Ultrafast nanoscale quantum dynamics of materials

提出的研究计划使用前沿的实验工具来探索材料和器件中的超快量子过程，直至原子尺度。其中一个主要目标是直接成像和控制超快量子过程和表面上的原子分辨率激发。在皮秒时间尺度（0.1 - 1000 ps）和纳米长度尺度（1 - 1000 nm）上，一直到单分子和原子（< 0.3 nm），材料中电荷载流子和激发的许多基本相互作用和动力学都发生了。例如，半导体和太阳能电池等器件结构中的电子可以在4ps的时间尺度上扩散100纳米的距离。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，正常状态电子重新组合成超导库珀对的时间在10- 400ps之间，而超导纳米线单光子光电探测器在吸收光子后产生纳米尺寸的正常状态区域，其响应时间在50ps左右。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的量子力学波函数的超快动力学。显然，在sub-ps时间尺度和sub-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，并使我们能够开发新的器件技术。在提出的研究计划中，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电导率动力学和载流子输运。太赫兹-STM是我们实验室开发的，它将太赫兹脉冲耦合到STM的尖锐金属尖端，并将用于直接成像原子尺度下材料中的超快量子过程。最近获得CFI创新基金的超快纳米尺度量子动力学（UltraNanoQD）将允许开发(i)用于快速样品周转的环境太赫兹-STM和（ii）具有四个独立控制的STM尖端的独特多探针太赫兹-STM系统，用于量子材料和器件中前所未有的成像和超快纳米尺度动力学控制。这将彻底改变我们做太赫兹- stm的方式，为在原子尺度上研究材料和器件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.