Showing papers on "Pulsed laser deposition published in 2018"

Electronic and transport properties of Li-doped NiO epitaxial thin films

Abstract: NiO is a p-type wide bandgap semiconductor of use in various electronic devices ranging from solar cells to transparent transistors. Understanding and improving its optical and transport properties have been of considerable interest. In this work, we have investigated the effect of Li doping on the electronic, optical and transport properties of NiO epitaxial thin films grown by pulsed laser deposition. We show that Li doping significantly increases the p-type conductivity of NiO, but all the films have relatively low room-temperature mobilities (<0.05 cm2 V−1 s−1). The conduction mechanism is better described by small-polaron hoping model in the temperature range of 200 K < T < 330 K, and variable range hopping at T < 200 K. A combination of X-ray photoemission and O K-edge X-ray absorption spectroscopic investigations reveal that the Fermi level gradually shifts toward the valence band maximum (VBM) and a new hole state develops with Li doping. Both the VBM and hole states are composed of primarily Zhang-Rice bound states, which accounts for the small polaron character (low mobility) of hole conduction. Our work provides guidelines for the search for p-type oxide materials and device optimization.

Robust ferroelectricity in epitaxial Hf1/2Zr1/2O2 thin films

Abstract: Ferroelectric orthorhombic Hf0.5Zr0.5O2 thin films have been stabilized epitaxially on La2/3Sr1/3MnO3/SrTiO3(001) by pulsed laser deposition. The epitaxial orthorhombic films, (111)-oriented and with a very flat surface, show robust ferroelectric properties at room temperature. They present a remnant polarization around 20 μC/cm2 without the need of a wake-up process, a large coercive electric field of around 3 MV/cm, an extremely long retention extending well beyond 10 years, and an endurance up to about 108 cycles. Such outstanding properties in the nascent research on epitaxial HfO2-based ferroelectric films can pave the way for a better understanding of the effects of orientation, interfaces, strain, and defects on ferroelectricity in HfO2.

Demonstration of high-responsivity epitaxial β-Ga2O3/GaN metal–heterojunction-metal broadband UV-A/UV-C detector

Abstract: We demonstrate epitaxial β-Ga2O3/GaN-based vertical metal–heterojunction-metal (MHM) broadband UV-A/UV-C photodetectors with high responsivity (3.7 A/W) at 256 and 365 nm, UV-to-visible rejection >103, and a photo-to-dark current ratio of ~100. A small (large) conduction (valence) band offset at the heterojunction of pulsed laser deposition (PLD)-grown β-Ga2O3 on metal organic chemical vapor deposition (MOCVD)-grown GaN-on-silicon with epitaxial registry, as confirmed by X-ray diffraction (XRD) azimuthal scanning, is exploited to realize detectors with an asymmetric photoresponse and is explained with one-dimensional (1D) band diagram simulations. The demonstrated novel vertical MHM detectors on silicon are fully scalable and promising for enabling focal plane arrays for broadband ultraviolet sensing.

Aluminium/gallium, indium/gallium, and aluminium/indium co-doped ZnO thin films deposited via aerosol assisted CVD

Abstract: Aluminium/gallium co-doped ZnO (AGZO), indium/gallium co-doped ZnO (IGZO), and aluminium/indium co-doped ZnO (AIZO) thin films were synthesised on glass substrates via aerosol assisted chemical vapour deposition (AACVD). The films were fully characterised by X-ray diffraction, X-ray photoelectron spectroscopy and scanning electron microscopy. The optoelectronic properties of the films were determined using UV/vis spectroscopy and Hall effect measurements. The AGZO film displayed the lowest resistivity (1.3 × 10−2 Ω cm) and highest carrier mobility (7.9 cm2 V−1 s−1), due the relatively low amount of disorder in the structure. The incorporation of In3+ resulted in the most disorder in the structure due to its large radius, which led to an increase in optical absorption, and a decrease in resistivity.

