Vanadium dioxide films have long attracted attention because of the phase transition between the semiconducting state and the metallic state at 68 degrees centigrade. Vanadium oxide films have been prepared by a variety of methods, including the annealing and oxidation of evaporated vanadium under controlled conditions. In this study we explore a different route by producing amorphous and crystalline VOx films by pulsed laser deposition and annealing under a variety of conditions. We found that that in amorphous films grown at lower temperatures and then annealed, persistent photoconductivity effects can be observed, while in epitaxial crystalline films grown at high temperature, persistent effects were not observed. Furthermore, it was found that for some crystalline films persistent optical effects were observed and that optical hysteresis was dependent on the amount of time after the film anneal.

Via metal organic deposition (MOD) sapphire substrates were multiple dip-coated with a molecular dispersive 8 mol% Y2O3 doped ZrO2 (8YSZ) sol to prepare dense, crack-free thin films. The thin films were consecutively exposed to a tempering program with several rapid thermal annealing (RTA) steps and a final dwell temperature between 500 °C and 1400 °C for 24 h. Grain growth, phase, stoichiometry and macroscopic density of the thin films were analyzed by XRD and SEM. Grain sizes ranged between a few nanometers in diameter at 500 °C and several hundreds of nanometers at 1400 °C.

Many studies of Barium Strontium Titanate (BST) thin films for RF / microwave applications have employed MgO, LaAlO3 or Pt/Si as the substrate material for BST deposition. However, there have been relatively few reports of BST films grown on sapphire, despite the excellent microwave properties of this material. In this investigation, BST thin films were deposited by RF magnetron sputtering on (001) single crystal c-plane sapphire substrates. Interdigitated capacitors (IDCs) patterned on the film surface were used to measure the dielectric tunability and loss tangent at microwave frequencies. Thick Au conductors were electroplated to minimize conductor losses. Post deposition annealing in air was found to significantly improve the tunability of the sputtered films.

First principles calculations using density functional theory (DFT) are reported for two layers of methane adsorbed on the (100) surface of MgO. The lowest energy structure determined has a first layer with C2v methanes adsorbed above magnesium atoms, with hydrogen atoms pointed towards neighboring oxygen atoms, and a rotation of 90° in between each neighboring methane. The second layer methane layer has a similar structure, except the hydrogen atoms are directed towards nearest neighbor magnesium atoms. It is found that the structure of the first layer has a large effect on the relative energies of proposed bilayer structures, as does the calculated separation between the two layers of methane. Competing roles of surface-adsorbate and adsorbate-adsorbate interactions are also discussed.

Titanium oxide thin films were prepared by filtered cathodic vacuum arc (FCVA) at low temperatures ranged from room temperature to 330°C. Spectroscopic study of the deposited films were carried out by X-ray diffraction, Raman Scattering, Fourier transform infrared spectroscopy (FTIR) and photoluminescence (PL), respectively. The films remained amorphous up to the substrate temperature of 230°C. Nanocrystalline titanium oxide thin films occurred at 330°C with the strongest peak intensity from anatase (101) plane. The average grain size was around 20 nm and no rutile phase could be found. Various allowed vibrational frequencies (e.g. 152, 199, 399, 640 cm−1) in Raman spectra and Ti-O-Ti transverse mode at 436 cm−1 in the FTIR spectrum evidently verified the presence of anatase phase in the films at 330°C. Moreover, at room temperature only crystalline film exhibited a PL peak with the center at 379 nm in PL spectrum and the origin was discussed.

Ti-Al was used as the electrode for RF magnetron sputtered BST film at a substrate temperature of 450°C for decoupling capacitor applications. X-ray diffraction analysis shows that the deposited film BST film is amorphous. Electrical characterizations of the devices performed by capacitance versus voltage measurements show a dielectric constant of about 55. With increase in annealing temperature above 450°C, the capacitance was found to decrease significantly.

