Search

Abstract: ZnO/Si heterojunctions were fabricated by growing ZnO thin films on p-type Si (100) substrate by pulsed laser deposition without buffer layers. The crystallinity of the heterojunction was analyzed by high resolution X-ray diffraction and atomic force microscopy. The optical quality of the film was analyzed by room temperature (RT) photoluminescence measurements. The high intense band to band emission confirmed the high quality of the ZnO thin films on Si. The electrical properties of the junction were studied by temperature dependent current–voltage measurements and RT capacitance–voltage (C–V) analysis. The charge carrier concentration and the barrier height (BH) were calculated, to be 5.6×1019 cm−3 and 0.6eV respectively from the C–V plot. The BH and ideality factor, calculated using the thermionic emission (TE) model, were found to be highly temperature dependent. We observed a much lower value in Richardson constant, 5.19×10−7 A/cm2 K2 than the theoretical value (32A/cm2 K2) for ZnO. This analysis revealed the existence of a Gaussian distribution (GD) with a standard deviation of σ2 =0.035V. By implementing the GD to the TE, the values of BH and Richardson constant were obtained as 1.3eV and 39.97A/cm2 K2 respectively from the modified Richardson plot. The obtained Richardson constant value is close to the theoretical value for n-ZnO. These high quality heterojunctions can be used for solar cell applications. [Copyright &y& Elsevier]

Abstract: Thin films of ZnO, Li doped ZnO (ZLO) and multilayer of ZnO and ZLO (ZnO/ZLO) were grown on silicon and corning glass substrates by pulsed laser deposition technique. Single phase formation and the crystalline qualities of the films were analyzed by X-ray diffraction and Li composition in the film was investigated to be 15wt% by X-ray photoelectron spectroscopy. Raman spectrum reveals the hexagonal wurtzite structure of ZnO, ZLO and ZnO/ZLO multilayer and confirms the single phase formation. Films grown on corning glass shows more than 80% transmittance in the visible region and the optical band gaps were calculated to be 3.245, 3.26 and 3.22eV for ZnO, ZLO and ZnO/ZLO, respectively. An efficient blue emission was observed in all films which were grown on silicon (100) substrate by photoluminescence (PL). PL measurements at different temperatures reveal that the PL emission intensity of ZnO/ZLO multilayer was weakly dependent on temperature as compared to the single layers of ZnO and ZLO and the wavelength of emission was independent of temperature. Our results indicate that ZnO/ZLO multilayer can be used for the fabrication of blue light emitting diodes. [Copyright &y& Elsevier]

Abstract: Bi1.5Zn1.0Nb1.5O7/Ba0.6Sr0.4TiO3/Bi1.5Zn1.0Nb1.5O7 tunable multilayer thin film has been fabricated by pulsed laser ablation and characterized. Phase composition and microstructure of multilayer films were characterized by X-ray diffraction, scanning electron microscopy (SEM) and atomic force microscopy (AFM). The film has very smooth surface with RMS roughness of 1.5–2nm and grain size of 100–150nm. Total film thickness has been measure to be 375nm. The BZN thin films at 300K, on Pt(111)/SiO2/Si substrate showed zero-field dielectric constant of 105 and dielectric loss tangent of 0.002 at frequency of 0.1MHz. Thin films annealed at 700°C shows the dielectric tunability of 18% with biasing field 500kV/cm at 0.1MHz. The multilayer thin film shows nonferroelectric behavior at room temperature. The good physical and electrical properties of multilayer thin films make them promising candidate for tunable microwave device applications. [Copyright &y& Elsevier]

