Zirconia Films Research Articles

Residual stress measurements in electron beam evaporated yttria doped zirconia films deposited on Si (111) substrates

Zirconia thin films with varying yttria concentrations (0, 4, and 10 mol. %) were grown on Si (111) substrates using electron beam physical vapor deposition technique. The residual stress as a function of depth on undoped and yttria doped zirconia films with different phases was determined using the modified sin2ψ technique by varying the x-ray angle of incidence. Surface profilometry was also used as a complementary technique for qualitative measurement of stress in these films. The residual stress profile revealed that tensile residual stress was present in the near-surface region and it decreased rapidly as a function of depth in all three films with different yttria concentration. The possible reasons for the film growth stress and stress gradient in the yttria doped zirconia films with different concentration of yttria are discussed.

Corrosion and biocompatibility behaviour of zirconia coating by EBPVD for biomedical applications

In the present study, zirconia (ZrO2) film was deposited onto 316L SS substrate by electron beam physical vapour deposition (EBPVD) technique. The microstructure of the ZrO2 film was studied using X-ray diffraction (XRD) and atomic force microscopy (AFM) and scanning electron microscopy (SEM). Hydrophilic nature was observed on ZrO2 coated film and least hydrophilic behaviour was found on bare 316L SS substrate. The bacterial adhesion test was performed against Streptococcus mutans (S. mutans) and revealed that ZrO2 film protects the bacterial adhesion on its surface. In-vitro cytotoxicity and biocompatibility behaviour of ZrO2 film were investigated using fibroblast cell line, which exhibited high degree of cell viability and proliferation rate rather than bare 316L SS substrate. Electrochemical studies were performed in acidulated artificial saliva (AS) solution containing 0.2% and 2% of sodium fluoride (NaF). The results revealed that ZrO2 coated 316L SS showed excellent corrosion resistant behaviour and can be considered as a potential bioimplant for dental applications.

Development and characterization of biaxially-textured lanthanum zirconate film grown on cold-rolled Ni-W substrate by chemical solution deposition

High temperature superconducting tapes based on cuprate compounds are nowadays available on long lengths by several companies. Because high superconducting properties are strongly influenced by the crystallographic orientation of the superconducting film, and because the appropriate crystallographic orientation is obtained through epitaxial film growth, the development of an oriented template is of crucial technological importance. In the rolling assisted biaxially textured substrate (RABiTS) technique, a strong cube texture is obtained by cold rolling fcc metal tape and high temperature annealing, followed by the deposition of one or more buffer layer by either physical vapor deposition (PVD) or chemical solution deposition (CSD). Using the latter approach, it has been recently shown that it is possible to combine substrate recrystallization and buffer layer growth in a single step if the onset of recrystallization occurs at a temperature lower than buffer layer nucleation. In the present contribution, a detailed investigation of biaxially-oriented La2Zr2O7 (LZO) buffer layer grown on cold-rolled Ni-W substrate by combined EBSD, AFM and TEM analyses is reported. It is shown that it is possible to obtain highly {001}〈110〉-textured LZO film directly on cold-rolled Ni-W substrate. Although some small polycrystalline regions appear, this approach leads to a strong suppression of grain boundary grooving typically occurring in RABiT-type substrates. Further, it is shown that, notwithstanding the microstructure of the metal substrate continues to evolve during the conversion heat treatment, the obtained LZO film is well adherent, without cracks or delamination.

Scratch Behavior of ZrO2 Thin Film Prepared by Atomic Layer Deposition Method on Silicon Wafer

To evaluate friction behaviour and adhesion strength of 130 nm-thick zirconia (ZrO2) film produceded by atomic layer deposition (ALD) on Si substrate, scratch tests were performed at two different scales; micro- and macro-scales. Surface morphology, roughness, crack propagations and interations between the surface and sliding indenter were also investigated. Scratch test was also conducted with Si substrate as a reference. The test results showed that friction coefficient (COF) was influenced by the scale of scratch test regardless of the tested materials. In microscale test, the 130 nm-thick zirconia film failed at the critical load of 96 mN and direct relationship between the generation of micro-cracks and friction coefficient was observed. Based on the Hertzian contact theory and experimental results, the macroscratch width was much greater than that in microscratch test although the maximum contact pressure were comparable in both cases. Further discussion was made with regard to the influence of the contact pressure on COF, crack generation and film removal. Various types of failure mode were identified through analyzing the mechanical response of scratch tracks both at micro- and macroscale tests. This study suggested that 130 nm-thick ALD-ZrO2 film showed better tribological and adhesion properties at microscale contact than macroscale contact.

