钙钛矿/银电极界面降解和离子迁移的原位研究

本文对CH_3NH_3PbI_3钙钛矿层与Ag电极之间的界面降解和离子迁移过程进行了全面地研究.利用原位光电子能谱检测于段,发现了Ag电极会诱导钙钛矿层的降解,导致PbI_2和AgI物种的形成以及Pb~(2+)离子在界面处还原成金属Pb物种.I 3d谱峰强度的反常增强为碘离子从CH_3NH_3PbI_3下表面迁移到Ag电极提供了直接的实验证据.此外,Ag电极和钙钛矿层接触会在CH_3NH_3PbI_3/Ag界面处诱导0.3 eV的界面偶极,这可能进一步促进碘离子扩散迁移,导致钙钛矿层的分解和Ag电极的侵蚀.     

光谱法结合分子动力学模拟研究臭氧对肌红蛋白结构的作用机制

臭氧(O₃)是一种具有强氧化性作用的杀菌消毒剂,因其安全无害等特点已被广泛用于肉制品生产加工的减菌处理,但O₃减菌处理对红肉色泽具有较强的负面作用,且其作用机制尚缺乏研究。针对肌红蛋白（Mb）存在状态是决定红色肉色泽关键因素的基础,通过紫外-可见吸收光谱法、荧光光谱法和圆二色光谱法（CD）研究O₃作用下Mb的光谱特性变化,结合蛋白质氧化特征指标分析和分子动力学模拟技术探究O₃对Mb分子的作用效果与机制。光谱研究结果表明,O₃处理可使Mb的紫外-可见光谱图在412 nm左右处的铁卟啉环特征峰及540和580 nm附近的氧合肌红蛋白（OMb）特征峰的强度减弱,其中铁卟啉环特征峰发生蓝移;利用固定激发波长280 nm下测定Mb内源性荧光和同步荧光光谱表明O₃会降低Mb的荧光强度,增大铁卟啉基团贡献的荧光峰强度和造成酪氨酸残基荧光光谱特征峰的蓝移;O₃作用使Mb三维荧光光谱特征峰强度的下降及光散射强度的增加。以上变化推断出O₃会促进Mb的氧化,造成其氨基酸残基疏水基团裸露,使Mb所处微环境及其蛋白构象改变;CD分析表明O₃与肌红蛋白接触时间越久,蛋白质二级结构变化越明显,造成α-螺旋的含量下降,无规则卷曲增加。辅以检测不同强度O₃处理Mb的含量及性质的变化,可知O₃处理使OMb含量下降,高铁肌红蛋白（MMb）含量增加,同时O₃处理Mb的羰基含量增加和巯基含量下降,这也进一步证实O₃作用促进了Mb的氧化,此外,O₃处理Mb表面疏水性的增强,说明O₃造成Mb体系微环境的极性变化。分子动力学模拟结果显示O₃会提高Mb肽链的RMSD值,影响Mb肽链的稳定性,减弱铁卟啉环与Mb肽链的相互作用;RMSF结果表明Mb活性口袋附近氨基酸残基的变化较大;蛋白质二级结构分析与光谱学试验研究结果一致,Mb的α-螺旋的含量下降,无规则卷曲增加。总而言之,O₃可作用于Mb的氨基酸残基,导致蛋白质二级结构和疏水性改变,并发生蛋白氧化及铁卟啉环暴露,进而引起红色肉色泽发生改变。该研究可为生鲜红肉护色技术制定等提供一定理论依据。     

刻蚀与退火对GaN欧姆接触的影响

使用干法刻蚀在GaN LED晶片上刻蚀n区,用电子束蒸发方法在n型GaN表面上淀积Ti/Al双金属层作为接触电极,在N2环境中进行退火.探讨不同的刻蚀方法和刻蚀条件及不同的退火条件对Ti/Al-n型GaN间欧姆接触的影响.     

