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ICQM Faculty member publishes an article in Nano Letters reporting dynamical evolution of anisotropic response in black phosphorus under ultrafast photoexcitation
《纳米快报》报道量子材料中心关于超快激光激发下黑磷各向异性响应的动态演化过程研究

As a bridge 2D material between graphene and transition metal dichalcogenide in terms of mobility and bandgap opening, black phosphorus (BP) has recently emerged as a promising material for high performance angle sensitive electronic and optoelectronic device for its high mobility and anisotropic electronic properties. Toward the application of BP in this direction, dynamical evolution of photo excited carriers and its induced transient change of anisotropic electronic properties are highly desired, but remain to be explored.

In the newly published paper “Dynamical Evolution of Anisotropic Response in Black Phosphorus under Ultrafast Photoexcitation”, Prof. Dong Sun’s experimental ultrafast spectroscopy group in collaboration with Prof. Ji Feng’s theoretic group have studied the dynamical evolution of anisotropic properties of black phosphorus under photo excitation using the angle-resolved transient reflection spectroscopy. The sample is provided by Professor Shuang Jia’s group, also affiliated with ICQM. The results show that conductivity ellipse of BP is stretched due to photoexcitation of hot carriers which implies BP becomes more anisotropic under photo excitation and relax isotropically thereafter. These results implies enhanced anisotropic performance of BP in high speed, high field electronic and optoelectronic devices. Furthermore, a two band model simulation by Professor Ji Feng’s group generally supports the observed dynamical enhancement of anisotropy, showing consistence between experiment and theory.

This work provides interesting device physics toward understanding angle sensitive operation behavior of various BP based electronic devices under high field working environment or optoelectronic devices when light illumination is involved. The paper has been published online on June 3, 2015: http://dx.doi.org/10.1021/acs.nanolett.5b01409Shaofeng Ge, a Ph.D student from Prof. Dong Sun’s group is the first author and Professor Dong Sun and Ji Feng share the corresponding author of this paper.

This project has been supported by the National Basic Research Program of China, the National Natural Science Foundation of China, the Recruitment Program of Global Experts, Beijing Natural Science Foundation and the Specialized Research Fund for the Doctoral Program of Higher Education of China.

Figure (a) Schematic diagram of polarization resolved transient reflection experiment. (b) Probe polarization dependence of transient reflection spectrum (upper figure) and the spectra with different probe polarization at fixed delays (lower figure). (c) Dynamical evolution of Re (σ) ellipse at different delays. ΔRe (σ) is doubled for clarity. Inset: Enlarged plot of area marked by red rectangle.

 

作为一种新型二维纳米材料,黑磷较高的载流子迁移率、受层数调控的带隙特性填补了石墨烯和过渡金属氧族化合物之间的空缺,因而迅速受到人们的广泛关注,同时特殊的晶体结构使它具有各向异性的光学及电学性质,使得它成为未来新型及高性能电子、光电子器件的理想材料。因此,黑磷光激发热载流子的动态演化过程以及其导致的黑磷各向异性特性的改变对于黑磷未来的大规模应用是至关重要的。

最近,北京大学量子材料中心孙栋研究员的超快光谱课题组和冯济研究员的理论课题组合作在《纳米快报》上发表了题为“Dynamical Evolution of Anisotropic Response in Black Phosphorus under Ultrafast Photoexcitation”的文章,利用偏振角度分辨瞬时反射光谱对黑磷在光激发下各向异性性质的动态演化过程进行了系统的研究。实验的样品来自于量子材料中心的贾爽课题组。实验结果显示,受到光激发产生的热载流子影响,黑磷的光电导椭球被拉伸,随后各项同性地弛豫到初始状态。这表明黑磷电子与光电子器件在高速强场工作条件下,各向异性得到增强。此外,冯济课题组通过两能带模型仿真给光激发下各向异性的增强提供了理论支持。

该工作为未来基于黑磷的电子器件在强场工作环境下及光电子器件在光辐射下的角度敏感工作特性提供了器件物理支持。论文于201663日在线发表于《纳米快报》:http://dx.doi.org/10.1021/acs.nanolett.5b01409。孙栋课题组的博士生葛韶峰为文章的第一作者,孙栋和冯济研究员为文章的通信作者,。

上述研究得到国家重大科学研究计划、国家自然科学基金、中组部“青年千人”计划、北京自然科学基金及高等学校博士学科点专项科研基金的支持。

(a) 偏振角分辨瞬时反射光谱实验示意图。(b) 不同探测光偏振下的瞬时反射光谱(上图)和特定时间延迟下,瞬时反射谱信号对探测光偏振的依赖关系(下图). (c) 光电导椭球在受到光激发后的动态演化过程。