Post-annealing Process Research Articles

(Digital Presentation) Simultaneous Transforming Residual Lithium Compounds and Stabilizing Surface Lattice Oxygen for Ni-Rich Cathode Via Atomic Layer Deposition and Post-Annealing

Unstable surface species such as residual lithium compounds and surface lattice oxygen at charge state are detrimental factors for the battery performance of Ni-rich cathode (LiNixCoyMn1−x−yO2, x ≥ 0.6, NCM), which induce serious side reactions and lead to rapid capacity loss during cycling. With the advantages of sufficient contacts between gas and solid, gas reactants are introduced to reducing residual lithium compounds via gas-solid reactions or building protective coatings to isolate surface lattice oxygen from the electrolyte via gas-phase deposition, which effectively enhances the cycling stability of NCM. Atomic layer deposition (ALD), as a special coating technology, possesses both the nature of the gas-solid reaction and gas-phase deposition. It is significant to investigate the mechanism of ALD in enhancing the cycling stability of NCM.Here, we report a method to improving the rate capacity and cycling stability of single-crystal NCM via Al2O3 and B2O3 ALD by constructing a highly Li-ions conductive and electrochemical stable surface. The ultrathin coatings are uniformly coated on the surface of NCM. Moreover, surface composition characterizations show the reductions of residual lithium compounds and formations of lithium-containing coatings after the ALD process. By adding a post-annealing process, Al3+ cations and BO3- polyanions doping form on the surface of NCM, which robustly enhanced the stability of surface lattice oxygen of NCM via strong Al-O bond and B-O bond. Moreover, as acidic oxides, B2O3 shows better performance than Al2O3 in reducing residual lithium compounds during the ALD process. Different from Al3+ cations doping occupying the transition metal ions position, BO3- polyanions doping occupies the oxygen ions position, which does not deteriorate the capacity of NCM. Transformation of residual lithium compounds and stabilizing surface lattice oxygen on NCM greatly decrease the formation of LiF and degradation of surface structure, which is the key to the improvement of rate capacity and cycling stability.

(Si)GeSn Isothermal Multilayer Growth for Specific Applications Using GeH4 and Ge2H6

The experimental demonstration of Ge1-xSnx alloys lasers opened group-IV materials towards high-performance electronic and photonic devices that can be easily integrated with the current Si semiconductor technology. In recent years, GeSn-based optoelectronic devices including light-emitting and detectors, modulators, and CMOS have been proven.The major challenges for the Ge1-xSnx epitaxy arise from the low solid solubility of Sn in Ge, the large lattice mismatch, and the reduced thermal stability between Ge and Sn. All these are becoming extremely critical at higher Sn contents. Non-equilibrium conditions offered by molecular beam epitaxy (MBE), chemical vapor deposition (CVD), flash lamp, or laser annealing have been lately investigated. Between them, CVD is to date the preferred growth technique for its current development compatible with the industry offering micron-thick layers with the highest crystal quality.While Tin-tetrachloride (SnCl4) becomes the standard Sn precursor, for Ge different gasses, like germane (GeH4) and digermane (Ge2H6) are used attempting to archive high Sn incorporation and high material quality. While Ge1-xSnx films with the same high Sn content can be obtained regardless of the used precursor, the advantages and disadvantages of each precursor are discussed in this work. The use of Ge2H6 is accompanied by high growth rates, being favorable in applications where relatively thick films are needed, such as laser structures. On the other hand, with a relatively low growth rate, GeH4 provides a greater thickness control, achieving clear and sharp interfaces in heterostructures. For this reason, GeH4 is the appropriate precursor for quantum transport or spintronic.The biggest challenge in heterostructure designs is going up and down in Sn content. The growth of a Ge1-ySny on a Ge1-xSnx, y<x, or SiGeSn layer cannot be performed by increasing the growth temperature. Post-annealing processes lead to strong crystallinity degradation of the already grown layer by strong Sn diffusion or Sn segregation due to the limited thermal stability of Ge1-xSnx alloys.In this work, we address simple methodologies to enhance the gradient or step Sn content without changing the process temperature. Controlling only the carrier gas flow while keeping the standard growth parameters constant, high-quality Ge1-xSnx alloys with uniform Sn content up to 15 at.% are obtained. The proposed method acts as guidance to produce Ge1-xSnx heterostructures that can be extended to any CVD reactor, independently of the used precursor, GeH4 or Ge2H6. Different devices structures are presented proving the applicability of the isothermal multilayer growth. Figure 1

