Thin Film Materials Research Articles

An Overview to Current Trends in Metal Oxide Thin Film Preparation Methods

Thin film preparation and coatings technology has been gaining attention as there is an increasing demand to the functionalized novel materials. Surface design through catalytically active materials such as metal oxides or zeolites as thin films and application through coating provides unique properties to the substance and result novel materials physically and chemically differing from their bulk form. Design technologies allow the preparation of structurally ordered thin films and coatings. Currently, designed thin film materials and coatings have a wide application range such as catalysis, sensing, anti- reflective surfaces, photovoltaics, or specialty design for targeted applications. This study provides a brief overview to the preparation methods of catalytically active coatings and thin film substances, which might be of industrial relevance in the case of the design for targeted applications.

Long-Range SECCM Enables High-Throughput Electrochemical Screening of High Entropy Alloy Electrocatalysts at Up-To-Industrial Current Densities.

High-entropy alloys (HEAs), especially in the form of compositional complex solid solutions (CCSS), have gained attention in the field of electrocatalysis. However, exploring their vast composition space concerning their electrocatalytic properties imposes significant challenges. Scanning electrochemical cell microscopy (SECCM) offers high-speed electrochemical analysis on surface areas with a lateral resolution down to tens of nm. However, high-precision piezo positioners often used for the motion of the tip limit the area of SECCM scans to the motion range of the piezo positioners which is typically a few tens of microns. To bridge this experimental gap, the study proposes a long-range SECCM system with a rapid gas-exchange environmental cell for high-throughput electrochemical characterization of 100mm diameter HEA thin-film material libraries (ML) obtained by combinatorial co-sputtering. Due to the gas-liquid interface at the positioned SECCM droplet on the sample, high-throughput evaluation under industrial current density conditions becomes feasible. This allows the direct correlation between electrocatalytic activity and material composition with high statistical reliability. The multidimensional data obtained accelerates materials discovery, development, and optimization.

Leveraging Deep Neural Networks for Estimating Vickers Hardness from Nanoindentation Hardness.

This research presents a comprehensive analysis of deep neural network models (DNNs) for the precise prediction of Vickers hardness (HV) in nitrided and carburized M50NiL steel samples, with hardness values spanning from 400 to 1000 HV. By conducting rigorous experimentation and obtaining corresponding nanoindentation data, we evaluated the performance of four distinct neural network architectures: Multilayer Perceptron (MLP), Convolutional Neural Network (CNN), Long Short-Term Memory network (LSTM), and Transformer. Our findings reveal that MLP and LSTM models excel in predictive accuracy and efficiency, with MLP showing exceptional iteration efficiency and predictive precision. The study validates models for broad application in various steel types and confirms nanoindentation as an effective direct measure for HV hardness in thin films and gradient-variable regions. This work contributes a validated and versatile approach to the hardness assessment of thin-film materials and those with intricate microstructures, enhancing material characterization and potential application in advanced material engineering.

Influence of the Porphyrin Structures on the Contact Angle of Water Wetting by Langmuir-Schaefer Films

Studying the contact angle of water droplets on the surfaces of thin films formed by organic compounds allows to establish hydrophilic/hydrophobic properties of the films. Knowledge of hydrophilicity/hydrophobicity makes it possible to optimize the composition and increase the adhesive properties of films, improving their functionality. In this study, the dependence of the contact angle of Langmuir-Schaefer films (LS-films) of three compounds: 5,10,15,20-tetraphenylporphyrin (I), 2-aza-21-carba-5,10,15,20-tetraphenyl-porphyrin (II), and 5,15-bis(2,6-bis(dodecycloxy)phenyl)porphyrin (III) was examined. Contact angle data were obtained for LS-films with different transfer numbers of floating layers of the studied porphyrins and different surface roughness. It was found that LS-films of compounds I and II are hydrophobic and their hydrophobicity increases with an increasing of transfer number. In addition, an increase in the surface roughness of the LS film of compound I compared to compound II reduces the value of the contact angle. Unlike porphyrins I and II, LS-films of compound III displayed hydrophilic properties. The obtained data can be used for the targeted design of compounds to create thin film materials of various purposes.

