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At least 1,333 records · Page 74
All sourcesNASA NTRSDOE OSTI
DOE OSTI2018

Selective enhancement of Selényi rings induced by the cross-correlation between the interfaces of a two-dimensional randomly rough dielectric film

By the use of both perturbative and non-perturbative solutions of the reduced Rayleigh equation, we present a detailed study of the scattering of light from two-dimensional weakly rough dielectric films. It is shown that for several rough film configurations, Selényi interference rings exist in the diffusely scattered light. For film systems supported by dielectric substrates where only one of the two interfaces of the film is weakly rough and the other planar, Selényi interference rings are observed at angular positions that can be determined from simple phase arguments. For such single-rough-interface films, we find and explain by a single scattering model that the contrast in the interference patterns is better when the top interface of the film (the interface facing the incident light) is rough than when the bottom interface is rough. When both film interfaces are rough, Selényi interference rings exist but a potential cross-correlation of the two rough interfaces of the film can be used to selectively enhance some of the interference rings while others are attenuated and might even disappear. This feature may in principle be used in determining the correlation properties of interfaces of films that otherwise would be difficult to access.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2020

X-ray photoelectron spectroscopy and rotating disk electrode measurements of smooth sputtered Fe-N-C films

Electrocatalysts for the oxygen reduction reaction (ORR) based on complexes of iron and nitrogen in a carbon matrix (Fe-N-C) are a promising alternative to platinum group metal (PGM) based catalysts in polymer electrolyte membrane (PEM) fuel cells. Further improvements of Fe-N-C catalysts would benefit from model thin film studies of activity and stability of catalytic sites, but synthesis of Fe-N-C model thin films is challenging. Here we report on synthesis and characterization of Fe-N-C thin films produced by co-sputtering iron and carbon in a reactive nitrogen atmosphere onto removable glassy carbon rotating disk electrode (RDE) tips. Scanning electron microscopy (SEM) measurements indicate that the Fe-N-C films deposited at high temperature are smoother than the films annealed at high temperature. Electrocatalytic activity measured on the thin Fe-N-C films is greater for both high-temperature samples than for the room-temperature sample. From the analysis of X-ray photoelectron spectroscopy (XPS) data, exposure of the films to high temperatures results in increased graphitization of the carbon with the Fe-N-C films, and increased relative amount of graphitic and hydrogenated nitrogen species. Overall the results of this study demonstrate the feasibility of a thin film model system approach for studying active sites in PGM-free catalysts.

14 SOLAR ENERGY↗
DOE OSTI2022

Irradiation-induced amorphization of UO 2 films prepared by spraying-assisted combustion synthesis

Spraying-assisted combustion synthesis with uranyl nitrate – acetylacetone – 2-methoxyethanol solutions was used to prepare UO 2 films on an aluminum alloy substrate. The tuning of the spraying parameters and annealing temperatures allowed the preparation of UO 2 films with thicknesses varying from 10–300 nm and 5–10 nm UO 2 grain size. High-resolution electron microscopy and X-ray photoelectron spectroscopy showed that increasing the annealing temperature promotes Mg diffusion from the substrate into the films. The incorporation of Mg reduced the overall crystallinity of the films. The irradiation with Ar 2+ ions (1.7 MeV energy and a fluence of 2 × 10 16 ions/cm 2 ) did not degrade the quality of the films. However, the Mg content significantly influenced the irradiation-induced restructuring of the UO 2 films. Irradiated films with low or no Mg content exhibit high crystallinity, and the UO 2 /Al interfacial layer becomes highly porous. Films with higher Mg content are mostly amorphized after irradiation. The origin of irradiation-induced amorphization was related to the formation of Mg y U 1-y O 2±x solid solutions. Chemically complex, pore-free, and amorphous Mg-Al-O film/substrate interfacial layers enable continuous Mg diffusion during irradiation. As a result, the gradual increase in Mg amounts triggers irradiation-induced precipitation of a crystalline MgO-rich phase within the amorphous films.

