Thin Nitride Research Articles

Passivation Effect of Rock-Salt Nitride Materials on a Planar p-Si Photocathode for Solar Water Reduction.

Photoelectrochemical water splitting, which uses sunlight to produce clean hydrogen fuel, is gaining traction with rising concerns about fossil fuels and pollution. Silicon (Si) photocathodes are promising for this process due to their light absorption and favorable band alignment for hydrogen production. However, limitations such as reflectance, low photovoltage, and rapid photocorrosion hinder their overall performance and stability. An interfacial insulating layer such as SiOx ensures superior durability to p-Si photocathodes. However, the inherent heterogeneity and intrinsic defects pose challenges to effective surface passivation. This study investigates the challenges of photocorrosion and utilization of a thin titanium nitride (TiN) passivation layer deposited using direct-current magnetron sputtering to protect the native silicon oxide (SiOx) layer. Additionally, a molybdenum oxynitride (Mo(O,N)x) bifunctional layer is employed to enhance both the electrocatalytic activity and durability of the photocathode. The presence of oxygen and nitrogen within this cocatalyst layer modifies the surface chemistry of the p-Si photocathode, promoting favorable interfacial interactions with electrolyte species during PEC reactions. This modification facilitates efficient charge transfer processes and accelerates reaction kinetics, ultimately optimizing the performance and operational lifetime of the photocathode. The resulting Mo(O,N)x/TiN/p-Si photocathode exhibited a remarkable onset potential of +0.46 VRHE in harsh acidic conditions under simulated sunlight (AM 1.5G illumination, 100 mW·cm-2). Notably, the photocathode demonstrated exceptional long-term stability exceeding 140 h, highlighting the combined TiN passivation and Mo(O,N)x cocatalyst as a protection strategy.

Plasmonic Nanocavity to Boost Single Photon Emission From Defects in Thin Hexagonal Boron Nitride

AbstractEfficient and compact single photon emission platforms operating at room temperature with ultrafast speed and high brightness will be fundamental components of the emerging quantum communications and computing fields. However, so far, it is very challenging to design practical deterministic single photon emitters based on nanoscale solid‐state materials that meet the fast emission rate and strong brightness demands. Here, a solution is provided to this longstanding problem by using metallic nanocavities integrated with hexagonal boron nitride (hBN) flakes with defects acting as nanoscale single photon emitters (SPEs) at room temperature. The presented hybrid nanophotonic structure creates a rapid speedup and large enhancement in single photon emission at room temperature. Hence, the nonclassical light emission performance is substantially improved compared to plain hBN flakes and hBN on gold‐layered structures without nanocavity. Extensive theoretical calculations are also performed to accurately model the new hybrid nanophotonic system and prove that the incorporation of plasmonic nanocavity is key to efficient SPE performance. The proposed quantum nanocavity single photon source is expected to be an element of paramount importance to the envisioned room‐temperature integrated quantum photonic networks.

Enhancing cardiovascular health monitoring: Simultaneous multi-artery cardiac markers recording with flexible and bio-compatible AlN piezoelectric sensors

Continuous monitoring of cardiovascular parameters like pulse wave velocity (PWV), blood pressure wave (BPW), stiffness index (SI), reflection index (RI), mean arterial pressure (MAP), and cardio-ankle vascular index (CAVI) has significant clinical importance for the early diagnosis of cardiovascular diseases (CVDs). Standard approaches, including echocardiography, impedance cardiography, or hemodynamic monitoring, are hindered by expensive and bulky apparatus and accessibility only in specialized facilities. Moreover, noninvasive techniques like sphygmomanometry, electrocardiography, and arterial tonometry often lack accuracy due to external electrical interferences, artifacts produced by unreliable electrode contacts, misreading from placement errors, or failure in detecting transient issues and trends. Here, we report a bio-compatible, flexible, noninvasive, low-cost piezoelectric sensor for continuous and real-time cardiovascular monitoring. The sensor, utilizing a thin aluminum nitride film on a flexible Kapton substrate, is used to extract heart rate, blood pressure waves, pulse wave velocities, and cardio-ankle vascular index from four arterial pulse sites: carotid, brachial, radial, and posterior tibial arteries. This simultaneous recording, for the first time in the same experiment, allows to provide a comprehensive cardiovascular patient's health profile. In a test with a 28-year-old male subject, the sensor yielded the SI = 7.1 ± 0.2 m/s, RI = 54.4 ± 0.5 %, MAP = 86.2 ± 1.5 mmHg, CAVI = 7.8 ± 0.2, and seven PWVs from the combination of the four different arterial positions, in good agreement with the typical values reported in the literature. These findings make the proposed technology a powerful tool to facilitate personalized medical diagnosis in preventing CVDs.

