Advanced Materials Research Vols. 79-82

Abstract: Au/NiCr/Ta soft multi-layered metal films were deposited on hard Si-(111) substrate by magnetron sputtering. The crystal orientation, Hardness (H) and Elastic modulus (E) were investigated as a function of substrate temperature by XRD and nanoindentation techniques. The XRD revealed that all films on Si-(111) substrate are Au-(111) preferred orientation, indicating there are no alloying phases in the films, which is different from Au/NiCr/Ta films on Al2O3 substrate with a mixture of Au-(111) and Au-(200) orientation. Nanoindentation tests at shallow indentation depths (h≤t/4) where the hardness is reliable for metal films on hard substrate. Au film at substrate temperature 200°C has the highest hardness 4.2GPa. Meanwhile, the H/E value also indicated that the Au/NiCr/Ta films have preferable wear resistance at substrate temperature 200°C.

Abstract: Lotus flower is a symbol of purity in Asian cultures, when growing from muddy waters it stays clean and uncontaminated. The "self-cleaning" surface of lotus leaf is hydrophobic and rough, showing hierarchical micro- and nano-scale structures. Stimulated by “lotus effect”, the microreliefs of lotus leaf was mimicked using PVDF film and the nano-scale protrusions on the top of the microreliefs were implemented by the mixed solution of dimethyldichlorosilane (DDS) and methyltrichlorosilane (MTS). A lotus-leaf-like surface of the PVDF film was clearly observed by SEM. Elemental composition analysis by XPS revealed that the nanostructure materials of PVDF film were polymethylsiloxane and polydimethylsiloxane. The superhydrophobic property of the mimicked self-cleaning surface was validated by the water contact angle and sliding angle on the lotus-leaf-like PVDF film, which are 155°and 4°, respectively. In this case, water drops can easily move across the PVDF film surface, carrying dirt particles away, leaving no contamination.

Abstract: Low hemocompatibility is a major problem of biomaterials that come in contact with blood. Surface modification has become an important way to improve the hemocompatibility of medical implants and interventional devices. Recently, researchers attempt to investigate the possibility of silicon oxynitride (Si-N-O) films to be applied as novel coating of blood-contacting biomaterials. However, no detailed investigation has been conducted. In this study, our work was focused on the optimization of the hemocompatibility of Si-N-O films prepared on single-crystal silicon wafers by unbalance magnetron sputtering (UBMS). The structure and chemical composition of films were characterized by X-ray photoelectron spectrometry (XPS), and their physical chemistry property was characterized by contact angle measurements. Platelet adhesion test was performed to investigate the platelet adhesion and activation. Our results suggested that films composed of Si3N4 and SiOx (x<2) exhibited better hemocompatibility than low temperature isotropic pyrolitic carbon (LTIC) that is a common material used in blood-contacting implants. It was also revealed that the higher N/O ratio in films composed of Si3N4 and SiOx (x<2) was attributed to the lower platelet adhesion and activation, and the interaction of samples with plasma proteins was demonstrated to play an important role in the adhesion and activation of platelets.

Abstract: In this present work, non-equilibrium coatings (like glassy state but not amorphous texture) were prepared by electric arc spraying using Zn-Al-Mg-RE-Si powder core spun alloy, and the effect of Mg content on corrosion resistance of coatings and the electrochemical properties of alloy coatings in corrosion process were investigated by CASS test, weight-loss test, XRD, SEM, polarization curves and electrochemical impedance spectroscopy. The results indicate that: The corrosion process of non-equilibrium coatings in CASS test includes corrosion inhibition stage and substrate corrosion stage; There appears much micro-crystallite and exists grain refinement in corrosion process; Before CASS test, the corrosion potential of non-equilibrium coatings shuffles when Mg content increases; Before CASS test and after CASS test at 120h and 216h, the corrosion current density approaches the minimum value and the corrosion rate is slowest when Mg content is 2%. Before CASS test, there appears the feature of Warburg impedance, but there did not appear the feature of Warburg impedance after CASS test at 120h and 216h. When Mg content is 2%, the charge-transfer resistance of coating is obviously higher than the coatings with other Mg content. Finally, an optimization composition of non-equilibrium coating—Zn-Al-2Mg-RE-Si coating is obtained by synthesis comparing.

