LaAlO3 Single Crystal Substrates Research Articles

Epitaxial strain manipulation of the cluster glass state in LaMnO3 films.

As a new-type magnetic state, the cluster glass state in manganite is arousing considerable attention due to its important theoretical value and extensive application prospects in condensed matter physics and spintronics. Due to the complex magnetic interactions, the cluster glass state is difficult to form and regulate in single films. Studies report a new phenomenon that epitaxial strain can regulate the formation of the cluster glass state in LaMnO3 (LMO) films. Comparing LMO thin films with different thicknesses grown on a (001)-oriented LaAlO3 (LAO) single crystal substrate, we found that the 20-nm-thick LMO film is more likely to form the cluster glass state than the 60-nm-thick and 120-nm-thick films. This can be attributed to the uneven distribution of strain and Mn ions in the depth profile. Our work demonstrates that thickness is an important method for regulating the formation of the cluster glass state in LMO films.

Preparation of high purity phase (Bi, Pb)-2223 superconducting films by sol–gel method

In this work, a (Bi, Pb)2Sr2Ca2Cu3O10+δ ((Bi, Pb)-2223) solution with good film-forming capability and chemical stability was synthesized through using metal acetates as raw materials, acrylic acid as an additive, and anhydrous methanol as a solvent to adjust the sol formula. Subsequently, (Bi, Pb)-2223 thin films were fabricated on LaAlO3 (LAO) single-crystal substrates via dip-coating technology at different heat treatment temperatures, and the structures and properties of (Bi, Pb)-2223 films were characterized. It was found that when the sol stoichiometric ratio of Bi: Pb: Sr: Ca: Cu was controlled at 1.9: 0.35: 2: 2: 3 and the gel film was heat-treated at 860 °C and dwelled for 120 min in an mixed atmosphere of N2: O2 = 96: 4, the prepared thin film with a pure (Bi, Pb)-2223 superconducting phase exhibited excellent biaxial texture, a dense surface structure, and had a T c of 106 K and a ΔT c of 6 K. The microstructure analysis revealed a layered epitaxial growth of the film along the LAO substrate with a regular arrangement of atoms and a consistent interlayer spacing.

Interpretation of complex optical properties and optical transitions of epitaxial LaMnO3 thin films

An in-depth analysis of the optical properties of epitaxial (001) oriented LaMnO3films grown on SrTiO3and LaAlO3single crystal substrates is performed by spectroscopic ellipsometry to determine the complex dielectric function (ε = ε1 + iε2) spectra from 0.12 to 5.89 eV. Density Functional Theory and many body perturbation theory within the G0W0 and the Bethe-Salpeter Equation approximations, are also employed to generate theoretical spectra in ε. Critical point energies (CPs) from 0.91 to 1.49 eV are interpreted as energy separation between eg and t2g orbitals. CPs from 3.31 to 3.53 eV and 3.75 to 5.23 are interpreted as Mn d exchange splitting and strong charge transfer transitions, respectively. Direct and indirect bandgaps from Tauc-plots are identified in the range of 0.100–0.594 eV. Anisotropy presents in LaMnO3 on LaAlO3 is attributed to substantial distortion in the out-of-plane epitaxial strain compared to LaMnO3 on SrTiO3. These findings provide a comprehensive understanding of the origins and characteristics of features observed in optical properties of epitaxial LaMnO3, offering insights for development of optical and electronic applications based on these materials.

Enhanced cation ordering, electron-spin-phonon interactions and Fano resonance in half-metallic Sr2FeMoO6 thin films

We report the presence of electron-spin-phonon interactions in half-metallic ferromagnetic Sr2FeMoO6 (SFMO) double perovskite thin films using temperature-dependent Raman spectroscopy. A series of SFMO thin films have been prepared on LaAlO3 (001) single-crystal substrate using the Pulsed Laser Deposition technique. These depositions have been made in different gas-conditions such as in vacuum, and under nitrogen and oxygen gas pressures. At room temperature, Raman spectra manifest a Fano feature which indicates the presence of electron-phonon coupling in the films. The electron-phonon coupling strength further changes with a change in deposition conditions. Magnetization results show that the SFMO film grown in vacuum has the highest saturation magnetization which suggests better cation ordering as compared to the other films. For enhanced understanding, Raman spectra were recorded at varied temperatures and the data were analyzed by theoretical model fittings. A parameter quantifying temperature-dependent anharmonic nature of phonons has been derived using Balkanski model fits. This parameter shows a drastic deviation in the vicinity of Curie temperatures, manifesting a spin-phonon coupling in SFMO films. We further show that the spin-phonon coupling strengthens with improved Fe–Mo ordering. Any experimental observation of spin-phonon coupling has not been reported for SFMO systems till date. The magnetization data corroborate well with these observations made by Raman measurements. Our results of Raman spectroscopy, magnetization and resistivity collectively suggest that the SFMO films exhibit electron-spin-phonon interactions, which are influenced by the cation ordering. We also devised out the method of relating the anharmonic nature of Raman modes with the degree of Fe–Mo ordering and spin-phonon coupling in double-perovskite materials.

