Tuning of CeO2 buffer layers for coated superconductors through doping

We investigated some buffer materials and those deposition conditions to obtain high- quality c-axis oriented EuBa2Cu3O x (EBCO) films on Si(001) substrates using dc magnetron sputtering. In case of the deposition of CeO2 and Y2O3 on Si, it has been found difficult to grow (001) oriented films because of the existence of SiO x films. Accordingly, (001) oriented YSZ films were deposited as the first buffer layer, and the second layer of CeO2 or Y2O3 which has a small lattice mismatch with EBCO was grown epitaxially on the YSZ layer. Syntheses of the YSZ, CeO2 and Y2O3 buffer layers with (001) orientation and high-quality c-axis EBCO films were examined. The c-axis oriented EBCO films with T ce’s of about 90K were obtained on YSZ(200A)\CeO2(150A) buffer layers at 600°C and on YSZ(200A)\Y2O3(300A) buffer layers at 650°C. The EBCO films on the YSZ\Y2O3 buffer layers were superior to those on the YSZ\CeO2 buffer layers in crystallinity.

VO2 thin films were deposited on soda lime glass substrates with ZnO, TiO2, SnO2, and CeO2 thin films applied as buffer layers between the VO2 films and the substrates in order to investigate the effect of buffer layer on the formation and the thermochromic properties of VO2 film. Buffer layers with thicknesses over 50 nm were found to affect the formation of VO2 film, which was confirmed by XRD spectra. By using ZnO, TiO2, and SnO2 buffer layers, monoclinic VO2 (VO2(M)) film was successfully fabricated on soda lime glass at 370 °C. On the contrary, films of VO2(B), which is known to have no phase transition near room temperature, were formed rather than VO2(M) when the film was deposited on CeO2 buffer layer at the same film deposition temperature. The excellent thermochromic properties of the films deposited on ZnO, TiO2, and SnO2 buffer layers were confirmed from the temperature dependence of electrical resistivity from room temperature to 80 °C. Especially, due to the tendency of ZnO thin film to grow with a high degree of preferred orientation on soda lime glass at low temperature, the VO2 film deposited on ZnO buffer layer exhibits the best thermochromic properties compared to those on other buffer layer materials used in this study. These results suggest that deposition of VO2 films on soda lime glass at low temperature with excellent thermochromic properties can be achieved by considering the buffer layer material having structural similarity with VO2. Moreover, the degree of crystallization of buffer layer is also related with that of VO2 film, and thus ZnO can be one of the most effective buffer layer materials.

Using first-principles total energy calculations, we have investigated the lattice and elastic constants in $\mathrm{Ga}{\mathrm{N}}_{x}{\mathrm{As}}_{1\ensuremath{-}x}$ alloys as functions of the nitrogen concentration $x$. Ab initio density functional theory is used to find the relaxed atomic configurations and elastic constants for substitutional nitrogen in supercells containing up to 128 atoms. The effect of ${\mathrm{N}}_{2}$ and NAs split interstitial substitutions (ISs) on the mechanical properties has also been calculated in cells up to 64 atoms. Atomic positions and geometries in all supercells have been relaxed, and the elastic constant tensors for simple cubic 8-atom supercells have been computed. Deviation of the lattice constants from Vegard's law due to IS is shown to be substantial. We provide analytical expressions for the concentration dependence of the lattice and elastic constants in $\mathrm{Ga}{\mathrm{N}}_{x}{\mathrm{As}}_{1\ensuremath{-}x}$ alloys, including normal and split-interstitial substitutions, and find the ratio ${r}_{b}$ of the bowing coefficients of the elastic constants ${C}_{11}$ and ${C}_{12}$.

Erbium oxide (Er2O3) coating layer is one of the suitable coatings to realize an advanced breeding blanket system because it has high electrical resistivity and hydrogen permeation suppression effect. In order to enhance these properties of Er2O3 coating, it is necessary to form a thick coating layer with high crystallinity. The formation of a double stacked coating layer on an austenitic stainless steel 316 substrate using an intermediate layer (buffer layer) was investigated for the thicker and high crystallinity of Er2O3 coating formation. Yttrium oxide (Y2O3) and cerium oxide (CeO2) were selected as buffer layer between the Er2O3 layer and austenitic stainless steel 316 substrate due to their similar lattice constant to that of Er2O3 crystal. The texture and grain growth direction of Er2O3 was controlled by the Y2O3 and CeO2 buffer layer. However, the suppression effect of hydrogen permeation by the double stacked coating was smaller than that of the single layer coating due to the thin Er2O3 formation.