Review of Graphene Growth From a Solid Carbon Source by Pulsed Laser Deposition (PLD)

Abstract: Graphene is a remarkable two-dimensional (2D) material that is of great interest to both academia and industry. It has outstanding electrical and thermal conductivity and good mechanical behavior with promising applications in electronic devices, supercapacitors, batteries, composite materials, flexible transparent displays, solar cells, and sensors. Several methods have been used to produce either pristine graphene or doped graphene. These include chemical vapor deposition (CVD), mechanical exfoliation, decomposition of SiC, liquid-phase exfoliation, pulsed laser deposition (PLD). Among these methods, PLD, which is routinely used for growing complex oxide thin films has proved to be an alternative to the more widely reported CVD method for producing graphene thin films, because of its advantages. Here we review the synthesis of graphene using PLD. We describe recent progress in preparing pristine graphene and doped graphene by PLD, including deposition processes and characterization. The goal of this complete survey is to describe the advantages of using the technique for graphene growth. The review will also help researchers to better understand graphene synthesis using the PLD technique.

Lanthanide Yb/Er co-doped semiconductor layered WSe2 nanosheets with near-infrared luminescence at telecommunication wavelengths

Abstract: Atomically thin layers of transition metal dichalcogenides (TMDs) have recently drawn great attention. However, doping strategies and controlled synthesis for wafer-scale TMDs are still in their early stages, greatly hindering the construction of devices and further basic studies. In this work, we develop the fast deposition of wafer-scale layered lanthanide ion Yb/Er co-doped WSe2 using pulsed laser deposition. WSe2 nanosheets were chosen as the host, while Yb3+ and Er3+ ions served as the sensitizer and activator, respectively. The obtained Yb/Er co-doped WSe2 layers exhibit good uniformity and high crystallinity with highly textured features. Under the excitation of a diode laser at 980 nm, down-conversion emission is observed at around 1540 nm, assigned to the emission transition between the 4I13/2 and 4I15/2 states of Er3+. Considering the significance of 1540 nm luminescence in the application of photonic technologies, this observation in the WSe2:Yb/Er nanosheets down to the monolayer provides a new opportunity for developing photonic devices at the 2D limit. Our work not only offers a general method to prepare wafer-scale lanthanide doped TMDs, but also to widely modulate the luminescence of atomically layered TMDs by introducing lanthanide ions.

Ferroelectricity mediated by ferroelastic domain switching in HfO2-based epitaxial thin films

Abstract: Herein, ferroelastic domain switching from the nonpolar b-axis to the polar c-axis oriented domain in 7%-YO1.5-substituted HfO2 (YHO-7) epitaxial ferroelectric films is demonstrated. Scanning transmission electron microscopy (STEM) indicates that the polarization of a pristine film deposited on a Sn-doped In2O3/(001)YSZ substrate by the pulsed laser deposition method tends to be along the in-plane direction to avoid a strong depolarization field with respect to the out-of-plane direction. Applying an electric field aids in ferroelastic domain switching in YHO-7 films. Such films exhibit ferroelectric characteristics with a relatively large saturated polarization around 30 μC/cm2 by polarization reorientation from the in-plane to the out-of-plane directions and an increased dielectric constant. The synchrotron X-ray diffraction measurements with a focused beam for the pristine and poled area indicate ferroelastic 90° domain switching as the odd number reflection disappears, which is only allowed in the nonpolar b-axis orientation. STEM observations also show a significant increase in the c-axis oriented domain. This observation of ferroelastic domain switching strongly supports the conclusion that the ferroelectricity of HfO2 originates from the non-centrosymmetric orthorhombic phase.

