–Einstein model fits reasonably well over the entire temperature range evaluated. The calculated fitting parameters are in good agreement with the estimated value of the Debye temperature calculated using the Madelung–Einstein approximation and the Hailing method. [Copyright &y& Elsevier]

Abstract: Amorphous thin films of As34Te44Ge10Si12 were prepared by thermal evaporation technique from its bulk glass onto glass substrates. The reflectance R and transmittance T have been measured in the spectral range 400–2500nm. The values of the refractive index n, the extinction coefficient k and the absorption coefficient α were calculated for the studied thin films in the thickness range 137.5–201nm. It is found that both n and k are independent of the film thickness. The refractive index n shows an anomalous behavior for the wavelength λ range 400–1100nm, while it has normal dispersion for the wavelength greater than 1100nm. The values of the dispersion energy E d , the oscillator energy E o , the lattice dielectric constant ε L and the high frequency dielectric constant ε ∞ have been determined. The value of ε L is greater than ε ∞ by 1.112, which indicates that there is free carrier contribution in polarization with very small concentration. The optical energy gap is calculated from the absorption coefficient α by Tauc''s extrapolation procedure and the type of transitions were found to be allowed indirect transitions with optical gap of 0.95eV for the sample under test. [Copyright &y& Elsevier]

Abstract: The reststrahlen region of SiC is analysed with the goal of establishing the origin of different shapes of this band, by varying the dielectric parameters involved when simulating the reststrahlen region as obtained by infrared reflectance. [ABSTRACT FROM AUTHOR]

Abstract: The deep donor and acceptor levels have been obtained for the muonium analog of isolated hydrogen impurities in six semiconductors. Using theoretical band alignments, we have shown that defect-level energies for Mu in these materials are pinned at a constant energy, but significantly above the energy predicted for . This difference implies that more materials should be subject to n-type doping by H, and fewer to p-type doping than initially predicted. We present our current understanding of deep vs. shallow state formation for Mu in both donor and acceptor sites, with emphasis on materials for which the theoretical results for H and experimental results for Mu are not in full qualitative agreement, and briefly discuss the origin of small differences expected between the defect energies for H and Mu. [Copyright &y& Elsevier]

Abstract: Uniform and defect-free homeotropic (HMT) alignment of ferroelectric liquid crystals (FLC) cells have been successfully achieved by a non-contact technique, namely, magnetic field-assisted alignment; otherwise such alignment is difficult by conventional methods. Frequency–temperature dependent dielectric studies, confirm the presence of stable molecular relaxation around the short axis of FLC molecule, throughout SmC*–SmA* phases with minimum low-frequency fluctuations, known as Goldstone modes. The proposed non-contact alignment method, combined with FLC-based HMT configuration, would be much promising for integrated-optoelectronic devices, such as micro-mirror displays. [Copyright &y& Elsevier]

Abstract: Undoped ZnO thin films of different thicknesses were prepared by r.f. sputtering in order to study the thickness effect upon their structural, morphological, electrical and optical properties. The results suggest that the film thickness seems to have no clear effect upon the orientation of the grains growth. Indeed, the analysis with X-ray diffraction show that the grains were always oriented according to the c(002)-axis perpendicular to substrate surface whatever the thickness is. However, the grain size was influenced enough by this parameter. An increase in the grain size versus the thickness was noted. For the electrical properties, measurements revealed behaviour very dependent upon thickness. The resistivity decreased from 25 to 1.5×10−3 Ωcm and the mobility increased from 2 to 37cm2 V−1 s−1 when the thickness increased from 70 to 1800nm while the carrier concentration seems to be less affected by the film thickness and varied slightly remaining around 1020 cm−3. Nevertheless, a tendency to a decrease was noticed. This behaviour in electrical properties was explained by the crystallinity and the grain size evolution. The optical measurements showed that all the samples have a strong transmission higher than 80% in the visible range. A slight shift of the absorption edge towards the large wavelengths was observed as the thickness increased. This result shows that the band gap is slightly decreases from 3.37 to 3.32eV with the film thickness vary from 0.32 to 0.88μm. [Copyright &y& Elsevier]