Enhancement of critical current densities by co-doping with Zr, Sn and Ce for Gd123 thin films fabricated by fluorine-free MOD method

Abstract We have fabricated GdBa2Cu3O7-δ thin films co-doped several types of BaMO3 (M=Zr, Sn, Ce) artificial pinning centers with different lattice constants and Young’s modulus from 2.0 to 5.0 mol% on LaAlO3 single crystal substrates by the FF-MOD method. When several types of BaMO3 are simultaneously introduced into Gd123 films by the FF-MOD method, Ba required for BaMO3 crystal growth is shared among them, each crystal growth is suppressed, and thus the crystals become finer and denser. This resulted in a remarkable enhancement of the critical current densities in magnetic fields. The maximum J c of 16.57 MA cm-2 at 0 T and 1.97 MA cm-2 at 3.0 T, 30 K obtained for the Gd123 film introduced three types of BaMO3 (M=Zr, Sn, Ce) with 4.0 mol% were 1.22 and 1.76 times larger than those for the film with the same amount of BaCeO3. This method shows a new strategy to improve Jc in magnetic fields of REBCO.

Ca3Co4O9-based transverse thermoelectric heat flux sensors with high sensitivity and fast response time

High-temperature thin film heat flux sensors have been fabricated by growing c-axis tilted epitaxial Ca3Co4O9 (CCO) thin films on 5° vicinal cut LaAlO3 (001) single crystal substrates. The layered structure of Ca3Co4O9 yields the significant Seebeck coefficient anisotropy between the ab-plane and c-axis, which could generate a voltage of the heat flux sensor via the transverse thermoelectric (TTE) effect of thin films. A sensitivity of 27.7 μV/(kW/m2) has been determined in such 5° tilted Ca3Co4O9 thin films, which is much larger than other reported ones based on the TTE effect from various materials. After a thermal treatment at 900 °C in air for 10 min, the sensitivity of such heat flux sensors is almost non-variable, which indicates that the temperature resistance of the CCO-based TTE heat flux sensor is as high as 900 °C. In addition, a fast response time of 45 μs has been identified in such CCO-based TTE heat flux sensors. These results demonstrate that the CCO is a promising candidate to manufacture the TTE heat flux sensors with the superiorly comprehensive performance, including the high temperature resistance, high sensitivity, and fast response.

Phase purity and surface morphology of high-Jc superconducting Bi2Sr2Ca1Cu2O8+δ thin films

Bi2Sr2Ca1Cu2O8+δ (Bi-2212) thin films with thicknesses less than 50 nm (<20 unit cells) are grown by pulsed-laser deposition (PLD) onto (001) LaAlO3 (LAO) single crystal substrates. Phase-pure and smooth c-axis oriented Bi-2212 films with optimal oxygen doping, critical temperature Tc0 up to 86 K, and critical current density Jc(60 K) above 1 MA/cm2 are obtained for samples that are annealed in situ at temperatures below 700 °C. At higher temperature Bi-2212 films on LAO substrates partially decompose to non-superconducting impurity phases, while films on MgO and SrTiO3 substrates are stable. The broadening ΔTc of the metal-to-superconductor resistive phase transition in magnetic fields is much larger for thin films of Bi-2212 as compared to YBa2Cu3O7. The magnetic field-induced suppression of Tc0 is stronger for Bi-2212 films containing impurity phases as compared to the phase-pure Bi-2212 films. The degradation of LAO substrate crystals after several steps of deposition and chemical removal of the Bi-2212 layer is investigated. New, commercially prepared substrates provide Bi-2212 films with smallest surface roughness (3 nm) and strong out-of-plane texture. However, thin films of almost the same quality are obtained on re-used LAO substrates that are mechanically polished after the chemical etching.