38 RADIATION CHEMISTRY, RADIOCHEMISTRY, AND NUCLEA↗
DOE OSTI2013

The structural, electrical, and optical properties of hydrogenated chromium-doped CdO films

Cadmium oxide thin films doped with different amounts of chromium and annealed in hydrogen atmosphere have been grown on glass substrates by means of physical vapour deposition (PVD) method. The structural, electrical, and optical properties of the prepared Cr-doped CdO (CdO:Cr–H) films were systematically studied. The structural investigations show that the incorporated Cr ions mainly occupied locations in interstitial positions of CdO lattice. The bandgap engineer by Cr incorporation and hydrogenation were studied. The variations of the electrical parameters of CdO:Cr–H films with Cr incorporation and hydrogenation were investigated. It was established that among the investigated samples, the largest mobility and conductivity were measured with 1.5%:Cr–H film. Therefore, hydrogenated CdO:Cr films can be effectively used in different applications of near infrared-transparent-conducting-oxide (NIR-TCO). - Graphical abstract: Optoelectronic properties of synthesised chromium-doped CdO thin films. It was established that the largest mobility (53.4 cm{sup 2}/V.s) and conductivity (2136.8 S/cm) were measured in 1.5%:Cr–H doped CdO film. Therefore, such films can be effectively used in near infrared-transparent-conducting-oxide (NIR-TCO). - Highlights: • The properties of CdO films annealed in H{sub 2} gas were systematically studied. • Cr{sup 3+} ions most likely occupied interstitial locations in CdO lattice and as donors. • Improvement of conductivity parameters with Cr doping and H annealing. • Bandgap narrowing observed with Cd-doping.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2015

Exfoliation of titanium oxide powder into nanosheets using hydrothermal reaction and its reassembly into flexible papers for thin-film capacitors

We have discovered a methodology to realize the fabrication of flexible metal oxide film using two-dimensional (2D) nanosheets. Atomic scale titanium oxide (TiO{sub x}) nanosheets were exfoliated from bulk TiO{sub x} powder that had a layered structure via the modified Sasaki’s method. The vacuum-assisted filtration generates films with laterally aligned TiO{sub x} nanosheets. The 2D sheet-like structure and hydrophilic nature of TiO{sub x} nanosheets enables the film consisting of TiO{sub x} nanosheets to be bendable. Also, we demonstrate the fabrication of electrochemical capacitors using this film. The mechanically flexible metal oxide film is expected to open up the possibility of fabricating flexible energy storage devices from 2D metal oxide nanosheets. - Graphical abstract: The modified Sasaki’s method, combined process of hydrothermal reaction and bulky ion exchange, enables to obtain TiO{sub x} monolayer nanosheets. The vacuum-assisted filtration generates bendable films with laterally aligned TiO{sub x} nanosheets. Also, we demonstrate the fabrication of electrochemical capacitors using this film. - Highlights: • TiO{sub x} single sheets, a novel 2-dimensional material, were exfoliated from bulk powders via the modified Sasaki’s method. • In our method, the acid treatment of TiO{sub x} bulk powders was simply modified by applying the hydrothermal reaction. • Then, the delamination procedures of large cation exchange were conducted following the method proposed by Sasaki et al. • Reassembly of TiO{sub x} sheets into flexible free-standing films was simply achieved via vacuum assisted filtration method. • TiO{sub x} films were used as a flexible supercapaictor electrode material.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2015

Influence of PbCl{sub 2} content in PbI{sub 2} solution of DMF on the absorption, crystal phase, morphology of lead halide thin films and photovoltaic performance in planar perovskite solar cells

