Wang Zesong

Structure and Tribological Properties of CrTiAlN Coatings Deposited by Multi-Arc Ion Plating

CrTiAlN coatings were prepared by using a home-made industrial scale multi-arc ion plating system. The coatings were found to be composites of face-center-cubic CrN and TiN. The surface roughness, microhardness, and tribological properties of the films were significantly affected by the nitrogen pressure and dc-pulsed bias voltage applied to the substrate. The CrTiAlN coatings with the smoothest surfaces were obtained at optimum conditions of nitrogen pressure of 5.0 Pa and bias voltage of −200 V. The samples were found to exhibit a hardness of 2900 HV0.05 with an average friction coefficient of 0.16 and wear rate of 1.5×10-16 m3/N·m against cemented carbide.

Degradation of ferroelectric and weak ferromagnetic properties of BiFeO3 films due to the diffusion of silicon atoms

Crystalline BiFeO3 (BFO) films each with a crystal structure of a distorted rhombohedral perovskite are characterized by X-ray diffraction (XRD) and high-resolution electron microscopy (HRTEM). The diffusion of silicon atoms from the substrate into the BiFeO3 film is detected by Rutherford backscattering spectrometry (RBS). The element analysis is performed by energy dispersive X-ray spectroscopy (EDS). Simulation results of RBS spectrum show a visualized distribution of silicon. X-ray photoelectron spectroscopy (XPS) indicates that a portion of silica is formed in the diffusion process of silicon atoms. Ferroelectric and weak ferromagnetic properties of the BFO films are degraded due to the diffusion of silicon atoms. The saturation magnetization decreases from 6.11 down to 0.75 emu/g, and the leakage current density increases from 3.8 × 10−4 up to 7.1 × 10−4 A/cm−2.

Preparation of graphene on Cu foils by ion implantation with negative carbon clusters

We report on few-layer graphene synthesized on Cu foils by ion implantation using negative carbon cluster ions, followed by annealing at 950 °C in vacuum. Raman spectroscopy reveals IG/I2D values varying from 1.55 to 2.38 depending on energy and dose of the cluster ions, indicating formation of multilayer graphene. The measurements show that the samples with more graphene layers have fewer defects. This is interpreted by graphene growth seeded by the first layers formed via outward diffusion of C from the Cu foil, though nonlinear damage and smoothing effects also play a role. Cluster ion implantation overcomes the solubility limit of carbon in Cu, providing a technique for multilayer graphene synthesis.

Ultrathin Carbon Films Prepared by Negative Cluster-Beam Technology

We develop a miniaturized chamber installed on a tandetron accelerator into which negative ions of small carbon clusters are transported. Negative clusters C−1-C−10 are obtained with beam currents of 1–104 nA at energies of 10–20 keV. C−2 beams of 0.2 μA are used to directly deposit carbon films on SiO2/Si substrates. Formation of ultrathin carbon films are demonstrated by Raman scattering, which reveals the evolution of the graphitic peak (1550 cm−2) with deposition time.

Low Friction-Coefficient TiBCN Nanocomposite Coatings Prepared by Cathode Arc Plasma Deposition*

TiBCN nanocomposite coatings were deposited on cemented carbide and Si (100) by a cathode arc plasma system, in which TiB2 cathodes were used in mixture gases of N2 and C2H2. X-ray diffraction shows that TiB2 and Ti2B5 peaks enhance at low flow rates of C2H2, but they shrink when the flow rate is over 200 sccm. An increase of deposition rate was obtained from different TiBCN thicknesses for the same deposition time measured by scanning electron microscopy. Atomic force microscopy shows that the surface roughnesses are ˜10 nm and ˜20 nm at C2H2 flow rates of 0-100 sccm and of 150-300 sccm, respectively. High resolution transmission electron microscopy and X-ray photoelectron spectroscopy show that the coatings consist of nanocrystal phases Ti2BB, TiB2 and TiN, and amorphous phase carbon and BN. The average crystal sizes embedded in the amorphous matrices are 200 nm and 10 nm at C2H2 flow rates of 200 sccm and 300 sccm, respectively. In Raman spectra, the D- and G-bands increase with C2H2 flows at low flow rates, but weaken at high flow rates. The microhardness of the coatings decreases from 28.6 GPa to 20 GPa as the C2H2 increases from 0 sccm to 300 sccm, and the ball-on-disk measurement shows a dramatic decrease of the friction coefficient from 0.84 to 0.13. The reason for the reduced hardness and friction coefficient with the change of C2H2 flow rates is discussed.

Influences of Bias Voltage and Target Current on Structure, Microhardness and Friction Coefficient of Multilayered TiAlN/ CrN Coatings Synthesized by Cathodic Arc Plasma Deposition

Multilayered TiAlN/CrN coatings have been synthesized on stainless steel substrates by cathodic arc plasma deposition using TiAl and Cr targets. Influences of the bias voltage, cathode current ratio ITiAl/ICr, and deposition pressure on the hardness and friction coefficient of the coatings were investigated. The measurement revealed existence of two cubic phases, face-center-cubic (Cr, Al)N and (Ti, Al)N, in the coatings deposited under various bias voltages except for the coating deposited at −400 V, which is amorphous. The hardness of the coatings was strongly dependent on the ITiAl/ICr ratio and deposition pressure, and reached a maximum of 33 GPa at an ITiAl/ICr ratio of 1.0 and a pressure of 1.0 Pa. The incorporation of the element chromium can reduce the density of pinholes in the coatings and assist the optimization of deposition conditions for high quality TiAlN/CrN coatings.

Optical and magnetic properties of InFeP layers prepared by Fe+ implantation

InFeP layers are prepared by ion implantation of InP with 100-keV Fe+ ions to a dose of 5 × 1016 cm−2 and investigated by optical, magnetic, and ion beam analysis measurements. Photoluminescence measurements show a deep-level peak at 1.035 eV due to Fe in InP and two exciton-related luminescences at 1.426 eV and 1.376 eV in the implanted samples annealed at 400 °C. Conversion electron Mossbauer spectroscopy reveals a doublet corresponding to Fe3+ ions in the indium sites. Atomic force microscopy and magnetic force microscopy show that magnetic clusters are formed in the annealing process. The magnetization-field hysteresis loops show ferromagnetic properties persisting up to room temperature with a coercive field of 100 Oe (1 Oe = 79.5775 A·m−1), saturation magnetization of 4.35 × 10−5 emu, and remnant magnetization of 4.4 × 10−6 emu.

Computerized Control and Operation of Rutherford Backscattering/Channeling for an in situ Ion Beam System and Its Application for Measurement of Si(001) and ZnO(001)

A computer-automated Rutherford backscattering/channeling (RBS/C) system is developed to provide in situ ion beam analysis of the accelerator-TEM system in Wuhan University. The basic system components are a PC equipped with a multichannel analyzer data acquisition board, motion control hardware including the Panmure stepping motor controller and integrated circuit modules, and a Labview programmed operating system with associated electronics. Single crystalline Si(001) and ZnO(001) implanted with Mn ions were characterized with this computerized setup. The crystalline quality χmin and channeling half angle of Si(001) were measured to be 4.65% and 0.52°, respectively, which are comparable to theoretical values 4.2% and 0.32°. The ion implantation induced damage depth profile derived from channeling and random spectrum is in reasonable agreement with the result calculated by the SRIM Monte-Carlo simulation code.