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Electrolytic capacitors are known to be fast devices with very low time constant and able to deliver high power. This class of capacitors is then an interesting technology to power miniaturized embedded electronics for Internet of Things applications. However, the current electrolytic capacitor suffers from its bulky size that does not fit with the miniaturization. To solve this issue, a proof‐of‐concept consisting of miniaturizing an electrolytic capacitor based on tantalum materials to give rise to a new class of electrolytic micro‐capacitors is proposed. To reach this ambitious objective, thin films (<100 nm) of tantalum metal (Ta), tantalum nitride (TaN), and tantalum oxide (Ta2O5) are deposited on a Si substrate by sputtering deposition method. After a careful optimization of the deposition parameters, Ta/Ta2O5 and TaN/Ta2O5 electrodes (Ta and TaN ≈45 nm and Ta2O5 ≈25 nm) and study their behaviors when biased at high voltage (>20 Volts) in aqueous electrolyte are produced. The Ta/Ta2O5 and TaN/Ta2O5 interfaces when the electrode is polarized near and beyond the breakdown voltage of the dielectric layer are carefully investigated. Polarizing the electrodes beyond the breakdown voltage are shown to result in anodization‐like mechanisms. In the case of the TaN/Ta2O5 electrode, an N‐rich porous layer grew within the Ta2O5 layer as polarization increased. A comparative study on the 2 stacked layers electrodes with different compositions (Ta/Ta2O5 and TaN/Ta2O5) but similar thicknesses (45/25 nm) is carried out: both electrodes show excellent capacitance retention of over 90% over 300 000 cycles. The frequency behavior of Ta/Ta2O5 and TaN/Ta2O5 electrodes shows that both are potential candidates in electrolytic micro‐capacitors for powering miniaturized electronics. [ABSTRACT FROM AUTHOR]

Proton Exchange Membrane Fuel Cells (PEMFCs) are promising technology to convert chemical energy from dihydrogen in electrical energy. HT-PEMFCs are working at high temperatures (above 120 °C) and with doped orthophosphoric acid H3PO4 PBI membranes. In such devices, bipolar metallic plates are used to provide reactive gas inside the fuel cell and collect the electrical current. The metallic elements used as bipolar plates, end plates, and interconnectors in acid electrolyte and gaseous fuel cells are severely damaged by a combination of oxidation (due in particular to the use of oxygen, whether pure or contained in the air) and corrosion (due in particular to acid effluents from the electrolyte). This degradation rapidly leads to the loss of the electrical conductivity of the metallic elements and today requires the use of very specific alloys, possibly coated with pure gold. The solution investigated in the present study is the use of a protective coating based on single-phase nitrides obtained by reactive magnetron sputtering or reactive HiPIMS (High-Power Impulse Magnetron Sputtering). The influence of the microstructure on the physical–chemical properties was studied. The electrochemical properties were quantified following two approaches. First, the corrosion current of the developed coatings was measured at room temperature and at higher temperatures using the Linear Sweep Voltammetry (LSV) technique. Then, Electrochemical Impedance Spectroscopy (EIS) measurements were performed to better identify and evaluate their corrosion-resistance performances. [ABSTRACT FROM AUTHOR]

This work presents the modification of the morphological, structural, chemical composition, mechanical, and tribological properties of the TaN film by the Zr addition on two substrates (Ti6Al4V and Si substrates) using DC magnetron co-sputtering. As a result, the TaN film presented a dense morphology and a structure combination of c-TaN and Ta phases, with a preferential (110) plane of the c-Ta phase. Nevertheless, adding Zr changed from denser to columnar morphology and a preferential (111) plane of the c-TaN phase related to the power applied to the Zr Target (PZr). These modifications caused the reduction of the hardness (H) and elastic modulus (E*) of the films, from values of 25.8 GPa of H and 221.5 GPa of E* for the TaN films to 18 GPa of H and 155.5 GPa for the TaZrN film at PZr = 55 W. In the same way, the failure modes and load capacity properties were modified with the addition of Zr to the TaN matrix, from buckling failure mode with LC1 of 8 N for TaN film to Chevron Tension Cracks failure mode with LC1 of 12.5 N for the TaZrN film at PZr = 45 W. Nevertheless, the wear rate decreased with the addition of Zr to TaN matrix, from 0.25 and 0.15 (m3/mN × 10-12) at 1 and 2 N of load for the surfaces coated with the TaN film to 0.12 and 0.08 (m3/mN × 10-12) at the same loads for the surfaces coated with TaZrN film at PZr = 45 W. [ABSTRACT FROM AUTHOR]

Photoelectrochemical (PEC) water splitting is a promising energy conversion strategy for directly converting solar energy into green hydrogen fuel. Constructing an efficient PEC device, finding an efficient photoanode material with a suitable band gap and favorable band-edge positions is essential. Tantalum nitride (Ta3N5) meets these fundamental requirements, and its theoretical maximum solar-to-hydrogen (STH) conversion efficiency can reach 15.9%. Consequently, it has been widely applied as a photoanode material for the PEC oxygen evolution reaction (OER). However, severe bulk and interface charge recombination, along with sluggish water oxygen kinetics, seriously limits its STH conversion efficiency for PEC water splitting. Herein, this feature article briefly reviews recent advances by our research group in improving the STH conversion efficiency of the Ta3N5 photoanode using various strategies, including defect engineering, construction of a gradient band structure, interface engineering, and surface modification of self-healing OER cocatalyst. Up to now, the obtained half-cell STH efficiency has exceeded 4%, providing a solid foundation for the development of tandem PEC devices for unbiased solar-driven overall water splitting toward practical application. [ABSTRACT FROM AUTHOR]