Current transport dynamics and stability characteristics of the NiO x based gate structure for normally-off GaN HEMTs

The application of p-type oxide typified with NiO x as cap layer in AlGaN/GaN high electron mobility transistor for normally-off operation has specific benefits, including etching free fabrication process, high hole density and elimination of Mg dopants diffusion effects. This work presents a device configuration exploration combining the p-NiO x gate cap layer and a thin AlGaN barrier layer. Calculation method for the threshold voltage has been discussed, which obtains good consistence with the experimental measurements. In addition, a nitrogen based post-annealing process was developed to improve the film stoichiometry for elevated gate controllability, realizing normally-off operation with enhanced channel conduction capability. The current transport dynamics in the gate stack as coupled with the NiO x /AlGaN interface states have also been studied, where a deep level trap was recognized in dominating the gate current characteristics and the gate stability performance under different forward gate bias conditions.

Optimizing the quality of epitaxial Y3Fe5O12 thin films via a two-step post-annealing process

Background: Yttrium iron garnet (Y3Fe5O12, YIG) is a prototype magnetic garnet, which possesses the lowest magnetic damping (α) value so far on the earth among all discovered or synthesized materials. This makes it the best candidate for categories of next generation spintronic devices, possessing great application potentials. Methods: A two-step annealing method, with first annealing carried out at a relative low temperature and second annealing at a relatively higher temperature, had been used for the first time to crystallize room temperature sputtered amorphous Y3Fe5O12 (YIG) films on Gd3Ga5O12 (GGG) substrates. The crystalline structure, surface morphology, static and dynamic magnetic properties of the obtained YIG films were characterized through X-ray diffraction (XRD), atomic force microscopy (AFM), vibrating sample magnetometer (VSM) and ferromagnetic resonance (FMR) systems, respectively. Results: It was found that the YIG films obtained via this elaborate annealing method, have a much smoother surface, lower coercivity field, and better dynamic magnetic properties, than that of the YIG films annealed by ordinary one-step approach. Particularly, the ferromagnetic resonance (FMR) linewidth of the best two-step annealed 25 nm YIG film is lower than ~7 Oe at frequency of 10 GHz. Conclusions: Our work clarifies that this two-step annealing approach can effectively improve the quality of the obtained epitaxial YIG films on GGG substrates.

Perovskite-Surface-Confined Grain Growth for High-Performance Perovskite Solar Cells.

The conventional post-annealing (CPA) process is frequently employed and regarded a crucial step for high-quality perovskite thin-films. However, most researchers end up with unwanted characteristics because controlling the evaporation rate of perovskite precursor solvents during heat treatment is difficult. Most perovskite thin-films result in rough surfaces with pinholes and small grains with multiple boundaries, if the evaporation of precursor solvents is not controlled in a timely manner, which negatively affects the performance of perovskite solar cells (PSCs). Here, we present a surface-confined post-annealing (SCPA) approach for controlling the evaporation of perovskite precursor solvents and promoting crystallinity, homogeneity, and surface morphology of the resulting perovskites. The SCPA method not only modulates the evaporation of residual solvents, resulting in pinhole-free thin-films with large grains and fewer grain boundaries, but it also reduces recombination sites and facilitates the transport of charges in the resulting perovskite thin-films. When the method is changed from CPA to SCPA, the power conversion efficiency of PSC improves from 18.94% to 21.59%. Furthermore, as compared to their CPA-based counterparts, SCPA-based PSCs have less hysteresis and increased long-term stability. The SCPA is a potentially universal method for improving the performance and stability of PSCs by modulating the quality of perovskite thin-films.

Sol-Gel-Derived Ni3Al Coating on Nickel Alloy for Oxidation Resistance in Supercritical Water Environments.

Although nickel-based alloys are widely used in industries due to their oxidation and corrosion resistance, the pursuit of better performance in harsh environments is still a great challenge. In this work, we developed a sol–gel method to synthesize Ni3Al coating on a nickel alloy, assisted by a post-annealing process, and investigated the oxidation-resistant performance. The coating thickness can be controlled by designing the deposition times, which keep the pure Ni3Al phase stable. In addition, the surface morphologies indicate that the coating is compact without obvious voids or cracks. Furthermore, the oxidation-resistant property of the coating was investigated by carrying out a supercritical water oxidation experiment. The crystalline structure and surface morphology of the samples before and after 72-h oxidation demonstrated the superior oxidation resistance of the coating. This work provides a convenient method to fabricate an oxidation-resistant coating on a nickel-based alloy, which would be significant for prolonging the service life of vessels under oxidation conditions, especially for supercritical water reactions.

