基于磁圆二向色谱的单层MoS_2激子能量和线宽温度依赖特性

以二硫化钼(MoS_2)为代表的过渡金属硫属化物属于二维层状材料,样品可以薄至单层.单层MoS_2是一种直接带隙半导体,在纳米逻辑器件、高速光电探测、纳米激光等领域具有广阔的应用前景.在实际应用中,温度是影响半导体材料能带结构和性质的主要因素之一.因此研究单层二维材料能带的温度依赖特性对理解其物理机理以及开展器件应用具有重要的意义.目前,在广泛采用的测量单层MoS_2反射谱的研究中,激子峰往往叠加在一个很强的光谱背底上,难以准确分辨激子的峰位和线宽.基于自行搭建的显微磁圆二向色谱系统,研究了单层MoS_2在65—300 K温度范围内的反射谱和磁圆二向色谱,结果表明磁圆二向色谱在研究单层材料激子能量和线宽方面具有明显的优势.通过分析变温的磁圆二向色谱,得到了不同温度下的A,B激子的跃迁能量和线宽.通过对激子能量和线宽的温度依赖关系进行拟合,进一步讨论了声子散射对激子线宽的影响.     

二维单层硒化钼和硒化钨晶体的声子辅助上转换荧光光谱

声子辅助的上转换荧光是固体激光制冷效应的基础. 激光制冷具有体积小、效率高、无振动干扰、无需制冷剂等优势而具有重要应用价值, 探索更多可以实现激光制冷效应的材料是相关领域的重要研究内容. 二维单层过渡金属硫属半导体化合物是直接带隙荧光材料, 其完美的晶格结构、辐射光子提取效率高等特征使其有望成为一种新型激光制冷材料. 以MoSe₂和WSe₂为例, 本文研究了不同波长激发下样品的上转换荧光, 并通过激光功率依赖性实验和温度依赖性实验证实了该上转换荧光过程的发光机制为声子辅助过程.     

高精度2×2阵列拼接光栅结构设计

 提出了一种大口径高精度2×2阵列光栅拼接结构,采用模块化和框架式结构设计,保证拼接结构的稳定性;设计了差动螺纹微调组件与压电驱动器相结合的微纳调整组件结构,实现拼接光栅微纳量级的调整要求;讨论了关键组件的设计和制造问题。设计制造的2×2阵列光栅实验样机的最大相对共面误差为17 μm,微纳调整组件的最小调整精度可以达到1.8 nm,分辨力为0.9 nm,初步光路实验表明,设计的拼接调整机构可以快速实时地调整2×2阵列光栅达到要求的精度,且稳定时间大于1 h。     

Photodetectors based on junctions of two-dimensional transition metal dichalcogenides

Transition metal dichalcogenides(TMDCs) have gained considerable attention because of their novel properties and great potential applications. The flakes of TMDCs not only have great light absorption from visible to near infrared, but also can be stacked together regardless of lattice mismatch like other two-dimensional(2D) materials. Along with the studies on intrinsic properties of TMDCs, the junctions based on TMDCs become more and more important in applications of photodetection. The junctions have shown many exciting possibilities to fully combine the advantages of TMDCs, other2 D materials, conventional and organic semiconductors together. Early studies have greatly enriched the application of TMDCs in photodetection. In this review, we investigate the efforts in photodetectors based on the junctions of TMDCs and analyze the properties of those photodetectors. Homojunctions based on TMDCs can be made by surface chemical doping,elemental doping and electrostatic gating. Heterojunction formed between TMDCs/2D materials, TMDCs/conventional semiconductors and TMDCs/organic semiconductor also deserve more attentions. We also compare the advantages and disadvantages of different junctions, and then give the prospects for the development of junctions based on TMDCs.     

Spin-polarized injection into a p-type GaAs layer from a Co2 MnAl injector

Electric luminescence and its circular polarization in a Co2 MnAl injector-based light emitting diode (LED) has been detected at the transition of e-A0 C , where injected spin-polarized electrons recombine with bound holes at carbon acceptors. A spin polarization degree of 24.6% is obtained at 77 K after spin-polarized electrons traverse a distance of 300 nm before they recombine with holes bound at neutral carbon acceptors in a p + -GaAs layer. The large volume of the p + -GaAs layer can facilitate the detection of weak electric luminescence (EL) from e-A 0C emission without being quenched at higher bias as in quantum wells. Moreover, unlike the interband electric luminescence in the p+ -GaAs layer, where the spin polarization of injected electrons is destroyed by a very effective electron-hole exchange scattering (BAP mechanism), the spin polarization of injected electrons seems to survive during their recombination with holes bound at carbon acceptors.     

高精度2×2阵列拼接光栅结构设计北大核心CSCD

提出了一种大口径高精度2×2阵列光栅拼接结构,采用模块化和框架式结构设计,保证拼接结构的稳定性;设计了差动螺纹微调组件与压电驱动器相结合的微纳调整组件结构,实现拼接光栅微纳量级的调整要求;讨论了关键组件的设计和制造问题。设计制造的2×2阵列光栅实验样机的最大相对共面误差为17μm,微纳调整组件的最小调整精度可以达到1.8 nm,分辨力为0.9 nm,初步光路实验表明,设计的拼接调整机构可以快速实时地调整2×2阵列光栅达到要求的精度,且稳定时间大于1 h。     

Stability of the positively charged manganese centre in GaAs heterostructures examined theoretically by the effective mass approximation calculation near the Γ critical point

This paper describes an n-i-p-i-n model heterostructure with a manganese (Mn)-doped p-type base region to check the stability of a positively charged manganese A_Mn⁺ centre with two holes weakly bound by a negatively charged 3d⁵(Mn) core of a local spin S=5/2 in the framework of the effective mass approximation near the Γ critical point (k～0). By including the carrier screening effect, the ground state energy and the binding energy of the second hole in the positively charged centre A_Mn⁺ are calculated within a hole concentration range from 1 × 10¹⁶ cm^-3 to 1 × 10¹⁷ cm^-3, which is achievable by biasing the structure under photo-excitation. For comparison, the ground-state energy of a single hole in the neutral A_Mn⁰ centre is calculated in the same concentration range. It turns out that the binding energy of the second hole in the A_Mn⁺ centre varies from 9.27 meV to 4.57 meV. We propose that the presence of the A_Mn⁺ centre can be examined by measuring the photoluminescence from recombination of electrons in the conduction band with the bound holes in the A_Mn⁺ centre since a high frequency dielectric constant of varepsilon _∞ =10.66 can be safely adopted in this case. The novel feature of the ability to tune the impurity level of the A_Mn⁺ centre makes it attractive for optically and electrically manipulating local magnetic spins in semiconductors.     

高速侵彻弹体层合木靶脱壳

利用实验和数值模拟方法研究一种利用层合松木靶作为脱壳装置的机械式脱壳方法。首先讨论了一种正交各向异性材料模型用于高速侵彻木材的可行性及其参数变化规律,结合美军的高速侵彻实验数据对数值模拟方案进行了验证与确认。在此基础上,讨论了不同弹靶作用下含弹托弹体对松木靶的侵彻/贯穿规律。数值模拟与实验研究结果表明:在垂直入射条件下,通过合理的层合木靶设计可对次口径发射弹体有效脱壳,高速侵彻弹体可垂直入射靶板,弹体速度衰减可控;在初始攻角入射条件下,层合靶将使高速侵彻弹体攻角放大。随入射速度增加,弹体贯穿层合木靶消耗动能增加,体现了木材具有明显的应变率增强效应。