In this study we perform a comparison of the reaction mechanism and the activation barrier for the rate-determining step in various metal nitrides (Ta3N5, Mn6N5, Fe3Mo3N, Co3Mo3N) for the ammonia synthesis reaction. The reactions are explained with simplified schematics and the energy profiles for the various reaction mechanisms are given in order to screen the catalytic activity of the catalysts for the ammonia synthesis reaction. We find that the catalytic activity ranks in the following order: Co3Mo3N > Fe3Mo3N > Ta3N5 > Mn6N5. We also find that the reaction mechanism proceeds either by a Langmuir–Hinshelwood and an Eley–Rideal/Mars–van Krevelen mechanism. This is an overview of about 10 years of computational research conducted to provide an overview of the progress established in this field of study. [ABSTRACT FROM AUTHOR]

Proton Exchange Membrane Fuel Cells (PEMFCs) are promising technology to convert chemical energy from dihydrogen in electrical energy. HT-PEMFCs are working at high temperatures (above 120 °C) and with doped orthophosphoric acid H3PO4 PBI membranes. In such devices, bipolar metallic plates are used to provide reactive gas inside the fuel cell and collect the electrical current. The metallic elements used as bipolar plates, end plates, and interconnectors in acid electrolyte and gaseous fuel cells are severely damaged by a combination of oxidation (due in particular to the use of oxygen, whether pure or contained in the air) and corrosion (due in particular to acid effluents from the electrolyte). This degradation rapidly leads to the loss of the electrical conductivity of the metallic elements and today requires the use of very specific alloys, possibly coated with pure gold. The solution investigated in the present study is the use of a protective coating based on single-phase nitrides obtained by reactive magnetron sputtering or reactive HiPIMS (High-Power Impulse Magnetron Sputtering). The influence of the microstructure on the physical–chemical properties was studied. The electrochemical properties were quantified following two approaches. First, the corrosion current of the developed coatings was measured at room temperature and at higher temperatures using the Linear Sweep Voltammetry (LSV) technique. Then, Electrochemical Impedance Spectroscopy (EIS) measurements were performed to better identify and evaluate their corrosion-resistance performances.

A novel nitrogen-vacancy Ta 3 N 5− x electrocatalyst is designed by utilizing "ship in a bottle" strategy to controllably construct nitrogen defects inside nanopores, effectively regulating sulfur redox reactions and achieving superior room-temperature sodium-sulfur batteries. [Display omitted] Resolving low sulfur reaction activity and severe polysulfide dissolution remains challenging in metal-sulfur batteries. Motivated by a theoretical prediction, herein, we strategically propose nitrogen-vacancy tantalum nitride (Ta 3 N 5 − x) impregnated inside the interconnected nanopores of nitrogen-decorated carbon matrix as a new electrocatalyst for regulating sulfur redox reactions in room-temperature sodium-sulfur batteries. Through a pore-constriction mechanism, the nitrogen vacancies are controllably constructed during the nucleation of Ta 3 N 5 − x. The defect manipulation on the local environment enables well-regulated Ta 5d-orbital energy level, not only modulating band structure toward enhanced intrinsic conductivity of Ta-based materials, but also promoting polysulfide stabilization and achieving bifunctional catalytic capability toward completely reversible polysulfide conversion. Moreover, the interconnected continuous Ta 3 N 5 − x -in-pore structure facilitates electron and sodium-ion transport and accommodates volume expansion of sulfur species while suppressing their shuttle behavior. Due to these attributes, the as-developed Ta 3 N 5 − x -based electrode achieves superior rate capability of 730 mAh g−1 at 3.35 A g−1, long-term cycling stability over 2000 cycles, and high areal capacity over 6 mAh cm−2 under high sulfur loading of 6.2 mg cm−2. This work not only presents a new sulfur electrocatalyst candidate for metal-sulfur batteries, but also sheds light on the controllable material design of defect structure in hopes of inspiring new ideas and directions for future research. [ABSTRACT FROM AUTHOR]

In this study we perform a comparison of the reaction mechanism and the activation barrier for the rate-determining step in various metal nitrides (Ta3N5, Mn6N5, Fe3Mo3N, Co3Mo3N) for the ammonia synthesis reaction. The reactions are explained with simplified schematics and the energy profiles for the various reaction mechanisms are given in order to screen the catalytic activity of the catalysts for the ammonia synthesis reaction. We find that the catalytic activity ranks in the following order: Co3Mo3N > Fe3Mo3N > Ta3N5 > Mn6N5. We also find that the reaction mechanism proceeds either by a Langmuir–Hinshelwood and an Eley–Rideal/Mars–van Krevelen mechanism. This is an overview of about 10 years of computational research conducted to provide an overview of the progress established in this field of study.

In this letter, a rectangular waveguide with controlled negative group delay (NGD) is proposed. The equivalent circuit of the structure is proposed and analyzed. The NGD value and NGD center frequency can be adjusted continuously by the corrugation width and height. Simulation results showed that NGD values of up to −0.7 ns were achievable. The fractional bandwidth was up to 5.67%, at which point the NGD response was observed. A prototype of the proposed structure was fabricated and characterized. Results showed that the fabricated structure was capable of generating a group delay of up to −0.09 ns at 18.9–20 GHz, which was consistent with theoretical and simulated predictions. To the best of our knowledge, this is the first time negative group delay has been achieved in the microwave‐band in a rectangular waveguide. [ABSTRACT FROM AUTHOR]

In this paper, Ta 1-x Mo x N films with varying Mo contents were deposited by reactive magnetrons sputter in mixed Ar/N 2 atmospheres at 350 °C. It's discovered that Ta 1-x Mo x N films at x = 0.13–0.86 maintains a NaCl type (B1) structure and a strong (200) preferred orientation. Besides, as Mo contents grow, the residual stress of films is attenuated from −3.24 GPa to −1.49 GPa, and the hardness of films first increases and then decreases. Specifically, with a nearly balanced Ta and Mo content (x = 0.57), the Ta 1-x Mo x N film exhibits higher hardness (39.5 ± 1.2 GPa) and elastic modulus (359.3 ± 8.8 GPa), up by 53.1% and 26.8% compared with TaN, higher fracture toughness, scratch critical load (91.5 N) and elasticity (76.7%). The Ta 1-x Mo x N film with x = 0.57 obtains lower coefficient of friction (0.417), and higher wear resistance (wear rate: 1.9 × 10−7 mm3/N*m). In addition, the density of states (DOS) in XPS valence band spectra from Ta 1-x Mo x N films is shifted toward lower binding energy with more Mo contents. Accordingly, the stronger metallic characteristics and the solid solution strengthening effect endow the Ta 1-x Mo x N films at x = 0.57 with higher hardness and toughness. [ABSTRACT FROM AUTHOR]

