Ferroelectric PLZT thick films grown by poly(1-vinylpyrrolidone-co-vinyl acetate) (PVP/VA)-modified sol–gel process
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Hu, Zhongqiang (ORCID:0000000275340427)↗
SEARCH · Engineering Papers
Results for “Film microstructures”
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Ion-Plated Soft Metallic Films Reduce Friction and Wear
Ion plating is ion-assisted or glow-discharge surface-deposition technique. In this process, ions or energetic atoms transfer energy, momentum, and charge to substrate and deposited surface film. Process controlled to modify physical characteristics of surface, subsurface chemical conditions, and surface and subsurface microstructures as well. Ion plating with such soft, thin metallic films as gold, silver, or lead has great potential for producing self-contained lubricating surfaces. Such films reduce friction, wear, and corrosion on sliding or rotating mechanical surfaces used in wide range of environments.
Spalvins, T.↗
Chemical bonding, optical constants, and electrical resistivity of sputter-deposited gallium oxide thin films
Gallium oxide (Ga{sub 2}O{sub 3}) thin films were made by sputter deposition employing a Ga{sub 2}O{sub 3} ceramic target for sputtering. The depositions were made over a wide range of substrate temperatures (T{sub s}), from 25 to 600 °C. The effect of T{sub s} on the chemical bonding, surface morphological characteristics, optical constants, and electrical properties of the grown films was evaluated using X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), spectroscopic ellipsometry (SE), and four-point probe measurements. XPS analyses indicate the binding energies (BE) of the Ga 2p doublet, i.e., the Ga 2p{sub 3/2} and Ga 2p{sub 1/2} peaks, are located at 1118.0 and 1145.0 eV, respectively, characterizing gallium in its highest chemical oxidation state (Ga{sup 3+}) in the grown films. The core level XPS spectra of O 1s indicate that the peak is centered at a BE ∼ 531 eV, which is also characteristic of Ga-O bonds in the Ga{sub 2}O{sub 3} phase. The granular morphology of the nanocrystalline Ga{sub 2}O{sub 3} films was evident from AFM measurements, which also indicate that the surface roughness of the films increases from 0.5 nm to 3.0 nm with increasing T{sub s}. The SE analyses indicate that the index of refraction (n) of Ga{sub 2}O{sub 3} films increases with increasing T{sub s} due to improved structural quality and packing density of the films. The n(λ) of all the Ga{sub 2}O{sub 3} films follows the Cauchy's dispersion relation. The room temperature electrical resistivity was high (∼200 Ω-cm) for amorphous Ga{sub 2}O{sub 3} films grown at T{sub s} = RT-300 °C and decreased to ∼1 Ω-cm for nanocrystalline Ga{sub 2}O{sub 3} films grown at T{sub s} ≥ 500–600 °C. A correlation between growth conditions, microstructure, optical constants, and electrical properties of Ga{sub 2}O{sub 3} films is derived.
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
Epitaxial Thin Film Growth on Recycled SrTiO 3 Substrates Toward Sustainable Processing of Complex Oxides
Complex oxide thin films cover a range of physical properties and multifunctionalities that are critical for logic, memory, and optical devices. Typically, the high‐quality epitaxial growth of these complex oxide thin films requires single crystalline oxide substrates such as SrTiO 3 (STO), MgO, LaAlO 3 , a‐Al 2 O 3, and many others. Recent successes in transferring these complex oxides as free‐standing films not only offer great opportunities in integrating complex oxides on other devices, but also present enormous opportunities in recycling the deposited substrates after transfer for cost‐effective and sustainable processing of complex oxide thin films. In this work, the surface modification effects introduced on the recycled STO are investigated, and their impacts on the microstructure and properties of subsequently grown epitaxial oxide thin films are assessed and compared with those grown on the pristine substrates. Detailed analyses using high‐resolution scanning transmission electron microscopy and geometric phase analysis demonstrate distinct strain states on the surfaces of the recycled STO versus the pristine substrates, suggesting a pre‐strain state in the recycled STO substrates due to the previous deposition layer. These findings offer opportunities in growing highly mismatched oxide films on the recycled STO substrates with enhanced physical properties. Specifically, yttrium iron garnet (Y 3 Fe 5 O 12 ) films grown on recycled STO present different ferromagnetic responses compared to that on the pristine substrates, underscoring the effects of surface modification. The study demonstrates the feasibility of reuse and redeposition using recycled substrates. Via careful handling and preparation, high‐quality epitaxial thin films can be grown on recycled substrates with comparable or even better structural and physical properties toward sustainable process of complex oxide devices.
