Effect of reactor pressure on the growth rate and structural properties of GaN films

The effect of reactor pressure on the growth rate, surface morphology and crystalline quality of GaN films grown on sapphire by metalorganic chemical vapor deposition is studied. The results show that as the reactor pressure increases from 2500 to 20000 Pa, the GaN surface becomes rough and the growth rate of GaN films decreases. The rough surface morphology is associated with the initial high temperature GaN islands, which are large with low density due to low adatom surface diffusion under high reactor pressure. These islands prolong the occurrence of 2D growth mode and decrease the growth rate of GaN film. Meanwhile, the large GaN islands with low density lead to the reduction of threading dislocation density during subsequent island growth and coalescence, and consequently decrease the full width at half maximum of X-ray rocking curve of the GaN film.     

Record of environmental change by α-cellulose δ13C of sphagnum peat at Shennongjia, 4000―1000 aBP

The Dajiuhu Basin at Shennongjia, located within typical East Asian Monsoon region, preserves a sub-alpine sphagnum peat deposition in its central area. The topmost 120 cm of the peat covers the last 4000 years according to AMS ^14C dating of pollen concentration. Carbon isotope of a-cellulose, extracted from sphagnum peat, provides a quantitative reconstruction of atmospheric relative humidity, based on transfer functions of C3 plants carbon isotopic fractionation equation and the bryophyte photosynthesis CO2 absorption rate equation. δ^13C, TOC and C/N variations reveal that the Dajiuhu area has experienced a long-term tendency to dry during 4000-1000 aBP, with a major transition happening around 3000 aBP. Four relative dry events are identified at 3400-3200, 3000-2600, 2200-2000 and 1600-1400 aBP, respectively, corresponding to those climate events documented in many global records. Three periodicities, 664 a, 302 a and 277 a enclosed in the atmospheric humidity of Dajiuhu are correlated to the cycles of solar activities. The weakening of East Asia summer monsoon during this period registered in the Dajiuhu peat is consistent with the synchronous weakening of Indian Monsoon. This trend may be attributed to gradual decrease of Northern Hemispheric summer solar insolation and the consequently southward migration of Intertropical Convergent Zone （ITCZ）.     

石膏上水基电泳沉积纳米氧化锆的结构和性能特点

研究评估了水基电泳沉积作为口腔纳米氧化锆全瓷修复体成型方式的可能性.试验通过配置固含量为85wt%的低粘度水基悬浮液,在齿科专用石膏上直接以电泳沉积的方式成型出纳米氧化锆陶瓷预成体,并研究了其结构和性能特点.结果显示：水基电泳沉积成型的方式可以成型出结构非常均一的纳米氧化锆预成体,其表面光滑,外形与石膏基底外形一致,在微观结构上与已商品化的齿科CerconCAD/CAM氧化锆预成瓷块相比,结构更加致密、均匀,且未见明显气泡、裂缝等缺陷 要达到〉99.9%TD,水基电泳沉积成型的纳米氧化锆3Y-TZP所需的烧结温度为1320℃,低于常规的干压成型工艺,力学性能与Cercon氧化锆全瓷修复材料相近,能够满足临床需要.     

长江口南支分流分沙比观测与分析

2007年2月在长江口南支进行沉积动力学参数的全潮观测,以获取枯季期间南北槽、南北港的分流分沙特征．结果表明,多数站位涨潮流速大于落潮流速,涨潮历时小于落潮历时,涨潮悬沙浓度大于落潮悬沙浓度,这种涨落潮不对称效应主要与径流作用和潮波变形有关．悬沙浓度与流速也有一定的相关关系,表明再悬浮作用较为显著．从净泄水量看,北港大于南港,南槽大于北槽,形成由陆向海输运的格局．输沙量则为由海向陆,尤以南槽和南港为最大,加之河流上游亦有来沙,最终在南支拦门沙附近海域形成较为显著的淤积状态．     