In this paper, the influence of PbCl{sub 2} content in PbI{sub 2} solution of DMF on the absorption, crystal phase and morphology of lead halide thin films was systematically investigated and the photovoltaic performance of the corresponding planar perovskite solar cells was evaluated. The result revealed that the various thickness lead halide thin film with the small sheet-like, porous morphology and low crystallinity can be produced by adding PbCl{sub 2} powder into PbI{sub 2} solution of DMF as a precursor solution. The planar perovskite solar cell based on the 300-nm-thick CH{sub 3}NH{sub 3}PbI{sub 3−x}Cl{sub x} thin film by the precursor solution with the mixture of 0.80 M PbI{sub 2} and 0.20 M PbCl{sub 2} exhibited the optimum photoelectric conversion efficiency of 10.12% along with an open-circuit voltage of 0.93 V, a short-circuit photocurrent density of 15.70 mA cm{sup −2} and a fill factor of 0.69. - Graphical abstract: The figure showed the surface and cross-sectional SEM images of lead halide thin films using the precursor solutions: (a) 0.80 M PbI{sub 2}, (b) 0.80 M PbI{sub 2}+0.20 M PbCl{sub 2}, (c) 0.80 M PbI{sub 2}+0.40 M PbCl{sub 2}, and (d) 0.80 M PbI{sub 2}+0.60 M PbCl{sub 2}. With the increase of the PbCl{sub 2} content in precursor solution, the size of the lead halide nanosheet decreased and the corresponding thin films gradually turned to be porous with low crystallinity. - Highlights: • Influence of PbCl{sub 2} content on absorption, crystal phase and morphology of thin film. • Influence of perovskite film thickness on photovoltaic performance of solar cell. • Lead halide thin film with small sheet-like, porous morphology and low crystallinity. • Planar solar cell with 300 nm-thick perovskite thin film achieved PCE of 10.12%.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2016

A chemical bath deposition route to facet-controlled Ag{sub 3}PO{sub 4} thin films with improved visible light photocatalytic activity

A facile, economic, and reproducible chemical bath deposition (CBD) method is developed for the fabrication of facet-controlled Ag{sub 3}PO{sub 4} thin films with enhanced visible light photocatalytic activity. The fine-control of bath temperature, precursor, complexing agent, substrate, and solution pH is fairly crucial in preparing the facet-selective thin film of Ag{sub 3}PO{sub 4} nanocrystal. The change of precursor from silver nitrate to silver acetate makes possible the tailoring of the crystal shape of Ag{sub 3}PO{sub 4} from cube to rhombic dodecahedron and also the bandgap tuning of the deposited films. The control of [Ag{sup +}]/[phosphate] ratio enables to maximize the loading amount of Ag{sub 3}PO{sub 4} crystals per the unit area of the deposited film. All the fabricated Ag{sub 3}PO{sub 4} thin films show high photocatalytic activity for visible light-induced degradation of organic molecules, which can be optimized by tailoring the crystal shape of the deposited crystals. This CBD method is also useful in preparing the facet-controlled hybrid film of Ag{sub 3}PO{sub 4}–ZnO photocatalyst. The present study clearly demonstrates the usefulness of the present CBD method for fabricating facet-controlled thin films of metal oxosalt and its nanohybrid. - Highlights: • The crystal facet of Ag{sub 3}PO{sub 4} films can be tuned by chemical bath deposition. • The crystal shape of Ag{sub 3}PO{sub 4} is tailorable from cube to rhombic dodecahedron. • Facet-tuned Ag{sub 3}PO{sub 4} film shows enhanced visible light photocatalyst activity.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2016

Aluminum doped nickel oxide thin film with improved electrochromic performance from layered double hydroxides precursor in situ pyrolytic route

Electrochromic materials with unique performance arouse great interest on account of potential application values in smart window, low-power display, automobile anti-glare rearview mirror, and e-papers. In this paper, high-performing Al-doped NiO porous electrochromic film grown on ITO substrate has been prepared via a layered double hydroxides(LDHs) precursor in situ pyrolytic route. The Al{sup 3+} ions distributed homogenously within the NiO matrix can significantly influence the crystallinity of Ni-Al LDH and NiO:Al{sup 3+} films. The electrochromic performance of the films were evaluated by means of UV–vis absorption spectroscopy, cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and chronoamperometry(CA) measurements. In addition, the ratio of Ni{sup 3+}/Ni{sup 2+} also varies with Al content which can lead to different electrochemical performances. Among the as-prepared films, NiO film prepared from Ni-Al (19:1) LDH show the best electrochromic performance with a high transparency of 96%, large optical modulation range (58.4%), fast switching speed (bleaching/coloration times are 1.8/4.2 s, respectively) and excellent durability (30% decrease after 2000 cycles). The improved performance was owed to the synergy of large NiO film specific surface area and porous morphology, as well as Al doping stifled the formation of Ni{sup 3+} making bleached state more pure. This LDHs precursor pyrolytic method is simple, low-cost and environmental benign and is feasible for the preparation of NiO:Al and other Al-doped oxide thin film. - Graphical abstract: The ratio of Ni{sup 3+}/Ni{sup 2+} varies with Al content which can lead to different electrochemical performances. Among the as-prepared films, NiO film prepared from Ni-Al (19:1) LDH show the best electrochromic performance with a high transparency of 96%, large optical modulation range, fast switching speed and excellent durability. Display Omitted.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2017

