Yizhen Bai

Mechanical and electronic properties of B12-based ternary crystals of orthorhombic phase

Using first-principles calculations, the structural, mechanical and electronic properties of the experimentally synthesized B(12)-based ternary crystals (AlMgB(14), AlNaB(14), AlLiB(14), Mg(2)B(14), MgSi(2)B(12), MgC(2)B(12), Li(2)Si(2)B(12) and Li(2)C(2)B(12)) have been investigated. The theoretical equilibrium lattice constants of these crystals agree with the experimental values. The Vickers hardness (H(v)) estimated from the theoretical Youngs moduli ranges from 20 to 30 GPa, and the MgC(2)B(12) compound (H(v) = 31.4 GPa) is harder than α-boron. Based on the electron density of states and Mulliken population analysis, the origination of hardness and interaction between the interstitial atoms and the B(12) framework were discussed. Scaled bond order of the B-B bonds was used to interpret the hardness of these B(12)-based ternary compounds. The crystal hardness is primarily determined by the B(12) icosahedral skeleton, whereas the contributions of metal atoms manifest as the electron transfer from metal to B atoms. We also calculated the ideal tensile strength of AlMgB(14) and MgC(2)B(12) and found that the <001> and <010> directions are their cleavage directions under tensile strains, respectively.

Influence of boron contents on properties of AlMgB films prepared by RF magnetron sputtering

Ternary AlMgB thin films were synthesized on silicon (100) substrate at 573 K by radio frequency (RF) magnetron sputtering method using one Al/Mg co-target and one boron target. The thickness of the as-deposited thin film was controlled to 500 nm by adjusting deposition time. The influences of sputtering powers on the elemental contents and structural and mechanical properties were investigated by electron probe microanalysis (EPMA), X-ray diffraction (XRD), high-resolution transmission electron microscopy (HR-TEM), and nanoindentation system. At the same time, the ball-on-disk tribometer was used to measure the friction behavior of the films. Experimental results indicate that the as-deposited boron-rich films are primarily amorphous structure and possess a dramatic high hardness up to 39 GPa with 99.03 at.% boron. Obviously, it has exceeded the hardness value of 32 GPa of pure AlMgB14 bulk material prepared by sintering method. Furthermore, the friction coefficients of the thin films exhibit an average value as low as 0.3, which is considered as the effect of self-lubricating.

The Influence of Gas Pressure and Bias Current on the Crystallinity of Highly boron-doped Diamond Films

Highly boron-doped diamond (BDD) films were deposited by hot filament chemical vapor deposition on a silicon substrate with different gas pressures and bias currents. The surface morphology and the structure of the diamond films were analyzed by scanning electron microscopy, Raman spectroscopy, and X-ray diffraction. Results indicated that the quality of the highly BDD films tended to be improved when the gas pressure decreased from 3 to 1.5kPa, whereas they showed an opposite trend with a further decrease of the gas pressure from 1.5 to 0.5 kPa. An appropriate bias current (3A) was favorable in improving the qualities of the diamond films and a higher bias current led to an increase of the non-diamond phase in the films.

Deposition and properties of highly c-oriented of InN films on sapphire substrates with ECR-plasma-enhanced MOCVD

InN films with highly c-axis preferred orientation were deposited on sapphire substrate by low-temperature electron cyclotron resonance plasma-enhanced metal organic chemical vapor deposition (ECR-PEMOCVD). Trimethyl indium (TMIn) and N2 were applied as precursors of In and N, respectively. The quality of as-grown InN films were systematically investigated as a function of TMIn fluxes by means of reflection high-energy electron diffraction (RHEED), X-ray diffraction analysis (XRD), and atomic force microscopy (AFM). The results show that the dense and uniform InN films with highly c-axis preferred orientation are successfully achieved on sapphire substrates under optimized TMIn flux of 0.8 ml·min−1. The InN films reported here will provide various opportunities for the development of high efficiency and high-performance semiconductor devices based on InN material.

Ti-Si-N films prepared by magnetron sputtering

A film growth mechanism, expressed in terms of depositing hard films onto the soft substrate, was proposed. Multicomponent thin films of Ti-Si-N were deposited onto Al substrate with a double-target magnetron sputtering system in an Ar-N2 gas mixture. The Ti-Si-N films were investigated by characterization techniques such as X-ray diffraction (XRD), atomic force microscope (AFM), electron probe microanalyzer (EPMA), scratch test and nanoindentation. The as-deposited films have a good adhesion to Al substrate and appear with smooth and lustrous surface. The films show nanocomposite structure with nano TiN grains embedded in an amorphous SiNx matrix. The maximum hardness of the films was achieved as high as 27 GPa. The influences of the N2 flow rate and substrate temperature on the growth rate and quality of the films were also discussed. For all samples, the Ar flow rate was maintained constant at 10 ml·min−1, while the flow rate of N2 was varied to analyze the structural changes related to chemical composition and friction coefficient. The low temperature in the deposited Ti-Si-N films favors the formation of crystalline TiN, and it leads to a lower hardness at low N2 flow rate. At the same time, the thin films deposited are all crystallized well and bonded firmly to Al substrate, with smooth and lustrous appearance and high hardness provided. The results indicate that magnetron sputtering is a promising method to deposit hard films onto soft substrate.

