Single Crystal Oxide Substrates Research Articles

Raman scattering characterization of vertical aligned 1D IrO 2 nanocrystals grown on single crystal oxide substrates

Raman scattering (RS) has been used as a technique for characterization of IrO 2 one dimensional (1D) nanocrystals (NCs) deposited on sapphire(100) and LiNbO 3(100) substrates under various conditions. The IrO 2 NCs were grown via metalorganic chemical vapor deposition method using (MeCp)(COD)Ir as the precursor and reactive magnetron sputtering using Ir metal target. The red-shifts and asymmetric broadening of the Raman lineshape for the NCs were analyzed by a modified spatial correlation (MSC) model, which includes the factor of stress induced shift. The proposed MSC model showed that the effects of stress and nanometric size can be separated in analyzing the observed Raman features. The usefulness of the experimental RS together with the MSC model analysis as a residual stress and structural characterization technique for 1D NCs has been demonstrated.

GRAIN GROWTH AND RESIDUAL STRESS IN BST THIN FILMS

ABSTRACT Residual stress plays an important role in the determination of properties and lifetime of thin film dielectric films. While residual stress can be caused by a variety of factors, grain growth is of particular importance. Using theoretical approaches the stress due to grain growth and coalescence are predicted for magnesium doped barium strontium titanate thin films on magnesium oxide single crystal substrates. Grain growth leads to large compressive stresses for larger grains, while grain coalescence yields extremely high tensile stresses in very thin films. How stress affects defect incorporation, stress relaxation pathways, and their impact on film properties are examined.

Epitaxial Growth Map for Bi4Ti3O12 Films: a Determining Factor for Crystal Orientation

Bi4Ti3O12 films were epitaxially grown at 600–750°C on various types of single-crystal oxide substrate by metal-organic chemical vapor deposition. In terms of the oxygen interatomic distances of the substrates used, the crystal orientations of the deposited epitaxial films were classified into three groups: (118), in-plane c-axis, and (001) orientations. The films on substrates with an oblong in-plane oxygen unit, had a (100)/(010) and/or (118) orientation, wheras those on substrates with a square in-plane oxygen unit had (001) or (hk0)/(kh0) orientation. There was an intermediate region between the (100)/(010) and (118) orientations at the present deposition temperature, where both orientations coexisted. As a result, the relationship between in-plane oxygen interatomic distances of the substrates and film orientation was summarized into an epitaxial growth map. This map is applicable to the epitaxial growth of other bismuth-layer-structured ferroelectric thin films.

High-throughput Studies on Photochemical Properties of Transition Metal-Doped SrTiO3 Epitaxial Thin Films

AbstractCombinatorial pulsed laser deposition approach is suitable to study complex effects such as composition, thickness and surface structure on thin film-based photocatalysis in high-throughput manner. We fabricated composition spreads and thickness gradient films of transition metal-doped SrTiO3(001) on various oxide single crystal substrates and evaluated their photocatalytic activity by the use of photoreduction of Ag+ in AgNO3 solution. We found anomalous film thickness and substrate effects on the Ag-photodeposition in the V-doped SrTiO3 epitaxial thin films grown on the Nb:SrTiO3(001) substrate.

Application of ion implantation for synthesis of copper nanoparticles in a zinc oxide matrix for obtaining new nonlinear optical materials

We have obtained a layered composite material by implantation of single crystal zinc oxide (ZnO) substrates with 160-keV Cu+ ions to a dose of 1016 or 1017 cm−2. The composite was studied by linear optical absorption spectroscopy; the nonlinear optical characteristics were determined by means of Z-scanning at a laser radiation wavelength of 532 nm. The appearance of the optical plasmon resonance bands in the spectra indicated that ion implantation to the higher dose provides for the formation of copper nanoparticles in a subsurface layer of ZnO. The new nonlinear optical material comprising metal nanoparticles in a ZnO matrix exhibits the phenomenon of self-defocusing and possesses a high nonlinear absorption coefficient (β=2.07×10−3 cm/W).

