The structural and morphological properties of planar, nonpolar (11-20) a-plane GaN layers grown by hydride vapor phase epitaxy on (1-102) r-plane sapphire substrates are characterized. We report on the effect of low temperature
(500/550/600/660 oC) AlN buffer layers on the structural properties of HVPE grown a-GaN layers. And for the comparison, low temperature GaN and InGaN buffer layers are also tried for the growth of a-plane GaN layers. The structural geometry
of a-GaN layers is severely affected on the growth condition of low temperature buffer layers. The most planar a-GaN could be obtained with GaCl3 pretreatment at the growth temperature of 820oC.
The a-plane GaN layer on r-plane Al2O3 substrate is grown by mixed-source hydride vapor phase epitaxy
(HVPE). The GaN/InGaN heterostructure is performed by selective area growth (SAG) method. The heterostructure consists
of a GaN layer, an InGaN layer and a Mg-doped GaN layer. NH3 and gallium (or indium) chloride formed by HCl which is flown over mixed-source are used as gallium (or indium) and nitrogen sources. The gas flow rates of HCl and NH3 are
maintained at 10 sccm and 500 sccm, respectively. The temperature of GaN source zone is 650oC. In case of InGaN, the temperature of source zone is 900oC. The growth temperatures of GaN and InGaN layers are 820oC and 850oC,
respectively. The EL (electroluminescence) peak of GaN/InGaN heterostructure is at nearly 460 nm and the FWHM (full
width at half maximum) is 0.67 eV. These results are demonstrated that the heterostructure of III-nitrides on r-plane sapphire can be successfully grown by mixed-source HVPE with multi-sliding boat system.
TiO2/PVP nanofibers were electrospun by varying the collector grounding design to improve the axial alignment offibers. The collectors are composed of two pieces of conductive substrates separated by a gap for the uniaxial alignment offibers (X design). The collectors consisting of two sets of substrates placed by 90o (XY design) equipped with a timer arealso prepared for biaxial alignment of fibers. Both collectors show that the charged nanofibers are stretched to span across thegap between the electrodes. Experimental results reveal that the latter collector is more effective on the directionality of2/PVP nanofibers due to the dissipation of accumulated electric charge between the collectors.Key words Nanofiber, Electrospinning, TiO2, PVP, Alignment, CollectorTiO2/PVP ..... .....†..... ...... , .. , 608-736(2007. 1. 12. .. )(2007. 1. 25. .... ). . TiO2/PVP ..... ... ..... ... ... ..... ...... ....... . .....
Cobalt (Co2+) doped ytria stabilized cubic zirconia (YSZ, Y2O3 : 25~50 wt%) single crystals grown by a skulmelting method were heat-treated in N2 at 1000oC for 5 hrs. The reddish brown single crystals were changed into eitherφ6.5 × t2 m) and round brilliant (φ10 m). The optical and structural properties were examined by UV-VIS spectrophotometerand XRD. These results are analyzed absorption by Co2+ (4A2(4F) → 4P) and Co3+, change of energy gap and lattice parameter.Key words YSZ, Co2+, Co3+, energy gap, lattice parameterCobalt. ... .... ... ....... (YSZ) .... ....... .......†.. ........ ..... , .. , 520-714(2007. 1. 9. .. )(2007. 1. 29. .... ). . .. (skull).... .. .... ... (Co2+). .. (doping). 25~50 wt%. .. .. Y2O3 ... .. .... ... ....... (YSZ) .... N2 ... 1000oC.. 5.. .. ... ... . .... ..... .