Comprehensive studies were done on the growth and characterization of TiNb2O7 (TNO) complex oxide thin films by pulsed laser deposition for the first time. The TNO thin films were successfully grown on Pt(200)/TiO2/SiO2/Si(100) substrates. The structure, surface morphology and chemical properties of as-grown thin films were studied as function of deposition temperature, pressure and laser fluence. The GIXRD and HRTEM analyses revealed that the as-grown TNO films were in the monoclinic crystal structure and independent of laser fluence. The HAADF STEM elemental mapping confirms the uniform composition of Ti, Nb and O in TNO thin films. The atomic force microscopy and field emission scanning microscopy shows that, the surface morphology and microstructure of TNO films varied significantly with respect to experimental conditions. The X-ray photoelectron spectroscopy quantitative results indicated that the binding energies of Ti and Nb elements shifted towards right with increasing oxygen partial pressure. The effects of oxygen partial pressure and laser fluence on as-grown TNO films were studied.

Resistive switching, a reversible change in electrical resistance of a dielectric layer through the application of a voltage bias, has propelled a field of research to form improved non-volatile memory device. Tantalum oxide has been investigated as the dielectric component of resistive switching devices as a leading candidate for a few years. Presented here is a structural and chemical investigation of TaOx devices with 55nm in diameter in the virgin, forming on, and switched off (reset) states for comparison using cross sectional TEM techniques including HRTEM, and EELS to gain further understanding of this material system. The nanodevices imaged in this study were switched below 100µA. Unique features found in this study are in agreement with previous hypotheses made by various researchers based on X-ray fluorescence microscopy of micron-scale devices, indicating a variation in oxygen concentration around the switching area.

The importance of ZnxMg1-xO is increasing day by day because of its wider bandgap than ZnO. This ternary semiconductor finds its application in the fields of optoelectronics, spintronics, superlattices due to its unique blueshifted UV-luminescent property. n- to p-type conduction which is the motive of the project can be achieved with increasing Mg content in ZnMgO. The optical characteristics of the nitrogen doped ZnxMg1-xO (x=0.85) grown on 2 inch Si <100>wafer by RF sputtering are studied and analyzed thoroughly using low temperature (15K) photoluminescence measurements. Nitrogen implantation was carried out by Plasma immersion Ion Implantation technique on the sample. Rapid Thermal Process was employed to remove defects resulting from implantation. The samples were annealed at 700°C, 800°C, 900°C, and 1000o C for 10 seconds in an oxygen ambient. Photoluminescence (PL) measurements were performed at low temperature (15K) which exhibited acceptor-bound-exciton peak (A°X) and donor-bound-acceptor pair (DAP) at 3.336 eV and 3.236 eV respectively. At 3.364 eV, S peak was found for the sample annealed at 800°C after implantation. This peak was attributed to the existence of ZnO-like composition. Localized and de-localized exciton peaks were found around 3.42 and 3.45 eV respectively. This result is very important because though dominant acceptor peak was not found but proper optimization of the parameters can lead to p-type ZnMgO which is the main motive of this project.

Investigation into the phenomenon of resistive switching, a reversible change in electrical resistance by the application of a voltage bias, has given rise to the device fabrication, DC electrical testing, and cross sectional TEM/EELS characterization of nanoscale resistive switching devices. Typically, resistive switching devices are composed of a thin oxide layer between two conductive electrodes where applied bias can alter the resistance states. In a cross-bar array, nonlinearity of device I-V relation is a highly desirable characteristic that helps to mitigate the sneak path current leakage issue. Negative differential resistance (NDR) switching behavior offers such nonlinearity and has been observed in TaOx nanoscale devices utilizing certain electrode materials. To investigate this phenomenon, nanodevices were fabricated by sputtering TaOx onto TiN nanovias capped Nb electrodes. Cross sectional TEM/EELS were performed to reveal the physical and chemical changes in these devices to explore possible origins of nonlinear behavior when these top electrode materials are utilized with TaOx films.