Ellipsometric spectra of polycrystalline thin film tantalum nitride (TaN) have been collected and analyzed to obtain the complex dielectric function (ɛ = ɛ1 + iɛ2) and complex refractive index (N = n + ik) spectra over the photon energy range of 0.059–8.500 eV. Complex optical properties are obtained for TaN in the as-deposited state and rapid thermal annealed at 750 °C for 30 s post deposition. A parametric expression including the contribution from intraband and interband transitions along with a structural model is used and fitted to experimental ellipsometric spectra using iterative least-square regression, which minimizes the unweighted error function or mean square error to extract complex optical properties. The parametric expression developed in this work is successful in describing and differentiating the optical response of measured as-deposited and annealed TaN films and can potentially be used to analyze the optical properties of similar TaN films regardless of their deposition techniques. [ABSTRACT FROM AUTHOR]

In this report, negative group delay (NGD) metamaterials based on split-ring resonators (SRRs) are discussed. A theoretical analysis is proposed to calculate the equivalent circuit parameters, NGD values, and S21 amplitudes of two types of SRRs. Metamaterials made from tantalum nitride are simulated, and the parameters of the two types of SRRs are discussed. Prototypes of metamaterials were fabricated and tested. Measured real-world results were found to be consistent with theoretical and simulated predictions. For EC-SRR, a negative group delay of up to −0.1 ns was achieved at 12–13 GHz. For SR-SRR of the same size as the out ring of EC-SRR, a negative group delay of up to −0.04 ns was achieved, with a loss lower than 2.7 dB. The proposed SRRs were applied to continuous transverse stub (CTS) antenna to reduce the beam walk. The simulation shows that the beam walk can be reduced using the proposed metamaterial. [ABSTRACT FROM AUTHOR]

Electrochemical hydrogen evolution is a highly efficient way to produce hydrogen, but since it is limited by high-cost electrocatalysts, the preparation of high-efficiency electrocatalysts with fewer or free noble metals is important. Here, Ta3N5 nanobelt (NB)-loaded Ru nanoparticle (NP) hybrids with various ratios, including 1~10 wt% Ru/Ta3N5, are constructed to electrocatalyze water splitting for a hydrogen evolution reaction (HER) in alkaline media. The results show that 5 wt% Ru/Ta3N5 NBs have good HER properties with an overpotential of 64.6 mV, a Tafel slope of 84.92 mV/dec at 10 mA/cm2 in 1 M of KOH solution, and good stability. The overpotential of the HER is lower than that of Pt/C (20 wt%) at current densities of 26.3 mA/cm2 or more. The morphologies and structures of the materials are characterized by scanning electron microscopy and high-resolution transmission electron microscopy, respectively. X-ray photoelectron energy spectroscopy (XPS) demonstrates that a good HER performance is generated by the synergistic effect and electronic transfer of Ru to Ta3N5. Our electrochemical analyses and theoretical calculations indicate that Ru/Ta3N5 interfaces play an important role as real active sites. [ABSTRACT FROM AUTHOR]

Tantalum nitride thin films with excellent surface-enhanced Raman spectroscopy (SERS) properties were prepared using a sol-gel method combined with ammonia reduction and nitridation process. The phase composition, surface morphology, optical properties, and SERS properties of the thin films were characterized using various techniques. X-ray diffraction and X-ray photoelectron spectroscopy analyses showed that a solid solution of tantalum oxynitride (TaO x N y) was formed in the film, rather than the standard Ta 3 N 5 crystal. As the reduction nitridation temperature increased, the surface roughness of the tantalum nitride thin film initially decreased and then increased. The tantalum nitride grains on the surface of the thin film provided more SERS 'hot spots'. Ultraviolet–visible absorption spectra revealed that the characteristic surface plasmon resonance absorption peak of the tantalum nitride thin film was around 550 nm. Tantalum nitride thin film obtained at 1000 °C exhibited the best surface Raman enhancement performance. Using Rhodamine 6G as the Raman probe molecule, the detection limit for tantalum nitride film SERS substrate reached 10−7 M, with an enhancement factor of 7.23 × 103. Additionally, the tantalum nitride thin film exhibited good uniformity and long-term stability. The results demonstrated that tantalum nitride thin films could exhibit SERS activity through electromagnetic enhancement and charge transfer mechanisms. • The thin films were synthesized using sol-gel method combined with ammonia reduction nitridation. • Increasing the nitridation temperature enhances SPR peaks and amplifies the local electromagnetic field effect. • Raising the nitridation temperature narrows the forbidden bandwidth of tantalum nitride film, facilitating charge transfer with probe molecules. [ABSTRACT FROM AUTHOR]

Highly durable and antimicrobial tantalum nitride/copper (TaN/Cu) nanocomposite coatings were deposited on D-9 stainless steel substrates by pulsed magnetron sputtering. The Cu content in the coating was varied in the range of 1.42–35.42 atomic % (at.%). The coatings were characterized by electron probe microanalyzer, X-ray diffraction, scanning electron microscope and atomic force microscope. The antibacterial properties of the TaN/Cu coatings against gram-negative Pseudomonas aeruginosa were evaluated using a cell culture test. The peak hardness and Young's modulus of TaN/Cu with 10.46 at.% Cu were 24 and 295 GPa, respectively, which amounted to 15 and 41.67% higher than Cu-free TaN. Among all, TaN/Cu with 10.46 at.% exhibited the lowest friction coefficient. The TaN/Cu coatings exhibited significantly higher antibacterial activity than Cu-free TaN against Pseudomonas aeruginosa. On TaN, the bacterial count was about 4 × 106 CFU, whereas it was dropped to 1.2 × 102 CFU in case of TaN/Cu with 10.46 at.% Cu. The bacterial count was decreased from 9 to 6 when the Cu content increased from 25.54 to 30.04 at.%. Live bacterial cells were observed in the SEM images of TaN, and dead cells were found on TaN/Cu. Overall, TaN/Cu with 10.46 at.% Cu was found to be a potential coating composition in terms of higher antimicrobial activity and mechanical durability. [ABSTRACT FROM AUTHOR]

