Tantalum Nitride Research Articles

Flux‐Assisted Synthesis of Prism‐like Octahedral Ta3N5 Single‐Crystals with Controllable Facets for Promoted Photocatalytic H2 Evolution

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.

Preparation of Ta3N5 Nanosheet by Nitridation of Monolayer Tantalum Oxide Nanosheet

AbstractTwo‐dimensional semiconducting materials have attracted attention as photocatalysts, electrode catalysts and electronic materials. However, preparation of metal nitride nanosheet is still a significant challenge. Here, we show a tantalum nitride (Ta3N5) nanosheet with a thickness of 1.5 nm prepared via tantalum oxide [TaO3]− nanosheet derived from layered rubisium tantalum oxide (RbTaO3). The monolayer tantalum oxide nanosheet was converted to Ta3N5 nanosheet with a [110] preferred orientation in the in‐plane direction during annealing under NH3 gas flow, and showed a photocatalytic activity for H2 evolution under visible light illumination (550 nm). The H2 evolution ratio of the ultrathin Ta3N5 nanosheet was much higher than that of bulk Ta3N5 prepared from Ta2O5 powder, indicating that nanosheet structure suppresses the recombination in the photocatalytic reaction.

Access to Optimum Working Voltage of Plasma Electrolytic Nitridation of Tantalum Alloys

Recently, efficient coatings with excellent adhesion to the substrate have been applied to metals through the plasma electrolytic nitriding (PEN) method, which is a cathodic atmospheric plasma process with a high deposition rate. The structure, microhardness, and corrosion resistance of coatings after cathodic PEN with different critical and plasma-formation voltages were investigated. The characterization of the layer phases and their microstructure were studied via optical microscopy, X-ray diffraction, and scanning electron microscopy. The corrosion resistances of the coated metal samples were also investigated. It was found that various voltages provided different phases of Ta4N, TaN0.43, TaN, Ta4N5, and a nitrogen solid solution in tantalum. The PEN process with critical and plasma-formation voltages of 185 and 220 V, respectively, had the best uniform coating, with sharp peaks of tantalum nitride high corrosion resistance and microhardness of about 1200 VHN, which was selected as the optimum sample for nitriding process.

Electromagnetic-Thermal-Electric Analysis of Indirectly-Heated RF MEMS Power Sensors With Different Terminal Resistor Dimensions

In this article, the design, fabrication and measurements are presented for an indirectly-heated RF MEMS thermoelectric power sensor with different terminal resistor dimensions. In this design, thermal isolation is achieved through a 20μm-thick MEMS substrate membrane using back etching technology. In order to maintain the stability of impedance matching, two low temperature coefficient of resistance (TCR) tantalum nitride (TaN ) resistors of 50 Ω are adopted to serve as heating sources. Considering the effect of the terminal resistor dimension on RF power sensing performance, six configuration sensors have been explored experimentally. Experimental results show that the output response of these devices has excellent RF-DC linearity with the power from 1 mW to 200 mW. And as the dimension of the terminal resistor gradually increases, their sensitivities are 77.3 μV/mW, 63.4 μV/mW, 56.3 μV/mW, 54.4 μV/mW, 49.5 μV/mW and 47.9 μV/mW at 10GHz, respectively. Meanwhile, the measured response time is 3.2 ms, 2.9 ms, 2.7 ms, 2.5 ms, 2.2 ms and 2.0 ms, respectively. This indicates that as the size of the terminal resistor increases, the corresponding sensitivity and response time are decreasing. Therefore, there is a trade-off consideration between high sensitivity and fast response time. Further, an electromagnetic-thermal-electric model of the indirectly-heated RF MEMS power sensor is proposed based on the Seebeck effect and heat transfer theory. Experiments and finite element method (FEM) simulation are performed to verify the validity of the proposed model. The results would be useful to improve future sensor designs and specific applications.