Astronomical telescopes continue to demand high-endurance high-reflectivity silver mirrors that can withstand years of exposure in earth-based observatory environments. The University of California Observatories Astronomical Coatings Lab has undertaken development of protected silver coatings suitable for telescope mirrors that maintain high reflectivity at wavelengths from 340 nm through the mid-infrared spectrum. We present promising results of enhanced corrosion barriers using plasma-enhanced atomic layer deposition (PEALD) of aluminum oxide (AlOx) as a top barrier layer. Novel coating recipes developed with ion-assisted electron beam deposition (IAEBD) of materials including yttrium fluoride and oxides of yttrium, tantalum, and silicon are used to compare the endurance of physical vapor deposition-grown barriers with PEALD-grown barriers of similar thickness. Samples of these mirror coatings were covered with conformal layers of AlOx deposited by PEALD using trimethylaluminum as a metal precursor and plasma-activated oxygen as an oxidant gas. Samples of coating recipes with and without PEALD oxide undergo aggressive high temperature/high humidity (HTHH) environmental testing in which samples are exposed to an environment of 80% humidity at 80°C for ten days in a simple test set-up. HTHH testing show visible results suggesting that the PEALD oxide offers enhanced robust protection against chemical corrosion and moisture from an accelerated aging environment. Mirror samples are further characterized by reflectivity/absorption before and after deposition of oxide coatings. AlOx is suitable for many applications and has been the initial material choice for this study.

Tin oxide is of great interest due to their potential technological applications, such as: gas sensors, energy conversion, catalysts and others. Appropriate doping can further enhance the conductivity of the SnO2 material with little loss of transparency. Isolated tin iron oxide fibers (Sn1-xFexO2-δ) with x (molar %) = 0, 2, 4, 6, 8 and 10 were prepared by the electrospinning technique. Anhydrous SnCl4, FeCl3·6H2O, different alcohols, chloroform and a polymer (PEO) were used as precursor materials. Appropriate mixture of these reagents defines the deposition solution. The samples were deposited on glass substrates and annealed at 500o C. The fibers are characterized by scanning electron microscopy (SEM), impedance spectroscopy and temperature dependence current-voltage measurements. The fibers with diameters between 2 to 12 microns were used for sensorial purpose. Thus, water vapor sensor responses were also measured and the experimental results are tested using the Freundlich isotherms model.

ZnO nanorods were synthesized by recrystallization of ZnO thin films during multiannealing process. It was found that the obtained ZnO nanorods showed well-controlled grown direction. The periodical oxygen introducing between reducing annealing processes was effective to help on the oxidization reaction, result in the ZnO nanorods growth significantly. With controlling the annealing parameters, the morphologies of ZnO nanorods could be also controlled. The low-temperature (less than 420°C) initial reducing annealing process contributed to control the density of ZnO nanorods. The multi-annealing processes could reduce the ZnO thin film to produce ZnO nanorods efficiently. The structural, optical and electrical properties of the ZnO nanorods were investigated. Finally, the obtained ZnO nanorods used as photoelectrodes demonstrated in a dye-sensitized solar cell, the overall conversion efficiency of 3.65% was achieved.

A high gain ZnO nanowire (NW) based photodetector was fabricated, which was sensitive to photoexcitation at or below 370 nm corresponding to the band-edge of ZnO. At an incident wavelength of 370 nm and a bias field of 5 kV/cm, the maximum responsivity was over 105 A/W corresponding to an extremely high photoconductive gain of the order of 106. Through this work we provide experimental evidence of the role of surface and defects in carrier dynamics, resulting in enhanced photoresponse. Using intensity and temperature dependence of the rise and decay rates of photocurrent, we present a detailed analysis that provides an estimate of the activation energies of carrier trapping mechanisms.

Zinc oxide thin films prepared by sol-gel and doped with different aluminum percentages were deposited by spray-pyrolysis deposition techniques on FTO and ITO substrates. The films were applied as the sensitive layer of pH-sensors EGFET devices. ZnO:Al films on FTO substrates shows a decrease in sensor quality with the dopant percentage increase. The opposite occurs when the substrate was ITO. The best quality film to be used as pH-sensor on FTO substrates was the ZnO:Al (3%) with 29 mV/pH sensitivity value and linear adjust of 0.99. For ITO substrates the best quality was achieved for ZnO:Al (10%), with sensitivity about 30 mV/pH and 0.99 linear adjust.