Rapid, cool sintering of wet processed yttria-stabilized zirconia ceramic electrolyte thin films

Here we report a photonic annealing process for yttria-stabilized zirconia films, which are one of the most well-known solid-state electrolytes for solid oxide fuel cells (SOFCs). Precursor films were coated using a wet-chemical method with a simple metal-organic precursor solution and directly annealed at standard pressure and temperature by two cycles of xenon flash lamp irradiation. The residual organics were almost completely decomposed in the first pre-annealing step, and the fluorite crystalline phases and good ionic conductivity were developed during the second annealing step. These films showed properties comparable to those of thermally annealed films. This process is much faster than conventional annealing processes (e.g. halogen furnaces); a few seconds compared to tens of hours, respectively. The significance of this work includes the treatment of solid-state electrolyte oxides for SOFCs and the demonstration of the feasibility of other oxide components for solid-state energy devices.

Low-Temperature Steam Annealing of Metal Oxide Thin Films from Aqueous Precursors: Enhanced Counterion Removal, Resistance to Water Absorption, and Dielectric Constant

Aqueous solution deposition has emerged as a potentially scalable, high-throughput route to functional metal oxide thin films. Aqueous routes, however, generally require elevated processing temperatures to produce fully condensed films that are resistant to water absorption. Herein, we report a low-processing-temperature method for preparing more fully condensed, stable metal oxide films from aqueous precursors. We show that a steam anneal at ≤200 °C reduces residual nitrates in zinc oxide, yttrium aluminum oxide, and lanthanum zirconium oxide (LZO) films. An in-depth study on LZO dielectric films reveals steam annealing also reduces residual chloride content, increases resistance to post-anneal water absorption, eliminates void formation, and enhances the dielectric constant. This investigation demonstrates that steam annealing directly affects the decomposition temperatures and chemical evolution of aqueous precursors, suggesting a general means for producing high-quality films at low processing tempera...

(Invited) Specific Metal-Metal Oxide Interactions in Efficient Electroreduction of Carbon Dioxide

Of particular interest to the preparation of advanced catalytic materials is efficient utilization of carbon nanostructures and noble metal nanoparticles, their stabilization and intentional activation, as well as organization into two-dimensional arrays, ultra-thin films or three-dimensional networks (e.g. through sequential attraction) on electrode surfaces. They can form nanosized materials with well-defined composition, structure and thickness that exhibit desirable electrocatalytic properties (e.g. toward reduction of CO2). We explore here the ability of polynuclear inorganic systems to stabilize and derivatize metal and carbon nanostructures. Here certain nanostructured metal oxides of zirconium, titanium, zinc or tungsten have been demonstrated to influence supported metal centers in ways other than simple dispersion over electrode area. Evidence is presented that the support can modify activity (presumably electronic nature) of catalytic metal nanoparticles (e.g. Cu, Ag, Au, Pd, Pt or Ru) thus affecting their chemisorptive and catalytic properties. Metal oxide nanospecies can generate –OH groups at low potentials that induce proton mobility at the photo(electro)chemical interface. Our research interests concern development of systems for the reduction (conventional/electrocatalytic or photoelectrochemical) of carbon dioxide. For example, nanosized Cu or Au naoparticles immobilized within ultra-thin films of tungsten oxide or zirconia have been considered. Reduction of carbon dioxide begins now at less negative potentials and is accompanied by significant enhancement of the CO2-reduction current densities. When it comes to photoelectrochemical reduction, we are also going to demonstrate utility of zirconia or zinc oxide over-layers on copper(I) oxide photocathodes irradiated with visible light in aqueous solutions. The possibility of generation of localized surface plasmons with use of gold or silver nanoparticles, will also be considered. Special attention will be paid to stability and controlled reactivity of the proposed systems.