Atomic and Electronic Structure of Defects in hBN: Enhancing Single-Defect Functionalities.

Defect centers in insulators play a critical role in creating important functionalities in materials: prototype qubits, single-photon sources, magnetic field probes, and pressure sensors. These functionalities are highly dependent on their midgap electronic structure and orbital/spin wave function contributions. However, in most cases, these fundamental properties remain unknown or speculative due to the defects being deeply embedded beneath the surface of highly resistive host crystals, thus impeding access through surface probes. Here, we directly inspected the atomic and electronic structures of defects in thin carbon-doped hexagonal boron nitride (hBN:C) by using scanning tunneling microscopy (STM) and scanning tunneling spectroscopy (STS). Such investigation adds direct information about the electronic midgap states to the well-established photoluminescence response (including single-photon emission) of intentionally created carbon defects in the most commonly investigated van der Waals insulator. Our joint atomic-scale experimental and theoretical investigations reveal two main categories of defects: (1) single-site defects manifesting as donor-like states with atomically resolved structures observable via STM and (2) multisite defect complexes exhibiting a ladder of empty and occupied midgap states characterized by distinct spatial geometries. Combining direct probing of midgap states through tunneling spectroscopy with the inspection of the optical response of insulators hosting specific defect structures holds promise for creating and enhancing functionalities realized with individual defects in the quantum limit. These findings underscore not only the versatility of hBN:C as a platform for quantum defect engineering but also its potential to drive advancements in atomic-scale optoelectronics.

Highly Sustainable h-BN Encapsulated MoS2 Hydrogen Evolution Catalysts.

Despite the importance of the stability of the 2D catalysts in harsh electrolyte solutions, most studies have focused on improving the catalytic performance of molybdenum disulfide (MoS2) catalysts rather than the sustainability of hydrogen evolution. In previous studies, the vulnerability of MoS2 crystals is reported that the moisture and oxygen molecules can cause the oxidation of MoS2 crystals, accelerating the degradation of crystal structure. Therefore, optimization of catalytic stability is crucial for approaching practical applications in 2D catalysts. Here, it is proposed that monolayered MoS2 catalysts passivated with an atomically thin hexagonal boron nitride (h-BN) layer can effectively sustain hydrogen evolution reaction (HER) and demonstrate the ultra-high current density (500mAcm⁻2 over 11 h) and super stable (64 h at 150mAcm⁻2) catalytic performance. It is further confirmed with density functional theory (DFT) calculations that the atomically thin h-BN layer effectively prevents direct adsorption of water/acid molecules while allowing the protons to be adsorbed/penetrated. The selective penetration of protons and prevention of crystal structure degradation lead to maintained catalytic activity and maximized catalytic stability in the h-BN covered MoS2 catalysts. These findings propose a promising opportunity for approaching the practical application of 2D MoS2 catalysts having long-term stability at high-current operation.

