Zirconia Films Research Articles

Electric Resistance Measurements of Anodic Oxide Films on Titanium and Zirconium

Valve metals such as titanium and zirconium can be subjected to anodization to form a thick compact oxide film in fluoride-free electrolytes at room temperature, and the thickness and structure of the film can be controlled by anodization conditions. Although various studies on the formation, characterization and application of anodic titanium oxide film as well as zirconium oxide film have been carried out so far, the electrical resistivity of the anodic oxide films is quite limited. In the present work, we measured electric resistance of the anodic oxide films formed on titanium and zirconium under various anodization conditions, aiming at investigating effects of anodization on electrical resistivity of anodic oxide films.

Oxidation Behavior of Additively Manufactured 316L in a Supercritical CO2 Environment

The general properties of additively manufactured (AM) metals have been fairly well characterized to this point with respect to mechanical behavior and even general corrosion response. However, as the fields of application of AM metals broadens, the need for unique/specialized evaluation is required. For instance, there remains a lack in understanding how AM metals behave under atmospheric corrosion exposure conditions where local heterogeneous environments govern the surface reactivity and susceptibility. Similarly, knowledge gaps exist in specialized environment, for example supercritical CO2 (sCO2). Materials and environment parameters such as composition, pressure, and temperature will influence corrosion susceptibility and/or oxidation properties. As AM metals often display vastly different microstructures from their wrought counterparts due to non-equilibrium cooling during processing, an understanding of their behavior in these environments is critical prior to possible application. Additionally, typical engineering design of oxy-combustion gas turbine systems used in these environments, results in atypical conditions, usually localized, that are well known to affect environmental performance of materials (such as crevices, welds, residual stresses, or galvanic coupling).Austenitic stainless steel, type 316L, specimens made by selectively laser melting (SLM) were exposed with their traditional wrought counterparts for comparison at 450°C and 7.6 MPa in pure sCO2 for one week. SLM samples were exposed in the as printed (a contour scan strategy was used) and the ground (ground to 1200 grit) state and compared to wrought samples ground to 1200 grit. Prior to exposure, samples were partially coated with a zirconia film to establish an initial true height to aid ellipsometry. Post exposure, oxide film thickness was measured with respect to the non-reactive coating height. Preliminary analysis of oxide film thickness measurements performed using ellipsometry showed a thinner oxide film grown on the in-process polished SLM samples (0.66 - 0.79 µm) versus the ground SLM (1.1 µm) or wrought samples (0.8 – 1.22 µm). Additional analysis was performed through scanning electron microscopy and focused ion beam combined with transmission electron microscopy to characterize the oxides formed and elucidate possible microstructural and/or morphological dependence of the film growth.SNL is managed and operated by NTESS under DOE NNSA contract DE-NA0003525. SAND2020-4568 A

Dielectric Micro‐ and Sub‐Micrometric Spacers for High‐Temperature Energy Converters

Dielectric microspacers (DMS) are important components in thermal energy converters. Engineered DMS are fabricated and characterized on different substrates by depositing patterned ceramic thin films of alumina (Al2O3) and zirconia (ZrO2) with a thickness ranging from 0.3 to 3 μm. Both Al2O3 and ZrO2 films are electrically and thermally optimized, finding zirconia more suitable as a thermal and electrical insulating material at high temperature, whereas the developed DMS are morphologically analyzed by scanning electron microscopy. The analysis of thermal simulations carried out with COMSOL Multiphysics allows identifying the best geometrical constraints for each single structure, whereas simulations carried out by the Fluent software allow identifying the best arrangement for DMS, leading to a solution with optimized pattern in terms of amount and spatial distribution so to achieve the required electrical and thermal insulation for practical applications. DMS are integrated within thermionic‐photovoltaic devices to be validated experimentally, and enhanced electron emission measurements are successfully performed at a cathode temperature up to 1350 °C to verify the operational feasibility and potential of this technology.