CO2 and H2O Coadsorption and Reaction on the Low-Index Surfaces of Tantalum Nitride: A First-Principles DFT-D3 Investigation

A comprehensive mechanistic insight into the photocatalytic reduction of CO2 by H2O is indispensable for the development of highly efficient and robust photocatalysts for artificial photosynthesis. This work presents first-principles mechanistic insights into the adsorption and activation of CO2 in the absence and presence of H2O on the (001), (010), and (110) surfaces of tantalum nitride (Ta3N5), a photocatalysts of significant technological interest. The stability of the different Ta3N surfaces is shown to dictate the strength of adsorption and the extent of activation of CO2 and H2O species, which bind strongest to the least stable Ta3N5(001) surface and weakest to the most stable Ta3N5(110) surface. The adsorption of the CO2 on the Ta3N5(001), (010), and (110) surfaces is demonstrated to be characterized by charge transfer from surface species to the CO2 molecule, resulting in its activation (i.e., forming negatively charged bent CO2−δ species, with elongated C–O bonds confirmed via vibrational frequency analyses). Compared to direct CO2 dissociation, H2O dissociates spontaneously on the Ta3N5 surfaces, providing the necessary hydrogen source for CO2 reduction reactions. The coadsorption reactions of CO2 and H2O are demonstrated to exhibit the strongest attractive interactions on the (010) surface, giving rise to proton transfer to the CO2 molecule, which causes its spontaneous dissociation to form CO and 2OH− species. These results demonstrate that Ta3N5, a narrow bandgap photocatalyst able to absorb visible light, can efficiently activate the CO2 molecule and photocatalytically reduce it with water to produce value-added fuels.

Band structure engineering and defect control of Ta3N5 for efficient photoelectrochemical water oxidation

Ta3N5 is a promising photoanode material with a theoretical maximum solar conversion efficiency of 15.9% for photoelectrochemical water splitting. However, the highest applied bias photon-to-current efficiency achieved so far is only 2.72%. To bridge the efficiency gap, effective carrier management strategies for Ta3N5 photoanodes should be developed. Here, we propose to use gradient Mg doping for band structure engineering and defect control of Ta3N5. The gradient Mg doping profile in Ta3N5 induces a gradient of the band edge energetics, which greatly enhances the charge separation efficiency. Furthermore, defect-related recombination is significantly suppressed due to the passivation effect of Mg dopants on deep-level defects and, more importantly, the matching of the gradient Mg doping profile with the distribution of defects within Ta3N5. As a result, a photoanode based on the gradient Mg-doped Ta3N5 delivers a low onset potential of 0.4 V versus that of a reversible hydrogen electrode and a high applied bias photon-to-current efficiency of 3.25 ± 0.05%. Despite the efforts to tune their properties, the efficiency of tantalum nitride photoanodes falls short of the theoretical value. Here, a gradient Mg doping strategy is introduced to engineer tantalum nitride’s band structure and control its defects, leading to an applied bias photon-to-current efficiency of 3.25%.

Analysis of the composition of tantalum nitride in CMOS metallization trenches using parallel angle‐resolved XPS

We demonstrate the utilization of parallel angle‐resolved X‐ray photoelectron spectroscopy (pAR‐XPS) as a useful tool to analyze ultrathin sputtered tantalum nitride (TaN) thin films in complementary metal‐oxide‐semiconductor (CMOS) trenches. The chemical composition of TaN was estimated by pAR‐XPS using a Theta 300i from Thermo Fischer. An improved lateral resolution was achieved by analyzing periodic structures. The XPS data was correlated with transmission electron microscopy (TEM) in combination with energy‐dispersive X‐ray spectroscopy (EDX) and time‐of‐flight secondary ion mass spectrometry (ToF‐SIMS) data. The results show that the nitrogen content in the TaN thin films was about 6% higher at the sidewall compared with the top and bottom of the trench.

High catalytic performance of a Pd-loaded TaN-TaC electrocatalyst for ethylene glycol oxidation in an alkaline medium

In this work, tantalum nitride and tantalum carbide (TaN-TaC) composites are prepared using a one-step calcination method. The resulting TaN-TaC composites have excellent conductivity, and therefore, potential applications in the electrode materials of fuel cells. Then, palladium nanoparticles loading on TaN-TaC (Pd/TaN-TaC) electrocatalysts are synthesized using the reflux method. The X-ray photoelectron spectroscopy results imply that the valance states of palladium are of the form Pd0 and Pd2+ on the surface of TaN-TaC composites. The electrocatalytic activity of the Pd/TaN-TaC catalysts is measured in a 0.5 mol L−1 KOH solution and 1 mol L−1 of ethylene glycol. These results imply that the Pd/TaN-TaC electrocatalyst modified glassy carbon electrode has a high catalytic activity for ethylene glycol electrooxidation in an alkaline medium. The dosage of Pd is 7% (mass ratio of Pd and TaN-TaC) and it exhibits the higher electrocatalytic activity, and superior to the commercial Pd/C (10%).