Modified post-annealing process with N, N-dimethylformamide vapor to control the growth of hybrid perovskite microstructure

The post-annealing treatment condition has a great impact on the orientation and growth of perovskite phases. In this study, the formation of CH3NH3PbI3 films was controlled using different post-annealing processes, including a modified N, N-dimethylformamide (DMF) vapor treatment. Field-emission scanning electron microscopy (FE-SEM), and X-ray diffraction (XRD) were used to characterize the microstructure of the perovskite films. An appropriate amount of DMF with a modified post-annealing setup dramatically improves the properties of the perovskite films, whereas an excess amount of DMF solvent leads to poor coverage and degraded films. The average grain size of the modified setup solvent-annealed perovskite film with 100 μL of DMF at 100 °C for 10 min reached ≈1.84 μm, almost five times larger than the mere 0.427 μm of the only thermally annealed at 100 °C for 10 min CH3NH3PbI3 film. The devices fabricated with the films with modified DMF vapor treatment showed improved photovoltaic performance, providing insight into the formation mechanism, and an effective method to improve the film quality of perovskite for photovoltaic application.

A crystal plasticity based approach to establish role of grain size and crystallographic texture in the Tension–Compression yield asymmetry and strain hardening behavior of a Magnesium–Silver–Rare Earth alloy

Existence of tension – compression yield asymmetry is a serious limitation to the load bearing capablities of Magnesium alloys in a number of light weight structural applications. The present work is aimed at nullifying the tension to compression asymmetry problem and strain hardening anomalies in a Magnesium – Silver – Rare Earth alloy by engineering different levels of microstructural conditions via friction stir processing and post process annealing. The existence and extent of yield asymmetry ratio in the range of microstructural conditions was experimentally obtained through quasistatic tensile and compression tests. The yield asymmetry problem was profoundly present in specimens of coarse grained microstructures when compared to their fine grained and ultra fine grained counterparts. The impact of the microstructure and associated mechanisms of plasticity on the macroscopic strain hardening behavior was established by Kock – Mecking's analysis. Crystal plasticity simulations using Viscoplastic Self Consistency approach revealed the consequential role of extension twinning mechanism for the existence of yield asymmetry and anomalies in strain hardening behavior. This was especially dominant with coarsening of grain size. Electron Microscopy and characterization were conducted thoroughly in partially deformed specimens to confirm the predictions of the above simulations. The role of crystallographic texture for inducing the polarity to Tension – Compression yield asymmetry was corroborated. A critical grain size in Magnesium – Silver – Rare earth alloy was hereby established which could nullify influences of extension twinning in yield asymmetry ratio.

Multimodal Single-Entity Electrochemical Fluoride Sensor for Fuel Cell Membrane Degradation Diagnostics

To the best of our knowledge, very few works have been done for the continuous real-time monitoring of Proton Exchange Membrane Fuel Cells (PEMFCs) membrane degradation based on fluoride-specific electrochemical microsensors. PEMFCs are eco-smart energy sources for efficient transportation but experience variable degradation rates that wear the Membrane Electrode Assembly (MEA), a critical component of the fuel cell’s functionality. Current market options lack specific diagnostics and a legitimate indication of when exactly the membrane needs to be replaced. As such, this work focused on manufacturing a sensor for measuring MEA degradation in real-time by selectively monitoring fluoride concentration in effluent water, a signature PEMFCs degradation status, through functionalized LaF3:(Au nanoparticle) thin films (∼60 nm). The sensor’s exceptional specificity/sensitivity has been achieved in real-time at a sub 10 ppb level, optimized through spin-coating deposition and post-annealing process. Its multimodal readout has been achieved and studied through the characterizations of open circuit potential, cyclic voltammetry, chronoamperometry, and differential pulse voltammetry revealing a consistent linear decrease of 15.7 mA cm−2 at 0 ppb to 10.2 mA cm−2, while also maintaining its low-cost, small size, and robustness.

