Search Results (18)

This work investigated the effect of high-nitrogen/low-hydrogen mixed atmosphere heat treatment on the electrochemical corrosion and wear resistance of plasma-sprayed FeCoNiCrAl high-entropy alloy (HEA) coatings. The HEA coatings were sequentially prepared through annealing at 400, 600, and 800 °C for 6 h. The heat treatment method was conducted in a vacuum tube furnace under 0.1 MPa total pressure, with gas flow rates set to 300 sccm N₂ and 100 sccm H₂. The XRD results indicated that the as-deposited coating exhibited α-Fe (BBC) and Al_0.9Ni_4.22 (FCC) phases, with an Fe_0.64N_0.36 nitride phase generated after 800 °C annealing. The electrochemical measurements suggested that an exceptional corrosion performance with higher thicknesses of passive film and double-layer capacitance can be detected based on the point defect model (PDM) and effective capacitance model. Wear tests revealed that the friction coefficient at 800 °C decreased by 3.84% compared to that in the as-sprayed state due to the formation of a dense nitride layer. Molecular orbital theory pointed out that the formation of bonding molecular orbitals, resulting from the overlap of valence electron orbitals of different atomic species in the HEA coating system, stabilized the structure by promoting atomic interactions. The wear mechanism associated with stress redistribution and energy balance from compositional synergy is proposed in this work. Full article

Direct chemical vapor deposition (CVD) growth of hexagonal boron nitride (h-BN) on insulating substrates offers a promising pathway to circumvent transfer-induced defects and enhance device integration. This comprehensive review systematically evaluates recent advances in CVD techniques for h-BN synthesis on insulating substrates, including metal–organic CVD (MOCVD), low-pressure CVD (LPCVD), atmospheric-pressure CVD (APCVD), and plasma-enhanced CVD (PECVD). Key challenges, including precursor selection, high-temperature processing, achieving single-crystalline films, and maintaining phase purity, are critically analyzed. Special emphasis is placed on comparative performance metrics across different growth methodologies. Furthermore, crucial research directions for future development in this field are outlined. This review aims to serve as a reference for advancing h-BN synthesis toward practical applications in next-generation electronic and optoelectronic devices. Full article

Low-temperature plasma nitriding is a thermochemical surface treatment that promotes surface hardening and wear resistance enhancement without compromising the corrosion resistance of sintered austenitic stainless steels. Hollow cathode radiofrequency (RF) plasma nitriding was conducted to evaluate the influence of the working pressure and nitriding time on the microstructure and thickness of the nitrided layers. A group of samples of sintered 316L austenitic stainless steel were plasma-nitrided at 400 °C for 4 h, varying the working pressure from 160 to 25 Pa, and the other group was treated at the same temperature, varying the nitriding time (2 h and 4 h) while keeping the pressure at 25 Pa. A higher pressure resulted in a thinner, non-homogeneous nitrided layer with an edge effect. Regardless of the nitriding duration, the lowest pressure (25 Pa) promoted the formation of a homogenously nitrided layer composed of nitrogen-expanded austenite that was free of iron or chromium nitride and harder and more scratching-wear-resistant than the soft steel substrate. Full article