Abstract: The structural, electronic and optical properties of GaP, GaAs and GaSb at ambient and under hydrostatic pressure have been calculated using the full potential linear augmented plane wave (FP-LAPW) method. The calculated lattice constant, bulk modulus and its pressure derivative are compared with available experimental data. The first and second order pressure coefficients for the (– energy gaps and hydrostatic deformation potential shows agreement with measurement. The linear pressure coefficients of the transition (– increases significantly as anion atomic number increases . The magnitude of linear pressure coefficient of the transition (–X) are small and usually negative. The variation of linear pressure coefficient of the transition (–L) are relatively small and follow similar trend as (–. Overall the calculated linear and nonlinear pressure coefficients show good agreement with the experimental data. The obtained dielectric function, refractive index, extinction coefficient and reflectivity are compared with measured data and show qualitatively good agreement. [Copyright &y& Elsevier]

Abstract: Optical absorption at room temperature of vacuum evaporated Ge x Te1− x (0.125⩽x⩽0.225) amorphous thin films has been studied as a function of composition. It was found that the optical absorption is due to a direct transition. The real and imaginary parts of the dielectric constant were determined. The single-oscillator energy (E o) and the energy dispersion parameter (E d) have been calculated and discussed in terms of the Wemple and Di-Domenico model. The relationship between the optical gap, the average heat of atomization and the coordination numbers has been determined. The optical properties of the amorphous thin films do not change monotonically with increasing Ge content. The observed behavior of the optical properties in the range of compositions studied are explained on the basis of the Bond Constraint Theory (BCT) and rigidity theory, which provide a powerful framework for understanding the structure and properties of amorphous materials. The non-monotonic variation of the optical properties indicates that a transition from floppy to rigid occurs in the Ge x Te1− x films. [Copyright &y& Elsevier]

Abstract: On the basis of propositions of the common fluctuation theory, peculiarities of small fluctuations in real physical systems with limited sizes are analyzed. It is established that small fluctuations should necessarily be divided into two types of fluctuations: “small” and “very small”. It is shown that the damping process of “small” fluctuations has relaxation character, while the damping process of “very small” fluctuations is of random character, i.e., it represents a random rectangular signal. The probability density of “very small” fluctuations is shown to be Gaussian. The agreement of the obtained results with experimental data acquired from semiconductor-based devices is analyzed. A relation between the generation–recombination noise and phonon number fluctuations in semiconductors is studied. On the basis of this consideration it is shown that the Schönfeld pulse spectrum preserves its well-known 1/f form only in the range of intermediate frequencies; at lower frequencies the spectrum gets saturated. An expression for the low-frequency limit of Schönfeld pulse 1/f law is obtained. [Copyright &y& Elsevier]

Abstract: ZnO:Ag films have been fabricated on a n-Si (111) substrate and then annealed in situ in an O2 ambient, using Ag2O as a silver dopant by pulsed laser deposition. Hall measurements reveal that the films prepared at 400 and 450°C show p-type behavior with a hole concentration of 6.3×1016–1.2×1017 cm–3 and a mobility of 2.48–3.30cm2/Vs. By combining Hall measurements, electron paramagnetic resonance (EPR) signals, and photoluminescence (PL) spectra, a correlation is observed between the free hole carriers, the Ag2+ centers, and the neutral acceptor bound excitons. Additionally, the p-ZnO:Ag/n-Si heterojunction shows a diode-like I–V characteristic. [Copyright &y& Elsevier]

Abstract: The synthesis and optical properties of the 5,5′,6,6′-tetraphenyl-2,2′-bi([1,3]dithiolo [4,5-b] [1,4]dithiinylidene)–2,3-dichloro-5,6-dicyano-p-benzoquinone (DDQ) complex thin film were investigated by the optical characterization. The optical constants such as refractive index, extinction coefficient and absorption coefficient were determined using the transmittance T(λ) and reflectance R(λ) spectra and the refractive index dispersion was analyzed using single oscillator of Wemple–Didomenico model. The single oscillator energy E 0 and the dispersion energy E d were calculated. The effect of temperature on refractive dispersion and optical band gap E g is also discussed. As a result, the annealing temperatures have an important effect on refractive index of thin film. [Copyright &y& Elsevier]

Abstract: The surface treatment effects of sapphire substrate on the ZnO thin films grown by magnetron sputtering were studied. The sapphire substrates properties have been investigated by means of atomic force microscopy (AFM) and X-ray diffraction rocking curves (XRCs). The results show that sapphire substrate surfaces have the best quality by CMP with subsequent chemical etching. The surface treatment effects of sapphire substrate on the ZnO thin films were examined by X-ray diffraction (XRD) and photoluminescence (PL) measurements. Results show that the intensity of (002) diffraction peak of ZnO thin films on sapphire substrates treated by CMP with subsequent chemical etching was strongest, FWHM of (002) diffraction peak is the narrowest and the intensity of UV peak of PL spectrum is strongest, indicating surface treatment on sapphire substrate preparation may improve ZnO thin films crystal quality and photoluminescent property. [Copyright &y& Elsevier]