Combination of severe plastic deformation and heat treatment for enhancing the corrosion resistance of a new Magnesium alloy

In the present study, various processes have been carried out on the extruded Mg-4Zn-4Al-0.6Ca-0.5Mn (wt%) alloy to achieve a low corrosion rate Magnesium (Mg) alloy. Microstructure studies revealed that the extruded alloy contained the needle-like Al-Mn second phases and the globular and elongated (Mg,Al)2Ca + ϕ(AlMgZn) phases. After solution treatment, the area fraction of the second phase decreased drastically from 5.1 % to 2.4 %. The later multi-directional forging (MDF) formed a modified ultrafine grain structure with an average grain size of 0.9 µm. The post-annealing process reduced the dislocation density of the heavily-deformed grains of the MDFed alloy, resulting in a grain size of 5.89 µm and an area fraction of 2.8 %. The annihilation of dislocations and homogeneous distribution of broken second phase particles after MDF and post-annealing processes improved the ultimate compressive strength and compressive strain from 352 MPa and 4.2 % for the extruded to 376 MPa and 5.1 % for the post-annealed alloy. Moreover, by applying solution treatment, MDF, and post-annealing, the corrosion rate of the extruded alloy drastically decreased from 2.13 mm/y to 0.76 mm/y due to grain refinement and reduced area fraction of phases and their random distribution. According to the corrosion results, the area fraction of second phase particles and the grain size obtained after different processes significantly influenced the corrosion properties, which was discussed in detail in the present study. On the one hand, the post-annealed alloy contained a significantly lower area fraction of particles than the extruded alloy, reducing micro-galvanic corrosion. On the other hand, significant grain refinement after the MDF process lowered the corrosion rate compared to the extruded alloy. However, the short-time annealing process annihilated the dislocations and high-energy sites while not significantly increasing the grain size and deteriorating the mechanical properties. Therefore, the combination of MDF and short-time annealing could be a remarkable route to obtaining the low corrosion rate and high strength Mg alloy.

Unusual temperature dependence of the photoluminescence emission of MgV centers in diamond

Magnesium-and germanium-vacancy centers were produced in diamond by ion implantation and the post-annealing process. Photoluminescence spectroscopy (PL) measurements were performed between 20 and 50 °C. The PL results of the GeV centers are in agreement with those found in the literature, while the MgV center is newly discovered and a not yet broadly investigated color center, but the room temperature PL results are in agreement with the first report. The temperature dependence of the MgV centers above room temperature is unusual: by increasing the temperature, its PL shifts to higher energies, contrary to what is observed for the GeV centers and other known centers in the literature. The zero phonon line width of both centers broadens by increasing the temperature in both investigated centers. The origin of the blue shift observed in the MgV centers as a confinement effect is discarded, because sample is bulk and its origin should lay on the influence of the temperature on the local static structure and the overlapping of the electronic wave functions. Our results show the ability of MgV to be used in future for thermometry. The center is bright and photostable, with a narrow full width at half maximum compared to other centers in diamond and its shift with the temperature is also larger.

Electrical-performance and reliability improvement of flexible low-temperature polycrystalline silicon thin-film transistors via post-annealing process

We investigated the improvement methods of the electrical characteristics and reliability of flexible low-temperature polycrystalline silicon (LTPS) thin-film transistors (TFTs) by optimizing the annealing process. We investigated the effect of annealing on the device properties via electrical measurement and density-of-state (DOS) analysis. The annealing temperature should be reduced for flexible LTPS TFTs compared to rigid devices because the range of the thermal stability of flexible substrate is narrower than that of the glass substrate. As the activation annealing temperature (T a) decreased, the threshold voltage and field-effect mobility (μ FE) decreased, and the subthreshold swing (SS) increased. When the post-annealing temperature (T pa) decreased, μ FE increased, and the changes in the other parameters were negligible. The DOS decreased with an increase in T a and a reduction in T pa. These results originated from ineffective dopant activation and defect curing due to the lower T a and the enhanced hydrogen defect passivation at the lower T pa. Therefore, flexible LTPS TFTs with reduced T a values exhibited similar μ FE values and lower SS values when the post-annealing process was omitted. Furthermore, removing the post-annealing process improved the reliability of the flexible LTPS TFTs with reduced T a values under electrical stress. According to a hot-carrier instability analysis, defect passivation by hydrogen was more stable than defect curing with a higher T a. Consequently, although T a was low for flexible LTPS TFTs, the electrical performance and reliability could be improved by optimizing the post-annealing process.