Surface characterization and electrochemical properties of tantalum nitride (TaN) nanostructured coatings produced by reactive DC magnetron sputtering

In this study, TaN nanostructured coatings were successfully produced on AISI 316 L stainless steel substrates using the reactive DC magnetron sputtering method. Among all of these coating processes, the only variable factor was the percentage of partial pressure of nitrogen gas (PN2) which was attended in the sputtering process. To do this, the percentage of partial pressure of nitrogen gas was chosen in different percentages of 5%, 10% and 15%. After the coatings formation, their microstructure, chemical composition and corrosion behavior were studied. The microstructure of the samples coated was studied by the scanning electron microscope (SEM), their elemental and phase composition by energy diffraction spectroscopy (EDS), X-ray diffraction (XRD) and elemental distribution was carried out by mapping (MAP) analysis. In order to study the corrosion behavior of coatings, the electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization (PDP) tests were carried out in a simulated body fluid (Ringer's solution). Immersion time of specimens was determined 1, 24, 48 h and 7 days in Ringer's solution. The results of different tests showed that coatings containing 15% nitrogen consisted of hard orthorhombic and hexagonal tantalum nitride phases, had free pores and denser microstructure. This coating exhibited better corrosion behavior than the other two ones in all of the immersion times. The corrosion resistance of this coating also increased by rising immersion time from 1 h to 7 days. In fact, the coating containing 15% of nitrogen being immersed for 7 days with a resistance of 118.68 (MΩ.cm2), had the highest corrosion resistance.

Impact of stress and doping effects on the polarization behavior and electrical characteristics of hafnium–zirconium oxides

In this study, we investigated the stress and doping effects of ferroelectric hafnium zirconium oxide (HfZrO) based on material analysis and electrical characteristics. The experimental results revealed that the ferroelectric crystalline phase is effectively transferred by mechanical stress of tantalum nitride (TaN) electrodes, and the origin of stress is mainly the thermal residual stress formed near the TaN and HfZrO interface. The ferroelectric polarization characteristics of HfZrO can be further modified by additional Al doping, which not only improves the leakage current of HfZrO due to the large bandgap of Al2O3 but also simultaneously stabilizes the ferroelectric domain switching under a large coercive field.

Surface Brillouin scattering study of tantalum nitride (TaN) thin films.

Elastic properties of TaN films on (001)Si are investigated by surface Brillouin scattering (SBS). The velocity dispersion is obtained from Brillouin frequency shifts and surface acoustic wave phase velocities derived from measured SBS spectra. The observed Rayleigh surface acoustic and Sezawa waves indicate a soft on hard configuration. The elastic stiffnesses from the best fit of the calculated and measured spectra were C11=288 and C44=80GPa. Using these elastic constants in the surface elastodynamic Green's function yielded theoretical Brillouin spectra in agreement with measured spectra. Employing a least squares fitting procedure to the elastic constants gives uncertainties in C11 and C44 as ±3.7 and ±2.5GPa, respectively.

Nondispersive Infrared Gas Analyzer for Partial Pressure Measurements of a Tantalum Alkylamide During Vapor Deposition Processes.