In this work, thin films of TaN were synthesized on 304 steel substrates using the reactive DC sputtering technique from a tantalum target in a nitrogen/argon atmosphere. All synthesis parameters such as gas ratio, pressure, gas flow, and substrate distance, among others, were fixed except the applied power of the source for different deposited coatings. The effect of the target power on the formation of the resulting phases and the microstructural and morphological characteristics was studied using XRD and AFM techniques, respectively, in order to understand the growth mechanisms. Phase, line profile, texture, and residual stress analysis were carried out from the X-ray diffraction patterns obtained. Atomic force microscopy analysis allowed us to obtain values for surface grain size and roughness which were related to growth mechanisms in accordance with XRD results. Results obtained showed a strong correlation between the growth energy with the crystallinity of the samples and the formation of the possible phases since the increase in the growth power caused the samples to evolve from an amorphous structure to a cubic monocrystalline structure. For all produced samples, the δ-TaN phase was observed despite the low N2 content used in the process (since for low N2 content it was expected to be possible to obtain films with α-Ta or hexagonal ε-TaN crystalline structure). In order to determine the corrosion resistance of the coatings, electrochemical impedance spectroscopy and polarization resistance were employed in the Tafel region. The results obtained through this evaluation showed a direct relationship between the power used and the improvement of the properties against corrosion for specific grain size values. [ABSTRACT FROM AUTHOR]

In this article, the depositions and functional characterizations of Ta-N and Ta-Al-N coatings for protection purposes, grown by reactive high-power impulse magnetron sputtering onto silicon substrates, are described. Nitride films were grown while changing the substrate polarization voltage (i.e., the applied bias voltage) during the process. Moreover, the effects of adding Al to form a ternary system and the resulting variation of the coatings' mechanical and tribological properties have been widely investigated by nanoindentation, scratch, and wear tests. Micro-Raman characterization has been applied to the wear tracks to explore the comprehensive tribo-environment and wear mechanism. Interestingly, Ta-Al-N films, despite significantly improved mechanical properties, show a premature failure with respect to Ta-N coatings. The wear mechanisms of Ta-N and Ta-Al-N systems were revealed to be very different. Indeed, Ta-Al-N films suffer higher oxidation phenomena during wear, with the formation of an oxidized surface tribofilm and a reduced wear resistance, while Ta-N coatings undergo plastic deformation at the wear surface, with a slightly adhesive effect. [ABSTRACT FROM AUTHOR]

Electrochemical hydrogen evolution is a highly efficient way to produce hydrogen, but since it is limited by high-cost electrocatalysts, the preparation of high-efficiency electrocatalysts with fewer or free noble metals is important. Here, Ta3N5 nanobelt (NB)-loaded Ru nanoparticle (NP) hybrids with various ratios, including 1~10 wt% Ru/Ta3N5, are constructed to electrocatalyze water splitting for a hydrogen evolution reaction (HER) in alkaline media. The results show that 5 wt% Ru/Ta3N5 NBs have good HER properties with an overpotential of 64.6 mV, a Tafel slope of 84.92 mV/dec at 10 mA/cm2 in 1 M of KOH solution, and good stability. The overpotential of the HER is lower than that of Pt/C (20 wt%) at current densities of 26.3 mA/cm2 or more. The morphologies and structures of the materials are characterized by scanning electron microscopy and high-resolution transmission electron microscopy, respectively. X-ray photoelectron energy spectroscopy (XPS) demonstrates that a good HER performance is generated by the synergistic effect and electronic transfer of Ru to Ta3N5. Our electrochemical analyses and theoretical calculations indicate that Ru/Ta3N5 interfaces play an important role as real active sites.

High-hardness TaN compacts with a diameter and height of 6 mm were synthesized through the phase transformation of CoSn-type into WC-type TaN under experimental conditions of high temperature and high pressure. The Vickers hardness of WC-type TaN compacts obtained at the pressure of 5 GPa and the temperature of 1873 K is found to be ~21.5 ± 1.5 GPa with a load of 3 Kg, which is comparable to that of the pure tungsten carbide compact (~20 GPa) and higher than those of ultrahigh temperature ceramics ZrB 2 and HfB 2 under the same load. The high hardness of WC-type TaN compacts presented in this work is attributed to the deviatoric strain and well-bonded nanograins. The synthesized WC-type TaN compacts also possess a high oxidation temperature (1072 K). These results suggest that the WC-type TaN with high hardness and high thermal stability holds great promise for industrial applications. [ABSTRACT FROM AUTHOR]

CrN/CrCN/TaN multilayer films were deposited onto the CoCrMo alloy substrates at different number layers as two, four and 8 layers by close-field unbalanced magnetron sputtering method. Microstructure and the tribo-logical properties of the films were characterized by XRD, SEM, pin-on-disk wear test, scratch test, micro hardness. CrN/CrCN/TaN multilayer coatings exhibited good adhesion properties on the CoCrMo alloy substrate. A very high hardness value of 60 GPa was obtained for 8 multilayered coating. As a result of the pin-on-disc wear tests, it was found that the tribological properties of the CoCrMo alloy were enhanced by coating its surface with this architecture by using close-field unbalanced magnetron system with used parameters.

