Hua-Chiang Wen

Observation of Growth of Human Fibroblasts on Silver Nanoparticles

Silver nanoparticles have drawn extensive attention as biomaterial components. Human fibroblasts were grown on various concentrations of silver nanoparticles during the period observation. Normal viability (0% silver particles) was increased from 6 to 72 hours, increasing the amount of human fibroblasts (1.5 × 104 to 7 × 106 cells/well) normally. Nevertheless, at higher concentrations of silver nanoparticles (50%) 1.11 × 105 cells/well remained after 72 hours. Results indicated that the increase in the concentration of silver nanoparticles reduced the number of fibroblasts and affected their fission. Silver nanoparticles were found under the membranes of fibroblast following dry treatment. The number of tissues declined because the silver nanoparticles interrupted the fission mechanism during their development in vivo.

Nanoscratch Characterization of GaN Epilayers on c- and a-Axis Sapphire Substrates

In this study, we used metal organic chemical vapor deposition to form gallium nitride (GaN) epilayers on c- and a-axis sapphire substrates and then used the nanoscratch technique and atomic force microscopy (AFM) to determine the nanotribological behavior and deformation characteristics of the GaN epilayers, respectively. The AFM morphological studies revealed that pile-up phenomena occurred on both sides of the scratches formed on the GaN epilayers. It is suggested that cracking dominates in the case of GaN epilayers while ploughing during the process of scratching; the appearances of the scratched surfaces were significantly different for the GaN epilayers on the c- and a-axis sapphire substrates. In addition, compared to the c-axis substrate, we obtained higher values of the coefficient of friction (μ) and deeper penetration of the scratches on the GaN a-axis sapphire sample when we set the ramped force at 4,000 μN. This discrepancy suggests that GaN epilayers grown on c-axis sapphire have higher shear resistances than those formed on a-axis sapphire. The occurrence of pile-up events indicates that the generation and motion of individual dislocation, which we measured under the sites of critical brittle transitions of the scratch track, resulted in ductile and/or brittle properties as a result of the deformed and strain-hardened lattice structure.

Effect of annealing treatment and nanomechanical properties for multilayer Si0.8Ge0.2–Si films

Multilayered silicon–germanium (SiGe) films consisting of alternating sublayers with different mechanical properties have been epitaxially deposited by an ultra-high vacuum chemical vapor deposition (UHV/ CVD) system. We report engineering of the mechanical properties of SiGe multilayer films by a commercial nanoindenter. From annealing treatment, it consists of an ex situ thermal treatments in furnace (600 C) and rapid thermal annealing (800 C) system. Subsequent roughness and microstructure of SiGe multilayer films were characterized by means of atomic force microscope (AFM) and transmission electron microscopy (TEM). The annealing treatment not only produced misfit dislocations as a significant role in the critical pileup event but also promoted hardness. The hardness of the films increased slightly and then gradually achieved a maximum value (from 12.6 ± 0.4 GPa to 14.2 ± 0.7 GPa) with increasing annealing temperature. This may be due to the relaxation effect from thermal annealing and is potential to provide the reliability behaviours to design periodical SiGe multilayer structure in further. 2010 Published by Elsevier Ltd.

Luminescence properties of mechanically nanoindented ZnSe

In this study, we used cathodoluminescence (CL) spectroscopy to examine the CL emissions of zinc selenide (ZnSe) single crystals that had been subjected to Berkovich nanoindentation. The CL spectra of the ZnSe exhibited both impurity emission peaks (1.8–2.4 eV band) and near-bandgap emission peaks (2.68 eV). Although CL emissions were generated during four unloading/reloading cycles, the decreased intensity of the impurity emission can be explained in terms of extended dislocation nucleation and propagation during nanoindentation. The resultant dislocation and microcracks were visualized using CL mapping and transmission electron microscopy. We suspect that the formation of a hysteresis loop during the four unloading/reloading cycles was due, in part, to massive dislocation activities induced by the indenter.

Nanomechanical properties of Ag solder bumps doped with Pd and Au

Abstract As an approach to increasing their reliability, we doped Ag solder bumps with Pd and Au alloys to enhance their creep resistance, which we characterized using a nanoindentation technique. The hardnesses of the pure Ag and the Ag solders doped with Pd:3%, Pd:5%, and Pd:2%-Au:3% were 0.6 ± 0.1, 1.8 ± 0.2, 2.8 ± 0.3, and 3.1 ± 0.5 GPa, respectively. Although the hardness of the Ag solder was enhanced significantly when it contained Pd:2%-Au:3%, it exhibited a lower creep exponent (n > 2). The mechanism of the thermal recovery of the sample appears to be associated with activation of dislocation sources—also the reason for the decrease in hardness. The compounds doped with Pd:2%-Au:3% displayed significantly greater bond strengths and creep exponents, whereas the Pd-only compounds exhibited poorer reliability.

Characterizations of ZnO thin films deposited onto langasite substrates by r.f. magnetron sputtering

We investigated in this study structural and nanomechanical properties of zinc oxide (ZnO) thin films deposited onto langasite substrates at 200degC through r.f. magnetron sputtering with an r.f. power at 200 W in an 02/Ar gas mixture for different deposition time at 1, 2, and 3 h. Surface morphologies and crystalline structural characteristics were examined using x-ray diffraction (XRD), scanning electron microscopy (SEM), and atomic force microscopy (AFM). The deposited film featured a polycrystalline nature, with (100), (002), and (101) peaks of hexagonal ZnO at 31.75deg, 34.35deg, and 36.31deg. As the deposition time increased, the ZnO film became predominantly oriented along the c-axis (002) and the surface roughness decreased. Through Berkovich nanoindentation following a continuous stiffness measurement (CSM) technique, the hardness and Youngs modulus of the ZnO thin films increased as the deposition time increased, with the best results being obtained for the deposition time of 3 h.