Defect Analysis and Reliability Characteristics of (HfZrO₄)1-x(SiO₂)x High-κ Dielectrics.

Hafnium zirconium silicon oxide ((HfZrO₄)1-x(SiO₂)x) materials were investigated through the defect analysis and reliability characterization for next generation high-κ dielectric. Silicate doped hafnium zirconium oxide (HfZrO4) films showed a reduction of negative flat-band voltage (Vfb) shift compared to pure HfZrO₄. This result was caused by a decrease in donor-like interface traps (Dit) and positive border traps (Nbt). As the silicon oxide (SiO₂) content increased, the Vfb was shifted in the positive direction from -1.23 to -1.10 to -0.91 V and the slope of the capacitance-voltage (C-V) curve increased. The nonparallel shift of the C-V characteristics was affected by the Dit, while the Nbt was responsible for the parallel C-V curve shift. The values of Dit reduced from 4.3 × 1011, 3.5 × 1011, and 3.0 × 1011 cm-2eV-1, as well as the values of Nbt were decreased from 5.24, 3.90 to 2.26 × 1012 cm-2. Finally, reduction of defects in the HfZrO₄-base film with an addition of SiO₂ affected the gate oxide reliability characteristics, such as gate leakage current (JG), bias temperature stress instability (BTSI), and time dependent gate dielectric breakdown (TDDB).

Comparative study of oxidizing ambient infused with varying nitrogen flow rates for fabrication of ternary nitrided AlZrO based MOS capacitor

High dielectric constant nitrided aluminum zirconium oxide films were successfully fabricated on silicon substrate via an oxidation process infused with different nitrogen gas flow rates at 800°C. The presence of nitrogen piling up at the interface could control the thickness of interfacial layer formation. An increase in the nitrogen gas flow rate might be effective in controlling the overall thickness of the films, yet the nitrogen piling up at the interface impeded the diffusion of oxygen to the interface. Consequently, the interface quality was affected, leading to degradation in the interface-state density. In addition, the generation of oxygen vacancies in the films, as well as the presence of nitrogen at the interstitial sites, would create a lattice polarization, which decreased the k values. Corresponding effects were also discussed in corroboration with energy band gap, effective oxide charges, and slow trap density, as well as interface-state density calculated from capacitance and conductance methods.

Enhancement of Oxidation of Formic Acid through Application of Zirconia Matrix for Immobilization of Noble Metal Catalytic Nanoparticles

Electrocatalytic activity of common noble metal (platinum, bimetallic platinum-ruthenium and palladium) nanoparticles (both unsupported and supported on Vulcan carriers) toward electrooxidation of formic acid in acid medium (0.5 mol dm–3 H2SO4) can be significantly enhanced by dispersing them over thin film of zirconia (ZrO2). The enhancement effects concern increases of the electrocatalytic current densities (normalized against the mass of noble metal catalysts) recorded under both cyclic voltammetric and chronoamperometric conditions. The observations can be rationalized in terms of the ability of zirconia nanostructures to provide active hydroxyl groups capable of inducing the removal of the inhibiting COOH or CO type adsorbates from their surfaces. The role of Vulcan carriers is in improving electronic conductivity, in addition to facilitating distribution of catalytic metal sites at the electrocatalytic interface. Regarding dissimilar mechanisms for HCOOH oxidations at Pt, PtRu and Pd nanoparticles, the activating capabilities of zirconia differ depending on the potential applied thus reflecting distinct nature of electronic or chemical interactions. Specific interactions between the zirconia support and noble metal nanoparticles are also possible, particularly in the case of Pd-based catalysts where the enhancement effects are the most pronounced. Finally, it should be emphasized that, historically, representatives of Russian school of electrochemistry, including V.S. Bagotsky, were one of the first world-wide who investigated the formic acid oxidation and emphasized the importance of metal—support interactions during electrooxidation of small organic molecules at noble metal nanoparticles.

