R.K.Y. Fu

Structure and properties of biomedical TiO2 films synthesized by dual plasma deposition

Abstract Titanium metal and titanium alloys are among the most widely used materials in biomedical devices because of their relatively high corrosion resistance and good biocompatibility. It has been suggested that the physiochemical and dielectric properties of the surface native oxide play a crucial role in the biocompatibility. There is increasing evidence that titanium may be extensively released in vivo and, under certain conditions, accumulated in adjacent tissues or transported to distant organs. Therefore, it is necessary to synthesize thicker and denser TiO 2 films on titanium to enhance its biomedical properties. In this paper, we discuss our fabrication technique utilizing dual plasma generated by metal vacuum arc and radio frequency. The films fabricated consist of rutile crystal, although the substrates are not heated. As the oxygen partial pressure is raised, the intensity of the (101) and (110) diffraction peaks increases, and that of the (002) diffraction peak decreases. The preferred orientation of the TiO 2 film shifts from (002) to (110) as a result of the competition between the surface free energy and ion bombardment. At low oxygen pressure, the TiO 2 grain growth is mainly affected by ion bombardment, whereas thermodynamic factors affect the film growth at higher oxygen partial pressure. When the oxygen partial pressure reaches 0.93×10 −2 Pa, further increase in the oxygen flow rate does not change the film composition. The film is completely oxidized and only comprises the TiO 2 phase. The microhardness of the TiO 2 films increases with the oxygen partial pressure and reaches a maximum value of 19 GPa at 1.7×10 −2 Pa.

Ion-cutting of Si onto glass by pulsed and direct-current plasma immersion ion implantation

Ion-cutting using plasma immersion ion implantation (PIII) was investigated for the integration of single crystalline Si layers on glass. In PIII, the sample is immersed in a plasma consisting of the ions of interest. A dc (direct current) or ac (alternating current) voltage is then applied to the sample to extract ions from the plasma and implant into the sample. PIII is inherently more efficient for high dose implantation. It was found that p-Si wafers implanted nominally at room temperature with H doses on the order of a few times 1016u2009cm−2 could be readily bonded to glass substrates with proper surface treatment similar to that used in conventional implantation for ion-cutting. The wafer surface of the as-implanted Si was converted from p-type to n-type. Upon bonding at room temperature, annealing (300u200a°C), and exfoliation (450u200a°C), the transferred Si layer on glass and the as-exfoliated surface of the implanted Si wafer remained n-type. Transmission electron microscopic examination showed a highly de...

Two-dimensional particle-in-cell plasma immersion ion implantation simulation of gear/windmill geometry in cylindrical co-ordinates along the (r-θ) plane

Plasma immersion ion implantation (PIII) into gear/windmill structures is simulated by the particle-in-cell (PIC) method in cylindrical co-ordinates. In cylindrical co-ordinates, the gear/windmill geometry becomes a periodic regular structure. An equal number of particles are placed inside the cell with the same angular and radial distance. The ion density represented by each particle is obtained and varies according to the radial distance of the particle. PIII simulation of a rectangular trench is carried out and compared with the cylindrical gear/windmill. The evolution and distribution of the potential and ion density contour lines are the same for these two geometries. The incident doses of a gear (windmill) will be larger than that of the trench. It is due to the space compression in cylindrical co-ordinates along the decreasing radial direction. The incident doses will thus be underestimated when treating a gear tooth using a rectangular trench.

Hemocompatibility and antibacterial properties of lanthanum oxide films synthesized by dual plasma deposition

Lanthanum oxide (La(2)O(3)) films with good hemocompatibility and antibacterial properties have been fabricated using dual plasma deposition. X-ray photoelectron spectroscopy (XPS) shows that La exists in the +3 oxidation state. The band gap of the materials is determined to be 3.6 eV. Activated partial thromboplastin time (APTT) and blood platelet adhesion tests were used to evaluate the blood compatibility. The bacteria, Staphylococcus aureus, were used in plate counting tests to determine the surface antibacterial properties. The APTT is a little longer than those of blood plasma and stainless steel (SS). Furthermore, the numbers of adhered, aggregated, and morphologically changed platelets are reduced compared with those on low-temperature isotropic carbon and SS. The antibacterial plate-counting test indicates that La(2)O(3) has good antibacterial activity against S. aureus. These unique hemocompatibility and antibacterial properties make La(2)O(3) useful in many biomedical applications.

Improved planar radio frequency inductively coupled plasma configuration in plasma immersion ion implantation

Plasmas with higher density and better uniformity are produced using an improved planar radio frequency (rf) inductively coupled plasma configuration in plasma immersion ion implantation (PIII). An axial magnetic field is produced by external electromagnetic coils outside the discharge chamber. The rf power can be effectively absorbed by the plasma in the vicinity of the electron gyrofrequency due to the enhanced resonant absorption of electromagnetic waves in the whistler wave range, which can propagate nearly along the magnetic field lines thus greatly increases the plasma density. The plasma is confined by a longitudinal multipolar cusp magnetic field made of permanent magnets outside the process chamber. It can improve the plasma uniformity without significantly affecting the ion density. The plasma density can be increased from 3×109 to 1×1010 cm−3 employing an axial magnetic field of several Gauss at 1000 W rf power and 5×10−4 Torr gas pressure. The nonuniformity of the plasma density is less than 1...

