Changrong Li

Improvement of blood compatibility of artificial heart valves via titanium oxide film coated on low temperature isotropic carbon

Abstract Titanium oxide film was coated on the surface of low temperature isotropic carbon (LTI-carbon) by ion beam enhanced deposition (IBED) to improve the blood compatibility of the LTI-carbon mechanical heart valve. The prepared film was found to be polycrystalline with Ti 2+ , Ti 3+ and Ti 4+ coexisting. This oxygen-lack n-type semiconductor film exhibits a better hemocompatibility than that of LTI-carbon in both in vitro and in vivo investigations. The reason is attributed to the surface energy and work function, which are two influencing factors on blood compatibility.

Competitive adsorption behavior of human serum albumin and fibrinogen on titanium oxide films coated on LTI-carbon by IBED

Titanium oxide films were deposited onto low temperature isotropic carbon (LTI-carbon), a prevailing material used for mechanical heart valve fabrication, by ion beam enhanced deposition (IBED). The composition and structure of the film were studied by glancing angle X-ray diffraction (GAXRD) and Auger electron analysis (AES). The results show that the film is dominated by polycrystalline Ti2O3, as well as TiO2. The elements are well distributed along the depth profile. The surface morphologies of LTI-carbon and titanium oxide film are very similar when observed by atomic force microscopy (AFM), which indicated that the surface morphology has no significant influence on the protein adsorption properties of the samples. The protein adsorption behavior was investigated in a HSA/HFG binary system by means of 125I labeling. The results show that both proteins adsorbed preferentially on LTI-carbon rather than on titanium oxide film. In the HSA/HFG binary system, the adsorption behavior of one protein is inhibited as the concentration of the other protein increases. When the concentrations of both proteins were kept constant, the amount of adsorbed HSA strongly increased with time on titanium oxide, but less so on LTI-carbon. However, the adsorption of HFG showed the opposite behavior. It is concluded that titanium oxide film exhibits a HSA-preferred adsorption property, whereas LTI-carbon shows no preferential adsorption. This is mainly attributed to the different surface energy of LTI-carbon and titanium oxide film.

Effect of O2 pressure on the synthesis of titanium oxide film by ion beam enhanced deposition

Abstract A series of titanium oxide films have been synthesized on silicon wafers by ion beam enhanced deposition at different O 2 pressures. X-ray Photoelectron Spectroscopy (XPS), X-ray Diffraction (XRD), Glancing Angle Diffraction and Rutherford Backscattering Spectroscopy (RBS) were used to analyze the composition, structure and orientation of the films. From the experimental results, it was found that: (1) the titanium oxide films synthesized at different O 2 pressures exhibit a polycrystal structure with preferred orientation; (2) when O 2 pressure is lower than 8.4×10 −4 Pa, the main composition of the film is TiO whose preferred orientation changed from (220) to (031) with the increase of O 2 pressure; (3) when O 2 pressure is higher than 8.4×10 −4 Pa, rutile-type TiO 2 with (200) preferred orientation was found to be the major composition of the film. The higher the O 2 pressure is, the more stable the composition and preferred orientation become.

Chemical composition and structure of titanium oxide films deposited on LTI-carbon by IBED

Abstract Titanium oxide films are deposited on low temperature isotropic carbon (LTI-carbon) by ion beam enhanced deposition (IBED). The chemical composition of the prepared films is analyzed by using X-ray photoelectron spectroscopy (XPS) and Rutherford backscattering spectroscopy (RBS). The structure of the prepared films is studied by glancing angle X-ray diffraction (GAXRD) and transmission electronic microscopy (TEM). The surface morphology of the film is observed by means of atomic force microscopy (AFM). The results show that the prepared films are polycrystalline with TiO, Ti 2 O 3 and TiO 2 as coexisting phases. The chemical composition is mainly influenced by O 2 pressure. The higher the O 2 pressure is, the higher the ratio of O/Ti is. The cross-sectional high resolution electron microscopy image show that a ‘titanium oxide/amorphous transitional layer/LTI-carbon’ layered structure has been formed. The structure of the films prepared at 80 keV, is more complex than that of the film prepared at 40 keV, as well as that the surface morphology of the film prepared at 80 keV is rougher.