pre-strained STO surfaces↗
Recrystallization and martensitic transformation in nanometric grain size Cu-Al-Ni thin films grown by DC sputtering at room temperature
Highlights: • Polycrystalline Cu-Al-Ni thin films with nanometric grain size are grown by DC sputtering. • Influence of thermal annealing process at low temperatures on the microstructure is analyzed. • Strained martensitic transformation is observed for films with grain size average of 30 nm. - Abstract: We report the recrystallization of metastable hexagonal and body centered cubic BCC phase in free-standing 6 μm thick Cu-Al-Ni films grown by DC sputtering at room temperature. The results show that the BCC phase recrystallizes to L2{sub 1} at around 533 K together with precipitation of γ{sub 2}-phase. Annealing temperatures (533 K–623 K) at short times (0–30 min) produce systematic increment of the fraction of γ{sub 2}-phase. Films with phase coexistence of hexagonal, γ{sub 2} and L2{sub 1} structure display temperature driven martensitic transformation. This transformation is observed for samples with austenite grain size of around 30 nm. In all cases, the martensitic transformation temperature (M{sub S}) notoriously decreases (compared to bulk) and systematically increases with the annealing temperatures and annealing time. In addition, the films display extended transformation and retransformation ranges along with asymmetric hysteresis, which may be associated to restitutive forces due to elastic deformations at martensite – martensite and martensite – austenite interfaces. Annealing temperatures above 623 K produce fast precipitation to equilibrium α- and γ{sub 2}-phases. The austenitic phase can be recovered after annealing over 1000 K and fast quenching in ice-water.
77 NANOSCIENCE AND NANOTECHNOLOGY↗
Interface structure in nanoscale multilayers near continuous-to-discontinuous regime
Interfacial atomic diffusion, reaction, and formation of microstructure in nanoscale level are investigated in W/B{sub 4}C multilayer (ML) system as functions of thickness in ultrathin limit. Hard x-ray reflectivity (XRR) and x-ray diffuse scattering in conjunction with x-ray absorption near edge spectroscopy (XANES) in soft x-ray and hard x-ray regimes and depth profiling x-ray photoelectron spectroscopy (XPS) have been used to precisely evaluate detailed interfacial structure by systematically varying the individual layer thickness from continuous-to-discontinuous regime. It is observed that the interfacial morphology undergoes an unexpected significant modification as the layer thickness varies from continuous-to-discontinuous regime. The interfacial atomic diffusion increases, the physical density of W layer decreases and that of B{sub 4}C layer increases, and further more interestingly the in-plane correlation length decreases substantially as the layer thickness varies from continuous-to-discontinuous regime. This is corroborated using combined XRR and x-ray diffused scattering analysis. XANES and XPS results show formation of more and more tungsten compounds at the interfaces as the layer thickness decreases below the percolation threshold due to increase in the contact area between the elements. The formation of compound enhances to minimize certain degree of disorder at the interfaces in the discontinuous region that enables to maintain the periodic structure in ML. The degree of interfacial atomic diffusion, interlayer interaction, and microstructure is correlated as a function of layer thickness during early stage of film growth.
71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
Surface defects on the Gd{sub 2}Zr{sub 2}O{sub 7} oxide films grown on textured NiW technical substrates by chemical solution method
Epitaxial growth of oxide thin films has attracted much interest because of their broad applications in various fields. In this study, we investigated the microstructure of textured Gd{sub 2}Zr{sub 2}O{sub 7} films grown on (001)〈100〉 orientated NiW alloy substrates by a chemical solution deposition (CSD) method. The aging effect of precursor solution on defect formation was thoroughly investigated. A slight difference was observed between the as-obtained and aged precursor solutions with respect to the phase purity and global texture of films prepared using these solutions. However, the surface morphologies are different, i.e., some regular-shaped regions (mainly hexagonal or dodecagonal) were observed on the film prepared using the as-obtained precursor, whereas the film prepared using the aged precursor exhibits a homogeneous structure. Electron backscatter diffraction and scanning electron microscopy analyses showed that the Gd{sub 2}Zr{sub 2}O{sub 7} grains present within the regular-shaped regions are polycrystalline, whereas those present in the surrounding are epitaxial. Some polycrystalline regions ranging from several micrometers to several tens of micrometers grew across the NiW grain boundaries underneath. To understand this phenomenon, the properties of the precursors and corresponding xerogel were studied by Fourier transform infrared spectroscopy and coupled thermogravimetry/differential thermal analysis. The results showed that both the solutions mainly contain small Gd−Zr−O clusters obtained by the reaction of zirconium acetylacetonate with propionic acid during the precursor synthesis. The regular-shaped regions were probably formed by large Gd−Zr−O frameworks with a metastable structure in the solution with limited aging time. This study demonstrates the importance of the precise control of chemical reaction path to enhance the stability and homogeneity of the precursors of the CSD route. - Highlights: •We investigate microstructure of Gd{sub 2}Zr{sub 2}O{sub 7} films grown by a chemical solution route. •The aging effect of precursor solution on formation of surface defect was thoroughly studied. •Gd−Zr−O clusters are present in the precursor solutions.
