Dong Chuang

Deposition of Hydrogen-Free Silicon Nitride Thin Films by Microwave ECR plasma Enhanced Magnetron Sputtering at Room Temperature

Hydrogen-free silicon nitride (SiNx) films were deposited at room temperature by microwave electron cyclotron resonance (MW-ECR) plasma enhanced unbalance magnetron sputtering system. Both Fourier-transform infrared spectroscopy and x-ray photoelectron spectroscopy are used to study the bonding type and the change of bonding structures of the silicon nitride films. The results indicate that the chemical structure and composition of SiNx films deposited by this technique depend strongly on the N2 flow rates, the stoichiometric SiNx film, which has the highest hardness of 22.9 GPa, could be obtained at lower N2 flow rate of 4 sccm.

COMPOSITION DESIGN OF HIGH-STRENGTH MARTENSITIC PRECIPITATION HARDENING STAINLESS STEELS BASED ON A CLUSTER MODEL

The present work investigates composition characteristics of martensitic precipita- tion hardening stainless steels using a cluster-plus-glue-atom model. In this kind of steels based on the basic ternary Fe-Ni-Cr, the lowest solubility limit of high-temperature austenite corresponds to the cluster formula (NiFe12)Cr3, where NiFe12 is a cuboctahedron centered by Ni and surrounded by 12 Fe atoms in fcc structure and Cr serves as glue atoms. New multi-component alloys were designed by adding C, Mo, Nb and Cu into the basic (NiFe12)Cr3 with self-magnification of cluster formula and similar element substitution. These alloys were prepared by copper mould suction casting method, then solid-solution treated at 1323 K for 2 h followed by water-quenching, and finally aged 753 K for 4 h. The experimental results show that the microstructures and properties of the serial solid-solution treated and aged alloys vary with alloying elements and their contents. Among them,

Bergman Clusters Related to Bulk Amorphous Alloys and Quasi-crystals

The fcc Zr2Ni and MgCu2-type phases, as primary crystallization phases from some bulk amorphous alloys, have similar Bergman clusters in the first-two-shell atomic arrangement, which also appears in the hp MgZn2-type Laves phase coexisting with icosahedral quasi-crystals in the TiZrNi system. Therefore, Bergman cluster may be a bridge linking bulk amorphous alloys and quasi-crystals. The stability of the Bergman clusters Zr31Ni14, Mg31Cu14 and Mg18Zn27 can be reflected by density of states at the Fermi level and distribution of charge density on the plane of (100) calculated by local density functional theory.

Ni-Hf metallic glasses and their atomic cluster formulas

Ni-Hf binary alloys are merely known as a category of marginal glass formers. In this system, the assessment of glass-forming abilities has not been made and the optimal glass-forming composition remains unclear. In the present work, Ni-Hf glass-forming compositions are explored using the atomic cluster plus glue atom model. Ni-Hf phase diagram shows a deep eutectic point at Ni65Hf35 which is associated two intermetallic phases, namely, Ni7Hf3 and Ni10Hf7. A predominant atomic cluster was first derived from the crystalline structures of the deep eutectic related phases, and several glass-forming compositions were determined considering the one or three glue atoms constraint condition. Rapid quenching results show that Ni71.43Hf28.57 and Ni68.75Hf31.25 metallic glasses can be made fully glassy. The latter can be well described with the model composition formula as [Ni-Ni7Hf5]Ni3. Among the melt-spun alloys, the Ni68.75Hf31.25 glass which locates in between the deep eutectic point and the Ni7Hf3 phase in the phase diagram, exhibited a highest crystallization temperature of 877 K and a lowest liquidus of 1482 K, and hence is suggested to be the optimal Ni-Hf glass former by the high reduced glass temperature criterion.

Deposition of diamond-like carbon films by high-intensity pulsed ion beam ablation at various substrate temperatures

Diamond-like carbon (DLC) films have been deposited on to Si substrates at substrate temperatures from 25°C to 400°C by a high-intensity pulsed-ion-beam (HIPIB) ablation deposition technique. The formation of DLC is confirmed by Raman spectroscopy. According to an x-ray photoelectron spectroscopy analysis, the concentration of sp3 carbon in the films is about 40% when the substrate temperature is below 300°C. With increasing substrate temperature from 25°C to 400°C, the concentration of sp3 carbon decreases from 43% to 8%. In other words, sp3 carbon is graphitized into sp2 carbon when the substrate temperature is above 300°C. The results of x-ray diffraction and atomic force microscopy show that, with increasing the substrate temperature, the surface roughness and the friction coefficient increase, and the microhardness and the residual stress of the films decrease.

Structures and Properties of Zr–N Films Prepared by ECR-Microwave Plasma Source Enhanced Direct-Current Magnetron Sputtering Under Different N2Partial Pressures

ZrN thin films were prepared on 45# steel by using ECR-microwave plasma source enhanced dc magnetron sputtering. The increase of the N2 partial pressure PN2 leads to phase transitions from ZrN and an orthorhombic ZrNx phase to an amorphous phase. At PN2 = 1.1×10−2Pa to 4.5×10−2Pa, the films contain both ZrN and ZrNx (a = 0.3585, b = 0.4443, c = 0.5798 nm). At PN2 = 5.0×10−2 Pa, the film shows a strong tendency towards the amorphous phase. The N concentration at different PN2 varies from 7.73 to 66.96% according to electron probe analysis. The microhardness of the samples, varying from 19.82 GPa to 26.73 GPa, first increases and then decreases with increasing PN2. The hardest sample has a wear rate of about 4.5×10−5 mg/min. The property changes are relative to the film structure due to different N2 partial pressures.

Ultra-Thin Silicon Carbon Nitride Film: a Promising Protective Coating for Read/Write Heads in Magnetic Storage Devices

Ultra-thin amorphous Si–C–N films, down to 2nm, have been synthesized by MW-ECR, plasma enhanced unbalanced magnetron sputtering. The friction coefficient of the film is only 0.11, determined in dry friction tests against the GCr15 ball at a load of 400 mN for 20 min. The films exhibit good protection against corrosion when they are immersed in a more severe corrosion environment of 0.1 mol/L oxalic acid for 12 h compared to the usual conditions (0.05 mol/L, 4 min) used in current computer industries. These good properties can be attributed to the smooth, dense and pore free structure of the film. These indicate that the Si–C–N film synthesized by the present technique may be a promising protective coating for read/write heads and other magnetic storage devices.

Characteristics of microwave discharge in a modified surfaguide with a large diameter

The characteristics of the microwave discharge are studied in a modified surfaguide with a large diameter. Experimental results show that there exist three discharging modes, one is the plasma mode, and the others are the waveguide modes. The discharge can jump between one of the waveguide modes and the plasma mode, and the corresponding hysteresis loop is influenced by the discharging pressure. In the higher pressure region, the hysteresis loop is wide enough so that the discharge in each mode is stable. In the middle pressure region, the discharge becomes unstable as a result of the hysteresis loop being sufficiently narrow. When the gas pressure is further decreased, the plasma mode disappears, while the mode jumps between the two waveguide modes always appear and are stable in the discharge region we have explored.