Advanced Materials Research Vols. 311-313

Abstract: Aggregation problem limits the use of silver nanoparticles (nano-Ag). Liquid chemical reduction method was used to fabricate silver/hydroxyapatite nanoparticles (nano-Ag/HA) by depositing nano-Ag on the surface of hydroxyapatite nanoparticles (nano-HA). The XRD result shows nano-Ag/HA is a hybrid composite of hydroxyapatite and face-centered cubic crystalline silver. The TEM result confirms the size and distribution of nano-Ag are dependent on the mass ratio of deposited nano-Ag and nano-HA, decreasing the mass ratio can obtain nano-Ag with smaller size and less particle aggregation, which can be contributed to the heterogeneous nucleation effect of nano-HA on nano-Ag. Silver/hydroxyapatite/alginate composite dressing was fabricated by spraying nano-Ag/HA onto the surface of the alginate dressing. The test result of disc diffusion method shows the evident antimicrobial activity against Escherichia coli (E. coli) is assigned to nano-Ag/HA, no significant difference can be found between the dressings with 0.01g and 0.02g nano-Ag.

Abstract: Drug was encapsulated in a novel copolymers of poly(lactic-co-glycolic acid) (PLGA) to investigate the sustained-release formulation of drug loaded polymer microspheres delivery system. Used a modified solid-in-oil-in-water (S/O/W) emulsion solvent evaporation method to prepare microspheres, its morphology and particle size distribution were estimated by scanning electron microscopy (SEM), the profile of in vitro drug release were assessed by High performance liquid chromatography (HPLC). Finally, an stable release buffer was utilized to obtain a detailed drug release profile, which was analyzed by HPLC also. Results showed that the microspheres morphology, encapsulation efficiency and the cumulative drug release efficiency were appropriate for veterinary medicine using. The modified preparation method was simple and optimized, PLGA microspheres with excellent controlled-release characteristics may serve as drug delivery carrier and may prolong the drug sustained-release effect.

Abstract: Different sterilization techniques such as Co(60) gamma irradiation and autoclaving were used to treat the regenerated Bombyx mori silk fibroin (RSF) in aqueous solutions. The effect of the two above mentioned sterilization methods on the conformational changes and gelation rate of RSF was studied. According to the analysis of circular dichroism spectroscopy, gamma irradiation may initiate the conformational transition from random coil to β-sheet for RSF, while autoclaving shows less significant influence on the structure changes of RSF in aqueous solutions. The results also indicate that gelation time decreased to 5 days after γ-irradiation treatment while gelation time increased to 31 days after autoclave treatment. Moreover, particles of RSF in solutions changed larger and gelation time increased when autoclaving treatment time extended. However, no detectable changes of RSF secondary structure were found investigated by XRD and FTIR. Which indicated that under both sterilization methods, the RSF structure was transformed from random coil to β-sheet structure after gelation.

Abstract: Many efforts had been reported to modify the structure of electropun nanofibers in order to obtain superior functional properties of poly(vinyl-alcohol) (PVA). This paper discusses the influence of chitosan on the morphology of electropun PVA nanofibers and their related properties. Spider–net and fiber–bridging structured PVA nanofibers are successfully fabricated by blending with chitosan. Chitosan as natural cationic polysaccharide increases the excess charge of the host polymer PVA. Nanofibers are diverged into thinner nanofibers and a continuous web formed when electrical voltage applied. The presence of additional OH- groups from chitosan and larger surface area of the net structure for hydrogen bonding enhance the hydrophilicity and mechanical properties of the nanofiber mat as compare to pure PVA which are evaluated through water contact angle and tensile testing respectively.

Abstract: One multiscalar microlaminate (MSML) with 5 thick layers of NiCoCrAl whose thickness were different interspersed with 66 thin layer stacks of NiCoCrAl/YSZ was fabricated by EB-PVD. Uniaxial tensile testing was performed and fracture was examined using SEM. The results show that the microlaminate exhibits brittle-like behavior without macroscopic plastic deformation in room temperature tensile tests and the maximum engineering stress is 212MPa. Examination of fracture surfaces from the samples reveals that ceramic layers fail by intergranular brittle fracture between columns, but metal layers display features of both ductile and brittle fracture. It is also found that the thicknesses of metal layers have a great effect on their failure modes. And interfacial debonding and bridging metal layers are observed. Moreover, the resistance of crack propagation in the microlaminate is discussed.

