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Postgrowth annealing was carried out on ZnO thin films grown by metal-organic chemical-vapor deposition. It was found from the scanning electron microscopy and atomic force microscopy measurements that the morphology of the thin films changed drastically after annealing. The as-grown thin films consist of fine nanoscale-sized sheets with random orientation. Upon annealing at 800 °C, the ZnO nanosheets changed to three-dimensional nanoneedles. The different types of the mass transport mechanisms are discussed and correlated with the experimental results. A coarsening kinetics developed by Lifshitz and Slyozov [J. Phys. Chem. Solids 19, 35 (1961)] and Wagner [Z. Elektrochem. 65, 581 (1961)] was used to estimate the activation energy of the coarsening process. The activation energy of the Ostwald ripening in ZnO films was estimated in the first attempt, and the value is at around 1.33 eV. Hall effect and photoluminescence measurements were carried out to investigate the effect of coarsening on electrical and optical properties of the ZnO thin films. [ABSTRACT FROM AUTHOR]

The optical band gap of ZnO thin films deposited on fused quartz by metal-organic chemical-vapor deposition was studied. The optical band gap of as-grown ZnO blueshifted from 3.13 to 4.06 eV as the growth temperature decreased from 500 to 200 °C. After annealing, the optical band gap shifted back to the single-crystal value. All the ZnO thin films studied show strong band-edge photoluminescence. X-ray diffraction measurements showed that samples deposited at low temperatures (<450 °C) consisted of amorphous and crystalline phases. The redshift of the optical band gap back to the original position after annealing was strong evidence that the blueshift was due to an amorphous phase. The unshifted photoluminescence spectra indicated that the luminescence was due to the crystalline phase of ZnO, which was in the form of nanocrystals embedded in the amorphous phase. [ABSTRACT FROM AUTHOR]

In this work, ultrathin WS2 nanosheets were synthesized through a facile solid-state reaction route. The as-synthesized samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The electrochemical performance of ultrathin WS2 nanosheets as anode material for lithium-ion batteries were systematically investigated by a variety of electrochemical testing techniques. It was found that WS2 nanosheets exhibited a relatively high reversible capacity and fine cycle performance. [ABSTRACT FROM AUTHOR]

As the magnetic storage density approaches 1 TB/in^2, a grand challenge is looming as how to read/write such a huge amount of data within a reasonable time. In this study, we demonstrate femtosecond demagnetization in 10-nm epitaxially grown Fe thin films by applying low-energy femtosecond laser pulses. We used time-resolved pump-probe Magneto Kerr Effect spectroscopy to record ultrafast laser induced demagnetization and its recovery. The demagnetization time was found to be 70 fs from the time-resolved hysteresis loops. The time scale is much shorter than the phonon thermalization time. Our results show that the demagnetization can be completed before electron-phonon equilibration is achieved, and therefore indicate the feasibility of ultrafast optical control of demagnetization responses for next generation femtosecond-switching magnetic storage devices. [ABSTRACT FROM AUTHOR]

[Fe1-δ(FeO)δ]x(TiO2)1-x (0≤δ≤0.91, 0.34≤x≤0.54) granular films were fabricated by magnetron sputtering. Large coercivity (HC = 10.5 kOe) and exchange-bias-field (HE = 6.5 kOe) at 5 K were found in the film with δ=0.84 and x = 0.48. AC susceptibility measurements exhibit a frequency (f) dependent peak Tf in the in-phase susceptibility curve. The fitting of the relation of Tf vs f with both the Vogel-Fulcher law and critical slowing down theory indicate that the evident enhancement of the HC and HE can be qualitatively ascribed to the existence of cluster-spin glass state. The results may help to deeply understand the origin of exchange bias and related effects. [ABSTRACT FROM AUTHOR]

Both ferroelectric Na0.5Bi0.5TiO3 (NBT) and K0.5Bi0.5TiO3 (KBT) are considered as the best known lead-free materials. In this experiment, we prepared NBT and KBT thin films on Pt/TiO2/SiO2/Si substrates by metalorganic solution deposition. The structural properties and surface morphologies were measured using X-ray diffraction and atomic force microscopy. The NBT and KBT films show higher leakage currents due to the oxygen vacancies in the films. The remanent polarization and coercive field of NBT (KBT) thin film are 9 (5.2) μC/cm2 and 50 (25) kV/cm at an applied electric field of 150 kV/cm. The relative dielectric constants of NBT and KBT are 340 and 316 at 1 MHz, respectively. [ABSTRACT FROM AUTHOR]

