Chiapyng Lee

Surface Modification with Poly(sulfobetaine methacrylate-co-acrylic acid) To Reduce Fibrinogen Adsorption, Platelet Adhesion, and Plasma Coagulation

Zwitterionic sulfobetaine methacrylate (SBMA) polymers were known to possess excellent antifouling properties due to high hydration capacity and neutral charge surface. In this study, copolymers of SBMA and acrylic acid (AA) with a variety of compositions were synthesized and were immobilized onto polymeric substrates with layer-by-layer polyelectrolyte films via electrostatic interaction. The amounts of platelet adhesion and fibrinogen adsorption were determined to evaluate hemocompatibility of poly(SBMA-co-AA)-modified substrates. Among various deposition conditions by modulating SBMA ratio in the copolymers and pH of the deposition solution, poly(SBMA(56)-co-AA(44)) deposited at pH 3.0 possessed the best hemocompatibility. This work demonstrated that poly(SBMA-co-AA) copolymers adsorbed on polyelectrolyte-base films via electrostatic interaction improve hemocompatibility effectively and are applicable for various substrates including TCPS, PU, and PDMS. Furthermore, poly(SBMA-co-AA)-coated substrate possesses great durability under rigorous conditions. The preliminary hemocompatibility tests regarding platelet adhesion, fibrinogen adsorption, and plasma coagulation suggest the potential of this technique for the application to blood-contacting biomedical devices.

Diffusion barrier properties of sputtered TaNx between Cu and Si using TaN as the target

TaNx films sputtered from a TaN target were used as diffusion barriers between Cu thin films and Si substrates. Material characteristics of TaNx films and metallurgical reactions of Cu/TaN x /Si systems annealed in the temperature range 400–900 ◦ C for 60 min were investigated by X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy, cross-sectional transmission electron microscopy, and sheet resistance measurements. We found that the deposition rate decreased with increasing bias. TaN, -Ta, and Ta2N phases appeared and/or coexisted in the films at specific biases. A step change in N/Ta ratio was observed whenever a bias was applied to the substrate. After depositing a copper overlayer, we observed that the variation percentage of sheet resistance for Cu (70 nm)/TaN x (25 nm, x = 0.37 and 0.81)/Si systems stayed at a constant value after annealing up to 700 ◦ C for 60 min; however, the sheet resistance increased dramatically after annealing above 700 and 800 ◦ C for Cu/TaN0.37/Si and Cu/TaN0.81/Si systems, respectively. At that point, the interface was seriously deteriorated and formation of Cu3Si was also observed.

Growth of Tantalum Nitride Films on Si by Radio Frequency Reactive Sputtering: Effect of N 2 / Ar Flow Ratio

Tantalum nitride (TaN) films are deposited on silicon substrates by radio frequency reactive sputtering of Ta in N 2 /Ar gas mixtures. The deposition rate, chemical composition, and crystalline microstructure are investigated by cross-sectional transmission electron microscopy, X-ray photoelectron spectroscopy, Auger electron spectroscopy, X-ray diffraction, and atomic force microscopy, respectively. Those results indicate that the deposition rate, film composition, and microstructure correlate well with the N 2 /Ar flow ratio. The deposition mechanism and kinetic model which control the film characteristics are presented as well.

Effect of SiH4/CH4 flow ratio on the growth of β‐SiC on Si by electron cyclotron resonance chemical vapor deposition at 500 °C

β‐SiC (3C–SiC) films were deposited on silicon substrates by electron cyclotron resonance chemical vapor deposition from SiH4/CH4/H2 mixtures at 500 °C. The crystalline structure and chemical composition of the deposited film were found to depend on the SiH4/CH4 flow ratio. With a sufficient energy supply from microwave power and a SiH4/CH4 flow ratio of 0.5 and lower, stoichiometric SiC could be deposited on Si substrates. Microcrystalline β‐SiC was grown at a SiH4/CH4 flow ratio of 0.5, whereas amorphous SiC was obtained at the SiH4/CH4 flow ratios lower than 0.5. When the SiH4/CH4 flow ratio was above 0.5, only polycrystalline Si could be deposited.

Nucleation and growth of highly oriented lead titanate thin films prepared by a sol-gel method

Abstract Highly (100)-oriented PbTiO 3 thin films were grown on Pt/Ti/Si(100) substrates by a sol-gel method. The nucleation and growth processes were investigated by X-ray diffraction (XRD) and atomic force microscopy (AFM), respectively. The chemical bondings and chemical composition of the films were also determined by X-ray photoelectron spectroscopy (XPS). A crystallization mechanism for controlling the film characteristics is presented.

