An approach is presented for the graft copolymerization of type I atelocollagen onto the surface of polyurethane (PU) films treated with ozone. Through inducing oxidization to modify PU surface by ozone, peroxide groups are easily generated on the surface. Those peroxides are broken by redox-polymerization, and provide active species which initiate graft polymerization by reacting with amines in the collagen molecules. The ozone oxidation time and voltage could readily control the amount of peroxide production. The surface density of generated peroxides on PU surface was determined by iodide method. The maximum concentration of peroxide was about 10.20 × 10 −8 mol/cm 2 when ozone oxidation was performed at 60 V for 30 min. After the reaction of PU by ozone oxidation, type I atelocollagen was graft-copolymerized onto the PU film. All the physical measurements on the collagen-grafted surface indicated that the PU surface was effectively covered with type I atelocollagen. The interaction of the collagen-grafted PU surface with fibroblasts could be greatly enhanced by the surface graft polymerization with type I atelocollagen. Attachment and proliferation of fibroblasts on the grafted type I atelocollagen were significantly enhanced, and it is assumed that the atelocollagen matrix supported the initial attachment and growth of cells. In the early stage of proliferation, collagen synthesis in fibroblasts was not activated and remained at a relatively low level due to the grafted type I atelocollagen, increasing only with fibroblast differentiation.
Superconductor-normal-superconductor (SNS) type step-edge junction dc SQUIDs were fabricated from YBa2Cu3O7−δ (YBCO) films with CaRuO3 as the normal metal by pulsed laser deposition and Ar+ beam patterning techniques. CaRuO3 films were grown epitaxially on YBCO and had a metallic conduction property. Current-voltage curves of the junctions showed a resistively shunted-junction behavior. Temperature dependence of the junction critical current was linear in agreement with the theory for junctions with the junction length shorter than twice of the normal coherence length (dN<2ξN). A well-behaving SQUID modulation signal was observed up to 52 K with a focusing parameter of 8.6.
Thin films of NdBa2Cu3O7−δ(NdBCO) were fabricated on SrTiO3 substrates by an off-axis rf sputtering. Disk shaped targets of 5 cm in diameter were prepared with stoichiometric composition of NdBCO by sintering at 1273 K in air. The sintered body was single phase and exhibited Tc(R=0)=92 K. The effects of several deposition parameters on the superconducting NdBCO thin films, e.g., gas pressure, substrate temperature, oxygen annealing process, and rf power were studied. The x-ray diffraction pattern showed the deposited thin films were highly c-axis oriented without any impurity phase. Thin films with Tc(R=0)=87 K could be obtained reproducibly at optimized conditions. Critical current density (Jc) of the patterned thin film was 106–107 A/cm2 at low temperature.
Surface morphology of pulsed laser deposited YBa2Cu3O7 films have been studied as a function of the plume angle with respect to the substrate’s normal. All the films showed c-oriented epitaxial growth according to x-ray diffraction analyses, and Tc(R=0)≥88 K and Jc≥106 A/cm2 at 77 K. Surface morphology, types of particles, and their number density, changed drastically with the deposition angle. As the angle was changed from 0° to 90°, particle type was changed from larger droplets to much smaller outgrowths with a gradual number density change. While larger droplets had the same composition as the target in accordance with their direct flight origination, smaller outgrowths were Cu rich and were believed to be byproducts of the locally inhomogeneous reaction of the ablated species resulting from their highly anisotropic momenta on the surface. High angle films were also found to contain a-oriented grains.
The effect of photolithographic treatments on the surface of a YBa2Cu3O7-δ thin film has been investigated by measuring the electrical contact resistance and performing X-ray photoemission spectroscopy (XPS) experiment. Water plays an important role in increasing the electrical contact resistance of the YBa2Cu3O7-δ thin film, as compared with the developer and photoresist (PR); water removes oxygen from the surface and increases the contact resistance. The chemical interaction with the PR or developer is not a key element in increasing the contact resistance. XPS spectra show that the oxygen concentration of the surface of a YBa2Cu3O7-δ thin film is reduced after the photolithographic process.
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