Department of Physics, University of Illinois at Urbana-Champaign , Urbana, Illinois 61801, United States.
ACS Nano. 2017 Jun 27;11(6):6328-6335. doi: 10.1021/acsnano.7b02649. Epub 2017 May 30.
Many processes of interest in quantum dots involve charge or energy transfer from one dot to another. Energy transfer in films of quantum dots as well as between linked quantum dots has been demonstrated by luminescence shift, and the ultrafast time-dependence of energy transfer processes has been resolved. Bandgap variation among dots (energy disorder) and dot separation are known to play an important role in how energy diffuses. Thus, it would be very useful if energy transfer could be visualized directly on a dot-by-dot basis among small clusters or within films of quantum dots. To that effect, we report single molecule optical absorption detected by scanning tunneling microscopy (SMA-STM) to image energy pooling from donor into acceptor dots on a dot-by-dot basis. We show that we can manipulate groups of quantum dots by pruning away the dominant acceptor dot, and switching the energy transfer path to a different acceptor dot. Our experimental data agrees well with a simple Monte Carlo lattice model of energy transfer, similar to models in the literature, in which excitation energy is transferred preferentially from dots with a larger bandgap to dots with a smaller bandgap.
许多与量子点相关的过程涉及到电荷或能量从一个量子点转移到另一个量子点。通过荧光移动已经证明了量子点薄膜和连接的量子点之间的能量转移，并且解决了能量转移过程的超快时间依赖性。点之间的能带隙变化（能量无序）和点分离被认为在能量扩散方面起着重要作用。因此，如果能在小簇之间或量子点薄膜中直接在点对的基础上可视化能量转移，这将非常有用。为此，我们报告了通过扫描隧道显微镜（SMA-STM）检测的单分子光吸收，以点对的基础上对从供体到受体点的能量汇聚进行成像。我们表明，我们可以通过修剪掉主要的受体点并将能量转移路径切换到不同的受体点来操纵量子点组。我们的实验数据与能量转移的简单蒙特卡罗格点模型非常吻合，类似于文献中的模型，其中激发能量优先从带隙较大的点转移到带隙较小的点。
