Transformation Of Thin Films Research Articles

Evolution of the phase structure, magnetic domain structure, and magnetic properties of annealed Fe72Ga28 thin films

In contrast to the disordered body-centered cubic (bcc) A2 phase, the ordered face-centered cubic (fcc) L12 phase exhibits negative magnetostriction (λ) and has a high elastic modulus (E). Therefore, an in-depth understanding of the microstructural evolution of Fe–Ga thin films from bcc A2 phase to fcc L12 phase is essential to obtain Fe–Ga thin films with desirable properties. The transformation of the phase structure, magnetic domain structure, and magnetic properties of Fe72Ga28 thin films is analyzed in this study. The phase transformation of the Fe72Ga28 thin film from A2 to A2 L12 occurred after heat treatment, as determined by high-resolution transmission electron microscopy (HRTEM) and glancing-incidence X-ray diffraction (GI-XRD). Non-continuous lattice distortion at the phase boundaries of A2 and L12 was also observed, as shown by geometric phase analysis (GPA) and electron backscattered scattering detection (EBSD). Numerous edge dislocations at the phase boundaries were revealed by HRTEM. A shift in the magnetic domain structure from the maze-like domain to maze-like domain and honeycomb-like domain was detected by magnetic force microscopy (MFM). The variation in magnetic properties was determined to be related to the structural transformation and ununiform lattice distortion between the phase boundaries of the A2 and L12.

Cation and anion topotactic transformations in cobaltite thin films leading to Ruddlesden-Popper phases

The ability to control a material's physical properties by ion migration is particularly important for the design of devices for emerging applications such as neuromorphic computing, magnetoionic switches, and next-generation memory and logic devices. The perovskite oxide LaSrCoO${}_{3}$ is an ideal system for investigating ion migration due to its high oxygen vacancy conductivity, relatively low oxygen vacancy formation energy, and strong coupling of the magnetic and electronic properties to its oxygen stoichiometry. This paper shows that it is possible to obtain a series of electronic and magnetic phases by systematically exposing the parent perovskite oxide to highly reducing annealing conditions. Under these conditions, the movement of both oxygen and cobalt ions in and out of the lattice represents a new direction for discovery of functional materials for brain-inspired computing.

Influence of point defects on phase transformation and optical properties of TiO2 thin films via multilayering deposition technique

Thin anatase TiO2 films with preferential (004) orientation were successfully fabricated via multilayering technique, growth and stop repeatedly, using DC-magnetron sputtering and annealed at a relatively low temperature. The multilayering deposition technique suppressed the number of oxygen vacancy defects in TiO2 films without interrupting the columnar growth. The main columnar structure oriented along (101) plane and along (004) plane. Confirmed by the texture coefficient, the preferential (004) orientation of TiO2 films increased with increasing number of compact layers and the highest value was observed for post-annealed films at 200 °C. The surface morphology analysis indicated that the increase of surface roughness with increasing number of compact layers was related to the promotion of crystallization. The optical properties of multilayer films revealed that high number of compact layers greatly enhanced their absorption in the entire visible region, expanded energy band gap and increased refractive index.

Multifunctional polymer-assisted spontaneous transformation of thin gold films into nanoparticles

In this document, we report an efficient synthesis of well-defined, soluble, high molecular weight, film-forming aromatic multifunctional homopolymers bearing two distinct functional groups per repeating unit. The polymers were obtained in nearly quantitative yields by a one-pot, room-temperature, non-stoichiometric superacid-catalyzed step-polymerization of derivatives of pyruvic acid with aromatic hydrocarbons. It was found that thin gold films (2–12 nm) sputtered onto the surface of a multifunctional homopolymer (PTBC) containing carboxy- and bromomethyl- functionalities in every repeating unit undergo spontaneous, solvent-free, room-temperature, quantitative transformation into nanoparticles. For the first time, the key factors affecting film-to-particle transformation were revealed. Internal factors are dependent on the polymer structure, its homogeneity, and the composition of the polymer/metal interface, while external factors include gold-film thickness, temperature and ageing atmosphere. By varying the functional-group combinations and aromatic fragments, a set of multifunctional homopolymers has been synthesized and it was found that the presence in the homopolymer of a repeating unit of two phenylene rings and two functional groups – bromomethyl and carbonyl – attached to the same carbon backbone atom (forming a so-called “Reactive site”) is critically important for film-particle transformation. The process is accelerated with increasing temperature, proceeds in ambient air, and is halted in a vacuum. The average grain size of the nanoparticles increased from 3 to 18 nm over a week at room temperature and from 5 to 27 nm over the same period at 40 °C. The size and shape of the nanoparticles are modulated by controlling the thickness of the gold film, the temperature and the ambient atmosphere. The transformation represents a very simple, one-step, environmentally-friendly process that is not dependent on any other chemical reagents, requires no previous temperature or high-energy processing, and can easily be scaled up to fabricate high-purity, fully accessible polymer-(film- or nanofiber-) supported gold nanoparticles of long-term stability.