This study reports the chemical vapor deposition of amorphous boron carbonitride films on Si(100) and SiO₂ substrates using a trimethylamine borane and nitrogen mixture. BC_xN_y films with different compositions were produced via variations in substrate temperature and type of gas-phase activation. The low-pressure chemical vapor deposition (LPCVD) and plasma-enhanced chemical vapor deposition (PECVD) methods were used. The “elemental composition—chemical bonding state—properties” relationship of synthesized BC_xN_y was systematically studied. The hydrophilicity, mechanical, and optical properties of the films are discussed in detail. The composition of films deposited by the LPCVD method at temperatures ranging from 673 to 973 K was close to that of boron carbide with a low nitrogen content (BC_xN_y). The refractive index of these films changed in the range from 2.43 to 2.56 and increased with temperature. The transparency of these films achieved 85%. LPCVD films were hydrophilic and the water contact angles varied between 53 and 63°; the surface free energy was 42–48 mN/m. The microhardness, Young’s modulus and elastic recovery of LPCVD films ranged within 24–28 GPa, 220–247 GPa, and 70–74%, respectively. The structure of the PECVD films was close to that of hexagonal boron nitride, and their composition can be described by the BC_xN_yO_z:H formula. In case of the PECVD process, the smooth films were only produced at low deposition temperatures (373–523 K). The refractive index of these films ranged from 1.51 to 1.67. The transparency of these films achieved 95%; the optical band gap was evaluated as 4.92–5.28 eV. Unlike LPCVD films, they were very soft, and their microhardness, Young’s modulus and elastic recovery were 0.8–1.4 GPa, 25–26 GPa, and 19–28%, respectively. A set of optimized process parameters to fabricate LPCVD BC_xN_y films with improved mechanical and PECVD films with high transparency is suggested. Full article

Carbon nanotube-based derivatives have attracted considerable research interest due to their unique structure and fascinating physicochemical properties. However, the controlled growth mechanism of these derivatives remains unclear, and the synthesis efficiency is low. Herein, we proposed a defect-induced strategy for the efficient heteroepitaxial growth of single-wall carbon nanotubes (SWCNTs)@hexagonal boron nitride (h-BN) films. Air plasma treatment was first performed to generate defects on the wall of SWCNTs. Then, atmospheric pressure chemical vapor deposition was conducted to grow h-BN on the surface of SWCNTs. Controlled experiments combined with first-principles calculations revealed that the induced defects on the wall of SWCNTs function as nucleation sites for the efficient heteroepitaxial growth of h-BN. Full article

High Power Impulse Magnetron Sputtering (HiPIMS) has generated a great deal of interest by offering significant advantages such as high target ionization rate, high plasma density, and the smooth surface of the sputtered films. This study discusses the deposition of copper nitride thin films via HiPIMS at different deposition pressures and then examines the impact of the deposition pressure on the structural and electrical properties of Cu₃N films. At low deposition pressure, Cu-rich Cu₃N films were obtained, which results in the n-type semiconductor behavior of the films. When the deposition pressure is increased to above 15 mtorr, Cu₃N phase forms, leading to a change in the conductivity type of the film from n-type to p-type. According to our analysis, the Cu₃N film deposited at 15 mtorr shows p-type conduction with the lowest resistivity of 0.024 Ω·cm and the highest carrier concentration of 1.43 × 10²⁰ cm⁻³. Furthermore, compared to the properties of Cu₃N films deposited via conventional direct current magnetron sputtering (DCMS), the films deposited via HiPIMS show better conductivity due to the higher ionization rate of HiPIMS. These results enhance the potential of Cu₃N films’ use in smart futuristic devices such as photodetection, photovoltaic absorbers, lithium-ion batteries, etc. Full article

This paper is concerned with plasma diagnosis on a N₂-H₂ gas mixture to determine the optimum parameters for the nitriding process. Plasma parameters such as pressure, RF-voltage, and DC-bias were varied for optimization. The active species such as ${\mathrm{N}}_2^{+}$ and NH were identified in plasma diagnosis. In the N₂-H₂ gas mixture, hydrogen imposed a great influence on plasma generation. The small addition of a hydrogen molecule into the gas mixture resulted in the highest yield of ${\mathrm{N}}_2^{+}$ions and NH radicals; the optimum hydrogen content was 20% in the mixture. The austenitic stainless-steel type AISI304 was nitrided at 673 K and 623 K to experimentally demonstrate that hydrogen gas content optimization is necessary to improve the surface hardness and to describe low temperature nitriding under high nitrogen flux at the surface. Full article