36 MATERIALS SCIENCE↗
Microstructural, optical and ethanol sensing properties of sprayed Li-doped Mn{sub 3}O{sub 4} thin films
Highlights: • Li doped Mn{sub 3}O{sub 4} was grown on glass substrate via the low cost effective spray pyrolysis technique. • Li doping notably tuned the optical band gap of Mn{sub 3}O{sub 4} thin film. • The incorporation of Li ions was found to provide an enhancement of ethanol sensitivity. - Abstract: Lithium-doped manganese oxide thin films have been deposited onto glass substrate by the spray pyrolysis technique. The effect on structural, morphological, optical and ethanol sensitivity properties of the films with different Li concentrations was investigated. The X-ray diffraction (XRD) studies of Li doped Mn{sub 3}O{sub 4} thin films revealed polycrystalline tetragonal structure with lattice parameters: a = 5.73 Å and c = 9.46 Å. The most intense band at 653.26 cm{sup −1} observed in room temperature Raman spectrum of all films corresponds to the tetragonal crystal structure of Mn{sub 3}O{sub 4}. Optical band gap energy was found to vary in the range of 2.23–2.82 eV by an increase in Li-doping concentration up to 15%. The resistance based gas sensing measurements showed a clear response already at a low ethanol concentration of 0.1%. The films showed promising ethanol sensing behavior; especially the sample doped with 3% of lithium exhibits the most excellent sensing performance.
36 MATERIALS SCIENCE↗
Spectroscopic ellipsometry investigations of optical anisotropy in obliquely deposited hafnia thin films
In present work, HfO{sub 2} thin films have been deposited at various oblique incidences on Si substrates by electron beam evaporation. These refractory oxide films exhibited anisotropy in refractive index predictably due to special columnar microstructure. Spectroscopic ellipsometry being a powerful tool for optical characterization has been employed to investigate optical anisotropy. It was observed that the film deposited at glancing angle (80°) exhibits the highest optical anisotropy. Further, anisotropy was noticed to decrease with lower values of deposition angles while effective refractive index depicts opposite trend. Variation in refractive index and anisotropy has been explained in light of atomic shadowing during growth of thin films at oblique angles.
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
Electron Microscopy of Natural and Epitaxial Diamond
Semiconducting diamond films have the potential for use as a material in which to build active electronic devices capable of operating at high temperatures or in high radiation environments. Ultimately, it is preferable to use low-defect-density single crystal diamond for device fabrication. We have previously investigated polycrystalline diamond films with transmission electron microscopy (TEM) and scanning electron microscopy (SEM), and homoepitaxial films with SEM-based techniques. This contribution describes some of our most recent observations of the microstructure of natural diamond single crystals and homoepitaxial diamond thin films using TEM.
Posthill, J. B.↗
Structural, electrical and multiferroic properties of La-doped mullite Bi{sub 2}Fe{sub 4}O{sub 9} thin films
Highlights: • Chemical solution deposited La-doped Bi{sub 2}Fe{sub 4}O{sub 9} thin film. • Structural, electrical and multiferroic properties were investigated. • La-doped Bi{sub 2}Fe{sub 4}O{sub 9} exhibited enhanced electrical and multiferroic properties. - Abstract: Thin films of (Bi{sub 2−x}La{sub x})Fe{sub 4}O{sub 9} (x = 0 and x = 0.05) were prepared on Pt(1 1 1)/Ti/SiO{sub 2}/Si(1 0 0) substrates by using a chemical solution deposition method to investigate structural, microstructural, electrical and multiferroic properties. Both the thin films were crystallized in mullite type phases with orthorhombic structures containing no secondary and impurity phases, which was confirmed by X-ray diffraction and Raman spectroscopy studies. The (Bi{sub 1.95}La{sub 0.05})Fe{sub 4}O{sub 9} thin film exhibited improved electrical and multiferroic properties at room-temperature. The leakage current density of the (Bi{sub 1.95}La{sub 0.05})Fe{sub 4}O{sub 9} thin film was one order of magnitude lower than that of the Bi{sub 2}Fe{sub 4}O{sub 9} thin film. Furthermore, in the thin film form, (Bi{sub 2−x}La{sub x})Fe{sub 4}O{sub 9} exhibited better stability against electrical breakdowns and enhanced multiferroic properties.