In this study, the growth of LbL film of polyallylamine hydrochloride (PAH), polyvinyl sulfonic acid (PVS) and glucose oxidase (GOx) in porous anodic alumina substrate (PAA) was accompanied by total reflectance technique. The PAA substrate was synthesized with aluminum anodisation and sample morphology was characterized by scanning electron microscopy (SEM).

The paper presents complex research of the structure and electrophysical properties of thin films on the basis of Cr2O3, V2O5 and SiO2 oxides compounds. The paper studies binary compounds films of Cr2O3 -V2O5 and Cr2O3 - V2O5 -SiO2 films. The method of electron-beam evaporation is used for the films deposition; glass is used as the substrate. The films structure is studied by the methods of slow electron diffraction, infrared spectroscopy, and electron paramagnetic resonance. The films composition is determined by the X-ray microanalysis.

In the course of studies the following regularities have been established:

- dependence of the films structure on their composition;

- dependence of electrophysical films properties on the their composition;

- dependence of volt-ampere characteristics on the films composition (memory effect);

- high film stability to the effect of electron flow and radiation in the discharge plasma.

At the present moment, zinc oxide is primarily being used as an electronic material for low-field thin-film transistor and transparent conducting oxide device applications. In this paper, we present some recent results on the steady-state electron transport within zinc oxide suggesting that this material may also be considered as an alternative material to gallium nitride for high-power and high-frequency electron device applications. The expected device performance that may be obtained from zinc oxide-based devices is then projected and contrasted with that expected from gallium nitride-based devices. It is shown that zinc oxide-based devices have a slight advantage when compared with the case of gallium nitride.

The effects of WO3 doping in 4,4’-bis-9-carbozyl biphenyl (CBP) were studied through detailed electrical device characterization. A series of hole-only devices have been fabricated, where the doping level was varied from 10-40mol% and the doped CBP thickness was varied from 5-40 nm. It was found that, to achieve effective doping for improved hole injection and transport, the doping level should be greater than 20mol% and the doped layer should be at least 10 nm thick. It was also found that an energy barrier exists at the doped and undoped CBP interface, resulting in an additional voltage drop. This finding was explained by a large downward shift of the Fermi level in WO3-doped CBP, which causes band bending and depletion at the interface. Finally, simplified green phosphorescent organic light-emitting diodes (OLEDs) with CBP as the hole transport and host material were fabricated. With a WO3-doped hole transport layer, the OLEDs attained brightness above 105 cd/m2 at 20 mA/cm2, and exhibited an improved reliability under constant-current stressing as compared to undoped OLEDs.

VO2 is one of the very few natural materials that can be used to modulate terahertz (THz) radiations. A 100-nm thick VO2, when in its metallic phase, has a charge density of more than ∼ 1015 cm-2 which will strongly reflect and absorb the THz radiation; while in its insulator state, the charge density is lowered by several orders of magnitude to be THz transparent. Therefore, exploiting the metal-insulator transition of VO2 is a potential approach to modulate or even switch THz radiation for THz optics. Here we report that VO2 epitaxial thin films on sapphire substrate exhibits 85% amplitude modulation depth in a broad bandwidth, while this value can be improved to 95% when VO2 film is coated on both sides of a substrate. We further demonstrate that with wafer bonding, 4-layered VO2 thin films exhibit a transmittance as low as -20 dB to -30 dB at their metallic state, enough for switching applications. We also report our proof-of-concept demonstration of THz spatial light modulator that exhibits amplitude modulation as large as 96%, -30 dB pixel-to-pixel crosstalk, and a broad THz bandwidth.

We have investigated the effect of oxygen pressure during growth (PO2) on the electronic and magnetic properties of PrAlO3 films grown on TiO2-terminated SrTiO3 substrates. The films are smooth, with flat terraces. Resistivity measurements show an increase in the sheet resistance as PO2 is increased from 10–3 to 10–4 torr, with an usual peak as a function of temperature for the sample grown in higher oxygen pressure. We measured a moderate positive magnetoresistance (MR) at low magnetic fields that evolves into a larger negative MR at high fields, for both PO2 samples. Hall effect data exhibit a complex temperature dependence that suggests a compensated carrier density. We observe behavior consistent with two different types of carriers at each of the two different interfaces.

