Thin Film Systems Research Articles

The influence of the nanostructure design on the corrosion behaviour of TiN thin films prepared by glancing angle deposition

This study reports on the influence of nanostructure design on the corrosion behaviour of titanium nitride (TiN) thin films, prepared by DC reactive magnetron sputtering, using the Glancing Angle Deposition (GLAD) technique. The primary objective was to explore how modifying the deposition geometry affects the growth design and surface features of TiN films (keeping roughly constant the N/Ti ratio) and compare these effects with those produced by changing the chemical composition within the same thin film system (N/Ti increasing ratios). For this, two groups of samples were prepared: Group 1 – the samples were prepared in the conventional geometry (normal growth) with varied nitrogen content (stoichiometric and non-stoichiometric films) and; Group 2 – the samples were prepared with modified growth geometries (inclined and zigzag, with increasing incidence angles), keeping an almost unchanged stoichiometry. The results revealed increased surface porosity and roughness for Group 2 films compared to Group 1, demonstrating that deposition geometry can affect more significantly the surface characteristics than the composition variations. Corrosion studies indicated that the films prepared within Group 2, despite having higher porosity, showed a more stable open circuit potential (OCP) and nobler values than the reference close-stoichiometric TiN0.92 film (reference sample) from Group 1. However, potentiodynamic polarization curves suggested higher corrosion kinetics for Group 2 films, most likely due to their increased surface heterogeneities. Electrochemical impedance spectroscopy (EIS) confirmed these findings, showing lower corrosion resistance for films prepared with inclined and zigzag geometries, if compared to the films prepared in conventional geometry (Group 1 samples).This study advances the current state of the art on this film's responses, by demonstrating that tailoring nanostructure design through deposition geometry offers a promising approach to optimize the corrosion behaviour of TiNx without the need to change its composition.

Solar Cells: Applications and Current Opinion

Due to the manufacturing process, silicon-based solar cells have conquered the marketplace, but their cost is not economic. As a result, thin-film manufacturing was done with low-cost, appealing materials generated using less expensive, scalable, and manufacturable procedures. The motivation behind this work is to develop low-cost, high-efficiency solar cells using chemical and electrochemical techniques. Thin film solar cell structure could be presented as glass, Cu structure, CdS window material, TCO, and CdTe absorber material. The absorber and window materials include layers such as CdS and CdTe, while Cu and TCO are the back and front contacts. By using CSS and chemical bath deposition (CBD), The usual method of making this structure is to grow window (CdS) and absorber (CdTe) materials. CBD is a batch method that generates enormous quantities of Cd-containing waste solutions each time, adding to the production process's high cost. Sputtering or PVD, including high vacuum conditions, is performed with back and front contacts. This research program focuses on developing an "all chemical-solar cell" structure. This study showed that CdS and CdTe materials may be employed and electrodeposited in thin-film solar cell systems, CBD and electroless techniques. Furthermore, the back and front contacts can be coated using the CdS electrolytic bath, which is utilized for seven months without being discarded, but the CBD bath lasts 2-3 days. The deposition rate of the thin films was about 50 - 100 times greater than reported values in the literature. The efficiency of the manufactured cells was between 1 and 6%, which was reduced by the duration of time. Twenty days after manufacturing a TCO, CdS, CdTe, the short-circuit current, Cu-Ag solar cell, and open-circuit voltage deposited by all chemical and electrochemical deposition techniques were 0.8 mA/cm2 and 8.8 mV, respectively. However, consistency and reproducibility remain unresolved. The growth of CdTe nanocrystalline thin film is one of the reasons it has been identified as having nanosized tracks. High-quality CdTe layers should be developed, or in cadmium solar cells, its layered structure is the form of a cadmium window and a zinc oxide buffer layer to increase the consistency of the solar cell efficiency.

Nonlinear resonance of fractional order viscoelastic PET films under temperature loading

The effects of oven temperature during printing on nonlinear vibration for fractional-order PET films are considered in this paper. The effect of temperature, fractional order modelling and some other parameters are analysed with respect to the response of the resonance. Fractional order kelvin-Voigt ontological relationship is used to describe the characteristics of viscoelastic materials. The differential equations for nonlinear vibrations are inferred according to the second law of Newton and the theory of von Karman. Discretization for nonlinear equations on locomotion using the Bubnov–Galerkin method. Forced co-oscillatory amplitude-frequency response equations for thin-films systems under temperature loading were calculated using the multiple scales method. Results of numeral results show that temperature, and fractional-order visco-elastic modelling influence the membrane's response to resonance. These results provide a basis for studying fractional-order visco-elastic films vibrations and identifying regions of stable operation in moving systems to prevent divergent instabilities for flexible electronic device manufacturing.