Real-time monitoring of order-disorder transformation of FePt thin films by light scattering

ABSTRACT An optical method is proposed to real-time monitor the order transformation of FePt thin films. By measuring the surface reflection amplitude, onset temperature can be determined correctly. In a heating process, order transformation drastically increases the surface roughness due to recrystallization and grain growth, resulting in rapid drop of surface reflectivity. By tracking this drop, the kinetic ordering temperature can be determined. Experimentally measured kinetic ordering temperature for Fe50.4Pt49.6, Fe46.6Pt53.4, and Fe52.7Pt47.3 thin films of 60 nm in thickness are 396°C, 437°C, and 368°C, respectively. They are in good agreement with the published DSC data.

Tracing the ionic evolution during ILG induced phase transformation in strontium cobaltite thin films

Ionic liquid gating (ILG) that drives the ions incorporate into or extract from the crystal lattice, has emerged as a new pathway to design materials. Although many intriguing emergent phenomena, novel physical properties and functionalities have been obtained, the gating mechanism governing the ion and charge transport remains unexplored. Here, by using the model system of brownmillerite SrCoO2.5 and the corresponding electric-field controlled tri-state phase transformation among the pristine SrCoO2.5, hydrogenated HSrCoO2.5 and oxidized perovskite SrCoO3−δ through the dual ion switch, the ionic diffusion and electronic transport processes were carefully investigated. Through controlling gating experiment by design, we find out that the collaborative interaction between charge transport and ion diffusion plays an essential role to prompt the hydrogen or oxygen ions incorporate into the crystal lattice of SrCoO2.5, and therefore leading to formation of new phases. At region closer to the electrode, the electron can shuttle more readily in (out) the material, correspondingly the incorporation of hydrogen (oxygen) ions and phase transformation is largely affiliated. With the compensated charge of electron as well as the reaction front gradually moving away from the electrode, the new phases would be developed successively across the entire thin film. This result unveils the underlying mechanism in the electric-field control of ionic incorporation and extraction, and therefore provides important strategy to achieve high efficient design of material functionalities in complex oxide materials.

Optical Identification of Materials Transformations in Oxide Thin Films.

Recent advances in high-throughput experimentation for combinatorial studies have accelerated the discovery and analysis of materials across a wide range of compositions and synthesis conditions. However, many of the more powerful characterization methods are limited by speed, cost, availability, and/or resolution. To make efficient use of these methods, there is value in developing approaches for identifying critical compositions and conditions to be used as a priori knowledge for follow-up characterization with high-precision techniques, such as micrometer-scale synchrotron-based X-ray diffraction (XRD). Here, we demonstrate the use of optical microscopy and reflectance spectroscopy to identify likely phase-change boundaries in thin film libraries. These methods are used to delineate possible metastable phase boundaries following lateral-gradient laser spike annealing (lg-LSA) of oxide materials. The set of boundaries are then compared with definitive determinations of structural transformations obtained using high-resolution XRD. We demonstrate that the optical methods detect more than 95% of the structural transformations in a composition-gradient La-Mn-O library and a Ga2O3 sample, both subject to an extensive set of lg-LSA anneals. Our results provide quantitative support for the value of optically detected transformations as a priori data to guide subsequent structural characterization, ultimately accelerating and enhancing the efficient implementation of micrometer-resolution XRD experiments.

Role of Rare Earth Elements and Entropy on the Anatase-To-Rutile Phase Transformation of TiO2 Thin Films Deposited by Ion Beam Sputtering.