P-type ZnO thin films were grown on sapphire substrates with and without nitrous oxide (N2O) by metal organic chemical vapor deposition (MOCVD). The intrinsic p-type ZnO films were achieved by controlling the Zn:O ratio in the range of 0.05-0.2 without N2O flow. Secondary ion mass spectroscopy (SIMS) showed that the films contained little or no nitrogen (N) impurities for all samples. The p-type behavior of the samples should be due to the intrinsic acceptor-like defects VZn, for ZnO film grown without nitrous oxide, and N, occupying O sites as acceptors for ZnO film grown with nitrous oxide. The best p-type ZnO film has low resistivity of 0.369 Ω-cm, high carrier density of 1.62 x 1019 cm-3, and mobility of 3.14 cmsup2;/V-s. The obtained p-type ZnO films possess a transmittance of nearly 100% in the visible region and strong near-band-edge emission. [ABSTRACT FROM AUTHOR]

Using a simple process of the deposition of ZnO thin films on SiOx/Si substrates and subsequent thermal annealing, we fabricated ZnO quantum dots embedded in silicon oxide matrix. The ZnO quantum dots were characterized using transmission electron microscopy, and time-integrated and time-resolved photoluminescences. We measured an exciton radiative lifetime of 65 ps at 4.3 K, which is much shorter than the exciton radiative lifetime of 322 ps in bulk ZnO. The short exciton radiative lifetime can be explained in terms of exciton superradiance. [ABSTRACT FROM AUTHOR]

Random lasing was observed from ZnO polycrystalline thin film deposited by filtered cathodic vacuum arc technique. It is found that the random lasing action results from exciton-exciton scattering process when the excitation intensity is low. However, with increasing excitation intensity, the well-resolved discrete lasing modes evolve into broad stimulated emission band due to electron-hole plasma formation when the photogenerated exciton density exceeds the Mott density. The short spontaneous emission decay time measured at low temperature suggests that the radiative recombination rate is enhanced by the nanosized ZnO grains in the polycrystalline film through exciton-light coupling. [ABSTRACT FROM AUTHOR]

Using optical pump-terahertz probe spectroscopy, we studied the dynamic behaviors of photoinduced insulator-metal phase transition in vanadium oxide thin films with different oxygen stoichiometry. We found that the insulator-metal phase transition of vanadium dioxide is very sensitive to oxygen stoichiometry: the increased oxygen content in vanadium oxide will reduce the magnitude of phase transition and change the dynamics of the phase transition. The transient complex photoconductivity of vanadium oxide thin films is investigated and analyzed with Drude-Smith model, supplying insight of the dynamic process of phase transition in vanadium oxide thin films. [ABSTRACT FROM AUTHOR]

The superconducting transition temperature Tc of multilayers of electron-doped cuprates, composed of underdoped (or undoped) and overdoped La2-xCexCuO4 (LCCO) and Pr2-xCexCuO4 (PCCO) thin films, is found to increase significantly with respect to the Tc of the corresponding single-phase films. By investigating the critical current density of superlattices with different doping levels and layer thicknesses, we find that the Tc enhancement is caused by a redistribution of charge over an anomalously large distance. [ABSTRACT FROM AUTHOR]

Abstract: UV pulsed laser deposition was employed for the fabrication of amorphous Ga–Ge–Te thin films. The local structure of the bulk glasses as well as corresponding thin films was studied using Raman scattering spectroscopy; the main structural motifs were found to be [GeTe4], eventually [GaTe4] corner-sharing tetrahedra and disordered Te chains. Optical functions of the films (refractive index, extinction coefficient) were characterized by variable angle spectroscopic ellipsometry. Photostability experiments showed all Ga–Ge–Te laser deposited films to be stable against 1550nm laser irradiation in an as-deposited state. In an annealed state, the most photostable composition seems to be Ga10Ge15Te75. This particular composition was further studied from the point of view of thermal stability and stability against ageing in as-deposited state. [Copyright &y& Elsevier]