Influence of IBED parameters on the composition and structure of titanium oxide films deposited on LTI-carbon

Abstract The chemical composition and structure of titanium oxide films deposited on Low Temperature Isotropic Carbon (LTI-carbon) by ion beam enhanced deposition (IBED) is jointly controlled by the process parameters of IBED. In this paper, the influence of O 2 pressure, substrate temperature and ion beam energy on the composition and structure of the prepared titanium oxide films was studied by means of X-ray Photo-Electron Spectroscopy (XPS), Rutherford Backscattering Spectroscopy (RBS), X-ray Diffraction (XRD) and Glancing Angle X-ray Diffraction (GAXRD). The results show that the prepared films are polycrystalline with TiO, Ti 2 O 3 and TiO 2 as coexisting phases. The influence of O 2 pressure is mainly on the composition of the film. Ion beam energy has a great influence on the structure of the film. Neither the composition nor the structure of the film is sensitive to substrate temperature that ranged from room temperature to 300°C.

Silicon membrane resonant-cavity-enhanced photodetector

A Si resonant-cavity-enhanced (RCE) photodiode was fabricated on a silicon membrane. The Si membrane was formed by etching from the back side of the silicon-on-insulator substrate with the buried SiO2 layer as etch-stop layer. A gold layer was deposited serving as an electrode layer and bottom mirror of the RCE photodiode. The photodiode had an external quantum efficiency of 33.8% at the resonant wavelength of 848 nm and a full width at half maximum (FWHM) of 17 nm. The responsivity was 4.6 times that of a conventional Si p-i-n photodiode with the same absorption layer thickness. (c) 2005 American Institute of Physics.

Influence of the cavity on the low-temperature photoluminescence of SiGe/Si multiquantum wells grown on a silicon-on-insulator substrate

The influences of the cavity on the low-temperature photoluminescence of Si0.59Ge0.41/Si multiquantum wells grown on silicon-on-insulator substrates are discussed. The positions of the modulated photoluminescence (PL) peaks not only relate to the nature of SiGe/Si multiquantum wells, but also relate to the characteristic of the cavity. With increasing temperature, a redshift of the modulated PL peak originating from the thermo-optical effect of the cavity is observed.

Fabrication of low cost Si-based tunable high performance resonant cavity enhanced photodetectors

Low cost Si-based tunable InGaAs RCE photodetectors operating at 1.3/spl sim/1.6 /spl mu/m were fabricated using sol-gel bonding. A tuning range of 14.5 nm, a quantum efficiency of 44% at 1476 nm and a 3-dB bandwidth of 1.8 GHz were obtained.

Comparison of the microstructure of titanium oxide films deposited on silicon and LTI-carbon

Abstract Titanium oxide films have been deposited on Si (100) wafer and low temperature isotropic carbon (LTI-carbon), the prevailing used material for fabrication of mechanical heart valve, by ion beam enhanced deposition (IBED). The structure of the prepared films is studied by X-ray diffraction (XRD), glancing angle X-ray diffraction (GAXRD) and transmission electron microscopy (TEM). The results show that ‘substrate/amorphous interlayer/titanium oxide’ layered structure was formed on both substrates. The predominant phase in the film deposited on silicon is rutile TiO 2 with a highly (100) preferred orientation. However, when the film is deposited on LTI-carbon substrate at the same process condition, the major phase is Ti 2 O 3 with random orientation. The structure difference between the films deposited on Si (100) and LTI-carbon is due to the formed phase rather than the substrate structure.

Defect-free GeSn alloy strips on Si by Sn self-catalyzed MBE method

The lateral growth of GeSn strips on Si(111) has been successfully achieved by Sn self-catalyzed MBE method. The effect of Sn catalysts on morphology and the quality of the materials were studied. The high quality GeSn on Si will contribute to development of Si-based optoelectronics.