Sunny C.H. Kwok

Activation of platelets adhered on amorphous hydrogenated carbon (a-C:H) films synthesized by plasma immersion ion implantation-deposition (PIII-D)

Amorphous carbon films have attracted much attention recently due to their good biocompatibility. Diamond-like carbon (DLC), one form of amorphous carbon that is widely used in many kinds of industries, has been proposed for use in blood contacting medical devices. However, the blood coagulation mechanism on DLC in a biological environment is not well understood. Platelet adhesion and activation are crucial events in the interactions between blood and the materials as they influence the subsequent formation of thrombus. In this work, the behavior of platelets adhered onto hydrogenated amorphous carbon films (a-C:H) is investigated. Hydrogenated amorphous carbon films with different hydrogen contents, structures, and chemical bonds were fabricated at room temperature using plasma immersion ion implantation-deposition (PIII-D). The wettability of the films was investigated by contact angle measurements using several common liquids. Platelet adhesion experiments were conducted to examine the interaction of blood with the films in vitro and the activation of adherent platelets. The results show that the behavior of the platelets adhered on the a-C:H films is influenced by their structure and chemical bond, and it appears that protein interaction plays a key role in the activation of the adherent platelets.

Hybrid evaporation: Glow discharge source for plasma immersion ion implantation

In order to achieve stable operation for elements with a low melting point or high vapor pressure, a quasiequilibrium evaporation–glow discharge evaporation source has been designed and investigated for plasma immersion ion implantation. The important relationship between the pressure in the evaporation chamber and the implantation chamber is studied for optimal performance. Our experimental results show that the hybrid evaporation–glow discharge source is an effective method to produce ions from materials with low melting point and high vapor pressure.

Haemocompatibility of hydrogenated amorphous carbon (a-C:H) films synthesized by plasma immersion ion implantation-deposition

Diamond-like-carbon has attracted much attention recently as a potential biomaterial in blood contacting biomedical devices. However, previous reports in this area have not adequately addressed the biocompatibility and acceptability of the materials in blood contacting applications. In this study, hydrogenated amorphous carbon (a-C:H) films were fabricated on silicon wafers (1 0 0) using plasma immersion ion implantation-deposition. A series of a-C:H films with different structures and chemical bonds were fabricated under different substrate voltages. The results indicate that film graphitization is promoted at higher substrate bias. The film deposited at a lower substrate bias of )75 V possesses better blood compatibility than the films at higher bias and stainless steel. Our results suggest two possible paths to improve the blood compatibility, suppression of the endogenic clotting system and reduction of platelet activation. 2003 Elsevier Science B.V. All rights reserved.

Corrosion resistance of AISI304 stainless steel treated by hybrid elevated-temperature, low-voltage/high-voltage nitrogen plasma immersion ion implantation

AISI304 stainless steel samples have been treated by a dual process involving low-voltage/elevated-temperature PIII/nitriding and subsequent high-voltage nitrogen PIII. Low-voltage PIII was conducted at 4 kV and about 350 °C, and the ion implant dose was 6×10 17 cm −2 . Afterwards, three of the treated samples were implanted by high-voltage PIII (25 kV) with an implant dose of about 3.4×10 17 ,7 ×10 17 , and 1.0 ×10 18 cm − 2 , respectively. Glancing-angle X-ray diffraction (GXRD) patterns reveal that the high-voltage PIII process facilitates the formation of expanded austenite phases, and secondary ion mass spectrometry (SIMS) depth profiling reveals oxygen enrichment in the top surface compared to the sample receiving only the low-voltage treatment. The samples treated by the dual process exhibit excellent corrosion resistance properties as indicated by a higher equilibrium/pitting potential and a lower dissolution current. This improvement may be attributed to the formation of an expanded austenite layer and thicker layer containing chromium oxide as well as nitrogen-enrichment in the top surface, etc.

Characteristics and anticoagulation behavior of polyethylene terephthalate modified by C2H2 plasma immersion ion implantation-deposition

Acetylene (C2H2) plasma immersion ion implantation-deposition (PIII-D) is conducted on polyethylene terephthalate (PET) to improve its blood compatibility. The structural and physicochemical properties of the modified surface are characterized by, Raman spectroscopy, x-ray photoelectron spectroscopy (XPS), and static contact angle measurement. Atomic force microscopy discloses that the average roughness (Ra) of film surface decreases from 58.9 nm to 11.4 nm after C2H2 PIII-D treats PET. Attenuated total reflection Fourier transform infrared spectroscopy shows that the specfic adsorption peaks for PET decrease after ion implantation and deposition. Raman spectroscopy indicates that a thin amorphous polymerlike carbon (PLC) film is formed in the PET. The effects of the surface modification on the chemical bonding of C, H, and O are examined by XPS and the results show that the ratio of sp3 C–C to sp2 C=C is 0.25. After C2H2 PIII-D, the polar component γp of surface energy increases from 2.4 mN/m to 12.3 mN/...