Effect of Linker Group on Thermoelectric Properties of Dimer Zinc Porphyrin-Based Molecular Junctions

The discovery of high-efficiency organic thermoelectric materials has the potential to pave the path for various energy-harvesting technologies and the development of flexible, transparent thin-film materials for Peltier coolers. Our study involves a comparison of the electrical and thermoelectric characteristics of four zinc porphyrin configurations. The results show that changing the linker between zinc diner units has an essential effect on the electrical conductance and thermopower values of these structures. Consequently, the thermoelectric figure of merit ZT will change which means the thermoelectric efficiency change.

Accelerating the Development of New Silicon-Based Anode Materials

In this work we have demonstrated the feasibility of using thin film systems as a steppingstone to accelerate the development of commercially relevant silicon-based anode materials for Li-ion batteries. Understanding new materials in conventional particle-based electrode systems is often complex. Lithium and electrolyte interact not only with the active material particles, but also with the different supporting components of the electrode, leaving it difficult to directly assess the electrochemical contribution of the active material. This is further complicated by the electrochemical behavior of such electrodes also being strongly dependent on processing conditions, like casting and drying procedures. Additionally, it is often also a challenge to synthesize such materials in particle form with the required chemical composition and monodispersity in the first place. Therefore, it would be highly beneficial to study and screen new anode materials without having to assume and assess these different factors. That is of particular importance during the optimization stage of the chemical composition for the active material, for which a significant number of samples is typically needed. Thus, evaluating the material in a thin film system is a simple and reproducible method of determining a material’s potential as a future anode material.Such thin films of active materials can reliably be made with a large range of thicknesses, compositions, element combinations and coatings, using multiple flexible and reproducible thin film deposition techniques available. In the present work, we have investigated silicon-based materials made by PECVD and sputtering: pure silicon and sub-stoichiometric versions of silicon nitride, silicon carbide, and silicon phosphide (SiNx, SiCx, SiPx). For evaluation of the applicability of the thin film model system, in several cases we have also compared the results to particles of the same material with similar chemical composition synthesized via a free space CVD process [1].Preliminary evaluation shows good agreement between results for thin film systems compared to what is known for particles of the same material. SiNx particles show good agreement with thin film results where a high nitrogen content decreases the capacity, while increasing the stability due to the formation of a stabilizing matrix around the active silicon [2]. Differences in the differential capacity analysis of similar materials in particle and thin film forms demonstrates the greater complexity in interpreting the data from the more intricate particle-based systems. SiCx is known to react in a similar fashion as SiNx where its coulombic efficiency and capacity decreases with increasing carbon-content, while its stability has been seen to increase due to a similar stabilizing matrix [3]. Reference s : [1] H. F. Andersen et al., ECS Trans., vol. 62, no. 1, pp. 97–105, 2014.[2] A. Ulvestad et al., ACS Nano, vol. 15, no. 10, pp. 16777–16787, 2021.[3] X. D. Huang et al., RSC Adv., vol. 8, no. 10, pp. 5189–5196, 2018.

(Invited) Thermal Atomic Layer Deposition of Elemental Antimony and Bismuth Films