Preparation of multi-purpose TiO2 pigment with improved properties for coating applications

A rutile-grade multipurpose TiO2 pigment with surface coatings of zirconia and alumina is prepared under controlled conditions. HRTEM, FTIR, ξ-Potential etc. were used to characterize the morphology, structure and electrokinetics. A continuous and compact film of zirconia was anchored on the base TiO2 particles surface as the innermost coating. A composite coating of alumina was precipitated under controlled conditions which facilitated the precipitation of both dense, compact and porous, boehmite alumina on the surface of zirconia-coated TiO2 particle surface. Comparative evaluation of the pigmentary properties of the coated pigment revealed superiority in durability and optical properties of the modified pigment over conventional enamel-grade and general-purpose grade TiO2 pigments respectively.

Stoichiometric redox reaction-controlled, combustion assisted spray pyrolyzed zirconia films on stainless steel

In this contribution, an efficient aqueous solution combustion technique was implemented to achieve zirconia films on stainless steel substrates at 400 °C, by low capital and facile spray pyrolysis of a combustible precursor comprising stoichiometric amounts of zirconium oxynitrate hydrate and glycine. Detailed derivation of stoichiometric redox reaction is emphasized in the present work. Thermal behaviour of combustible precursor revealed the combustion temperature at ∼220 °C. Crystalline tetragonal zirconia film was deposited at 400 °C with a wavy morphological surface inferred from diffraction patterns and microstructural studies, respectively. Besides, an approach to fabricate spray pyrolysed YSZ films through combustion at 400 °C was successfully accomplished. These films can have a potential impact on biomedical and thermal barrier applications.

Low-temperature ZrO2 thin films obtained by polymeric route for electronic applications

In this work, zirconium oxide (ZrO2) films obtained by the polymer-assisted chemical solution method were evaluated. Thin films are obtained using dip-coating with dipping rates from 1 to 100 mm/min, and annealing temperatures from 150 to 450 °C. The films present amorphous structure even with annealing at 450 °C, bandgap of 5.4 eV and a non-porous surface. The zirconia films were electrically characterized applied to a metal–insulator–metal capacitor (MIM-c) configuration. The dielectric layer presents high capacitance and impedance, highly dependent on the dipping rates and annealing temperature. The outcomes from the MIM-c investigated demonstrate that this low-temperature zirconia film may be an alternative for application in flexible electronic devices as insulating layer. More interesting results like higher capacitance and higher operation frequencies are obtained for zirconia layers obtained at 350 °C due to better dipole formation in the film enhanced by the thinner films and a better elimination of polymeric ligands in the film.

Enhancement of oxidation of dimethyl ether through application of zirconia matrix for immobilization of noble metal catalytic nanoparticles

Electrocatalytic activity of Pt and bimetallic PtRu nanoparticles (both Vulcan supported and unsupported) toward electrooxidation of dimethyl ether (DME), a potential small organic molecule fuel, in an acid medium (0.5 mol dm−3 H2SO4) has been significantly enhanced by dispersing them over a thin film of zirconia (ZrO2). The enhancement effects concern increases of the DME electrocatalytic current densities recorded under both cyclic voltammetric and chronoamperometric conditions. Similar effects have been observed for the oxidation of methanol. Regarding the dissimilar DME electrooxidation mechanisms at Pt and PtRu catalytic centers, the activating capabilities of zirconia seem to originate from the high population of reactive –OH groups favoring mobility of protons and the capability of inducing the oxidative removal of poisoning (CO-type) intermediates both at platinum and ruthenium catalytic sites. In the presence of the zirconia matrix, the onset potential for the oxidation of DME (particularly at PtRu) is shifted more than 50 mV toward less positive potentials. Mutual metal-support interactions are also postulated.