The role of polymer films on the oxidation of magnetite nanoparticles

A detailed investigation about the role of polymer films on the oxidation process of magnetite nanoparticles (∼7 nm diameter), under laser irradiation is performed employing micro Raman spectroscopy. To support this investigation, Fe{sub 3}O{sub 4}-np are synthesized by the co-precipitation method and assembled layer-by-layer with sodium sulfonated polystyrene (PSS). Polymer films (Fe{sub 3}O{sub 4}-np/PSS){sub n} with n=2,3,5,7,10 and 25 bilayers are employed as a model system to study the oxidation process under laser irradiation. Raman data are further processed by principal component analysis. Our findings suggest that PSS protects Fe{sub 3}O{sub 4}-np from oxidation when compared to powder samples, even for the sample with the greater number of bilayers. Further, the oxidation of magnetite to maghemite occurs preferably for thinner films up to 7 bilayers, while the onset for the formation of the hematite phase depends on the laser intensity for thicker films. Water takes part on the oxidation processes of magnetite, the oxidation/phase transformation of Fe{sub 3}O{sub 4}-np is intensified in films with more bilayers, since more water is included in those films. Encapsulation of Fe{sub 3}O{sub 4}-np by PSS in layer-by-layer films showed to be very efficient to avoid the oxidation process in nanosized magnetite. - Graphical abstract: Encapsulation of Fe{sub 3}O{sub 4}-np by PSS in layer-by-layer films avoids the oxidation and phase transformation of nanosized magnetite. - Highlights: • (Fe{sub 3}O{sub 4}-np/PSS){sub n} nanofilms, with n=2 up to 25, where layer-by-layer assembled. • The influence of film architecture on the Fe{sub 3}O{sub 4}-np oxidation was investigated through Raman spectroscopy. • Encapsulation of Fe{sub 3}O{sub 4}-np by PSS showed to be very efficient to avoid the Fe{sub 3}O{sub 4}-np oxidation.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2017

Growth and magnetoelectric properties of (00l)-oriented La{sub 0.67}Sr{sub 0.33}MnO{sub 3}/PbZr{sub 0.52}Ti{sub 0.48}O{sub 3} heterostructure films

C-axis oriented La{sub 0.67}Sr{sub 0.33}MnO{sub 3}(LSMO)/PbZr{sub 0.52}Ti{sub 0.48}O{sub 3}(PZT) films are fabricated successfully by sol-gel method on LaAlO{sub 3} (00l) substrates. The structure, composition and morphology of the films are investigated by X-ray diffractometer (XRD, θ-2θ scan, ω-scan and ϕ-scan), X-ray photoelectron spectroscope (XPS), field emission scanning electron microscope (FESEM) and high resolution transmission electron microscope (HRTEM). The electric and magnetic properties of randomly and c-axis oriented LSMO/PZT films are studied comparably using ferroelectric testing apparatus and physical property measurement system (PPMS). It is found that the epitaxial LSMO/PZT composite films show well controlled growth along c-axis, and much better magnetoelectric properties than the randomly oriented ones. The ME voltage coefficient increases from 23 mV cm{sup −1} Oe{sup −1} for the randomly oriented LSMO/PZT composite films to 52 mV cm{sup −1} Oe{sup −1} for c-axis oriented ones prepared using the low cost sol-gel method presented in this study, which shows high potential in promising applications. - Highlights: •Epitaxial LSMO/PZT films were fabricated successfully by sol-gel method on LAO (00l) substrate. •The prepared films exhibit well-defined multiferroic properties for the epitaxial LSMO/PZT films. •Epitaxial LSMO/PZT films show superior magnetoelectric properties to the randomly oriented ones.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Characterization of thin films prepared by co-sputtering iron and titanium precursors and thermal oxidation under air atmosphere

