Epitaxial Growth Relationship Research Articles

A novel method for preparing α-Al2O3 (Cr2O3)/Fe–Al composite coating with high hydrogen isotopes permeation resistance

α-Al2O3 as a preferred material for hydrogen isotopes permeation barrier (HIPB) can effectively prevent hydrogen embrittlement in structural steel and has higher thermal stability. However, its application is limited by the issue that it is hard to prepare α-Al2O3 at relatively low temperature and its formation temperature is too high (>1000 °C) to damage the mechanical properties of structural steel. To overcome this issue, this paper presents a novel method (combining Al electrodeposition, aluminizing, Cr deposition and air oxidation) for the preparation of α-Al2O3 (Cr2O3)/Fe–Al composite coating on 316 L stainless steel for the first time. The formation temperature of α-Al2O3 was successfully reduced to 800 °C. The post-oxidation samples were characterized by SEM, XPS, XRD, EDS and TEM. The results showed that the oxide film was composed of highly crystalline α-Al2O3 and Cr2O3 nanoparticles, where the later were diffusely distributed in the internal α-Al2O3 film. And there was an epitaxial growth relationship between α-Al2O3 and Cr2O3. The low-temperature formation of the α-Al2O3 film was due to the fact that the Cr2O3 nanoparticles formed during the oxidation process acted as templates and nucleation sites, which reduced the nucleation barrier of α-Al2O3. Deuterium permeation tests showed that its deuterium permeation reduction factor (DPRF) was 8892 at 500 °C, which met the standard for practical application.

Preparation of epitaxial La2-xGdxZr2O7 buffer layer for coated conductors using sol-gel method

La2-xGdxZr2O7 (LGZO) films were prepared on Ni-5at.%W rolling-assisted biaxially textured substrate (RABiTS-NiW) using sol-gel method. The lattice parameter of lanthanum zirconate was changed by gadolinium element doping, which reduced the lattice constant of lanthanum zirconate buffer layer to have a better match with the lattice of NiW substrate. In particular, the grain growth texture of the buffer layer film has been analyzed by X-ray diffraction, EBSD, SEM and TEM. The results show that the La1.25Gd0.75Zr2O7 film has the highest c-axis preferred orientation and dense microstructure. EBSD measurement reveals that the excellent grain-growth texture is formed within La1.25Gd0.75Zr2O7 film and the most misorientation angle is around 3°. Moreover, the epitaxial growth relationship of NiW(002)//La1.25Gd0.75Zr2O7(004) as well as NiW(200)//La1.25Gd0.75Zr2O7(440) is demonstrated by atomic resolution TEM observation. By means of suitable element substitution, the La1.25Gd0.75Zr2O7 is a quite promising candidate of single-phase buffer layer between YBa2Cu3O7-x and NiW substrate.

Target-Directed Design of Phase Transition Path for Complex Structures of Rod-Coil Block Copolymers.

We apply the string method to the self-consistent mean-field theory framework of the rod–coil block copolymer system to calculate the minimum energy pathways in the rearrangement transitions of lamellae and cylinders with different orientations under certain epitaxial growth relationship. Metastable phases appearing in the reordering transition pathway tend to form the structure at low χN side of the order–order transition boundary compared with the initial phase. In particular, for complex network, metastable phases, such as single gyroid and perforated lamellae, need to select a rearrangement transition between lamellae or cylinders near the order–disorder transition boundary with the same epitaxial growth relationship but different orientations. It is confirmed that this strategy for obtaining complex metastable phases by rational design of rearrangement transition between specific phases in the phase diagram can be applied to a wide range of χN as well as the coil–coil block copolymer system. We further investigate the rearrangement transition behavior combining with the analysis of contribution from the free energy, entropy, degree of mixing between different blocks, and the average orientation degree of rods during the phase transitions. Based on this mechanism, we have developed a target-directed design strategy for constructing self-assembled metastable structures of rod–coil block copolymers.

