T.C. Ma

Preparation, structure and properties of TaN and TaC films obtained by ion beam assisted deposition

Abstract Tantalum nitride and tantalum carbide films were prepared by the method of ion beam assisted deposition (IBAD). The results of tranmission electron microscopy (TEM) and X-ray diffraction showed that the films are all fcc structures and the grain sizes in the films are very small (about 10 to 20 nm). The composition depth profile and chemical binding character of films were determined by Auger electron spectroscopy (AES) and X-ray photo-electron spectroscopy (XPS). Measurements of film properties, such as microhardness, adhesion of film to substrate, and surface resistance, were made on a microhardness tester, a scratch tester and a bridge of resistance measurement with four-pole probe, respectively. The residual stress, dislocation density and dislocation distribution in the films were calculated by a method called X-ray diffraction line profile analysis developed by Wilkens and Wang et al. According to the elastic theory of dislocations, the microhardness of films was also calculated by using the parameters of dislocations obtained.

Characterization of a high-intensity unipolar-mode pulsed ion source with improved magnetically insulated diode

A magnetically insulated ion diode (MID) with an improved external-magnetic field system has been developed and installed onto a TEMP-6-type high-intensity pulsed ion source in order to produce a high-intensity pulsed ion beam (HIPIB) for surface modification of materials. The external-magnetic field MID is operated in unipolar mode based on dielectric high-voltage flashover, and a double coaxial pulse-forming line (PFL) powered with a Marx generator is used to form the unipolar pulse of nanosecond width. A specially designed cathode has been constructed with a forked connection to two symmetrically installed transformers to improve the effect of the magnetic field and thus increase the stability of generation and propagation of the ion beam. It was found that the efficient generation of HIPIB mainly depended on the magnetic field strength, the gas pressures in reverse and output switches of PFL, and the anode–cathode (A–K) gap of the external-magnetic field MID. A proper magnetic field strength was found...

Surface morphology of titanium irradiated by high-intensity pulsed ion beam

Abstract Surface morphology of pure Ti irradiated by high-intensity pulsed ion beam (HIPIB) with ion current density of 60–250 A/cm 2 and shot number of 1–30 at 220 kV has been investigated by using profilometer, scanning electron microscopy and atomic force microscopy to explore the interaction mechanism between HIPIB and metallic materials. Two kinds of samples were prepared with different initial surface roughness ( R a ), i.e. high-roughness and low-roughness Ti, respectively. A similar change trend of R a was found on the irradiated surfaces for both the two kinds of samples that increase of the R a was obtained with few shot number and then continuous decrease of the R a to a surface smoothing was with multi-shot irradiation. However, the increase of R a on the irradiated low-roughness Ti was greatly limited as compared to the high-roughness case. It is demonstrated that surface smoothing and roughening of irradiated Ti can be realized under optimization of the parameters by combining adjustments of ion current density and shot number. The morphology features on the irradiated high-roughness Ti were craters and waviness for roughened surfaces and some vague or apparent texture with disappearance of the craters for smoothed surfaces. For the low-roughness Ti, no distinct craters were formed except for some obvious texture. The micro-non-uniformity (micro-protrusions) on the irradiated surfaces causes the cratering on pure Ti by inducing a selective ablation under HIPIB irradiation. The locally more intense liquid evaporation and droplet ejection from the irradiated surfaces of different morphologies led to disturbance of the molten surface layer in the different scales, resulting in the surface roughening and smoothing.

Plasma-based low-energy ion implantation for low-temperature surface engineering

Abstract This paper summarizes the plasma-based low-energy ion implantation technique, including plasma source ion nitriding/carburizing and plasma source low-energy ion enhanced deposition of thin films, developed from a combination of two techniques based on conventional plasma-based ion implantation and low-energy ion beam implantation for improvement in wear resistance and corrosion resistance for metals and alloys. An electron cyclotron resonance (ECR) microwave plasma source is used to produce the plasma with the high plasma density, electron temperature and ionization degree. The ions are accelerated from the plasma by a low pulsed negative bias of −0.4–−3 kV, which is similar to the cathode potential of conventional plasma thermo-chemical diffusion processing. The low process temperature is in the range from 150°C to 500°C, which corresponds to the upper limit of conventional ion beam implantation and to the lower limit of plasma thermo-chemical diffusion processing, respectively. Low-energy ion implantation and simultaneous indiffusion is the main mass transfer mechanism, and direct thermo-chemical diffusion absorption is an additional mass transfer mechanism for formation of the nitrided/carburized layer and thin film. It has been proved that plasma-based low-energy ion implantation technique has the potential for applications in industry for surface modification of metals and alloys.

Crater formation on the surface of titanium irradiated by a high-intensity pulsed ion beam

Abstract Surface morphology and roughness of pure Ti irradiated by a high-intensity pulsed ion beam (HIPIB) have been investigated by using scanning electronic microscopy and profilometry in order to explore the interaction mechanism between HIPIB and metallic materials. Two groups of Ti samples of different initial surface roughness (Ra) were prepared to determine the effect of original surface states on the crater formation as a result of HIPIB irradiation. Particularly, the cratering behavior under various irradiation intensities was clarified by examining large Ti samples of high initial roughness with Ra of 0.18 μm. It is noted that no obvious cratering took place on Ti of low initial roughness. For high-roughness Ti, the Ra significantly increased from an initial value of 0.18 μm to the maximal 0.43 μm at 250 A/cm2 with 1 shot, and then decreased continuously to a final 0.06 μm with 30 shots presenting a planar ablated surface. The similar trend for Ra was also found for the low-roughness Ti, but the maximal value was limited to 0.18 μm from the initial 0.07 μm. The micro non-uniformity of the original surfaces resulted in the cratering on pure Ti by inducing a selective ablation and disturbance of the molten surfaces under HIPIB irradiation. A more uniform ablated Ti surface without crater formation was obtained by multi-shot irradiation due to the gradually decreased non-uniformity at the repetitive ablation.