Abstract: ZnO thin films were prepared by reactive RF magnetron sputtering at various deposition temperatures. They were annealed in oxygen ambient at various annealing temperatures. The microstructures and photoluminescence characteristics of ZnO films were investigated. The grain size of the ZnO thin film that was deposited at room temperature (RT) after annealing exceeded that of the film that was deposited at . Excess Zn atoms were considered to be present in the ZnO film that was deposited at RT, so the film was non-stoichiometric ZnO. No visible emission of either of the ZnO films deposited at the two temperatures was observed before annealing. Following annealing at high temperature, the green emission from the ZnO film that was deposited at RT was stronger than that of the film that was deposited at . The relationship between the non-stoichiometry of the thin film and the visible emission was discussed. The luminescent centers that correspond to green emission are defects; the concentration of defects was higher in the ZnO thin film that was deposited at RT than in the film that was deposited at . [Copyright &y& Elsevier]

Abstract: Stoichiometric bulk ingot material of the quaternary CdGaInSe4 was prepared by direct fusion of the constituent elements in vacuum-sealed silica tubes. Nearly stoichiometric films could be deposited by thermal evaporation of the ingot material in 10−3 Pa vacuum at a deposition rate 1.5nm/s. Crystal structure investigation was carried out using X-ray diffractometry and transmission electron diffraction. Elemental composition was determined by means of energy-dispersive X-ray spectrometry. CdGaInSe4 possesses a tetragonal defective chalcopyrite structure (space group ) with lattice parameters a=0.5665nm and c=1.1221nm. All the films exhibited n-type conduction and ohmic behaviour with metallic films of Au, Cd, In, Ag and Sb. However, in the case of Al a nonlinear behaviour occurs. Analysis of the temperature dependence of the dark conductivity in the range 130–470K has revealed three operating conduction mechanisms; a variable range hopping conduction process dominating at low temperatures below 270K, followed by a transport of the charge carriers across intercrystalline barriers and grain boundaries in the temperature range 270–353K, and finally an extrinsic conduction above 353K. [Copyright &y& Elsevier]

Abstract: Thin film binary alloys of In x Se1− x (0.05⩽x⩽0.30) have been prepared by the thermal evaporation technique. The optical transmission and reflection spectrum of these films were measured in the range 300–1100nm. Both refractive index, n and extinction coefficient k have been determined from transmission and reflection measurements in terms of Murmann''s equations. The dispersion of the refractive index is discussed in terms of the single-oscillator Wemple–DiDomenico model. The width of band tail is determined and the optical absorption edge is described using the ‘non-direct transition’ model proposed by Tauc. Finally, the relationship between the optical gap and chemical composition in In x Se1− x amorphous system is discussed in terms of the average heat of atomization H s and average coordination number N c. The results of these calculations can be used rationalize the observed optical properties of these materials. Finally, the chemical bond approach has been also applied to interpret the decrease of the glass optical gap with increasing In content. [Copyright &y& Elsevier]

Abstract: This paper shows that the use of conventional analytical procedures to determine defect parameters from DLTS spectra may lead to erroneous results for high-resistivity semiconductors. The effect is observed when the temperature range of a DLTS peak encompasses the temperature at which the equilibrium Fermi level intersects the energy level of defect under study. Based on this Fermi level effect, a procedure is proposed to determine the occupancy levels for defects with a strong temperature dependence of the carrier capture cross-section. It has been found that the procedure can be useful for characterization of positive-U states through to negative-U centers in semiconductors. [Copyright &y& Elsevier]

Abstract: The accumulation layer of organic thin film field-effect transistors extends away from the gate insulator/semiconductor interface by only a few molecular layers into the semiconductor thin film. The structure of these first few layers are thus crucially important to the electrical properties of devices and to the design of other functional structures incorporating organic/inorganic interfaces. We have used scanning tunneling microscopy to image the vacancies and grain boundaries in pentacene thin films on Si (001) substrates chemically terminated by styrene. The styrene termination allows pentacene molecules to form in a crystal structure similar to that of pentacene layers on the insulating substrates. In addition, by incorporating specially designed molecular monolayers at the interface between the gate insulator and the pentacene thin film, it is possible to form novel photoinduced charge-transfer structures. Tuning the chemical properties of the self-assembled monolayers affords a new degree of control in tuning the properties of these devices. [Copyright &y& Elsevier]