A Polyimide Composite-Based Electromagnetic Cantilever Structure for Smart Grid Current Sensing.

Polyimides (PIs) have been extensively used in thin film and micro-electromechanical system (MEMS) processes based on their excellent thermal and mechanical stability and high glass transition temperature. This research explores the development of a novel multilayer and multifunctional polymer composite electro-piezomagnetic device that can function as an energy harvester or sensor for current-carrying wires or magnetic field sensing. The devices consist of four layers of composite materials with a polyimide matrix. The composites have various nanoparticles to alter the functionality of each layer. Nanoparticles of Ag were used to increase the electrical conductivity of polyimide and act as electrodes; lead zirconate titanate was used to make the piezoelectric composite layer; and either neodymium iron boron (NdFeB) or Terfenol-D was used to make the magnetic and magnetostrictive composite layer, which was used as the proof mass. A novel all-polymer multifunctional polyimide composite cantilever was developed to operate at low frequencies. This paper compares the performance of the different magnetic masses, shapes, and concentrations, as well as the development of an all-magnetostrictive device to detect voltage or current changes when coupled to the magnetic field from a current-carrying wire. The PI/PZT cantilever with the PI/NdFeB proof mass demonstrated higher voltage output compared to the PI/Terfenol-D proof mass device. However, the magnetostrictive composite film could be operated without a piezoelectric film based on the Villari effect, which consisted of a single PI-Terfenol-D film. The paper illustrates the potential to develop an all-polymer composite MEMS device capable of acting as a magnetic field or current sensor.

Modeling, Calculation and Realization of Au/Nb2O5 Substrates for Surface Plasmon Resonance Sensors

Introduction. Sensor devices based on the surface plasmon resonance (SRP) phenomenon are widely used among the tools of information and diagnostic technologies. The main part of a device based on the surface plasmon resonance phenomenon is a sensor substrate, which consists of a glass plate, a film of plasma-supporting metal, usually gold, and additional layers to increase the sensitivity of the research. Depending on the thickness of the additional dielectric layers, the following types of sensors can be implemented: a conventional SPR sensor with a gold film without a dielectric; an Au/dielectric SPR sensor with a dielectric thickness less than the critical one, in which the system can maintain the plasmonic mode; a waveguide sensor on a metal sublayer, with a dielectric thickness sufficient for the emergence of waveguide modes. The Au/Nb2O5 thin-film system is promising for creating sensor substrates due to the high refractive index of Nb2O5 and its exceptional chemical and mechanical resistance. The purpose of the work. This work is devoted to computer modelling, calculation of performance characteristics and implementation of Au/Nb2O5 sensor substrates for SPR devices, including the Plasmontest series devices developed at the Institute of Cybernetics of the National Academy of Sciences of Ukraine. The behaviour of the characteristics of the SPR substrates with a plasma-supporting gold film, SPR substrates with sensitivity enhancement by an additional layer of Nb2O5 of nanometre thickness and with a waveguide layer of Nb2O5 thickness more than 150 nm are analysed. Calculations were performed for both refractive sensors on SPR and biosensors. Results. The theoretical analysis was carried out by computer modelling in Winspall and calculations in MATLAB using the Fresnel equations and the matrix method, which allowed a comprehensive analysis of the shape of the reflection curves, angular sensitivity, resolution and angular ranges for sensors with different dielectric coatings. It is shown that at a thickness of 0-10 nm, the Au/Nb2O5 structure will work as a SPR sensor with increased sensitivity, and at a thickness of 150-210 nm as a waveguide sensor on a metal sublayer. But, as calculations have shown, only the Au/Nb2O5 SPR sensor is promising for practical implementation to increase the sensitivity of biosensor measurements. The work carried out on the development of thin-film technology, which includes vacuum deposition of a thin-film structure of adhesive Nb (1–2 nm), plasma-supported Au (50 nm), Nb (3–5 nm) and thermal annealing (to oxidise the top layer of niobium), made it possible to implement Au/Nb2O5 substrates for SPR studies. Experimental studies have shown that the angular sensitivity of the Au/Nb2O5 refractometric SPR sensor is 1.5 times higher than that of a SPR sensor with a single Au film at niobium oxide layer thickness of about 6 nm. Thus, the experimentally determined increase in the angular sensitivity of the Au-Nb2O5 SPR sensor is consistent with the theoretical data. Conclusions. Calculations have shown an increase in the angular sensitivity of SPR sensors for Au/Nb2O5 sensor substrates compared to conventional Au film substrates for both refractometric (1.6 times) and biosensor (1.8 times) studies. The sensors on Au/Nb2O5 substrates for SPR studies, which we have designed and practically implemented, are cheap to manufacture, have higher sensitivity, and due to the exceptional chemical and mechanical stability of Nb2O5, can be used repeatedly in rather aggressive environments. Keywords: computer modelling, surface plasmon resonance, sensor, refractometer, biosensor.