WC-Co cermet was plasma-nitrided with the assistance of a hollow cathode ion source at 400 °C under a vacuum of 3–8 Pa. Hot film chemical vapor deposition (HFCVD) of a diamond coating was carried out on the nitrided specimen, without chemical etching. Scanning electronic microscopy, electron probing microscopy, X-ray diffraction, and X-ray photoelectron spectroscopy were used to characterize the surface microstructure of the nitride specimens and the coatings. A thin surface conversion layer with a specific structure was formed, in which the primary Co binder was transformed into Co-rich particles. The Co-rich particles consisted of a γ-Co core and a Co₄N outer layer. This specific surface conversion layer significantly suppresses the out-diffusion and catalytic graphitization of Co during HFCVD. The existent phase, morphology, and density distribution of Co compounds can be tuned by varying the nitriding parameters, such as gas media, ionization ratio, bombardment energy flux, and nitriding duration. Full article

Silicon nitride waveguides have emerged as an excellent platform for photonic applications, including nonlinear optical signal processing, owing to their relatively high Kerr nonlinearity, negligible two photon absorption, and wide transparent bandwidth. In this paper, we propose an effective approach using 3D finite element method to optimize the dispersion characteristics of silicon nitride waveguides for four-wave mixing (FWM) applications. Numerical studies show that a flat and low dispersion profile can be achieved in a silicon nitride waveguide with the optimized dimensions. Near-zero dispersion of 1.16 ps/km/nm and 0.97 ps/km/nm at a wavelength of 1550 nm are obtained for plasma-enhanced chemical vapor deposition (PECVD) and low-pressure chemical vapor deposition (LPCVD) silicon nitride waveguides, respectively. The fabricated micro-ring resonator with the optimized dimensions exhibits near-zero dispersion of −0.04 to −0.1 ps/m/nm over a wavelength range of 130 nm which agrees with the numerical simulation results. FWM results show that near-zero phase mismatch and high conversion efficiencies larger than −12 dB using a low pump power of 0.5 W in a 13-cm long silicon nitride waveguide are achieved. Full article

We report on low-temperature and low-pressure deposition conditions of 140 °C and 1.5 mTorr, respectively, to achieve high-optical quality silicon nitride thin films. We deposit the silicon nitride films using an electron cyclotron resonance plasma-enhanced chemical vapour deposition (ECR-PECVD) chamber with Ar-diluted SiH₄, and N₂ gas. Variable-angle spectroscopic ellipsometry was used to determine the thickness and refractive index of the silicon nitride films, which ranged from 300 to 650 nm and 1.8 to 2.1 at 638 nm, respectively. We used Rutherford backscattering spectrometry to determine the chemical composition of the films, including oxygen contamination, and elastic recoil detection to characterize the removal of hydrogen after annealing. The as-deposited films are found to have variable relative silicon and nitrogen compositions with significant oxygen content and hydrogen incorporation of 10–20 and 17–21%, respectively. Atomic force microscopy measurements show a decrease in root mean square roughness after annealing for a variety of films. Prism coupling measurements show losses as low as 1.3, 0.3 and 1.5 ± 0.1 dB/cm at 638, 980 and 1550 nm, respectively, without the need for post-process annealing. Based on this study, we find that the as-deposited ECR-PECVD SiO_xN_y:H_z films have a suitable thickness, refractive index and optical loss for their use in visible and near-infrared integrated photonic devices. Full article

The formation of gallium nitride (GaN) semi-polar and non-polar nanostructures is of importance for improving light extraction/absorption of optoelectronic devices, creating optical resonant cavities or reducing the defect density. However, very limited studies of nanotexturing via dry etching have been performed, in comparison to wet etching. In this paper, we investigate the formation and morphology of semi-polar ($11\overline{2}2$) and non-polar ($11\overline{2}0$) GaN nanorods using inductively coupled plasma (ICP) etching. The impact of gas chemistry, pressure, temperature, radio-frequency (RF) and ICP power and time are explored. A dominant chemical component is found to have a significant impact on the morphology, being impacted by the polarity of the planes. In contrast, increasing the physical component enables the impact of crystal orientation to be minimized to achieve a circular nanorod profile with inclined sidewalls. These conditions were obtained for a small percentage of chlorine (Cl₂) within the Cl₂ + argon (Ar) plasma combined with a low pressure. Damage to the crystal was reduced by lowering the direct current (DC) bias through a reduction of the RF power and an increase of the ICP power. Full article

