Search Results (96)

Despite the growing preference for solid-state pH sensors due to their advantages over glass pH electrodes, their practical application is still limited by challenges, particularly in metal-oxide based systems. The main issue is their susceptibility to redox-active species such as dissolved oxygen, ascorbic acid, sulfides, and transition-metal ions. In this work, the effects of representative redox interferents, with particular emphasis on ascorbic acid, together with dissolved oxygen and potassium permanganate, were investigated and mitigated through the application of Ta₂O₅/Nafion overlayers. The solid-state metal-oxide pH-sensitive electrodes were fabricated with laser micro-etching of radio-frequency (RF) sputtered RuO₂ thin films deposited on ceramic Al₂O₃ substrates. The resulting RuO₂ electrodes exhibited excellent potentiometric pH sensing characteristics, including near-Nernstian sensitivity (58.8 mV pH⁻¹ at 25 °C), highly linear response over a wide pH range (pH 2–12, R² > 0.9999), minimal hysteresis (1.3 mV), low potential drift (2.9 mV h⁻¹), and fast response times (<30 s). Following on from our previous work, which demonstrated that the Ta₂O₅/Nafion solid-state sensor could measure beverage pH accurately, here we explain why that architecture works by systematically investigating the role of Ta₂O₅ and Nafion in suppressing redox interference and improving measurement stability in complex sample matrices. The results demonstrate that RuO₂ electrodes modified with combined Ta₂O₅/Nafion thin films exhibit significantly enhanced measurement stability compared to unmodified RuO₂ electrodes, owing to effective suppression of potential fluctuations induced by dissolved oxygen and representative redox couples, particularly those associated with ascorbic acid interference. These findings could give a promising strategy for improving the robustness and reliability of solid-state RuO₂-based pH sensors in complex electrochemical environments. Full article

The multilayers of Ta/Pd/[CoFeB (0.3 nm)/Pd]×5/Pd films were fabricated by ultra-high-vacuum (UHV) magnetron sputtering and subsequently annealed at temperatures (T_A) ranging from 100 °C to 400 °C. The magnetic measurements were performed with the applied field oriented parallel and perpendicular to the film plane to evaluate the out-of-plane magnetic anisotropy (PMA). A maximum effective PMA energy density (K_eff) of ≈7.82 × 10⁵ erg/cc and a small out-of-plane saturation magnetisation (M_s⊥) were achieved at the optimal T_A. The evolution of PMA is associated with interfacial atomic migration and oxidation processes, as confirmed by X-ray photoelectron spectroscopy (XPS). Annealing at 300 °C initiates the formation of TaB and TaOB interfacial phases, whereas annealing at 400 °C promotes the enhanced growth of Ta₂O₅ and TaB, along with additional TaOB formation owing to increased oxygen migration. These thermally stable Ta–boride phases lead to pronounced modifications in the magnetic properties. Consequently, oxygen migration and interfacial reactions at elevated temperatures primarily alter the chemical states of the B 1s, Pd 3d, and Ta 4f orbitals, thereby influencing the PMA. The field-dependent electrical resistance (MR) study demonstrates that annealing at 100–400 °C optimises the anisotropic effect in the [CoFeB/Pd]×5-based multilayers. However, higher temperatures can trigger atomic intermixing, which degrades PMA strength and the resistance response. Moreover, the samples were further characterised by their structural, anomalous Hall effect (AHE) and magnetoresonance (MRO) properties. Overall, controlled T_A-driven oxygen diffusion and interfacial oxidation enable effective tuning of the PMA, MR, and MRO properties of ultrathin [CoFeB/Pd]×5 multilayers, highlighting their strong potential for spin–orbit torque (SOT), Dzyaloshinskii–Moriya interaction (DMI), and magnetic skyrmion-based spintronic devices. Full article

This communication discusses the problem of depositing equiatomic metal alloy films. It is shown that this problem can be solved using a magnetron equipped with a target constructed using a new “multilayer target” paradigm. This target, sputtered in an argon environment, consists of several parallel metal plates mounted on the magnetron axis. A method based on the equality of the sputtered fluxes generated by the plates is proposed for calculating the geometric dimensions of the plates. This equality leads to a system of algebraic equations, which are proposed to be solved under the assumption of a uniform discharge current density distribution in the sputtering region of the target. The communication describes two types of targets in which the plates have slots of different shapes. In one case, the slots are shaped as sectors of a ring with a given angle. In the other, the plates are shaped as rings. As examples, the geometric dimensions of targets for a balanced magnetron system intended for the deposition of films of equiatomic Ti_0.33Ta_0.33Nb_0.33 and Ti_0.25Ta_0.25Nb_0.25Mo_0.25 alloys are calculated. The presentation is accompanied by the results of individual experiments. This report is preliminary in nature; experimental verification is ongoing. The application of the new paradigm in magnetron target design facilitates the fabrication of films of nanostructured medium- and high-entropy alloys with specified chemical compositions, which is the central theme of the Special Issue devoted to functional nanomaterials. Full article