The role played by oxygen vacancies and rare earth (RE) elements in the anatase-to-rutile (A–R) phase transformation of titanium dioxide (TiO2) is still a matter of controversy. Here, we report the A–R transformation of TiO2 thin solid films as obtained by ion beam sputtering a RE-decorated titanium target in an oxygen-rich atmosphere. The samples correspond to undoped, single-doped (Sm, Tm, and Tb), and codoped (Sm:Tb, Sm:Tm, and Sm:Tb:Tm) TiO2 films. In the as-prepared form, the films are amorphous and contain ∼0.5 at. % of each RE. The structural modifications of the TiO2 films due to the RE elements and the annealing treatments in an oxygen atmosphere are described according to the experimental results provided by Raman scattering, X-ray photoelectron spectroscopy, and optical measurements. The A–R transformation depends on both the annealing temperature and the characteristics of the undoped, single-doped, and codoped TiO2 films. As reported in the literature, the A–R transformation can be inhibited or enhanced by the presence of impurities and is mostly related to energetic contributions. The experimental results were analyzed, considering the essential and stabilizing role of the entropy of mixing in the A–R transformation due to the introduction of more and multiple quantum states originated in vacancies and impurities in the anatase phase.

Piezoelectric PZT thin-film transformers with a ring–dot structure

In this study, we present the design, the modeling, the fabrication, and the characterization of ring–dot type piezoelectric thin-film transformers (PTFTs). The structure of the PTFTs was a simple circular plate of Pb(Zr,Ti)O3 (PZT) thin film on a Si layer with ring–dot top electrodes and it was suspended by four pantograph-shaped bridges. We estimated the performance of the PTFTs by finite-element method simulations. In accordance with the FEM simulation model, PZT thin films were deposited on silicon-on-insulator substrates and microfabricated into PTFTs with ring–dot structures. From the produced devices, an admittance circle measurement was carried out, enabling us to predict performance. The actual output characteristics of the PTFTs were clearly observed at a resonance frequency (f r) of 4.57 MHz. At this point, a voltage gain of 0.22 and a power density of 704 W cm−3 were measured, under a load resistance (R L) of 22 Ω.

Vibrational studies on Cu2ZnSnS4 thin films prepared by single step reactive DC magnetron sputtering

Cu2ZnSnS4 (CZTS) is a potential absorber material among its contemporary contenders for thin film solar cells. Controlling secondary phases in CZTS is a major concern. In the present study, CZTS thin films are prepared by a single step deposition technique: sputtering of individual metal targets of copper, zinc and tin in the sulfide plasma. The control on secondary phase formation and better microstructure properties are realized in the CZTS thin films prepared at low tin-target powers. The vibrational modes investigated by Raman measurement reveal transformation of CZTS thin films from less stable stannite phase to the stable kesterite phase under low Sn-power (30 W and 40 W) conditions.

Paraelectric/antiferroelectric/ferroelectric phase transformation in As-deposited ZrO2 thin films by the TiN capping engineering

Based on the engineering of the TiN capping layer, the tailoring of the crystalline phases and the paraelectric(PE)/antiferroelectric(AFE)/ferroelectric(FE) properties of nanoscale ZrO2 thin films are demonstrated without any post-annealing treatment. The capping by the TiN layer leads to the conversion of ZrO2 from the PE to the AFE electrical characteristics, while the removal of the TiN capping layer results in the AFE-to-FE phase transformation of ZrO2. The nano-beam electron diffraction, high-resolution transmission electron microscopy and X-ray diffraction characterizations identify the presence of the AFE tetragonal and FE orthorhombic phases in ZrO2, and the observations reveal the emergence of the out-of-plane compressive and in-plane tensile strains in the ZrO2 layers by the TiN capping layer as well. The results demonstrate the significant impact of the TiN capping layer effect on the crystalline phases and dielectric properties of nanoscale thin films at a low temperature, which may play an important role in the FE/AFE applications which need a low thermal budget.

Exploration of a Novel HTS Thin-Film Device Combined With Roles of Transformer and Overcurrent Limiter

A novel high-temperature superconducting (HTS) thin-film device based on double-sided YBa <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> Cu <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">7-</sub> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> (YBCO) thin film, combined with roles of transformer and overcurrent limiter, is proposed and tested in this article. Due to the effective improvement on the power density, operating frequency, repeatability, functional integration, and low profile of the high-frequency converters, thin-film transformer (TFT) has been widely employed in power conversion fields. In contrast to the normal conductive materials, the surface resistance of the HTS materials is much smaller. Thus, the TFT fabricated by HTS thin film has lower Joule losses and higher power conversion efficiency. We designed the double-sided YBCO thin-film-based HTS-TFT and measured its parameters at liquid nitrogen (LN <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> ). As a comparison, we also developed the copper (Cu) based TFT and measured the same parameters at LN <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> and room temperature. Besides, we also tested the overcurrent limiting performance of the HTS-TFT, which is based on the state change from superconductivity to normal state. It can be found from the contrastive experiments that the HTS-TFT has better operating parameters than the Cu-TFT; meanwhile, the overcurrent can be limited by the HTS winding effectively.