Fabrication of Highly Metallic TiN Films by Pulsed Laser Deposition Method for Plasmonic Applications

Abstract: We report the fabrication of titanium nitride (TiN) films with the “best” plasmonic behavior reported so far by the pulsed laser deposition method. Even though the deposition is done at room temperature (∼25 °C) and grown on an amorphous native oxide of a silicon wafer, the plasmonic property of the TiN is comparable to that of gold, which is a conventional plasmonic material in the visible to near-infrared region. Because of the highly plasmonic nature of the TiN, the near field around the TiN nanostructure can be as high as that of a gold nanostructure. A room-temperature process without a strict requirement on the substrate allows depositing a TiN film even on a flexible polymer film without degrading its property. Our results pave the way for using TiN as a truly practical plasmonic material, replacing the use of noble metals.

Single Crystal High Entropy Perovskite Oxide Epitaxial Films

Abstract: The first examples of single crystal epitaxial thin films of a high entropy perovskite oxide are synthesized. Pulsed laser deposition is used to grow the configurationally disordered ABO3 perovskite, Ba(Zr0.2Sn0.2Ti0.2Hf0.2Nb0.2)O3, epitaxially on SrTiO3 and MgO substrates. X-ray diffraction and scanning transmission electron microscopy demonstrate that the films are single phase with excellent crystallinity and atomically abrupt interfaces to the underlying substrates. Atomically-resolved electron energy loss spectroscopy mapping shows a uniform and random distribution of all B-site cations. The ability to stabilize perovskites with this level of configurational disorder offers new possibilities for designing materials from a much broader combinatorial cation pallet while providing a fresh avenue for fundamental studies in strongly correlated quantum materials where local disorder can play a critical role in determining macroscopic properties.

Controlling microstructure and film growth of relaxor-ferroelectric thin films for high break-down strength and energy-storage performance

Abstract: The relaxor ferroelectric Pb 0.9 La 0.1 (Zr 0.52 Ti 0.48 )O 3 (PLZT) thin films were deposited using pulsed laser deposition, and their microstructures, break-down field strengths and energy storage performances were investigated as a function of the buffer layer and electrode. A large recoverable energy-storage density ( U reco ) of 23.2 J/cm 3 and high energy-storage efficiency ( η ) of 91.6% obtained in the epitaxial PLZT film grown on SrRuO 3 /SrTiO 3 /Si are much higher than those in the textured PLZT film ( U reco = 21.9 J/cm 3 , η = 87.8%) on SrRuO 3 /Ca 2 Nb 3 O 10 -nanosheet/Si and the polycrystalline PLZT film ( U reco = 17.6 J/cm 3 , η = 82.6%) on Pt/Ti/SiO 2 /Si, under the same condition of 1500 kV/cm and 1 kHz, due to the slim polarization loop and significant antiferroelectric-like behavior. Owing to the high break-down strength (BDS) of 2500 kV/cm, a giant U reco value of 40.2 J/cm 3 was obtained for the epitaxial PLZT film, in which U reco values of 28.4 J/cm 3 (at BDS of 2000 kV/cm) and 20.2 J/cm 3 (at BDS of 1700 kV/cm), respectively, were obtained in the textured and polycrystalline PLZT films. The excellent fatigue-free properties and high thermal stability were also observed in these films.

Revealing the Performance-Limiting Factors in α‑SnWO 4 Photoanodes for Solar Water Splitting

Abstract: α-SnWO4 is an n-type metal oxide semiconductor that has recently attracted attention as a top absorber material in a D4-tandem device for highly efficient solar water splitting due to the combination of an ideal bandgap (∼1.9 eV) and a relatively negative photocurrent onset potential (∼0 V vs RHE). However, up to now, α-SnWO4 photoanodes have not shown high photoconversion efficiencies for reasons that have not yet been fully elucidated. In this work, phase-pure α-SnWO4 films are successfully prepared by pulsed laser deposition. The favorable band alignment is confirmed, and key carrier transport properties, such as charge carrier mobility, lifetime, and diffusion length are reported for the first time. In addition, a hole-conducting NiOx layer is introduced to protect the surface of the α-SnWO4 films from oxidation. The NiOx layer is found to increase the photocurrent for sulfite oxidation by a factor of ∼100, setting a new benchmark for the photocurrent and quantum efficiency of α-SnWO4. These results p...