36 MATERIALS SCIENCE↗
Low-voltage magnetoelectric coupling in membrane heterostructures
Strain-mediated magnetoelectric (ME) coupling in ferroelectric (FE)/ferromagnetic (FM) heterostructures offers a unique opportunity for both fundamental scientific research and low-power multifunctional devices. Relaxor-FEs, such as (1-x)Pb(Mg 1/3 Nb 2/3 )O 3 -(x)PbTiO 3 (PMN-xPT), are ideal FE layer candidates because of their giant piezoelectricity. However, thin films of PMN-PT suffer from substrate clamping, which substantially reduces piezoelectric in-plane strains. Here, we demonstrate low-voltage ME coupling in an all-thin-film heterostructure that uses the anisotropic strains induced by the (011) orientation of PMN-PT. We completely remove PMN-PT films from their substrate and couple with FM Ni overlayers to create membrane PMN-PT/Ni heterostructures showing 90° Ni magnetization rotation with 3 V PMN-PT bias, much less than the bulk PMN-PT ~100-V requirement. Scanning transmission electron microscopy and phase-field simulations clarify the membrane response. These results provide a crucial step toward understanding the microstructural behavior of PMN-PT thin films for use in piezo-driven ME heterostructures.
36 MATERIALS SCIENCE↗
Rapid Epitaxial Growth of GdBa{sub 2}Cu{sub 3}O{sub 7-σ} Films by Dilute Co Doping
The effect of dilute Co doping on the epitaxial growth of GdBCO films was investigated by self-developed fluorine-free polymer-assisted metal-organic deposition (PA-MOD) method. Under the same sintering heat treatment, dilute Co doping dramatically improved the crystallinity, microstructure, and critical current density (J{sub c}) of GdBCO films. High J{sub c} of 4.0 MA/cm{sup 2} at 77 K and self-field was obtained in Co-doped film after only sintering for 30 min, which is eight times of the J{sub c} for the undoped film. Also, Co-doped GdBCO film sintered for as short as 20 min still possesses a high J{sub c} of 1.5 MA/cm{sup 2}, whereas the J{sub c} is 0 for the similarly sintered pure film. These results suggest that dilute Co doping facilitates the epitaxial growth of the high-performance GdBCO film.
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
Fine–scale structural features of intercritically aged HSLA-100 plate steel and their influence on yield strength and low-temperature impact toughness
Highlights: • The fine-scale microstructure of HSLA-100 steel intercritically aged at 677 °C was characterized. • Continuous austenite films evolved into isolated islands; large islands transformed to brittle martensite upon quenching. • Copper precipitates in martensite were coarse, and some sub-grain coarsening occurred within martensite. • Intercritically aged steel possessed an inferior strength-toughness balance as compared with sub-critically aged steel. - Abstract: Fine-scale structural features of an HSLA-100 steel intercritically aged at 950 K (677 °C) for 4.2 ks (70 min.) were investigated via transmission electron microscopy. The microstructure consisted of approximately 90 vol. pct. of low‑carbon lath martensite. Average lath width was about 0.25 μm, unchanged from the as-quenched condition, owing to a high number density of epsilon‑copper precipitates at these boundaries. About 10 vol. pct. of medium‑carbon austenite existed as coarsened, broken-up islands between laths; martensite lath boundary coverage by austenite was notably reduced compared to the as-quenched condition. Greater continuity between adjacent low‑carbon martensite laths was accompanied by coarse copper precipitates within laths and an order of magnitude lower dislocation density than the as-quenched martensite. Collectively, these features produced a sub-grain coarsening effect. Austenite islands larger than about 0.5 μm were unstable with respect to the formation of fresh, medium‑carbon martensite regions. Copper precipitation within austenite islands (owing to carbon and copper enrichment) might also have contributed to austenite transformation upon quenching. Intercritical aging was associated with a strong-and-undesirable deviation from strength-toughness behavior at sub-critical aging temperatures. Two key factors were identified as being responsible for this negative outcome: (i) a sub-grain coarsening effect associated with “delamellarization” of low‑carbon martensite and austenite and (ii) the formation of brittle martensite upon quenching. Quantitative estimates of the changes in strength and impact toughness are provided for microstructural differences between intercritically aged and subcritically aged material.