Highlights: • Thin films of mixed iron and titanium oxide were prepared by Ti-Fe annealing. • Segregation and phase separation of iron and titanium oxides are observed. • Formation of iron rich (Fe{sub x}O) nanoparticles at the surface region is revealed. • Formation of thin films with high refractive index can be obtained. - Abstract: Nanocomposites of metal oxides are useful materials for operation in many energy conversion systems. In this study, such nanocomposites were prepared by oxidation of mixtures of iron and titanium precursor metallic thin films at 520 °C under air atmosphere. The metallic films with different iron percentages were obtained by radio frequency (RF) magnetron sputtering on glass and silicon substrates. The films were characterized by means of X-ray Diffraction (XRD), Raman spectroscopy, UV–Vis spectroscopy, High Resolution Scanning Transmission Electron Microscopy (HRSTEM), Ellipsometry and X-ray Photo-electron Spectroscopy (XPS). The results show that these films present mainly two nanometric phases, namely Fe{sub 2}O{sub 3} and TiO{sub 2}. A phase separation was observed; the film surface was found to be iron rich oxide or clusters of iron rich oxide (Fe{sub x}O{sub y}, x > y), whereas titanium accumulated deeply in the bulk, forming TiO{sub 2} far below the film surface. A red shift of optical absorption as well as a relatively stable high refractive index (varying between 3.1 and 3.5) over a broad band of optical frequencies was observed for the films containing higher iron initial concentrations.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Correlation between thickness dependent nanoscale structural chemistry and superconducting properties of ultrathin epitaxial NbN films

NbN-based superconductors have attracted interest for superconducting circuits, quantum computation and high frequency devices. The superconducting properties of NbN films are predominately reliant on the microstructure, therefore, an atomic-level understanding of the structure-chemistry is required to achieve high quality epitaxial NbN films. Here, in this study, the thickness-dependent superconducting properties of NbN films (5, 10, and 50 nm) within NbN/AlN/Al 2 O 3 heterostructures are investigated. NbN and AlN were epitaxially grown by an industrial scale physical vapor deposition technique. The role of nanoscale chemistry on the ultrathin NbN superconducting film is investigated at the atomic level for the first time via atom probe tomography, providing three-dimensional atomic distribution, chemical homogeneity, effect of impurities, specially, in secondary phase formations and interfacial abruptness. The NbN film with 5 nm of thickness demonstrates a superconducting transition temperature of 11.2 K as compared to 50 nm NbN films with a transition temperature of 15.3 K. These thickness dependent variation of superconducting properties are associated with the chemical inhomogeneity in terms of in-plane N:Nb distribution, secondary phase formations and NbN/AlN interfacial abruptness as a function of the NbN films thicknesses. The analysis depicts the interplay between the surface/interface and the superconducting properties of ultrathin NbN films. These results provide insights on material design and growth that will enable the development of optimized superconducting NbN films for quantum devices.

36 MATERIALS SCIENCE↗
DOE OSTI2011

Thickness dependent transport and magnetotransport in CSD grown La{sub 0.7}Pb{sub 0.3}MnO{sub 3} manganite films

Highlights: {yields} Thickness dependent transport and MR of CSD grown La{sub 0.7}Pb{sub 0.3}MnO{sub 3} manganite films. {yields} Chemical Solution Deposition (CSD) is the low cost, simple and easy to handle. {yields} Prominent strain effect in lower thickness films. {yields} 3D lattice strain and microstructure govern the transport and MR in the films. {yields} Low temperature resistivity minima is also affected by 3D lattice strain. -- Abstract: We report the effect of film thickness on transport and magnetotransport in La{sub 0.7}Pb{sub 0.3}MnO{sub 3} (LPMO) manganite films grown on single crystalline LaAlO{sub 3} substrate using chemical solution deposition (CSD) technique. AFM measurements show the island type grain growth responsible for the strain at the film-substrate interface, while structural studies using XRD shows the presence of thickness dependent compressive strain in the films which modifies the transport and magnetotransport in LPMO/LAO films. The observation of low temperature resistivity minima behavior in all the LPMO films has been explained in the context of electron-electron scattering mechanism. The ZFC-FC magnetization measurements show the glassy state behavior below T{sub min}.