Highly conductive PdCoO2 ultrathin films for transparent electrodes

Abstract: We report on the successful synthesis of highly conductive PdCoO2 ultrathin films on Al2O3 (0001) by pulsed laser deposition. The thin films grow along the c-axis of the layered delafossite structure of PdCoO2, corresponding to the alternating stacking of conductive Pd layers and CoO2 octahedra. The thickness-dependent transport measurement reveals that each Pd layer has a homogeneous sheet conductance as high as 5.5 mS in the samples thicker than the critical thickness of 2.1 nm. Even at the critical thickness, high conductivity exceeding 104 S cm−1 is achieved. Optical transmittance spectra exhibit high optical transparency of PdCoO2 thin films particularly in the near-infrared region. The concomitant high values of electrical conductivity and optical transmittance make PdCoO2 ultrathin films promising transparent electrodes for triangular-lattice-based materials.

Thickness-dependent crystal structure and electric properties of epitaxial ferroelectric Y2O3-HfO2 films

Abstract: The thickness dependences of the crystal structure and electric properties of (111)-oriented epitaxial 0.07YO1.5-0.93HfO2 (YHO7) ferroelectric films were investigated for the film thickness range of 10–115 nm. The YHO7 films were grown by pulsed laser deposition or sputtering at room temperature and subsequent heat treatment. As a substrate for the epitaxial growth of the YHO7 film, (111)-oriented 10 wt. % Sn-doped In2O3(ITO)//(111) yttria-stabilized zirconia was used. X-ray diffraction measurements confirmed that the main crystal phase of these YHO7 films was ferroelectric orthorhombic for up to 115-nm-thick films. Small film-thickness dependences of remanent polarization (Pr) and saturation polarization (Ps) were observed. Thickness dependence of the coercive field (Ec) is also small, and this behavior does not resemble that of conventional ferroelectric films such as Pb(Zr,Ti)O3. Additionally, non-oriented polycrystalline YHO7 films are reported to have similar thickness dependence of Ec and almost the same Ec value to epitaxial YHO7 films. We suggest that the ferroelectric domain is significantly small for both epitaxial and polycrystalline films. Such small domains remain even in thicker films, giving rise to thickness-independent Ec.

Electric field-induced phase transition and energy storage performance of highly-textured PbZrO3 antiferroelectric films with a deposition temperature dependence

Abstract: Thin PbZrO3 (PZO) antiferroelectric films with (001)-preferred orientation were deposited on SrRuO3/Ca2Nb3O10-nanosheet/Si substrates using pulsed laser deposition. Variation of the deposition temperature was found to play a key role in the control of the microstructure and strongly influence the energy storage performance of the thin film. The critical phase switching field, where the aligned antiferroelectric (AFE) domains start to transform into the ferroelectric (FE) state, decreased with increasing temperature. On the other hand, the content of the FE phase in the AFE PZO thin films increased with increasing deposition temperature. A large recoverable energy-storage density of 16.8 J/cm3 and high energy-storage efficiency of 69.2% under an electric field of 1000 kV/cm were achieved in the films deposited at 525 °C. This performance was due to the high forward switching field and backward switching field values and the low difference between these two fields. Moreover, the PZO thin films showed great charge-discharge cycling life with fatigue-free performance up to 1010 cycles and good thermal stability from room temperature to 100 °C.