Neural interfaces created using thin-film fabrication rely primarily on conductive metal traces for electrical interconnects. Here, we explore the use of tantalum (Ta) metal interconnects as a replacement for noble-metal interconnects such as Au, Pt or Ir. Ta has been investigated previously for interconnect metallization in flexible silicon ribbon cables, but the structure and properties of tantalum for neural device metallization have not been extensively reported. In the present work, Ta metal was sputter-deposited onto amorphous silicon carbide (a-SiC), with and without a base titanium (Ti) adhesion layer, and investigated as interconnect metallization. In the absence of a Ti adhesion layer, resistivity measurements revealed a factor of six difference between Ta resistivity depending on the presence of the Ti base layer, with direct deposition on a-SiC nucleating high resistivity β-Ta (ρ = 197 ± 31 µΩ·cm, mean ± standard deviation) and Ta deposited on Ti nucleating low resistivity α-Ta (ρ = 35 ± 6 µΩ·cm). X-ray diffraction confirmed the existence of the two crystal structures. Ta feature sizes of 2 µm were created using photolithography and reactive ion etching (RIE). Finally, planar microelectrode array test structures using α-Ta and Au trace metallization with low-impedance ruthenium oxide (RuO_x) electrodes were fabricated and investigated by cyclic voltammetry (CV) and current pulsing in saline. These devices underwent 500 CV cycles between −0.6 and +0.6 V without evidence of degradation. In response to charge-balanced, biphasic current pulses at 4 nC/phase, a 21 mV increase in access voltage was observed with α-Ta metallization compared to Au. These results warrant further investigation of Ta as thin-film metallization interconnects for neural interface devices. Full article

Background: Tantalum in cytotoxicity tests showed no toxicity effect, as well as promoting bone regeneration through the differentiation, proliferation, mineralisation and adhesion of osteoblasts in in vitro and in vivo studies. This study aims to determine and compare the chemical composition, roughness and wettability of non-coated commercially pure titanium (CpTi) disc surfaces with CpTi discs that have been coated with tantalum oxynitride film (TaON) via a modified plasma sputtering coating technique. Methods: Two groups were tested that included the TaON-coated CpTi discs and non-coated CpTi discs. A modified reactive plasma sputtering apparatus was used for coating the CpTi discs with TaON at different time durations, i.e., 4, 6, and 8 h. The surface properties of the coated and non-coated discs were studied using X-ray diffraction (XRD) analysis, energy dispersive spectroscopy (EDS), scanning electron microscopy (SEM), and contact angle measurement. Results and Conclusions: The results showed that 8 h was the best coating duration. The XRD analysis showed the presence of a new peak in the case of the TaON-coated CpTi disc that was absent in the non-coated CpTi disc. Furthermore, the SEM analysis revealed that the TaON-coated CpTi disc showed a better distribution of surface roughness compared to the non-coated disc. The non-coated CpTi discs showed lower wettability compared to the TaON-coated CpTi discs. The result shows the importance of a TaON coat in changing the surface properties of CpTi which will be used in dental implants; this result will enhance the idea of surface treatment and its relationship with the enhancement and acceleration of bone formation around dental implants in future. The novelty of the newly modified reactive plasma sputtering technique used in this study as a coating technique for CpTi discs lies in the promising tantalum oxynitride, as Ta had no toxicity effect in cytotoxicity tests and promoted adhesion, proliferation, differentiation, the mineralisation of osteoblasts and bone regeneration in vitro and in vivo. The mean target of the work is to enhance the osseointegration of CPTi dental implants with different surface coatings including Ta oxide, nitride and oxynitride. The results of the first two coatings are already published, and the third coating technique is investigated in this study. Full article