Studies on strontium-doped lead zirconate titanate (PSZT) have been reported for its high piezoelectric and ferroelectric properties. For PSZT to exhibit pronounced piezoelectric behaviour it must have a crystalline grain structure (perovskite orientation). This paper is a study of the deposition of PSZT thin films by RF magnetron sputtering and the effect of cooling rate, after deposition at temperatures between 500 °C and 700 °C. X-Ray Diffraction (XRD) results are used to show how a cooling rate of 5 °C/min increases the degree of perovskite orientation in sputtered films, when compared to a cooling rate of 15 °C/min. The absence of significant shifts in the positions of diffraction peak patterns in XRD results are used to demonstrate low stress in the deposited films. Atomic Force Microscope (AFM) imaging is used to show the crystalline nature of the PSZT thin films.

The long-wavelength optical phonons and dielectric constants of PLD-grown MgxZn1−xO films are studied by combination of infrared spectroscopic ellipsometry and Raman scattering spectroscopy. The ternary alloy MgxZn1−xO exhibits a phase transition with change of coordination number from four-fold coordinated, hexagonal wurtzite structure (ZnO) to six-fold coordinated, cubic rocksalt structure (MgO). It is found that both phonon mode frequencies and dielectric constants change abruptly upon phase transition, which is assigned to the change of coordination number. The change of dielectric constants can be related to the change of electronic properties, for instance, the exciton binding energy. In a simple approach, the exciton binding energy depends on the reduced exciton mass and the static dielectric constant. By comparison with experimental values of the exciton binding energies it is found that the reduced exciton mass must increase by a factor of about two upon face transition from wurtzite to rocksalt structure.

Boron-doped zinc oxide (ZnO) films deposited by Low-Pressure Chemical Vapor Deposition (LPCVD) technique are used as Transparent Conductive Oxide (TCO) to contact thin-film silicon solar cells. In this paper, the effect of boron introduced as dopant during ZnO formation is studied. These films are highly transparent in the visible range, whereas in the near infrared region their transmittance decreases with the increase of boron content due to free carrier absorption (FCA). A shifting of the fondamental band gap is also observed. The resistivity decreases of about one order of magnitude with the increase of the doping ratio ([B2H6]/[DEZ]) from 0 to 2. This resistivity drop is mainly due to an increase of the free carrier concentration. In low doped samples, Hall mobility increases with grain size, whereas it shows no grain size dependence in highly doped layers. This suggest that the scattering by grain-boundary is the main limiting factor for transport in low doped ZnO samples, whereas in highly doped ZnO films transport is controlled by the ionized impurity scattering within the grains.

Ba0.3Sr0.7TiO3 (BST) thin film composite structures were fabricated by means of a selective epitaxial growth process. The epitaxial growth of BST on SrRuO3 electrode surface was selectively achieved at 450∼485°C using a prepatterned ultra-thin amorphous BST layer that locally prevented crystallization. This self build-up mechanism resulted in a columnar composite structure, where epitaxial and amorphous BST columns are electrically connected in parallel. The epitaxial BST showed a high permittivity and a high tunability, whereas the amorphous BST showed a significantly lower permittivity and a very weak tunable behavior. The effective permittivity of the composite capacitors decreased linearly upon increasing the amorphous BST concentration q, while the tunability stayed fairly unchanged until q reached 70%, which agrees with the theoretical ferroelectric/dielectric parallel composite model. The results also give indirect evidence of a good separation between both BST phases.

Sm2−xCexCuO4 (SCCO) is well known as an n-type superconductor with large physical anisotropies. In order to enhance the thermoelectric conversion performance, we have prepared the SCCO epitaxial films and controlled a crystallographic orientation, a carrier concentration and an introduction of nano-structures. The SCCO films and nano-structures consisting of CeO2 were fabricated using pulsed laser deposition method on SrTiO3 single crystalline substrates. Due to the orientation control and the optimization of carrier concentration, a low resistivity and a high Seebeck coefficient were achieved, and a power factor (PF) reached 1.14×10−3 W/mK2 at 323 K in the SCCO film with x × = 0.02. In addition, we measured the nano-structural effect on the PF of SCCO films. As a result, the PF showed a maximum in the film on a certain shape of the nano-structures. We speculate that the low resistivity was achieved by a formation of high Ce concentration layer near the interface between film and nano-structure.

On base of the structural characteristics of near-surface regions of a SrTiO3 (001) (STO (001)) single-crystal plate revealed by means of wide-angle X-ray scattering (WAXS), X-ray fluorescence spectroscopy and high-resolution transmission electron microscopy, structural changes in the STO (001) single-crystal plate under the influence of an external electric field at room temperature can be described as the tunable and reversible formation of Ruddlesden-Popper-phases of the quasi-binary system SrO-TiO2. The WAXS behavior implies the use of the reversible phase-transition for adaptive X-ray optics.

