Thin Film Materials Research Articles

Interplanetary Student Nanospacecraft: Development of the LEO Demonstrator ESTCube-2

Nanosatellites have established their importance in low-Earth orbit (LEO), and it is common for student teams to build them for educational and technology demonstration purposes. The next challenge is the technology maturity for deep-space missions. The LEO serves as a relevant environment for maturing the spacecraft design. Here we present the ESTCube-2 mission, which will be launched onboard VEGA-C VV23. The satellite was developed as a technology demonstrator for the future deep-space mission by the Estonian Student Satellite Program. The ultimate vision of the program is to use the electric solar wind sail (E-sail) technology in an interplanetary environment to traverse the solar system using lightweight propulsion means. Additional experiments were added to demonstrate all necessary technologies to use the E-sail payload onboard ESTCube-3, the next nanospacecraft targeting the lunar orbit. The E-sail demonstration requires a high-angular velocity spin-up to deploy a tether, resulting in a need for a custom satellite bus. In addition, the satellite includes deep-space prototypes: deployable structures; compact avionics stack electronics (including side panels); star tracker; reaction wheels; and cold–gas propulsion. During the development, two additional payloads were added to the design of ESTCube-2, one for Earth observation of the Normalized Difference Vegetation Index and the other for corrosion testing in the space of thin-film materials. The ESTCube-2 satellite has been finished and tested in time for delivery to the launcher. Eventually, the project proved highly complex, making the team lower its ambitions and optimize the development of electronics, software, and mechanical structure. The ESTCube-2 team dealt with budgetary constraints, student management problems during a pandemic, and issues in the documentation approach. Beyond management techniques, the project required leadership that kept the team aware of the big picture and willing to finish a complex satellite platform. The paper discusses the ESTCube-2 design and its development, highlights the team’s main technical, management, and leadership issues, and presents suggestions for nanosatellite and nanospacecraft developers.

Capturing the Dynamics of Ti Diffusion Across TixW1−x/Cu Heterostructures using X‐Ray Photoelectron Spectroscopy

AbstractInterdiffusion phenomena between adjacent materials are highly prevalent in semiconductor device architectures and can present a major reliability challenge for the industry. To fully capture these phenomena, experimental approaches must go beyond static and post‐mortem studies to include in situ and in‐operando setups. Here, soft and hard X‐ray photoelectron spectroscopy (SXPS and HAXPES) is used to monitor diffusion in real‐time across a proxy device. The device consists of a Si/SiO2/TixW1−x(300 nm)/Cu(25 nm) thin film material stack, with the TixW1−x film (x = 0.054, 0.115, 0.148) acting as a diffusion barrier between Si and Cu. The interdiffusion is monitored through the continuous collection of spectra whilst in situ annealing to 673 K. Ti within the TiW is found to be highly mobile during annealing, diffusing out of the barrier and accumulating at the Cu surface. Increasing the Ti concentration within the TixW1−x film increases the quantity of accumulated Ti, and Ti is first detected at the Cu surface at temperatures as low as 550 K. Surprisingly, at low Ti concentrations (x = 0.054), W is also mobile and diffuses alongside Ti. By monitoring the Ti 1s core level with HAXPES, the surface‐accumulated Ti was observed to undergo oxidation even under ultra‐high vacuum conditions, highlighting the reactivity of Ti in this system. These results provide crucial evidence for the importance of diffusion barrier composition on their efficacy during device application, delivering insights into the mechanisms underlying their effectiveness and limitations.

Nanostructured CuO Thin-Film-Based Conductometric Sensors for Real-Time Tracking of Sweat Loss.