Preparation and electrical properties of ultra-thin Bi2212 films by sol-gel method

In order to achieve flexible applications of superconducting thin film materials in devices, the surface quality of the film is critical. The thickness of the film is one of the important factors affecting its surface quality. In this paper, Bi2212 superconducting thin films of different thicknesses were prepared on LaAlO3(100) and SrTiO3(100) single crystal substrates by sol-gel method and the effects of film thickness and different heterogeneous structures on their crystallographic, morphological and superconducting properties were investigated. The results showed that the roughness gradually increased with increasing Bi2212 thickness at the initial stage of film growth and stabilized after reaching a certain thickness, while the superconducting properties were destroyed at very small sample thickness, which was consistent in both single-crystal substrate films. In the Bi2212/LaAlO3 structure, the surface quality of the sample was excellent with a roughness of 5.4 nm at a thickness of about 18 nm for Bi2212, and the growth of the precipitated phase was inhibited to a greater extent. The film also had good superconductivity. This work provided a further research basis for the preparation of high quality Bi2212 films and offers further possibilities for their practical application.

Conductive path and local oxygen-vacancy dynamics: Case study of crosshatched oxides

By employing scanning probe microscopy, conductive path and local oxygen-vacancy dynamics have been investigated in crosshatched La0.7Sr0.3MnO3 thin films grown onto flat and vicinal LaAlO3(001) single crystal substrates. Consistent with prior studies, the crosshatch topography was observed first by dynamical force microscopy as the epi-stain started to release with increasing film thickness. Second, by using conductive atomic force microscopy (CAFM), conductive crosshatch and dots (locally aligned or random) were unravelled, however, not all of which necessarily coincided with that shown in the in situ atomic force microscopy. Furthermore, the current–voltage responses were probed by CAFM, revealing the occurrence of threshold and/or memristive switchings. Our results demonstrate that the resistive switching relies on the evolution of the local profile and concentration of oxygen vacancies, which, in the crosshatched films, are modulated by both the misfit and threading dislocations.

Tunable Perpendicular Magnetoresistive Sensor Driven by Shape and Substrate Induced Magnetic Anisotropy

AbstractControl of magnetization reversal processes is a key issue for the implementation of magnetic materials in technological applications. The modulation of shape magnetic anisotropy in nanowire structures with a high aspect ratio is an efficient way to tune sharp in‐plane magnetic switching. However, control of fast magnetization reversal processes induced by perpendicular magnetic fields is much more challenging. Here, tunable sharp magnetoresistance changes, triggered by out‐of‐plane magnetic fields, are demonstrated in thin permalloy strips grown on LaAlO3 single crystal substrates. Micromagnetic simulations are used to evaluate the resistance changes of the strips at different applied field values and directions and correlate them with the magnetic domain distribution. The experimentally observed sharp magnetic switching, tailored by the shape anisotropy of the strips, is properly accounted for by numerical simulations when considering a substrate‐induced uniaxial magnetic anisotropy. These results are promising for the design of magnetic sensors and other advanced magnetoresistive devices working with perpendicular magnetic fields by using simple structures.

Electron doping of NdNiO3 thin films using dual chamber CaH2 annealing

Hydrogen donor doping has been exploited as a strategy to manipulate the electronic structure and electrical properties of functional oxide systems. Especially, the development of synthetic methods to achieve electron doping of perovskite rare-earth nickelate thin films utilizing interstitial hydrogen is highly desirable considering the rich electronic phase diagram hosting several functional properties. In this work, we present the hydrogenation of NdNiO3 (NNO) thin films using CaH2 annealing and the resulting giant modulation of electrical resistivity in hydrogenated NNO (H–NNO) thin films. Magnetron sputtering was employed to deposit epitaxial ∼60 ​nm-thin NNO films on single crystal LaAlO3 (LAO) substrates. The formation of the pristine perovskite NNO phase was realized after annealing the films at 500 ​°C for 24 h. CaH2 annealing of NNO thin films for time durations ranging from 1 to 6 ​h was performed in a vacuumed ampule with two interconnected chambers at 280 ​°C. The two-chamber design enables a simple and clean approach for hydrogen doping without physical contact between the powder and sample of interest. X-ray diffraction and Raman spectroscopy revealed the formation of NNO in pristine samples, and the subsequent hydrogen incorporation upon CaH2 annealing without forming any impurity phases. The conversion of the oxidation state of Ni towards +2 upon CaH2 annealing was probed using X-ray photoelectron spectroscopy and X-ray absorption spectroscopy. Consequently, a substantial increase in the room-temperature resistivity was observed upon CaH2 annealing indicating the formation of a strongly correlated electronic configuration of Ni in H–NNO due to electron doping. Overall, the findings of this study highlight the versatility of CaH2 annealing as an electron doping method to tune the electrical properties of correlated oxides at low temperatures.

