Epitaxial Growth Of CeO Research Articles

Chemical Solution Growth and Oxygen Diffusion Behavior of Doped CeO2−δ Buffers in Coated Conductors

Ba-, La-, and Zr-doped CeO2−δ films and undoped CeO2−δ film with (00 l) preferred orientation have been prepared on biaxially textured Ni–W substrates by metal organic decomposition (MOD) method. The influences of valences and ionic radii of dopants on the epitaxial growth of CeO2−δ films and oxygen diffusion in the buffer layer were explored by X-ray diffraction (XRD) and atomic force microscopy (AFM). The doping cations with different radii cause the change of the lattice parameter of CeO2−δ film and the mismatch between Ni–W substrate and epitaxial film, which modifies the compressive strain resulted from the elastically lattice deformation in the films. Our results show that the compressive strain is beneficial to the c-axial texture formation of CeO2−δ film. In addition, ionic radius has influence on the surface roughness and the out-of-plane texture of the film. Moreover, the oxygen diffusion results from the inherent variation of the thermodynamic factors, in particular the migration energy of oxygen ions. Meanwhile, larger radius of doping cation would lead to the decrease of the migration energies of oxygen ion due to the steric effect. So compared with the Ba- and La-doped CeO2−δ films, the Zr-doped CeO2−δ film shows slight oxygen diffusion. These results are significant to improving the properties of buffer layer for coated conductors.

Influence of Annealing Atmosphere on Epitaxial Growth Process of the CeO2 Buffer Layer for Coated Conductors

The epitaxial growth of the buffer layer on a textured metal substrate has a significant influence on the performance of coated conductors, which provides the potential to support a high current for electric utility and high magnetic field applications at 77 K. In this paper, we have fabricated the CeO2 buffer layer on YSZ (yttria-stabilized zirconia) (00l) single crystal substrates by the chemical solution deposition (CSD) method in different annealing atmospheres. The results show that both the thermal decomposition behavior of the precursor solution and the annealing atmosphere have an important effect on the epitaxial growth process of the CeO2 buffer layer. The large oxygen partial pressure in annealing atmosphere is to the disadvantage of the epitaxial growth of CeO2 (00l) crystal face with high energy. Moreover, the epitaxial growth of the CeO2 (00l) crystal plane goes against a decrease in the surface roughness of the CeO2 film. Therefore, it can be considered that the orientation growth of the CeO2 buffer layer and its surface morphology evolution may be related to the thermal decomposition behavior of precursor solution and the change of oxygen vacancies concentration.

Fast Growth Processes of Buffer Layers for YBCO Coated Conductors on Biaxially-Textured Ni Tapes

Epitaxial growth of CeO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> buffer layers on biaxially textured (001) Ni tapes was studied using reel-to-reel pulsed laser deposition. Relationship between microstructure and deposition parameters was systematically studied in order to develop reliable long tape coating processes. Prior to buffer layer deposition, Ni tapes were in situ annealed in forming gas (97% argon + 3% hydrogen) under various pressures and tape speeds to accelerate reel-to-reel annealing processes. It was found that orientation and texture of CeO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> buffer layers were sensitive to deposition parameters. X-ray diffraction analyses showed that CeO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> buffer layers had pure (001) orientation at forming gas pressure of 5 mTorr and 700degC. Under optimized deposition conditions, highly (001) oriented CeO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> buffer layers have been achieved at a high tape speed of 20-50 m/h. In-lane texture of CeO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> buffer layers was 7 degree which was comparable to the value of Ni tapes.

Epitaxial growth of CeO2 on silicon and distribution of element concentration at the interface

To investigate the composition of interfaces of thin CeO2 films on silicon, two diagnostic approaches, the elemental and phase composition analyses by Auger spectra under ion profiling, are used. The interrelation between the conditions of epitaxial growth of CeO2 and features of distribution of elements at the film-substrate interface is traced.