A nondispersive infrared gas analyzer was demonstrated for investigating metal alkylamide precursor delivery for microelectronics vapor deposition processes. The nondispersive infrared analyzer was designed to simultaneously measure the partial pressure of pentakis(dimethylamido) tantalum, a metal precursor employed in high volume manufacturing vapor deposition processes to deposit tantalum nitride, and dimethylamine, the primary decomposition product of pentakis(dimethylamido) tantalum at typical delivery conditions for these applications. This sensor was based on direct absorption of pentakis(dimethylamido) tantalum and dimethylamine in the fingerprint spectral region. The nondispersive infrared analyzer optical response was calibrated by measuring absorbance as a function of dimethylamine and pentakis(dimethylamido) tantalum density. The difference between the mass of material removed from the ampoule during flow tests as measured gravimetrically and as determined optically, by calculating flow rates from the nondispersive infrared analyzer measurements, was only ≈2 %. The minimum detectable molecular densities for pentakis(dimethylamido) tantalum and dimethylamine were ≈2 × 1013 cm-3 and ≈5 × 1014 cm-3, respectively (with no signal averaging and for a sampling rate of 200 Hz), and the corresponding partial pressures were ≈0.1 Pa and ≈2 Pa for pentakis(dimethylamido) tantalum and dimethylamine, respectively (for an optical flow cell temperature of 93 ℃). Pentakis(dimethylamido) tantalum could be detected at all conditions of this investigation and likely the majority of conditions relevant to high volume manufacturing tantalum nitride deposition. Dimethylamine was not detected at all conditions in this study, because of a lower nondispersive infrared analyzer sensitivity to dimethylamine compared to pentakis(dimethylamido) tantalum and because conditions of this study were selected to minimize DMA production. While this nondispersive infrared gas analyzer was specifically developed for pentakis(dimethylamido) tantalum and dimethylamine, it is suitable for characterizing the vapor delivery of other metal alkylamide precursors and the corresponding amine decomposition products, although in the case of some metal alkylamides a different bandpass filter would be required.

A Novel Thermistor-Based RF Power Sensor With Wheatstone Bridge Fabricating on MEMS Membrane

A novel thermistor-based RF power sensor with Wheatstone full-bridge structure is proposed using MEMS technology combined with monolithic microwave integrated circuit (MMIC) process in this paper. A MEMS substrate membrane is carefully designed beneath the hot area by back etching technology. Such a design can effectively suppress the longitudinal heat loss, which facilitates the improvement of sensitivity. In addition, in this design, low TCR (temperature coefficient of resistance) TaN (tantalum nitride) resistors are adopted to achieve the stability of impedance matching. Measurement results show that the output response of this device has excellent linearity with the power from 1 to 200mV. Considering the effect of the distance between the hot and cold areas, three sensor configurations with different arrangements of thermistors were investigated experimentally. And their corresponding sensitivities are 0.16 mV/mW, 0.19 mV/mW and 0.22 mV/mW at 10GHz, respectively. Meanwhile, the measured response times of these three configuration sensors are 20.7 ms, 22.3 ms and 27.2 ms, respectively. Therefore, there is a trade-off consideration between high sensitivity and fast response time. Moreover, the measured return losses are less than −20 dB in the frequency range from 10 MHz to 20GHz. This indicates that these devices have good matching characteristics. The proposed thermistor-based RF MEMS power sensor demonstrates a good performance, especially high sensitivity and stable impedance match, providing great application potential. [2020-0260]

Cobalt Doping in Tantalum Nitride Thin Films Prepared by Sputtering

Cobalt Doping in Tantalum Nitride Thin Films Prepared by Sputtering

Surface defect passivation of Ta3N5 photoanode via pyridine grafting for enhanced photoelectrochemical performance.

Tantalum nitride (Ta3N5) is a promising photoanode material for photoelectrochemical (PEC) water splitting, while the Ta3N5/Ta photoanode synthesized via general thermal oxidation and nitridation on a Ta foil method usually has serious carrier recombination at the surface, which usually reduces the PEC activities. Herein, we demonstrate an efficient strategy of decorating pyridine, a small organic molecule at the surface of the Ta3N5/Ta photoanode, to alleviate the surface recombination. Such decoration yields a stable photocurrent density of 4.4 mA cm-2 at 1.23 VRHE under AM 1.5G (air mass 1.5 global, 100 mW cm-2) simulated sunlight, which is about 1.4 times higher than that of Ta3N5/Ta without modification, and the photocurrent density still remained ∼100% of its original value after a 5 h stability test. Further characterization of the incident photon-to-current conversion efficiency and absorbed photon-to-current efficiency of the pyridine/Ta3N5/Ta photoanode showed a significant increase to 62% and 72% at 500 nm, respectively. The enhanced pyridine/Ta3N5/Ta PEC performance can be attributed to minimizing the density of nitrogen vacancies due to the passivation of pyridine grafting, which results in the decreased recombination centers and improved charge separation efficiency at the surface. We thus believe that our study of surface passivation by using small organic molecules provides an alternative to address the surface recombination of Ta3N5 based photoelectrodes.

Mechanosynthesis of metastable cubic δ-Ta1−xN

The formation of the cubic δ-Ta1−xN 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-Ta1−xN 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-Ta1−xN 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-Ta1−xN 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.

