LZO Films Research Articles

ZnO and La-doped ZnO films by USP method and their characterizations for ultraviolet photodetectors and photocatalysis applications

In this study, ZnO, Zn1-xLaxO [2, 5, 10, 15 at.%] thin films were grown on glass substrates using the spray-pyrolysis technique, to investigate the effect of doping on the structural, morphological, thermoelectric and optical properties of the layers, Also the samples were tested as UV photodetectors and photocatalyst for MB degradation. Firstly, diffraction patterns showed a hexagonal structure, with preferential grain orientation along the (002) direction, for pure ZnO and 2%La_ZnO layers, and at 5 at.% the preferential orientation changes, and crystallite sizes range from 10 nm to 19 nm. However, SEM images reveal that the ZnO and 2%La_ZnO layers are nanorods distributed over their surfaces, and the other 5%LZO, 10%LZO and 15%LZO layers characterized by nanocrystals were hexagonal prisms. The UV–visible analysis of the prepared layers shows high transparency (80–90%) in the visible range, with a constant optical gap of 3.26 eV. Thermoelectric measurements show that the ZnO and LZO layers are non-degenerate, with a maximum charge concentration of 9.18 × 1017 cm−3 for the 15% LZO films. The thin films show an ability for UV detection, while the 5%La_ZnO layers remain the best for UV photodetection with a good sensitivity (5.07) compared with the other layers. In terms of methyl blue degradation, the 5%La_ZnO thin films had a better degradation of 95%.

Mg doping effects on the microstructure and piezoelectric characteristics of ZnO:Li films deposited at room temperature using an RF sputtering deposition method

In this work, Density functional theory (DFT + U) was used to simulate Mg doped LZO (ZnO:Li 3 mol%) based on an atomic substitution concept. The calculation results indicate the piezoelectric constants e33, e31 and lattice constant a have a tendency to increase significantly due to Mg doping effects. Also, an RF magnetron sputtering system was used to prepare Mg-doped LZO films (ZnO: Li 3 mol%) with Mg doping concentrations of 0, 3, 6, 9 mol% at room temperature. A further analysis shows that when the proposed films are deposited at room temperature, Li atoms will bond with oxygen atoms to form Li2O2 to help to enhance the piezoelectric properties of the films. This is also found to be one of the reasons for the error in the simulated lattice constants.In addition, the doping of Mg induces lateral tensile stress in the ZnO structure. This phenomenon can produce lattice distortion and change the asymmetry of the ZnO atomic center at room temperature, thus improving the piezoelectric properties (piezoelectric coefficient d33 is increased from 4.5 to 26.3 pm/V). The reported d33 value is the highest compared to other reports on ZnO-based films deposited at room temperature.

Creation of multiple defect states in RF sputtered lidoped ZnO nanocrystalline thin films

Undoped and Lithium doped ZnO nanocrystalline thin films were grown by radio frequency magnetron sputtering. The effects of Li incorporation on the structural, morphological and optical properties of ZnO thin films were investigated. XRD and FESEM measurements confirmed the nanocrystalline nature of the films. XPS studies affirmed the presence of Li in ZnO films. The optical band gap of LZO films increased with Li doping. Room temperature PL spectra of films showed multiple emission peaks in the visible range indicating the creation of various defect states and it is proposed that white light emission is possible in LZO based materials by controlling the doping.

Investigation of epitaxial growth of La2Zr2O7 thin films with different carbonaceous phases

During the metal–organic deposition (MOD) process, the carbon-rich impurities remaining in a film are harmful to the epitaxial growth of the oxide film. Thus, it is of great importance to investigate epitaxial growth of oxide films with different carbonaceous phases. To control the carbonaceous phases in the as-fabricated LZO film, different dopant concentrations and annealing atmospheres have been suggested during the MOD process. A characterization of specimens was performed using X-ray diffraction θ–2θ scans, out-of-plane and in-plane scans, X-ray photoelectron spectroscopy, electron backscattering diffraction, and atomic force microscopy. It was found that a small number of carbonaceous phases, regardless of their type, has no obvious negative influence on the growth orientation of the film. Moreover, because some bridge-pillar spots in the graphene layer enable the epitaxial growth of oxide film, the texture degree of LZO film doped with a high concentration of reduced graphene oxide (RGO) is even sharpened. With increasing doping RGO concentration, the surface roughness of the LZO film increases, which indicates an exaggerated impact of the surface defects on the metallic substrate on the grain size of the LZO film doped with RGO. Different oxygen partial pressures in the annealing atmosphere determine the type of carbonaceous phase in the as-prepared oxide film. The carbonate species formed in the film under high oxygen partial pressure have a negative influence on the texture degree and the surface flatness of LZO film, while low oxygen partial pressure favors the reduction of the residual carbon in the film. Therefore, oxide films with high performance can be achieved by controlling the presence of the positive carbonaceous phases in the film during the introduction of an appropriate artificial doping source and the selection of a suitable annealing atmosphere.