Reoxidation Behavior of the Direct Reduced Iron and Hot Briquetted Iron during Handling and Their Integration into Electric Arc Furnace Steelmaking: A Review

This paper studies the integration of direct reduced iron (DRI) and hot briquetted iron (HBI) into the steelmaking process via an electric arc furnace (EAF). Considering a variety of DRI production techniques distinguished by different reactor types, this paper provides a comparative overview of the current state. It delves into significant challenges, such as the susceptibility of DRI to reoxidation and the necessity of thorough handling to maintain its quality. The effectiveness of several reoxidation mitigation strategies, including the application of thin oxide layers, briquetting, various coatings, and nitride formation in ammonia-based reduction processes, is evaluated. Most existing studies have primarily focused on the reoxidation of DRI rather than on HBI, despite the fact that HBI may undergo reoxidation. The importance of DRI/HBI in offering an alternative to the integrated steelmaking route is highlighted, focusing on how it changes the EAF process compared to those for melting scrap. This paper also identifies several research prospects for further DRI/HBI applications in steel production.

Anneal-free ultra-low loss silicon nitride integrated photonics

Heterogeneous and monolithic integration of the versatile low-loss silicon nitride platform with low-temperature materials such as silicon electronics and photonics, III–V compound semiconductors, lithium niobate, organics, and glasses has been inhibited by the need for high-temperature annealing as well as the need for different process flows for thin and thick waveguides. New techniques are needed to maintain the state-of-the-art losses, nonlinear properties, and CMOS-compatible processes while enabling this next generation of 3D silicon nitride integration. We report a significant advance in silicon nitride integrated photonics, demonstrating the lowest losses to date for an anneal-free process at a maximum temperature 250 °C, with the same deuterated silane based fabrication flow, for nitride and oxide, for an order of magnitude range in nitride thickness without requiring stress mitigation or polishing. We report record low anneal-free losses for both nitride core and oxide cladding, enabling 1.77 dB m-1 loss and 14.9 million Q for 80 nm nitride core waveguides, more than half an order magnitude lower loss than previously reported sub 300 °C process. For 800 nm-thick nitride, we achieve as good as 8.66 dB m−1 loss and 4.03 million Q, the highest reported Q for a low temperature processed resonator with equivalent device area, with a median of loss and Q of 13.9 dB m−1 and 2.59 million each respectively. We demonstrate laser stabilization with over 4 orders of magnitude frequency noise reduction using a thin nitride reference cavity, and using a thick nitride micro-resonator we demonstrate OPO, over two octave supercontinuum generation, and four-wave mixing and parametric gain with the lowest reported optical parametric oscillation threshold per unit resonator length. These results represent a significant step towards a uniform ultra-low loss silicon nitride homogeneous and heterogeneous platform for both thin and thick waveguides capable of linear and nonlinear photonic circuits and integration with low-temperature materials and processes.

Thermal engineering increases current density in AlGaN/GaN superlattice devices

Aluminum gallium nitride/gallium nitride multi-channel superlattice devices are receiving increasing attention as a new paradigm for driving the power density of gallium nitride based transistors toward their theoretical limit. However, the superior electrical performance of superlattice-based transistors is currently limited by excessive Joule-heating. This Letter evaluates what impact the number of superlattice channels and the buffer layer composition has on the reduction of the thermal resistance, i.e., Joule heating, of AlGaN/GaN superlattice devices. A record low thermal resistance (12.51 ± 0.34 K mm W−1) was measured via scanning thermal microscopy for non-castellated superlattice AlGaN/GaN devices with a 100 μm channel width. Overall, the use of a thin gallium nitride buffer layer, in place of a thick aluminum gallium nitride layer, reduced the buffer thermal resistance enabling the accommodation of more superlattice channels (10 vs 6), therefore augmenting the maximum power density of these devices. The superlattice device proposed here not only provides an enhanced thermal dissipation solution for high power density radio frequency electronics, but it also has the benefit of fewer fabrication steps in comparison with previously reported castellated multichannel devices.