Phase stability and mechanical response of tantalum nitrides to electronic excitation effect

Based on an analysis ofelectronic structures and phonon spectra calculationsas a function of electronic temperature Te using the density functional theory, we investigated the phase stability and mechanical responseto electronic excitation effect on variousphases of tantalum nitrides TaNx with fully or partially occupied nitrogen sublattices. The results suggest that the cubic phase exhibits lattice instability at room temperature, while the hexagonal phases are dynamically stable. The phase stability increases in the sequence TaN (δ-type), TaN0.43, TaN0.5, TaN (AsNi type), TaN0.83, TaN (θ-type), and TaN (ε-type). The nonmetal vacancies exhibit enhanced latticestability with hexagonal phasescompared to the cubicphase. The electronic excitation effect providedextra stability for cubic δ-TaNwith the increase inelectronic temperature, whilethe excitation results in a lower degree of stability for hexagonal phases.The physical origin of electronic excitation effects on both the cubic and hexagonal phase stability of TaN can be attributed to the peculiarities of their electronicdensities of states near the Fermi level and a combination of three different types of bonding characteristics.The counterintuitivebehavior oflattice stabilities appears or disappears as a response to mechanical properties under electronic excitation.

Phase-Exchange-Driven Wake-Up and Fatigue in Ferroelectric Hafnium Zirconium Oxide Films.

Ferroelectric hafnium zirconium oxide holds great promise for a broad spectrum of complementary metal-oxide-semiconductor (CMOS) compatible and scaled microelectronic applications, including memory, low-voltage transistors, and infrared sensors, among others. An outstanding challenge hindering the implementation of this material is polarization instability during field cycling. In this study, the nanoscale phenomena contributing to both polarization fatigue and wake-up are reported. Using synchrotron X-ray diffraction, the conversion of non-polar tetragonal and polar orthorhombic phases to a non-polar monoclinic phase while field cycling devices comprising noble metal contacts is observed. This phase exchange accompanies a diminishing ferroelectric remanent polarization and provides device-scale crystallographic evidence of phase exchange leading to ferroelectric fatigue in these structures. A reduction in the full width at half-maximum of the superimposed tetragonal (101) and orthorhombic (111) diffraction reflections is observed to accompany wake-up in structures comprising tantalum nitride and tungsten electrodes. Combined with polarization and relative permittivity measurements, the observed peak narrowing and a shift in position to lower angles is attributed, in part, to a phase exchange of the non-polar tetragonal to the polar orthorhombic phase during wake-up. These results provide insight into the role of electrodes in the performance of hafnium oxide-based ferroelectrics and mechanisms driving wake-up and fatigue, and demonstrate a non-destructive means to characterize the phase changes accompanying polarization instabilities.

MD-Simulation of Duty Cycle and TaN Interlayer Effects on the Surface Properties of Ta Coatings Deposited by Pulsed-DC Plasma Assisted Chemical Vapor Deposition

In this work, molecular dynamics (MD) simulations were employed to investigate the effects of duty cycle changes and utilization of tantalum nitride interlayer on the surface roughness and adhesion of Ta coating deposited by pulsed-DC plasma assisted chemical vapor deposition. To examine the simulation results, some selected deposition conditions were experimentally implemented and characterized through scanning electron microscopy, atomic force microscopy (AFM) and microscratch tests. The Ta and Ta/TaN coatings were deposited on AISI316L stainless steel substrate in a plasma atmosphere consist of Ar, H2, N2 and TaCl5 vapor at 350 °C. The results showed that at the same duty cycles the surface roughness of Ta/TaN coating is at least 40% less than that of the single layer Ta coating. By increasing the duty cycle from 17 to 40%, the surface roughness significantly decreases about 80%. This is attributed to the further exposure of surface against high energy ions bombardment at higher duty cycles. The presence of TaN interlayer due to its lower lattice mismatch with Ta (under 2%), contributes to the nucleation of Ta grains which consequently leads to reducing the surface roughness. The enhanced adhesion of the Ta coatings on TaN is discussed in view of improving the interfacial stresses as shown by the MD simulations. The MD simulations results were shown to be in good agreement with the experimental data.

Clinoenstatite/Tantalum Coating for Enhancement of Biocompatibility and Corrosion Protection of Mg Alloy.

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.