The elements antimony (Sb) and bismuth (Bi) are important components of many thin film materials. In many applications, films need to be grown in high aspect ratio features with perfect conformality and Angstrom-level control of film thicknesses. Atomic layer deposition (ALD) is a method that can afford uniform thickness and conformal films, even in narrow and deep nanoscale features. To date, there have been several ALD processes reported for elemental Sb films using SbCl3 and Sb(SiR3)3 (R = Me, Et), but no reports of Bi films grown by ALD have been published.1,2 Herein, several families of thermal ALD processes will be described for the growth of elemental Sb and Bi films. Precursors that were explored for Sb and Bi include SbCl3, BiCl3, BiPh3, and Bi(NMe2)3. Reducing precursors encompassed 2-methyl-1,4-bis(trimethylsilyl)-2,5-cyclohexadiene,3 1,4-bis(trimethylsilyl)-1,4-dihydropyrazine,3 and nitrogen sources such as ammonia, hydrazine, alkyl hydrazines, and alkyl amines. The processes employing the nitrogen co-reactants are proposed to occur through unstable SbN and BiN, which then decompose with loss of N2 to afford elemental Sb and Bi films. Self-limited Sb and Bi film growth was established between 25 and 175 °C. High purity Sb (>98%) and Bi (>94%) films were demonstrated by X-ray photoelectron spectroscopy analysis. X-ray diffraction analyses revealed the growth of crystalline Sb and Bi films. The results of additional film characterization will be presented. Al Hareri, M.; Emslie, D. J. H. Chem. Mater. 2022, 34, 2400-2409.Pore, V.; Knapas, K.; Hatanpää, T.; Sarnet, T.; Kemell, M.; Ritala, M.; Leskelä, M.; Mizohata, K. Chem. Mater. 2011, 23, 247– 254.Klesko, J. P.; Thrush, C. M.; Winter, C. H. Chem. Mater. 2015, 27, 4918-4921.

Scanning Tunneling Spectroscopy Method for the Prediction of Semiconductor Heterojunction Performance as a Prequel for Device Development.

The prediction of semiconductor device performance is a persistent challenge in materials science, and the ability to anticipate useful specifications prior to construction is crucial for enhancing the overall efficiency. In this study, we investigate the constituents of a solar cell by employing scanning tunneling microscopy (STM) and spectroscopy (STS). Through our observations, we identify a spatial distribution of the dopant type in thin films of materials that were designed to present major p-doping for germanium sulfide (GeS) and dominant n-doping for tin disulfide (SnS2). By generating separate STS maps for each semiconductor film and conducting a statistical analysis of the gap and doping distribution, we determine intrinsic limitations for the solar cell efficiency that must be understood prior to processing. Subsequently, we fabricate a solar cell utilizing these materials (GeS and SnS2) via vapor phase deposition and carry out a characterization using standard J-V curves under both dark/illuminated irradiance conditions. Our devices corroborate the expected reduced efficiency due to doping fluctuation but exhibit stable photocurrent responses. As originally planned, quantum efficiency measurements reveal that the peak efficiency of our solar cell coincides with the range where the standard silicon solar cells sharply decline. Our STS method is suggested as a prequel to device development in novel material junctions or deposition processes where fluctuations of doping levels are retrieved due to intrinsic material characteristics such as the occurrence of defects, roughness, local chemical segregation, and faceting or step bunching.

Enhancement of electrical conductivity and lateral photovoltaic sensitivity via mechanical bending in flexible Cr:In2O3 films

Functional oxide thin film materials have drawn extensive attention due to their rich tunable properties. Here, we deposited Cr-doped In2O3 thin films on flexible mica substrates and investigated the tunable effect of bending strain on their electrical transport and lateral photovoltaic properties. By applying mechanical bending with different curvature, a range of bending strains from compressive (-0.084%) to tensile (0.083%) in the Cr-doped In2O3 thin films was achieved. As the bending strain increased, the lateral photovoltage based on the thermoelectric effect and the electrical conductivity significantly increased. The flexoelectric effect induced by bending strain plays a key role in the mechanical bending tunable effect. In the Cr:In2O3 thin films, bending strain simultaneously increased both the electrical conductivity and the Seebeck coefficient, while reducing the thermal conductivity, highlighting its potential value in enhancing the performance of thermoelectric materials.

Negative Capacitance Effect Using a Pure Imaginary Electric Mobility Controlled By an Adiabatic Parameter in Thin Film Materials Based On Drude Model

Existence of a pure imaginary mobility of charge carriers in organic polymers materials, precisely the poly p-phenylene vinylene is explored in this work. Indeed, we propose a new model of dynamic equation of particles able to carry electric charges, we introduce a control parameter of the adiabatic evolution combined with a phase difference between the external perturbation of the material and the position of carrier, leading from then on to the non-use of the complex mobility. This model after transformation allowed us to demonstrate the existence of negative capacitance at low and high frequencies in the poly p-phenylene vinylene. Also thanks to this new model, we were able to obtain results in line with the experimental ones, thus confirming the validity of our model

High-Strength Amorphous Silicon Carbide for Nanomechanics.