An Electrochromic window (ECW) is a strong candidate for an optical shutter. An ECW is composed of the conductive polymer as a working electrode and V2O5 as a counter electrode. The ECW technology switches between colored and bleached stages. In this paper the modification of a V2O5 thin film as a counter electrode is studied to increase contrast ratio of ECWs by adding TiO2 into V2O5. The dependence of the intercalation properties and transmissivity of V2O5-TiO2 composite films on various chemical compositions, a preparation and characterization of the films for use as a transparent ion storage layer in organic ECWs are focused on in this paper. A V2O5-TiO2 composite film was synthesized with sol-gel electrophoresis deposition method. Indium Tin Oxide (ITO) coated glass was used as an electrically conductive and transparent substrate. A V2O5-TiO2 composite film with V/Ti ratio of 70/30 in the reduced state showed 6 to 13% improvement of transmissivity between 380 nm and 800 nm wavelengths as compared to a V2O5 thin film in the same state. Li+ intercalation rate was also observed to be higher. The composite film exhibited twice of capacitance than that of the V2O5 film. An ECW with the composite film exhibited 6% higher contrast ratio than that with the V2O5 film. The contrast ratio of the ECW, measured as Δ%T, was equal to 56%, and ranged from 2% to 58% between the colored and bleached state measured at 580 nm wavelength. The color change response speed was also faster, i.e., only two seconds between fully colored and bleached stages.

Key words: electrochromic window (ECW), V2O5-TiO2 composite film, contrast ratio, transmissivity, Li+ intercalation rate

Transparent conducting oxides (TCOs) have recently attracted considerable attention due to their potential in making "invisible electronic circuits". Among different TCOs, ZnO is probably one of the most promising candidates due to its desirable optical and electrical properties. In the transistor, metal and metal-dielectric in general are used as the gate on the active channel layer to control the flow of carriers. In order to obtain high mobility, the interface between the gate and ZnO must be well controlled so that the unwanted surface recombination can be minimized. Although studies of metal/ZnO have been well documented, only a few are seen on metal/dielectric/ZnO. Here, we report a systematic study on AlOx/ZnO and MgOx/ZnO interfaces for the potential use on transistor. From previous optical measurements, both the photoluminescence (PL) and cathodoluminescence (CL) show that the cap layers improves the emission characteristics of ZnO by enhancing the band-edge emission while at the same time reducing the unwanted deep-level emissions [K.C. Hui, H.C. Ong, P.F. Lee, J.Y. Dai, Appl. Phys. Lett. 86, 152116 (2005)]. On the contrary, in this study, we find post-thermal annealing of AlOx/ZnO and MgOx/ZnO gradually degrades the emission as well as charge transport properties, which indicates defects evolve upon annealing. By using secondary ion mass spectroscopy (SIMS), we elucidate out-diffusion of Zn into the oxide layer is the root cause of degrading the optical and electrical properties of oxide/ZnO.

PLZT 9.5/65/35 ceramic films were prepared from the sol-gel solutions containing the stress-relaxing agent of polyvinylpyrrolidone(PVP) with the molecular weight of 40000, 360000 and 630000 (abbreviated as PVP40, PVP360 and PVP630) respectively. It is found that PVP40 can increase the critical thickness of the PLZT films to 0.22μm(compared with the critical thickness of 0.077μm in case of without PVP) and PVP360 and PVP630 can increase the critical thickness up to 0.49μm and 0.93μm individually. With the molecular weight of PVP increasing, the perovskite formation in the PLZT films was improved but the morphology of the films tended to be nano-porous. The films modified by PVP360 can be densified by optimizing the heat treatment conditions. When pyrolyzed at 600°C and then annealed at 700°C, the one-coating films with the thickness of 0.5μm were dense and exhibited a very slim hysteresis loop with the remnant polarization of 5.96×10−4μC/cm2 and coercive field of 21.51kV/cm, and a transmittance of around 90% and above in the wavelength of 450nm∼900nm.