Influence of annealing atmosphere on the performance of a β-Ga2O3 thin film and photodetector

Abstract: β-Ga2O3 epitaxial thin films were deposited by laser molecular beam epitaxy (LMBE) and annealed at 800°C for 30 minutes in air and oxygen atmospheres, respectively. Photodetectors were fabricated using as-grown and annealed Ga2O3 epilayers. The influence of the annealing atmosphere on the crystal structure and optical properties of Ga2O3 films was investigated. X-ray diffraction (XRD) measurements show that the in-plane compressive strain of Ga2O3 thin films could be relaxed after high temperature thermal annealing. Compared with the as-grown sample, the annealed samples exhibit a red shift of absorption edge in the transmittance spectra, indicating a reduced bandgap. According to the XPS measurement results, the atomic ratios of O to Ga also increased for the annealed samples. Moreover, the oxygen-annealed photodetector achieves a larger photocurrent, higher responsivity and better time-dependent photoresponse than the other two samples, which may be attributed to the decrease in the number of oxygen vacancies.

Tunable critical temperature for superconductivity in FeSe thin films by pulsed laser deposition.

Abstract: Stabilized FeSe thin films in ambient pressure with tunable superconducting critical temperature would be a promising candidate for superconducting electronic devices. By carefully controlling the depositions on twelve kinds of substrates using a pulsed laser deposition technique single crystalline FeSe thin films were fabricated. The high quality of the thin films was confirmed by X-ray diffraction with a full width at half maximum of 0.515° in the rocking curve and clear four-fold symmetry in φ-scan. The films have a maximum T c ~ 15 K on the CaF2 substrate and were stable in ambient conditions air for more than half a year. Slightly tuning the stoichiometry of the FeSe targets, the superconducting critical temperature becomes adjustable below 15 K with quite narrow transition width less than 2 K. These FeSe thin films deposited on different substrates are optimized respectively. The Tc of these optimized films show a relation with the out-of-plane (c-axis) lattice parameter of the FeSe films.

Tunable Electrical and Optical Properties of Nickel Oxide (NiOx) Thin Films for Fully Transparent NiOx–Ga2O3 p–n Junction Diodes

Abstract: One of the major limitations of oxide semiconductors technology is the lack of proper p-type materials to enable devices such as pn junctions, light-emitting diodes, and photodetectors. This limitation has resulted in an increased research focus on these materials. In this work, p-type NiOx thin films with tunable optical and electrical properties as well as its dependence with oxygen pressure during pulsed laser deposition are demonstrated. The control of NiOx films resistivity ranged from ∼109 to ∼102 Ω cm, showing a p-type behavior with Eg tuning from 3.4 to 3.9 eV. Chemical composition and the resulting band diagrams are also discussed. The all-oxide NiOx–Ga2O3 pn junction showed very low leakage current, an ideality factor of ∼2, 105 on/off ratio, and 0.6 V built-in potential. Its J–V temperature dependence is also analyzed. C–V measurements demonstrate diodes with a carrier concentration of 1015 cm–3 for the Ga2O3 layer, which is fully depleted. These results show a stable, promising diode, attracti...

Band alignment at β-(AlxGa1−x)2O3/β-Ga2O3 (100) interface fabricated by pulsed-laser deposition

Abstract: High-quality β-(AlxGa1−x)2O3 (x = 0–0.37) films were epitaxially grown on β-Ga2O3 (100) substrates by oxygen-radical-assisted pulsed-laser deposition with repeating alternate ablation of single crystals of β-Ga2O3 and α-Al2O3. The bandgap was tuned from 4.55 ± 0.01 eV (x = 0) to 5.20 ± 0.02 eV (x = 0.37), where bowing behavior was observed. The band alignment at the β-(AlxGa1−x)2O3/β-Ga2O3 interfaces was found to be type-I with conduction- and valence-band offsets of 0.52 ± 0.08 eV (0.37 ± 0.08 eV) and 0.13 ± 0.07 eV (0.02 ± 0.07 eV) for x = 0.37 (0.27), respectively. The large conduction-band offsets are ascribed to the dominant contribution of the cation-site substitution to the conduction band.