Characteristics of sputtered TaBx thin films as diffusion barriers between copper and silicon

Abstract Ta–B–N thin films were prepared by rf-magnetron sputtering from a TaB2 target in N2/Ar reactive gas mixtures and then used as diffusion barriers between Cu and Si substrates. In order to investigate the performance of Cu/Ta–B–N/Si contact systems, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), four-point probe measurement, scanning electron microscopy (SEM), cross-sectional transmission electron microscopy (XTEM), and Auger electron spectroscopy (AES) depth profile were used. Results of this study indicate that the barrier characteristics are significantly affected by the nitrogen content. In addition, the failure mechanism for the Cu/Ta–B–N/Si contact systems is also discussed herein.

Diffusion of Copper in Titanium Zirconium Nitride Thin Films

Honeywell Electronic Materials Star Center, Sunnyvale, California, USAThe diffusion coefficient of Cu in~Ti, Zr!N was measured by X-ray diffraction~XRD! and four-point probe~FPP! analyses afterannealing Cu/~Ti, Zr!N/Si multilayered samples in the temperature range of 500-900°C. Cu diffusion in~Ti, Zr!N had componentsfrom both the grain boundaries and the lattice based on diffusional analysis. This study suggests that for the measurement of thediffusion coefficient of Cu, FPP analysis is more precise and sensitive than XRD analysis. Additionally,~Ti, Zr!N has better Cudiffusion barrier properties than those of TaN and TiN.© 2004 The Electrochemical Society. @DOI: 10.1149/1.1644355# All rights reserved.Manuscript received May 1, 2003. Available electronically January 22, 2004.

Modulation of hemocompatibility of polysulfone by polyelectrolyte multilayer films.

Polyelectrolyte multilayer (PEM) films have been recently applied to surface modification of biomaterials. Cellular interactions with PEM films consisted of weak polyelectrolytes are greatly affected by the conditions of polyelectrolyte deposition, such as pH of polyelectrolyte solution. Previous studies indicated that the adhesion of several types of mammalian cells to PAH/PAA multilayer films was hindered by low pH and high layer numbers. The objective of this study is to evaluate whether the hemocompatibility of polysulfone can be modulated by deposition of poly(allylamine hydrochloride) (PAH)/poly(acrylic acid) (PAA) multilayer films. PAH/PAA multilayer films with different layer numbers were assembled onto polysulfone at either pH 2.0 or pH 6.5. The number of platelet adhesion and the morphology of adherent platelets were determined to evaluate hemocompatibility of modified substrates. Compared to non-treat polysulfone, the PEM films developed at pH 2.0 decreased platelet adhesion, while those built at pH 6.5 enhanced platelet deposition. Platelet adhesion was found positively correlated to polyclonal antibodies binding to surface-bound fibrinogen. The extent of platelet spreading was increased with layer numbers of PEM films, suggesting that the adherent platelets on thick PEM films were prone to activation. In conclusion, PAH/PAA films with few layers developed at pH 2.0 possessed better hemocompatibility compared to other substrates.

Deposition of polycrystalline {beta}-SiC films on Si substrates at room temperature

Polycrystalline β-SiC, with grain size up to 1500 A, has been room-temperature-deposited on Si substrates by electron cyclotron resonance chemical vapor deposition. Microwave power and the hydrogen carrier gas are the key parameters to lower the deposition temperature. According to the results of the cross-sectional transmission electron microscopy, the grain size appeared to be in the same scale as that deposited at 500 °C while a large amount of plasma-induced defects were observed in the Si substrate for the room-temperature-deposited samples. Hence, a CH4-plasma treatment prior to the β-SiC film growth was adopted, forming a SiC-like interfacial layer to suppress the substrate damages.

Microcrystalline SiC Films Grown by Electron Cyclotron Resonance Chemical Vapor Deposition at Low Temperatures

The characteristics of microcrystalline silicon carbide (µ c-SiC) films deposited using an electron cyclotron resonance chemical vapor deposition system at low temperatures have been investigated. The effect of microwave (MW) power on the SiC crystallinity is studied. According to the results of Fourier transform infrared absorption spectra, plan-view transmission electron microscopy, and the plasmon loss peaks in X-ray photoelectron spectroscopy, Si-C bonds form when the MW power is above 500 W for deposition at 500° C. The SiC crystallinity improves monotonically with MW power. The amount of incorporated carbon atoms in the grown films increases with MW power up to the concentration of 50% at 1500 W. The dependence of the surface morphology and the mean roughness of the films on MW power is examined using the contact mode atomic force microscopy.