Structure and Mechanical Properties of Microwave-Absorbing Co-C Coatings Obtained by Magnetron Sputtering

This article is devoted to the study of microwave-absorbing properties of Co-C coating applied by magnetron sputtering. This article presents the main results of the manufacturing of a Co-C coating by magnetron sputtering, and the evaluation of experimental and computational research data on the relationship between the structure and properties of the obtained films. The structure of Co-C systems has been modeled to control the resulting structures using X-ray diffraction analysis. The structural-phase state of the resulting thin-film Co-C systems and the microwave-absorbing properties of coatings were studied using the transmission line method, consisting of a vector network analyzer, an air coaxial line, a software program, and an external computer. It has been established that on the resulting Co-C film the reflection coefficient in the frequency range of 8.2–12.4 GHz varies in the range of 900 → 718 mU, with reflection losses of −0.86 → −2.57 dB, and a standing wave coefficient of 19 → 6.8. An analysis of the obtained data indicates the presence of losses of electromagnetic energy in the studied frequency range.

Microstructural behavior of CNT-PDMS thin-films for multifunctional systems

Heterogeneous ribbed and non-ribbed carbon nanotube (CNT)-PDMS thin-film systems manufactured by large-scale rolling exhibit large-strain and high strain-rate characteristics with favorable surface behaviors, such as superhydrophobicity and drag reduction. However, it is not well understood how the multi-phase microstructure and material properties of non-ribbed thin-films are related to the surface material behavior and fracture. Hence, the objective of this investigation is to characterize the large-strain mechanical behavior and the microstructure of various CNT-PDMS compositions to understand how the CNT loading, agglomeration, distribution, and orientation affect the mechanical behavior and fracture of CNT-PDMS unribbed systems. Non-ribbed thin tensile testing specimens were fabricated for neat PDMS and CNT-PDMS with different weight CNT distributions to understand non-ribbed behavior. The ultimate strain, strength, and global stress–strain behavior were obtained by uniaxial mechanical testing. Scanning electron microscopy (SEM) of the fracture surface was also obtained for each sample to analyze the microstructure and relate the damage mode to the different weight distributions. Based on these experimental measurements and observations, large-strain, hyperelastic and hyper-viscoelastic material models were used to characterize the material behavior. The hyper-viscoelastic material model was shown to provide the most accurate material description of the thin-film behavior of the viscoelastic PDMS with the high-strength CNTs.

Microstructure modulation of a Bi4Ti3O12 thin film system by combining the effect of a simple processing methodology with a co-doping strategy involving Nd3+ and Nb5+

A microstructure based on plate-like grains is expected in the obtaining of Bi4Ti3O12 ferroelectric ceramics, promoted by the Aurivillius crystalline structure that this material exhibit. This grain morphology would lead to conductivity making the functional response unpractical. In this frame, we address the control of the crystal growth which leads to this grain morphology by combining the effect of a simple thin film obtaining procedure with doping strategies. On the one hand, an aqueous solution-gel plus spin-coating methodology is performed here for the obtaining of these thin films. On the other hand, a simultaneous incorporation of Nd3+ and Nb5+ in the crystal lattice replacing Bi3+ and Ti4+, respectively, is conducted in this contribution. The results obtained by X-ray diffraction, UV–visible measurements and FESEM confirm that the incorporated dopants are able to block (or at least control) the mentioned crystal growth.