Thermal hysteresis measurement of the VO 2 dielectric function for its metal-insulator transition by visible-IR ellipsometry

Abstract: The real and imaginary parts of the dielectric function of VO2 thin films, deposited on r-plane sapphire via pulsed laser deposition, are measured by means of visible-infrared ellipsometry for wavelengths ranging from 0.4 to 15 μm and temperatures within its phase transition. For both the insulator-to-metal (heating) and metal-to-insulator (cooling) transitions, it is shown that the two ellipsometric signals exhibit three temperature-driven behaviors, which are well described by appropriate combinations of the Tauc-Lorentz, Gaussian, and Drude oscillator models. By fitting Bruggeman's effective medium model for the dielectric function to the corresponding measured experimental values, using the volumetric fraction of the VO2 metallic domains as a fitting parameter for different temperatures within the VO2 phase transition, we have found that this model is suitable for describing the dielectric function in visible and near-infrared wavelengths (∼0.4 to ∼3.0 μm), but it generally fails for longer infrared ones. Furthermore, the hysteresis loop of the VO2 emissivity averaged over a relevant interval of wavelengths is determined and shown to vary from ∼0.49, in the insulator phase, to ∼0.16, in the metallic one. These values, based on the VO2 dielectric function, are consistent with previous measurements reported in the literature, and therefore, our measured data are expected to be useful for describing the behavior of VO2 films involved in optical and radiative applications.

Enhanced Lithium Transport by Control of Crystal Orientation in Spinel LiMn2O4 Thin Film Cathodes

Abstract: A promising cathode material for rechargeable batteries is LiMn2O4, which exhibits higher operating voltage, reduced toxicity and lower costs as compared to commonly used LiCoO2 cathodes. However, LiMn2O4 suffers from limited cycle life, as excessive capacity fading occurs during battery cycling due to dissolution of Mn into the acidic electrolyte. Here, we show that by structural engineering of stable, epitaxial LiMn2O4 thin films the electrochemical properties can be enhanced as compared to polycrystalline samples. Control of the specific crystal orientation of the LiMn2O4 thin films resulted in dramatic differences in surface morphology with pyramidal, rooftop or flat features for respectively (100), (110), and (111) orientations. All three types of LiMn2O4 films expose predominantly ⟨111⟩ crystal facets, which is the lowest energy state surface for this spinel structure. The (100)-oriented LiMn2O4 films exhibited the highest capacities and (dis)charging rates up to 33C, and good cyclability over a th...

Tuning Pt–Ir Interactions for NH3 Electrocatalysis

Abstract: PtxIr100–x thin films (8 nm thick) were deposited on MgO(100) substrates by pulsed laser deposition at 600 °C. As shown by X-ray diffraction and X-ray photoelectron spectroscopy analyses, the formation of fcc bulk and surface PtIr solid solution was observed over the whole compositional range despite the large miscibility gap exhibited by these elements below ca. 1000 °C. Moreover, pole figures indicate that all films exhibit a Pt(001)[010]//[010](001)MgO cube-on-cube epitaxial relationship, which is consistent with AFM images. Cyclic voltammetry measurements performed in alkaline solutions confirmed both the presence of Ir atoms at the surface and the (100) surface orientation of all PtxIr100–x surfaces. The highest electrocatalytic activity for the electrooxidation of NH3 was observed for the Pt74Ir26(100) surface with a current density of ca. 1.0 mA cm–2 at 0.71 V vs RHE, which is 25% higher than that on Pt(100). The reasons underlying this behavior are discussed.

Intrinsic hydrophilic nature of epitaxial thin-film of rare-earth oxide grown by pulsed laser deposition.

Abstract: Herein, we report a systematic study of water contact angle (WCA) of rare-earth oxide thin-films. These ultra-smooth and epitaxial thin-films were grown using pulsed laser deposition and then characterized using X-Ray diffraction (XRD), Rutherford backscattering spectroscopy (RBS), and atomic force microscopy (AFM). Through both the traditional sessile drop and the novel f–d method, we found that the films were intrinsically hydrophilic (WCA < 10°) just after being removed from the growth chamber, but their WCAs evolved with an exposure to the atmosphere with time to reach their eventual saturation values near 90° (but always stay ‘technically’ hydrophilic). X-Ray photoelectron spectroscopy analysis was used to further investigate qualitatively the nature of hydrocarbon contamination on the freshly prepared as well as the environmentally exposed REO thin-film samples as a function of the exposure time after they were removed from the deposition chamber. A clear correlation between the carbon coverage of the surface and the increase in WCA was observed for all of the rare-earth films, indicating the extrinsic nature of the surface wetting properties of these films and having no relation to the electronic configuration of the rare-earth atoms as proposed by Azimi et al.