Growth of Biaxially-Textured La2Zr2O7 and Zr-doped CeO2 on Cold-Rolled Ni‐W Substrate by CSD

The growth of oriented buffer layers by chemical solution deposition (CSD) on cube-textured Ni-based substrate is a key point for the development of low-cost YBa <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> Cu <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">7</sub> -x (YBCO) coated conductor. Among the suitable compounds, La <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> Zr <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">7</sub> (LZO) and CeO2 are of particular interest as they enabled an all-chemical route for the fabrication of YBCO coated conductor. It has been recently shown that CSD films can be grown by direct precurson solution deposition on as-rolled, i.e., without cube orientation, metallic substrate. In particular, LZO film with biaxially {001}<;110> texture has been successfully grown on either pure copper or Ni-W alloy substrate. In the present contribution, the deposition either LZO or Zr-doped CeO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> (CZO) on as-rolled Ni 3.5 at% W (Ni-W) substrate is reported. It is shown that film orientation enhances using low-roughness substrates, with an area fraction of {001}<;110> oriented film as high as 96.4% for LZO and 95.4% for CZO. In both cases, the films are well adherent, without blister formation or delamination. Moreover, the film acts as a planarization layer, by smoothing Ni-W intrinsic roughness, also in correspondence of Ni-W grain boundary, where no grooving seems to appear on film surface.

High-κ Lanthanum Zirconium Oxide Thin Film Dielectrics from Aqueous Solution Precursors.

Metal oxide thin films are critical components in modern electronic applications. In particular, high-κ dielectrics are of interest for reducing power consumption in metal-insulator-semiconductor (MIS) field-effect transistors. Although thin-film materials are typically produced via vacuum-based methods, solution deposition offers a scalable and cost-efficient alternative. We report an all-inorganic aqueous solution route to amorphous lanthanum zirconium oxide (La2Zr2O7, LZO) dielectric thin films. LZO films were spin-cast from aqueous solutions of metal nitrates and annealed at temperatures between 300 and 600 °C to produce dense, defect-free, and smooth films with subnanometer roughness. Dielectric constants of 12.2-16.4 and loss tangents <0.6% were obtained for MIS devices utilizing LZO as the dielectric layer (1 kHz). Leakage currents <10-7 A cm-2 at 4 MV cm-1 were measured for samples annealed at 600 °C. The excellent surface morphology, high dielectric constants, and low leakage current densities makes these LZO dielectrics promising candidates for thin-film transistor devices.

Tailoring the crystallographic orientation of MOD-derived La2Zr2O7 buffer layers for coated conductors

Well-textured metal-organic-deposited (MOD) Lanthanum Zirconate (La2Zr2O7, LZO) films were spin-coated on biaxially textured Ni–5at.%W substrates for low cost production of YBa2Cu3O7−δ (YBCO) coated conductors. Control of the crystallographic orientation of LZO buffers is of significance to achieve YBCO films with high current carrying capability by means of the selective MOD-seed layer and annealing conditions. X-ray diffraction analysis indicated that the three-layer LZO films on MOD-seed layer, especially MOD–CeO2, showed a significant improvement in out-of-plane and in-plane textures. The surface analysis revealed a typical dense, cracks-free, and homogenous morphology. 500nm-thick YBCO films epitaxially grown on three-layer LZO buffer layers without seed layer, on seed MOD-Y2O3 and MOD-CeO2 by direct-current sputtering, yielded critical current density (Jc) at 77K of 0.6MA/cm2, 1.2MA/cm2 and 1.4MA/cm2, respectively, exhibiting that the superconducting properties were governed by the crystallographic texture of the underlying buffer layer.

