Yang Shiqin

Study on Vanadium Films Deposited on Concave Object by Conventional Direct Current and High Power Pulsed Magnetron Sputtering

Abstract High power pulsed magnetron sputtering (HPPMS) is a novel tool to fabricate films with high quality. In this paper, vanadium films on concave object have been deposited by HPPMS and conventional direct current magnetron sputtering (DCMS) under the condition of the same average power. The plasma composition, crystalline structure, surface morphology and film thickness have been investigated. The results show that the plasma produced by HPPMS is composed of Ar(1+), V(0) and a certain amount of V(1+). In contrast, the plasma produced by DCMS is composed of Ar(1+), V(0) and a very small amount of V(1+). Both films fabricated by HPPMS and DCMS demonstrate the similar microstructures. The HPPMS vanadium films are dense and flat on the top surface while the surface of DCMS vanadium films presents very sharp peak with larger height. The DCMS vanadium films exhibit a porous columnar grain structure. In contrast, the HPPMS vanadium films have slightly columnar and denser structure. The thickness of the HPPMS vanadium films is less than that of DCMS vanadium films. Compared with the surface on the top, the thickness of the DCMS vanadium films is decreased to about 32% at the side wall and to about 55% at the bottom. However, the HPPMS vanadium films can reach a thickness of about 35% at the side wall and 69% at the bottom relative to that on the top surface. HPPMS shows a better uniformity in the film thickness on concave object.

Surface Properties of AZ31B Magnesium Alloy by Oxygen Plasma Immersion Ion Implantation

Oxygen plasma immersion ion implantation (PIII) has been conducted on AZ31B magnesium alloy using different bias voltages. The modified layer is mainly composed of MgO and some MgAl2O4. Results form Rutherford backscattering spectrometry (RBS) and X-ray photoelectron spectroscopy (XPS) indicate that the bias voltage has a significant impact on the structure of the films. The oxygen implant fluences and the thickness of the implanted layer increase with higher bias voltages. A high bias voltage such as 60 kV leads to an unexpected increments in the oxygen-rich layers thickness compared to those of the samples implanted at 20 kV and 40 kV. The hardness is hardly enhanced by oxygen PIII. The corrosion resistance of magnesium alloy may be improved by a proper implantation voltage.

Uniformity of TiN Films Fabricated by Hollow Cathode Discharge

Titanium nitride (TiN) films were deposited on AISI 304 stainless steel substrates using hollow cathode plasma physical vapor deposition (HC-PVD). Titanium was introduced by eroding the Ti cathode nozzle and TiN was formed in the presence of a nitrogen plasma excited by radio frequency (RF). The substrate bias voltage was varied from 0 to −300 V and the uniformity in film thickness, surface roughness, crystal size, microhardness and wear resistance for the film with a diameter of 20 mm was evaluated. Although the central zone of the plasma had the highest ion density, the film thickness did not vary appreciably across the sample. The results from atomic force microscopy (AFM) revealed a low surface roughness dominated by an island-like morphology with a similar crystal size on the entire surface. Higher microhardness was measured at the central zone of the sample. The sample treated at −200 V had excellent tribological properties and uniformity.

Uniformity of Plasma Density and Film Thickness of Coatings Deposited Inside a Cylindrical Tube by Radio Frequency Sputtering

Plasma surface modification of the inner wall of a slender tube is quite difficult to achieve using conventional means. In the work described here, an inner coaxial radio frequency (RF) copper electrode is utilized to produce the plasma and also acts as the sputtered target to deposit copper films in a tube. The influence of RF power, gas pressure, and bias voltage on the distribution of plasma density and the uniformity of film thickness is investigated. The experimental results show that the plasma density is higher at the two ends and lower in the middle of the tube. A higher RF power and pressure as well as larger tube bias lead to a higher plasma density. Changes in the discharge parameter only affect the plasma density uniformity slightly. The variation in the film thickness is consistent with that of the plasma density along the tube axis for different RF power and pressure. Although the plasma density increases with higher tube biases, there is an optimal bias to obtain the highest deposition rate. It can be attributed to the reduction in self-sputtering of the copper electrode and re-sputtering effects of the deposited film at higher tube biases.