Influence of oxygen percentage on in vitro bioactivity of zirconia thin films obtained by RF magnetron sputtering

The zirconia (ZrO2) films were deposited using radio-frequency magnetron sputtering (RFMS) from a pure zirconium target in Ar-O2 gas mixture with different percentage of the oxygen. The effect of Oxygen percentage on the film’s characteristics was investigated by Raman spectroscopy, X-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM), and tribology test. Also, the contact angle of the films was measured in order to evaluate their hydrophobicity. Additionally, in vitro test in artificial blood plasma and further SEM observations were performed to study bioactivity of the films. The experimental results showed that the roughness, the porosity and the thickness of the films depend on the oxygen percentage. According to XRD and Raman spectroscopy results, the films present a polymorph phase of monoclinic and tetragonal. Zirconia films at low oxygen percentage showed better hydrophobic behavior with 114.5° at 15% of oxygen. These films also exhibit a lower friction coefficient and wear rate (0.22 and 6 × 10−07 mm3/m respectively). However the best bioactive behavior was exhibited by the films deposited at 25% of oxygen due to their higher roughness and porosity. In fact, it was found that the bioactivity of the films is highly dependent on the porosity and roughness of the films.

Compositional dependence of linear and nonlinear optical response in crystalline hafnium zirconium oxide thin films

Composition dependence of second harmonic generation, refractive index, extinction coefficient, and optical bandgap in 20 nm thick crystalline Hf1−xZrxO2 (0 ≤ x ≤ 1) thin films is reported. The refractive index exhibits a general increase with increasing ZrO2 content with all values within the range of 1.98–2.14 from 880 nm to 400 nm wavelengths. A composition dependence of the indirect optical bandgap is observed, decreasing from 5.81 eV for HfO2 to 5.17 eV for Hf0.4Zr0.6O2. The bandgap increases for compositions with x > 0.6, reaching 5.31 eV for Hf0.1Zr0.9O2. Second harmonic signals are measured for 880 nm incident light. The magnitude of the second harmonic signal scales with the magnitude of the remanant polarization in the composition series. Film compositions that display near zero remanent polarizations exhibit minimal second harmonic generation while those with maximum remanent polarization also display the largest second harmonic signal. The results are discussed in the context of ferroelectric phase assemblage in the hafnium zirconium oxide films and demonstrate a path toward a silicon-compatible integrated nonlinear optical material.

SUBSTRATE MATERIAL INFLUENCE ON THE THERMOCHEMICAL LASER WRITING OF DIFFRACTIVE STRUCTURES ON ZIRCONIUM FILMS

The paper is devoted to comparing the features of the formation of oxide microstructures during direct laser writing on thin (100 nm) zirconium films deposited on glass and fused silica substrates to identify the most stable and predicted writing modes. The presence of self-induced oxide quasiperiodic structures was detected during continuous laser writing on zirconium films deposited on glass substrates. The effect of the formation of nanostructures, which are parallel cracks in the oxide layer and have a period equal to the recording step (250-500 nm), formed during the writing process on zirconium films deposited on a quartz substrate is revealed. The advantages of fused silica as a substrate material for direct laser writing on zirconium films are shown due to the higher softening temperature of fused silica compared to glass.

Cross-Plane Thermal Conductance of Phosphonate-Based Self-Assembled Monolayers and Self-Assembled Nanodielectrics.