Composition effect on transport and microwave properties of YBCO thin films prepared by metalorganic chemical vapor deposition

YBa2Cu3O7−δ (YBCO) thin films deposited on LaAlO3 single-crystal substrates have great potential for application in microwave field due to their low microwave surface resistance (Rs). In order to prepare high-performance films and facilitate adjustment of experimental parameters, we designed novel metalorganic chemical vapor deposition system. This system adopts single liquid-source pulse feed that provides facile control over film composition through the adjustment of Y, Ba, and Cu ratios in precursors. Here, we thoroughly study influence of film composition on performance. By conducting energy-dispersive spectroscopy measurements, Y, Ba, and Cu composition ranges of 21–24%, 28–31%, and 46–54%, respectively, are found to optimize YBCO film transport and microwave properties. Composition affects purity of film phase which in turns determines film performance. To confirm this observation, we adjust ratio through input–output relationship to obtain film with composition ratio within abovementioned optimal range. Obtained YBCO film has critical current density of 2.8 MA/cm2 at 77 K and 0 T and Rs of 0.285 mΩ at 77 K and 10 GHz. The full width at half maximum of YBCO (005) peak and (103) plane, measured via X-ray diffraction, are 0.235° and 0.762°, respectively.

Preparation of a series of new buffer materials for coated conductors

New buffer layer materials RESbO3 (RE = Y, Sm, Dy, and Ho), Gd1−xCaxBiO3, Gd1−xPbxBiO3, and Eu1−xCaxBiO3 for coated conductors were deposited on a single crystal LaAlO3 substrate through the self-developed polymer-assisted chemical solution deposition method, and YSbO3 was also deposited on CeO2/NiW. Then, the results of x-ray diffraction patterns and SEM indicate high c-axis oriented, smooth, compact, and seamless properties of fabricated new buffer layers, which satisfied the subsequent growth of the superconducting layer. This work offers an effective method to prepare new buffer layers for coated conductors and may provide a new way to search materials with minimal mismatched lattice.

The intrinsic Josephson effect of Bi-2212 superconducting thin films prepared by sol-gel method

In this paper, Bi2Sr2Ca1Cu2O8+σ (Bi-2212) superconducting thin films was prepared by using a sol-gel method on a LaAlO3 (LAO) single crystal substrate, with acetates of bismuth, strontium, calcium, and copper as the starting raw materials. A step structure was specifically designed to measure the intrinsic Josephson effect. The microstructure of the Bi-2212 thin films and their epitaxial growth on the LAO substrate were analyzed by a Cs-corrected transmission electron microscope (Cs-TEM) with an atomic-level resolution and the electrical properties were measured. The results showed that the prepared Bi-2212 thin films had good epitaxial growth characteristics and good in-plane and out-plane growth texture and that its critical transition temperature, Tc, was 87 K. The interface between the substrate and the film was well-defined; the films grow epitaxially on the substrate from the CuO layer, with a highly ordered atom arrangement. The I–V characteristic curve of the prepared step micro-bridging sample showed zero-voltage overcurrent phenomenon, and the critical current was 2.3 mA. In addition, multiple current-voltage jumps were observed on the curve, indicating that the prepared biaxial texture thin films showed the intrinsic Josephson effect.