Cerium oxide (CeO 2) buffer layers for preparation of high- Jc YBCO films on large-area sapphire substrates (30 cm × 10 cm) by coating pyrolysis

Ternary alloy semiconductor of germanium-silicon-tin (GeSiSn) has attracted for electronic and optoelectronic applications, because this group-IV alloy material provides energy band engineering independent on the lattice constant like group III-V compound semiconductors [1]. In addition, GeSiSn/Ge(Sn) heterostructure realizes type-I energy band alignment with a sufficiently large band offset at both conduction and valence band edges with no or very small lattice mismatching [2,3], and that is preferable for effective carrier confinement for light emitting devices and high mobility transistors. On the other hand, there are still challenges for crystal growth with strain and band engineering of group-IV ternary alloy semiconductor thin films. GeSn is one of promising candidates for optoelectronic applications since it realizes direct transition group-IV semiconductor. GeSn with an in-plane lattice constant larger than Ge is better to enhance the emission efficiency, as the conduction band edge of the gamma-valley lowers than that of the L-valley with large lattice constant and/or in-plane tensile strain. Thus, a buffer layer such as GeSiSn with a lattice constant sufficiently larger than Ge is required to obtain direct transition GeSn thin films, and lattice-constant engineering technology of buffer and GeSn layers should be developed with well-controlled strain relaxation technique. Recently, we explored effective strain engineering technique of GeSiSn ternary alloy epitaxial layers on Ge and Si substrate to obtain much larger in-plane lattice constant. We investigated the effect of low-temperature growth of Ge buffer layer on the strain relaxation of GeSiSn layer [4,5]. Also, we examined the ion implantation technique into substrate to enhance the strain relaxation of GeSiSn epitaxial layers grown on Ge substrate [6]. We can achieve GeSiSn epitaxial layers with the enhancement of strain relaxation and the lattice constant larger than Ge, although the crystalline quality of these epitaxial layers should be still improved. We previously reported that the strain direction as compressive and tensile ones is significantly influence of GeSiSn epitaxial layers [7]. The control of strain structure and its relaxation process is keys to obtain high crystalline quality of GeSiSn and GeSn heteroepitaxial layers for improving the electronic and optoelectronic properties of group-IV heterostructures.

Epitaxial growth of CeO2 films on Al2O3 (11̄02) substrates and the effect of CeO2 buffer layers on the growth orientation and superconducting properties of EuBa2Cu3O7-δ (EBCO) were investigated. CeO2 and EBCO films were prepared by rf and dc magnetron sputtering, respectively, and were characterized by X-ray diffraction (θ-2θ scan and ϕ scan), atomic force microscopy (AFM) and high resolution scanning electron microscopy. Epitaxial (001) CeO2 films were obtained at an off-center distance (D on-off) of 3.5 cm and a substrate temperature of 660°C. The structural and superconducting properties of EBCO films deposited at 650°C depended on the thickness of the CeO2 buffer layer. The EBCO films deposited on CeO2 50-400-Å-thick buffer layers had T ce's of 90 K or above. The high-T c EBCO films had in-plane epitaxial orientation relationships of Al2O3 [112̄0]\\varparallelCeO2 [100]\\varparallelEBCO[110]. The EBCO films on the thin CeO2 buffer layers had rectangular grains similar to those on MgO(001) substrates. The critical current density of the EBCO films with T ce=90 K was about 6 ×105 A/cm2 in zero field at 77.3 K. The T ce varied largely and decreased with increasing CeO2 buffer layer thickness above 500 Å. AFM observation of a 1000-Å-thick CeO2 film showed growth of bamboo-like crystal grains 1700 Å long and 300 Å wide along the direction of CeO2 [110]. The ravine depths were about 100 Å. The EBCO films on the thick CeO2 buffer layer (>500 Å) exhibited poor superconducting behavior and gave (103) or (110) diffraction peaks.

Ab initio density functional theory is employed to investigate the structural, elastic, electronic and optical properties of the half-Heusler NaScSi alloy. The lattice constants are very near to the available theoretical data. In addition, besides the GGA approximation, the modified Becke–Johnson exchange potential is also used to improve the direct X→X band gap value. Furthermore, the elastic constants and related elastic moduli confirm its stability and brittle behaviour in the type I structure. The influence of pressure on Cij constants, bulk modulus B, Cauchy pressure, Poisson ratio ν, shear modulus, B/G ratio and anisotropy factor A are analysed. Additionally, the strong absorption is extended between the visible domain and that of the ultraviolet is predicted.