Self-assembled nanodielectrics (SANDs) consist of alternating layers of polarized phosphonate-functionalized azastibazolium π-electron (PAE) and high-k dielectric metal oxide (ZrO2 or HfOx) films. SANDs are desirable gate dielectrics materials for thin-film transistor applications because of their excellent properties such as low-temperature fabrication, large dielectric strength, and large capacitance. In this paper, we investigate the cross-plane thermal boundary conductance of SANDs using the frequency domain thermoreflectance (FDTR) technique. First, we characterize the thermal conductance of PAE self-assembled monolayers (SAMs), inverted-PAE (IPAE) SAMs, and mixed PAE-IPAE SAMs, sandwiched between thin gold and silica (SiO2) films at the top and bottom surfaces. Next, we quantify the thermal conductance of SAND-n with different numbers (n) of PAE-ZrO2 layers and thicknesses ranging between 4.7 and 11.3 nm. From the FDTR measurements, we observe that the thermal boundary conductance of the SAMs can be tuned between 42.1 ± 4.6 MW/(m2 K) and 52.4 ± 2.5 MW/(m2 K), based on the relative density of the PAE and IPAE chromophores. In the SAND-n samples, we observe a monotonic decrease in the thermal conductance with increasing n. We use the measured thermal conductance data in a series resistance model to estimate a thermal interface conductance of 695 MW/(m2 K) for the contact between the PAE chromophore and the zirconium dioxide films, which is an order of magnitude larger than the SAMs. We attribute the improved thermal conductance to stronger adhesion between the PAE chromophore and the zirconium dioxide films, as compared to the weakly bonded SAMs to the gold and silicon dioxide films.

Apparent relaxation of in-plane residual stress of sol–gel-derived crystalline and glass oxide thin films

Crystalline or glass oxide thin films with thickness of ca. 50–210 nm and porosity of ca. 5–17% were prepared on Si(100) wafers by the sol–gel method. The films were left standing at room temperature in dry and humid atmosphere as well as in water for varying periods of time. We measured the in-plane residual stress of the films as a function of time during storing at room temperature by measuring the radius of curvature of the substrate surface. The anatase, silica, and ceria films had tensile in-plane residual stress when fired at 1000 °C, 600 °C, and 800 °C, respectively. Such tensile stress was found to decrease with time, finally becoming constant, at room temperature, where the rate and extent of stress reduction were larger in the order, “in water” > “in humid atmosphere” > “in dry atmosphere.” On the other hand, the silica films had compressive in-plane residual stress when fired at 1000 °C. Such compressive stress was stable, not decreasing with time, at room temperature. The ceria film, after showing a decrease in tensile stress in humid atmosphere, exhibited an increase in stress when heated at 300 °C. When stored again at room temperature in humid atmosphere, the film showed a decrease in stress with time over again. Then we excluded the structural relaxation as the origin of the tensile stress reduction at room temperature, considering the stability of the compressive stress and the reversibility of the tensile stress. The ceria films showed a decrease in tensile stress even when stored in acetone and n-heptane vapors, suggesting that the film expansion resulting from the vapor-molecule adsorption may be the origin of the decrease in tensile stress. Yttria-stabilized zirconia films fired at 1000 °C also had tensile stress. The stress, however, was constant with time at room temperature, the reason for which is unknown, and further studies should be made.

The formation of oriented barium carbonate from the decomposition of yttria-doped barium zirconate films

Yttria doped barium zirconate (BZY) thin films show promise thanks to their high proton conductivities and their possibility for use in studying fundamental processes such as exsolution. This work demonstrates that highly oriented BZY thin (45 nm) films on (100) single crystal strontium titanate decompose into oriented barium carbonate rods and yttria stabilized zirconia when exposed to industrial grade Ar or pure CO2 at 800 °C. It is shown with transmission electron microscopy that the rods nucleate on the BZY surface. The causes and modes of decomposition in these thin films are discussed in detail.

Structure and properties of zirconium oxide films doped with yttrium oxide obtained by laser deposition in vacuum