Enhanced sweat sensors lead to real-time, sustained, noninvasive tracking of sweat loss, ensure insight into individual health conditions at the molecular level, and have obtained prominent interest for their hopeful implementations in customized health tracking. Metal-oxide-based nanostructured electrochemical amperometric sensing materials are the best selection for continuous sweat monitoring devices owing to their high stability, high-sensing capacity, cost-effectiveness, miniaturization, and wide applicability. In this research, CuO thin films have been fabricated by successive ionic layer adsorption and reaction technique (SILAR) with and without the addition of Lawsonia inermis L. (Henna, (LiL)) leaf extract (C10H6O3, 2-hydroxy-1,4-naphthoquinone) with a high-sensitive and rapid response for sweat solution. Despite the pristine film being responsive to the 65.50 mM sweat solution (S = 2.66), the response characteristic improves to 3.95 for the 1.0% LiL-implemented CuO film. Unmodified, 1.0% LiL and 3.0% LiL-substituted thin-film materials assure considerable linearity with linear regression ranges, R2, of 0.989, 0.997, and 0.998, respectively. It is noteworthy here that this research aims to determine an enhanced system that could potentially be implemented in real-life sweat-tracking administrations. Real-time sweat loss tracking capabilities of CuO samples was found to be promising. Derived from these outcomes, we concluded that the fabricated nanostructured CuO-based sensing system is a useful application for the continuous observation of sweat loss as a biological argument and compatibility with other microelectronic technologies.

New optical soliton solutions of thin-film ferroelectric material equation via the complete discrimination system method

In this paper, our main aim is to construct the optical soliton solutions of the well-known thin-film ferroelectric material equation, which describes the propagation of polarization in thin-film materials. Because it has been found that solitary waves may be important for the propagation of polarization fields in ferroelectrics, we investigate its optical soliton solutions using the complete discrimination system technique in this study. As a result, the optical soliton solutions and various solutions are acquired, covering the elliptic double periodic function solution, Jacobian elliptic function solution etc. It appears that bright and singular waves can be propagated in thin-film ferroelectric materials. The richness of the solutions obtained will be conducive to further understand the whole picture of the dynamic behavior of wave propagation in thin-film material. Moreover, this research methods and results are efficacious and can be applied to the exploration of more complex phenomena. Finally, via giving some fixed parameter values, we plot 3D, 2D, density and contour graphs of some obtained solutions for presenting in visual form.

Magnetic Materials, Thin Films and Nanostructures

In this first volume, we cover relevant aspects of chemical and physical processes of the production and characterization of magnetic materials in bulk, thin films, nanostructures, and/or nanocomposites, as well as modeling aspects involving such structures. Accordingly, this volume presents eleven original research and review works on the challenges and trends covering fundamental and experimental work, with a special focus on the design, synthesis, and characterization of various types of magnetic materials, and the study of their structure–property relationships. State-of-the-art results on the development of new experimental concepts, leading to the transfer, chemical transformation, and high-resolution patterning of advanced thin films and nanomaterials, and to the design and fabrication of devices, are also presented and discussed.

Influence of Co-Content on the Optical and Structural Properties of TiOx Thin Films Prepared by Gas Impulse Magnetron Sputtering

Nonstoichiometric (Ti,Co)Ox coatings were prepared using gas-impulse magnetron sputtering (GIMS). The properties of coatings with 3 at.%, 19 at.%, 44 at.%, and 60 at.% Co content were compared to those of TiOx and CoOx films. Structural studies with the aid of GIXRD indicated the amorphous nature of (Ti,Co)Ox. The fine-columnar, homogeneous microstructure was observed on SEM images, where cracks were identified only for films with a high Co content. On the basis of XPS measurements, TiO2, CoO, and Co3O4 forms were found on their surface. Optical studies showed that these films were semi-transparent (T > 46%), and that the amount of cobalt in the film had a significant impact on the decrease in the transparency level. A shift in the absorption edge position (from 337 to 387 nm) and a decrease in their optical bandgap energy (from 3.02 eV to more than 2.60 eV) were observed. The hardness of the prepared films changed slightly (ca. 6.5 GPa), but only the CoOx film showed a slightly lower hardness value than the rest of the coatings (4.8 GPa). The described studies allowed partial classification of non-stoichiometric (Ti,Co)Ox thin-film materials according to their functionality.

