ABSTRACT
Pulse management of white light to maximize the sintering efficiency of a rapid (msec) and substrate-protective method, intense pulsed light (IPL), was studied systematically with a printable Cu nanoink. An excessive pulse energy that induces deleterious defects on the Cu film along with damage on a plastic substrate was dissipated into multiple sub-pulses while maintaining a total energy budget over the threshold level for successful Cu sintering. Electrical properties of the metal layers were analyzed in conjunction with pulse formation factors such as average energy, pulse duration, peak power and pulse number to determine their respective effects on IPL sintering. In the quantitative results, the optimized sintering conditions of copper nanoparticles with a mean diameter of 30 nm and a fixed total irradiated pulse energy of 32 J cm(-2) were a pulse number and pulse width of > 4 and < 3 msec, respectively.
ABSTRACT
ZnO epitaxial layers were grown on GaN underlying films by metalorganic chemical vapor deposition at various temperatures. An increase in growth temperature led to morphological changes from a smooth film with hexagonal-shaped surface pits to honeycomb-like nanostructures with deep hollow, and additionally resulted in a decrease in dislocation density in the interfacial layers. The reduced dislocation density at the higher growth temperature was attributed to an increase in the size of the critical nucleus and the low nucleation density at the initial stage. The shifts in the peak positions in the X-ray diffraction and photoluminescence were also observed in the samples grown at different temperatures, and were caused by the variation of residual strains after the complete coalescence of the nuclei.
ABSTRACT
Vertically well-aligned Ga-doped ZnO nanorods with different Ga content were grown by thermal evaporation on a ZnO template. The Ga-doped ZnO nanorods synthesized with 50 wt% Ga with respect to the Zn content showed minimum compressive stress relative to the ZnO template, which led to a rapid growth rate along the c-axis due to the rapid release of stored strain energy. A further increase in the Ga content improved the conductivity of the nanorods due to the substitutional incorporation of Ga atoms in the Zn sites based on a decrease in lattice spacing. A p-n diode structure with Ga-doped ZnO nanorods as an n-type layer displayed a distinct white light luminescence from the side view of the device, showing weak ultraviolet and various deep-level emissions.
ABSTRACT
Ceramide is implicated in the regulation of various signaling pathways leading to proliferation, differentiation or apoptotic cell death, but there have been few investigations about the effects of ceramide on the cell growth and the melanogenesis of melanocytes. In the present study, we investigated the effects of cell-permeable ceramide on Malme-3M human melanoma cell line. MTT proliferation assay showed that C2-ceramide inhibited the growth of Malme-3M cells in a dose-dependent manner. Cell cycle analysis confirmed the inhibition of DNA synthesis by a reduction in the S phase and an increase in the G0/G1 phase. Flow cytometric analysis for apoptotic cells and morphological observations indicated that the antiproliferative effect of C2-ceramide was not due to apoptosis. We next investigated the effects of C2-ceramide on the pigmentation of Malme-3M melanoma cells. The results showed that C2-ceramide induced only a slight decrease of tyrosinase activity and melanin synthesis. To investigate the ceramide signaling pathway, we studied the influence of C2-ceramide on extracellular signal-regulated kinase (ERK) and Akt activation by Western blot. We demonstrated that the amount of phosphorylated Akt was decreased by C2-ceramide, whereas ERK was activated transiently. Because of a well-known involvement of ceramide in apoptosis, we further investigated the level of caspase-3 and HSP70 after treatment of C2-ceramide. We found that the caspase-3 was not activated and the expression of HSP70 increased moderately. In conclusion, C2-ceramide inhibited the cell growth of Malme-3M cells without the induction of apoptosis. We suggest that increased HSP70 may be related to the resistance against apoptosis.