(WMoTaNb)SiN refractory high-entropy nitride films were deposited via magnetron cosputtering, and the Si content was systematically regulated by varying the Si target power to investigate its influence on the microstructure, mechanical properties, oxidation resistance, and oxyhydrogen-flame ablation behavior. All the films exhibited dense columnar architectures with a distinct FCC + BCC dual-phase structure, whereas increasing the Si target power led to a gradual increase in the deposition rate and Si incorporation. The mechanical properties displayed a non-monotonic relationship with the Si target power, with film applied at an intermediate level of Si target power showing the highest hardness, approximately 28.5 GPa, and improved elastic recovery. Tribological evaluations using a GCr15 steel ball revealed that this film exhibited the lowest wear rate of 4.1 × 10⁻⁶ mm³·N⁻¹·m⁻¹ and a narrower wear track, which was attributed to reduced plastic deformation and the development of an oxygen-enriched tribofilm during sliding. High-temperature oxidation at 1000 °C in air revealed that Si incorporation significantly modified oxide-scale evolution by refining the oxidation products and altering the scale architecture, while the protection of the scale was governed by its continuity and compactness rather than its thickness alone. Oxyhydrogen-flame ablation tests revealed that the degradation behavior was primarily driven by the competition between oxidation-induced mass increase and ablation-induced material loss, with localized film disruption and substrate exposure playing a decisive role. In summary, the findings illustrate that an optimal Si target power establishes a favorable equilibrium between mechanical strength, tribological efficiency, oxidation resistance, and ablation performance, underscoring the potential of (WMoTaNb)SiN films for protective applications in complex mechanical and extreme thermal environments. Full article

The structure and composition of a refractory Ni-containing CrMoNbTaVW high-entropy-alloy (HEA) thin film were investigated. The HEA thin film with a thickness of 5 μm was grown via conventional direct current magnetron sputtering from a multiple-elemental compound target. The Ni-containing HEA thin film with a Ni concentration of 3.6 at. % exhibits a single-phase body-centered cubic (BCC) crystal structure with a lattice parameter of a = 0.316 nm. The grains in the HEA thin film are columns, extended in the growth direction. They are not aligned exactly perpendicular to the substrate surface. The thin film grows in a polycrystalline structure with a tendency to preferred orientation or texture. Energy-dispersive X-ray analyses of the HEA thin film show near-equal atomic concentrations of Cr, Mo, Nb, Ta, V, and W elements in the range 15–17 at. % with almost uniform distribution. In contrast, Ni is not uniformly distributed in the film, and grains with a different Ni concentrations were observed. The defects observed in the HEA thin film are mainly single dislocations or an assembly of dislocations, which could be caused by residual stresses in the layer forming during the growth of the HEA thin film. Full article

Machine learning (ML) offers a powerful paradigm for accelerating performance prediction of high-entropy alloys (HEAs). The present study proposed an ML framework based on the ridge regression algorithm for predicting the hardness of MoNbTaW HEA films. By comparing various feature-screening strategies, an optimized feature set comprising three features, namely δG, Λ, and Ω, was selected from 20 candidate physical features. The model based on this feature set exhibited strong predictive performance. In 10-fold cross-validation, R² was 0.86, RMSE was 0.41 GPa and MAE was 0.31 GPa. On the reserved validation set, R² was 0.88, RMSE was 0.37 GPa, and MAE was 0.31 GPa. The model further revealed the influence trends of constituent elements and key features on hardness. By using ML to mine useful information from a dataset of HEA film samples prepared via magnetron sputtering, this work provides an approach for rapid and cost-effective design of HEAs. Full article

This study focused on the measurement requirements of Digital Image Correlation (DIC) in high-temperature environments of aero-engines and systematically investigated the applicability and stability of high-temperature speckle materials. Five common coating materials (Ti, TiN, Ta, NiCr alloy, and SiC) were selected. Corresponding thin films were deposited on Al₂O₃ ceramic substrates using magnetron sputtering technology, and their surface color evolution from room temperature up to 1200 °C was examined. The film compositions were analyzed by Raman spectroscopy and X-ray photoelectron spectroscopy (XPS), revealing the mechanisms behind the color changes. The results indicate that Ti, TiN, Ta, and NiCr alloy exhibit significant color variations, which leads to insufficient color contrast for high-temperature speckle patterns. Further investigation shows that depositing an outer SiO₂ coating can improve surface scattering and reflection, while also inhibiting oxygen penetration, thereby enhancing oxidation resistance and improving speckle contrast. The SiC/SiO₂ composite structure demonstrates excellent thermal stability, making it an ideal speckle material for high-temperature DIC measurements. Full article