Growth of Semi-Insulating GaN by Using Two-Step AIN Buffer Layer

Semi-insulating GaN is grown by using a two-step A1N buffer layer by metalorganic chemical vapour deposition. The sheet resistance of as-grown semi-insulating GaN is dramatically increased to 10^13 Ω/sq by using two-step A1N buffer instead of the traditional low-temperature GaN buffer. The high sheet resistance of as-grown GaN over 10^13 Ω/sq is due to inserting an insulating buffer layer （two-step A1N buffer） between the high-temperature GaN layer and a sapphire substrate which blocks diffusion of oxygen and overcomes the weakness of generating high density carrier near interface of GaN and sapphire when a low-temperature GaN buffer is used. The result suggests that the high conductive feature of unintentionally doped GaN is mainly contributed from the highly conductive channel near interface between GaN and the sapphire substrate, which is indirectly manifested by room-temperature photoluminescence excited by an incident laser beam radiating on growth surface and on the substrate. The functions of the two-step A1N buffer layer in reducing screw dislocation and improving crystal quality of GaN are also discussed.     

初中化学“铁和其他金属”的教学法

根据教学大纲及课本体会到本章的教学目的有下列几点: 1.使学生初步认识钢铁和几种重要有色金属的性质、用途,以及它们在国民经济中所起的作用。 2.介绍从矿石中冶炼铸铁的基本原理,与主要的生产过程,给学生以化学冶金初步的基本知识。 3.使学生明了“合金”的概念,并知道几种最重要的合金的组成性质和用途。 4.通过我国和苏联钢铁工业发展状况,和它在经济建设和国防建设上所起的作用,说明我国在社会主义工业化首先发展重工业的重大意义。     

Semiclassical calculation of Rydberg He2^＋ molecular of recurrence spectra ion in a magnetic field

Making use of the molecular closed-orbit theory and a new model potential for the Rydberg molecule, we have calculated the recurrence spectra of He^2＋ molecular ion in a magnetic field for different quantum defects. The Fourier transform spectra of He^2＋ molecular ion may be used to perform a direct comparison between peaks in the spectra and the scaled action values of closed orbits of the excited electron in external fields. We find that the spectral modulations can be analysed in terms of the scattering of the excited electron on the molecular core. Unlike the case of the Rydberg atom where the elastic scattering is predominant, modulations produced by inelastic scattering are also vital to the photoabsorption spectrum of the Rydberg molecule. Our results are in good agreement with the quantum results, which suggests that our method is correct.     

Theoretical analysis and simulation of conjugate heights for dual-conjugate AO system in lidar

A multi-conjugate adaptive optics （MCAO） can offer a possibility of widening field of view （FOV） characterized by the isoplanatic angle, and the choose of conjugate height becomes a basic problem for MCAO, which influences the size of iosplanatic angle. Considering the application of lidar, the isoplanatic angle＇s expressions of two deformable mirrors （DMs） MCAO for uplink and downlink are deduced. The effects of conjugate heights for dual-conjugate AO are thoughtfully discussed, and the isoplanatic angles are further analyzed. The results show that the isopanatic angle varies with the conjugate height and reaches the maximum as the conjugate height is at the optimal altitude. Moreover, the optimal conjugate height changes with the propagation distance.     

不断进取迎接未来

不断进取迎接未来我们是《大学化学》的老订户和热心读者，同时也曾多次投稿，在这块学术园地上种上了几束“花草”，我们一直关心着《大学化学》的成长和进步。十年来，我们在这块教学研究园地上获取了丰富的信息和营养，对教学工作受益匪浅。对于广大作者无私地奉献出自...     

量子反应散射的非弹性散射表达式

对于原子-双原子分子的反应散射采用核间距作坐标。经过坐标的质量标度化,坐标旋转及换成超球坐标,则量子反应散射具有与非弹性散射相似的表达式。在此描述下,反应体系自然地、均匀地由反应态转化为产物态,避免了不同排列通道间的坐标变换。     

多把钥匙问题的一般情形

在计数问题中常常遇到多把钥匙开锁问题.主要解决下列三个问题:(1)计算至少需要几把锁;(2)每人至少要掌握几把钥匙;(3)如何将钥匙进行适当的分配.本文引进了内集族及与之相应的外集族、临界集族的概念,把多把钥匙开锁问题推广到一般情形,并在一般情形时解决了前述三个问题.本文还对集族中两两互不包含的集合的基数作出了估计.