Deposition of Ti–Si–N films on Al substrates by magnetron sputtering

Abstract The objective of this work is to settle the problem of adhesion between hard films and soft metal substrates. Hard Ti–Si–N films were deposited onto soft Al substrates with a double target magnetron sputtering system. The composition, structure, surface morphologies and mechanical properties were characterised by electron probe microanalyser, X-ray diffraction, atomic force microscope, scratch test and nanoindentation respectively. The as-deposited films had good adhesion to the Al substrates and had a smooth and lustrous surface. The maximum hardness of the films achieved was as high as 27·2 GPa at the Si target power of 80 W.

Synthesis and characterization of amorphous Al–Mg–B prepared by various deposition temperatures

Amorphous Al–Mg–B thin films were synthesized via a combinatorial sputtering approach. The properties of Al–Mg–B films with the varying deposition temperature was investigated. The deposition temperature was found to dominate the hardness of the amorphous as-deposited film. The hardness increases with increasing deposition temperature and may even exceed that of crystalline AlMgB14 material. The high hardness may be attributed to the existence of randomly distributed B12 icosahedra structure. Therefore, the thin film that was deposited on cemented carbide shows well-cutting performances in turning Ti alloy bar. At the same time, an appropriate method of pretreatment is the key to ensure the coating tool with the excellent adhesion by impact fracture test.

Bias effects on AlMgB thin films prepared by magnetron sputtering

AlMgB thin films were deposited on silicon (100) substrate using a three-target magnetron sputtering system in argon atmosphere. The influence of negative bias voltage on the thickness, morphology, microstructure, local bonding and hardness of the deposited films was investigated. Experimental results show that all films are X-ray amorphous, and the properties of the deposited films have a strong dependence on the applied substrates negative bias voltage. Deposited at high negative bias voltage, the AlMgB thin films are found to be generally dense, having a smooth surface and containing more well-formed B12 icosahedra, which consequently increase the hardness of the deposited films. However, deposited at low negative bias voltage, the AlMgB thin films exhibit loose structure, coarse surface and contain few B12 icosahedra. It is shown that the hardness of the dense and smooth AlMgB thin films can reach 22u2005GPa at the negative bias voltage of 400u2005V.

Effect of deposition pressure on mechanical properties of Al–Mg–B thin films

Abstract This work explored the effect of deposition pressure on the properties of the ternary Al–Mg–B thin films deposited on Si substrate at high deposition temperature (600°C) by magnetron sputtering system with one pure boron target and one Al/Mg co-target. The influences of the deposition pressure on the elemental contents, deposition rate, surface roughness, structure and mechanical properties were investigated by Electron microprobe analysis (EPMA), 3D surface profiler, X-ray diffraction (XRD), Fourier transforms infrared spectroscopy (FTIR), and nanoindentation experiments respectively. Experimental results indicated that the amorphous thin films deposited at 0·5 Pa had a smooth surface and displayed the maximum hardness and Young’s modulus of 35 and 322 GPa respectively. From the results of this work, high quality Al–Mg–B hard thin films can be obtained by magnetron sputtering under an optimum deposition pressure of 0·5 Pa.

GaN Films deposited on ITO coated glass

Abstract GaN films have been fabricated on tin doped indium oxide (ITO) coated glass substrates by electron cyclotron resonance plasma enhanced metal organic chemical vapour deposition. Trimethyl gallium (TMGa) and N2 were acted as precursors of Ga and N respectively. A GaN buffer layer was introduced to reduce the internal stress between the substrate and the GaN films. Then, the deposition process was performed in N2 rich atmosphere at a constant substrate temperature as low as 460°C. The TMGa flowrate was fixed at 1·5 sccm and N2 flowrate varies from 80 to 110 sccm to investigate the influence of N2 flux rates on the films’ properties. Reflection high energy electron diffraction and X-ray diffraction results indicate that all deposits are highly c axis oriented, whereas the characteristics of photoluminescence spectra are strongly affected by the N2 flowrates. GaN films prepared at 100 sccm has a smooth surface and exhibits the optimal illumination performance. This inexpensive GaN/ITO/glass structure has potential application in optoelectronic devices.