Epitaxial growth of gradient Ce1−xZrxO2 buffer layer for YBa2Cu3O7−δ coated conductors

A Ce1−xZrxO2 (CZO) buffer layer architecture with gradient change of Zr-doped concentration along the thickness direction of CZO films was fabricated on rolling assisted biaxially textured NiW metallic substrate by sol–gel method. With the change of Zr-doped concentration, the lattice parameters of CZO of each layer also show a gradient variation. It can not only effectively reduce interfacial stress between the buffer layer and the metallic substrate, but also improve the surface quality of the CZO film. In this work, an epitaxial growth relationship and dense microstructure are discerned in the gradient CZO film, as determined by the comprehensive analysis of X-ray diffraction and scanning electron microscopy. YBCO superconductor films have been deposited on the gradient CZO buffer layers to evaluate the quality of such a gradient buffer layer. TEM measurements reveal that NiW/CZO/YBCO coated conductor (CC) with excellent epitaxial growth relationship is achieved. The superconducting transition temperature of the sample is 90 K and the critical current density Jc reaches 1.9 MA/cm2.

Preparation of biaxially textured Ce1-x(Y0.2Zr0.8)xOδ buffer layers on RABiTS NiW tapes by chemical solution deposition

Highly (100)-oriented Ce1-x(Y0.2Zr0.8)xOδ (CYZO) films were prepared on biaxially textured NiW substrates by a chemical solution deposition approach using metal inorganic salts as starting materials. It has been found that both the preferential orientation and surface roughness of CYZO films decrease gradually with increasing of the doping percentage of Y3+ and Zr4+ ions. The epitaxial growth relationship of (220)CYZO//(200)NiW and [00 l]CYZO//[001]NiW was demonstrated by XRD texture measurement as well as atomic resolution STEM observation. XRD, Raman and XPS spectra results indicate that Y3+ and Zr4+ ions were indeed introduced into CeO2 lattice to substitute Ce4+ ions and form cubic fluorite CYZO solid solution. Moreover, CeO2 buffer layer can be endowed a strong enough capability to prevent element diffusion through co-doping of yttrium and zirconium, provided that an optimal doping ratio of them is adopted. This will provide a new approach to fabricating strong-barrier single buffer layer for coated conductor.

Highly (001)-oriented zirconium-doped ceria films grown on biaxially textured nickel tungsten substrates through an inorganic-salts-based chemical solution deposition route

In this work, Zr-doped CeO2 (Ce1-xZrxO2, CZO) films with (001) preferential orientation were fabricated on biaxially textured NiW alloy substrates by using a novel sol-gel method. The precursor solutions were synthesized through a newly developed process using common inorganic metal salts of Zr and Ce as the starting materials instead of organic salts. The influence of annealing temperature and the Ce/Zr mole ratio in the precursor solutions on the growth texture of CZO films was investigated. The precursor solutions with the concentration of 0.3 mol/L were coated on the Ni5W substrates using a dip-coating method and then heat-treated at 1050 °C for an hour under a reducing atmosphere of high-purity Ar with 5 vol% H2. The CZO thin films show excellent c-axis preferential orientation when the content of Zr in CZO thin film is less than 40%. The full width of half maximum of the phi scan of (111) reflection and omega scan of (200) reflection of CZO films is as low as the value of about 5° and 6°, respectively. Moreover, it is found that the inside of CZO thin film exhibits quite dense and uniform without cracks and porosity with the aid of the scanning transmission electron microscopy analysis by which the epitaxial growth relationship of (220)CZO // (200)NiW between CZO and NiW is simultaneously confirmed. Finally, highly (00 l)-oriented YBCO film with good superconducting properties was deposited on CZO buffered NiW substrate. The above results indicate that the CZO film is a quite promising candidate of single buffer layer architecture for YBCO coated conductor.

Characterization of structural defects in SnSe2 thin films grown by molecular beam epitaxy on GaAs (111)B substrates

Tin selenide thin films have been grown by molecular beam epitaxy on GaAs (111)B substrates at a growth temperature of 150°C, and a microstructural study has been carried out, primarily using the technique of transmission electron microscopy. The Se:Sn flux ratio during growth was systematically varied and found to have a strong impact on the resultant crystal structure and quality. Low flux ratios (Se:Sn=3:1) led to defective films consisting primarily of SnSe, whereas high flux ratios (Se:Sn>10:1) gave higher quality, single-phase SnSe2. The structure of the monoselenide films was found to be consistent with the Space Group Pnma with the epitaxial growth relationship of [011]SnSe//[11¯0]GaAs, while the diselenide films were consistent with the Space Group P3¯m1, and had the epitaxial growth relationship [21¯1¯0]SnSe2//[11¯0]GaAs.