Development of a Thin-Film NMC System for the Investigation and Suppression of Harmful Reactions Occurring on the Surface of Cathode Materials in Li-Ion Batteries

Materials with the stoichiometry Li(NixMnyCoz)O2 (NMC) have emerged as promising candidates for use as cathodes in Li-ion batteries for electric vehicles. This is primarily due to their high capacity, which increases with the nickel content (Ni-rich NMC). However, the increase in nickel also leads to a decrease in the stability of the material, hindering market introduction [1]. Much of these stability issues emanate from the surface of the material and move subsurface towards the bulk during battery operation [2]. The internal electrode architecture of traditional composite battery cathodes, containing active materials, carbon additives, and binders, complicates the study of the surface reactions. For this reason, we developed a thin-film model system of Ni-rich NMC with a high surface area-to-volume ratio to exacerbate the effect of the surface reactions, enabling easier characterization of the surface without influence of the bulk.The interfacial reactions occurring when NMC is exposed to air was investigated using the thin-film system. These experiments were supported by thermodynamic calculations to propose a mechanism of what reactions occur on the surface. Our study showed that the surface of NMC is stable in inert environments, however, when exposed to air (in particular H2O and CO2) the active material at the surface reacts to form Li2CO3, coinciding with loss of Li2O and protonation of the material, forming transition metal oxyhydroxides. We found that this phenomenon can be reversed by performing a heat treatment, moving Li2O back into the film. However, during the annealing process, an additional reaction between the film and substrate takes place. This, once again, leads to the active material being deficient in Li2O. To compensate for this deficiency, Li2CO3 was deposited onto NMC prior to annealing. The thermodynamical properties of each film were approximated from their electrochemical behavior. It was found that the film treated with Li2CO3 before annealing was thermodynamically similar to what is expected for an NMC cathode. These results contribute to the understanding of the interfacial reactions that take place on the surface of NMC cathodes. Additionally, the study proposes strategies to mitigate and compensate for these reactions.

(Invited) Amplified Spontaneous Emission Dynamics of a Lead Halide Perovskite Crystal as Revealed by Femtosecond Transient Absorption Microscopy

Organic-inorganic lead halide perovskite materials (e.g. CH3NH3PbX3, CsPbX3, X=Cl, Br, I) have various attractive properties not only for solar cells but also for LED and nanoscale lasers because of their wavelength tunability and low lasing threshold. Such an efficient lasing is indispensable for their applications, and the essential needs are miniaturization and low threshold. While this material was reported in 2009 for use in solar cells, it is also expected to be used in light-emitting and laser devices due to its easy tunability of emission wavelength and low-cost fabrication. However, the low-threshold lasing mechanism of lead halide perovskites has not been established due to various theories on the interaction state between light and carriers generated in the cavity at the initial stage and the carrier-carrier interaction state, which has greatly hindered progress in improving performance. In the present study, we have measured transient absorption spectra of a single CH₃NH₃PbBr₃ microcrystal using a femtosecond transient absorption microscopy to reveal the initial carrier process that induces nonlinear luminescence[1].CH3NH3PbBr3 crystals were prepared by a previously reported method. Aqueous lead(II) acetate solution (100 mg/mL) was dropped onto a glass slide and dried at 60°C for 30 min to obtain a film of lead acetate. Microcrystals of CH3NH3PbBr3 were then obtained by immersing the film in methylammonium bromide solution (5 mg/mL) with isopropanol as a solvent for 20 hours at room temperature in air.For transient absorption measurements, a regeneratively amplified femtosecond pulse (Spectra-Physics, Solstice, 795 nm, 1 kHz) was split in two; the second harmonic of one beam was used as the excitation light, and the white light generated with the other beam by introducing it into an optical parametric amplifier (Light Conversion, TOPAS) and focusing the obtained signal light (1.3 mm) into a CaF2 plate was used as the probe light.Fig. 1(a) shows the transient absorption spectra of lead halide perovskite excited at the intensities over the lasing threshold. The spectral signals that were not observed before the time origin (-1 ps) were significantly observed with modulated spectral shape after the time origin (≥0 fs). The spectral bleaching around 540 nm indicates carrier generation by the excitation light, and the relaxation of the bleaching indicates the recombination of electrons and holes. Furthermore, at around 557 nm, a bleaching signal appeared as shown in Fig. 1(b), that was not represented in the transient absorption spectrum excited at the intensity below the lasing threshold. This signal is suggested to be due to amplified stimulated emission. Spectral modulation is often observed as interference of light propagating in thin-film systems. The thickness of the perovskite crystals is around 200-300 nm, which is suitable to observe the optical interference. However, generally, this interference tends to become lower in frequency as one observes longer wavelengths, which is essentially different from the modulation observed here. The spectra modulation appeared immediately after the carrier was generated, and the modulation continued for up to 1ns. These results suggest that the modulation is caused by the electric field effect of the generated carriers on the electron spectrum. Franz-Keldysh’s theory is often used for spectral modulation in the presence of an electric field. In reflectance transient absorption spectroscopy, the electric field modulated spectrum has been explained in the GaInP2 system by Franz-Keldysh’s theory in systems where charges are generated on the semiconductor surfaces[2]. These results indicate the spectral modulation occurred from the charges separated on the surface of the crystal. We will discuss the mechanism of amplified spontaneous emission and low threshold lasing dynamics at the conference site. Funding: This study was partly supported by KAKENHI (Grant Number JP22H04755, JP19K05190) and JST FOREST (JPMJFR213G).