Synthesis and characterization of pure and Cu-doped WO3 thin films for high performance of toxic gas sensing applications

Oxygen vacancies and the high surface area of nanostructured materials offers stronger gas adsorption active sites for improved gas sensing performance. In the present work, we have deposited WO3-based thin films using a chemical spray pyrolysis technique at a substrate temperature of 400 °C with other optimized preparation parameters. Besides, this study reports the influence of Cu doping at various weight percentages on the structural, morphological, optical and toxic gas sensing properties of WO3 films in detail. The crystalline structure of the material was investigated using the X-ray diffraction technique. Each X-ray diffraction analysis of the films demonstrated a polycrystalline nature, matching the hexagonal phase of WO3 with the (200) plane of preferential orientation of crystal growth. The optical characteristics of the thin film's material were analyzed by UV–Vis absorption spectroscopy. The optical energy bandgap (Eg) of the deposited thin films was estimated using the Tauc relation, and the value was decreased along with the increase in the Cu-doping concentration. The surface roughness of the films has been investigated using atomic force microscopy. The TEM patterns of sprayed Cu-doped WO3 thin films exhibit nanocrystalline features. Detecting toxic gasses is of great importance across the globe due to an alarming enhancement in respiratory, ocular, skin, and lung diseases. Hence, cost-effective and room temperature-operated Cu-doped WO3 thin film sensors to trace low concentrations of toxic gasses have been investigated and systematically reported. It is observed that the sensor response is to be increased with the increase in Cu-doping concentration, particularly the 4 wt.% Cu-doped sensor exhibited a response value of 7.2 and fast response and recovery times in the presence of 50 ppm ammonia vapor.

Orthogonal‐Stacking Integration of Highly Conductive Silicide Nanowire Network as Flexible and Transparent Thin Films

AbstractFlexible and transparent conductive (FTC) thin films are indispensable elements in building high‐performance flexible or soft electronics and displays. Slim inorganic nanowires (NWs), with excellent conductivity and durability, are ideal one‐dimensional ingredients to weave a quasi‐continuous FTC network. However, a precise spatial arrangement of these ultrathin NWs, to form an optimal interconnected network, represents still a difficult challenge. In this work, a catalytic growth of orderly SiNW arrays, via an in‐plane solid‐liquid‐solid mechanism, and an orthogonal‐stacking integration of the SiNWs into a 2‐layer cross‐linked network, followed by a direct alloy formation and soldering of highly conductive SiNi alloy NWs upon a flexible polyimide polymer, is demonstrated. It is also shown that the flexibility of the SiNi FTC network can be significantly enhanced with an elastic spring design of the silicide NW channels, leading to an impressive transmittance of ≈90%, a moderately equivalent sheet resistance of 130 Ω sq−1 and a durable flexibility that can sustain repetitive bending to a 2 mm radius for >1000 cycles. These results highlight the unique capabilities of an optimal spatial arrangement, precise assembly/soldering and elastic geometry design of alloy NWs to enable a new generation of high‐performance FTC thin film material for future flexible electronics, displays, and bio‐interfaced sensors.

A Combinatorial Approach for the Solution Deposition of Thin Films

Optimization of thin film deposition is often the limiting step in the discovery of new materials and device development. Over the years, high-throughput combinatorial methods were developed for the deposition of thin films from the gas phase. However, very few reports focused on combinatorial thin film deposition from solution. Here, we introduce a combinatorial approach for the deposition of thin films from solution. The flow deposition setup allows for simultaneously studying the effect of two critical parameters, deposition time and deposition temperature, on a single sample. As a proof of concept, we demonstrate the solution deposition of PbS thin films, which resulted in a library of 25 deposition condition combinations on a single GaAs (100) substrate. X-ray diffraction and scanning electron microscopy combined with focused ion beam cross-sectional sample preparation confirmed the formation of high-quality PbS films and showed the morphology evolution as a function of these two deposition parameters. This method can be easily adapted for cost-effective and rapid combinatorial studies of a large variety of solution-deposited thin film materials.