Fabrication and characterization of La2Zr2O7 films on different buffer architectures for YBa2Cu3O7−δ coated conductors by RF magnetron sputtering

La2Zr2O7 (LZO) films were grown on different buffer architectures by radio frequency magnetron sputtering for the large-scale application of YBa2Cu3O7−x (YBCO)-coated conductors. The three different buffer architectures were cerium oxide (CeO2), yttria-stabilized zirconia (YSZ)/CeO2, and CeO2/YSZ/CeO2. The microstructure and surface morphology of the LZO film were studied by X-ray diffraction, optical microscopy, field emission scanning electron microscopy, and atomic force microscopy. The LZO films prepared on the CeO2, YSZ/CeO2, and CeO2/YSZ/CeO2 buffer architectures were preferentially c-axis-oriented and highly textured. The in-plane texture of LZO film on CeO2 single-buffer architecture was ∆ φ = 5.5° and the out-of-plane texture was ∆ ω = 3.4°. All the LZO films had very smooth surfaces, but LZO films grown on YSZ/CeO2 and CeO2/YSZ/CeO2 buffer architectures had cracks. The highly textured LZO film grown on CeO2-seed buffered NiW tape was suitable for the epitaxial growth of YBCO film with high currents.

Growth and Characterization of La2Zr2O7 Buffer Layers Deposited by Chemical Solution Deposition

Abstract The deposition and characterization of La2Zr2O7 thin films deposited by metal-organic decomposition method on both single crystal SrTiO3 and cube textured Ni-5 at.%W substrates are presented. Metal acetylacetonates in propionic acid solution was used. The results showed that LZO films are epitaxially grown with smooth surface with rms roughness around 2 nm. YBa2Cu3O7-δ films, deposited by pulsed laser deposition technique on LZO buffer layers, showed critical temperature of 90 K and critical current density in self magnetic field Jc = 1.6 and 13 MA/cm2 at 77 K and 4.2 K, respectively. A better Jc retention in magnetic field for YBCO films deposited on LZO/STO than YBCO on bare STO is observed indicating a rather strong vortex pinning as confirmed by microwave measurements.

Thick lanthanum zirconate buffer layers from water-based precursor solutions on Ni-5%W substrates

In this work, water-based precursor solutions suitable for dip-coating of thick La 2Zr 2O 7 (LZO) buffer layers for coated conductors on Ni-5%W substrates were developed. The solutions were prepared based on chelate chemistry using water as the main solvent. The effect of polymer addition on the maximum crack-free thickness of the deposited films was investigated. This novel solution preparation method revealed the possibility to grow single, crack-free layers with thicknesses ranging 100–280 nm with good crystallinity and an in-plane grain misalignment with average FWHM of 6.55°. TEM studies illustrated the presence of nanovoids, typical for CSD–LZO films annealed under Ar-5%H 2 gas flow. The appropriate buffer layer action of the film in preventing the Ni diffusion was studied using XPS. It was found that the Ni diffusion was restricted to the first 30 nm of a 140 nm thick film. The surface texture of the film was improved using a seed layer.

Behavior of oxygen diffusion in buffer layers for coated conductors

We have evaluated the effect of annealing in oxygen atmosphere on the structure, texture and phase transformation of LZO films deposited on YSZ (yttria-stabilized zirconia) (0 0 l) single crystal substrates and textured NiW substrates by metal-organic deposition (MOD) method. The results show that the structure stability of the LZO films is heavily dependent on the oxygen partial pressure in annealing process. Then we have in details studied the behavior of oxygen diffusion in three kinds of buffer layer architectures on NiW substrates by varying the temperature, oxygen partial pressure and dwelling time in the annealing process. The oxygen diffusion within buffer layers leads to the oxidation of substrate, and even the texture and structure of buffer layers are destroyed with the increase of the thickness of the oxides layer related to NiW substrate. It reveals that the relative volume of oxides related to NiW substrate increases exponentially with the annealing temperature, and increases linearly with the annealing time at logarithmic scale. The relative intensity of texture peaks of buffer layers decreases and even disappears with the increase of the oxygen partial pressure in annealing process because of the acceleration of the oxidation reaction of substrate. The influence of annealing temperature, oxygen partial pressure and dwelling time on the oxygen diffusion is related to the intrinsic oxygen diffusion coefficient of buffer layers materials. Compared with the increase of oxygen partial pressure, the elongation of dwelling time shows a less effect on the oxidation rate of NiW substrate and a weak destruction of the texture of buffer layers. Except choosing the oxide materials with small oxygen diffusion coefficient as buffer layers in coated conductors, the degree of oxidation about NiW substrate could be greatly controlled and it would result in the less destruction of texture and structure of buffer layers by adjusting the annealing temperature, oxygen partial pressure and dwelling time in the process of YBCO deposition.