36 MATERIALS SCIENCE↗
Amorphous complexions alter the tensile failure of nanocrystalline Cu-Zr alloys
Grain boundary-based mechanisms are known to control the plastic deformation and failure of nanocrystalline metals, with manipulation of the boundary structure a promising path for tuning this response. In this study, the role of interfacial structural disorder on plasticity and failure of nanocrystalline Cu-Zr alloys is investigated with in situ scanning electron microscopy tensile deformation experiments. Two model materials are created, one with only the typical ordered grain boundaries and another with amorphous intergranular films interspersed into the boundary network, while the microstructures are otherwise identical. Hence, the importance of complexion type on plasticity and failure is isolated by only varying complexion structure. Here, the tensile experiments show that failure of the samples containing amorphous films is significantly retarded, as evidenced by an increase in the cross-sectional area reduction, a decrease in the occurrence of shear-dominated failure, a decrease in strain localization, and fracture surfaces with more elongated dimple features. As a whole, this study provides direct evidence that structural disorder at the grain boundaries can be beneficial for improving the ductility of nanocrystalline metals.
36 MATERIALS SCIENCE↗
Properties of the Barium–Strontium Titanate Films Deposited onto the Silicon Substrate by rf Cathode Sputtering
Using rf cathode sputtering of a target in the oxygen atmosphere, Ba{sub 0.6}Sr{sub 0.4}TiO{sub 3} solid solution thin films have been formed on the single-crystal Si(001) cut surface and their crystal structure, microstructure, and optical characteristics have been investigated. It is shown that the films are optically anisotropic, polycrystalline, and have a c axis preferred direction perpendicular to the substrate. The a and b axes in the substrate plane have no preferred direction. It has been established that, during the synthesis, a buffer layer with a thickness of about 20 nm forms between the film and substrate, which is optically equivalent to silicon oxide.
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
High energy-storage performance of 0.9Pb(Mg{sub 1/3}Nb{sub 2/3})O{sub 3}-0.1PbTiO{sub 3} relaxor ferroelectric thin films prepared by RF magnetron sputtering
Highlights: • High-quality PMN-PT 90/10 RFE thin films were prepared by RF magnetron sputtering. • The maximum discharged density of 31.3 J/cm{sup 3} was obtained in the 750-nm-thick film. • PMN-PT RFE films might be a promising material for energy-storage application. - Abstract: 0.9Pb(Mg{sub 1/3}Nb{sub 2/3})O{sub 3}-0.1PbTiO{sub 3} (PMN-PT 90/10) relaxor ferroelectric thin films with different thicknesses were deposited on the LaNiO{sub 3}/Si (100) by the radio-frequency (RF) magnetron sputtering technique. The effects of thickness and deposition temperature on the microstructure, dielectric properties and the energy-storage performance of the thin films were investigated in detail. X-ray diffraction spectra indicated that the thin films had crystallized into a pure perovskite phase with a (100)-preferred orientation after annealed at 700 °C. Moreover, all the PMN-PT 90/10 thin films showed the uniform and crack-free surface microstructure. As a result, a larger recoverable energy density of 31.3 J/cm{sup 3} was achieved in the 750-nm-thick film under 2640 kV/cm at room temperature. Thus, PMN-PT 90/10 relaxor thin films are the promising candidate for energy-storage capacitor application.
36 MATERIALS SCIENCE↗
Phase stability and B-site ordering in La{sub 2}NiMnO{sub 6} thin films
Thin films of multiferroic double-perovskite La{sub 2}NiMnO{sub 6} are prepared on (001)-oriented SrTiO{sub 3}, (La{sub 0.289}Sr{sub 0.712})(Al{sub 0.633}Ta{sub 0.356})O{sub 3}, and LaSrAlO{sub 4} substrates by pulsed laser deposition. Microstructure investigation by advanced electron microscopy shows that the La{sub 2}NiMnO{sub 6} films have a monoclinic structure on the SrTiO{sub 3} substrates and a rhombohedral structure on the (La{sub 0.289}Sr{sub 0.712})(Al{sub 0.633}Ta{sub 0.356})O{sub 3} and LaSrAlO{sub 4} substrates. Atomic-scale elemental maps of the monoclinic and rhombohedral phases reveal a short-range and/or partial ordering of the B-sites. In addition, domains and columnar grains are found in the films. Our results demonstrate that the phase and microstructure of the La{sub 2}NiMnO{sub 6} films can be tuned by epitaxial strains induced by different substrates.
71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