Highly durable and antimicrobial tantalum nitride/copper (TaN/Cu) nanocomposite coatings were deposited on D-9 stainless steel substrates by pulsed magnetron sputtering. The Cu content in the coating was varied in the range of 1.42–35.42 atomic % (at.%). The coatings were characterized by electron probe microanalyzer, X-ray diffraction, scanning electron microscope and atomic force microscope. The antibacterial properties of the TaN/Cu coatings against gram-negative Pseudomonas aeruginosa were evaluated using a cell culture test. The peak hardness and Young’s modulus of TaN/Cu with 10.46 at.% Cu were 24 and 295 GPa, respectively, which amounted to 15 and 41.67% higher than Cu-free TaN. Among all, TaN/Cu with 10.46 at.% exhibited the lowest friction coefficient. The TaN/Cu coatings exhibited significantly higher antibacterial activity than Cu-free TaN against Pseudomonas aeruginosa. On TaN, the bacterial count was about 4 × 106 CFU, whereas it was dropped to 1.2 × 102 CFU in case of TaN/Cu with 10.46 at.% Cu. The bacterial count was decreased from 9 to 6 when the Cu content increased from 25.54 to 30.04 at.%. Live bacterial cells were observed in the SEM images of TaN, and dead cells were found on TaN/Cu. Overall, TaN/Cu with 10.46 at.% Cu was found to be a potential coating composition in terms of higher antimicrobial activity and mechanical durability.

Crystal facet engineering has emerged as one of the most important strategies for designing highly efficient photocatalysts with improved charge separation efficiency. Tantalum nitride (Ta3N5) is one of the most popular visible‐light‐responsive photocatalysts, but the controllable synthesis of well‐shaped Ta3N5 single‐crystals with clear facets is still challenging due to the harsh synthesis conditions. Herein, the first demonstration is given that prism‐like octahedral Ta3N5 single crystals with preferential exposure of {001}, {010}, and {102} facets can be synthesized via the mixed KCl–LiCl flux. Meanwhile, the effects of flux type (KCl, LiCl, and KCl–LiCl), flux ratio, nitridation time, etc. on the phase composition, crystallinity, and morphology of Ta3N5 are studied. Detailed structural characterizations verify its high crystallinity and relatively low defect density. Furthermore, growth of the Ta3N5 single crystal with controllable facets is demonstrated to follow a bottom‐up growth mechanism involving dissolution, recrystallization, and precipitation processes. As a probe test, the as‐obtained Ta3N5 single crystals exhibit about five times the promoted photocatalytic H2 evolution rate with respect to the conventional Ta3N5 nanoparticles, demonstrating the advantages of the specific facet‐defined structure. This finding offers a new avenue to prepare (oxy)nitrides with facets exposed for promising solar energy conversion. [ABSTRACT FROM AUTHOR]

The most recent advancement in implant development is to meet materials that accelerate bone formation at the interface of bone implant and improve Osseo integration. Lean Duplex Stainless Steel as an implantation material needs several enhancements to the surface's properties chemically and physically. The application of surface modifications over the implant is an important method for improving the surface properties of LDX. Reactive Sputtering has some benefits for surface modification, including changing surface topography, increasing hardness and surface roughness, improving surface antibacterial activity and adhesion strength. Coating LDX 2101 DSS with Ta2O5 at times (2,4,6,8, and 10) hrs was used by a modified reactive sputtering technique. Analysis of surface characterization for samples before and then after the sputtering process was performed by micro hardness test, "x-ray diffraction", XRD analysis, "scanning electron microscope", SEM, and "field emission scanning electron microscope" (FE.SEM), "energy dispersive spectroscopy" (EDS), "Atomic force microscope" (AFM), Antibacterial study and Adhesion strength were done on the samples surfaces and compared to uncoated one. The current results indicate that the formation of Ta2O5 layers on the surface of the alloy was achieved, which would improve the surface characteristics, hardness, inhibited bacterial activity and adhesion strength of LDX 2101 DSS for orthopedic applications. [ABSTRACT FROM AUTHOR]

The synthesis of polynitrogen compounds is of great importance due to their potential as high‐energy‐density materials (HEDM), but because of the intrinsic instability of these compounds, their synthesis and stabilization is a fundamental challenge. Polymeric nitrogen units which may be stabilized in compounds with metals at high pressure are now restricted to non‐branched chains with an average N−N bond order of 1.25, limiting their HEDM performances. Herein, we demonstrate the synthesis of a novel polynitrogen compound TaN5 via a direct reaction between tantalum and nitrogen in a diamond anvil cell at circa 100 GPa. TaN5 is the first example of a material containing branched all‐single‐bonded nitrogen chains [N55−]∞. Apart from that we discover two novel Ta–N compounds: TaN4 with finite N44− chains and the incommensurately modulated compound TaN2−x, which is recoverable at ambient conditions. [ABSTRACT FROM AUTHOR]

Stainless steel (SS 304) has good mechanical strength and corrosion resistance properties, but it is not resistive to halides corrosion which limits the use of SS 304 in seawater applications. In this regard, the present work has been focused on the investigation of anticorrosive nature of Ta2O5 (tantalum pentoxide), Ta3N5 (tantalum nitride) and TaON (tantalum oxynitride) films deposited on AISI 304 stainless steel by RF reactive magnetron sputtering technique for anticorrosive applications. The predominant influencing factors especially film composition and surface morphology of the coatings were characterized by XRD, FE-SEM and AFM. The anticorrosive properties of the coatings were investigated through potentiodynamic polarization (Tafel) test and electrochemical impedance spectroscopy in 1M NaCl solution at room temperature. The morphological results showed that the films are uniform with low surface roughness, i.e., less than 10 nm. The contact angle and corrosion study of the films revealed that the tantalum oxynitride film, with nanoscale roughness, has greatly enhanced the corrosion protection of the stainless steel in 1M NaCl solution. The tantalum oxynitride film showed hydrophobic nature and the corrosion current density in the order of 10-11 A/cm2, which led to better anticorrosive behavior. The highest polarization resistance (Rp) was observed for tantalum oxynitride film, i.e., 3.14 MΩ. Overall, tantalum-based coatings have reduced the corrosion rate and enhanced the inhibition efficiency (more than 50%) in comparison with the bare SS 304 substrate. [ABSTRACT FROM AUTHOR]