Epitaxial Growth of CeO&lt;sub&gt;2&lt;/sub&gt; Buffer Layers on Both YSZ Single Crystal and Textured Ni5W Substrates by MOD Method

CeO2 has been considered as one of the most lattice compatible and chemically stable materials for YBa2Cu3O7-x coated conductors. In this paper, we presented the epitaxial growth of CeO2 thin film on both YSZ single crystal and cube textured Ni5W substrates by MOD method. Homogenous, crack-free and dense CeO2 thin films on both substrates with sharp biaxially cube texture were fabricated by post-annealing the precursor films at 1000-1150°C. For the CeO2 film on the textured Ni5W substrate, the FWHM values of (111) Phi-scan and (002) rocking curve were around 6°and 7°, respectively, the surface roughness was less than 2 nm over an area of 1μm×1μm observed by AFM. It was found that the CeO2 thin film improved both the in-plane orientation and surface roughness of the Ni5W substrate, indicating that the as deposited CeO2 films were suitable for the further growth of YBCO superconductor layer.

Electron beam induced orientation selective epitaxial growth of [formula omitted] layers on Si(1 0 0) substrates

From studies on the epitaxial growth of CeO 2 layers on Si(1 0 0) substrates using reactive DC magnetron sputtering, it has been found that the epitaxial CeO 2 layer with (1 0 0) or (1 1 0) orientation is selectively grown by controlling substrate bias and the growth rate. Optimum bias for the CeO 2 (1 0 0) layer growth was ± 15 V . In order to develop this technology into two-dimensional orientation selectivity, we attempt to grow CeO 2 (1 0 0) by low energy electron irradiation, as an alternative way to substrate bias application. It proved that electron beams in two energy regions of 30–40 and 80–100 eV are effective on preferential growth of CeO 2 (1 0 0) layers.

Epitaxial growth of CeO2/yttria-stabilized ZrO2 double layer films on biaxially textured Ni tape via electrostatic spray assisted vapour deposition

Epitaxial growth of CeO2 and yttria-stabilized ZrO2 (YSZ) double layer films has been successfully carried out on biaxially textured nickel substrates at a temperature between 400 and 600 °C using electrostatic spray assisted vapour deposition method. The structure of the double layer was characterized by X-ray diffraction and scanning electron microscopy. The results show that highly oriented CeO2/YSZ double buffer films were formed epitaxially onto biaxially textured Ni substrates. The orientation relationships between YSZ layer and Ni substrate are 001YSZ//001Ni and 110YSZ//100Ni, while the orientation relationships between CeO2 and YSZ are 001CeO2//001YSZ and 100CeO2//100YSZ.

An experimental study of the main involved parameters in the epitaxial growth of CeO 2 buffer layers on nickel tapes

In order to investigate the optimal conditions for highly oriented and epitaxial buffer layers on nickel based tapes, we have grown several sequences of cerium oxide films by pulsed laser deposition technique. Amongst the usual parameters governing this procedure and connected to obtain high quality buffer layers, three of them have requested a special attention through this work: the target–substrate distance, the buffer layer deposition temperature and the gas atmosphere inside the vacuum chamber during the growing process. Based on the following results, we have found a full crossed relation amongst them, which develops in obtaining textured layers of highly oriented CeO 2 along the (0 0 1) ordered nickel substrate.

Evolution of texture of CeO 2 thin film buffer layers prepared by ion-assisted deposition

Evolution of texture in CeO 2 thin films was studied using biased magnetron sputtering and ion beam assisted magnetron sputtering. Films deposited onto polycrystalline Hastelloy metal substrates by biased magnetron sputtering develop preferential (002) growth as the energy of the ions is increased from zero to above 100 eV. For ion beam assisted magnetron sputtering (magnetron IBAD), with the ion beam directed at 55° to the substrate normal, the evolution of biaxial alignment is controlled by the ion beam energy and the ion/atom arrival rate ratio. Ion beam energies >200 eV and ion/atom ratios >0.3 lead to perfect biaxial alignment with one pole aligned along the ion beam direction. Epitaxial growth of CeO 2 films was observed for MgO(001) substrates at 750°C without any ion assistance, and on yttria-stabilised zirconia (001) buffer layers at room temperature and a bias of −80 V.

Epitaxial growth of CeO 2(1 0 0) films on Si(1 0 0) substrates by dual ion beams reactive sputtering

The epitaxial growth of CeO 2(1 0 0) films on (1 0 0) silicon substrates by dual ion beams sputtering was studied. The measurements of X-ray θ-2θ pattern, ϕ-scan and rocking curve indicated that the CeO 2 films had good epitaxial characteristics with (1 0 0) orientation. The experiments showed that the substrate temperature had only a weak influence on the orientation in a wide temperature range. In contrast to this, the oxygen pressure during the deposition had a strong influence on the growth.