Influencing the structural, vibrational and electronic properties of pulsed laser deposited PrNi0.95Cu0.05O3 thin films by tuning epitaxial strain

The variation of epitaxial strain in thin films via thickness modification is an established way for influencing the structural and transport properties in low dimensional mott materials. To understand the effect of strain on physical properties, we have prepared a series of PrNi0.95Cu0.05O3 thin films on single crystal LaAlO3 (001) substrate, with varied thickness (5 - 25 nm) using pulsed laser deposition technique. The crystallographic structure of these films is highly oriented towards the (001) axis. The c-axis lattice constant and the unit cell volume decreases with increasing thickness, and therefore, the epitaxial strain tends to partially relax. This partial relaxation of the strain causes a substantial softening of the Raman modes. Temperature-dependent Raman spectra are analyzed to estimate two key parameters, i.e., Grüneisen parameter and first-order temperature coefficient. Power-dependent Raman Spectroscopy and the above-mentioned two parameters have been used to estimate the thermal conductivity of the 25 nm thin film. Balkanski model for three phonon processes has been used to understand the anharmonic contribution in the system, which scales with thickness. The theoretical fits to the temperature-dependent resistivity plots suggest that the films exhibit non-Fermi liquid behavior.

Analyses of Substrate-Dependent Broadband Microwave (1–40 GHz) Dielectric Properties of Pulsed Laser Deposited Ba0.5Sr0.5TiO3 Films

Ba0.5Sr0.5TiO3 (BST-0.5) thin films (600 nm) were deposited on single crystal MgO, SrTiO3 (STO), and LaAlO3 (LAO) substrates by pulsed laser deposition at an oxygen partial pressure of 80 mTorr and temperature of 720 °C. X-ray diffraction and in situ reflection high-energy electron diffraction routinely ascertained the epitaxial quality of the (100)-oriented nanocrystalline films. The broadband microwave (1–40 GHz) dielectric properties were measured using coplanar waveguide transmission line test structures. The out-of-plane relative permittivity (ε⏊/) exhibited strong substrate-dependent dielectric (relaxation) dispersions with their attendant peaks in loss tangent (tanδ), with the former dropping sharply from tens of thousands to ~1000 by 10 GHz. Although homogeneous in-plane strain (ϵǁ), enhances ε⏊/ with εMgOBST−0.5⏊/&gt;εSTOBST−0.5⏊/&gt;εLAOBST−0.5⏊/ at lower frequencies, two crossover points at 8.6 GHz and 18 GHz eventually change the trend to: εSTOBST−0.5⏊/&gt;εLAOBST−0.5⏊/&gt;εMgOBST−0.5⏊/. The dispersions are qualitatively interpreted using (a) theoretically calculated (T)−(ϵǁ) phase diagram for single crystal and single domain BST-0.5 film, (b) theoretically predicted ϵǁ-dependent, ε⏊/ anomaly that does not account for frequency dependence, and (c) literature reports on intrinsic and extrinsic microstructural effects, including defects-induced inhomogeneous strain and strain gradients. From the Vendik and Zubko model, the defect parameter metric, ξs, was estimated to be 0.51 at 40 GHz for BST-0.5 film on STO.

High Electron and Low Heat Transports of 1D Atomic Defect Tunnels Stabilized in Tungsten Oxide Epitaxial Films

The coexistence of high electron conduction and low heat conduction are essentially important to realize efficient thermal management materials such as thermoelectric materials. Although introducing 0D point defects (Fig. a) or 2D layers (Fig. c) is known as an effective way to reduce the heat conduction, there is a dilemma that the electron conduction is also reduced due to that electrons and phonons are scattered simultaneously by impurities, defects, and boundaries. Here we show that introducing a 1D atomic defect tunnel is an excellent solution to solve this dilemma. (Fig. b) In this structure, the probability of that phonon hits the 1D atomic defect tunnel or wire is much higher than that of introducing 0D defect or dot event though 1D defect density is low. In order to verify this hypothesis experimentally, we selected oxygen deficient tungsten oxide epitaxial film as the candidate material. The WO x films (2.7 < x < 3.0) were heteroepitaxial grown by the pulsed laser deposition technique on (001) and (110) LaAlO3 single crystal substrates under oxygen atmosphere. The oxygen pressure was precisely controlled from 2 to 13 Pa during the deposition. As a result, we found that 1D atomic defect tunnels can be introduced in tungsten oxide epitaxial films by oxygen removal. In order to visualize the atomic arrangement of the WO x films, high-angle annular dark-field (HADDF) scanning transmission electron microscopy (STEM) was performed. The resultant WO x epitaxial films contain 1D atomic defect tunnel in the in-plane direction and the density increased with decreasing x. The thermal conductivity (κ) of the films drastically decreased from ~7 W m-1 K-1 to ~1.5 W m-1 K-1 in order to minimize κ with increasing 1D defects. The κ values of WO x films are close to that of amorphous WO x , which shows minimum κ. On the other hand, the electrical conductivity (σ) in the in-plane direction of WO x film dramatically increased from ~10-1 S cm-1 to ~103 S cm-1. Since the oxygen removal reduces the valence state of tungsten, carrier electron concentration increases with increasing 1D defects. The introduction of 1D defect tunnels does not affect the electron propagation but selectively suppresses only the phonon propagation most likely due to the fact that mean free path is much shorter for the carrier electron compared to the phonon. Thus, high electron conduction and low heat conduction coexist in oxygen-deficient tungsten oxide epitaxial films. The present finding would be useful to design efficient thermal management materials such as thermoelectric materials. Figure 1

