To better understand the response of oxygen vacancy concentration to applied potential, the lattice parameter of pulsed laser deposited La0.6Sr0.4Co1-xFexO3-δ thin films was monitored using in situ X-ray diffraction. We demonstrate that the chemical expansion under applied potential depends on the cathode morphology, which determines the contribution of different reaction pathways. We investigated applied potential dependent lattice expansion on La0.6Sr0.4Co1-xFexO3-δ with 3 different Co:Fe ratios in an attempt to connect bulk chemical expansion data to thin films. We find that the chemical expansion trends in thin films are different than expected from bulk data.

The electrodeposition of hydrated ruthenium dioxide (hRuO2) on Ti interdigitated current collectors deposited onto silicon substrate has been investigated with the objective of preparing a high capacitance and high power micro-supercapacitor (µ-SC) device. Ti current collectors were synthesised by typical photolithography processes, and hRuO2 thin films were electrodeposited from ruthenium chloride precursors. Device specific capacitances exceeding 20 mF·cm−2 were obtained, and more than 80 % of that value is retained even at scan rate as high as 1 V∙s−1 in 0.5 M H2SO4. The mean specific power per active surface area of the device is 368 mW·cm−2. The device is stable and 90% of the initial capacity is retained after 105 cycles (1 V potential window). The characteristic response time of the hRuO2 µ-SC is 250 ms, with low ESR (0.61 Ω cm−2) and EDR (0.07 Ω cm−2) values. All these characteristics demonstrate the potential of such µ-SC devices to be part of the next generation of micro-supercapacitors.

Non-stoichiometric and impurity doped titanium dioxide materials are good candidates for use in high temperature thermoelectric devices. Nanolayers of non-stoichiometric (TiO2-x) thin films were deposited on Al-foil by atomic layer deposition growth method. X-ray diffraction experiments showed anatase phase for these nanolayers. This crystal structure was maintained even after an annealing treatment of 600 °C for 60 minutes under an O2 pressure of ∼ 10 psi. This investigation presents for the first time how Al-foil can be functionalized by manipulating the Seebeck coefficient of these TiO2-x nanolayers.

In our work on laser scribing CdTe solar cells we have found what appears to be an unpublished laser material interaction that allows precise laser etching of SnO2 films to an arbitrary thickness with high uniformity. This precise and efficient laser etching mechanism allows arbitrary reduction of the film thickness in a controlled manner on the scale of tens of nm. In addition to the fine depth selection, we find that there develops a pulse duration dependent microstructure on the surface. This micro microstructure results in a strong diffraction effect in the visible portion of the spectrum. In this work we propose a physical mechanism behind this novel depth selective laser interaction as well as the resultant micro-structure. Finally we demonstrate and propose some possible applications for this process.

KNbO3 thick films were deposited on (100)c SrRuO3//(100)SrTiO3 substrates at 240 °C for 3 h by hydrothermal method. Film thickness increased linearly with increasing the deposition number of times and 130 μm thickness was achieved by the 6 time deposition. XRD analysis showed the growth of epitaxial orthorhombic films with the mixture orientation of (100), (010) and (001). Cross-sectional SEM observation showed that the 130 μm-thick film was dense and no obvious voids inside the film. In addition, the crystal structure change along film thickness direction was not detected from the cross-sectional Raman spectral observation.

Zinc Oxide (ZnO) Thin-Film Transistors (TFTs) using Aluminum (Al) and Aluminum-doped zinc Oxide (AZO) as Source-Drain (S-D) contacts are reported. The fabrication process was carried out using five photolithography steps with a maximum processing temperature of 100 °C, which makes the process compatible with flexible/transparent applications. The AZO and ZnO films were deposited using Pulsed Laser Deposition (PLD). Aluminum was deposited using ebeam. The devices showed mobilities >10 cm2/V-s, threshold voltage in the range of 7 V and On/Off current ratios >105. The resistance analysis showed that AZO is a better contact with lower contact resistance as identified in the TFTs. The AZO and ZnO stacks characterized by UV-V shows an optical transmission >80 %.

The metallic nickel (Ni) deposited on an n-Si substrate with resistivity of 4 – 6 Ω∙cm was oxidized by the ultra-violet (UV) oxidation technique to form a p-NiO/n-Si heterojunction diode. The rectifying current-voltage (I-V) characteristic confirmed formation of a pn junction. The capacitance-voltage (C-V) characteristic further identified an abrupt p+n junction between NiO and n-Si. The photocurrent increased with the increased wavelength of laser under illumination of the diode. The voltage-dependent photocurrent suggests that the carriers generated in the depletion region of Si was effectively collected but not outside the depletion region. A low diffusion length of holes was attributed to Ni diffusion in Si caused by the substrate heating during the UV oxidation.

The surface structure of oxide materials may be the limiting factor in controlling switching properties at interfaces. Here we investigate and correlate the surface structure and electronic properties of BaTiO3 substrates. By using low energy electron diffraction and scanning tunneling microscopy we are able to identify surface reconstructions based on annealing treatments. We then investigate the effect of contact size on the transport properties on oxide surfaces utilizing atomic force microscopy. Our results show the critical importance of controlling surface structure to optimize electronic properties at oxide interfaces.