Simulation of epitaxial growth of CeO 2 on YSZ(100) and SrTiO 3 on MgO(100) for YBa 2Cu 3O 7− x deposition

A simulation based on the optimization of the interaction energy between the atoms at both sides of the different film and film-substrate interfaces has been used to qualitatively predict their relative in-plane positioning and orientation. The method has been applied to YBa 2Cu 3O 7 (YBCO), CeO 2 and SrTiO 3 films on yttria stabilized zirconia (YSZ) (100) and MgO(100) single crystals. It allows to predict cube-on-cube epitaxial growth of CeO 2 on YSZ(100) and SrTiO 3 on MgO(100). [00h] oriented YBCO epitaxial growth should take place on the buffers with [0h0] axes rotated 45° away from [100] direction of CeO 2, and parallel to [100] direction on SrTiO 3. The computed relationships are in agreement to the results obtained in laser ablation deposited YBCO/YSZ(100), YBCO/CeO 2/YSZ(100), YBCO/MgO(100) and YBCO/SrTiO 3/MgO structures as well as other reported results.

Biaxially aligned buffer layers of cerium oxide, yttria stabilized zirconia, and their bilayers

Biaxially aligned cerium oxide (CeO2) and yttria stabilized zirconia (YSZ) films were deposited on Ni-based metal (Hastelloy C276) substrates held at room temperature using ion beam assisted (IBAD) magnetron deposition with the ion beam directed at 55° to the normal of the film plane. In addition, we achieved, room-temperature epitaxial growth of CeO2 by bias sputtering to form biaxially aligned CeO2/YSZ bilayers. The crystalline structure and in-plane orientation of films was investigated by x-ray diffraction techniques. Both the IBAD CeO2 and YSZ films, and the CeO2/YSZ bilayers have a (111) pole in the ion beam direction.

Epitaxial growth of CeO2 on MgO by pulsed laser deposition

CeO2 thin films have been deposited on single-crystal MgO(001) substrates by the pulsed laser ablation technique. The composition, phase formation, crystalline quality of the films, and the film/substrate orientation relationships have been analyzed by the complementary use of Rutherford backscattering spectrometry and X-ray diffraction analysis. The films grown under vacuum at temperatures lower than 700°C are not crystalline. The quality of the films is largely improved at higher temperatures. So, highly textured (00l) CeO2 films are grown at 750°C under vacuum with a crystallinity comparable to that of monocrystals. The film/substrate epitaxial relationships present well defined in-plane orientations at 0° and at 45°. The relative amount of film grown in each one of these orientations is largely determined by the growth conditions.

Epitaxial Growth of Oxide Thin Films on (001) Metal Surfaces Using Pulsed-Laser Deposition

ABSTRACTThe epitaxial growth of CeO2 on various (001) metal surfaces using pulsed-laser deposition is discussed. In particular, the growth of (001) CeO2 on (001) Pd, Ag, and Ni is described. Emphasis is given to the specific deposition conditions which successfully alleviate the formation ornative oxides at the metal/metal oxide interface. The control of the epitaxial relationships between the oriented oxides films and the underlying noble and oxidizing metal surfaces is addressed.

Effect of Electron Incidence in Epitaxial Growth of CeO2(110) Layers on Si(100) Substrates

ABSTRACTWith the aim of lowering epitaxial growth temperature, the effect of electron incidence is studied in the epitaxial growth of CeO2(110) layers on Si(100) substrates by electron-beam evaporation in an ultrahigh vacuum. Two growth methods are employed: evaporation under substrate bias application and electron-beam assisted evaporation. In evaporation at positive substrate bias, electrons and anions from an evaporation source are attracted to the substrate surface, resulting in successful epitaxial temperature lowering. It is clarified that facilitation of the epitaxial growth is attributed only to electron incidence. The electronic current component is measured to be on the order of 10−4 A, about half of the total current. In using electron-beam assisted evaporation for higher current (10−3 A), electron-beam irradiation is demonstrated to have a much greater effect in both the growth temperature lowering and the crystalline quality improvement. The epitaxial growth facilitation effect increases with electron energy in both evaporation methods. It is clarified that the epitaxial growth temperature is lowered to 720°C, i. e., epitaxial growth temperature lowering of ∼100°C compared with the conventional growth method, both by evaporation with substrate bias at +240 V and 240 eV-electron-beam assisted evaporation, wherein the latter produces higher crystalline quality layers.