The thin films deposited in vacuum (2 ⋅ 10–2 mm Hg) on the silicon and glass substrates under the multi-pulse high-frequency (10 –15 kHz) laser exposure (laser radiation power density 100 MW/cm2 and the distance from the target to the substrate 40 mm) for zirconium oxide ZrO2 ceramics doped with yttrium oxide 5 % Y2O3. The morphology of the obtained films was studied using atomic force microscopy. The features of transmission spectra in the visible, near infrared and middle infrared region were revealed. The transmission of the zirconium oxide film on the silicon substrate reached 12 % in the spectral region from 1.0 to 2.5 μm, and in the region from 2.6 to 6.0 μm was 4.7 %. On a glass substrate, the transmittance at a wavelength of 643 nm was 60 %, and at a wavelength of 2500 nm it reached 87 %. In the middle infrared region, transmission at a frequency of 2548 cm–1 was 70 % and reached 75 % at a frequency of 3566 cm–1. The volt-ampere and capacitance-voltage characteristics of the obtained zirconium oxide films were characterized by non-linearity, including hysteresis, and are probably due to the presence of discrete surface states with a wide energy spectrum associated with nanoparticles and nanocrystalline film inclusions.

Magnetic behavior of Fe-doped zirconia studied by synchrotron radiation measurements and first-principles simulations

Exploiting first-principles simulations and x-ray absorption near edge spectroscopy (XANES) in high magnetic fields, we investigated the magnetic properties of thin films of zirconia doped with Fe impurities. In our ${\mathrm{Zr}}_{1\ensuremath{-}x}{\mathrm{Fe}}_{x}{\mathrm{O}}_{2\ensuremath{-}y}$ samples, grown by atomic layer deposition (ALD), the Fe dopants are uniformly distributed, ranging from diluted ($x\ensuremath{\simeq}2\text{--}3%$) up to high ($x\ensuremath{\simeq}25%$) atomic concentration. By x-ray magnetic circular dichroism (XMCD), we carefully analyzed, for samples having different Fe concentration, the magnetic moments as a function of temperature, in the range from 5 K up to 150 K, studying the best dopant concentration range maximizing the magnetic signal. Surprisingly, the iron magnetic moment measured for diluted concentrations degrades as the concentration of magnetic dopant increases. On the basis of ab initio simulations, we propose that the microscopic mechanisms responsible for the peculiar magnetic properties of this compound can be explained by oxygen-mediated superexchange mechanism between the Fe dopants producing, at high dopant concentration, an antiferromagnetic coupling between two Fe atoms. We identify and discuss the role of O vacancies to control such microscopic mechanisms.

In-situ electrochemical study of zirconium alloy in high temperature hydrogenated Water conditions

The electrochemical characteristics of a Zr-Nb-Sn zirconium alloy have been investigated at 360 ℃ in simulated primary water condition of pressurized water reactor with two different dissolved hydrogen contents. In-situ electrochemical impedance spectroscopy experiment was performed for 100 d, and the thickness and resistivity of the zirconium oxide films were measured as function of time. The results show that there is a difference in oxide resistivity as function of dissolved hydrogen content in the environment. The resistivity of the oxide film on Zr-Nb-Sn alloy is lower at higher dissolved hydrogen condition, resulting in a higher corrosion rate at that condition.

Radiation response of zirconium silicate P-MOS capacitor

The chemical bonding of zirconium silicate films were examined by FTIR. The capacitance-voltage (C-V) measurements before and after irradiation were performed at high frequency. Furthermore, significant changes were observed depending on the radiation dose of the oxide traps and the intensity of the interface state. The sensitivity of this MOS capacitor is 4.3, 31.3 and 15.6 times less sensitive compared to the same thickness as Sm2O3, Al2O3 and Gd2O3. Therefore, it can be used as radiation-resistant material in nuclear reactors and space applications due to its stable electrical characteristics compared to other defined dielectrics. Interface states, (Nit) Barrier potential (Φb) and oxide traps (Not) have also been investigated depending on the radiation effects. Φb is one of these important electrical properties. Φb values decreased with increasing in radiation dose. Besides, radiation and frequency dependent dielectric constant (ε′), dielectric loss (ε″) and dielectric loss tangent (tanδ) and conductivity (σac) of zirconium silicate were investigated. It is concluded that high-k zirconium Silicate is suitable for electronics applications in radiation harsh environment.