Estimation of fatigue life of TiN coatings using cyclic micro-impact testing

We studied the behaviour of a thin titanium nitride (TiN) coating (1.5 µm thick) on a tool steel substrate under dynamic and cyclic impacts through an approach combining experimental testing and computational modelling. Dynamic impact testing was used to investigate the load-dependent dynamic hardness and assess the energy-dissipation capabilities of the coating system. In cyclic impact tests, the coating-substrate system experienced permanent plastic deformation in each cycle, ultimately leading to coating failure. Chemical analysis identified an interlayer between the coating and the substrate that influenced the coating response, while cross-sectional analysis revealed the extent of coating damage due to cycling and impact load. A three-dimensional map was constructed, connecting the acceleration load, sensed depth, and cycles to the coating failure, and an empirical equation was used to characterise the relationship between the depth and cycles to failure. The computational model examined the traction component distribution during loading and unloading, focusing on normal and shear tractions. These findings suggested the potential significance of normal traction in the interfacial fatigue failure due to impact.

High-temperature oxidation and diffusion studies on selected Al–Cr–Fe–Ni high-entropy alloys for potential application in thermal barrier coatings

In this work, the properties of two high-entropy alloys (HEAs) Al25Cr20Fe20Ni35 and Al20Cr20Fe20Ni40 (at.%) were compared for potential application as bond coats in thermal barrier coatings (TBCs). For this reason, both their oxidation resistance under isothermal and thermal shock conditions, as well as diffusion phenomena occurring at the substrate-HEA diffusion couple interface, were investigated. It was determined that both alloys demonstrate good phase stability and oxidation resistance during prolonged exposure to air atmosphere at 1000°C. In the initial 100 h period, selective aluminum oxidation is responsible for the protective scale growth on both materials under both isothermal and thermal shock conditions. However, only the Al20Cr20Fe20Ni40 high entropy alloy maintains a single Al2O3 layer for over 1000 h of oxidation with cyclic temperature changes. On the other hand, diffusion studies indicate that mainly iron and chromium travel between the ferritic steel substrate and the HEAs. Aluminum diffusion is seemingly limited by the unexpected formation of a thin aluminum nitride layer at the interface between the materials. From all these results it can be concluded that the Al20Cr20Fe20Ni40 alloy shows more promise for application in TBCs based on high entropy materials than Al25Cr20Fe20Ni35.

Ultra-High-Efficiency Corrosion Protection of Metallic Surface Based on Thin and Dense Hexagonal Boron Nitride Coating Films.

Quest for ultrathin and highly effective anticorrosion coating films is critical for both fundamental community of materials science and industrial economics. A two-dimensional hexagonal boron nitride (h-BN) film is a newly developed effective anticorrosion material due to its superior impermeability, thermal stability, and chemical stability. However, research in growth and anticorrosion properties of large-area dense h-BN coating films still lies in its infancy. Here, we report on the synthesis of a large-area and continuous dense few-layer (∼4) h-BN coating film onto a metal surface by chemical vapor deposition (CVD) and its anticorrosion properties both in air and seawater environments. Cu coated in h-BN, which functions as an anticorrosive coating, exhibits an impressively reduced corrosion rate (CR) in a 3.5% NaCl solution (which mimics a seawater environment) when compared to bare Cu (approximately 27 times). At 200 °C, the h-BN coating can prevent Cu foil's surface from oxidizing, although doing so will cause a significant amount of oxide particles to simultaneously form on the bare Cu surface. In the meantime, the performance of the h-BN film remains unaltered after 100 days in an atmospheric environment, demonstrating the ultrahigh stability and corrosion resistance of the as-grown h-BN film.