Characterisation of well-adhered ZrO2 layers produced on structured reactors using the sonochemical sol–gel method

The aim of this study was to obtain thin zirconium dioxide coatings on structured reactors using the sonochemical sol-gel method. The preparation method of metal oxide layers on metallic structures was based on the synergistic combination of three approaches: the application of ultrasonic irradiation during the synthesis of Zr sol-gel based on a precursor solution containing zirconium(IV) n-propoxide, the addition of stabilszing agents, and the deposition of ZrO2 on the metallic structures using the dip-coating method. As a result, dense, uniform zirconium dioxide films were obtained on the FeCrAlloy supports. The structured reactors were characterised by various physicochemical methods, such as BET, AFM, EDX, XRF, XRD, XPS and in situ Raman spectroscopy. The results of the structural analysis by Raman and XPS spectroscopy confirmed that the metallic surface was covered by a ZrO2 layer without any impurities. SEM/EDX mapping revealed that the deposited ZrO2 covered the metallic support uniformly. The mechanical and high temperature tests showed that the developed ultrasound assisted sol-gel method is an efficient way to obtain thin, well-adhered zirconium dioxide layers on the structured reactors. The prepared metallic supports covered with thin ZrO2 layers may be a good alternative to layered structured reactors in several dynamics flow processes, for example for gas exhaust abatement.

Room-temperature UV-ozone assisted solution process for zirconium oxide films with high dielectric properties

Abstract A facile, low-cost, and room-temperature UV-ozone (UVO) assisted solution process was employed to prepare zirconium oxide (ZrO x ) films with high dielectric properties. ZrO x films were deposited by a simple spin-coating of zirconium acetylacetonate (ZrAcAc) precursor in the environment-friendly solvent of ethanol. The smooth and amorphous ZrO x films by UVO exhibit average visible transmittances over 90% and energy bandgap of 5.7 eV. Low leakage current of 6.0 × 10 −8 A/cm 2 at 3 MV/cm and high dielectric constant of 13 (100 Hz) were achieved for ZrO x dielectrics at the nearly room temperature. Moreover, a fully room-temperature solution-processed oxide thin films transistor (TFT) with UVO assisted ZrO x dielectric films achieved acceptable performances, such as a low operating voltage of 3 V, high carrier mobility of 1.65 cm 2 V −1 s −1 , and on/off current ratio about 10 4 –10 5 . Our work indicates that simple room-temperature UVO is highly potential for low-temperature, solution-processed and high-performance oxide films and devices.

Self-ion irradiation effects on mechanical properties of nanocrystalline zirconium films

Abstract

Infrared properties of sol–gel derived zirconia film

We examined infrared transmission characteristics of a sol–gel derived zirconia film and the antireflective (AR) effect of this film for an Si substrate in the midinfrared region. The surface reflection loss of an Si plate is high (∼30%) because of the high refractive index (3.42) in the infrared region. We employed zirconia nanoparticle dispersion with 15 wt. % (1-butanol solvent) as starting sol solution. Then, the dispersion was coated with Si substrate at a spin-coating speed of 2000 rpm, and the substrate was heated to 150°C. The number of coatings was repeated seven times. As a result, the transmittance at 5.6-μm wavelength was enhanced to 66.2%, and we found that the coated film worked efficiently as the AR film up to 10-μm wavelength. Additionally, by heating the substrate to 800°C, the large absorptions at 2.9-, 6.4-, and 6.9-μm wavelengths could be suppressed because the hydroxy group in the film was reduced. Its peak transmittance was 67.9% at 4.9-μm wavelength.

Chemical solution deposited thin films of titanium, chromium, zirconium, and tin oxides

TiO2, Cr2O3, ZrO2, and SnO2 films with thicknesses of ∼10–100 nm were produced via dipping into solution and subsequent annealing in air. The films were studied by the methods of scanning electron microscopy, elemental X-ray spectral analysis, optical spectroscopy, and X-ray diffraction. The electrical conductivity of the films in air and in a vacuum was measured. The adhesion of most of the films to the substrate was found to be high. A crystalline structure was observed for films thicker than 10 nm. The films have a specific surface resistance of 108–1012 Ω in air and 109–1014 Ω in a vacuum. The films are promising as coatings for various purposes, including the development of structures of the core–shell type.