Tantalum nitride (TaN) coatings are valued for their hardness, chemical inertness, and biocompatibility; however, they lack intrinsic antibacterial properties, which limits their application in biomedical environments. Introducing copper (Cu) into the TaN matrix offers a potential solution by combining TaN’s mechanical and chemical durability with Cu’s well-documented antimicrobial action. This study explores how varying copper incorporation affects the structural, electrical, photocatalytic, and antibacterial characteristics of TaCuN multilayer films synthesized via reactive magnetron sputtering. Three thin TaCuN films were fabricated using a high-power reactive magnetron co-sputtering system, varying the Cu target power to control the composition. Structural and morphological analysis was performed using X-ray diffraction (XRD), scanning/transmission electron microscopy (STEM/TEM), and energy-dispersive X-ray spectroscopy (EDS). Electrical conductivity was studied along and across the film surfaces at temperatures ranging from 20 to 375 K using AC impedance spectroscopy. Optical and photocatalytic properties were assessed using UV–Vis spectroscopy and methylene blue degradation tests. Antibacterial activity against Staphylococcus aureus was analyzed under visible light using CFU reduction tests. XRD and TEM analyses revealed a multilayered four-zone architecture with alternating Ta-, Cu-, and N-rich phases and a dominant cubic δ-TaN pattern. The layers exhibited pronounced conductivity anisotropy, with in-plane conductivity (~10³ Ω⁻¹ cm⁻¹) exceeding cross-plane conductivity by ~10⁷ times, attributed to the formation of a metallic conduction channel in the mid-layer. Optical spectra indicated limited light absorption above 300 nm and negligible photocatalytic activity. Increasing the Cu content substantially enhanced antibacterial efficiency, with the highest-Cu sample achieving 95.6 % bacterial growth reduction. Morphological evaluation indicated that smooth film surfaces (Ra < 0.2 μm) effectively minimized bacterial adhesion. Reactive magnetron sputtering enables the precise engineering of TaCuN multilayers, combining high electrical anisotropy with robust antibacterial functionality. The optimized TaCuN coating offers promising potential in biomedical and protective applications where both conductivity and microbial resistance are required. Full article

Refractory metals typically exhibit limited room temperature ductility, hampering their widespread application. Recent advances in refractory high-entropy alloys have focused on finding optimum combinations of strength and ductility but require exploring vast compositional spaces. To facilitate such a search process, a method for fast assessment of intrinsic ductility would be highly advantageous. Herein, we propose a novel approach to screen for a refractory alloy’s ‘intrinsic ductility’ by leveraging the established technique of thin film fragmentation testing, which has been successfully used to evaluate stretchability of flexible electronics. We conducted in-depth investigations of sputtered tungsten thin films to identify the processing-induced extrinsic variables that can affect the crack onset strain (COS) under uniaxial loading. By tuning the process parameters for film deposition, Nb, Mo, Ta and W samples were fabricated with comparable thicknesses and residual stress levels. The films’ COS values were compared to the ductility levels of bulk counterpart materials, and the conditions for meaningful comparison are discussed. This approach offers a simple, inexpensive, and rapid means of screening based on relative intrinsic ductility of thin metal films and should also be applicable to the study of high-entropy alloy films. Full article

Reactive co-sputtering was applied to deposit TaN-(Ag,Cu) nanocomposite films on Si and tool steels. Prior to post-deposition annealing, the films were deposited with TaN cap (diffusion barrier) layers in various thicknesses in order to slow down the nucleation and growth of emerging Ag and Cu particles. The thickness of the cap layers was set at 5, 10, 20, or 50 nm. The films were then annealed using Rapid Thermal Annealing (RTA) at 400 °C to induce the nucleation and growth of Ag and Cu nanoparticles. These films’ surface morphologies and structures were examined. The samples were tested for their anti-wear and antibacterial behaviors against Gram-positive S. aureus and Gram-negative E. coli, with a variation in cap layer thickness. It is found that, through the application of TaN cap layers, the out-diffusion of Ag and Cu atoms may be slowed down. The surface concentrations of Ag and Cu might decrease from 35 at.% and 17 at.% to 18 at.% and 6 at.%, respectively, when the cap layer thickness increases to 50 nm (after being annealed for 12 min). The diffusion mechanism is proposed to explain the formation of nanoparticles on the surface through boundary diffusion. Antibacterial behaviors against both bacteria, as well as tribological properties, could still be effective but become less significant with an increase in the cap layer thickness. The antibacterial efficiency after 3 h testing decreased from 99% to 5% and 8% against E. coli and S. aureus, respectively. At 12 h, all the samples reached >99% antibacterial efficiency, despite the variation in cap thickness. For sliding wear, the wear rate was doubled when the cap thickness increased to 50 nm (when the normal load was 1 N). On the other hand, the difference was minor when the normal load was changed to 5 N. The sliding lifetime of the samples was studied using a tribometer. The total lifetime may increase with an increase in the cap thickness. The wear is found to be due to the oxidation of Ag and Cu nanoparticles, which results in the loss of low coefficient behaviors. Full article