Abstract: The dielectric response of pulsed laser ablated Bi1.5Zn1.0Nb1.5O7 (BZN) thin films are investigated within the temperature range of 300–660 K and frequency range of 100 Hz–100 kHz. Thin film exhibited a strong dielectric relaxation behavior. A sharp rise in dielectric constant of BZN thin film at high temperatures is related to disorder in cation and anion lattices. Observed dielectric relaxation implies a redistribution of charges within the unit cell. This phenomenon suggests that the large change in dielectric constant is due to a dynamical rise of dipolar fluctuations in the unit cell. XPS spectra of BZN (A2B2O6O′) cubic pyrochlore, confirm that the relaxation corresponds to the ionic hopping among the A and O′ positions of several local potential minima. Barrier height for hopping is distributed between 0 and 0.94 eV. The O spectrum confirms presence of two types of oxygen in BZN thin film. The disorder in charge neutralized thin film is correlated with XPS spectra. [ABSTRACT FROM AUTHOR]

For the first time, a pulsed laser ablation deposition (PLD) method has been employed for the synthesis of antiferroelectric lead zirconate, PbZrO3, (PZ) nanotubes within the pores of anodic aluminum oxide (AAO) templates. The structure and morphology of fabricated PZ nanotubes were characterized by number of techniques, including scanning electron microscope (SEM), X-ray diffraction (XRD) and transmission electron microscope (TEM)analysis. After postannealing at 650 °C, the PZ nanotubes exhibited a polycrystalline microstructure, and X-ray diffraction studies revealed that they are of an orthorhombic distorted perovskite crystal structure. TEM analysis confirmed that the obtained PZ nanotubes are composed of nanoparticles in the range of 3–7 nm and the thickness of the wall of the nanotubes is around 10 nm. [ABSTRACT FROM AUTHOR]

Abstract: Ferroelectric c-oriented Bi2VO5.5 (BVO) thin films (thickness ≈300nm) were fabricated by pulsed laser deposition on corning glass substrates. Nonlinear refractive index (n 2) and two photon absorption coefficient (β) were measured by Z-scan technique at 532nm wavelength delivering pulses with 10ns duration. Relatively large values of n 2 =2.05±0.2×10−10 cm2/W and β =9.36±0.3cm/MW were obtained for BVO thin films. Origin of the large optical nonlinearities in BVO thin films was discussed based on bond–orbital theory of transition metal oxides. [Copyright &y& Elsevier]

Abstract: Homogeneous thin films of Sr0.6Ca0.4TiO3 (SCT40) and asymmetric multilayer of SrTiO3 (STO) and CaTiO3 (CTO) were fabricated on Pt/Ti/SiO2/Si substrates by using pulsed laser deposition technique. The electrical behavior of films was observed within a temperature range of 153K–373K. A feeble dielectric peak of SCT40 thin film at 273K is justified as paraelectric to antiferroelectric phase transition. Moreover, the Curie–Weiss temperature, determined from the ε′(T) data above the transition temperature is found to be negative. Using Landau theory, the negative Curie–Weiss temperature is interpreted in terms of an antiferroelectric transition. The asymmetric multilayer exhibits a broad dielectric peak at 273K, and is attributed to interdiffusion at several interfaces of multilayer. The average dielectric constants for homogeneous Sr0.6Ca0.4TiO3 films (∼650) and asymmetric multilayered films (∼350) at room temperature are recognized as a consequence of grain size effect. Small frequency dispersion in the real part of the dielectric constants and relatively low dielectric losses for both cases ensure high quality of the films applicable for next generation integrated devices. [Copyright &y& Elsevier]

Abstract: Zinc oxide (ZnO) and indium doped ZnO (IZO) thin films with different indium compositions were grown by pulsed laser deposition technique on corning glass substrate. The effect of indium concentration on the structural, morphological, optical and electrical properties of the film was studied. The films were oriented along c-direction with wurtzite structure and highly transparent with an average transmittance of more than 80% in the visible wavelength region. The energy band gap was found to decrease with increasing indium concentration. High transparency makes the films useful as optical windows while the high band gap values support the idea that the film could be a good candidate for optoelectronic devices. The value of resistivity observed to decrease initially with doping concentration and subsequently increases. IZO with 1% of indium showed the lowest resistivity of 2.41×10−2 Ωcm and large transmittance in the visible wavelength region. Especially 1% IZO thin film was observed to be a suitable transparent conducting oxide material to potentially replace indium tin oxide. [Copyright &y& Elsevier]

