Junhua Xu

Bio: Junhua Xu is an academic researcher from Jiangsu University. The author has contributed to research in topics: Microstructure & Sputter deposition. The author has an hindex of 17, co-authored 67 publications receiving 732 citations.

The improvement of oxidation resistance, mechanical and tribological properties of W2N films by doping silicon

Abstract: W-Si-N composite films were deposited on both stainless steel and silicon wafers using a reactive magnetron system. The silicon content of the film was varied to evaluate the effect of silicon on films' elemental composition, microstructure, oxidation resistance, mechanical and tribological properties. These series of test were conducted using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and high resolution transmission electron microscopy (HRTEM) analytical tools. The W-Si-N films showed a two-phase structure of solid solution face-centered cubic (fcc) W(Si)N x and an amorphous Si 3 N 4 . The thermal stability and the oxidation resistant temperature of W-Si-N films increased from about 380 °C at 0 at% Si to about 650 °C at 31.2 at% Si with the incorporation of Si into W 2 N matrix. The hardness of the films increased continuously from 26 GPa at 0 at% Si to 40 GPa at 23.5 at% Si which was due to solid strengthening and fine-grained strengthening. The silicon content affected the tribological properties of the film at room temperature but this was mainly influenced by the yield pressure, H/E ratio and elastic recovery, since lubricant tribo-film WO 3 was detected on all surfaces of the W-Si-N films. There was an initial gradual decrease in average coefficient of friction and wear rate until a minimum, but a further increase in silicon content resulted in increase in both friction coefficient and wear rates. The least coefficient of friction and wear rate values were 0.30 and 8.7 × 10 − 8 mm 3 /N·mm at 23.5 at% Si.

Recent progress of transition metal nitrides for efficient electrocatalytic water splitting

Abstract: The hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) constitute the two main processes in electrochemical water splitting to produce high-purity hydrogen and oxygen as alternatives to fossil fuel. Catalysts are crucial to high-efficiency conversion of water to hydrogen and oxygen. Although transition metal nitrides (TMNs) are promising HER and OER catalysts due to the unique electronic structure and high electrical conductivity, single-phase nitrides have inferior activity compared to Pt-group metals because of the unsatisfactory metal–hydrogen (M–H) bonding strength. TMNs-based composites in combination with other metals, carbon materials, and metallic compounds have been demonstrated to possess improved catalytic properties because the modified electronic structure leads to balanced M–H bonding strength, synergistic effects, and improved electrochemical stability. Herein, recent progress pertaining to TMNs is reviewed from the perspective of advanced catalysts for electrochemical water splitting. The challenges and future opportunities confronting TMNs-based catalysts are also discussed.

Continuous Ultra-Thin MOS2 Films Grown by Low-Temperature Physical Vapor Deposition (Postprint)

Abstract: : Uniform growth of pristine two dimensional (2D) materials over large areas at lower temperatures without sacrifice of their unique physical properties is a critical pre-requisite for seamless integration of next-generation van der Waals heterostructures into functional devices. This Letter describes a vapor phase growth technique for precisely controlled synthesis of continuous, uniform molecular layers of MoS2 on silicon dioxide and highly oriented pyrolitic graphite substrates of over several square centimeters at 350 deg C. Synthesis of few-layer MoS2 in this ultra-high vacuum physical vapor deposition process yields materials with key optical and electronic properties identical to exfoliated layers. The films are composed of nano-scale domains with strong chemical binding between domain boundaries, allowing lift-off from the substrate and electronic transport measurements from contacts with separation on the order of centimeters.