Controlling plasma-based surface modifications of an austenitic alloy by thermochemical and athermal diffusions

Under nitrogen plasma immersion ion implantation, the energy density per pulse EPulse/A was found to be proportional to the amount of the N-expanded austenite phase (γN) in a superaustenitic stainless steel, as previously seen for an austenitic-ferritic alloy. Since γN occurs in a range of stoichiometries, the parameter was also contrasted with the ion fluence Γ, which affects the retained dose. Γ varies inversely with EPulse/A and influences oppositely the properties of the modified surfaces. The temperature was the same among the treatments (320 °C) to rule out thermal diffusion as an extra variable. The increase of EPulse/A (for applied voltages 6.2–10.4 kV) produces thicker layers (1.4–2.2 µm), as an increase in lattice defects and stresses enhances N-diffusion, while high Γ values favor the N-saturation at the top surface for the opposite reason. The lowest Epulse/A (6.2–9.5 kV) result in brittle cases with a possible thin nitrides layer on top, whereas γN prevails in the ductile layer produced by the highest one (10.4 kV). The N-concentration governs the strength against plastic deformation: hardness varies up to 32% from the highest (6.2 kV) to the lowest Γ treatment (10.4 kV). In summary, the correlation of Epulse/A with Γ is indispensable for controlling properties of the modified surfaces for performance purposes.

Penning ion source based surface modification of titanium by nitrogen ion implantation

The nitrogen ions of the Penning ion source are bombarded on commercially available pure titanium substrates in pulses of about 5.6 μs duration. A thin film (∼500 nm) of multiphase titanium nitride is produced without additional heating of the substrate. The surface modification is studied for various energies of implanted ions at a low flux density. The 2.4 × 109 ions of specific energy are bombarded on the sample in each single pulse of the ion. Each sample is exposed to one thousand such pulses at a repetition rate of 0.1 Hz. The corresponding energy flux was transferred to the sample, promoting the growth of a thin nitride layer. X-ray diffraction (XRD) analysis demonstrates the formation of a monocrystalline multiphase titanium nitride thin film. The XRD spectra show the multiphase reflections of Ti4N2 (111), Ti9N3.87 (009), and Ti12N7 (0012) that depend on the energy of the ion beam. Ti4N2 is observed to be the dominant phase in this ion implantation process. The morphological and compositional changes of ion implanted samples are investigated using field emission scanning electron microscopy (SEM) along with energy dispersive x-ray spectroscopy (EDX). Raman scattering analysis of treated samples verified the XRD results. The penetration depth of nitrogen ions inside the titanium is calculated using the SRIM code. Vickers hardness has improved three times compared to the original sample.

Signal-enhanced multi-core fiber-based WaveFlex biosensor for ultra-sensitive xanthine detection.

In this work, we introduce a novel multimode fiber (MMF) - seven core fiber (SCF) - MMF (MCM) optical fiber biosensor, also known as the WaveFlex biosensor (plasma wave assisted fiber biosensor), based on localized surface plasmon resonance (LSPR) for qualitative detection of xanthine. Xanthine is a purine base widely distributed in human blood and tissues, and commonly used as an indicator for various disease detections. The MCM sensor incorporates a tapered optical fiber structure, fabricated using the combiner manufacturing system (CMS), and is designed with SCF and MMF. By effectively harnessing LSPR, the sensor boosts the attachment points of biomolecules on the probe surface through immobilized tungsten disulfide (WS2)-thin layers, gold nanoparticles (AuNPs), and carbon nitride quantum dots (C3N-QDs). The functionalization of xanthine oxidase (XO) on the sensing probe further enhances the sensor's specificity. The proposed WaveFlex biosensor exhibits a remarkable sensitivity of 3.2 nm/mM and a low detection limit of 96.75 µM within the linear detection range of 100 - 900 µM. Moreover, the sensor probe demonstrates excellent reusability, reproducibility, stability, and selectivity. With its sensitivity, biocompatibility, and immense potential for detecting human serum and fish products, this WaveFlex biosensor presents a promising platform for future applications.