Abstract: The paper investigated the effect of chemical etching and temperature on the optical properties and microstructures of porous silicon layer fabricated by the pulse electrochemically etching by means of the reflectance spectroscopy and photoluminescence spectroscopy. The relationship between the optical thickness (nd) and refractive index n of porous silicon layer and the chemical etching time and temperature has been detailedly studied. With increasing the chemical etching times, the reflectance spectra exhibit the more intense interference oscillations, which mean the uniformity and interface smoothness of porous silicon layers become better, meanwhile, results in decreasing the optical thickness and refractive index, indicating a higher porosity. Moreover, the intensity of photoluminescence spectra increases, and the envelope curves of photoluminescence spectra exhibit a trend of red-shift, which implied the average diameter of silicon nanocrystallite became larger. The chemical etching rate of the optical thickness intensely increases with the chemical etching temperature.

Abstract: This paper investigates a combination of Ni acetate solution induced crystallization and microwave induced crystallization of a-Si thin film. Ni acetate solution was coated over amorphous Si thin film for evenly spread of Ni metal source. The Ni inducing source was formed from Ni acetate powder dissolved in de-ionized water or ethanol. The crystallization using Ni acetate solution was a Ni-silicide mediated process, the same process used with Ni metal layer. Compared to Ni metal layer induced crystallization by conventional furnace annealing, it finds that the crystallization temperature was lowered to 450 °C and the time of crystallization was reduced. Using Ni acetate solution induced crystallization is propitious to big area crystallization. After the processing, the poly-Si grain size was found about 0.1-0.5μm. The crystallization of a-Si thin films was enhanced by applying microwaves and Ni acetate solution to the thin films. The technique that combines Ni solution induced crystallization with microwave annealing has potential applications in thin-film transistors (TFT’s) and solar cell.

Abstract: The Ni-based reticular MnOx catalytic materials with high porosity and high specific area were prepared by the electrodeposition method. XRD and SEM were employed to characterize the phase structure and morphology of the MnOx films before and after heat treatment. The phase structure has changed from irregular amorphous structure to compacting crystal structure on the effect of heat treatment. The results show that the phase in the film is γ-MnO₂ after aging. The electrodeposition mechanism of MnO₂ has also been studied in this paper. MnO₂ was deposited by the hydrolysis reaction of Mn2+ in electrolyte and the disproportionation reaction of unstable Mn³⁺ ions. A large number of hydrogen was released during the whole deposition process.

Abstract: This work presents a preparation of composite aluminum anodizing oxide film and its coloring process. When a kind of ultra fine silicon particle with negative charge was doped into the micropores of film by electrochemical method, the obtained composite film has bulk density of 3.53 g•cm^-3, cavity ratio of 10.6 % and thickness of over 20 µm. Compared to traditional aluminum anodizing oxide films, the obtained new film gives higher hardness and mechanical properties. XRD analysis showed that silicon particles in composite oxide film were mainly composed of feldspar NaAlSi₃O₈. Furthermore, a kind of malonamide azo-colorant was introduced into the micropores of composite oxide film by in-situ synthesis to give various colors, where the malonyl group was as a bridge between aluminum oxide film and diazonium group. Properties evluation tests shows that the obtained colored decoration film exhibits high resistance to heat, salt-fog, mold and nature corrosion. Therefore, the composite aluminum anodizing oxide film is a promising candidate for application in stringent condition needing high protection as well as bright color.

Abstract: Double passivation layers, Si₃N₄ on Si₃N₄ (Si₃N₄ / Si₃N₄), have been implemented onto the top and bottom surface passivation film layers for a gamma-gate AlGaN/GaN HEMT using Plasma Enhanced Chemical Vapor Deposition (PECVD). The effects of the reduced current collapse electro characteristics were then compared to devices using double passivation as SiO₂ on SiO₂ (SiO₂ / SiO₂). Both samples were tested under the same conditions: V_ds = 0 to 15 V and V_gs = 1 to -5 V. The Si₃N₄ / Si₃N₄ passivation results show a maximum saturation current density (I_{ds max}) of 761 mA/mm, a peak extrinsic trans conductance (g_{m max}) of 200 mS/mm, and threshold voltages of (V_th) -4.5 V, which increases up to 18% and 5% than those of SiO2/SiO2 double passivation.