Stopping power and energy-loss straggling of slow protons in a strongly coupled degenerate electron gas

Abstract At low velocities the analytical expressions of stopping power and energy-loss straggling of slow protons in a degenerate electron gas are obtained using local-field correction dielectric theory. A comparison of our theoretical results with experimental data is made.

Surface roughness, scratch resistance and tribological properties of hydrogenated amorphous carbon coatings prepared by low-pressure dielectric barrier discharge

Abstract In this study, we explored the surface roughness, scratch resistance and tribological properties of hydrogenated amorphous carbon (a-C:H) coatings deposited on silicon substrates from low-pressure dielectric barrier discharge (DBD) plasmas of CH 4 by using an atomic force microscope (AFM), AFM-based scratch testing technique and lateral force microscope. The AFM and scratch measurements show that the surface roughness and scratch resistance of these a-C:H coatings strongly depend on the Pd value (the product of CH 4 pressure P , and discharge gas spacing d ) and the a-C:H coatings deposited at suitable Pd value (typically 350 Pa mm) exhibit lower surface roughness and better scratch resistance. The a-C:H coatings deposited at the Pd value of 350–1750 Pa mm have the typical friction coefficient of approximately 0.13. The lower friction coefficient (0.11) of the a-C:H coating deposited at the smaller Pd value of 245 Pa mm can be associated with its graphite-like surface structure. The results indicate the coating structure changes from the one of graphite-like to diamond-like to polymer-like with the Pd value increasing from 245 to 1750 Pa mm. The relationship between the measured coating properties and the DBD deposition processes was presented.

The role of energetic atoms in the deposition of Au/Au(001) thin films : a computer simulation study

The behavior of Au/Au (100) thin film growth with energetic deposition has been investigated by kinetic Monte Carlo simulations with the description of the deposition process of energetic atoms based on molecular dynamics simulation results. We present the simulation results on the morphology, islands distribution, Bragg intensity and roughness of homoepitaxial Au (100)-films growth with energetic deposition at various substrate temperatures. We found the energetic atoms can promote the nucleation and island growth in the early stages of film growth and thus enhance the smoothness of the film surface at the temperatures of film growth in three-dimensional mode and in quasi-two-dimensional mode. The atomistic mechanism that promotes the nucleation and island growth and enhances the smoothness of the film surface is discussed.

Ion beam synthesis of Ni-Fe-Si layer by TEM

Nickel and iron ions were selected to be implanted sequentially into (100) orientation silicon wafers to synthesize Ni-Fe-Si ternary silicide film. By using the metal-vapour vacuum-are ion-implantation system MEVVA 80-10, a ternary silicide layer of gamma-Fe0.6Ni0.4Si2 with CaF2 structure has been formed at implantation conditions of 7 x 10(16) Ni ions cm(-2) and 1.4 x 10(17) Fe ions cm(-2). With increase in annealing temperature, the grain size in the layer grows and the gamma phase is decomposed into nickel-rich and iron-rich phases. In the temperature range from 500 to 600 degrees C, a valuable structure of beta-Feo(0.6)Ni(0.4)Si(2)/CaF2-Fe0.35Ni0.65Si2/Si can be obtained. At proper annealing conditions, the gamma phase is decomposed into NiSi2 and FeSi2 phases. The morphology evolution of Ni-Fe-Si ternary silicide with increasing annealing temperature ranges from the layer thickness increasing to the film shrinking into isolated islands at 850 degrees C

Effect of Mo and Mo+N implantation on corrosion resistance of austenitic stainless steel

Abstract A study has been made of the effects of Mo and Mo + N implantations on the corrosion resistance of AISI 304L stainless steel. Mo ion implantation was performed with doses ranging from 1 × 10 14 to 3 × 10 17 Mo cm −2 at an acceleration voltage of 65 kV, using an MEVVA IV 80-10 implanter. N ion implantation into some Mo-implanted specimens was carried out with a dose of 1 × 10 17 N cm −2 at 65 kV. The corrosion resistance of the implanted steel was investigated by an electrochemical method in 0.5 M H 2 SO 4 , 0.5 M HCl and 0.6 M NaCl solutions. After both Mo and Mo + N implantations, the free corrosion current density ( I corr ) decreased and the breakdown potential ( E b ) increased in HCl. Their modification effects saturated with the very low dose of 1 × 10 14 Mo cm −2 . Following 1 × 10 17 N cm −2 implantation, the critical and passive current densities in the acid solutions of H 2 SO 4 and HCl also declined at the very low dose of 1 × 10 14 Mo cm −2 , and increased at a dose of 1 × 10 16 Mo cm −2 . These results indicated that Mo + N double ion implantation with a very low Mo dose is useful for improving the corrosion resistance of 304L stainless steel under acidic conditions. In the neutral solution of NaCl, both the I corr and E b characteristics for the 304L stainless steel modified by Mo and Mo + N implantations improved with increasing Mo dose; the improvement caused by Mo + N double ion implantation tended to be greater than that for Mo single ion implantation. In conclusion, we propose that Mo + N double ion implantation into 304L stainless steel can be expected to form a surface resistant to various corrosion conditions, depending on the choice of implantation dose of Mo ions.