The electrical properties of single Pt (30 nm) and Pt (30 nm)/Ni (30nm)/Au(50nm) multilayer contacts on moderately doped p-ZnO (Na = 5.0 × 1017 /−3) were investigated. Although linear current-voltage characteristics were observed for all samples, a sample that was annealed for 1 min at a temperature above 500 °C resulted in an ohmic contact with good characteristics. The best ohmic contact to p-type ZnO was obtained using a Pt/Ni/Au multilayer contact that was annealed at 600 °C for 1 min under a N2 ambient, showing a specific contact resistance Rc of 1.97 × 10−5 Ω cm2. The fundamental mechanisms for the lower contact resistivity of Pt/Ni/Au contacts are discussed based on glancing angle x-ray diffraction results and Auger depth profile analysis of the multilayer alloying process. Furthermore, we fabricated a ZnO p-n homojunction using Pt/Ni/Au and Ti/Au as the p-type and n-type ohmic contact metal, respectively. The threshold voltage was determined to be about 3.7 V, comparable to the bandgap energy of ZnO.

Perovskite oxide cobaltites with composition La0.4Sr0.6Co0.8Fe0.2O3 have been prepared by an acetic acid-based gel route. Then, cathodes were deposited onto porous ceramic substrates, like the usual electrolytes Cerium Gadolinium Oxide (CGO), by spray, spin coating and dip-coating. The structure and morphology of the layers were characterized by XRD and SEM, respectively. Electrical properties are characterized by complex impedance measurements. Finally, the correlation between structural characteristics and electrical properties is discussed.

Reproducible nanoscale surface lithography have been produced on La00.66Ba0.33MnO3 thin films using Atomic Force Microscopy. Using an anodic oxidation technique, structures were produced using both positive tip bias voltages as well as negative tip voltages. The electric field produced by applying a positive tip bias acts to reduce the region near the surface, whereas negative tip bias causes an oxidation reaction. Using a positive tip bias, stable structures were consistently achieved which demonstrated a linear dependence of height and width on tip voltage and writing speed. Heights ranged from 5 – 50 nm and widths from 400 – 2000 nm. Negative bias voltages produced a rapid oxidation of the surface, resulting in uncontrollable writing. After etching with a 50% HCL solution it was found that controlled writing was possible with negative bias voltages.

We are developing Colossal Magnetoresistive (CMR) manganite thin film bolometric sensors to be employed as total energy detectors for beam diagnostics of the Linear Coherent Light Source (LCLS) Free Electron Laser (FEL) (at the Stanford Linear Accelerator). LCLS is an ultra bright, ultra short coherent x-ray source whose peak brightness will exceed that of third generation x-ray sources by about ten orders of magnitude and average brightness by three orders of magnitudes. It is expected to produce 1012 x-rays per 200 fs pulse with a repeat frequency of 120 Hz through self-amplified stimulated emission. In characterizing the beam, it will be necessary to measure the total energy of the FEL pulse. The Advanced Detector Group at Lawrence Livermore Laboratory has developed a scheme for FEL total energy measurements based on bolometric detection and are collaborating with Towson University to implement such a detector using CMR manganite thin films. Here we discuss the basic scheme, results of simulations of the thermal response and the materials development efforts towards fabricating the thin film detectors.

A series of highly near-infrared (NIR) transparent In2O3 thin films has been grown by ion-assisted deposition (IAD) at room temperature, and their optical and electrical properties characterized. The NIR transparency and the plasma edge can be engineered through control of the film deposition conditions. The as-deposited In2O3 thin films were employed as transparent electrodes for direct electro-optic (EO) characterization measurements via the Teng-Man technique. Using LiNbO3 as the standard, the relationship between the degree of electrode NIR transparency and Teng-Man EO measurement accuracy was evaluated. It is found that In2O3 electrodes can be tailored to be highly NIR transparent, thus providing more accurate Teng-Man EO coefficient quantification than ITO (tin-doped indium oxide). In addition, the EO coefficients of stilbazolium-based self-assembled superlattice (SAS) thin films were directly determined for the first time by the Teng-Man technique using an optimized In2O3 electrode. EO coefficients r33 of 42.2, 13.1, and 6.4 pm/V are obtained at 633, 1064, and 1310 nm, respectively.