Morphological and crystallographic characteristics of HfOx with different oxygen concentrations (0 ≤ x ≤ 2.5) and thicknesses (18 nm ≤ t ≤ 310 nm) were analyzed in this work before and after thermal annealing at 700°C in N2 atmosphere for 1h. The morphology of the as-deposited, low oxygen concentration films (t = 100 nm) is formed by a well-defined granular structure with grains around 20 nm in diameter. For higher oxygen concentration, the roughness increases, as a consequence of a very porous surface morphology. At the same time, the crystallographic structure changes from HCP with a {0002} preferred orientation to an amorphous structure as oxygen concentration increases. As the thickness of the HfO2 films increases, we also observed the formation of a high surface porosity, with pore diameter ranging from 80 nm to 120 nm. The changes observed in morphology and crystallinity of the films, as we increase the concentration of contaminants, occurs because of the lowering of the adatoms surface diffusion, which prevents them from reaching lower energy points during the formation of the microstructure of the films. Furthermore, this lowered surface diffusion favors the process of grain renucleation, which leads to roughness increasing, and to an enhancement of the formation of porous surfaces. After annealing, all films exhibit the monoclinic crystallographic phase associated with HfO2. Surface morphology of the films is consistent with a polycrystalline structure with grain diameters varying between 10 nm and 200 nm. As their size increases, the grains become very faceted, a finding consistent with the improvement in film crystallinity. Our results suggest that long-time annealing promotes the diffusion of oxygen from the SiO2-Hf interface to the film, compensating any O2 deficit in the film. Formation of the monoclinic phase is also favored by the improvement in the film stoichiometry promoted by thermal treatment. Also, the critical size of the nuclei, associated with a grain growth in a particular crystallographic orientation, decreases as a consequence of the high temperature during thermal annealing. Therefore, formation of faceted grains and increasing of surface roughness are favored in thicker films.

ZnO thin films were deposited using the DC pulsed magnetron sputtering technique to study how composition and structure influences their magnetic properties. Low sputtering powers and high substrate temperatures were used to increase adatom mobility during deposition, resulting in increased crystallite size and reduced residual stress in the films. Another set of ZnO films were Mn-doped using a second magnetron gun and the amount of doping was changed by controlling the RF sputtering power. For these films, the crystallite size increased with the amount of Mn. The magnetic properties of these materials were counterintuitive; not intentionally doped ZnO showed the highest magnetization and magnetization decreased with increasing Mn concentration.

Thermoelectric (TE) materials have gained renewed interests in last decades for both power generation and energy conservation from waste-heat harvesting. Research in the discovery of best TE materials such as, bulk materials, complex structures, and low dimensional play crucial role to achieve high efficiency TE materials. Wide bandgap materials like ZnO can be promising candidate for high efficiency TE power generation owing to its low-cost, nontoxicity, and stability at high temperatures. In this paper, room temperature TE properties of thin film ZnO grown by metal organic vapor deposition (MOCVD) are reported. TE properties of thin film GaN are also studied as reference to that of thin film ZnO. Moreover, high resolution x-ray diffraction (HRXRD), room temperature photoluminescence (PL) with deep ultraviolet (DUV) spectroscopy (excitation at 248nm), hall effect, and thermal gradient methods have been employed to investigate the effect of structural, optical, electrical, and thermal properties of the samples, respectively. The effect of doping concentrations and structural defects on Seebeck coefficients of thin film ZnO are systematically studied and discussed in this work.

Atomic layer deposition (ALD) was used to deposit a laminate structure of alternating SiO2 and TiO2 monolayers onto a Si wafer. The resulting samples were analyzed in detail by X-ray photoelectron spectroscopy (XPS) revealing a distinct O 1s signature due to the presence of Si-O-Ti species. These findings are in good agreement with those reported for thin ALD films of TiO2 grown on SiO2.

Ca2MnO4 nanoparticles were prepared by the Pechini method and acid treated to extract Ca2+ ions. Structural, morphological and spectroscopic analyses by XRD, SEM/EDX, TEM/EDS and Raman revealed the formation of an amorphous outer layer at the particles surface with a preserved inner crystalline bulk. Thanks to the outer layer, which is electrochemically active, the acid-treated compounds showed capacity up to 150 Ah/kg. The crystalline bulk improved cycling stability, allowing reaching capacity retention up to 70% after 30 cycles.