Multi-component low and high entropy metallic coatings synthesized by pulsed magnetron sputtering

This paper presents the findings of the synthesis of multicomponent (Al, W, Ni, Ti, Nb) alloy coatings from mosaic targets. For the study, a pulsed magnetron sputtering method was employed under different plasma generation conditions: modulation frequency (10 Hz and 1000 Hz), and power (600 W and 1000 W). The processes achieved two types of alloy coatings, high entropy and classical alloys. After the deposition processes, scanning electron microscopy, X-ray diffraction, and energy-dispersive X-ray spectroscopy techniques were employed to find the morphology, thickness, and chemical and phase compositions of the coatings. Nanohardness and its related parameters, namely H3/Er2, H/E, and 1/Er2H ratios, were measured. An annealing treatment was performed to estimate the stability range for the selected coatings. The results indicated the formation of as-deposited coatings exhibiting an amorphous structure as a single-phase solid solution. The process parameters had an influence on the resulting morphology—a dense and homogenous as well as a columnar morphology, was obtained. The study compared the properties of high-entropy alloy (HEA) coatings and classical alloy coatings concerning their structure and chemical and phase composition. It was found that the change of frequency modulation and the post-annealing process contributed to the increase in the hardness of the material in the case of HEA coatings.

Improved artificial synapse performance of Pt/HfO2/BiFeO3/HfO2/TiN memristor through N2 annealing

A high-performance synaptic plasticity memristor based on Pt/HfO2/BiFeO3/HfO2/TiN structure was developed by magnetron sputtering technology, and the effects of N2 annealing treatment on its resistance and synaptic bionic properties were studied. The results show that with the N2 post annealing process, the memristor can exhibits excellent switching windows, outstanding uniformity and high durability. An improvement of ON/OFF resistance ratio of at least two orders of magnitude is achieved, and the pulse endurance can remain stable up to 106 s. Moreover, the basic synaptic biomimetic function is realized due to its excellent multi-level storage properties, and the conductivity of the memristor is modulated by multilayer perception (MLP) algorithm to simulate handwritten digital image recognition. Overall, its linearity and stability of the artificial synapse in the regulation process still have the space to be improved for the application, so it can be efficiently regulated by rapid thermal processing. It is convinced the tri-layer post-annealing HfO2-based devices hold the application potential of neuromorphic computing in the next generation memory devices.

Improvement of Device Characteristics of Low Temperature IGZO Thin-film Transistors through Laser Post Annealing

High-performance thin-film transistors (TFTs) produced at low temperatures are required for ultrahigh- resolution and flexible display applications. The scientific community has been studying unconventional techniques to investigate low voltage flexible devices and low power flexible circuits for the past decade. In particular, metal oxide semiconductors, such as indium gallium zinc oxide (IGZO), have made significant progress as amorphous silicon replacements for electronics and commercial displays. On the other hand, developing metal oxide transistors with low processing temperatures remains a difficulty. The hightemperature annealing process causes very instability in the plastic substrate. Here, we introduce IGZO TFTs that shows enhanced electrical properties environmental stability by laser post-annealing. After annealing process, the laser post-annealing process was given at 80 MHz, pulse width 140 fs, for 50 seconds. The improved electrical characteristics of this laser post-annealed IGZO TFTs were: 9.03 cm&lt;sup&gt;2&lt;/sup&gt;/Vs; 2.2×10&lt;sup&gt;7&lt;/sup&gt; on/off current ratio. The IGZO TFT to which laser post-annealing was applied had a flat surface, and it was confirmed that the combination of internal metal and oxygen was urged, and the leakage current problem was improved by suppressing excessive generation of oxygen vacancy. Furthermore, the voltage transfer curve was measured after fabricating the N-MOS logic inverter circuit, this inverter showed a value of 80.8% the total noise margin.

In situ encapsulation hollow FeP spheres into high yield 3D N, P-codoped graphenic framework as advanced anode material for high-performance supercapacitors

The performance of carbon-based materials as negative electrodes for supercapacitors can be effectively enhanced through the method like increasing the surface area and active sites as well as heteroatoms doping, while the limited capacitance caused by the surface adsorption mechanism restricts the further improvement of capacitance. Herein, we design hollow and porous FeP spheres (H-FeP) in-situ encapsulated into 3D honeycomb-like porous graphitic N, P-codoping carbon (PGNPC) by a unique post-annealing strategy. The post-annealing process acts as an efficient modification strategy in two aspects: the formation of a porous graphitic carbon framework during the catalytic reaction between iron oxide with carbon and the morphology changing from solid to hollow by introducing the Kirkendall diffusion process. With the synergetic effect of introducing hollow FeP into carbon, the N, P-codoping and 3D porous graphitic carbon framework ensure the as-prepared materials with enhanced performance for negative electrodes. Thus, H-FeP@PGNPC materials display outstanding specific capacitance (696 F g−1), high rate capacity and cycling stability. Using multi-shelled Mn3O4 encapsulated in rGO as the positive electrode, the assembled asymmetric supercapacitor exhibits high specific capacitance and energy density with negligible capacity loss (retain 90% after 5000 cycles).