In this study, the electrochemical corrosion behavior of TiAlZrTaNb nitride thin films deposited on 304 stainless steel substrates was investigated. The thin films were synthesized using high-power impulse magnetron sputtering (HiPIMS) and are classified as high-entropy alloys (HEAs). The microstructure, morphology, and chemical composition of the coatings were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy-dispersive X-ray spectroscopy (EDS), respectively. Corrosion resistance was evaluated through electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization tests, employing tap water, acetic acid, and citric acid solutions at room temperature as electrolytes. The results demonstrated that the TiAlZrTaNbN coating exhibits a dense and homogeneous structure with a uniform elemental distribution. XRD analysis revealed the presence of face-centered cubic (FCC) crystalline phases, which significantly contribute to the coating’s corrosion resistance. Furthermore, the coating displayed exceptional corrosion performance in both acetic acid and citric acid electrolytes—simulating food environments with a pH ≤ 4.5—as revealed by a substantial reduction in corrosion current density and a positive shift in corrosion potential. These findings provide valuable insights into the properties of TiAlZrTaNbN coatings and underscore their potential for enhancing the durability of mechanical components employed in the food industry. Full article

Tantalum nitride (TaN) is a typical transition metal nitride characterized by a wide range of tunable resistivity. Low-resistance TaN even exhibits a resistivity similar to that of metals. Given that electrical resistance influences secondary electron emission (SEE) behavior, this study investigates the relationship between TaN film resistivity and SEE characteristics. Five TaN films were deposited by varying the N₂ gas flow rate during sputtering. Morphological analyses revealed that the film thicknesses ranged from approximately 197 to 281 nm. X-ray photoelectron spectroscopy (XPS) results indicated that the Ta:N atomic ratio of the films ranged from approximately 0.53 to 0.87. Furthermore, XPS detected non-adsorbed oxygen on the surfaces of the TaN films, and more detailed XPS analysis revealed the formation of TaON compounds on the surfaces due to oxygen exposure. X-ray diffraction patterns confirmed that the TaN films contained two crystal phases: Ta₂N (002) and TaN (200). Sheet resistivity tests showed that the resistivity of the TaN films ranged from 5.67 × 10⁻³ to 2.43 Ω·cm. Furthermore, the lower the Ta:N atomic ratio was, the lower the electrical resistivity of the films became. SEE coefficient (SEEC) showed a clear positive correlation with the films’ electrical resistivity. Specifically, films with lower resistivity exhibited reduced SEEC values. When the N₂ gas flow rate was 16 sccm (N₂:Ar = 16:0), the film exhibited the smallest SEEC (maximum ~1.88); when the N₂ flow rate was 0 sccm (N₂:Ar = 0:16), the film showed the largest SEEC (maximum ~2.25). This research provides valuable references for expanding the application of TaN films in engineering scenarios involving electrical resistivity adjustment and SEE applications. Full article

The interfacial Dzyaloshinskii–Moriya interaction (DMI) plays a pivotal role in stabilising and controlling the motion of chiral spin textures, such as Néel-type bubble domains, in ultrathin magnetic films—an essential feature for next-generation spintronic devices. In this work, we investigate domain wall (DW) dynamics in magnetron-sputtered Ta(3 nm)/Pt(3 nm)/Co(1 nm)/RuO₂(1 nm) [Ru(1 nm)]/Pt(3 nm) multilayers, benchmarking their behaviour against control stacks. Vibrating sample magnetometry (VSM) was employed to determine saturation magnetisation and perpendicular magnetic anisotropy (PMA), while polar magneto-optical Kerr effect (P-MOKE) measurements provided coercivity data. Kerr microscopy visualised the expansion of bubble-shaped domains under combined perpendicular and in-plane magnetic fields, enabling the extraction of effective DMI fields. Brillouin light scattering (BLS) spectroscopy quantified the asymmetric propagation of spin waves, and micromagnetic simulations corroborated the experimental findings. The Pt/Co/RuO₂ system exhibits a Dzyaloshinskii–Moriya interaction (DMI) constant of ≈1.08 mJ/m², slightly higher than the Pt/Co/Ru system (≈1.03 mJ/m²) and much higher than the Pt/Co control (≈0.23 mJ/m²). Correspondingly, domain walls in the RuO₂-capped films show pronounced velocity asymmetry under in-plane fields, whereas the symmetric Pt/Co/Pt shows negligible asymmetry. Despite lower depinning fields in the Ru-capped sample, its domain walls move faster than those in the RuO₂-capped sample, indicating reduced pinning. Our results demonstrate that integrating RuO₂ significantly alters interfacial spin–orbit interactions. Full article