Anomalous Epitaxial Growth in Thermally Sprayed YSZ and LZ Splats

Thermally sprayed coatings are essentially layered materials, and lamellar interfaces are of great importance to coatings’ performances. In the present study, to investigate the microstructures and defect features at thermally sprayed coating interfaces, homoepitaxial 8 mol.% yttria-stabilized zirconia (YSZ) and heteroepitaxial lanthanum zirconia (LZ) films were fabricated. The epitaxial interfaces were examined by high-resolution transmission electron microscope (HR-TEM) in detail. As a result, we report, for the first time, an anomalous incommensurate homoepitaxial growth with mismatch-induced dislocations in thermally sprayed YSZ splats to create a homointerface. We also find the anomalous heteroepitaxial growth in thermally sprayed LZ splats. The mechanism of the anomalous incommensurate growth was analyzed in detail. Essentially, it is a pseudo-heteroepitaxy because of the lattice mismatch between the film and the locally heated substrate, as the locally heated substrate is significantly strained by its cold surroundings. Moreover, the super-high-density dislocations were found in the interfacial region, which resulted from sufficient thermal fluctuations and extremely rapid cooling rates. Both the anomalous lattice mismatch and super-high-density dislocations lead to weak interfaces and violent cracking in thermally sprayed coatings. These were also the essential differences between the conventional and the present epitaxy by thermal spray technique.

Thermal expansion and residual stress behaviour of electron beam evaporated yttria stabilized zirconia films on Inconel-690 substrates

Nuclear vitrification components used in melter pot made of Ni-base superalloys degrade prematurely due to alloy-waste glass interaction and the formation of secondary precipitates. Deposition of cubic yttria stabilized zirconia (c-YSZ) coating has been recommended as a diffusion barrier material to delay or reduce the failure of the alloy and to enable an extended life. In the present work, c-YSZ films have been deposited on Inconel-690 substrate by electron beam evaporation technique at various substrate temperatures from 673 K to 973 K. The residual stress in the film surface and at the film/substrate interface was measured using grazing incidence x-ray diffraction (GIXRD) with various incidence angles. It was observed that the residual stress at the film/substrate interface region changes from tensile to compressive when the substrate temperature was increased from 673 K to 973 K during deposition. Furthermore, the thermal expansion coefficient (TEC) of Inconel-690 substrate and YSZ film coated Inconel-690 substrate were determined by high temperature (HTXRD) measurement in the temperature range of 298–1273 K with 100 K interval. The linear TECs of Inconel-690 and YSZ coated Inconel-690 at 1273 K were found to be 1.53 × 10−5 K−1 and 6.04 × 10−6 K−1, respectively.

Cohesive strength of zirconia/molybdenum interfaces and grain boundaries in molybdenum: A comparative study

We present calculations within density functional theory on the thermodynamic stability and mechanical properties of t-ZrO2(001)/Mo(001) interfaces. The interfacial strength is evaluated by applying energy-based (work of separation) and stress-based (theoretical strength) criteria for different cleavage planes. The lowest energy for crack propagation is obtained for a cut creating a stoichiometric ZrO2(001) surface. Our results reveal that molybdenum grain boundaries contaminated with oxygen are less stable against brittle fracture than pure Mo GBs. Addition of Zr, however, can strengthen Mo grain boundaries that contain oxygen by forming an ultrathin zirconia film between Mo grains. The stress required to cleave an ultrathin zirconia film is equal to that required for a pure Mo GB.

High NOx Reduction Activity of an Ultrathin Zirconia Film Covering a Cu Surface: A DFT Study

NO reduction by CO over a c-ZrO2(110) ultrathin film covering a Cu(110) surface (ZrO2/Cu) has been examined by means of density-functional theory calculations. Spontaneous transfer of electronic charge from Cu to zirconia gives the latter an ability to reduce oxidants. Gaining this excess charge, NO adsorbs and activates on the cationic Zr site of the oxide surface. Thus activated, two NO on adjacent Zr sites can react to form ONNO with an activation energy of 0.39 eV (8.9 kcal/mol), which readily decomposes into N2O and an O adatom. N2O also decomposes into N2 and an O adatom with negligible activation energy of 0.06 eV (1.4 kcal/mol). CO reacts off the O adatoms left on the surface as CO2 with an activation energy of 0.36 eV (8.2 kcal/mol), completing a redox cycle. These results indicate high potentials of oxide-covered metal catalysts (metal@oxide) for NOx abatement.