Effects of Cu-doping on the vibrational and electronic properties of epitaxial PrNiO3 thin films

We have synthesized a series of epitaxial PrNi1-xCuxO3 (x = 0–0.1) thin films (12 nm) on single crystal LaAlO3 substrate by pulsed laser deposition (PLD) method and studied the effects on vibrational and electronic properties of the prepared films. Raman spectroscopy emerges as an alternate tool to indicate an increment in octahedral tilt angles due to Cu-doping. However, this change in the tilting angle does not change the overall structural symmetry in the series. For a comparative study by temperature-dependent Raman spectroscopy, two films with x = 0 (undoped) and 0.10 (maximally doped) were chosen. The presence of anisotropic Grüneisen parameter in the system indicates that Raman frequencies associated with NiO6 octahedral vibrations are more sensitive to temperature as compared to that of NiO bond stretching frequencies. Moreover, the system undergoes more thermal expansion with temperature after inclusion of Cu-doping. Temperature-dependent Raman line width fitted with Balkanski model signifies that the anharmonicity in the system increases with Cu-doping. All the films exhibit steady metallicity below 300 K. The theoretical fits to the temperature-dependent resistivity indicate the existence of Non-Fermi Liquid transport, where all fitting parameters vary depending on Cu-doping.

All chemical solution deposition of epitaxial porous BiFe0.93Mn0.07O3 thin films

BiFeO3 as a type of single-phase room temperature multiferroic materials has aroused intensive investigations in recent years. Construction of porous BiFeO3 thin films is helpful for integration of other materials with desirable functionalities. Here, epitaxial BiFe0.93Mn0.07O3 (001) thin films were prepared on SrRuO3-buffered LaAlO3 (001) single crystal substrates by an all-solution chemical solution deposition, which is beneficial for large area thin film fabrication with low cost. Through addition of F-127 copolymer into the precursor solution, pores can be effectively introduced in BiFe0.93Mn0.07O3 (001) thin films while the epitaxy can be maintained. The amount of pores is gradually increased with increasing of the F-127 addition. The leakage current density is not obviously changed and the conduction mechanism can be well fitted through Ohmic behavior. Electric field dependent polarization hysteresis loops can be effectively maintained and the room temperature magnetic moment is obviously improved with the introduction of pores in epitaxial BiFe0.93Mn0.07O3 (001) thin films. The results will provide a facile route to fabricate large area epitaxial porous BiFeO3 thin films as an effective template for integration of other materials to realize desirable functionalities.

Tuning proton-coupled electron transfer by crystal orientation for efficient water oxidization on double perovskite oxides

Developing highly efficient and cost-effective oxygen evolution reaction (OER) electrocatalysts is critical for many energy devices. While regulating the proton-coupled electron transfer (PCET) process via introducing additive into the system has been reported effective in promoting OER activity, controlling the PCET process by tuning the intrinsic material properties remains a challenging task. In this work, we take double perovskite oxide PrBa0.5Sr0.5Co1.5Fe0.5O5+δ (PBSCF) as a model system to demonstrate enhancing OER activity through the promotion of PCET by tuning the crystal orientation and correlated proton diffusion. OER kinetics on PBSCF thin films with (100), (110), and (111) orientation, deposited on single crystal LaAlO3 substrates, were investigated using electrochemical measurements, density functional theory (DFT) calculations, and synchrotron-based near ambient X-ray photoelectron spectroscopy. The results clearly show that the OER activity and the ease of deprotonation depend on orientation and follow the order of (100) > (110) > (111). Correlated with OER activity, proton diffusion is found to be the fastest in the (100) film, followed by (110) and (111) films. Our results point out a way of boosting PCET and OER activity, which can also be successfully applied to a wide range of crucial applications in green energy and environment.