Nanostructured Magnéli-Phase W18O49 Thin Films for Photoelectrochemical Water Splitting

Converting water into hydrogen through the photo-electrochemical (PEC) process is one of the most exciting approaches in this field, and there is a quest to design or search for new electro-photo-catalytic materials. In this work, simple steps for fabrication and transformation of metallic tungsten thin film into the photo-active Magnéli-phase (W18O49) of tungsten oxide thin film is demonstrated. The post-annealing temperature has a significant impact on the phase evolution of tungsten film into W18O49. The film thickness of W18O49 is controlled by controlling the sputtering time (or deposition time) of W film. The PEC performance of the as-prepared electrodes is evaluated by monitoring the water oxidation reaction under visible radiation. The PEC findings reveal a correlation between PEC performance and phase, morphology, and thickness of the film. The as-derived W18O49 can efficiently catalyze the water oxidation reaction at neutral solution pH, generating 0.6 and 1.4 mA cm−1 photo-current at 0.6 and 0.8 V vs. Saturated calomel electrode (SCE), respectively, in addition to excellent stability. The electrical conductivity and the charge transfer kinetics are investigated employing the electrochemical impedance spectroscopic (EIS) technique.

Effect of PbI2 surface treatment with DMSO vapor on the properties and photodetector characteristics of CH3NH3PbI3–Cl perovskite films synthesized by a PbS-to-PbI2-to-perovskite sequence

Abstract In this work, we present the effect of the treatment of PbI2 thin films with dimethyl sulfoxide (DMSO) vapor on the final characteristics and properties of CH3NH3PbI3–xClx perovskite synthesized from a three-step approach. This is an additional step, thus, it changes the previous approach to a four-step sequence, which, for the present research, consists in the following: (1) chemical solution deposition of PbS thin films over glass substrates; (2) chemical transformation of the deposited PbS thin films into PbI2 by means of a gas–solid reaction with iodine vapor; (3) surface treatment of the synthesized PbI2 thin films with DMSO vapor, being this step the driving force of the present research; and (4) chemical transformation of the DMSO-treated PbI2 thin films into CH3NH3PbI3–xClx perovskite films by means of a liquid–solid reaction with a spin-coated solution mix of methylammonium iodide/chloride. We particularly present here the effect of four exposure times to DMSO vapor (5, 10, 15, and 20 min), which were compared against an untreated reference. The thin films of all the synthesized materials were uniform and strongly adhered to the glass substrate. The PbI2 and perovskite samples were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), and ultraviolet–visible (UV–Vis) and fluorescence spectroscopies. It was observed that all the DMSO-treated PbI2 films present pores and, thus, show a decrease of transmittance. They also lead to subsequent perovskite samples that present blurred grain boundaries, which are less pronounced in comparison to the reference perovskite, which was synthesized from PbI2 with no DMSO treatment. This resultant morphology, translated in a better continuity of the perovskite material, was attributed as the cause of the increased photocurrent and responsivity of the photodetector fabricated from perovskite synthesized from DMSO-treated PbI2 film, as compared with the photodetector fabricated with the reference perovskite. Therefore, the treatment of PbI2 thin films with DMSO vapor is beneficial for improving the photodetector characteristics of CH3NH3PbI3–xClx perovskites.

Formation of multilayer structure and evolution of shape recovery characteristics in proton irradiated TiNi alloy thin films

TiNi thin films have attracted wide attentions as actuator materials in the micro-electro-mechanical systems (MEMs) for aerospace craft. However, multiple irradiation, such as the proton, was generally considered as an essential expired factor for the materials used in the aerospace. The present paper focused on the microstructure, martensitic transformation and shape recovery property of TiNi thin films after being irradiated by proton. A single layer structure B19′ phase to a dual-phase (B2 and B19′) with multilayer structure after proton irradiation have been revealed through a combination technique of grazing incidence (GI) XRD and TEM. As-formed irradiated films with amorphous layer and B2 austenite phase displayed a two-step martensitic transformation behavior, which occurred in the irradiated and the unirradiated layer. In contrast, the unirradiated counterparts just exhibited a single-step martensitic transformation. In addition, some defects could be seen after the TiNi films being irradiated. Such defects could induce a stress field that produces the R phase in the B2 phase. Furthermore, the synergistic effect of preferential sputtering effect and inverse Kirkendall effect induced the GP zones in the irradiated layer after 120 keV proton irradiation. The existence of amorphous phase and precipitation significantly deteriorated the shape recovery property.