Fabrication of columnar structured lanthanum zirconate films by laser CVD

AbstractColumnar lanthanum zirconate (LZ) films were deposited by laser chemical vapor deposition (LCVD). The effects of deposition conditions, preheat temperature and laser power, on crystal structure, morphology, and deposition rate were investigated. A large region in the terms of preheat temperature and laser power for the formation of cubic pyrochlore‐structured LZ films was mapped under a fixed total pressure of 950 Pa. The morphology of LZ films without laser irradiation showed a dense and glass‐like structure with a flat cauliflower surface. It was changed into a columnar structure with an unflat cauliflower surface by low‐power laser irradiation during deposition process. The transformation occurred once a critical laser power beyond 16 W/cm2. Thus, the effect of laser on the deposition of LZ films was a result of double‐side action including both pyrolytic effect and photolytic effect. Plasma gas around the substrate resulted in significant increases in deposition temperature and deposition rate due to self‐propagating high‐temperature reactions between the precursors and O2. The maximum deposition rate can reach 250 μm/h by LCVD.

Porosity and optical properties of zirconia films prepared by plasma ion assisted deposition.

The porosity of zirconia films prepared by plasma ion assisted deposition has been investigated by means of optical (spectrophotometric) and nonoptical analytic techniques such as transmission electron microscopy, x-ray reflection, and energy dispersive x-ray spectroscopy. A discrimination between large (open) and small (closed) pores was achieved by means of measurement of the thermal and vacuum-to-air shift. Depending on the level of plasma assistance during film preparation, the porosity was found to vary between 30vol.% and nearly 0vol.%. With decreasing porosity, the surface roughness determined by atomic force microscopy tends to decrease as well.

Argon Annealed ALD-ZrO2/SiON Gate Stack for Advanced CMOS Devices

We report on the fabrication of ultra-thin silicon oxynitride (SiON ~ 5.34 nm) as sacrificial layer (SL) for n-Si/ALD-ZrO2 gate stack followed by the post deposition annealing (PDA) of ZrO2 in argon ambient. The surface morphological studies include atomic force microscopy (AFM) and field emission scanning electron microscopy (FESEM) whereas the thicknesses of the grown films were confirmed by both ellipsometry and FESEM cross-sectional studies. The surface topographical study suggests the r.m.s. roughness of 0.796 nm for nano zirconia film after rapid thermal annealing (RTA). Electrical parameters such as dielectric constant (K), effective oxide thickness (EOT), leakage current density (J), effective oxide charge (Qeff) and series resistance (Rs) were extracted through C-V and I-V measurements and the determined values of K, J, EOT, Qeff and Rs at 100 KHz are 26, 8.75 × 10-9 A/cm2, 2.1 nm, 0.42 × 1013 cm-2 and 4.54 KΩ respectively. The concept of SiON SL has significantly suppressed the existing unacceptable gate leakage current and the interfacial traps owing to appropriate segregation of nitrogen at the interface of SiON/ZrO2. Moreover, PDA of ZrO2 film in argon ambient at 5000 C has reduced the r.m.s. roughness and also contributed to the overall reduction of gate leakage current density, thereby, making ALD-ZrO2/SiON gate stack quite attractive for advanced CMOS devices.

Zirconium oxide films: deposition techniques and their applications in dye-sensitized solar cells

Zirconium oxide (ZrO2) is acquiring considerable attention of most of the research groups and leading to a large number of publications due to its unique properties, especially in the context of emerging trends in the third generation of solar cell research. ZrO2 films offer magnificent aspects related to physicochemical properties, and the properties are found to be dependent on synthesis methods. In the present review, various deposition techniques used to grow zirconium oxide thin films and their application to enhance the quantum efficiency of titanium oxide (TiO2) based dye-sensitized solar cells (DSSCs) are discussed. Also, the modulated performances of DSSCs fabricated by growing the conformal ZrO2 insulating films to retard interfacial recombination dynamics on preformed TiO2 films are discussed.