Electrical and optical properties of oxygen doped GaN grown by MOCVD using N2O

Oxygen doped GaN has been grown by metalorganic chemical vapor deposition using N₂O as oxygen dopant source. The layers were deposited on 2″ sapphire substrates from trimethylgallium and especially dried ammonia using nitrogen (N₂) as carrier gas. Prior to the growth of the films, an AIN nucleation layer with a thickness of about 300? was grown using trimethylaluminum. The films were deposited at 1085°C at a growth rate of 1.0 μm/h and showed a specular, mirrorlike surface. Not intentionally doped layers have high resistivity (>20 kW/square). The gas phase concentration of the N₂O was varied between 25 and 400 ppm with respect to the total gas volume. The doped layers were n-type with carrier concentrations in the range of 4×10¹⁶ cm⁻³ to 4×10¹⁸ cm⁻³ as measured by Hall effect. The observed carrier concentration increased with increasing N₂O concentration. Low temperature photoluminescence experiments performed on the doped layers revealed besides free A and B exciton emission an exciton bound to a shallow donor. With increasing N₂O concentration in the gas phase, the intensity of the donor bound exciton increased relative to that of the free excitons. These observations indicate that oxygen behaves as a shallow donor in GaN. This interpretation is supported by covalent radius and electronegativity arguments.     

溶胶－凝胶二氧化硅驻极体薄膜的物理化学改性

实验研究了由溶胶－凝胶法制备二氧化硅驻极体薄膜的工艺。用红外透射谱、扫描电子显微镜以及驻极体等温表面电位测量和热刺激放电等实验考察了热处理和化学表面修正两个关键工艺对溶胶－凝胶二氧化硅样品驻极体性能的影响。结果表明经过高温条件下一定时间的热处理和化学表面修正，可以制备出性能优良的驻极体薄膜     

In Situ FTIR Study of the Formation of an Organosilane Layer at the Silica/Solution Interface

An FTIR experiment especially designed to study the growth of an organosilane layer at the interface between a solution and a flat silica surface is presented. High sensitivity is achieved by using the attenuated total reflection (ATR) technique in a liquid flow cell. The ATR crystal, either silicon or germanium, is covered with a very thin silica layer. Chemical reactions of a mono-and a di-hydrolyzable silane with the silica substrate have been investigated. The grafting of a submonolayer of the first reagent has been monitored by following the C-H and SiO-H vibrations. The density of grafted molecules has been estimated and information on the nature of the chemical bonding has been achieved. Evidence for the chain-polymerization of the dihydrolyzable silane at the substrate/solution interface has been inferred from the appearance of a Si-O-Si absorption band.     

30CrMnsi联接环断裂失效分析

对断裂的联接环进行了化学成分、机械性能、显微组织核验，指出回火工艺不当、锻造缺陷以及原材料化学成分不合格，是造成断裂事故的主要原因．在此基础上．提出了改进措施．     

专家系统在化工中的应用进展

本文综述了近年来专家系统在化工领域的应用状况，并指出今后的发展趋势。     

Use of chemical variation and predation as plant defenses byEncelia farinosa against a specialist herbivore

Larvae of the monophagous herbivore,Trirhabda geminata, selectively eat particular plants and plant parts of its natural host,Encelia farinosa. Measurements of leaf damage and larval positions on branches through time support this observation. Time-lapse movie photography revealed that larvae are sufficiently mobile to search most of a plant in a 48-hr period and that aggregations were the result of larval activity and not directly the result of oviposition. Experiments withT. geminata larvae on artificial diets containing a range of natural concentrations of chemical extracts fromE. farinosa leaves showed that the larvae grew significantly slower and had a lower overall survivorship at the high concentration. Combining the results of all choice tests, larvae appeared unable to distinguish between high- and low-concentration agar diets. Considered individually, larval preferences for natural production concentrations changed as the season progressed. Early-season larvae preferred low-concentration leaves, while late-season larvae preferred high-concentrations. Measurements of chemical and nitrogen content of leaves selected by larvae in the field confirmed this pattern. Percent parasitism in field-collected larvae increased with season as the larval population decreased. This combination of slowed growth and increasing parasitism and predation is a putative defense strategy ofEncelia farinosa to prevent adaptation by a specialist herbivore to the total range of compounds elaborated.     

铂与氢、水和苯分子相互作用的量子化学研究

采用量子化学程序Gaussian98(A.9)从头算的B3LYP方法，全优化计算铂对氢、水和苯的化学吸附作用，得到了3种相关络合物PtX、PtXX和Ptxxx(X=H，H2O或C6H6)的平衡几何构型和电子结构信息，并探讨了这些络合物的成键性质，以及苯环与铂原子之间的分子轨道作用性质。结果表明，苯环与铂原子之间有很强的成键作用，并随着游离氢原子和水分子的参与，作用强度有很大变化。苯分子吸附在金属铂上，它的芳香性得到不同程度的降低，苯环被活化，苯环与铂原子之间形成η^2型π键络合物；水参与作用后，苯环与铂原子之间形成σ络合物；氢和水同时参与作用后，苯环与铂原子之间仅有很弱的π轨道作用。     

烧结钕铁硼永磁体的镍及镍磷合金镀层

综述了钕铁硼永磁体材料的表面电镀镍及化学镀镍磷合金的研究进展，提出了从铵铁硼材料的特殊性来选择恰当的前处理和镀覆工艺，就有获得优质的保护镀层。     

埃及Ain Sukhna Ezz带钢厂的电弧炉

埃及Ain Sukhna Ezz带钢厂的电弧炉是达涅利公司建造的最大的电弧炉之一,由于可选用多种入炉原料,采用最优化熔炼和精炼方法,可在电弧炉上以转炉生产成本生产转炉优质钢种.     

流程模拟中分解与切断的计算机处理方法探讨

探讨在化工过程模拟计算中对大系统分解及排出单元模拟优先顺序，找出切断流的最佳切断位置的一种新方法。