Abstract: We have synthesized Ga1− x Mn x As1− y P y and Ga1− x Mn x P1− y N y by the combination of ion implantation and pulsed-laser melting. We find that the incorporation of isovalent impurities with smaller atomic radii leads to a realignment of the magnetic easy axis in Ga1− x Mn x P1− y N y /GaP and Ga1− x Mn x As1− y P y /GaAs thin films from in-plane to out-of-plane. This tensile-strain-induced magnetic anisotropy is reminiscent of that observed in Ga1− x Mn x As grown on larger lattice constant (In, Ga)As buffer layers indicating that the role of strain in determining magnetic anisotropy is fundamental to III–Mn–V materials. In addition, we observe a decrease in the ferromagnetic Curie temperature in Ga1− x Mn x As1− y P y with increasing y from 0 to 0.028. Such a decrease may result from localization of holes as the P/As ratio on the Group V sublattice increases. [Copyright &y& Elsevier]

Abstract: We investigated the optical and structural properties of ZnO thin films grown under the same growth condition by metalorganic chemical vapor deposition (MOCVD) on various substrates such as p-Si, n-GaN, c-sapphire, a-sapphire, glass, and ITO glass. The thickness and surface roughness of the ZnO films increased with increasing lattice mismatch between the film and substrate. The ZnO films on c-sapphire showed a higher carrier concentration and conductivity than the ZnO thin films on a-sapphire and glass. In addition, the intensity of the near band-edge emission and transmittance increased with decreasing lattice mismatch between the film and substrate. [Copyright &y& Elsevier]

Abstract: Non-polar (112¯0) and semi-polar (112¯2) GaN thin films were grown heteroepitaxially on r-plane and m-plane sapphire, respectively. As-grown films suffered from a high density of defects. Epitaxial lateral overgrowth was shown to be an effective technique for lowering the defect density when stripes of masking material were oriented along the in-plane GaN m-axis for both (112¯0)- and (112¯2)-oriented films. Parallel stripes of SiO x 5μm wide with 5μm spacing were fabricated using traditional wet-chemistry photolithography, and subsequent regrowth occurred through the window regions and over the mask. Growth-related extended defects terminate at the interface with the mask, and are absent in overgrown material where dislocation formation and propagation are limited. A novel double-processing technique was attempted on (112¯0)-oriented GaN by initially regrowing to create high-aspect features in the window, and then depositing SiO x on top of the mesas. Further regrowth occurred over both sets of masks, to produce a continuous film across the entire wafer. [Copyright &y& Elsevier]

Abstract: The nature of defect states associated with group III impurities (Ga, In, and Tl) in PbTe, a narrow band-gap semiconductor, has been studied within density functional theory and supercell model. For all three impurities (both substitutional—at the Pb site and interstitial—at the tetrahedral site), there is a hyper-deep defect state which lies about 0.5–1.0eV below the valence band. It is a highly localized bonding state between the impurity s-orbital and the surrounding p-orbitals of the Te atoms. The corresponding anti-bonding state, denoted as the deep defect state, lies in the band-gap region. Its precise position vis-à-vis the conduction- and valence-band extrema controls the unusual properties exhibited by these defects. [Copyright &y& Elsevier]

Abstract: A silicon nanoporous pillar array (Si-NPA) with micrometer/nanometer hierarchical structure was fabricated by hydrothermal etching, followed by spin-coating barium strontium titanate (BST) on Si-NPA substrate. The photoluminescence (PL) spectra of the Si-NPA and BST/Si-NPA thin film were investigated. The emission band of freshly prepared Si-NPA located at ∼630nm, and a blueshift at ∼425nm as well as degradation in intensity after annealing at 600°C for 1h was observed, which might be explained by a quantum confinement effect model. BST ferroelectric material provided a static-electric field and induced the excited carriers in Si-NPA to migrate toward the opposite direction and recombine in an interfacial oxide layer. Therefore, BST enhanced blue emission of Si-NPA as well as passivated Si-NPA. [Copyright &y& Elsevier]

Abstract: In the paper we consider size effects on phase transitions and polar properties of thin antiferroelectric films. We extend the phenomenological approach proposed by Kittel for thin films allowing for gradient (correlation) energy and depolarization field energy. Surface piezoelectric effect as well as misfit strain appear due to lattice constants mismatch between the film and its substrate. Direct variational method is used to derive the free energy with renormalized coefficients depending on the film thickness. Obtained free energy expression allows the calculation of phase diagrams and all electro-physical properties by a conventional minimization procedure. Approximate analytical expressions for the paraelectric–antiferroelectric–ferroelectric transition temperature dependences on film thickness, polarization gradient coefficient, and extrapolation lengths were obtained. The thickness dependence of the electric field critical value that causes antiferroelectric–ferroelectric phase transition was calculated. Under favorable conditions the antiferroelectric phase at first transforms into ferroelectric one and then into paraelectric phase with the decrease of the film thickness. Proposed theoretical consideration explains the experimental results obtained in antiferroelectric PbZrO3 thin films. [Copyright &y& Elsevier]