Abstract: Epitaxial heterostructures of La0.6Sr0.4MnO3/0.7Pb(Mg1/3Nb2/3)O3–0.3PbTiO3 were fabricated on LaNiO3 coated LaAlO3 (100) substrates by pulsed laser ablation. Ferromagnetic and ferroelectric hysteresis established their biferroic nature. Dielectric behaviour studied under different magnetic fields over a wide range of temperatures revealed that the capacitance in these heterostructures varies with the applied magnetic field. Appearance of magnetocapacitance and its dependence on temperature and magnetic field strength strongly indicated the possibility of strain mediated magnetoelectric coupling in these heterostructures. [Copyright &y& Elsevier]

Abstract: Bi2V1−x Nb x O5.5 {(x =0, 0.1, 0.2, 0.3, 0.4), (BVN)} thin films were grown by pulsed laser deposition on (111) Pt/TiO2/SiO2/Si and Corning glass substrates and investigated systematically for their microstructural, optical and ac conduction properties. The undoped bismuth vanadate, Bi2VO5.5 (BVO) thin films were highly textured and have been associated with the c-axis oriented grains of the layered perovskite structure, while the Nb doped films consisted of randomly oriented crystallites. The scanning electron microscopy of the films indicates that the grain size increases with increase in Nb content. The optical transmission studies carried out on the samples deposited on Corning glass substrates revealed that these films were nearly 80% transparent in the 400–900nm range and the band gap of Nb doped BVO thin films was slightly higher (3.13eV for x =0.4) than that of the undoped (2.91eV) films. The dielectric constant of the Nb doped films increased with increase in Nb content, while the dielectric loss decreased especially in the 3–100kHz frequency range. At a particular frequency, the conductivity decreased with increase in Nb content in the BVN thin films. In the higher temperature range, the activation energy varied from 0.61eV (x =0.1) to 0.76eV (x =0.4) measured at 100Hz. The frequency analysis of the dielectric and ac conduction properties of these films suggests the conduction process in these films to be via oxygen ion vacancy motion through various defect sites. [Copyright &y& Elsevier]

Sodium-ion thin-film micro-batteries form a niche sector of energy storage devices. Sodium titanate, Na 2 Ti 6 O 13 (NTO) thin films were deposited by pulsed laser deposition (PLD) using solid-state synthesized polycrystalline Na 2 Ti 6 O 13 compound. The phase-purity and crystallinity of NTO in bulk and thin-film forms were confirmed by Rietveld refinement. Electron microscopy and atomic force microscopy revealed the formation of uniform ∼100 nm thin film with roughness of ∼4 nm consisting of homogeneous nanoscale grains. These PLD-deposited NTO thin-films, when tested in Na-half cell architecture, delivered a near theoretical reversible capacity close to 42 mA h g −1 involving Ti 4+ /Ti 3+ redox activity along with good cycling stability and rate kinetics. Na 2 Ti 6 O 13 can work as an efficient and safe anode in designing sodium-ion thin-film micro-batteries. [ABSTRACT FROM AUTHOR]

Abstract: The ferroelectric Pb(Zr0.48Ti0.52)O3 (PZT) thin films prepared by the pulsed laser deposition technique were studied for their response to high energy lithium ion irradiation through impedance spectroscopy. The Debye peaks, observed in the impedance and modulus plots of irradiated films, shifts towards higher frequencies compared to those of unirradiated films. This is equivalent to the trend observed with increase in temperature in the unirradiated films due to the dielectric relaxation. The irradiated films showed a decrease in the grain resistance compared to the unirradiated films. The activation energy of dielectric relaxation increases from 1.25eV of unirradiated film to 1.62eV of irradiated film. The observed modifications in the irradiated film were ascribed to the modifications in the grain structure due to the high value of electronic energy loss. [Copyright &y& Elsevier]