Preparation and microstructural study of CeO2 thin films

Epitaxial and textured ceria films were prepared by conventional electron-beam evaporation on (001) LaAlO3, (11̄02) R-cut sapphire, (001) Au, and (001) Pd substrates using ceramic and metallic sources. Deposition temperature and deposition rate were varied to determine their effects on the formation of the CeO2 films. It was also found that the epitaxial formation of CeO2 films varied with different substrates and evaporation sources. Ceria films grew epitaxially on sapphire with a deposition rate less than 0.5 Å/s in the temperature range of 650–750 °C using either ceramic or metallic source. The epitaxial growth of CeO2 on LaAlO3 occurred at deposition rates as high as 1.0 Å/s at a deposition temperature as low as 600 °C using a metallic source, while on the (001) Au substrate, only a textured structure was observed between 580 and 700 °C and at deposition rates from 0.3 to 1.0 Å/s. On a (001) Pd substrate, the deposited CeO2 films showed a different microstructure corresponding to ceramic and metallic sources at deposition rates of 0.2–0.5 Å/s and from 700 to 750 °C. The epitaxial ceria films were achieved using a ceramic source, while the polycrystalline ceria films of multiple twinning were obtained using the metallic source. The epitaxial growth temperature of CeO2 on these substrates was empirically found to be around 700 °C (i.e., 0.35 Tm).

CeO2/YSZ and SrTiO3/YSZ Double Buffer Layers Deposited on Si(100) by Laser Ablation

AbstractYttria stabilized zirconia (YSZ), SrTiO3 and CeO2 thin films have been widely used as buffer layers in YBa2Cu3O7-x (YBCO) deposition on silicon substrates. YBCO superconducting properties are limited by lattice mismatches between YSZ and YBCO, and chemical interaction of CeO2 and SrTiO3 with silicon. In order to avoid these problems we have deposited CeO2/YSZ/Si(100) and SrTiO3/YSZ/Si(100) bilayers by laser ablation. Wide temperature and pressure ranges have been studied. The influence of the intermediate layer on the CeO2 and SrTiO3 films properties has been studied. Previous studies were performed on films of each material on Si(100) and YSZ(100) single crystals. The surface of the films and bilayers is smooth without microcracks and only few droplets are found. Only small interdiffusion is observed in all the cases. Texture of the films changes with deposition conditions. Epitaxial growth of CeO2 has been found both on YSZ(100) single crystals and YSZ buffers on Si(100).

Study on Epitaxial Growth of CeO2 (110)/Si(100) in Conjunction with Substrate Off-Orientation

AbstractThe substrate off-orientation effect is systematically studied on epitaxial CeO2(110) layers on Si(100), and the crystalline quality is significantly improved by enhancement of domains whose 〈110〉 is perpendicular to the offset-direction (Si〈110〉). AFM measurements indicate that the CeO2 layer surface consists of stripe-shaped facets and that their size is typically 100˜200 nm long, 20 nm wide and ∼3 nm high for a 150 nm-thick layer. RHEED and XTEM reveal that CeO2〈110〉 axis is inclined from wafer normal by the off-angle. The step arrangement at Si surface observed by XTEM relates closely to the inclination of the facets. It is found that off-orientation (≥∼,2.5°) leads to single crystal layer formation. RBS analyses verify that the crystalline quality is significantly improved, especially at the surface. The best result is obtained at the off-angle of 2.5°.

Growth Mechanism of Epitaxial Oxide Films by Laser MBE

ABSTRACTCrystallographic structure and valence state of CeO2 and Nd2-O3 films deposited by laser MBE on Si substrates were investigated by reflection high energy electron diffraction (RHEED) and X-ray photoelectron spectroscopy (XPS). In contrast with epitaxial growth of CeO2 (111) and Nd2O3(111) on Si (111), epitaxial films were not obtained on Si(001). Partially reduced mixed valence (4+ and 3+) Ce was indicated to exist by XPS in the cerium oxide film within 2nm from the interface with Si. Beyond this transition layer, two-dimensional growth of CeO2 film on Si(111) was verified from in situ RHEED and as well as on Si(001) from XPS measurements.