Stress-induced magnetization for epitaxial spinel ferrite filmsthrough interface engineering

This study found “stress-induced magnetization” for epitaxial ferrite films with spinel structure. We grew (111)- and (001)-epitaxial Ni0.17Zn0.23Fe2.60O4(NZF) films on CeO2∕Y0.15Zr0.85O1.93(YSZ)∕Si(001) and oxide single-crystal substrates, respectively. There is a window of lattice mismatch (between 0 and 6.5%) to achieve bulk saturation magnetization (Ms). An NZF film grown on CeO2∕YSZ∕∕Si(001) showed tensile stress, but that stress was relaxed by introducing a ZnCo2O4(ZC) buffer layer. NZF films grown on SrTiO3(ST)(001) and (La,Sr)(Al,Ta)O3(LSAT)(001) had compressive stress, which was enhanced by introducing a ZC buffer layer. In both cases, bulk Ms was achieved by introducing the ZC buffer layer. This similarity suggests that magnetization can be controlled by the stress.

The contact angle between liquid iron and a single-crystal magnesium oxide substrate at 1873 K

The contact angle between liquid iron and a single-crystal magnesium oxide substrate at 1873 K

Growing and characterization of La 0.8Sr 0.2MnO 3 thin films on single crystal oxide substrate

La 0.8Sr 0.2MnO 3 (LSMO) displays a transition from a low temperature metallic phase to an insulator high temperature phase. Depending on Sr concentration, the transition temperature may occur above room temperature. This property may be used for integrated microelectronic devices like limiter of current and/or voltage. The weak lattice mismatch between the LSMO and different substrates like LaAlO 3 (0 0 1) or SrTiO 3 (1 0 0) favors an epitaxial growth of LSMO deposited by pulsed laser ablation techniques. Analyses by X-ray diffraction, infrared reflectivity spectroscopy and temperature dependence of the resistivity allow the optimization of growing condition. The aim is to reach or at least to approach the crystal properties. The target was elaborated by organic gel-assisted citrate process. The X-ray diffractograms show that the films have a c-axis orientation. The film thicknesses have been deduced from the interferences observed in infrared spectra in the semi-transparent regime at high frequencies. The measurements of resistivity versus temperature show that the transition temperature reaches 325 K for optimized growing conditions. The conductivity of the film approaches that of the crystal at the transition temperature.

Strongly coupled critical current density values achieved in Y1Ba2Cu3O7−δ coated conductors with near-single-crystal texture

One of the most intensely researched subjects in the development of YBa2Cu3O7−δ (YBCO)-based coated conductors is the methodology for achieving ever-sharper film texture on flexible metal substrates. This is a critical issue due to the intrinsic weak-link behavior that results in depressed critical current density (Jc) in polycrystalline YBCO. Using ion-beam-assisted deposition of magnesium oxide, we have achieved YBCO texture on superalloy substrates approaching that on single-crystal oxide substrates. This advance has allowed us to fabricate coated conductor samples with Jcs that are as high as for films on oxide crystals; for example, >2 MA/cm2 (75 K, self-field) at a YBCO thickness of ∼1.5 μm.

Preparation and characterization of epitxial Co-alloy magnetic thin films on oxide single-crystal substrates

Co-alloy single-crystal thin films were prepared on SrTiO 3(1 1 1), LaAlO 3(0 0 0 1), and Al 2O 3(0 0 0 1) substrates. The film structure was studied using X-ray diffraction and high-resolution transmission electron microscopy. It is shown that epitaxial growth of a CoCrPt magnetic layer strongly depends on the substrate and underlayer materials.

