Department of Chemistry, University of Illinois at Urbana-Champaign, Urbana, IL 61801.
Beckman Institute for Advanced Science and Technology, University of Illinois at Urbana-Champaign, Urbana, IL 61801.
Proc Natl Acad Sci U S A. 2021 Mar 16;118(11). doi: 10.1073/pnas.2023083118. Epub 2021 Mar 8.
Time- and space-resolved excited states at the individual nanoparticle level provide fundamental insights into heterogeneous energy, electron, and heat flow dynamics. Here, we optically excite carbon dots to image electron-phonon dynamics within single dots and nanoscale thermal transport between two dots. We use a scanning tunneling microscope tip as a detector of the optically excited state, via optical blocking of electron tunneling, to record movies of carrier dynamics in the 0.1-500-ps time range. The excited-state electron density migrates from the bulk to molecular-scale (∼1 nm) surface defects, followed by heterogeneous relaxation of individual dots to either long-lived fluorescent states or back to the ground state. We also image the coupling of optical phonons in individual carbon dots with conduction electrons in gold as an ultrafast energy transfer mechanism between two nearby dots. Although individual dots are highly heterogeneous, their averaged dynamics is consistent with previous bulk optical spectroscopy and nanoscale heat transfer studies, revealing the different mechanisms that contribute to the bulk average.
在单个纳米粒子水平上对激发态的时空分辨，为非均相能量、电子和热流动力学提供了基本的认识。在这里，我们用光激发碳点，以在单个点内成像电子-声子动力学，并在两个点之间成像纳米尺度的热传输。我们使用扫描隧道显微镜针尖作为光激发态的探测器，通过电子隧穿的光学阻断，记录载流子动力学在 0.1-500 ps 时间范围内的电影。激发态电子密度从体相迁移到分子尺度（约 1nm）的表面缺陷，然后单个点发生非均相弛豫，要么回到长寿命荧光态，要么回到基态。我们还通过单个碳点中的光学声子与金中的传导电子的耦合，成像两个附近点之间的超快能量转移机制。尽管单个点具有高度的非均质性，但它们的平均动力学与之前的体相光学光谱和纳米尺度热传输研究一致，揭示了对体相平均值有贡献的不同机制。