(Invited) Minimizing or Maximizing Contact Effects in Organic Electronics

Contact resistance is an umbrella term capturing various current-limiting mechanisms existing at and around metal/semiconductor junctions of an electronic device. Despite its known detrimental impact on the performance of organic, oxide, and 2D semiconductor electronics, a quantitative and predictive description of contact resistance is still lacking. At the same time, recent evidences show that contact resistance can actually provide benefits to certain applications, thus challenging our common belief. This presentation will clarify why contact issues are so critical to the operation of general thin-film systems, and highlight our recent results on re-defining the role of contact resistance in organic diodes and transistors.

Influence of the external magnetic field on structural characteristics of granular Co-Cu thin film alloys

We present the results of experimental studies of the influence of an external magnetic field on the structural characteristics (surface roughness and structural entropy) of nanogranular thin-film system based on Co and Cu. The samples CoxCu100-x in a wide range of compositions (17 at. % ≤ x ≤ 69 at. %) with the thickness of d = 35 nm were obtained by electron-beam co-evaporation using two independent electron guns. After obtaining, the films were annealed in a vacuum at a temperature of 800 K for 30 min. The studies of magnetoresistive properties have shown that the maximum giant magnetoresistance (GMR) amplitude (1.7 % in the transverse and 1.6 % in the longitudinal measurement geometries) in a magnetic field of H = 4.5 kOe at room temperature was observed in the Co21Cu79 film alloy. Transmission electron microscopy showed that this sample contains hcp-Co granules with a size of L = 5 ÷ 12 nm in a matrix of metastable fcc-Cu(Co) solid solution. The influence of the external magnetic field on the structural characteristics and surface morphology of the Co21Cu79 thin-film alloy was investigated using atomic force microscopy (AFM). It was found that a first impact of application of external magnetic field with H = 0.5 kOe causes a decrease in the values of the arithmetic mean Ra, and quadratic mean Rq, of the film roughness and structural entropy S. A decreases in Ra by 8.5 %, Rq by 6.5 %, and structural entropy S by 6.5 % were observed. After application of a larger magnetic field with H = 1.0 kOe and during the subsequent relaxation of the structure within 15 h after the field is turned off, the values of the structural parameters of the film surface did not change significantly.

Photoactivation of Millimeters Thick Liquid Crystal Elastomers with Broadband Visible Light Using Donor-Acceptor Stenhouse Adducts.

Light-responsive liquid crystal elastomers (LCEs) are stimuli-responsive materials that facilitate the conversion of light energy into a mechanical response. In this work, a novel polysiloxane-based LCE with donor-acceptor Stenhouse adduct (DASA) side-chains is synthesized using a late-stage functionalization strategy. It is demonstrated that this approach does not compromise the molecular alignment observed in the traditional Finkelmann method. This easy, single-batch process provides a robust platform to access well-aligned, light-responsive LCE films with thickness ranging from 400µm to a 14-layer stack that is 5mm thick. Upon irradiation with low-intensity broadband visible light (100-200mW cm-2), these systems undergo 2D planar actuation and complete bleaching. Conversely, exposure to higher-intensity visible light induces bending followed by contraction (300mW cm-2). These processes are repeatable over several cycles. Finally, it is demonstrated how light intensity and the resulting heat generation influences the photothermal stationary state equilibrium of DASA, thereby controlling its photoresponsive properties. This work establishes the groundwork for advancement of LCE-based actuators beyond thin film and UV-light reliant systems.