Single-crystal and Nano-columnar Growth of Gadolinium-doped Ceria Thin Films on Oxide Substrates Studied Using Electron Microscopy

ABSTRACTGadolinium-doped ceria (GDC) thin films were grown by pulsed laser ablation on various oxide single crystal substrates including MgO, YSZ, LAO, NGO, and STO with different film-substrate lattice mismatch ratios. The film microstructures were characterized mainly by using electron microscopy. A clear influence of the filmsubstrate lattice mismatch on the film crystallinity has been observed. The GDC films usually exhibit columnar grain growth for a large range of film-substrate lattice mismatch ratios. A cube-on-cube growth of GDC film on MgO has been observed with a surprisingly high lattice mismatch ratio of 28%. The highest film crystallinity is obtained on the LAO substrates under a small compressive strain. This single-crystalline GDC film shows no columnar grain growth but presents a novel directionally-aligned precipitated Gd-rich nanoparticle system, which plays a specific role in relaxing various kinds of strain fields induced during the thin film growth to ensure the film crystallinity.

Self-organized Fabrication of Ordered Nanostructures of Variable Periodicity on Nonstoichiometric Metal Oxide Materials

We report the controlled fabrication of self-organized nanostructures by the use of solid-state reaction between a deposited film and a metal oxide single-crystal substrate. Long-range ordered nanocrystals are formed by the reaction of Mg−Ti−O on MgO(001) and Ba−Ti−O on TiO2(001). The size and the periodicity of the nanocrystals can be changed by deposition conditions.

Crystallographic and Magnetic Properties of CoCrPt Thin Films Investigated Using Single-Crystal Perpendicular Magnetic Thin Film Samples

AbstractConditions to prepare good single-crystal CoCrPt magnetic thin film with the easy magnetization axis perpendicular to the film plane were investigated using oxide single-crystal substrates, Al2O3(0001), LaAlO3(0001), mica(0001), SrTiO3(111), and MgO(111). The best CoCrPt(0001) single-crystal thin film was obtained on an Al2O3(0001) substrate employing a non-magnetic CoCrRu underlayer. The crystallographic quality of single-crystal thin film was investigated using X-ray diffraction and high-resolution transmission electron microscopy. Some intrinsic magnetic properties (Hk, Ku) were determined for the single-crystal CoCrxPty thin films for a compositional range of x=17-20at% and y=0-17at%.

Diamond film growth in an oxygen atmosphere

We propose a new method for the synthesis of diamond films via a hydrogen-free vapor-phase route of pulsed laser ablation of a graphite target in a low-pressure pure oxygen atmosphere. The evidence from microscopic, diffraction and spectroscopic techniques indicates that high-quality diamond crystals can be nucleated and grown epitaxially on sapphire (single-crystal aluminum oxide) substrates without diamond-powder treatment at temperatures lower than 600°C under the optimized growth conditions of oxygen pressure and pulsed KrF-excimer laser ablation. The spectroscopic property of a laser plasma plume produced during pulsed laser ablation of graphite in an oxygen atmosphere was examined by using time-resolved optical emission measurements in order to discuss the vapor-phase reaction and film growth mechanism.

In-plane aligned YBCO thick films grown in situ by high temperature ultrasonic spray pyrolysis

Ultrasonic spray pyrolysis (USP)has been used to deposit thick films (up to 5 micron) ofYBa2Cu3O7-x in situ on single-crystaloxide substrates, and single-crystal and texturedpolycrystalline Ag foil of different orientations. Epitaxialfilms grow with a strong level of in-plane texture on the singlecrystal oxide substrates (<3° full width at half maximum)and on (100) and (110) oriented Ag. Films grown under optimizedconditions have onset Tc of 91 K with transition widths of~ 6 K. The films are fully connected and Jc are~ 1.0×104A cm-2 at 77 K and ~5×105A cm-2 at 20 K.