Construction of layered SnS2 and g-C3N4 nanoarchitectonics towards pollution degradation and H2 generation

Two dimensional (2D)/2D heterostructures with much interface is advantage to improve the transfer of photogenerated carriers. In this paper, SnS2 nanosheets were horizontally grown on superior thin graphic carbon nitride (g-C3N4) nanosheets to construct 2D/2D heterostructures with enhanced photocatalytic performance. The g-C3N4 nanosheets (CN) were obtained by a two-step thermal polymerization at 600 and 700 °C. the growth of SnS2 nanosheets was then carried out using a solvothermal synthesis. Preparation parameters including temperature, reaction time, and precursor components were tested to get optimized SnS2/g-C3N4 composite sample 8SnS2-CN. A Z-scheme mechanism was proposed for the discussion of photocatalytic process. The degradation test of Rhodamine B (Rh B) indicated that the degradation rate of Rh B using sample 8SnS2-CN was twice quick compared with g-C3N4 nanosheets, in which Rh B degradation was completed within 15 min. The photocatalytic hydrogen production rate of sample 8SnS2-CN was about 6 times that that of sample CN, which is 1818.75 μmol g−1 L−1. Enhanced photocatalytic performance is ascribed to SnS2 deposited to form well-developed interface which improved the separation and transfer of photogenerated carriers. In addition, the growth of SnS2 was also expended the photo adsorption.

Surface activation of atomically thin metal nitride by confined nanoclusters to trigger pH-universal hydrogen evolution

Surface activation of atomically thin metal nitride by confined nanoclusters to trigger pH-universal hydrogen evolution

Thin film aluminum nitride surface acoustic wave resonators for quantum acoustodynamics

Quantum excitations of macroscopic surface acoustic waves (SAWs) have been tailored to control, communicate, and transduce stationary and flying quantum states. However, the limited lifetime of these hybrid quantum systems remains critical obstacles to extend their applications in quantum information processing. Here, we present potentials of thin film aluminum nitride to on-chip integrated phonons with superconducting qubits over previous bulk piezoelectric substrates. We have reported high-quality thin film GHz-SAW resonators with the highest internal quality factor Qi of 4.92×104 in the quantum regime. The internal losses of SAW resonators are systematically investigated by tuning the parameters of sample layout, power, and temperature. Our results manifest that SAWs on piezoelectric films are readily integrated with standard fabrication of Josephson junction quantum circuits and offer excellent acoustic platforms for high-coherence quantum acoustodynamics architectures.

Autonomous sputter synthesis of thin film nitrides with composition controlled by Bayesian optimization of optical plasma emission

Autonomous sputter synthesis of thin film nitrides with composition controlled by Bayesian optimization of optical plasma emission

Heterogeneous integration of superconducting thin films and epitaxial semiconductor heterostructures with lithium niobate

We report on scalable heterointegration of superconducting electrodes and epitaxial semiconductor quantum dots (QDs) on strong piezoelectric and optically nonlinear lithium niobate. The implemented processes combine the sputter-deposited thin film superconductor niobium nitride and III–V compound semiconductor membranes onto the host substrate. The superconducting thin film is employed as a zero-resistivity electrode material for a surface acoustic wave resonator with internal quality factors representing a three-fold enhancement compared to identical devices with normal conducting electrodes. Superconducting operation of resonators is achieved to temperatures and electrical radio frequency powers . Heterogeneously integrated single QDs couple to the resonant phononic field of the surface acoustic wave resonator operated in the superconducting regime. Position and frequency selective coupling mediated by deformation potential coupling is validated using time-integrated and time-resolved optical spectroscopy. Furthermore, acoustoelectric charge state control is achieved in a modified device geometry harnessing large piezoelectric fields inside the resonator. The hybrid QD—surface acoustic wave resonator can be scaled to higher operation frequencies and smaller mode volumes for quantum phase modulation and transduction between photons and phonons via the QD. Finally, the employed materials allow for the realization of other types of optoelectronic devices, including superconducting single photon detectors and integrated photonic and phononic circuits.

Optical properties of pulsed dc magnetron sputtered thin film tantalum nitride by spectroscopic ellipsometry

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.