Characterization of MOD-derived La 2Zr 2O 7 epi-layers on textured Ni5W substrates by electron backscattered diffraction

La 2Zr 2O 7 (LZO) buffer layers derived by metal organic deposition (MOD) were epitaxially grown on cube textured Ni5W substrates modified with an island-distributed LZO seed layer, and electron backscattered diffraction (EBSD) was employed to characterize the crystallographic relationship of the {0 0 1}〈1 1 0〉 rotated cube textured LZO grains with respect to the {0 0 1}〈1 0 0〉 cube textured Ni5W substrate. The uniformly distributed, islanded seed layer can effectively optimize the orientation of the double-layered LZO films, as proved by X-ray diffraction and EBSD analyses. It is concluded that the accelerating voltage is crucial for determinating the crystallographic orientation of the multilayer sample. Information about the epi-layer and the substrate was obtained at different accelerating voltages, which revealed, in particular, a superposed pattern of both layers.

METAL-DOPED ZnO THIN FILMS: SYNTHESIS, ETCHING CHARACTERISTIC, AND APPLICATION TEST FOR ORGANIC LIGHT EMITTING DIODE (OLED) DEVICES

Metal-doped ZnO films with various metal contents ( Al , Ag and Li of 0–10 wt.%) were prepared by RF magnetron sputtering system with specially designed ZnO targets. The structural, optical and electrical properties of MZO films depended on the type and content of doping in target. Electrical resistivity of LZO thin films increased with increasing Li doping amounts between 0 and 4 wt.%, suggesting that an epitaxial LZO film has high resistivity. We observed morphology in pure ZnO films by using different etchant. In addition, etching rate were contrasted with the etchant concentration and pH. The etching rate is proportional exponentially to pH value. These data will be the technical basis for TCO application. Also, the dry etching rate decreased with increasing the Cl 2 concentration in CH 4/ H 2/ Ar + additive Cl 2 gas mixture but metal dopants were etched effectively.

Magneto-Optical Investigations of LZO Buffer Layer Thickness Effects on YBCO Microstructure in the Simple NiW/LZO/YBCO Structure

The NiRABiTS/La2Zr2O7MOD/YBa2Cu3 O7MOCVD structure is a promising architecture for (YBCO) coated conductors. We succeeded in growing highly textured superconducting YBCO films on LZO-buffered Ni-5 at%W (NiW) substrates by metalorganic chemical vapor deposition (MOCVD). A single LZO buffer layer grown by metalorganic decomposition (MOD) is sufficient to ensure structural compatibility between YBCO and Ni, and to protect the substrate from oxidation during YBCO deposition. Textured Ni substrates obtained by rolling technique have intrinsic defects such as grain boundaries and rolling scratches. It is not easy to highlight their effects on LZO and YBCO films by usual measurements like XRD or SEM. The combination of Electron Backscattered Diffraction (EBSD) and Magneto-Optics imaging (MO) is useful to image grain boundaries and flux distribution in coated conductors. It provides complementary information on superconducting film qualities. These two techniques allowed us to understand how the microstructure of the LZO buffer layer and thus of the YBCO film is linked to the current density in this simple heterostructure.

Thin La 2Zr 2O 7 films made from a water-based solution

Thin films of La 2Zr 2O 7 (LZO) are highly regarded as possible buffer layers in the coated conductor configuration. This report describes a new synthesis for thin crystalline LZO films, based on a largely water-based solution, mainly containing metal acetates, acetic acid and an organic amine-base: triethanolamine. Initially, a thin layer of amorphous material is deposited on the textured Ni-5 at%W substrate by means of dip-coating. Only by careful control of the thermal treatment can the layer be transformed into a crystalline layer. Important parameters in this respect are the heating rate and the dwell time. The amorphous gel is analysed by HR-TGA/DTA and HR-TEM. The textured layers are analysed by XRD, pole figures, RHEED, AFM and SEM.