The Electrical Properties of Epitaxial Grown Sc-Doped (Na<sub>0.</sub><sub>8</sub><sub>5</sub>K<sub>0.15</sub>)<sub>0.5</sub>Bi<sub>0.5</sub>TiO<sub>3</sub> Thin Film Prepared by Sol-Gel Method

Sc-doped (Na0.85K0.15)0.5Bi0.5TiO3 (NKBT-Sc) thin film was deposited on electrical conductive Nb-doped SrTiO3 [100] (Nb:STO) single crystal substrate via an aqueous sol–gel method. Structure analysis by x-ray diffraction and high resolution transmission electron microscopy proves the epitaxial growth relationship between the NKBT-Sc thin film and Nb:STO substrate. Well saturated ferroelectric hysteresis loops with remnant polarization of 26.14 μC/cm2 and typical butterfly shape displacement–voltage loop with effective piezoelectric coefficient d33* of 92 pm/V were observed, which were much higher than the NKBT-Sc thin film deposited on platinized silicon substrate. The precision LCR Meter exhibits a butterfly shape of dielectric constant and electric field curve, which is typical nature for the ferroelectric characteristics of the [001]-epitaxial NKBT-Sc thin film.

High‐Speed Preparation of Highly (100)‐Oriented CeO2 Film by Laser Chemical Vapor Deposition

CeO2 films were prepared at deposition temperature ranged from 947 to 1096 K (corresponding laser power was from 52 to 185 W) on (100) LaAlO3 single crystal substrate by laser chemical vapor deposition. At deposition temperature of 1027–1096 K (laser power was from 115 to 185 W), highly (100)‐oriented CeO2 films with wedge‐caped columnar grains were prepared, whose epitaxial growth relationship was CeO2 [100]//LAO [100] (CeO2 [010]//LAO [011]). Their full width at half maximum of the ω‐scan on the (200) reflection and that of the ϕ‐scan on the (220) reflection were 0.8°–1.8° and 0.7°–1.2°, respectively. The highest deposition rate at which CeO2 film with pure (100) preferred orientation could be obtained was 30 μm h−1.

Enhancement by La-Al-O Doping in Y-Ba-Cu-O Films Both in Self-Field and Under Magnetic Field

To enhance the J c of YBa 2 Cu 3 O 7-X (YBCO) films both in self-field and under magnetic field, an effective strategy is to introduce artificial pinning centers and keep a good YBCO matrix at the same time. Here, we propose a new dopant: LaAlO 3 (LAO), based on its chemical stability and small mismatch toward YBCO. A series of YBCO films with different LAO doping contents was fabricated on LAO single-crystal substrates by metal organic deposition. We observed by X-ray diffractometer measurements and scanning electron microscopy observations that although a large amount of LAO is added, YBCO still keeps a good epitaxial growth relationship with LAO. Compared with a pure YBCO film, the J c value of a 5.0% LAO-doped sample is enhanced more than three times in self-field 77 K and seven times at 77 K and 1.5 T, respectively. These results indicate that LAO doping can effectively enhance the J c of YBCO films both in self-field and in applied magnetic fields.

Epitaxial Growth of Copper Film by MOCVD

Copper thin films were deposited on single crystal sapphire substrate via metal-organic MOCVD using Cu (acac)2 as precursor. X-ray diffraction (XRD) and Scanning Electronic Microscope (SEM) were employed for studying preferred orientation and microstructure. Atomic Force Microscope was utilized in order to characterize roughness of copper thin layer. By calculation of the Gibbs free energy, the reactions have been deeply understood. Depositions were carried out at various substrate temperatures in the rage 473K to 673K. It has been revealed that temperature determined the orientation and microstructure of copper films. At 673K, copper films have exhibited preferred orientation, smooth surface and connected grains, which proved that this copper thin film can act as precursor. Based on the study of epitaxial growth of copper films, a schematic diagram of epitaxial growth relationship is suggested for the step by step depositions processes.