• Ta 3 N 5 nanotubes are surface modified with a composite Co-based cocatalyst. • Co(OH) x /CoPi composite cocatalyst is electrodeposited and optimized. • Ta 3 N 5 nanotubes optimized with Co(OH) x /CoPi reached 6.3 mA/cm2 under 1 Sun. • Ta 3 N 5 nanotubes are non-toxic towards human cell line HeLa S3. In this work, Co-based cocatalysts are electrodeposited on mesoporous Ta 3 N 5 nanotubes. The electrodeposition time is varied and the optimized photoelectrode reaches a photocurrent density of 6.3 mA/cm2 at 1.23 V vs. SHE, under simulated solar illumination of 1 Sun, in 1 M NaOH. The best performing electrode, apart from the high photocurrent density, shows improved stability under intense photoelectrochemical water splitting conditions. The dual function of the cocatalyst to improve not only the photoelectrochemical performance, but also the stability, is highlighted. Moreover, we adopted a simple protocol to assess the toxicity of Co and Ta contained nanostructured materials (representing used photoelectrodes) employing the human cell line HeLa S3 as target cells. [ABSTRACT FROM AUTHOR]

The formation of the cubic δ -Ta 1− x N phase by high-energy ball-milling from tantalum and boron nitride (h-BN) is explored. Two different molar ratios Ta:BN, 1:1 and 2:1, were used. X-ray diffraction, scanning electron microscopy, surface area analysis by the Brunauer-Emmett-Teller method, and thermogravimetric analysis were used to characterize the products obtained. In both molar ratios and after a few minutes of milling, the mechanosynthesis of δ -Ta 1− x N was observed. Increasing the entropy of the system by introducing vacancies and point defects by the high-energy ball-milling process seems to stabilize the cubic δ -Ta 1− x N phase, as previous theoretical studies had reported. The phase obtained depends on the molar ratio used: in the molar ratio 1:1 a non-stoichiometric δ -Ta 1− x N phase is obtained, while in the molar ratio 2:1 a stoichiometric δ -TaN phase and secondary phases are obtained. The amorphous boron remains dispersed in the material until the mechanical energy is high enough to trigger the formation of tantalum borides. [ABSTRACT FROM AUTHOR]

A tantalum nitride (Ta3N5) photocatalyst with a bandgap of 2.1 eV and theoretical solar‐to‐hydrogen efficiency of 15.9% is an extremely promising candidate for solar water splitting, but its intrinsic/extrinsic structure properties such as existence of reduced tantalum species render its present performance to be far from theoretical expectation. Herein, an attempt is made to adopt foreign Sc atoms with similar ionic radius to Ta atoms to modulate the structure and photocatalytic property of Ta3N5. Based on detailed characterizations, the partial lattice substitution of Sc to Ta atoms is revealed to be feasible to well inhibit the formation of defect sites and favor enhancement of charge separation and transfer ability. In addition, the Sc ions doping has an unobvious effect on the morphology and size of Ta3N5 as well as bandgap structure. Resulting from the promoted charge separation caused by Sc doping and promoted surface catalysis caused by loading of the CoOx cocatalyst, the photocatalytic water oxidation activity of Ta3N5 can be promoted by about one order. The results demonstrate the feasibility of the Sc ions doping strategy in improving the structure and performance of Ta3N5, as is expected to be extended to other systems. [ABSTRACT FROM AUTHOR]

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Owing to exploring the influence of the N atoms ordering in Ta2N compounds on their properties, the stability, elastic, and electronic properties of Ta2N compounds (Ta2N-I: P3¯ml and Ta2N-II: P3¯1m) were investigated using first-principles calculations based on density functional theory. Ta2N-II is energetically favorable according to the enthalpy of formation. Elastic constants were employed to reveal the stronger resistance to deformation, but weaker anisotropy, in Ta2N-II. A ductile-brittle transition was found between Ta2N-I (ductile) and Ta2N-II (brittle). The partial density of states showed a stronger orbital hybridization of Ta-d and N-p in Ta2N-II, resulting in stronger covalent bonding. The charge density difference illustrated the interaction of the Ta-N bond and electron distribution of Ta2N.

In this paper, the effect of nitrogen flow rates on the physical properties of thin TaN films deposited on glass and silicon substrates using reactive DC magnetron sputtering was experimentally studied. The structural and optical properties of the films were evaluated by X-ray diffraction, atomic force microscopy, and optical spectrophotometry. X-ray diffraction patterns revealed that the phase composition evolves from pure metallic δ-Ta body centred cubic to tantalum nitride δ-TaN rock-salt structure. However, when the N2 flow rate exceeds 2 sccm, the films will show a poorly defined crystallization composed of mixture of fcc TaN phase and amorphous phases. Scanning electron microscopy and atomic force microscopy images revealed that the films deposited at high nitrogen flow rate possess smooth surface, good quality and lower roughness. The optical characterisation confirms that they are two groups of samples. The first have an metallic character with high reflectance and the second group are more transparent with an dielectric character with an absorption gap around 1.8 eV. [ABSTRACT FROM AUTHOR]

We have studied the feasibility of preparing tantalum and niobium nitrides by reducing Та2O5, Nb2O5, Mg4Та2O9, and Mg4Nb2O9 with magnesium vapor. The process was run in two steps: (1) reduction of the oxides at a temperature of 820°C and a residual argon pressure of 5 kPa in the reactor for 4 h and (2) nitridation of the reduction products in a nitrogen atmosphere at 820 and 900°C for 1–12 h. The phase composition of the powders after leaching out the magnesium oxide was determined on DRF-2 and DRON-4 X‑ray diffractometers. The specific surface area was determined by BET adsorption measurements on a Micromeritics TriStar II 3020 analyzer. When Ta2O5 was used as precursor, the nitridation product contained θ-TaN, ε-TaN, and Ta2N. The use of Nb2O5 as a precursor led to the formation of face-centered cubic NbN, hexagonal close-packed NbN, Nb2N, and Nb4N3. The Mg4Ta2O9 and Mg4Nb2O9 reduction products did not absorb nitrogen. The results obtained are discussed in detail. [ABSTRACT FROM AUTHOR]

