CdSeS合金结构量子点的多激子俄歇复合过程

多激子效应通常是指吸收单个光子产生多个激子的过程,该效应不仅可以为研究基于量子点的太阳能电池开拓新思路,还可以为提高太阳能电池的光电转换效率提供新方法.但是,超快多激子产生和复合机制尚不明确.这里以CdSeS合金结构量子点为研究对象,研究了其多激子生成和复合动力学.稳态吸收光谱显示, 510, 468和430 nm附近的稳态吸收峰,分别对应1S_(3/2)(h)-1S(e)(或1S), 2S_(3/2)(h)-1S(e)(或2S)和1P_P(3/2)(h)-1P(e)(或1P)激子的吸收带.通过飞秒时间分辨瞬态吸收光谱和纳秒时间分辨荧光光谱两种时间分辨光谱技术对CdSeS合金结构量子点的超快动力学进行了探究,结果显示, 1S激子的双激子复合时间大概是80 ps,这一时间比传统量子点的双激子复合时间(小于50 ps)延长了近一倍,结合最近发展的超快界面电荷分离技术,在激子湮灭之前将其利用起来,这一时间的延长将有很大的应用前景;其中,在2S和1P激子中除上述双激子复合外,还存在一个通过声子耦合路径的空穴弛豫过程,时间大概是5—6 ps.最后,利用纳秒时间分辨荧光光谱得到该样品体系单激子复合的时间约为200 ns.     

He离子辐照6H-SiC引入缺陷的光谱研究

实验采用300 keV的He²⁺辐照6H-SiC,辐照温度分别为室温,450,600和750 ℃,辐照剂量范围为1×10¹⁵–1×10¹⁷ cm^-2,辐照完成后对样品进行拉曼散射和紫外可见透射光谱测试与研究. 这两种分析方法的实验结果表明,He离子辐照产生的缺陷以及缺陷的恢复与辐照剂量和辐照温度有着直接关系. 室温下辐照会使晶体出现非晶化,体现在拉曼特征峰消失,相对拉曼强度达到饱和(同时出现了较强的Si-Si峰);高温下辐照伴随着晶体缺陷的恢复过程,当氦泡未存在时,高温辐照很容易导致Frenkel对、缺陷团簇等缺陷恢复,当氦泡存在时,氦泡会抑制缺陷恢复,体现在相对拉曼强度和相对吸收系数曲线斜率的变化趋势上. 本文重点讨论了高温辐照情况下氦泡对缺陷聚集与恢复的影响,并与高温下硅离子辐照碳化硅结果进行了对比. 关键词： 6H-SiC 氦泡 拉曼散射光谱 紫外可见透射光谱     

基于HIRFL 的高温应力材料载能离子辐照实验装置

针对未来先进核能装置候选结构材料在高温和应力等条件下抗辐照性能的评价与快速筛选的需求,基于兰州重离子研究装置( HIRFL ) 可提供的离子束流条件,设计制作了国内第一套高温应力材料载能离子辐照装置。该装置由束流扫描及探测系统、高温系统、应力系统、真空冷却系统和远程控制系统等5 部分组成,可以同时提供高温和拉/ 压应力下材料的离子束均匀辐照件,温区覆盖了室温至1 200 °C范围,拉/ 压应力范围为0 ~1176 N,x-y 方向均匀扫描面积可大于40 mmx40 mm。利用该装置,已经成功进行了多次高温和应力条件下载能离子辐照先进核能装置候选材料的实验研究,并取得了初步成果。In order to expedite the evaluation of properties of irradiated materials and the selection of candidate materials for future nuclear energy systems, we developed a specific ion irradiation equipment installed on the Heavy Ion Research Facility of Lanzhou ( HIRFL ) for materials under high temperature and stress. This equipment consists of ion beam scanning and detector system, high temperature load system, stress load system, water cooling system as well as telecommunication and control system. It can supply a wide range of temperature (from room temperature to 1 200 °C ) and stress ( pull / push from 0 to 1 176 N) simultaneously for materials under ion irradiation. The x-y scanning area with high uniformity is larger than 40 mm40 mm. This is the first suit of ion irradiation equipment made in China that can be used to study co-operating effects of high temperature and stress in an irradiated material. It has been successfully used several times for materials irradiations under high temperatures and stress, which proved that the new equipment has very good performances in experiments.     

Effects of Grain Boundary Characteristics on Its Capability to Trap Point Defects in Tungsten

As recombination centers of vacancies(Vs) and self-interstitial atoms(SIAs), firstly grain boundaries(GBs)should have strong capability of trapping point defects. In this study, abilities to trap Vs and SIAs of eight symmetric tilt GBs in tungsten are investigated through first-principles calculations. On the one hand, vacancy formation energy E~f_V rapidly increases then slowly decreases as the hard-sphere radius r_0 of the vacancy increases.The value of E~f_V is the largest when r_0 is about 1.38 ?, which is half the distance between the nearest atoms in equilibrium single crystal tungsten. That is, any denser or looser atomic configuration around GBs than that in bulk is helpful to form a vacancy. On the other hand, SIA formation energy E~f_(SIA) at GBs decreases monotonically with increasing the hard-sphere radius of the interstitial sites, which indicates that GBs with larger interstitial sites have stronger ability to trap SIAs. Based on the data obtained for GBs investigated in this study, it is found that the ability to trap Vs increases as the GB energy increases, and the capability of trapping SIAs linearly increases as the excess volume of GB increases. Due to its lowest GB energy and smallest excess volume among all GBs studied, twin GB ∑3(110)[111] has the weakest capability to trap both Vs and SIAs.     