Diode Equation for Sandwich-Type Thin-Film Photovoltaic Devices Limited by Bimolecular Recombination

Analytical diode models that relate the current to key material parameters are invaluable for understanding the device physics in photovoltaic (PV) devices. However, a diode model that accurately describes the current in thin-film PVs based on low-mobility semiconductors (including organic solar cells) limited by bimolecular recombination has been lacking. Previous models neglect effects of injected charge carriers, which are the predominant source for bimolecular recombination in thin-film PV systems with Ohmic contacts. In this work, we derive a unified diode equation for thin-film PVs based on undoped semiconductors limited by bimolecular recombination. Based on a regional approximation approach, we derive an analytical model for the current accounting for the interplay between charge-carrier extraction, injection, and bimolecular recombination. The analytical model is validated by numerical simulations and tested experimentally on organic solar cells. Our findings provide key insights into the mechanisms driving and limiting charge collection, and ultimately the power-conversion efficiency, in low-mobility PV devices. The presented framework is material agnostic and generally applicable to sandwich-type thin-film PV devices, including photodiodes and indoor light-harvesting cells. Published by the American Physical Society 2024

A Practical Approach for Determination of Thermal Stress and Temperature-Dependent Material Properties in Multilayered Thin Films.

Multilayered thin films are essential to most microelectro-mechanical systems (MEMSs). The reliability and predictability of the behavior of such systems, especially when intended for usage at high temperatures or in harsh environments, demand the consideration of thermo-mechanical properties of the individual films of the multilayer arrangement during the design stage. This paper introduces a newly derived analytical model for the convenient indirect determination of the temperature-dependent Young's modulus and the thermally induced stress of individual layers within a multilayered thin film system, i.e., a multilayer-adapted Stoney equation. It is based on sample curvature measurement and requires data from only a single experiment. Experimental and numerical investigations of the new models are carried out using a five-layered sample of a RuAl metallization system developed for wireless high-temperature acoustic sensing. The results highlight the usability of the new model in practical MEMS analysis, enabling insights into complex layer stacks by overcoming current experimental limitations.

High-Throughput Micro-Combinatorial TEM Phase Mapping of the DC Magnetron Sputtered YxTi1-xOy Thin Layer System.

High-throughput methods are extremely important in today's materials science, especially in the case of thin film characterization. The micro-combinatorial method enables the deposition and characterization of entire multicomponent thin film systems within a single sample. In this paper, we report the application of this method for the comprehensive TEM characterization of the Y-Ti-O layer system. Variable composition samples (YxTi1-xOy) were prepared by dual DC magnetron sputtering, covering the entire (0 ≤ x ≤ 1) concentration range. The structure and morphology of phases formed in both as-deposited and annealed samples at 600, 700, and 800 °C were revealed as a function of Y-Ti composition (x). A comprehensive map showing the appropriate amorphous and crystalline phases, and their occurrence regions of the whole Y-Ti-O layer system, was revealed. Thanks to the applied method, it was shown with ease that at the given experimental conditions, the Y2Ti2O7 phase with a pyrochlore structure forms already at 700 °C without the TiO2 and Y2O3 by-phases, which is remarkably lower than the required temperature for most physical preparation methods, demonstrating the importance and benefits of creating phase maps in materials science and technology.

Additive roles of antiferromagnetically coupled elements in the magnetic proximity effect in the GdFeCo/Pt system

Interfacial magnetic interactions between different elements are the origin of various spin-transport phenomena in multi-elemental magnetic systems. We investigate the coupling between the magnetic moments of the rare-earth, transition-metal, and heavy-metal elements across the interface in a GdFeCo/Pt thin film, an archetype system to investigate ferrimagnetic spintronics. The Pt magnetic moments induced by the antiferromagnetically aligned FeCo and Gd moments are measured using element-resolved x-ray measurements. It is revealed that the proximity-induced Pt magnetic moments are always aligned parallel to the FeCo magnetic moments, even below the ferrimagnetic compensation temperature where FeCo has a smaller moment than Gd. This is understood by a theoretical model showing distinct effects of the rare-earth Gd 4f and transition-metal FeCo 3d magnetic moments on the Pt electronic states. In particular, the Gd and FeCo work in-phase to align the Pt moment in the same direction, despite their antiferromagnetic configuration. The unexpected additive roles of the two antiferromagnetically coupled elements exemplify the importance of detailed interactions among the constituent elements in understanding magnetic and spintronic properties of thin film systems.

