Study on irradiation-induced defects in GaAs/AlGaAs core–shell nanowires via photoluminescence technique

To gain a physical insight into the radiation effect on nanowires(NWs), the time resolved photoluminescence(TRPL)technique is used to investigate the carrier dynamic behaviors in GaAs/AlGaAs core–shell NWs before and after 1-MeV proton irradiation with fluences ranging from 1.0 × 10~(12) cm~(-2) to 3.0 × 10~(13) cm~(-2). It is found that the degradations of spectral peak intensity and minority carrier lifetime show similar trends against irradiation fluence, which is closely related to the displacement defects induced by irradiation. We also find that the proton irradiation-induced defects behave as Shockley–Read–Hall(SRH) recombination center trapping free carriers. Finally, the defect concentration could be estimated through measuring the minority carrier lifetime.     

Anharmonic oxygen vibration and mode softening in Tl2Ba2Ca2Cu3O10 superconductor

The softening of the IR active 300 cm⁻¹ phonon mode in Tl-2223 superconductor, aroundT _c has been explained by considering a sixth order polarization potential at the off-center oxygen ion site in the Tl-O plane, and by using a nonlinear lattice dynamical theory. The present theory explains, more or less satisfactorily, the unusual temperature dependence of oxygen ion vibration and frequency shifts at higher temperature. The existence of strong nonlinear electron-phonon interaction atT _c has been emphasized.     

Generation of new longitudinal modes in an amplifying dye solution

A novel phenomenon is reported for the first time that the generation of the newlongitudinal modes in amplifying multi-longitudinal mode laser in a dye amplifier.The newmodes are located on the violet side within the gain band of the amplifing medium.The phe-nomenon is explained by the theory of third-order nonlinear polarization in the case of four-wave resonances.The intensity of the new modes created are comparable with or even higherthan that of the original modes.The effect can be expected to serve as a new method for ex-tention of spectral tuning ranges of laser.     

溴化苄及其阳离子红外光谱的理论研究

利用密度泛函理论（DFT）在B3LYP/6-311G++（d,p）水平上对溴化苄分子进行了结构优化和频率计算,得到了该分子的稳定构型和全部振动模式。计算得到的几何参数通过与苯分子的实验值相比,发现理论值与其相吻合;理论计算和实验测得的红外光谱数据的比较分析表明,理论计算与实验测量结果符合得较好,并对其振动模式进行了归属。最后,在B3LYP/6-311G++（d,p）水平上计算得到了溴化苄阳离子的红外光谱,并与溴化苄进行了比较,计算表明电离对振动偶极距产生了较大影响。     

Radiation damage in Si photodiodes by high-temperature irradiation

Results are presented of a detailed study of the effects of high-temperature 4-MeV neutron irradiation on the performance degradation of Si pin photodiodes together with the radiation-induced defects, observed by deep level transient spectroscopy. The degradation of the device performance and the introduction rate of the lattice defects decrease with increasing sample temperature during irradiation. For a 250°C irradiation, the reduction of the reverse current is only 20% of the starting value. This result suggests that the creation and recovery of the radiation damage proceeds simultaneously at high temperatures. Carbon-related complex as hole capture levels is also mainly responsible for the device degradation for high-temperature neutron irradiation.     

用一维光子带隙结构增强硫化镉双光子吸收研究

用真空镀膜方法制备了含有单个CdS缺陷层的具有不同周期和结构参量的TiO2／SiO2一维光子晶体。用抽运一探测技术研究了CdS缺陷层的双光子吸收（TPA）现象。实验结果表明：一维光子晶体中CdS缺陷层的双光子吸收显著增强。不同周期和结构参量的一维光子晶体中CdS缺陷层的双光子吸收系数不同。双光子吸收的增强来源于由光局域化导致的缺陷层的电场强度的增加。缺陷层电场强度与一维光子晶体的结构有关,如周期,光子带隙的位置与宽度及缺陷模式等因素都会影响缺陷层电场强度。采用四分之一波长的高低折射率介质层和与入射波长匹配的缺陷模可以得到最大的缺陷层电场强度。     