For decades, mechanical resonators with high sensitivity have been realized using thin-film materials under high tensile loads. Although there are remarkable strides in achieving low-dissipation mechanical sensors by utilizing high tensile stress, the performance of even the best strategy is limited by the tensile fracture strength of the resonator materials. In this study, a wafer-scale amorphous thin film is uncovered, which has the highest ultimate tensile strength ever measured for a nanostructured amorphous material. This silicon carbide (SiC) material exhibits an ultimate tensile strength of over 10 GPa, reaching the regime reserved for strong crystalline materials and approaching levels experimentally shown in graphene nanoribbons. Amorphous SiC strings with high aspect ratios are fabricated, with mechanical modes exceeding quality factors 108 at room temperature, the highest value achieves among SiC resonators. These performances are demonstrated faithfully after characterizing the mechanical properties of the thin film using the resonance behaviors of free-standing resonators. This robust thin-film material has significant potential for applications in nanomechanical sensors, solar cells, biological applications, space exploration, and other areas requiring strength and stability in dynamic environments. The findings of this study open up new possibilities for the use of amorphous thin-film materials in high-performanceapplications.

Raman scattering monitoring of thin film materials for atomic layer etching/deposition in the nano-semiconductor process integration

According to Moore's law, the semiconductor industry is experiencing certain challenges in terms of adapting to highly sophisticated integrated technology. Therefore, controlling materials at the atomic scale is considered a mandatory requirement for further development. To this end, atomic layer deposition and etching skills are being increasingly researched as potential solutions. However, several considerations exist for adopting atomic technology with respect to surface analysis. This review primarily focuses on the use of Raman scattering for evaluating atomic-layered materials. Raman scattering analysis is expected to gradually expand as a semiconductor process and mass-production monitoring technology. As this can enhance the applications of this method, our review can form the basis for establishing Raman scattering analysis as a new trend for atomic-scale monitoring.

Low Ti Additions to Stabilize Ru‐Ir Electrocatalysts for the Oxygen Evolution Reaction

AbstractAnodic oxygen evolution reaction (OER) challenges large scale application of proton exchange membrane water electrolyzers (PEMWE) due to sluggish kinetics, high overpotential and extremely corrosive environment. While Ir oxides currently provide the best balance between activity and stability, the scarcity of Ir and corresponding high market price lead to poor cost‐benefit factors. Mixing Ir with more stable non‐precious Ti reduces the noble metal loading and may implicate stabilization, while addition of more catalytically active Ru ensures a high reaction rate. Here, we examine the activity‐stability behavior of Ru‐Ir‐Ti thin film material libraries with low Ti‐content under the OER conditions. The high sensitivity to the dissolution of the individual alloy components was achieved by using online and off‐line inductively coupled plasma mass spectrometry (ICP‐MS) analysis. Our data reveal that even low Ti additions improve the stability of Ru‐Ir catalysts without sacrificing activity. In particular, 5 at. % of Ti enable stability increase of Ir in the Ru‐Ir catalyst by a factor of 3. Moreover, this catalyst exhibits higher activity compared to the Ti‐free Ru‐Ir alloys with similar Ir content. Observed activity‐stability trends are discussed in light of X‐ray photoelectron spectroscopy data.

Exploring the Influence of P3HT on PTCA Crystallization and Phase Behavior in Thin Films.

The thermal properties and alignment of crystallinity of materials in thin films play crucial roles in the performance and reliability of various devices, especially in the fields of electronics, materials science, and engineering. The slight variations in the molecular packing of the active layer can make considerable differences in the optical and thermal properties. Herein, we aim to investigate the tuning of the physical properties of a blended thin film of n-type small organic molecules of perylene-3,4,9,10-tetracarboxylic acid (PTCA-SMs) with the mixing of the p-type polymer poly(3-hexylthiophene) (P3HT). The resulting thin films exhibit an enhanced surface crystallinity compared to the pristine material, leading to the formation of long crystallites, and these crystallites are thermally stable in the solid state, as confirmed by X-ray diffraction (XRD), atomic force microscopy (AFM), and thermal analysis using variable-temperature spectroscopic ellipsometry (VTSE) and differential scanning calorimetry (DSC). We believe that the crystalline structure of the obtained P3HT/PTCA-SMs blends is a combination of edge-on and face-on orientations, which enable the potential use of this material as an active layer in organic electronics.