Structure and mechanical properties of diamondlike carbon films produced by hollow-cathode plasma deposition

Diamondlike carbon (DLC) films are deposited on AISI 304 stainless-steel substrates using hollow-cathode chemical vapor deposition. The effects of the substrate bias on the structural and mechanical properties of the films are studied. X-ray photoelectron spectroscopy reveals the existence of Cue5fbC (sp2) and C–C (sp3) functional groups in the films, and Raman spectra show that the ratio of the G (graphite) peak to the D (disorder) peak depends on the sample bias. The DLC film deposited at −50V bias has the highest sp3 content, and this is consistent with the G-band position and D-band full width at half maximum as a result of substrate biasing. The sample bias also has a critical influence on the thickness and hardness of the deposited films. The largest thickness (1700nm) and highest hardness (HV1099) are achieved at a bias voltage of −50V. All the films show low friction coefficients, and the sample treated at −200V gives rise to the lowest friction coefficient.

Influence of bias voltage on the tribological properties of titanium nitride films fabricated by dynamic plasma ion implantation/deposition ☆

Dynamic plasma ion implantation/deposition (PIID) combining gas and metal plasmas has been proven to be an effective technique to fabricate titanium nitride films. Pulsed vacuum arc and simultaneous substrate biasing can provide the capability to optimize film properties through flexible matching of processing parameters. In this work, titanium nitride films were synthesized on AISI304 stainless steel samples using filtered titanium cathodic arc and hot filament glow discharge. The effects of the substrate bias (8, 16 and 23 kV) on the tribological properties were investigated. The bias voltage has a slight influence on the film thickness and friction coefficient. The pin-on-disk experimental results demonstrate that a higher bias voltage (e.g. 23 kV) leads to better tribological properties compared to a lower bias. Under our testing conditions, the slide time to result in rapid friction increase for the 23 kV sample is 1.25 times that of the 8 kV sample. The wear tracks on the 23 kV sample are more irregular than those on the untreated or 8 kV sample. The improvement is believed to be related to the higher adhesion induced by ion mixing and formation of the surface layer incorporating titanium, nitrogen, and oxygen.

Fabrication and optical properties of C/β-SiC/Si hybrid rolled-up microtubes

C/β-SiC/Si hybrid microtubes have been fabricated by releasing prestressed C/Si bilayer structures and treating with a postannealing process. Detailed characterization reveals the synthesis of β-SiC via a solid phase reaction at the C/Si interface. Remarkably, the production of β-SiC is promoted in the tube wall by rolled-up bonding of adjacent windings, which increases the area of the C/Si interface by a factor of 2. The Raman spectra acquired from the hybrid microtubes disclose peaks pertaining to the optical phonon modes of β-SiC that exhibit obvious downshifts due to surface effects on the SiC nanoparticles. Moreover, two light emission bands are detected from a hybrid microtube and their origin is discussed based on spectral analyses.

Low energy-consumption plasma electrolytic oxidation based on grid cathode

Plasma electrolytic oxidation (PEO) has attracted widespread attention owing to the simplicity of operation and the excellent properties of the formed coating. However, wider applications of PEO have been limited due to the high power consumption. This work describes the design and performance of a novel technique named shorter distance PEO (SD-PEO), which is intended for lowering the energy consumption. The key feature of the method is the application of grid cathode to eliminate the gaseous envelope effect and to block of the exchange of charge carries during SD-PEO process. Compared to PEO carried out at a normal electrode distance, e.g., 50 mm, both the voltage drop and the joule heat consumed in the electrolyte at a shorter distance, e.g., of 5 mm (SD-PEO) are relatively small. Consequently, the energy consumption rendered by the novel SD-PEO method may decrease by more than 25%. Our results reveal that SD-PEO is a low energy-consumption microarc oxidation technique with more potential in industry applications.

Corrosion resistance and antithrombogenic behavior of La and Nd ion implanted stainless steels

Lanthanide ions such as lanthanum (La) and neodymium (Nd) were implanted into 316 stainless steel samples using metal vapor vacuum arc to improve the surface corrosion resistance and antithrombogenic properties. X-ray photoelectron spectroscopy shows that lanthanum and neodymium exist in the +3 oxidation state in the surface layer. The corrosion properties of the implanted and untreated control samples were investigated utilizing electrochemical tests and our results show that La and Nd implantations enhance the surface corrosion resistance. In vitro activated partial thromboplastin time (APTT) tests were used to evaluate the antithrombogenic properties. The APTT time of the implanted samples was observed to be prolonged compared to that of the unimplanted stainless steel control. La and Nd ion implantations can be used to improve the surface corrosion resistance and biomedical properties of 316 stainless steels.