Mesoporous TiO2 nanoparticle assemblies have been synthesized via a surfactant-assisted aggregating process. The products feature a three-dimensional network of interconnected anatase-TiO2 NPs with large internal BET surface area (ca. 142–152 m2g-1) and uniform pores (ca. 7–8 nm). Preliminary catalytic experiments indicated that these mesophases exhibit excellent catalytic activity in UV-visible light oxidation of 1-phenylethanol with molecular oxygen.

VO2films were deposited on sapphire, ITO glass and 200 nm thick silicon nitride membranes by Pulsed Laser Deposition (PLD). The electrical and optical properties have been investigated. Joule heating devices fabricated on silicon nitride membranes switches from semiconductor phase to metal phase by applying a constant voltage across two metal contacts. Compared to the devices fabricated on the normal substrates, such as sapphire, silicon or glasses, the switching speed of the devices on membrane is an order of magnitude faster. Decreasing the area and thickness of VO2 on top of thinner membranes allows kHz bandwidth to be achieved.

SnO2 based sensor structures prepared by rf magnetron sputtering technique have been studied for detecting H2 gas. Pd catalyst was integrated onto the SnO2 thin film in the form of clusters and nano-particles to obtain enhanced sensing response characteristics. The prepared sensor structures have been studied over a temperature range of 50-250°C for sensing response towards 500 ppm H2 gas. The sensor with Pd catalyst dispersed in the form of nanoparticles was found to exhibit an enhanced sensing response of 1.9×103 at a relatively low operating temperature of 150°C with a fast response time of 2 s and recovery time of 65 s towards 500 ppm H2 gas. The origin of enhanced sensing response is identified in the light of the enhanced spill over of H2 gas molecules on the uncovered surface of SnO2 thin film.

Commercially available tenorite (CuO) nanoparticles (NPs) were investigated in particular with respect to their suitability for photovoltaic applications. NPs with a diameter of about 30 nm were step wise annealed up to 1000°C in nitrogen atmosphere. The influence of the annealing treatment on the structural and electronic properties was investigated by Raman, photoluminescence (PL) and photothermal deflection spectroscopy (PDS) as well as X-ray diffraction measurements. Size, shape, and phase of the untreated NPs are analyzed by TEM measurements. The PL and PDS results show a strong increase of the tenorite band edge emission at about 1.3 eV accompanied by a decreasing sub gap absorption with increasing annealing temperature up to 700°C. According to literature, a phase transition from tenorite to cuprite (Cu2O) was expected and observed after annealing at 800°C. Strong cuprite band edge emission at about 2 eV accompanied by very weak defect and possibly tenorite band edge emission was found for samples annealed at 800°C and 1000°C.

Solar water splitting has shown promise as a source of environmentally friendly hydrogen fuel. Understanding the interactions between semiconductor surfaces and water is essential to improve conversion efficiencies of water splitting systems. TiO2 has been widely adopted as a reference material and rutile surfaces have been studied experimentally and theoretically. Scanning Tunneling Microscopy (STM) is commonly used to study surfaces, as it probes the atomic and electronic structure of the surface layer. A systematic and transferable method to simulate constant current STM images using local atomic basis set methods is reported. This consists of adding more diffuse p and d functions to the basis sets of surface O and Ti atoms, in order to describe the long range tails of the conduction and valence bands (and, thus, the vacuum above the surface). The rutile TiO2 (110) surface is considered as a case study.

We have deposited porous ZnO films on aluminum-doped ZnO (ZnO/AZO) and fluorine-doped tin oxide (ZnO/FTO) transparent substrates, and annealed both in air at 500°C. X-ray diffraction measurements of the nanoporous ZnO films after heat treatment showed that, ZnO/AZO film exhibited a dominant (002) diffraction while the ZnO/FTO showed mixed diffraction peaks with the (100) and (101) being dominant. Dye-sensitized solar cells (DSC) based on the sensitization of the porous ZnO films on AZO and FTO substrates with an indoline dye were constructed. The photoaction spectrum, which is a measure of the degree of sunlight harvesting, was broad and higher in the ZnO/AZO DSC than that of the ZnO/FTO DSC. Conversion efficiency of 7.3 % was obtained for the ZnO/AZO DSC while 4.5 % was recorded for the ZnO/FTO. The superior photovoltaic performance of the ZnO/AZO DSC is attributed to better ZnO film orientation after thermal treatment and the higher sunlight harvesting.

Oblique angle deposition (OAD) is a self-organizing physical vapor deposition (PVD) technique that has been used to grow sculpted 3D nanostructures including helices, slanted rods, and zigzag structures, and other shapes. OAD structures can be fabricated from virtually any material that can be deposited using PVD including: polymers, metals, semiconductors, oxides, and nitrides. The control over the nano-scale structural anisotropy of these materials allows one to tailor their electrical, magnetic, mechanical, crystalline, and optical properties. Through the careful design of the OAD structure and material selection this technique can be used to create photonic materials (1D, 2D, and 3D) with unique properties. We will discuss ongoing work using OAD to develop oxide thin film interference filters that can withstand extreme temperatures (800-1000° C) at mTorr vacuum levels, which are being developed for thermal photovoltaic applications.