The changes in tungsten (W) film growth and resistance are studied using different titanium nitride (TiN) and tantalum nitride (TaN) underlayer films. The underlayers are analyzed by surface characterization techniques to obtain the differences in surface morphology and grain sizes that influence the growth of W on these films. Different precursors and processes used for TiN deposition affect the W growth and film properties. It is important to monitor the changes in incoming TiN resistance as a part of the W process qualification. This enables maintaining W process stability and reducing fab downtime due to false fails. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • A synergistic approach in suppressing charge recombination is designed for Ta 3 N 5 photocatalyst. • The charge separation in bulk, interface and on surface of Ta 3 N 5 photocatalyst is drastically improved through the multi-strategy approach. • A ˜ 38 times higher H 2 evolution rate (56.3 μmol h−1) on new hollow Ta 3 N 5 than that of bulk counterpart is achieved. Abstract Rational design of photocatalysts is essential to achieve efficient solar energy conversion. For narrow bandgap Ta 3 N 5 photocatalyst, various charge recombination occurring in the bulk, interface and on the surface significantly impairs its activity for solar hydrogen (H 2) generation. Herein, a synergistic engineering approach is designed to solve this critical recombination challenge. First, hollow spherical structure of Ta 3 N 5 with Mg doping is prepared to not only reduce the charge migration distance and increase the surface area, but also increase the electron mobility for facilitated charge transfer. Second, an MgO nano-layer covers the surface of hollow Ta 3 N 5 structure to passivate surface defects, thus promoting the interfacial charge transfer between Ta 3 N 5 and co-catalysts. Finally, dual co-catalysts (Pt/CoO x) for redox reactions are loaded onto the hollow Ta 3 N 5 structure to reduce the surface recombination and overcome the sluggish surface reaction. Remarkably, the combination of hollow structure, Mg2+ doping, MgO interfacial layer, and dual co-catalysts effectively improves the charge separation and transfer in Ta 3 N 5 photocatalyst. This newly designed photocatalyst exhibits a considerably improved H 2 generation performance of 56.3 μmol h−1 under simulated sunlight, compared to that of reference Pt/Ta 3 N 5 hollow spheres. [ABSTRACT FROM AUTHOR]

Abstract Tantalum nitride (TaN) ultra-thin films deposited by Atomic Layer Deposition (ALD) are efficient diffusion barriers for copper interconnects embedded in silica matrix. The present paper reports a methodical investigation of the first stages of TaN ALD growth on either dense SiO 2 or nanoporous SiOCH surfaces. The deposited TaN x phases, film microstructure, chemistry and resistivity were characterized at different steps of ALD growth (from 0 to 160 ALD-cycles). While a granular morphology combining orthorhombic-Ta 3 N 5 (o-Ta 3 N 5) and cubic-TaN (c-TaN) was obtained on SiOCH, a continuous film mainly composed of o-Ta 3 N 5 was found when deposited on dense SiO 2. In both cases, TaN x films were not completely-crystallized. The electrical behavior is shown to be mainly driven by film morphology rather than by the intrinsic conductivity of the deposited phases. Growth modes on both surfaces are then discussed in terms of surface chemical reactivity: two growth timelines are proposed to explain the observed phenomena (film continuity, deposited phase, conductivity). As this methodical approach shows the major interest for a deposition on SiO 2 substrate, a surface functionalization of SiOCH has also been performed. It was determined that a 3 nm-thick SiO 2 layer capping the SiOCH surface is enough to recover the required properties for optimal TaN deposition. Highlights • Ultra-thin TaN films were deposited by ALD on SiO 2 and nanoporous SiOCH surfaces. • A granular morphology combining o-Ta 3 N 5 and c-TaN was obtained on SiOCH. • A continuous film mainly composed of o-Ta 3 N 5 was deposited on dense SiO 2. • Film resistivity is driven by morphology rather than by intrinsic phase conductivity. • A 3 nm-thick SiO 2 capping layer is enough to recover the required TaN properties. [ABSTRACT FROM AUTHOR]

Biodegradable Mg alloys have appeared as the most appealing metals for biomedical applications, particularly as temporary bone implants. However, issues regarding high corrosion rate and biocompatibility restrict their application. Hence, in the present work, nanostructured clinoenstatite (CLT, MgSiO3)/tantalum nitride (TaN) was deposited on the Mg-Ca-Zn alloy via electrophoretic deposition (EPD) along with physical vapor deposition (PVD) to improve the corrosion and biological characteristics of the Mg-Ca-Zn alloy. The TaN intermediate layer with bubble like morphology possessed a compact and homogenous structure with a thickness of about 950 nm while the thick CLT over-layer (~15 μm) displayed a less compact structure containing nano-porosities as well as nanoparticles with spherical morphology. The electrochemical tests demonstrated that the as prepared CLT/TaN film is able to substantially increase the anticorrosion property of Mg-Ca-Zn bare alloy. Cytocompatibility outcomes indicated that formation of CLT and TaN on the Mg bare alloy surface enhanced cell viability, proliferation and growth, implying excellent biocompatibility. Taken together, the CLT/TaN coating exhibits appropriate characteristic including anticorrosion property and biocompatibility in order to employ in biomedical files.

The relevance of the research. The new proposed technology for obtaining refractory nitrides has several advantages: low energy consumption, no need for complex equipment, nitrogen is used to produce nitrides, synthesis is carried out at atmospheric pressure. The main aim of the research is to determine experimentally the composition of combustion products of aluminum nanopowder and tantalum pentoxide mixtures in air and in liquid nitrogen. Object: tantalum nitride synthesis product obtained by burning the aluminum nanopowder mixture with tantalum pentoxide in air. Methodsh: x-ray analysis (diffractometer Difrey-401), differential thermal analysis (DTA) (thermoanalyzer SDT Q600 Instrument company). According to the results of the DTA the authors have calculated four parameters of activity of the mixtures: oxidation onset temperature (Tst.ox, °C), oxidation level (α, %), maximal oxidation rate (vmax, mg/min), specific thermal effect (ΔН, J/g). Results. The authors determined the parameters of activity of aluminum nanopowder with tantalum pentoxide mixtures. It is revealed that along with nitride and aluminum oxide in the products a crystalline phase of metallic tantalum is formed. The maximum yield of tantalum was 54 rel. %. It was shown experimentally that at aluminum nanopowder combustion in air, aluminum recovers tantalum pentoxide, which interacts with air nitrogen to form crystalline Ta2N tantalum nitride. According to X-ray, in the combustion products of a mixture of aluminum nanopowder with tantalum pentoxide, the crystalline phases of α- and β-tantalum are found. At the same time, tantalum nitride was not detected when the sample was burned in liquid nitrogen.