Abstract: Ferroelectric SrBi2Ta2O9 (SBT) thin films were grown on p-type (100) Si substrates by radio frequency sputtering technique. The crystallinity of the films was studied using grazing incidence X-ray diffraction pattern. The spectra showed the films were polycrystalline with dominant orientation along (115) plane. The surface morphology was investigated by atomic force microscope. The chemical composition was studied by Rutherford back-scattering, which yielded a near stoichiometric composition of SBT. The capacitance–voltage characteristics of Al/SBT/Si capacitors measured at 100kHz showed a hysteresis nature with a clockwise rotation and the memory window of the hysteresis loop was 0.88V with the gate voltage ±5V. The interface trap density was calculated by using Hills method at room temperature and a value in the order of 1011–1012 eV−1 cm−2 was found depending on the crystallization temperature at midgap region. [Copyright &y& Elsevier]

Abstract: The symmetric and asymmetric charge distribution of bonding electrons in silicon and gallium arsenide has been studied using experimental powder X-ray data sets. The mid-bond electron densities from the origin are found to be 0.787 and 1.725e/Å3 at 1.175 and 1.222Å, respectively, for Si and n-GaAs. The effectiveness of powder data sets in precise bonding studies has been verified. Multipole analysis of the valence charge distribution has also been done. The thermal vibration parameters have been studied and presented for both these systems. The magnitudes of the non-nuclear maxima of both these systems are consistent with those obtained using single-crystal studies. [Copyright &y& Elsevier]

Abstract: A large amount of experimental and theoretical work has been devoted to understand memory effects (ME) in the solid vortex lattice (VL) but has remained, however, controversial until now. In the vicinity of the anomaly known as the peak effect (PE) both the VL mobility and the measured critical current density are found to be dependent of the dynamical history of the sample, in both low T c (LTS) and high T c (HTS) superconductors. Experiments in YBa2Cu3O7 (YBCO) crystals have shown that the mobility of the VL increases after assisting the system with a symmetric AC field (or current) of moderated amplitude. On the other hand, after an asymmetric AC field assists vortices, the VL becomes less mobile. These features indicate that ME in these samples cannot be ascribed to an equilibration process, but probably are related to the organization of the lattice after nearest neighbor re-accommodation or induced plastic VL deformation. Recently, we have shown evidence that in YBCO the PE is a dynamic anomaly observed in the non-linear response, and is absent in the Labusch constant derived from the linear Campbell regime. However, this behavior seems not to be extensive to other systems as the traditional LTS NbSe2. In this work, the AC response in the PE region of NbSe2 and YBCO samples are presented and compared. Very salient differences both in the linear and non-linear response as well as in the ME characteristics indicate that a different physics governs the PE phenomena in each case. [Copyright &y& Elsevier]

Abstract: Zn1− x Co x O (nominal x=5 and 30at%) powders were prepared by mechanical alloying the binary oxides ZnO and CoO. The incorporation of Co element into the wurtzite structure with increasing milling times was followed by X-ray diffraction. Some basic properties of these bulk powder materials were investigated in order to contribute to the comprehension of the development of magnetism in these semiconductors. The change in optical properties with addition of Co was studied by photoluminescence and the corresponding magnetic properties were evaluated by field-cooling and zero-field-cooling magnetization measurements. [Copyright &y& Elsevier]

Abstract: In this contribution we present a study of the magnetic properties of MnAs thin films grown over GaAs(111) substrates, performed by ferromagnetic resonance experiments. We have calculated the magneto-crystalline anisotropy of the system analyzing the angular dependence of the resonance field with the applied field direction. The anisotropy measured for these films is much smaller than the calculated for MnAs bulk samples and MnAs/GaAs(100) thin films. We propose different microscopic mechanism for addressing the change in the anisotropy. [Copyright &y& Elsevier]

Abstract: The red photoluminescence (PL) band (peaked between 610 and 640nm) from electrochemically deposited ZnO thin films is studied. The absorption coefficient is obtained from diffuse reflectance measurements. The absorption band edge depends on deposition conditions. The PL peak follows the shift of the band edge. A similar correlation appears when cooling down to 20K. This suggests that PL is due to a transition from an intrinsic shallow state to an intrinsic deep state. Comparing against ZnO samples showing green PL, the shallow nature of the state is confirmed. [Copyright &y& Elsevier]