Effect of low-energy proton on the microstructure, martensitic transformation and mechanical properties of irradiated Ni-rich TiNi alloy thin films

Effect of low-energy proton on the microstructure, martensitic transformation and mechanical properties of irradiated Ni-rich TiNi alloy thin films

A Benchmark Study for Phase Transformation of Shape Memory Alloy Based Split Ring Resonator Structure Under a Heating and Cooling Thermal Cycle

In this benchmark study, the integration of shape memory alloy thin film on to a split ring resonator is investigated. Split ring resonators are artificially produced structures which are used to generate magnetic response. One of the applications that can be met in the literature is the solar panel ones where they are benefitted for the electric generation from the resonance of it. Unfortunately, this application is very sensitive to the shape, geometry and dimensions which can be affected from ambient conditions easily. At this particular stage, to compensate the dimensional inconsistencies by shape memory alloy thin film is chosen in an ongoing project. Due to the nature of the shape memory alloy, not only the material properties but also the geometry of the structure can also change. By taking the advantage of this unique feature, the applicability of coupling shape memory alloy thin film by split ring resonator is investigated. And as an initial step of this research, the phase transformation of shape memory alloy thin film is investigated with regard to varying ambient conditions which are simulated by the change of convection conditions and exposure time. The temperature evolution of two significant point is tracked under these conditions and furthermore the change of martensite volume fraction is examined which will enlighten the path for the further steps on this investigation.

Vital role of Ar ambient pressure in controlled properties of nanocrystalline CdS thin films

A report on the manipulation of structural, optical, and electrical properties of nanocrystalline CdS (ncCdS) thin films in the framework of varying Ar ambient pressure in pulsed laser deposition (PLD) is presented here. Increase in Ar ambient pressure results in reduction of crystallite size which in turns increases the structural imperfections and structural phase transformation of ncCdS thin films. The most significant observation here is the bleaching of multiphonon Raman modes (MRMs) particularly LO + 2E2, 2LO + 2E2, etc. in ncCdS thin films. An acute investigation on the reason of bleaching of LO + 2E2, 2LO + 2E2, etc. modes is carried out here and concluded that it is due to the fading of E2 mode with increasing Ar pressure as confirmed by low-frequency micro-Raman measurements. UV–visible absorption and photoluminescence spectroscopies are used to examine the optical properties like bandgap and possible electronic transitions in ncCdS thin films. Further, transport properties of ncCdS thin films are investigated using Hall measurement and I–V characteristics.

Design and analysis of a high temperature superconducting thin film transformer

A novel thin film transformer based on double sided YBa2Cu3O7−x (YBCO) thin films with high operating performance, named a high temperature superconducting thin film transformer (HTS-TFT), is proposed and tested. In this paper, we designed and fabricated four different types of HTS-TFT based on double sided YBCO thin film and measured their respective operating parameters (including winding resistance, winding inductance, coupling coefficient, and quality-factor) at liquid nitrogen temperature (LN2, 77 K). As the comparative experiment to the HTS-TFT, we also developed the same four types of copper (Cu)-TFT and measured their parameters at both room temperature (RT, 298 K) and LN2, to evaluate their behavior. It can be found from the comparative experiments between the HTS-TFTs and Cu-TFTs that the HTS-TFTs (in LN2) possess better operating parameters than the Cu-TFTs (in LN2 and RT) and they operate as expected in the power conversion tests. The significance of this work is that the HTS-TFTs can be employed in wireless power transfer systems and other power conversion fields, offering a performance enhancement to power transmission efficiency.

Property engineering through nanomaterial chemical transformation of colloidal nanocrystal thin films

Herein, we introduce a unique nanomaterial chemical transformation (NCT) process whereby selenium (Se) anion is introduced to colloidal silver (Ag) nanocrystals (NCs) to create nanostructured silver selenide (Ag2Se). We present a complete suite of material characterizations, including chemical, structural, optical, and electrical characterizations to understand the details of the transformation process. The Ag2Se thin-films obtained through the NCT process exhibit degenerately-doped n-type semiconductor characteristics with high carrier mobility. We discuss the chemical mechanism that drives the material transformation and elucidates the origin of doping in these semiconducting thin-films. We also demonstrate the robustness of Ag2Se thin-films toward mechanical strain and temperature cycling stress for flexible device applications. We believed that the NCT process demonstrated here is of wide applicability to other material systems which can open up new avenues for solid-state chemistry and device engineering research.