Strained-layer semiconductor films offer tremendous potential with regards to optoelectronic applications for high speed communications, mobile communications, sensing, and novel logic devices. It is an unfortunate reality that many of the possible film/substrate combinations that could be exploited technologically are off limits because of large differences in lattice parameters, chemical compatibilities, or thermal expansion rates. These mechanical, chemical, and thermal incompatibilities manifest themselves primarily in terms of lattice defects such as dislocations and antiphase boundaries, and in some cases through enhanced surface roughness. An additional limitation, from a production point of view, is money. Device manufacturers as a rule want the cheapest substrate possible. Freeing the heteroepitaxial world of the bonds of (near) lattice matching would vastly expand the types of working devices that could be grown. As a result, a great deal of effort has been expended finding schemes to integrate dissimilar film/substrate materials while preserving the perfection of the film layer. One such scheme receiving significant attention lately is the so-called compliant substrate approach.

Nonlocal hcp kernel functions based on ab initio calculations: Pertinent dislocation problems revisited

Epitaxial growth of CeO2 buffer layers on biaxially textured (001)Ni tapes was studied using pulsed laser deposition. Relationships between microstructure and deposition parameters were systematically studied in order to develop reliable long tape coating processes. It was found that orientation and texture of CeO2 buffer layers were sensitive to deposition parameters. X-ray diffraction analyses showed that CeO2 buffer layers had pure (001) orientation at 860 °C. Under optimized deposition conditions, highly (001) oriented CeO2 buffer layers have been achieved at a high deposition rate of 1.5 nm/s in-plane texture and out-plane texture of CeO2 buffer layers were 4.25 degrees and 5.85 degrees, respectively.

In this work, we address issues pertinent to the understanding of the structural and electronic properties of ${\mathrm{Si}}_{1\ensuremath{-}x}{\mathrm{Ge}}_{x}$ alloys, namely, (i) how does the lattice constant mismatch between bulk Si and bulk Ge manifest itself in the alloy system? and (ii) what are the relevant strain release mechanisms? To provide answers to these questions, we have carried out an in-depth study of the changes in the local geometric and electronic structures arising from the strain relaxation in ${\mathrm{Si}}_{1\ensuremath{-}x}{\mathrm{Ge}}_{x}$ alloys. We first compute the optimized lattice constant for different compositions (x) by fully relaxing the system and by minimizing the total energy with respect to the lattice constant at each composition, using an ab initio molecular dynamics scheme. The optimized lattice constant, while exhibiting a general trend of linear dependence on the composition (Vegard's law), shows a negative deviation from Vegard's law in the vicinity of $x=0.5.$ We delineate the mechanisms responsible for each one of the above features. We show that the radial-strain relaxation through bond stretching is responsible for the overall trend of linear dependence of the lattice constant on the composition. On the other hand, the negative deviation from Vegard's law is shown to arise from the angular-strain relaxation. More specifically, the combined effect of the local bond-angle deviations from the tetrahedral angle and the magnitudes of the corresponding peaks for the partial-angle distribution function determines the negative deviation from Vegard's law. The electronic origin of the changes in the local geometric structure due to strain relaxation is also presented in this work. In particular, the correlation between the bond charges and the bond-lengths for Si-Si, Ge-Ge, and Si-Ge pairs in ${\mathrm{Si}}_{1\ensuremath{-}x}{\mathrm{Ge}}_{x}$ alloys for different compositions is explicitly shown. Our calculation of the average coordination number as a function of composition indicates a random occupation of Si and Ge on the lattice sites, suggesting that Si and Ge atoms are fully miscible in the alloy system.