Highly conductive PdCoO2 ultrathin films for transparent electrodes

Abstract: We report on the successful synthesis of highly conductive PdCoO2 ultrathin films on Al2O3 (0001) by pulsed laser deposition. The thin films grow along the c-axis of the layered delafossite structure of PdCoO2, corresponding to the alternating stacking of conductive Pd layers and CoO2 octahedra. The thickness-dependent transport measurement reveals that each Pd layer has a homogeneous sheet conductance as high as 5.5 mS in the samples thicker than the critical thickness of 2.1 nm. Even at the critical thickness, high conductivity exceeding 104 Scm-1 is achieved. Optical transmittance spectra exhibit high optical transparency of PdCoO2 thin films particularly in the near-infrared region. The concomitant high values of electrical conductivity and optical transmittance make PdCoO2 ultrathin films as promising transparent electrodes for triangular-lattice-based materials.

In Vitro Corrosion Behaviour of Ti–6Al–4V and 316L Stainless Steel Alloys for Biomedical Implant Applications

Abstract: Pulsed laser deposition technique is one of the methods to coat the hydroxyapatite on 316L stainless steel and Ti–6Al–4V implants, which is used in orthopaedics and dentistry applications. In this study, hydroxyapatite (HAP) ceramics in the form of calcium phosphate were deposited on Ti–6Al–4V and 316L stainless steel by the pulsed laser deposition method. The coated thin film was characterised by X-ray diffraction (XRD), scanning electron microscopy with energy-dispersive spectroscopy (EDS) and atomic microscopy. The corrosion studies were carried out on coated and uncoated samples using potentiodynamic polarisation studies in simulated body fluid (Hanks’ solution). The bioactivity of the Hap-coated samples on Ti–6Al–4V and 316L stainless steel was evaluated by immersing them in simulated body fluid for 9 days. XRD and EDS analyses confirmed the presence of HAP. The corrosion studies showed that the treated samples have better corrosion resistance compared to Ti–6Al–4V and 316L stainless-steel substrates. The formation of apatite on treated samples revealed the bioactivity of the HAP-coated substrates. HAP-coated Ti–6Al–4V provides higher corrosion protection than the HAP-coated 316L stainless-steel substrates.

Epitaxial ferroelectric Hf0.5Zr0.5O2 thin film on a buffered YSZ substrate through interface reaction

Abstract: In this study, we used pulsed laser deposition to successfully grow epitaxial Hf0.5Zr0.5O2 (HZO) films on (001)-, (011)- and (111)-oriented yttria-stabilized zirconia (YSZ) substrates using TiN as the bottom electrode. It is found that the TiO2 buffer layer formed by the interface reaction is the key to epitaxial growth. The epitaxial HZO films (∼15 nm in thickness) exhibit ferroelectric behaviour with a remnant polarization of 7–30 μC cm−2 and a coercive field of 1.1–2.3 MV cm−1. Using piezoresponse force microscopy, polar domains can be written/read and reversibly switched with a phase change of 180° in all the films. X-ray diffraction and high-resolution transmission electron microscopy reveal the presence of nano domains, and a clear epitaxial relation among different layers whose interfaces are relaxed by reconstruction. X-ray absorption spectroscopy provides deep insight into the microstructural origin of ferroelectricity in HZO. A large interface strain stabilized ferroelectric state is observed which is manifested as the non-centrosymmetric Pca21 phase.