The Oxidation of Methanol to Formaldehyde on TiO2(110)-Supported Vanadia Films

The reaction of methanol on TiO2(110)-supported vanadium oxide was studied using temperature-programmed desorption (TPD) and high-resolution electron energy loss spectroscopy (HREELS). TPD results show that methanol is oxidized to formaldehyde on monolayer and submonolayer vanadia films on TiO2(110), whereas both clean TiO2(110) and multilayer vanadia films supported on TiO2(110) are relatively inactive for this reaction. HREELS results demonstrate that methoxides are the primary surface intermediates in the oxidation of methanol to formaldehyde on the supported vanadium layers. The reactivity trends obtained for the model catalysts used in this study are similar to those observed for high surface area analogues. This suggests that vanadia films supported on single-crystal metal oxide substrates are excellent model systems for studying the relationships between the structure and reactivity of supported oxide catalysts.

Coated conductor development by photo-assisted MOICVD growth of YBCO thick films and buffer layers

YBa 2Cu 3O 7−x films have been deposited by photo-assisted MOCVD at commercially viable rates on both single crystal oxide substrates and atomically textured metallic substrates. CeO 2 and YSZ buffer layers have also been developed by photo-assisted MOCVD for deposition on metallic substrates at rates approaching 1 μm/min. The resulting buffer layers show good duplicate of the moderate order of the underlying metallic substrates, and the subsequent YBCO layers show similar moderate atomic order with resulting J c ∼ 5 × 10 5 A/cm 2.

Development of High Critical Current YBCO Coated Conductors By Photo-Assisted MOCVD

ABSTRACTYBa2Cu3O7 (YBCO) films have been deposited by photo-assisted MOCVD at rates of greater than 0.3μm/min on both single crystal oxide substrates and atomically textured metallic substrates. The YBCO films of thickness from 0.5μm to 3μm deposited on LaAlO3 substrates are shown to be highly atomically ordered with Jc&gt; 1 × 106 A/cm2. CeO2 buffer layers have also been developed by photo-assisted MOCVD for the integration of YBCO with metallic substrates. The CeO2 layers were found to be crack-free when grown on nickel even above 1 micron thickness, and exhibited crystal orientation and in-plane alignment similar to that of the atomically textured Ni substrates. YBCO films grown on the thick CeO2 buffer layers on nickel substrates have shown promising results with Jc∼6 × 105 A/cm2.

Surface and Interface of Double Oxides. Characterization and Application of the Ultrasmooth Surface Nanostructure of Metal Oxides.

Nano-scale surface structures of single crystal metal oxides, especially the perovskite oxides were examined by coaxial impact collision ion scattering spectroscopy (CAICISS) and atomic force microscopy (AFM). CAICISS measurements enabled us to determine the terminating atomic species and their arrangements of single-crystal perovskite oxide substrates and epitaxial oxide films. Through thermal-annealing of the single crystal oxide substrates, atomically flat terrace and stepped structures were developed on the surface. The atomic-scale substrate engineering made it possible to attain the novel heteroepitaxial growth such as step-decoration epitaxy resulting in the nanowire structures and diamond epitaxy on the ultrasmooth sapphire substrate. The novel application of the ultrasmooth oxide substrate to the AFM observation stage for DNA molecules was also presented.

Thin Na0.5K0.5NbO3 Films for Varactor Applications

AbstractSingle phase Na0.5K0.5NbO3 (NKN) thin films have been pulsed laser deposited on SiO2/Si(C-01) wafers and LaAlO3(001) and MgO(001) single crystals. Radio frequency (up to 1 MHz) and microwave (up to 50 GHz) dielectric spectroscopy studies have been carried out to characterize thin NKN films for electrically tunable microwave device applications. Films on single crystal oxide substrates showed tunabilities as high as 30-40 % at 40 V bias and dissipation factor of 0.01-0.02 at 1 MHz. The films on Si substrates showed low dielectric losses of &lt; 0.01, and low leakage currents. Dielectric properties of ferroelectric films on Si substrates at low frequencies are greatly influenced by the depletion capacitance and the resistance inserted by semiconductor substrate. Microwave frequency measurements for NKN film on Si wafers yield more than 10 % tunability at 50 GHz and loss tan σ &lt;0.1 at 10 GHz.