Excellence in Research: Dynamics of Photogenerated Charge Carriers in Mixed Dimensional van der Waals Heterostructures

非技术描述：原子薄的二维半导体纳米结构是一种有趣的替代体半导体，支撑着当前的光学和电子技术。这些包括石墨烯和过渡金属二硫属化物的纳米结构在面外方向上表现出较弱的键合，因此可以与广泛的有机和无机半导体集成，而没有限制常规半导体器件的材料相容性要求。将二维纳米结构与零维和一维纳米结构相结合的混合维系统通过定制每个组件的属性为工程设计设备提供了新的自由度。然而，关于不同类型的纳米结构内部和之间的电荷载流子的移动，仍然存在重要的问题。这项研究使用多种实验工具来阐明混合维系统中激发电荷载流子的性质。该项目为来自北卡罗来纳州中央大学代表性不足的少数民族学生的本科生和研究生研究人员提供了机会，并扩大了机构的研究能力。作为该项目的一部分，材料和研究方法被注入到本科和研究生物理课程中，向更广泛的学生群体介绍纳米科学和材料科学。技术说明：该项目的科学目标是提高对混合维货车德瓦尔斯异质结构中载流子动力学和电荷输运的基本理解，该异质结构将二维过渡金属二硫属化物（MoS 2，WS 2）与一维无机金属硫属化物（CdSxSe 1-x）半导体纳米线和零维有机半导体（并五苯，酞菁锌）集成在一起。零维和一维分量的局部形态和能带能量预计将显著影响这些异质结构中光生载流子的动力学。该项目的实验方法侧重于制造具有受控形态和带偏移的异质结构，并使用相关超快光学显微镜，开尔文探针显微镜和时间分辨毫米波光电导测量来表征这些异质结构，以跟踪光激发电荷载流子在宽范围的时间和长度尺度上的演变。这些测量解决了在电荷载流子弛豫期间发生的多个步骤，包括激子解离、跨界面的电荷转移、电荷转移态的寿命和载流子扩散，通过比较来自异质结构和单个组件的数据，并揭示了纳米或微米该奖项反映了NSF的法定使命，并被认为是值得通过使用基金会的智力价值和更广泛的影响审查标准。

Nontechnical Description: Atomically thin two-dimensional semiconductor nanostructures are an intriguing alternative to bulk semiconductors that underpin much of current optical and electronic technology. These nanostructures, which include graphene and transition metal dichalcogenides, exhibit weaker bonding in the out-of-plane direction and can thus be integrated with a broad range of organic and inorganic semiconductors without the materials compatibility requirements limiting conventional semiconductor devices. Mixed dimensional systems combining two dimensional nanostructures with zero- and one-dimensional nanostructures offer new degrees of freedom to engineer devices by tailoring the properties of each component. Significant questions remain, however, regarding the movement of charge carriers within and between the different types of nanostructures. This research is using multiple experimental tools to elucidate the properties of excited charge carriers in mixed dimensional systems. This project provides opportunities for undergraduate and graduate student researchers drawn from the predominantly underrepresented minority student population of North Carolina Central University and expands institutional research capabilities. Materials and research methods studied as part of this project are infused into undergraduate and graduate physics courses, introducing nanoscience and materials science to a broader group of students. Technical Description: The scientific goal of this project is to improve the fundamental understanding of carrier dynamics and charge transport in mixed-dimensional van der Waals heterostructures integrating two-dimensional transition metal dichalcogenides (MoS2, WS2) with one-dimensional inorganic metal chalcogenide (CdSxSe1-x) semiconductor nanowires and zero-dimensional organic semiconductors (pentacene, zinc phthalocyanine). The local morphologies and band energies of the zero- and one-dimensional components is expected to significantly impact the dynamics of photogenerated charge carriers in these heterostructures. The experimental approach of this project focuses on fabrication of heterostructures with controlled morphologies and band offsets, and characterization of these heterostructures using correlated ultrafast optical microscopy, Kelvin probe microscopy, and time resolved millimeter wave photoconductivity measurements to track the evolution of photoexcited charge carriers across a wide range of time and length scales. These measurements address multiple steps that occur during relaxation of charge carriers, including exciton dissociation, charge transfer across the interface, lifetimes of charge transfer states and carrier diffusion through comparison of data from heterostructures and individual components, and shed light on the influence of nano- or micro-scale morphology through spatially resolved mapping.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.