A low-temperature (400 °C) glow plasma nitriding layer on AISI 904L austenitic stainless steel was obtained at various NH₃ pressures and studied using electrochemical method, X-ray diffraction, and scanning Kelvin probe. The pressure of NH₃ dominated the microstructure of the nitriding layer. The saturation degree of γN controlled corrosion performance and microhardness. Insufficient NH₃ pressure (<100 Pa) resulted in discontinuous nitride caking coverage, whereas excessive NH₃ pressure (>100 Pa) facilitated the transformation of the nitriding layer to harmful nitrides (CrN) due to a localized overheating effect caused by the over-sputtering current. Full article

Stacked SiGe/Si structures are widely used as the units for gate-all-around nanowire transistors (GAA NWTs) which are a promising candidate beyond fin field effective transistors (FinFETs) technologies in near future. These structures deal with a several challenges brought by the shrinking of device dimensions. The preparation of inner spacers is one of the most critical processes for GAA nano-scale transistors. This study focuses on two key processes: inner spacer film conformal deposition and accurate etching. The results show that low pressure chemical vapor deposition (LPCVD) silicon nitride has a good film filling effect; a precise and controllable silicon nitride inner spacer structure is prepared by using an inductively coupled plasma (ICP) tool and a new gas mixtures of CH₂F₂/CH₄/O₂/Ar. Silicon nitride inner spacer etch has a high etch selectivity ratio, exceeding 100:1 to Si and more than 30:1 to SiO₂. High anisotropy with an excellent vertical/lateral etch ratio exceeding 80:1 is successfully demonstrated. It also provides a solution to the key process challenges of nano-transistors beyond 5 nm node. Full article

The optimization of mesa etch for a quasi-vertical gallium nitride (GaN) Schottky barrier diode (SBD) by inductively coupled plasma (ICP) etching was comprehensively investigated in this work, including selection of the etching mask, ICP power, radio frequency (RF) power, ratio of mixed gas, flow rate, and chamber pressure, etc. In particular, the microtrench at the bottom corner of the mesa sidewall was eliminated by a combination of ICP dry etching and tetramethylammonium hydroxide (TMAH) wet treatment. Finally, a highly anisotropic profile of the mesa sidewall was realized by using the optimized etch recipe, and a quasi-vertical GaN SBD was demonstrated, achieving a low reverse current density of 10⁻⁸ A/cm² at −10 V. Full article

Filling epoxy resin (EP) with boron nitride (BN) nanosheets (BNNSs) can effectively improve the thermal conductivity of BN/EP nanocomposites. However, due to the few hydroxyl groups on the surface of BNNSs, silane coupling agent (SCA) cannot effectively modify BNNSs. The agglomeration of BNNSs is severe, which significantly reduces the AC breakdown strength of the composites. Therefore, this paper uses atmospheric pressure bipolar nanosecond pulse dielectric barrier discharge (DBD) Ar+H₂O low temperature plasma to hydroxylate BNNSs to improve the AC breakdown strength and thermal conductivity of the composites. X-ray photoelectron spectroscopy (XPS) shows that the hydroxyl content of the BNNSs surface increases nearly two fold after plasma modification. Fourier transform infrared spectroscopy (FTIR) and thermogravimetric analysis (TGA) show that plasma modification enhances the dehydration condensation reaction of BNNSs with SCA, and the coating amount of SCA on the BNNSs surface increases by 45%. The breakdown test shows that the AC breakdown strength of the composites after plasma modification is improved under different filling contents. With the filling content of BNNSs increasing from 10% to 20%, the composites can maintain a certain insulation strength. Meanwhile, the thermal conductivity of the composites increases by 67% as the filling content increases from 10% (SCA treated) to 20% (plasma and SCA treated). Therefore, the plasma hydroxylation modification method used in this paper can provide a basis for the preparation of high thermal conductivity insulating materials. Full article