Improvement of some physical and magnetic properties of nanocrystalline Fe15–Ni85/ITO thin films by galvanostatic pretreatment process

In this research, a comparative study on some physical and magnetic properties of nanocrystalline Fe15–Ni85 thin films with and without galvanostatic pretreatment (GPT) process deposited on conductive and transparent indium tin oxide substrates using the electrodeposition method is carried out. The films exhibit the non-preferential deposition of more noble Ni. The films, irrespective of the GPT process, show a single face-centered cubic structure with the preferential orientation of crystallites along the (111) plane. The Ni-Fe thin film with the GPT exhibits a smaller crystallite size and a stronger [111] texture than the Ni-Fe thin film without the GPT. The films exhibit in-plane magnetic hysteresis loops with a magnetic squareness ratio of about 0.10 ± 0.01 independent of the GPT. The main advantages of the Ni-Fe thin film with the GPT are the smooth surface with smaller particles and the in-plane magnetization, which shows a significant reduction of the coercive field. The results obtained in this study are expected to be useful for future experimental studies of Ni-Fe thin film materials.

Analytical and experimental investigation of the mode-II energy release rate of electrodes using a plasticity-assisted zero-degree peeling configuration

Lithium-ion batteries integrate heterogeneous materials such as active layers and current collectors, resulting in interfaces prone to delamination during the charge/discharge process. The mode-II energy release rate is a key index to evaluate the interfacial adhesion properties and structural integrity of electrodes. In this study, an analytical model considering the energy balance principle and a nonlinear constitutive model was established to characterize the mode-II energy release rate. A novel plasticity-assisted zero-degree peeling test (PAZDPT) is proposed to obtain a stable crack propagation stage where the peeling force is determined to calculate the mode-II energy release rate. Several parameter studies were conducted to verify the approximation of the stress distributions and simplification of the analytical model. The accuracy of the analytical model was validated against finite-element calculations. The results demonstrated an excellent agreement between the theoretical calculation and numerical results. Moreover, PAZDPT is conducive to steady crack propagation because it restricts the energy accumulation around the crack tip. The analytical model and newly proposed PAZDPT can also be extended to determine the mode-II energy release rate of other types of interfaces in bilayer thin-film materials.

Adsorption of Tannic Acid onto Gold Surfaces

Thin film coatings are widely applicable in materials for consumer products, electronics, optical coatings, and even biomedical applications. Wet coating can be an effective method to obtain thin films of functional materials, and this technique has recently been studied in depth for the formation of bioinspired polyphenolic films. Naturally occurring polyphenols such as tannic acid (TA) have garnered interest due to their roles in biological processes and their applicability as antioxidants, antibacterial agents, and corrosion inhibitors. Understanding the adsorption of polyphenols to surfaces is a core aspect in the fabrication processes of thin films of these materials. In this work, the adsorption of TA to gold surfaces is measured using a quartz crystal microbalance with dissipation monitoring (QCMD) and surface plasmon resonance (SPR) for a wide range of TA concentrations. The adsorption kinetics, aggregation, and stability of TA solutions in physiological-like conditions are studied. Unexpectedly, it is found that the adsorption rates depend only weakly on concentration because of the presence of TA aggregates that do not adsorb. The mechanism of layer formation is also investigated, finding that TA monolayers readily adsorb onto gold with flat or edge-on molecular orientations dependent on the solution concentration. A mix of orientations in the intermediate case leads to slow multilayer adsorption.

Minimization of the electrical contact resistance in thin-film thermoelectric device

High electrical contact resistance refrains the performance of thin-film thermoelectric devices at the demonstrative level. Here, an additional Ti contact layer is developed to minimize the electrical contact resistance to ∼4.8 Ω in an as-assembled thin-film device with 50 pairs of p–n junctions. A detailed interface characterization demonstrates that the low electrical contact resistance should be mainly attributed to the partial epitaxial growth of Bi2Te3-based thin-film materials. Correspondingly, the superlow electrical contact resistance facilitates the applicability of the out-of-plane thin-film device and results in an ultrahigh surface output power density of ∼81 μW cm−2 at a low temperature difference of 5 K. This study illustrates the Ti contact layer that strengthens the contact between Cu electrodes and Bi2Te3-based thermoelectric thin films mainly through partial epitaxial growth and contributes to high-performance thin-film thermoelectric devices.