Investigation on orientation, epitaxial growth and microstructure of a-axis-, c-axis-, (103)/(110)- and (113)-oriented YBa2Cu3O7−δ films prepared on (001), (110) and (111) SrTiO3 single crystal substrates by spray atomizing and coprecipitating laser chemical vapor deposition

a-axis-, c-axis-, (103)/(110)- and (113)-oriented YBa2Cu3O7−δ (YBCO) films were pareared by spray atomizing and coprecipitating laser chemical vapor deposition. The surface of the a-axis-oriented YBCO film consisted of rectangular needle-like grains whose in-plane epitaxial growth relationship was YBCO [100] // STO [001] (YBCO [001] // STO [100]), and that of the c-axis-oriented YBCO film consisted of dense flat surface with epitaxial growth relationship of YBCO [001] // STO [001] (YBCO [100] //STO [100]). For the (103)/(110)-oriented and (113)-oriented YBCO film, they showed wedge-shaped and triangle-shaped grains, with corresponding in-plane epitaxial growth relationship of YBCO [110] // STO [110] (YBCO [010] // STO [010]) and YBCO [100] // STO [100] (YBCO [113] // STO [111], respectively.

Single-crystal PbTiO3/PbZrO3 composite fibers formed by diffusion and epitaxial growth

Single-crystal PbTiO3/PbZrO3 (PT/PZ) composite fibers were prepared under hydrothermal conditions for the first time, which had an epitaxial growth relationship between single-crystal perovskite PT nanofibers and PZ crystals.

Magnetic and optical properties of epitaxial n-type Cu-doped ZnO thin films deposited on sapphire substrates

In this paper, we report on pulsed laser deposition of n-type Cu-doped ZnO thin films on c-plane sapphire substrates at 700°C. XRD and HRTEM were employed to study the epitaxial growth relationship between the Zn1−xCuxO film and sapphire substrate. Absorption measurements showed excitonic nature of the thin films and a decrease in the bandgap energy with increased Cu concentration was observed. Such as-deposited films showed room temperature ferromagnetism with Curie temperature (Tc) at around 320 K. The moment per Cu atom decreases as the Cu concentration increases. The largest magnetic moment about 0.81μB/Cu atom was observed for Zn0.95Cu0.05O thin films. The presence of any magnetic second phase was ruled out and the ferromagnetism was attributed to Cu ions substituted directly into the ZnO lattice.

Structure and magnetic properties of L10 FePt film with Ag heat sink layer

In this work, the L10 FePt films with a Ag heat sink layer for the application of heating assisted magnetic recording (HAMR) were developed. It was found that the crystalline orientation of the FePt layer depended on the texture of the fcc Ag layer, which was strongly affected by the deposition conditions. The (200) textured Ag layer can induce the L10 FePt (001) texture films due to epitaxial growth with the epitaxial growth relationship of FePt (001) [100]//Ag (001) [100]//CrRu (002) [110] and thus can act as the heat sink layer for HAMR application,. The magnetic properties of the L10 FePt films were maintained with the thickness of the Ag heat sink layer from 30 to 100 nm.

Fabrication and properties of epitaxial growth BiScO3–PbTiO3 thin film via a hydrothermal method

Bi Sc O 3 – Pb Ti O 3 thin film was hydrothermally deposited on Nb-doped SrTiO3 [100] single crystal substrate at 180°C with a large thickness of 3.1μm. The x-ray diffraction and high resolution transmission electron microscopy confirmed the epitaxial growth relationship between the BSPT thin film and Nb-STO substrate. Single-crystal-like polarization hysteresis loops were observed, with the remanent polarization of 30μC∕cm2. Piezoelectric force microscopy revealed a single +c domain structure of the film, while exceptional linear piezoelectric response was observed with the effective piezoelectric constant d33* of 65pm∕V. The temperature dependence of the effective d33* indicated that this film exhibited a high temperature stability.