Highlights • High conductivity, nearly stoichiometric ALD TiN x films from TiCl 4 and N 2 H 4. • Organometallic grown TaN x and TiN x films show low surface roughness. • N 2 H 4 acts as a reducing agent and good proton donor to Ta and Ti ligands. Abstract Thermal ALD of TaN x and TiN x films was performed using hydrazine (N 2 H 4) as a reactive N-containing source. Ultralow temperature (100 °C and 300 °C) growth of TaN x was observed using N 2 H 4 and tris(diethylamido)(tert -butylimido) tantalum (TBTDET); XPS showed nearly stoichiometric Ta 3 N 5 films were deposited with below 10% O and 5% C incorporation. Stoichiometric TiN x films grown at 300 °C with tetrakis(dimethylamido) titanium (TDMAT) showed an RMS roughness below 2 nm consistent with good nucleation density. High conductivity nitride films were grown by a thermal low-temperature TiN x ALD process using anhydrous N 2 H 4 and titanium tetrachloride (TiCl 4) from 300 to 400 °C; uniform, nearly stoichiometric films of 0.44 nm RMS roughness were deposited. Compared to NH 3 grown films, XPS confirmed N 2 H 4 grown films contained fewer O, C, and Cl impurities consistent with lower resistivities being observed with N 2 H 4. The data is consistent with N 2 H 4 serving as a reducing agent and a good proton donor to Ta and Ti ligands. [ABSTRACT FROM AUTHOR]

Abstract The research and development of nuclear fusion reactors are going on conducting to acquire a next-generation energy source. It is supposed to be that the reduced activation ferritic/martensitic (RAFM) steel F82H is adopted as a structural material of the blanket module, which is the device set on the inner wall of fusion reactors. As welding for thicker plates of F82H, multi-pass welding will be adopted to the joints. In the case of multi-pass welding, hot cracking is one of serious defects in welds and is concerned in welds reheated by following weld passes. Therefore, the objectives of this study are to evaluate hot crack susceptibility in multi-pass welds of F82H and to clarify the cause of hot cracking in multi-pass welds of F82H. The hot crack susceptibility in multi-pass welds is evaluated by the longitudinal Varestraint test with double-bead and triple-bead types. From the observation of fractured surface occurred in welds of F82H after the Varestraitnt test, the crack is identified as ductility-dip crack. The cause of hot crack in multi-pass welds of F82H is clarified by Vickers hardness test, SEM microstructure observations and X-ray diffraction pattern analyses. Based on these tests, when multi-pass welding is conducted for the F82H steels with high Ta contents, it should be considered to control welding conditions for prevention of hot cracking in weld metal as well as high strength martensitic steels. These results suggest that the cause of the crack is intragranular hardening by the precipitation of TaN during welding thermal cycles. [ABSTRACT FROM AUTHOR]

Abstract A polylaminate coating with intersecting tantalum and tantalum nitride (TaN/Ta/TaN/Ta/TaN/Ta, TaN is the outermost layer) is deposited on surface of 430 stainless steel bipolar plate for high temperature proton exchange membrane fuel cell by a reactive magnetron sputtering method. Electrochemical tests including potentiodynamic, potentiostatic polarisation and electrochemical impedance spectroscopy, are carried out to evaluate the corrosion resistance and stability of the polylaminate TaN/Ta coating in simulating high temperature proton exchange membrane fuel cell environments (85% H 3 PO 4 solution at 80 °C and 130 °C). Results show that the polylaminate TaN/Ta coating greatly improve the corrosion resistance of 430 stainless steel, which can provide almost 100% protection of the substrate in both high temperature proton exchange membrane fuel cell anode and cathode environment. Besides, the interfacial contact resistance of coated 430 stainless steel (9.03 mΩ cm2) is much lower than that of bare substrate (106.74 mΩ cm2). Furthermore, different from the highly increased interfacial contact resistance of bare specimen, the coated 430 stainless steel shows a minor increase resistance after potentiostatic tests in 85% H 3 PO 4 solution at 130 °C. Highlights • Electrochemical behaviour of 430 SS is firstly investigated in HT-PEMFC environment. • A polylaminate coating with intersecting Ta and TaN had been prepared on 430 SS. • Corrosion resistance in HT-PEMFC conditions and the ICR are evaluated. • PL-TaN/Ta-430 shows greatly improved surface conductivity and corrosion resistance. [ABSTRACT FROM AUTHOR]

Tantalum nitride (TaN) films were deposited onto SiO 2 /Si and multilayer ceramic (MLC) substrates with a reactive direct current magnetron sputtering method. After they were kept at different N 2 partial pressures and substrate temperatures, these were characterized for their electrical, structural, and mechanical properties for use as thin film resistors (TFRs). Results of X-ray diffraction analysis, observation of microstructure, sheet resistance measurement, and accelerated degradation tests highly indicated that TaN films with high crystalline phases, good surface roughness, stable deposition rates, appropriate sheet resistances, and high reliabilities could be obtained if N 2 partial pressure was maintained at around 20%. Adhesive strengths of TaN films grown on MLC substrates were increased with increasing substrate temperature up to 300 °C. A low resistance change was confirmed by temperature coefficient of resistance variation as a function of temperature, implying high reliability and durability. Results of this study suggest that TFRs described in this study are suitable for embedded passive resistors with practical applications, including controlled resistances for fabricated TaN based TFRs with different widths. [ABSTRACT FROM AUTHOR]