36 MATERIALS SCIENCE↗
DOE OSTI2011

Effect of boron doping on optical properties of sol-gel based nanostructured zinc oxide films on glass

Graphical abstract: Room temperature fine structured UV-vis PL emissions (a) as phonon replicas in 1 at.% boron doped film originated from LO phonon evidenced from Near Grazing Incidence Angle (NGIA) IR spectral study (b). Highlights: Black-Right-Pointing-Pointer Sol-gel based boron doped nanostructured ZnO thin films deposited on pure silica glass using crystalline boric acid as boron source. Black-Right-Pointing-Pointer Observed first time, room temperature fine structured PL emissions in 1 at.% doped film as phonon replicas originated from LO phonon (both IR and Raman active). Black-Right-Pointing-Pointer Boron doping controls the LO phonon energy in addition to visible reflection, band gap and grain size. Black-Right-Pointing-Pointer The films possessed mixed crystal phases with hexagonal as major phase. -- Abstract: Boron doped zinc oxide thin films ({approx}80 nm) were deposited onto pure silica glass by sol-gel dip coating technique from the precursor sol/solution of 4.0 wt.% equivalent oxide content. The boron concentration was varied from 0 to 2 at.% w.r.t. Zn using crystalline boric acid. The nanostructured feature of the films was visualized by FESEM images and the largest cluster size of ZnO was found in 1 at.% boron doped film (B1ZO). The presence of mixed crystal phases with hexagonal as major phase was identified from XRD reflections of the films. Particle size, optical band gap, visible specular reflection, room temperature photoluminescence (PL) emissions (3.24-2.28 eV), infra-red (IR) and Raman active longitudinal optical (LO) phonon vibration were found to be dependent on dopant concentration. For the first time, we report the room temperature fine structured PL emissions as phonon replicas originated from the LO phonon (both IR and Raman active) in 1 at.% boron doped zinc oxide film.

36 MATERIALS SCIENCE↗
DOE OSTI2011

Thin film growth of boron nitride on {alpha}-Al{sub 2}O{sub 3} (0 0 1) substrates by reactive sputtering

Highlights: Black-Right-Pointing-Pointer A BN film grown on {alpha}-Al{sub 2}O{sub 3} (0 0 1) had a structure in which h-BN sheet stacking continued through almost the whole film thickness. Black-Right-Pointing-Pointer The structure was characterized by X-ray diffraction, ATR-IR, and XPS. Black-Right-Pointing-Pointer Tauc plots suggested the film had direct band gap and the optical band gap was close to that of bulk h-BN. -- Abstract: Boron nitride thin films were grown on {alpha}-Al{sub 2}O{sub 3} (0 0 1) substrates by reactive magnetron sputtering. Infrared attenuated total reflection (ATR) spectra of the films gave an intense signal associated with in-plane B-N stretching TO mode of short range ordered structure of BN hexagonal sheets. X-ray diffraction for the film prepared at a low working pressure (ca. 1 Multiplication-Sign 10{sup -3} Torr) gave a diffraction peak at slightly lower angle than that corresponding to crystal plane h-BN (0 0 2). It is notable that crystal thickness calculated from X-ray peak linewidth (45 nm) was close to film thickness (53 nm), revealing well developed sheet stacking along the direction perpendicular to the substrate surface. When the substrates of MgO (0 0 1) and Si (0 0 1) were used, the short-range ordered structure of h-BN sheet was formed but the films gave no X-ray diffraction. The film showed optical band gap of 5.9 eV, being close to that for bulk crystalline h-BN.

36 MATERIALS SCIENCE↗
DOE OSTI2012

Evolution of different structural phases of TiO{sub 2} films with oxygen partial pressure and Fe doping and their electrical properties