Advancing Energy‐Storage Performance in Freestanding Ferroelectric Thin Films: Insights from Phase‐Field Simulations

AbstractAdvances in flexible electronics are driving the development of ferroelectric thin‐film capacitors toward flexibility and high energy storage performance. In the present work, the synergistic combination of mechanical bending and defect dipole engineering is demonstrated to significantly enhance the energy storage performance of freestanding ferroelectric thin films, achieved through the generation of a narrower and right‐shifted polarization‐electric field hysteresis loop. The recoverable energy storage density of freestanding PbZr0.52Ti0.48O3 thin films increases from 99.7 J cm−3 in the strain (defect) ‐free state to 349.6 J cm−3, marking a significant increase of 251%. The collective impact of the flexoelectric field, bending tensile strain, and defect dipoles contributes to this enhancement. The demonstrated synergistic optimization strategy has potential applicability to flexible ferroelectric thin film systems. Moreover, the energy storage properties of flexible ferroelectric thin films can be further fine‐tuned by adjusting bending angles and defect dipole concentrations, offering a versatile platform for control and performance optimization.

Nanomechanical and Microstructural Characterization of Biocompatible Ti3Au Thin Films Grown on Glass and Ti6Al4V Substrates.

Ti-Au intermetallic-based material systems are being extensively studied as next-generation thin film coatings to extend the lifetime of implant devices. These coatings are being developed for application to the articulating surfaces of total joint implants and, therefore, must have excellent biocompatibility combined with superior mechanical hardness and wear resistance. However, these key characteristics of Ti-Au coatings are heavily dependent upon factors such as the surface properties and temperature of the underlying substrate during thin film deposition. In this work, Ti3Au thin films were deposited by magnetron sputtering on both glass and Ti6Al4V substrates at an ambient and elevated substrate temperature of 275 °C. These films were studied for their mechanical properties by the nanoindentation technique in both variable load and fixed load mode using a Berkovich tip. XRD patterns and cross-sectional SEM images detail the microstructure, while AFM images present the surface morphologies of these Ti3Au thin films. The biocompatibility potential of the films is assessed by cytotoxicity tests in L929 mouse fibroblast cells using Alamar blue assay, while leached ion concentrations in the film extracts are quantified using ICPOEMS. The standard deviation for hardness of films deposited on glass substrates is ∼4 times lower than that on Ti6Al4V substrates and is correlated with a corresponding increase in surface roughness from 2 nm for glass to 40 nm for Ti6Al4V substrates. Elevating substrate temperature leads to an increase in film hardness from 5.1 to 8.9 GPa and is related to the development of a superhard β phase of the Ti3Au intermetallic. The standard deviation of this peak mechanical hardness value is reduced by ∼3 times when measured in fixed load mode compared to the variable load mode due to the effect of nanoindentation tip penetration depth. All tested Ti-Au thin films also exhibit excellent biocompatibility against L929 fibroblast cells, as viability levels are above 95% and leached Ti, Al, V, and Au ion concentrations are below 0.1 ppm. Overall, this work demonstrates a novel Ti3Au thin film system with a unique combination of high hardness and excellent biocompatibility with potential to be developed into a new wear-resistant coating to extend the lifetime of articulating total joint implants.

Artificial Domain Patterning in Ultrathin Ferroelectric Films via Modifying the Surface Electrostatic Boundary Conditions.

Nanoscale spatially controlled modulation of the properties of ferroelectrics via artificial domain pattering is crucial to their emerging optoelectronics applications. New patterning strategies to achieve high precision and efficiency and to link the resultant domain structures with device functionalities are being sought. Here, we present an epitaxial heterostructure of SrRuO3/PbTiO3/SrRuO3, wherein the domain configuration is delicately determined by the charge screening conditions in the SrRuO3 layer and the substrate strains. Chemical etching of the top SrRuO3 layer leads to a transition from in-plane a domains to out-of-plane c domains, accompanied by a giant (>105) modification in the second harmonic generation response. The modulation effect, coupled with the plasmonic resonance effect from SrRuO3, enables a highly flexible design of nonlinear optical devices, as demonstrated by a simulated split-ring resonator metasurface. This domain patterning strategy may be extended to more thin-film ferroelectric systems with domain stabilities amenable to electrostatic boundary conditions.