Room-temperature electroluminescence from H-plasma-implanted silicon

We have investigated the electroluminescence (EL) characteristics of hydrogen-plasma-immersion ion-implanted silicon. For the first time, white light was obtained at room temperature from the samples annealing at a temperature of more than 600 °C. We have investigated the current–voltage curves of the device and the relationship between the EL intensity and current density. We analysed the distribution of hydrogen and the microstructure of samples using secondary ion mass spectrometry and transmission electron microscopy. Experimental results show that hydrogen-related complexes and nanocavities in the amorphous layer are not the causes of the emission. The flat cavities with silicon oxide at the surface may be the key to the EL.

Optimal duct bias for transport of cathodic-arc plasmas

Carbon and titanium plasmas are used to investigate the effects of duct bias on the plasma transport through the magnetic duct of a cathodic-arc plasma source as a function of the magnetic-field strength and arc current so as to determine the optimal duct bias, at which the magnetic duct produces the maximum efficiency for plasma transport. The influence of the guiding magnetic field and arc current on the optimal duct bias is investigated. The optimal duct bias increases with the plasma density for carbon plasma, while the relationship is the opposite for the titanium plasma. The carbon-plasma behavior can be explained by a plasma-diffusion model presented in this paper, since the electron-ion collision frequency /spl nu//sub ei/ is less than the electron-cyclotron frequency /spl nu//sub c,e/. On the other hand, in a titanium plasma, /spl nu//sub ei/ is larger than /spl nu//sub c,e/, so this model is inaccurate. Our result shows that different kinds of plasmas have different transport behavior through the magnetic duct and thus, the duct parameters must be carefully chosen in order to achieve the optimal transport efficiency.

Effects of layer patterns on magnetic and other properties of single and multilayered Fe–C films

The structure and magnetic properties of Fe–C films synthesized using dual cathodes and coaxial cathodes in a filtered high current pulsed cathodic vacuum arc were studied. By altering the experimental parameters such as the trigger sequence, period, and pulse length, a series of single and multilayered Fe–C films were deposited. X-ray photoelectron spectroscopy and cross-sectional transmission electron microscopy were utilized to study the composition and microstructure of the films. The magnetic properties were studied using a superconducting quantum interference device magnetometer. The hysteresis loops show that the magnetic properties are controlled by the pattern of the layers and Fe concentration in the films. The reduction in the coercive field when Fe layers are mixed with ta-C layers is a key result and confirms that magnetically soft materials can be created by the multilayer method. The relationship between the magnetic properties and the structure of single and multilayered Fe–C films is disc...

Deposition of Iron-Containing Single-And Multi-Layered Amorphous Carbon Films using Dual-Target Filtered Pulsed Cathodic Vacuum Arc (FCVA)

Summary form only given. The filtered pulsed cathodic vacuum arc (FCVA) technique is designed to produce plasmas from solid targets. Single element target is traditionally employed, but it cannot satisfy the needs when two or more elements are needed for plasma implantation or deposition. Introducing gases into the chamber and using alloys or composite targets are some of the solutions. These methods, however, have some problems such as difficulty to produce films with precise composition and it is not easy to prepare composite targets. In this paper, filtered pulsed cathodic vacuum arc deposition utilizing dual targets is presented. The approach is attractive because we are able to control the firing sequence of the targets to produce various combinations of plasmas. Using this unique technique, we have synthesized iron-containing single- and multi-layered amorphous carbon films. The films that are characterized by scanning electron microscopy (SEM), energy-dispersive X-ray spectrometry (EDS) and transmission electron microscopy (TEM) exhibit excellent properties

Synthesis of Calcium, Sodium and Phosphorus Incorporated Carbon Films using Plasma Immersion Ion Implantation and Deposition (PIII&D)

Summary form only given. Doped with selected impurities has been shown to be an attractive approach to enhance the properties of amorphous carbon or diamond-like carbon (DLC) films for different application. The surface, mechanical, biological and other properties can be selectively enhanced. In this work, we fabricated calcium, sodium, and phosphorus doped carbon films and evaluated their surface properties. The samples were synthesized by plasma immersion ion implantation and deposition (PIII&D) using a novel evaporation-based plasma source. The films were characterized by X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), and transmission electron microscopy (TEM). Our results demonstrate that the evaporation source is a viable means to fabricate DLC films doped with elements that are difficult to introduce by other methods and that doping DLC films with the proper elements can enhance the surface properties of the materials