Nanocone-shaped Ni-electroplated carbon fiber composite films for electromagnetic shielding applications

This study developed a series of lightweight composite films with adjustable reflectivity and superior mechanical properties. Carbon fiber (CF) was electroplated with both conventional and nanocone-shaped Ni coatings to create Ni-plated carbon fiber (CF@Ni), which was then further classified into conventional Ni carbon fiber (CF@CN) and nanocone-shaped Ni carbon fiber (CF@NN). CF@Ni fibers were sheared and filtered to produce Ni-plated carbon fiber fabric (CFF@Ni), which was then encapsulated in polyimide resin (PI) to form the final thin film materials (CF@Ni/PI). The shielding performance and mechanical properties of these CF@Ni/PI thin films have been comprehensively investigated. The study found that the nanocone-shaped Ni-plated samples exhibited superior performance. Absorption loss was dominant when a relatively low amount of Ni-plated carbon fiber was added, while reflection loss dominated when a relatively high amount was added. Adding 0.3 g of nanocone-shaped Ni carbon fiber created a 1.2 mm thin film with a shielding effectiveness of 71 dB and a tensile strength of 22.4 MPa. Additionally, the thin film demonstrated excellent flexibility and durability. Due to its exceptional mechanical properties and flexibility, this composite film holds significant potential in the fields of microelectronics and intelligent electronic devices.

Recognizing and correcting for errors in frequency-dependent modulation spectroscopy

This work shows how to acquire reliable data from frequency dependent continuous-wave modulation spectroscopy. We demonstrate this through the example of continuous-wave photoinduced absorption (cwPA), a characterization technique useful for studying long-lived photoexcitations in thin-film solar cell materials. Experimental errors arising at moderate frequencies in modulation spectroscopy are identified and corrected for. Limitations of the detectors and electronics are seen to cause both signal loss and phase shifts. Imperfect charge collection in the detector leads to wavelength-dependent correction factors, while phase shifts caused by the experimental setup call for frequency-dependent corrections. The methods outlined in this work act as a guide to avoid pitfalls in setting up modulation spectroscopy measurements and correcting for limitations.

Dynamical features and sensitivity visualization of thin-film Polarisation equation

The present investigation describes the dynamical behavior, multi-stability, and traveling wave solutions of thin-film polarisation equations (TFPE) which describes the propagation of waves in thin-film ferroelectric materials. The extended direct algebraic technique is used to construct the traveling wave patterns. Visual representations of a few randomly selected solutions are provided for physical comprehension. The ordinary differential equation can be expressed in the planar dynamical system using the Galilean transformation. Using various initial conditions for the unperturbed dynamical system, phase portraits with various sorts of trajectories are created. Additionally, the Runge-Kutta method is used to plot nonlinear periodic waves and super nonlinear waves. Additionally, the Hamiltonian function for this undisturbed dynamical system is computed and shown. It also included the source term with amplitude and frequency parameters for the chaotic and quasi-periodic behaviors, and the system is also stated in the non-autonomous form. For the dynamical system under investigation, multi-stability is also thoroughly described. Furthermore, a full inspection of the sensitivity of the perturbed dynamical structure under various initial conditions has been conducted.