基于数字图像处理技术的树脂眼镜镜片缺陷检测研究

通过设计的镜片自动检测光学硬件系统,给出了树脂镜片精细杂质图像处理措施,将图像差分法应用于镜片图像边缘的去除;同时解决了镜片检测灰尘影响的问题;另外运用改进型的归一法解决杂质计数问题,为自动化分级分拣系统的研发提供重要的数据支持,为镜片缺陷检测系统的后续分级分拣的数字控制模块提供了可操作性。该检测系统检测精度为0.03 mm、速度为1片/s,检测误差控制在5%。     

GaN基HEMT器件的缺陷研究综述

GaN基高电子迁移率晶体管(HEMT)因具有高输出功率密度、高工作频率、高工作温度等优良特性,在高频大功率等领域具有广泛应用前景。目前,HEMT器件在材料生长和工艺制备方面都取得了巨大的进步。但是,由缺陷产生的陷阱效应一直是限制其发展的重要原因。本文首先论述了HEMT器件中的表面态、界面缺陷和体缺陷所在位置及其产生的原因。然后,阐述了由陷阱效应引起的器件电流崩塌、栅延迟、漏延迟、Kink效应等现象,从器件结构设计和工艺设计角度,总结提出了改善缺陷相关问题的主要措施,其中着重总结了器件盖帽层、表面处理、钝化层和场板结构4个方面的最新研究进展。最后,探索了GaN基HEMT器件在缺陷相关问题上的未来优化方向。     

铅在铁路岩石边坡创面人工土壤中的迁移特性研究

山区大规模的铁路建设产生了大量的岩石边坡,前期研究表明边坡创面人工土壤受Pb污染,且有中等程度的富集。土壤类型、植被搭配类型是影响Pb迁移特性的重要因素,而目前却未见人工土壤及植被搭配类型对Pb迁移特性影响的相关报道。该研究以铁路岩石边坡创面人工土壤为对象,利用原子吸收分光光度法、红外光谱法分析了人工土壤对Pb的吸附-解吸特性及机制;运用野外人工模拟降雨实验,进一步考察在暴雨径流作用下,Pb在不同植被搭配类型的边坡人工土壤中的迁移过程。结果表明人工土壤对Pb的吸附量随着溶液平衡浓度的增加而急速增加,等温曲线呈“S”型,Freundlich方程能较好地描述人工土壤对Pb的吸附行为,R2为0.91。二次幂函数方程能较好描述NH₄AC对铅的解吸过程,R2为0.96。人工土壤有高岭石红外光谱特征吸收峰,属于高岭石型图谱。高岭石表面-OH、腐殖质表面-OH和-COOH参与吸附作用,置换出H+。人工土壤易将交通运输产生的Pb固定,但又容易再次释放。不同植被搭配类型边坡Pb流失量表现为草本＞草本+灌木＞草本+灌木+乔木。暴雨径流作用下Pb随沉积物相流失是边坡创面人工土壤Pb流失的主体,边坡土壤的侵蚀是导致Pb迁移扩散的主要原因,因此促进边坡植被的恢复,减小边坡人工土壤的侵蚀作用是防止Pb迁移扩散的关键。     

Breather trapping and breather transmission in a DNA model with an interface

We study the dynamics of moving discrete breathers in an interfaced piecewise DNA molecule. This is a DNA chain in which all the base pairs are identical and there exists an interface such that the base pairs dipole moments at each side are oriented in opposite directions. The Hamiltonian of the Peyrard-Bishop model is augmented with a term that includes the dipole-dipole coupling between base pairs. Numerical simulations show the existence of two dynamical regimes. If the translational kinetic energy of a moving breather launched towards the interface is below a critical value, it is trapped in a region around the interface collecting vibrational energy. For an energy larger than the critical value, the breather is transmitted and continues travelling along the double strand with lower velocity. Reflection phenomena never occur. The same study has been carried out when a single dipole is oriented in opposite direction to the other ones. When moving breathers collide with the single inverted dipole, the same effects appear. These results emphasize the importance of this simple type of local inhomogeneity as it creates a mechanism for the trapping of energy. Finally, the simulations show that, under favorable conditions, several launched moving breathers can be trapped successively at the interface region producing an accumulation of vibrational energy. Moreover, an additional colliding moving breather can produce a saturation of energy and a moving breather with all the accumulated energy is transmitted to the chain.