Abstract: TiO2 films were fabricated on stainless steel (SS) substrate by plasma surface alloying and thermal oxidation duplex process. Composition and microstructure of the films were characterized using glow discharge spectrometer (GDOES), X-ray photoelectron spectroscopy (XPS) and XRD. Results reveal that the TiO2 films are dense, homogeneous and existed in a complete anatase structure. Both Ti and O elements show gradient distribution in the films. The wear behavior of TiO2 films in Hanks’ solution indicates that the films display much better wear resistance and antifriction performance than that of SS substrate. Electrochemistry noise tests indicate that the TiO2 films effectively retard the local pitting and crevice corrosion of the SS substrate.

Abstract: Indium Tin Oxide (ITO) films on polyethylene terephthalate (PET) sandwiching TiO2 buffer layers with different sputtering time have been prepared by rf-magnetron sputtering. Scanning Electron Microscope images of the TiO2 buffer layers showed the non-continuous growth in a typical sputtered film growing process. (400) oriented diffraction peaks appeared in all the ITO/TiO2/PET films. The electrical properties were measured by four point probe method and van der Pauw method. The variations of the resistivity and hall mobility on the sputtering time of TiO2 layer were studied. Furthermore, an exponential decay correlation of resistivity and the grain size was fitted. But the linear relationship between the ITO grain size and the mobility indicated by the grain boundary scattering theory didn’t appear here. The reason is believed to neglect the influence of the local variations of the lattice spacing and some other important scattering mechanisms such as lattice, ionized impurity, neutral impurity scattering, etc.

Abstract: -C-Fe-Si/SiC coated Fe nanocapsules were prepared by arc evaporating the mixture of Fe and SiC powders in He and H2 atmosphere, and their microstructure, surface compositions and electromagnetic(EM) properties(2–18GHz) were investigated by means of high-resolution transmission electron microscopy, X-ray photoelectron spectroscopy, and network analyzer, respectively. The reflection loss R of less than –20 dB was obtained in the frequency range of 3.13–13.6 GHz with an absorber thickness of 2.0–5.5 mm. An optimal reflection loss of–37.2 dB was reached at 5.6GHz with an absorber thickness of 4.5mm. The microwave absorptive mechanisms of -C-Fe-Si/SiC coated Fe nanocapsules absorbent were discussed.

Abstract: Thermochromic vanadium dioxide (VO2) exhibits a semi-conducting to metallic phase transition at about 68°C, involving strong variations in electrical and optical properties. A simple method was proposed to prepare VO2 thin films from easily gained V2O5 thin films. The detailed thermodynamic calculation was done and the results show that V2O5 will decompose to VO2 when the post annealing temperature reaches 550°C at the atmospheric pressure of less than 0.06Pa. The initial V2O5 films were prepared by sol-gel method on fused-quartz substrates. Different post annealing conditions were studied. The derived VO2 thin film samples were characterized using X-ray diffraction and X-ray photoelectron spectroscopy. The electrical resistance and infrared emissivity of VO2 thin films under different temperatures were measured. The results show that the VO2 thin film derived from the V2O5 thin film annealed at 550°C for 10 hours is pure dioxide of vanadium without other valences. It was observed that the resistance of VO2 thin film with thickness about 600nm can change by 4 orders of magnitude and the 7.5-14μm emissivity can change by 0.6 during the phase transition.

Abstract: Ni-MF/Al2O3 composite was fabricated using traditional method. The specimens covered with graphite were sintered at 1400°C, and the microstructure and mechanical properties of Ni-MF/Al2O3 composites were studied. Results showed that the flexural strength and fracture toughness of the composites were dramatically changed with the content of nickel. When the content of Ni was 15 wt% and no-coated MF was 10%, the composite obtained better mechanical properties, its flexural strength and fracture toughness were up to 734.40 MPa and 10.17 MPa•m1/2 respectively. The toughening mechanisms of the composites were attributed to the fiber extraction and debonding, metal bridging and deforming plastically.

Abstract: Titanium nitride coatings were prepared on common glass slides using TiCl4 and NH3 by atmospheric pressure chemical vapor deposition. The deposition temperature range from 450-650 °C was applied. X-ray diffraction, scanning electron microscope, energy dispersive X-ray Spectrometer, four-point probe sheet resistance instrument and UV-Vis spectrometer were employed to characterize the obtained coatings. The crystallization and electrical conductivity of the coatings was improved with increasing deposition temperature. The reflectance and transmittance spectra showed all the coatings exhibited solar control performance. The coating prepared at 650 °C presented the optimum solar control performance in the present study.