Damage removal and strain relaxation in As+-implanted Si0.57Ge0.43 epilayers grown by gas source molecular beam epitaxy

The damage removal and strain relaxation in the As+-implanted Si0.57Ge0.43 epilayers were studied by double-crystal x-ray diffractometry and transmission electron microscopy. The results presented in this paper indicate that rapid thermal annealing at temperatures higher than 950 degrees C results in complete removal of irradiation damage accompained by the formation of GeAs precipitates which enhance the removal process of dislocations.

中国天山过去43年大气环境变化：来自冰芯草酸根记录的证据

中、低纬度地区山地冰川有机酸记录的研究是目前国际冰芯地球化学研究的前沿之一。中国天山乌鲁木齐河源一号冰川为一中纬度山地冰川。对其冰芯的草酸根含量的分析显示，其冰芯所记录的过去43年草酸根变化的总体特征是在一个背景值基础上存在着含量的突变峰值。草酸根的背景值含量在1ng／g左右，在部分冰芯段，其含量甚至低于测试分析的检测限；而大多数草酸根峰值的含量都达到或超过了10ng／g。草酸根的平均含量为3．6±9．2ng／g(x^-±1σ，N=534)，其中70％以上由峰值构成。50年代后期是草酸根的一个低值期，平均含量略高于本底值；至60-70年代达到最高值，平均含量为5．0ng／g；80年代草酸根平均含量又下降到接近50年代后期的水平；至90年代回落到本底值附近。草酸根的主要来源是人类活动对大气所造成的污染。其过去43年平均含量的变化大致与中国西部工业和环境保护事业的发展历程相一致，是西部区域大气污染变化的一种反应。

Comonomer sequence distribution in metallocene-based ethylene/1-butene (S-34) and ethylene/1-hexene (S-43) copolymers

Metallocene based polyethylenes were prepared by SMOPEC's "metallocene adduct" technology in a gas phase fluidized bed model reactor. The C-13-NMR spectra of ethylene/1-butene (S-34) and ethylene/1-hexene(S-43) copolymers were studied in a manner analogous to that established by Hsieh and Cheng. The comonomer sequence distributions of copolymer samples were obtained. The results show that these metallocene based copolymers contain a small amount of butene and hexene, and the EE and EEE sequences are dominant.