INVESTIGATION OF MICROSTRUCTURE AND CONDUCTIVE MECHANISM OF HIGH DENSITY POLYETHYLENE/CARBON BLACK PARTICLE COMPOSITE BY POSITRON ANNIHILATION LIFETIME SPECTROSCOPY

The microstructure and conductive mechanism of high density polyethylene/carbon black (HDPE/CB) composite were investigated by positron annihilation lifetime spectroscopy (PALS). The PALS were measured in two series of samples, one with various CB contents in the composites and the other with various gamma-irradiation doses in HDPE/CB composite containing 20 wt% CB. It was found that CB particles distribute in the amorphous regions, the CB critical content value in HDPE/CB composite is about 16.7 wt% and the suitable gamma-irradiation dose for improving the conductive behavior of HDPE/CB composite is about 20 Mrad. The result observed for the second set of samples suggests that gamma-irradiation causes not only cross-linking in amorphous regions but also destruction of the partial crystalline structure. Therefore, a suitable irradiation dose, about 20 Mrad, can induce sufficient cross-linking in the amorphous regions without enhancing the decomposition of crystalline structure, so that the positive temperature coefficient (PTC) effect remains while the negative temperature coefficient (NTC) effect is suppressed. A new interpretation of the conductive mechanism, which might provide a more detailed explanation of the PTC effect and the NTC effect has been proposed.

Defect Characterization of 6H-SiC Studied by Slow Positron Beam

在成长得当、照耀电子的 6H-SiC 晶片的缺点形成和退火的行为被可变精力的慢正电子横梁调查。为n类型成长得当的样品，那退火，被发现减少缺点集中由于再结合与空隙，并且当它在真空为 30 min 在 1400 °C 被退火时，厚 Si 层在顶上被发现的 20 nm 原文如此底层，它是当在高温度阶段退火了时，扩散到表面的 Si 原子的一个直接证明。在退火的高温度期间上演，我们发现明显的表面效果发生那导致了更高的 Sparameter 结束到表面。这可以被 Si 原子的散开在退火期间引起到表面。在 n 类型 6H-SiC 的 10 兆电子伏电子照耀以后，正电子有效散开长度从 86.2 nm 减少了到 39.1 nm。这证明有一些缺点，在 n 类型 6H-SiC 创造。但是在 p 类型， 6H-SiC 由 10 个兆电子伏电子照耀，变化是很小的。这可能因为空缺缺点的相反的费用。除了在在 300 ° C 被退火以后，它的缺点集中增加了之外，成长得当的 6H-SiC 的取样的一样的退火行为也为 1.8 件兆电子伏照耀电子的 6H-SiC 样品被观察。这可以作为碳空缺的产生被解释，由于也在 divacancies 和硅之间的再结合空隙，或费用状态的费用。