Formation of High-Quality, Epitaxial La2Zr2O7Layers on Biaxially Textured Substrates by Slot-Die Coating of Chemical Solution Precursors

Crystallization studies were performed of epitaxial La{sub 2}Zr{sub 2}O{sub 7} (LZO) films on biaxially textured Ni-3at.%W substrates having thin Y{sub 2}O{sub 3} (10 nm) seed layers. LZO films were deposited under controlled humid atmosphere using reel-to-reel slot-die coating of chemical solution precursors. Controlled crystallization under various processing conditions has revealed a broad phase space for obtaining high-quality, epitaxial LZO films without microcracks, with no degradation of crystallographic texture and with high surface crystallinity. Crack-free and strong c-axis aligned LZO films with no random orientation were obtained even at relatively low annealing temperatures of 850-950 C in flowing one atmosphere gas mixtures of Ar-4% H2 with an effective oxygen partial pressure of P(O2){approx}10{sup -22} atm. Texture and reflection high-energy electron diffraction analyses reveal that low-temperature-annealed samples have strong cube-on-cube epitaxy and high surface crystallinity, comparable to those of LZO film annealed at high temperature of 1100 C. In addition, these samples have a smoother surface morphology than films annealed at higher temperatures. Ni diffusion rate into the LZO buffer film is also expected to be significantly reduced at the lower annealing temperatures.

LZO covered Cu-based substrates

A Cu-based substrate has been made by electrodepositing a Ni layer on top of cube-textured Cu tape obtained by an alternating mechanical/thermal treatment. It could be found that the volume fraction of the cube texture component of Cu tapes increased with the annealing temperatures for an optimized rolling process. When the annealing temperature is at 800 °C, the sharpness of cube texture is best. In order to fabricate LZO films on the Cu-based substrate, a Ni layer was added on top of the Cu tape by electroplating. The thickness of Ni layer not only affects the texture sharpness of the substrate, but also affects its thermal stability of texture. A thickness of 15 μm was efficient to protect the Cu tapes. Fabricating well bi-axially textured LZO film on this bi-metallic substrate proves that this new Cu-based substrate is a good choice for coated conductor.

YBCO coated conductors prepared by chemical solution deposition: A TEM study

Recently large attention has been devoted to chemical solution deposition (CSD) as a promising method for fabricating low-cost YBCO coated conductors. We present an extensive transmission electron microscopy (TEM) cross-section analysis of CSD grown La 2Zr 2O 7 (LZO) buffer layers on flexible Ni–5at%W substrates. The high performance of these chemical solution derived buffer layers was confirmed by a YBCO critical current density J c of 0.84 MA/cm 2 achieved for a coated conductor sample with a layer sequence Ni–5at%W/LZO (CSD)/CeO 2 (CSD)/YBCO, where the YBCO film was deposited by pulsed laser deposition (PLD). TEM sample preparation was carried out by conventional mechanical polishing and ion milling techniques. TEM bright-field images of the LZO films and nickel substrates were acquired under two-beam conditions. The layer thicknesses and nanovoid size were determined for the LZO buffer layers. Moreover, the interfaces between the different layers were investigated and identified. Electron diffraction patterns were obtained in order to determine the microscopic texture of the samples. Despite the presence of nanovoids in the LZO buffer layers, they act as efficient Ni diffusion barriers.

Effect of Relative Humidity on the Crystallization of Sol−Gel Lanthanum Zirconium Oxide Films

The ambient relative humidity during the coating process significantly influences the crystallographic texture and microstructure of the films processed. Using Y2O3 coated biaxially textured Ni−5 atom % W substrates, we have determined that there is a threshold humidity level above which highly oriented LZO films can be processed. However, below the threshold level, a significant portion of the film grows with a random polycrystalline orientation.

La 2Zr 2O 7 films on Cu–Ni alloy by chemical solution deposition process

Films of La 2Zr 2O 7 (=LZO) have been formed by chemical solution deposition technique (CSD) on new bi-axially textured Cu–Ni alloy tapes based on rolled constantan (Cu 55Ni 45) Rabits. The precursor used was acetylacetonates treated in propionic acid (0.1–0.87 mol/l) and then deposited by spin-coating. The LZO film starts to crystallize above 850 °C, the film nucleates bi-axially textured on the substrate (with unit cell axis rotated 45° from those of the substrate). The top part of the film is not textured even after long annealing time at 1100 °C, but the interfacial part is bi-axially textured. Thus, synthesis of bi-axially textured films on Cu 55Ni 45 Rabits seems possible but more works are needed to optimize its properties.