He 离子注入引起的高纯钨硬化

完成了不同注量或温度下100 keV 的He 离子注入高纯钨的实验,并利用纳米压痕技术测量了材料的微观力学性能。所有注入样品的纳米硬度值都高于未注入样品的纳米硬度值。对于室温注入样品,随着注量的增加,样品抗弹性变形能力下降;当注量不高于5x1017 ions/cm2 时,钨的纳米硬度峰值随着注量的增加而增加;注量为1x1018 ions/cm2 的钨样品的纳米硬度峰值反而降低。高温注入样品的抗弹性变形能力优于室温注入样品的抗弹性变形能力;随着注入温度的增加,样品的平均纳米硬度值和弹性模量略有下降。分析讨论了He 注入钨硬化和抗弹性形变能力降低的可能原因。Tungsten has been selected as divertor materials in fusion reactors because of its high thermal conductivity,high melting point, low expansion coefficient and high threshold energy for sputtering etc. The paper presents the hardening behaviour of high pure tungsten by 100 keV He+ with different fluences from 5x1016 ions/cm2 to 1x1018ions/cm2 at room temperature, and with fluence of 1x1018 ions/cm2 at higher temperatures (400, 600 and 800 °C). The microscopic mechanical properties of these samples were investigated by nano-indentation technology. The results show that all of the implanted samples harden obviously. The reason for hardening may be that defects of interstitial dislocation loops or dense helium bubbles etc induced by helium implantation obstacle the movement of dislocation. The peak nanohardness of the samples increased with the fluences increasing when the fluence is not more than 5x1017 ions/cm2, while the nano-hardness value of the implanted sample with the fluence of 1x1018 ions/cm2 decreases and the nano-hardness changes little in the region of 50 nm to 200 nm from surface. For all the implanted samples with 1x1018 ions/cm2 at higher temperatures, their nano-hardness values are similar, but show a trend of decrease with increasing temperature.The reason may be the decrease of the defects’ density during implantation at higher temperatures. In addition, the capability of resisting deformation for the implanted tungsten reduces with increasing fluence and increases a little at higher temperatures.     

250 keV He+ 离子注入钽酸锂改性研究

室温下,将能量为250 keV He+ 离子注入z 切钽酸锂单晶,注量范围5.0x1014~5.0x1016 He+/cm2,应用三维轮廓仪、X射线衍射(XRD)、紫外可见(UV-Vis ) 光学吸收谱对未注入和注入样品进行了表征和分析。分析结果表明,在注量达到5.0x1016He+/cm2 时,样品表面出现大量凸起条纹,同时晶格沿着[001] 方向出现明显肿胀,吸收边则表现出明显的注量相关性。注入样品在空气中放置60 d后,最高注量的样品表面原来凸起的条纹变为细长的裂纹,晶格应变及光学吸收边均出现较大的恢复。讨论了样品表面形貌、晶格应变和光学吸收边与He 行为的关系。The effects of 250 keV He + implantation in the fluence from 5.0x1014 to 5.0x1016 He+/cm2 on lithium tantalate at room temperature were investigated by 3D surface profiler, XRD and UV-Vis optical absorption spectroscopies.The experimental results show that a large number of raised stripes appear on the surface of the sample and the significant lattice swelling occurs along the direction [ 001 ] at the fluence of 5.0x1016 He+/cm2. The dependence of changes absorption edge on the fluences was revealed. After the samples had been exposed to the air for 60 days, the raised stripes on the surface have evolved into narrow cracks. Furthermore, the lattice strain and the optical absorption edge has also recovered dramatically. The relationship between surface morphology, lattice strain, optical absorption edge and behaviorof He-ions was discussed.     

Structural Distortion and Defects in Ti_3AlC_2 irradiated by Fe and He Ions

Ti_3AlC_2 samples are irradiated in advance by 3.5 MeV Fe-ion to the fluence of 1.0×10~(16) ion/cm~2,and then are implanted by 500 keV He-ion with the fluence of 1.0×10~(17) ion/cm~2 at room temperature.The irradiated samples are investigated by grazing incidence x-ray diffraction(GIXRD) and transmission electron microscopy(TEM).GIXRD results show serious structural distortion,but without amorphization in the irradiated samples.Fe-ion irradiation and He-ion implantation create much more serious structural distortion than single Fe-ion irradiation.TEM results reveal that there are a large number of defect clusters in the damage region,and dense spherical He bubbles appear in the He depositional region.It seems that the pre-damage does not influence the growth of He bubbles,but He-ion implantation influences the pre-created defect configurations.