Simulation and fabrication of titanium dioxide thin films for supercapacitor electrode applications

Nanostructured thin-film electrode materials are proposed for supercapacitors due to their outstanding performance over bulk materials. In this work, we fabricated a TiO2 nanotube film over a titanium foil using a top-down approach for supercapacitor electrodes. We noticed that the fabricated nanotubes are uniform and well aligned, confirmed by FESEM; the TiO2 nanotube parameters were further simulated using COMSOL Multiphysics. Simulations show an areal capacitance of 1.19393 pF/cm2 with oxidation and reduction peak currents of 6.18921×10[Formula: see text] A and −6.0320×10[Formula: see text] A, respectively, at 10 mV/s scan rate. The as-prepared nanotubes show a poor areal capacitance of 1.0193 F/cm2, which is improved to 12.8764 F/cm2 at a scan rate of 10 mV/s, that is approximately 12.63 times with oxidation and reduction peak currents of 0.129 mA/cm2 and −0.105 mA/cm2, respectively, by performing an electrochemical etching. Further, the surface roughness of both as-prepared and etched samples is studied to comment on their surface area changes. The effect of the etched sample is studied, compared and validated with simulation, which reveals that the etched TiO2 nanotubes thin-film sample shows considerable similarity with the simulation results.

Suppression of Secondary Electron Emissions on the Graphene-Coated Polyimide Materials Prepared by Chemical Vapor Deposition

Polyimide thin-film materials are widely used in aerospace and particle gas pedals, etc., but the phenomenon of secondary electron emission occurred under vacuum conditions. The graphene-coated polyimide materials were prepared for this phenomenon to suppress secondary electron emissions. The graphene coating was prepared on the polyimide surface through chemical vapor deposition (CVD). Scanning electron microscope images (SEM), X-ray photoelectron spectrometer images (XPS), Raman spectroscopy, atomic force microscopy (AFM), and other analytical methods were used to characterize the properties of the prepared materials. The C1s XPS fine spectra and Raman curve analyses showed that the material has an abundant sp2 hybridized structure, and the sp2 structure can reduce secondary electron emissions. The C, O, and N contents in the tested samples were 65.85, 20.47, and 13.68 at.%, respectively. It was examined that the graphene coating had an inhibitory effect on the secondary electron emissions of polyimide materials, and the secondary electron emission yield (SEY) was significantly reduced. The results of secondary electron tests showed that the maximum SEY (δmax) of the polyimide material decreased from 1.72 to 1.52 after the preparation of the graphene coating. The mechanism of using a graphene coating to reduce the SEY of polyimide was analyzed from experimental and theoretical perspectives. The results of this study can provide research ideas for polyimide thin film materials in aerospace, particle gas pedals, and other applications.

Toward the development of a new smart composite structure based on piezoelectric polymer and flax fiber materials: Manufacturing and experimental characterization

Although technologies and processes for creating smart composite structures have been established, significant limitations still necessitate additional research to overcome. Indeed, numerous studies have highlighted the challenges of embedding active elements, often leading to compromises in the structural integrity of smart composite materials. In contrast, this study introduces a novel perspective, offering innovative insights and valuable contributions to the existing knowledge. The primary contribution of this study lies in addressing the critical need for the seamless integration of active materials within composite structures. To demonstrate this, our study considers the potential integration of Polyvinylidene Fluoride (PVDF), a polymer-based piezoelectric material, with pre-impregnated unidirectional flax fibers to produce a smart composite structure. The consolidation molding process was adopted to manufacture the smart composite samples for investigations. Experimental analysis were then considered to evaluate the influence of the embedded PVDF film on the mechanical performance of the structure and to assess the resulting functional properties. X-ray micro-computed tomography and an additional strength-of-material test approach, Interlaminar Shear Strength (ILSS), were performed to explore the impact of the insertion on the integrity of the laminate structure. On the other hand, we conducted vibration tests to assess the electromechanical properties. The tomography results reveal void elimination in the edges of the active material insert, which could be attributed to the choice of thin film materials. Moreover, the ILSS results highlight the minimal impact of PVDF material on mechanical performance, showcasing a mere 0.69% degradation of the material strength. These results are comparable to the recently reported works but with an appreciable margin of improvement. The vibration test response demonstrates the ability of the embedded piezoelectric material to generate voltage, which validates our integration procedure. The smart composite material’s sensitivity to ambient vibrations and its power generation potential show promise for sensing and energy harvesting.