Abstract: In a superconducting mesoscopic sample, with dimensions comparable to the London penetration depth, some properties are qualitatively different to those found in the bulk material. These properties include magnetization, vortex dynamics and ordering of the vortex lattice. In order to detect the small signals produced by this kind of samples, new instruments designed for the microscale are needed. In this work we use micromechanical oscillators to study the magnetic properties of a disk with a diameter of and a thickness of . The discussion of our results is based on the existence and contribution of inter and intra layer currents. [Copyright &y& Elsevier]

Abstract: We have measured the current–voltage characteristics at room temperature of a nanocrystalline TiO2 thin film fabricated by reactive RF-sputtering deposition and sandwiched between ITO (indium–tin–oxide)-buffered glass substrate and an indium top electrode. The I–V characteristics are ohmic for low voltages and become non-linear, hysteretic and asymmetric as the voltage is increased. The system is shown to be well represented by two distinct resistance states in the non-ohmic region. Current transient evolutions were also measured for constant voltage excitations. The resistance is stable in time for voltages in the ohmic regime. In contrast, for voltages in the non-ohmic regime, the resistance has a small variation for a short period of time (order of tens seconds) and then increases with time. For those transients, long characteristic times (on the order of tens of minutes up to hours) were found. The behavior of the system is discussed on the basis of experimental results reported in the literature for similar systems and existing models for electric-field induced resistive switching. [Copyright &y& Elsevier]

Abstract: The mechanisms of electrical conduction in thin films have been investigated. The samples were rf-diode reactive sputtered films deposited in gas atmospheres where changes in and film structure had been achieved by varying the flow rate and the substrate temperature. The electrical transport properties of these samples were investigated by measuring the conductivity as a function of temperature between 17K and room temperature. At the temperature range between 200 and 290K the best fit to the experimental data was obtained assuming a dependence characteristic of adiabatic variable range hopping. At lower temperature the activation energy for the conductivity tends to zero. The results suggest that the conduction mechanism is adiabatic small polaron hopping, which switches to conduction in a polaron band at low temperatures. [Copyright &y& Elsevier]

Abstract: In this work, we report analysis of magnetization fluctuations for the CaLaBaCu3O7− δ superconducting system. We describe a procedure for extracting the penetration depth λ(T) and the coherence length ξ parameters from the magnetization, as a function of the applied magnetic field. This procedure takes the vortex fluctuation into account. The data of the magnetization excess ΔM(T) are analyzed for different values of temperature in the interval from 65 to 73K. For several magnetic fields we observed a crossover in the magnetization curves at the characteristic temperature value T *=72.2K. We calculated the data of magnetization excess from the curves of magnetization as a function of the logarithm of the applied field. This procedure was performed for polycrystalline samples of CaLaBaCu3O7− δ by using the proposition of Bulaevskii, Ledvij and Kogan. We notice that the values for these superconducting parameters are in agreement with reports for high-temperature superconductors. [Copyright &y& Elsevier]

Abstract: Fe-doped nanosized SnO2 powders were prepared by mechanosynthesis using rutile SnO2 and hematite Fe2O3 as starting materials. The estimated grain size of the obtained rutile structure was between 10 and 20nm. Mössbauer spectroscopy shows the presence of two interactions corresponding to 3+ and 2+ iron oxidation states with similar relative fractions. The magnetic measurements exhibit ferromagnetic- (FML) and superparamagnetic-like (SML) behavior. Evidence of a system of strongly interacting particles was found. [Copyright &y& Elsevier]

Abstract: We present an ab initio study of pure and doped TiO2 in the rutile and anatase phases. The main purpose of this work is to determine the role played by different defects and different crystal structures in the appearance of magnetic order. The calculations were performed for varying impurity and vacancy concentrations in both TiO2 structures. For Co impurities the local magnetic moment remained almost independent of the concentration and distribution while for Cu this is not the case, there is magnetism for low concentrations that disappears for the higher ones. Impurity–impurity interactions in both structures favor linear ordering of them. Magnetism in undoped samples appears for certain vacancy concentrations and structural strain. [Copyright &y& Elsevier]