MgB2 Thin Films Fabricated by Pulsed Laser Deposition Using Nd:YAG Laser in an In Situ Two-Step Process

Magnesium diboride (MgB2) thin films on r-cut sapphire (r-Al2O3) single crystals were fabricated by a precursor, which was obtained at room temperature via a pulsed laser deposition (PLD) method using a Nd:YAG laser, and an in situ postannealing process. The onset superconducting transition, Tconset, and zero-resistivity transition, Tczero, were observed at 33.6 and 31.7 K, respectively, in the MgB2 thin films prepared by a Mg-rich target with a ratio of Mg:B = 3:2. The critical current density, Jc, calculated from magnetization measurements reached up to 0.9 × 106 A cm−2 at 20 K and 0 T. The broad angular Jc peak was found at 28 K when the magnetic fields were applied in a direction parallel to the film surface (θ = 90°). This could be indicative of the granular structure with randomly oriented grains. Our results demonstrate that this process is a promising candidate for the fabrication of MgB2 superconducting devices.

Photocatalytic β-In2S3 nanoflowers synthesized by thermal assembly of In2S3 nanosheets

Three-dimensional (3D) β-In2S3 offers photocatalytic advantages by virtue of its strong and broadband optical absorption resulting from its large effective surface area and a high density of sulfur vacancies. However, the use of surfactants and reducing agents complicates the synthesis process and causes undesirable agglomeration while forming the 3D structures, degrading the photocatalytic efficiency of 3D In2S3. Here we have prepared the surfactant-free In2S3 nanoflowers by the thermal assembly of two-dimensional (2D) In2S3 nanosheets and achieved a substantial enhancement of the optical absorption and the tunable bandgap narrowing. We show that owing to the intrinsic structure of our In2S3 nanoflowers that preserves the unit geometry of 2D In2S3 nanosheets, the rate of photocatalytic performance was enhanced by 200% just by the post-annealing process. The facile method used to prepare In2S3 nanoflowers expedites the practical application of 3D In2S3 for energy and environmental purposes.

Perspective on solid-phase epitaxy as a method for searching novel topological phases in pyrochlore iridate thin films

Pyrochlore iridates exhibit various novel topological phenomena due to their topology and electron correlation. Notably, pyrochlore iridate was the first proposed material system shown to host the time-reversal symmetry broken Weyl semimetal phase. After this profound theoretical proposal, extensive experimental attempts have been made to synthesize high-quality samples in both bulk and film forms. In particular, adjusting thin film geometry represents a practical way to tune the U/t (U: Coulomb interaction and t: for hopping parameter) and identify the various topological phases in the regime U ∼ λ (λ: spin–orbit interaction). However, the instability of pyrochlore iridates at high temperature and low oxygen pressure has long been a barrier to growing pyrochlore iridate thin films by conventional film growth methods. To overcome this, pyrochlore iridate films have often been grown by the solid-phase epitaxy method, which uses a metastable amorphous layer grown at low temperature. During a high temperature post-annealing process, the layer in contact with a single crystalline substrate will crystallize epitaxially in the solid state by rearranging atoms at the interface. Here, we present a perspective on the solid-phase epitaxy as a method to synthesize epitaxial pyrochlore iridate thin films and a way to search for novel correlated phenomena.

Fabrication and characterization of monocrystalline Zn2TiO4 films on MgO (111) substrates by PLD

Cubic Zn2TiO4 films were deposited on MgO (111) single crystal substrates using pulsed laser deposition (PLD). With the assistance of post-annealing process, the best epitaxial Zn2TiO4 film with only (111) single plane was obtained at 950[Formula: see text]C. For the best Zn2TiO4 single crystalline film, the full width at half maximum (FWHM) of the XRD [Formula: see text] rocking curve for the Zn2TiO4 (111) diffraction peak was only 0.12[Formula: see text]. From the TEM spectrum, the film had a regular lattice arrangement and strong periodicity. Structural analysis indicated that the out-plane and in-plane epitaxial arrangement of the film/substrate separately were Zn2TiO4 (111)//MgO (111) and Zn2TiO4 [10[Formula: see text]]//MgO &lt;10[Formula: see text]&gt;. The optical properties of the films were investigated in detail. After removing the influence of the transmittance of the substrate, the relative transmittance of the films exceeded 90% and the optical band gap of the films varied between 3.84 and 4.38 eV.