Effect of Ag content on friction and wear properties of TiCN/Ag films in different service environments

Thin-film materials require improved performance to withstand complex and harsh environments as the modern industry evolves. In this study, a series of TiCN/Ag films were fabricated to enhance the frictional properties of the films and extend the lifetime of friction sliding components. The microstructure, mechanical properties, friction, and wear properties of the films were investigated in different service environments. The results showed that the film comprised fcc-TiN, fcc-Ag, amorphous carbon, and amorphous carbon nitride. As the Ag content increased, the hardness of the film first increased, then decreased rapidly, after which the decreasing trend became stable. When the Ag content was 1.8 at%, the optimal hardness and elastic modulus of the films were 29.7 GPa and 228.09 GPa, respectively. Under oil lubrication conditions, Ag atoms can catalyze the formation of a highly graphitized carbon-based friction film on the TiCN/Ag worn surface, thereby enhancing the friction and wear properties of the films. In the air friction, the soft-phase Ag with a low shear modulus acts as a lubricant, and the friction coefficient decreases with an increase in Ag content; however, the consumption of Ag during friction increases the wear rate. In the 3.5 wt% NaCl solution, as the Ag content increased, the surface roughness and corrosion current of the film increased, while the corrosion potential and resistance of the film decreased, resulting in an increase in the friction coefficient and wear rate.

The electromigration study of thin-film structured Sn3.5Ag and Ag using continuous observation and reliability enhancement approach

Thin-film materials have been widely used in advanced technologies because of their flexible structure and superior working performance. However, the reliability of thin films that are employed in electronic devices has become an increasing concern. In this study, thin-film-structured Ag and Sn3.5Ag samples were prepared to observe their reliability behaviors during electromigration (EM) tests at low and high current densities. Under a low current density (8.89 × 104 A/cm2), the Ag stripe shows good resistance to EM, and microstructural changes are only observed in the Sn3.5Ag sample. In the high current density test (8.89 × 105 A/cm2), the microstructures of both samples undergo a significant change; however, the Ag sample shows superior performance than the Sn3.5Ag sample in terms of total experimental duration. Ag exhibits a better EM resistivity than Sn3.5Ag owing to the difference in EM activation energy causing the difference in atomic diffusivity. Moreover, it shows that pre-heating is an efficient method to enhance the EM resistivity of thin-film metals. The findings of this study provide a criterion for manufacturers to select suitable thin-film metals as far as EM is concerned and how to minimize the impact due to EM.

Suppression of Strain Relaxation in VO2/TiO2 Multilayered Films

Strained VO2 films grown on (001) rutile TiO2 exhibit an abrupt insulator-to-metal transition (IMT) around room temperature. The transition temperature (Tc) increases when the critical thickness of ∼15 nm is exceeded. The strain relaxation is responsible for crack formation. Here, we show that inserting thin TiO2 layers suppresses the strain relaxation of VO2. We fabricated several VO2/TiO2/VO2 trilayer films on (001) TiO2 substrates. Each film had a VO2 film of 8 nm, but the TiO2 thickness was varied. Strained VO2/TiO2 multilayer films show IMT with clear hysteresis around room temperature when the TiO2 thickness exceeds 4 nm. In addition, we fabricated 8 nm thick VO2/9 nm thick TiO2 multilayered films. Tc is maintained around room temperature even though the total VO2 thickness is ∼50 nm. The present results provide a useful design concept of thin-film materials for thermochromic applications of strained VO2.

Thin-Film Coupling Membrane

When using ultrasonic probes with removable wedges, the acoustic coupling between wedge and probe is usually effected by means of a gel or grease. This tends to evaporate over time and requires occasional replacement of the gel. In manual ultrasonic testing, where the kit is disassembled daily or when the wedges are often replaced with different angled wedges, this is not usually a problem. However, in a production environment where the same probe and wedge may be used for several days at a time, the requirement to re-couple the probe to the wedge might be inconvenient. This paper provides a description of a solid thin-film coupling material that can significantly prolong the interval between re-coupling.