Epitaxial Growth of B-Axis Oriented BaTi<sub>2</sub>O<sub>5</sub> Films by Laser Ablation

A new lead-free ferroelectric BaTi2O5 film was first prepared by laser ablation. BaTi2O5 films in a single phase were obtained at substrate temperatures (Tsub) from 900 to 1050 K and oxygen partial pressures (PO2) from vacuum (10-6 Pa) to 30 Pa. The films exhibited a (710) and/or (020) preferred orientation, depending on Tsub and PO2. At PO2 = 12.5 Pa and Tsub = 950 - 1000 K, the BaTi2O5 film was b-axis oriented and epitaxially grown on MgO (100) substrate with a rectangularly crossed texture. The epitaxial growth relationship between the film and the substrate were BaTi2O5 (020) [100] // MgO (100) [001] and BaTi2O5 (020) [100] // MgO (100) [010].

FePt (001) texture development on an Fe–Ta–C magnetic soft underlayer with SiO2/MgO as an intermediate layer

In order to develop the FePt (001) texture on an Fe–Ta–C magnetic soft underlayer (SUL), a combined SiO2/MgO intermediate layer is used between the SUL and FePt/MgO laminated recording layer. The function of the amorphous SiO2 layer is to cut the epitaxial growth relationship between the SUL and recording layer and to establish the MgO (200) texture. The thin FePt layers are epitaxially grown on the MgO layers and transformed into (001)-textured L10 FePt films upon annealing. Increasing the surface roughness of the Fe–Ta–C SUL from 0.74 to 2.35 nm does not significantly affect the FePt (001) texture, but has an effect on the FePt grain c-axis dispersion and the FePt L10 phase ordering.

Comparison of the Microstructure of AlN Films Grown by MOCVD and by PLD on Sapphire Substrates

ABSTRACT(0001) aluminium nitride thin films were grown epitaxially on (0001) Sapphire substrates by MOCVD at 1200° C and PLD at 800° C. Both films have the same epitaxial growth relationship: (0001)AlN//(0001)Sap, and the same in-plane relationship which shows a 30° rotation between A1N and Sapphire: [ 12 10]AlN//[0 110]Sap and [10 10]AlN //[ 2110]Sap. The full width at half maximum (FWHM) of x-ray rocking curve of the MOCVD A1N film was 0.16° and PLD A1N film was 0.2°. Films grown by both MOCVD and PLD showed high crystalline quality. HRTEM images showed that these films are single crystalline with very low density of defects.Dislocations in the film parallel to the film / substrate interface were observed in both A1N films. Atomic force microscopy images showed that the MOCVD films have flatter and larger terraces than the PLD films. The PLD technique for A1N growth needs to be improved further. But both films have a surface roughness of approximately 100nm.

Epitaxial Growth of Pt(001) Thin Films on MgO(001) Under Oxidizing Conditions

AbstractEpitaxial Pt(001) thin films have been grown on MgO(001) substrates using dc magnetron sputtering with an Ar/O2 mixture at 700°C. The width (FWHM) of the rocking curve of the Pt(002) peak is between 0.16° and 0.20°, which is only 0.05° wider than that of the MgO (002) peak of the cleaved substrate. The film surface roughness is about 1 nm (rms) for a 240 nm thick Pt film. No grain structure could be observed using SEM. In contrast, the films deposited at 700 °C with pure Ar, have both Pt(111) and Pt(001) oriented growth, as shown by XRD Θ - 2 Θ scans, with the Pt(111) peak having the largest intensity. BaTiO3 epitaxial films have also been deposited on Pt(001)/MgO(001). The width (FWHM) of the rocking curve of the BaTiO3(200) peak is 0.4°. The surface morphology of the epitaxial BaTiO3(100) thin films on Pt(001)/MgO(001) is featureless. XRD pole figure measurements on Pt/BaTiO3/Pt trilayer shown a very good in-plane alignment of all layers. The epitaxial growth relationship was also confirmed by TEM electron diffraction and cross-section imaging. The Pt/BaTiO3/Pt epitaxial trilayer could serve as a prototype for ferroelectric capacitors and may be able to improve the electrical properties of the capacitors.