The development of the magnetic tunnel junctions with perpendicular easy axis using interfacial anisotropy [1–4] (p-MTJs) has been intensively advanced toward realization of high performance spin-transfer-torque magnetoresistive random access memories (STT-MRAMs). The p-MTJs used in the STT-MRAMs are required to withstand 400°C annealing to be compatible with CMOS back-end-of-line-process. Although we have demonstrated the thermal tolerance against 400°C annealing for the free layer in the CoFeB/MgO-based p-MTJs [5], we also found variation of properties in synthetic ferrimagnetic (SyF) reference layer. We revealed that the variation was caused by the diffusion of Fe in the CoFeB reference layer toward the bottom Co/Pt pinned layer after annealing [6]. We simultaneously observed degradation of perpendicular anisotropy of the Co/Pt multi layer. Perpendicular anisotropy of Co/Pt is influenced by the Co/Pt thickness ratio, buffer layer material, and roughness [7]. In this study, we focus on modification of the buffer layer and reveal that degradation can be suppressed by employing a surface modification treatment (SMT) of the Pt buffer layer. MTJ stacks from the substrate side, Ta /Pt buffer layer/with or without SMT/ [Co/Pt] <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</inf> /Co /Ru/ [Co /Pt] <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> /Co /Ta /CoFeB /MgO barrier/free layer/top electrode, were deposited on a 300-mm $\Phi $ thermally oxidized Si wafer using a DC/RF magnetron sputtering system at room temperature (Fig.1(a)). In the SMT process, the Pt buffer layer was exposed to an ion plasma. The upper layers on the Pt buffer layer were deposited without breaking the vacuum. After deposition, samples were annealed at 350 °C for 2 h or 400 °C for 1 h in vacuum without applying magnetic field. The out-of-plane magnetic moment per unit area versus magnetic field (m-H) curves of the blanket films were measured by a vibrating sample magnetometer, and the film structures were investigated by energy dispersive x-ray spectroscopy (EDX) and high-resolution X-ray diffraction (HRXRD) using Cu Ka radiation. As shown in Fig. 1(b) and 1(c), perpendicular anisotropy of the SyF reference layer without SMT degraded after 400 °C annealing, while that of the SyF reference layer with SMT hardly changed. Interestingly, after annealing at 400 °C, magnetic moment variation in the top and bottom parts of the reference layer is observed in the stack without SMT due to Fe diffusion from the CoFeB reference layer toward the bottom Co/Pt layer, as we previously reported [6]. In contrast, the magnetic moments of the top and bottom parts of the reference layer in the stack with SMT are almost the same. This indicates that Fe diffusion in the reference layer is suppressed by the SMT of the Pt buffer layer. In order to verify this hypothesis, we performed cross-sectional EDX line analysis (Fig. 2). In the stack without SMT, Fe element in the CoFeB reference layer is observed in the other layers such as the top and bottom Co/Pt multilayers after annealing at 400 °C Fig. 2(a)), which indicates that Fe diffused toward the bottom Co/Pt layer. In contrast, in the stack with SMT, Fe element is observed only in the CoFeB layer in the as-deposited state and after annealing at 400 °C Fig. 2(b)). These results are consistent with the variation of magnetic properties shown in Fig. 1(b) and 1(c). In order to clarify the reason for the suppression of perpendicular anisotropy degradation of the Co/Pt multilayer after 400 °C annealing by SMT, we evaluated the crystal structure of the Co/Pt multilayer using HRXRD. X-ray diffraction analysis revealed that the ions penetrated the Pt buffer layer, expanding the Pt lattice constant and enhancing Co/Pt grain growth, which well oriented to the fcc (111) closed-packed plane parallel to the substrate surface. This caused larger perpendicular anisotropy in the Co/Pt multilayer and higher thermal tolerance. In addition, this may suppress Fe diffusion from the CoFeB reference layer toward the bottom Co/Pt layer. This work is supported by CIES's Industrial Affiliation on STT MRAM program, and JST ACCEL Grant Number JPMJAC1301, Japan, and JST-OPERA.

In this paper, ITO films with the oxide buffer layers were deposited by magnetron sputtering technique onto the PES. The oxide buffer layer was formed by a radio frequency (RF) magnetron sputtering method, using SiO2 or TiO2 target. The ITO layers were deposited by a low-frequency (LF) magnetron sputtering technique onto PES/Buffer layer. The sheet resistances of ITO films with the oxide buffer layers grown onto PES substrate were investigated as a function of time in the air and the vacuum. In both cases, the increasing rates of the sheet resistance of the PES/Buffer layer/ITO films are lower than those of the PES/ITO films. In addition, the increasing rates of sheet resistances of the films with the TiO2 buffer layer are lower than those of the films with the SiO2 buffer layer.

A NdBaCuO superconducting thin film was grown by mist microwave-plasma chemical vapor deposition (MPCVD) using a CeO2 buffer layer on a MgO(001) substrate. After the CeO2 buffer layer was deposited on the MgO(001) substrate at 1173 K by MPCVD, a NdBaCuO film was grown at 1223 K. The Tc-zero (zero resistance) value of the NdBaCuO film with the CeO2 buffer layer was 90.1 K, and it was about 10 K higher than that without the CeO2 buffer layer. The surface roughness of the NdBaCuO film was less than 5 nm.