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

卓越研究：混合维范德华异质结构中光生电荷载流子的动力学

• 批准号: 1901128
• 负责人: Marvin Wu
• 金额: $ 40.64万
• 依托单位: North Carolina Central University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2019
• 资助国家: 美国
• 起止时间: 2019-07-01 至 2024-06-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1901128&HistoricalAwards=false
• 关键词: Excellence; Research; Dynamics; Photogenerated; Charge

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.

非技术描述：原子薄的二维半导体纳米结构是块状半导体的一种有趣的替代方案，块状半导体是当前大部分光学和电子技术的基础。这些纳米结构包括石墨烯和过渡金属二卤化物，在平面外方向显示出较弱的成键，因此可以与广泛的有机和无机半导体集成，而不需要限制传统半导体器件的材料兼容性要求。将二维纳米结构与零维和一维纳米结构相结合的混合维度系统通过定制每个组件的属性，为设计设备提供了新的自由度。然而，关于载流子在不同类型的纳米结构内和之间的移动仍然存在重大问题。本研究使用多种实验手段来阐明混合维度体系中激发载流子的性质。该项目为来自北卡罗来纳中央大学主要代表人数不足的少数族裔学生群体的本科生和研究生研究人员提供了机会，并扩大了机构研究能力。作为这个项目的一部分，材料和研究方法被注入到本科生和研究生的物理课程中，向更广泛的学生群体介绍纳米科学和材料科学。技术描述：该项目的科学目标是提高对混合维范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卤化物(MoS_2，WS_2)与一维无机金属硫化物(CdS_xSe1-x)半导体纳米线和零维有机半导体(并五苯，酞菁锌)结合在一起。零维和一维组分的局域形貌和能带能量有望显著影响这些异质结中光生载流子的动力学。这个项目的实验方法集中在制备具有可控形貌和能带偏移的异质结构，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导测量来表征这些异质结构，以跟踪在广泛的时间和长度尺度上光激发电荷载流子的演化。这些测量解决了载流子弛豫过程中发生的多个步骤，包括激子解离、界面上的电荷转移、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，并通过空间分辨映射揭示了纳米或微米尺度形貌的影响。这一奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。