A Comparative Investigation on the Microstructure and Thermal Resistance of W-Film Sensor Using dc Magnetron Sputtering and High-Power Pulsed Magnetron Sputtering

Traditional dc magnetron sputtering has a low ionization rate when preparing metallic thin films. With the development of thin film science and the market demand for thin film material applications, it is necessary to improve the density of magnetron-sputtered films. High-power pulsed magnetron sputtering (HiPIMS) technology is a physical vapor deposition technology with a high ionization rate and high energy. Therefore, in this work, HiPIMS was applied to prepare metallic tungsten films and compare the surface morphology and microstructure of metallic tungsten films deposited using HiPIMS and dc magnetron sputtering (dcMS) technology under different pulse lengths, as well as related thermal resistance performance, followed by annealing treatment for comparative analysis. We used AFM, SEM, XRD, and plasma characterization testing to comprehensively analyze the changes in the TCR value, stability, repeatability and other related performance of the metallic tungsten thin-film sensor deposited by the HiPIMS technology. It was determined that the thin film prepared by the HiPIMS method is denser, with fewer defects, and the film sensor was stable. The 400 °C annealed sample prepared using HiPIMS with a 100 μs pulse length reaches the largest recorded TCR values of 1.05 × 10−3 K−1. In addition, it shows better stability in repeated tests.

Analytical solitary wave solutions of a time-fractional thin-film ferroelectric material equation involving beta-derivative using modified auxiliary equation method

The main objective of current paper is to examine the impacts of fractional parameters on the dynamic response of soliton waves in a nonlinear time-fractional thin-film ferroelectric materials equation (TFFEME). To achieve such a goal, the TFFEME is first rehabilitated into ordinary differential equation using a complex wave transformation. Solitary wave solutions of the governing equation, representing the dynamics of waves in the material and plays a vital rule in many branches of physics and hydrodynamics, are then constructed through applying the modified auxiliary equation method (MAEM). The extracted solutions are demonstrated using definition of the beta derivative to understand their dynamical behavior. The hyperbolic, periodic and trigonometric function solutions are used to derive the analytical solutions for the given model. As a result, dark, bright, periodic and solitary wave solitons are obtained. The fractional impact of the above derivative on the physical phenomena is observed. The 2D and 3D graphs are also shown to confirm the behavior of analytical wave solutions.

Ordered LiFe5O8 thin films prepared by pulsed laser deposition as an anode material for all-solid thin film batteries

The search for obtaining a Co free low-cost and high-capacity anode thin film material for high energy density all-solid thin film batteries has been driving the increasing innovation and research in Li-ion battery (LIB) technology. In the present case, LiFe5O8 (LFO) thin films are prepared by pulsed laser deposition (PLD) technique and their electrochemical properties, Li ion dynamics, conducting processes at various frequencies and current rates are explored. LFO thin films are seen to crystallize in ordered α -phase with an inverse spinel structure. Chemical state of all the elements is analysed using X-ray photoelectron spectroscopy method. Cyclic voltammeter (CV) study carried out between 0–3 V shows the reduction peak at 0.76 V initially and in the later cycles at 0.86 V with a small shift depicting the exact conversion type behaviour of the LFO thin film. LFO thin film exhibits specific discharge capacity of 25 μAh/cm2 at 10 μA/cm2 current density during the first cycle. Rate capability measurements are carried out at various current densities of 10, 20, 30, 40, 50 and 10 μA/cm2. Li-ion diffusion coefficient during the de-lithiation and lithiation process is seen to be 3.78 × 10−14 cm2/s and 1.41 × 10−13 cm2/s, respectively. CV studies at various scan rates indicates that the mechanism of Li+ storage is dominated by a diffusion-controlled process at low scan rates and with increasing scan rate it becomes a surface-controlled process. Electrochemical impedance studies at various frequencies shows the decrease in charge transfer resistance with increasing cycles. Combined structural, chemical, electrochemical and impedance studies of LFO thin films indicates that these films can be employed for fabricating Co and Ni free all-solid thin film Li-ion batteries for energy storage applications.