Highlights: ► Fe doped and undoped TiO{sub 2} films are grown with varying oxygen partial pressure (OPP). ► Different structural and electrical phases of TiO{sub 2} films evolve with OPP. ► Phases obtained at different OPP are not same for films with different Fe doping. ► XPS confirms Fe is not in metal cluster form. ► Charge ordering is observed in magneli phase of Fe doped and undoped TiO{sub 2} films. -- Abstract: We have studied the influence of oxygen partial pressure (OPP; 250 mTorr–1 × 10{sup −5} Torr) and Fe doping (2 and 4 at.%) on structural and electrical properties of TiO{sub 2} thin films on LaAlO{sub 3} substrates. X-ray photoelectron spectroscopy suggests that Fe is not in metal cluster form. It is found that the evolution of the three phases; anatase, rutile and brookite of TiO{sub 2} as well as the magneli phase (Ti{sub n}O{sub 2n−1}) strongly depends on the OPP and Fe doping concentration. All the films grown at 250 mTorr show insulating behavior, whereas films grown at 1 × 10{sup −2} and 1 × 10{sup −4} Torr reveal high temperature metallic to low temperature semiconducting transition. Interestingly, films deposited at 1 × 10{sup −5} Torr reveal charge ordering, which is contributed to the magneli phase of TiO{sub 2}. The present study suggests that functionality of TiO{sub 2} thin film based devices can be tuned by properly selecting the OPP and dopant concentration.

36 MATERIALS SCIENCE↗
DOE OSTI2012

Properties of Cu-doped ZnO films by RF sputtering method: Thickness dependence

We present results concerning the thickness dependence of structural, morphological and optical properties of the Zn{sub 0.98}Cu{sub 0.02}O films deposited on glass substrates using radio frequency (RF) sputtering method. The microstructure and the chemical state of oxygen, copper and zinc in ZnO and Zn{sub 0.98}Cu{sub 0.02}O films were investigated by X-ray diffraction spectroscopy (XRD) and X-ray photoelectron spectroscopy (XPS), respectively. The results indicate that Zn{sub 0.98}Cu{sub 0.02}O films are the wurtzite structure with strong c-axis orientation. Crystallinity of the films is closely related to the film thickness. With increasing film thickness, there are more surface (mainly nanopores) defects existing in the Zn{sub 0.98}Cu{sub 0.02}O films and surface roughness increases. XRD and XPS data show that the valence state of copper in the Zn{sub 0.98}Cu{sub 0.02}O films is Cu{sup 2+}. The transparency of all films is more than 85% in the visible region.

36 MATERIALS SCIENCE↗
DOE OSTI2013

Influence of the process parameters on the spray pyrolysis technique, on the synthesis of gadolinium doped-ceria thin film

Graphical abstract: Gas-tight CGO made by spray pyrolysis suitable to be used as SOFC electrolyte. Display Omitted Highlights: ► Dense and crystalline CGO films deposited by spray pyrolysis on various substrates. ► Solvent did not have a strong influence on the film microstructure, defect concentration or thickness. ► The substrate did not have a strong influence on the film microstructure, defect concentration or thickness. ► Films with at least 2.5 μm of thickness presented high impermeability. ► The films obtained are suitable to use as a SOFC electrolyte. -- Abstract: This work presents the results of a process of optimization applied to gadolinia-doped ceria (Ce{sub 0.8}Gd{sub 0.2}O{sub 1.9−x}, or CGO) thin films, deposited by spray pyrolysis (SP). Spray pyrolysis is a high thermal deposition method that combines material deposition and heat treatment. This combination is advantageous since the post-deposition heat treatment step is not necessary. However, stresses are solidified in the coating during the deposition, which may lead to the initiation of a crack in the coating. The aim of this work was to achieve thin, dense, and continuous CGO coatings, which may be used as gas separation membranes and as a solid state electrochemical interfaces. Dense, flat, low-defect substrates such as silica slides, silicon mono crystal wafers, and porous substrates were used as substrates in this work. Cerium ammonium nitrate and gadolinium acetylacetonate were dissolved in ethanol and butyl carbitol to form a precursor solution that was sprayed on the heated substrates. Process parameters such as solvent composition, deposition rate and different heating regimes were analyzed. The microstructure was analyzed by secondary electron microscopy (SEM) and was found that thin, dense, and defect-free films could be produced on dense and porous substrates. The results obtained show that it is possible to obtain a CGO dense film deposited by spray pyrolysis. X-ray diffraction (XRD) analysis showed that the films were crystalline after the deposition without requiring post-deposition heat treatment. The crystallite size does not vary significantly as a function of the annealing temperature.

36 MATERIALS SCIENCE↗