Ultrafast nanoscale quantum dynamics of materials

材料的超快纳米级量子动力学拟议的研究计划使用领先的实验工具，探索材料和设备中的超快量子过程，直到原子尺度。其中一个主要目标是直接成像和控制超快量子过程和激发表面原子分辨率。 在材料中存在许多基本的电荷载流子和激发的相互作用和动力学，这些相互作用和动力学发生在皮秒时间尺度（0.1 - 1000 ps）和纳米长度尺度（1 - 1000 nm）上，一直到单个分子和原子（< 0.3 nm）。例如，半导体和器件结构（如太阳能电池）中的电子可以在4ps的时间尺度上扩散100 nm的距离。然而，直接成像材料中的载流子扩散如何受到局部原子环境的影响一直具有挑战性。在超导体中，正常态电子回到超导库珀对的复合时间范围为10-400 ps，并且在吸收光子时产生纳米尺寸的正常态区域的超导纳米线单光子光电探测器已经表现出约50 ps的超快响应时间。然而，还没有人直接在纳米尺度上对超导体中的皮秒非平衡动力学进行成像。此外，物理学的主要目标之一是直接成像纳米结构和分子中量子力学波函数的超快动力学。显然，在亚ps时间尺度和亚nm长度尺度上直接探测材料和器件的能力将对我们理解它们的行为方式产生重大影响，并将使我们能够开发新的器件技术。 在拟议的研究计划中，我们将使用时间分辨太赫兹光谱（TRTS）和太赫兹扫描隧道显微镜（THz-STM）来探测和直接成像材料中的超快纳米级量子过程。飞秒激光源用于产生光激发脉冲以及单周期、ps持续时间的太赫兹（THz）脉冲。TRTS将用于探索半导体纳米线和纳米晶体薄膜以及量子材料和纳米结构中的纳米级超快导电动力学和载流子输运。我们实验室开发的THz-STM将THz脉冲耦合到STM的尖锐金属尖端，并将用于直接成像材料中的超快量子过程，直至原子尺度。最近获得的CFI创新基金Ultrafast Nanoscale Quantum Dynamics（UltraNanoQD）将允许开发（i）用于快速样品周转的环境THz-STM和（ii）具有四个独立控制的STM尖端的独特多探针THz-STM系统，用于量子材料和器件中超快纳米级动力学的前所未有的成像和控制。这将彻底改变我们做THz-STM的方式，为原子尺度上材料和设备的基本超快过程提供一个新的窗口。

Ultrafast nanoscale quantum dynamics of materials The proposed research program uses leading-edge experimental tools to explore ultrafast quantum processes in materials and devices down to the atomic scale. One of the main objectives is to directly image and control ultrafast quantum processes and excitations on surfaces with atomic resolution. There are many fundamental interactions and dynamics of charge carriers and excitations in materials that occur over picosecond time scales (0.1 - 1000 ps) and nanometer length scales (1 - 1000 nm) all the way down to single molecules and atoms (< 0.3 nm). For example, electrons in semiconductors and device structures such as solar cells can diffuse distances of 100 nm over 4 ps time scales. However, direct imaging of how carrier diffusion in materials is affected by the local atomic environment has been challenging. In superconductors, the recombination time of normal-state electrons back into superconducting Cooper pairs ranges from 10-400 ps, and superconducting nanowire single-photon photodetectors that produce nanometer-sized normal-state regions upon absorption of a photon have exhibited ultrafast response times around 50 ps. However, no one has ever directly imaged picosecond nonequilibrium dynamics in superconductors on the nanoscale. In addition, one of the main goals in physics is to directly image the ultrafast dynamics of quantum mechanical wave functions in nanostructures and molecules. Clearly, the ability to directly probe materials and devices on sub-ps time scales and sub-nm length scales will have a significant impact on our understanding of why they behave the way they do and will enable us to develop new device technologies. In the proposed research program, we will use time-resolved terahertz spectroscopy (TRTS) and terahertz scanning tunneling microscopy (THz-STM) to probe and directly image ultrafast nanoscale quantum processes in materials. Femtosecond laser sources are used to generate optical excitation pulses as well as single-cycle, ps-duration terahertz (THz) pulses. TRTS will be used to explore nanoscale ultrafast conductivity dynamics and carrier transport in films of semiconductor nanowires and nanocrystals, as well as in quantum materials and nanostructures. THz-STM, which was developed in our lab, couples THz pulses to the sharp metal tip of an STM and will be used to directly image ultrafast quantum processes in materials down to the atomic scale. A recently awarded CFI Innovation Fund, Ultrafast Nanoscale Quantum Dynamics (UltraNanoQD), will allow for the development of (i) ambient THz-STM for rapid sample turnaround and (ii) a unique multi-probe THz-STM system with four independently-controlled STM tips for unprecedented imaging and control of ultrafast nanoscale dynamics in quantum materials and devices. This will revolutionize how we do THz-STM, providing a new window into fundamental ultrafast processes in materials and devices on the atomic scale.