Current Issue : January - March Volume : 2012 Issue Number : 1 Articles : 5 Articles
The electronic band structure variations of single-walled carbon nanotubes (SWCNTs) using Huckle/tight binding approximation theory are studied. According to the chirality indices, the related expressions for energy dispersion variations of these elements are derived and plotted for zigzag and chiral nanotubes....
The fabrication of GaAs- and InP-based III-V semiconductor nanowires with axial/radial heterostructures by using selective-area metal-organic vapor-phase epitaxy is reviewed. Nanowires, with a diameter of 50ââ?¬â??300?nm and with a length of up to 10?Ã?µm, have been grown along the < 1 1 1 >B or < 1 1 1>A crystallographic orientation from lithography-defined SiO2 mask openings on a group III-V semiconductor substrate surface. An InGaAs quantum well (QW) in GaAs/InGaAs nanowires and a GaAs QW in GaAs/AlGaAs or GaAs/GaAsP nanowires have been fabricated for the axial heterostructures to investigate photoluminescence spectra from QWs with various thicknesses. Transmission electron microscopy combined with energy dispersive X-ray spectroscopy measurements have been used to analyze the crystal structure and the atomic composition profile for the nanowires. GaAs/AlGaAs, InP/InAs/InP, and GaAs/GaAsP core-shell structures have been found to be effective for the radial heterostructures to increase photoluminescence intensity and have enabled laser emissions from a single GaAs/GaAsP nanowire waveguide. The results have indicated that the core-shell structure is indispensable for surface passivation and practical use of nanowire optoelectronics devices....
We investigated the relationship between differences in multiwalled carbon nanotubes (MWCNTs) and the biological responses they elicit in order to develop biocompatible MWCNTs. We exposed human bronchial epithelial (BEAS-2B) cells to two sizes and six grades of MWCNTs and measured the resulting cell viability, total reactive oxygen and/or nitrogen species (tROS/RNS) production, and cytokine secretion. Although differences in cellular tROS production were associated with differences in grades of MWCNTs, the graphitization temperature of MWCNTs apparently did not influence tROS production. However, cell viability was affected by MWCNT graphitization temperature and diameter. Moreover, cytokine secretion was apparently affected by treatment temperature, but not MWCNT diameter. We concluded that the highest temperature resulted in the most biocompatibility because impurities and carbon defects were removed from the MWCNTs. However, other mechanisms are possible. Therefore, it is important to optimize each type of MWCNT by monitoring biological responses that type elicits during the manufacturing stage for applications involving biology and medicine....
Copolymers based on fluorene-thiophene units have presented promising efficiencies in photovoltaic devices applications. They present good transport properties mainly after thermal treatment of the polymer films. Here, we investigate the properties of bilayer devices formed by the heterojunction of the polymer F8T2 with variable thickness and the fullerene. The series resistance of the equivalent circuit associated with the device increases as the polymer film gets thicker. The current-voltage characteristics of the bilayer devices follow the Mott-Gurney law of SCLC. For the best performing device we measured 2.1% of power conversion efficiency....
A hybrid magnesium alloy nanocomposite containing TiC nanoparticle reinforcement was fabricated using solidification processing followed by hot extrusion. The nanocomposite exhibited similar grain size to the monolithic hybrid alloy, reasonable TiC nanoparticle distribution, nondominant (0 0 0 2) texture in the longitudinal direction, and 16% higher hardness than the monolithic hybrid alloy. Compared to the monolithic hybrid alloy, the nanocomposite simultaneously exhibited higher tensile yield strength (0.2% TYS), ultimate tensile strength (UTS), failure strain, and work of fracture (WOF) (+14%, +7%, +81%, and +92%, resp.). Compared to the monolithic hybrid alloy, the nanocomposite exhibited lower compressive yield strength (0.2% CYS) and higher ultimate compressive strength (UCS), failure strain, and WOF (ââ?¬â??11%, +7%, +4%, and +15%, resp.). The advantageous effects of TiC nanoparticle addition on the enhancement of tensile and compressive properties of the hybrid magnesium alloy are investigated in this paper....
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