读者之声

本期学术论文审稿意见二则本期第19-21页刊登的"腔室长时间使用造成的工艺漂移对微晶硅薄膜性质的影响"一文,考察了等离子体增强化学气相沉积(PECVD)高压制备微     

热处理对电沉积Ni-Fe合金箔微观结构和磁性能的影响

对电沉积得到的Ni-Fe坡莫合金箔,在氢气气氛下进行退火处理,退火温度分别为850,1000和1150℃,保温时间均为5h.在扫描电子显微镜(SEM)和光学显微镜下观察合金箔断面和表面的显微结构,利用XRD检测合金箔的晶体结构,利用软磁材料直流磁性测试仪装置测得合金箔的直流磁特性.实验结果表明:在850～1150℃温度下热处理时,退火温度越高,合金箔的直流磁性能越好;经过退火热处理后合金箔的晶粒明显长大,而且合金箔存在明显的择优取向.     

电沉积和硒化制备CuInSe2薄膜

以石墨为阳极、钛片为阴极,采用恒电流法制备Cu-In预制膜,然后硒化处理得到CuInSe2薄膜.分析了预制膜和CuInSe2薄膜的相组成及其影响因素.结果表明:采用不同的电沉积工艺,可以得到不同相组成的Cu-In预制膜.在保证Cu/In小于1的条件下,降低InCl3浓度和H3Cit/CuCl2浓度比,选择较高电流,可以获得具有CuIn相和Cu2In相的Cu-In预制膜.含有CuIn相和Cu2In相的Cu-In预制膜,经硒化得到的CuInSe2薄膜具有单一CuInSe2相组成,并且符合化学剂量比要求;而只含有CuIn相的预制膜硒化后除了有CuInSe2相外还出现了CuSe相.     

生物净化槽中茵群结构在梭鱼草(Pontederia cordata L)不同生长期的动态变化

为探究引入植物对生物净化槽处理黑臭河水的影响及机理,结合水质理化指标的动态变化,采用了ERIC-PCR指纹图谱技术来分析生物净化槽内的微生物群落结构在植物不同生长阶段的变化特征,比较植物与填料不同工艺组合对微生物群落结构的影响.结果发现:引种梭鱼草(Pontederia cordata L)的生物净化槽对主要污染物COD_(cr),NH_3-N和TP的去除率分别提高了19.8%～69.4%,18.2%～68%和23.9%～77.2%;微生物群落结构随植物不同生长发育阶段而变化,分蘖期优势菌群的种类和数量最多,同期净化效果也最好;从三种工艺的运行效果来看,植物+组合填料搭配最合适.     

铝掺杂氧化锌薄膜电学特性的研究

利用脉冲激光沉积法,在氧气氛下(氧分压为20 Pa)以硅为基体制备了ZnO:Al透明导电膜.靶材选用(ZnO)1-x(Al2O3)x陶瓷靶,沉积过程中基体温度保持在600℃.通过对膜进行霍尔效应测量及SEM、XRD测试分析,研究了靶材中的化学配比(掺杂比)对膜的电学特性的影响.结果表明:掺杂比影响着膜的电学性能和膜的结晶状况.掺杂铝的质量分数为1.37%时所获得的ZnO薄膜具有最小的电阻率.     

克拉玛依油田六区克下组冲积扇砾岩储层沉积特征

在岩心观察基础上,运用地质、测井等资料,从单井相分析入手,通过连井对比剖面扩大到全区范围,研究了克拉玛依油田六区克下组的储层特征和砂砾岩展布规律。克拉玛依油田六区克下组为退积型冲积扇相沉积,六区为单一扇体的一部分。识别出克下组扇顶、扇中和扇缘亚相的分布,分析了各亚相的储层特征和砂体展布规律。研究表明,扇顶、扇中和扇缘亚相储层的总体岩性分别为砾岩、细砾岩和粗砂岩、中细砂岩。砂体的平面展布形式分别为连片状、宽带状和窄条状。