Abstract: The standard methods of determination of the dominant conduction mechanisms in high-permittivity dielectrics were discussed for the case of very thin films. The outcomes from the estimation method were tested on the theoretical results obtained by the use of a comprehensive model describing the I–V characteristics of Ta2O5/SiO2 stacked layers. It is shown that the standard method based on the determination of a slope in Poole–Frenkel plot provides only a rough estimation that may lead in some cases to essentially incorrect results. The observed disagreement is explained by the modifications induced by the presence of an unavoidably grown SiO2-like few nanometers thick interfacial layer. [Copyright &y& Elsevier]

Abstract: The effect of annealing on the properties of La0.7Sr0.3MnO3 (LSMO) thin film deposited on Si substrates by DC sputtering has been investigated by X-ray diffraction (XRD), electrical and magnetic measurements. As-grown films show a lower metal–insulator transition (T MI) temperature than annealed films. As the annealing temperature increases, significantly higher T MI values are observed up to 270K. We suggest that the increase of effective hole doping, induced by cationic vacancies due to the excess oxygen, is a possible reason for the observed trend in T MI. Annealing improves the magnetic homogeneity of the grain and grain boundaries. These improvements are favorable to enhance the intrinsic properties of the compound especially the decrease of resistivity. The decrease in resistivity induces the MR ratio to increase. This result is attractive for CMR application studies. [Copyright &y& Elsevier]

Abstract: The emission band spectra of undoped Tl2In2Se3S layered crystals have been studied in the temperature range of 25–63K and the wavelength region of 570–700nm. A broad photoluminescence band centered at 633nm (1.96eV) was observed at T=25K. Variation of emission band has been studied as a function of excitation laser intensity in the 2.7–111.4mWcm−2 range. Radiative transitions from shallow donor level located at 0.03eV below the bottom of conduction band to deep acceptor level located at 0.23eV above the top of the valence band were suggested to be responsible for the observed PL band. From X-ray powder diffraction and optical absorption study, the parameters of monoclinic unit cell and the energy of indirect band gap were determined, respectively. [Copyright &y& Elsevier]

Abstract: We have successfully synthesized PrSrCaMnO thin films (with a nominal structure of Pr0.7Sr0.05Ca0.25MnO3) and some heterostructure thin films on LaAlO3 (100) single-crystal substrates by a newly invented precursor film sintering technique. The XRD analysis showed that the PCSMO thin films by the PFS method consisted of epitaxially grown single-phase perovskite structures, oriented to the c-axis direction and without secondary phases. LPL, PLP and LCMO thin films prepared by the PFS method were all epitaxially grown thin films with good quality, which were confirmed by XRD patterns. The effect of the critical sintering temperature was carefully studied based on XRD patterns and SEM images. It was found that the sintering temperature higher than 1200°C gave rise to high-quality epitaxial thin films, but a secondary phase appeared at this temperature. Large values of the MR of PCSMO, LCMO and LPL thin films have been observed. Besides, the advantages of the PFS method include simple equipments, common chemical compounds and a variety of shapes of the prepared thin films. [Copyright &y& Elsevier]

Abstract: In the framework of self-consistency effective medium approximation, we derive an expression for the effective resistivity of the Miller–Abrahams resistor networks with hopping conductivities, and we compare it with results of numerical simulations of such networks. In our approach we modify the effective medium approximation to include the presence of the Josephson junctions in granular (low- and high- ) superconductors. [Copyright &y& Elsevier]

Abstract: Multilayer thin films consisting of alternating iron and carbon layers were deposited from a pulsed cathodic arc with magnetic filter to remove macroparticles. The magnetic moment of the films was measured as a function of applied field for various repeat distances of the multilayer. The films were ferromagnetic and, at one repeat distance, showed very low coercivity and a small-area hysteresis loop. The films were examined using cross-section transmission electron microscopy. For the magnetically very soft films, single iron crystallites were found to cross the entire film thickness. The carbon layers may contribute to the magnetic properties by paramagnetic coupling of the spins known to be present. [Copyright &y& Elsevier]

Abstract: Photonic crystals prepared via the Langmuir–Blodgett (LB) method are shown to be quite different to those structures prepared by other self-assembly approaches. In LB prepared films the layer spacing is expanded relative to that expected for a true FCC structure while the correlation between layers is reduced. The resulting films are thus best described as (2+1) dimensional in nature, since they do not possess the full three-dimensional (3-D) ordering present in opaline structures. A simple analysis of Bragg reflection peaks for a sample prepared from silica particles of diameter ca. 250nm reveals layer spacing for the LB-grown films of 0.941D, where D is the particle diameter. We account for these phenomena in terms of a model in which each layer of spheres forms within the confines of the LB trough before being transferred as a complete layer to the substrate. Under such conditions the likelihood of the spheres finding the optimum sites for the formation of a true FCC structure is low and the resulting structures, although still consisting of ordered layers, do not adopt the FCC structure and hence they may not be described as ‘opals’. Results are also presented for bilayer (size matched) heterostructure photonic crystals. For the size-matched bilayer systems where the diameter of one set of particles is twice that of the other, it is shown that when sampled in a particular geometry, cooperative effects can occur involving the first-order Bragg reflections from the layer of smaller particles combining with the second-order Bragg reflections from the layer of larger particles. As a consequence an enhancement of the intensity of the first-order Bragg peak from the layer comprised of the smaller particles is observed in the binary heterostructure. [Copyright &y& Elsevier]

Abstract: Mesoporous gold sponge has optical properties that can be intermediate between those of metals and insulators, with a flat spectral response that is unlike that of bulk gold. Films of different thicknesses were produced and an extension of the Lorentz–Drude (LD) model used to model their spectral behavior. We found that it was necessary to include an additional special oscillator centered at 1.4eV in order to model the unusual spectral response. This is quite unlike bulk gold, which can be modeled using a standard two-oscillator LD model. [Copyright &y& Elsevier]

Abstract: The resistivity and Seebeck coefficients of YBaCo2− x Fe x O5+ δ (0⩽x⩽0.8) were measured from room temperature (RT) to 800°C. It was found that all compositions behave as p-type semiconductors in the temperature range of RT–300°C. When temperature is above about 300°C, both electrical resistivity and Seebeck coefficients increase with the increase of temperature due to oxygen desorption from the lattices. Fe doping tends to increase resistivity and Seebeck coefficients in all the temperature ranges measured. The calculated activation energy of conductivity is larger than that of thermopower in the semiconductor region, which means that the conduction mechanism may be determined as a small polaron hopping model. [Copyright &y& Elsevier]

Abstract: Thallium gallium sulfide, TlGaS2, a semiconductor compound, was prepared by solid-state reaction technique. Its crystal structure was determined by single-crystal X-ray diffraction. This material crystallizes in the monoclinic system with space group C2/c (No. 15), and unit cell parameters , , , . The structural refinement converged to , and . The structure consists of a three-dimensional arrangement of distorted TlS8 and GaS4 polyhedrons. Four GaS4 tetrahedra form adamantine-like units of the type Ga4S10, which in turn connect through the corners forming layers that run along the [100] direction. [Copyright &y& Elsevier]

Abstract: Magnetron sputtering is a promising technique for the growth of oxide materials including ZnO, which allows deposition of films at low temperatures with good electrical properties. The current–voltage (I–V) characteristics of Au Schottky contacts on magnetron sputtered ZnO films have been measured over a temperature range of 278–358K. Both effective barrier height (φ B,eff) and ideality factor (n) are found to be a function of temperature, and this behavior has been interpreted on the basis of a Gaussian distribution of barrier heights due to barrier height inhomogeneities that prevail at the interface. Density of states (DOS) near the Fermi level is determined using a model based on the space charge limited current (SCLC). The dispersion in both real and imaginary parts of the dielectric constant at low frequencies, with increase in temperature is attributed to the space charge effect. Complex impedance plots exhibited two semicircles, which corresponds to bulk grains and the grain boundaries. [Copyright &y& Elsevier]

Abstract: Bulk glasses of the Ge5Se25Te70 system were prepared by the conventional melt-quenching technique. Thin films with a thickness of 150nm of Ge5Se25Te70 were prepared by the thermal evaporation technique on glass substrates. The crystallization mechanism has been studied by using differential scanning calorimeter (DSC) technique. The effect of heat treatment on the structure transformation was investigated by X-ray diffraction and the scanning electron microscope. The effect of heat treatment on the optical properties was also investigated. [Copyright &y& Elsevier]

Abstract: The electronic structure of rutile-type crystals Sn1− x M x O2, M=As, Sb, Bi, V, Nb, Ta, 0⩽x⩽0.25 was studied using the linear muffin–tin orbital method within the tight-binding approximation. It was shown that additional bands consisting of the valence ns states for Sn1− x As x O2, Sn1− x Sb x O2, Sn1− x Bi x O2 and (n−1)d states for Sn1− x V x O2, Sn1− x Nb x O2, Sn1− x Ta x O2 appear in the electronic spectrum and define the type of the conductivity. The values of cohesive energies and chemical bonding of Sn0.75M0.25O2 were calculated. On the basis of the calculation results, the relative stability and type of conductivity of the compound are discussed. [Copyright &y& Elsevier]