Department of Chemistry, University of California, Irvine , Irvine, California 92697, United States.
Department of Chemistry, Pennsylvania State University , University Park, Pennsylvania 16802, United States.
ACS Nano. 2017 Nov 28;11(11):11466-11474. doi: 10.1021/acsnano.7b06183. Epub 2017 Oct 12.
Atomically terminated and nanoscopically smooth silver tips effectively focus light on the angstrom scale, allowing tip-enhanced Raman spectromicroscopy (TER-sm) with single molecule sensitivity and submolecular spatial resolution. Through measurements carried out on cobalt-tetraphenylporphyrin (CoTPP) adsorbed on Au(111), we highlight peculiarities of vibrational spectromicroscopy with light confined on the angstrom scale. Field-gradient-driven spectra, orientational fingerprinting, and sculpting of local fields by atomic morphology of the junction are elucidated through measurements that range from 2D arrays at room temperature to single molecule manipulations at 5 K. Notably, vibrational Stark tuning within molecules, reflecting intramolecular charge distributions, becomes accessible when light is more localized than the interrogated normal modes. The Stark images of CoTPP reveal that it is saddled, and the distortion is accompanied by charge transfer to gold through the two anchoring pyrroles.
原子终止且纳米平滑的银尖端可有效地将光聚焦到埃尺度，从而实现具有单分子灵敏度和亚分子空间分辨率的尖端增强拉曼光谱（TER-sm）。通过在 Au(111) 上吸附的钴四苯基卟啉（CoTPP）进行的测量，我们突出了在埃尺度上限制光的振动光谱学的特点。场梯度驱动的光谱、取向指纹和由结的原子形态对局部场的塑造，通过从室温下的 2D 阵列到 5 K 下的单个分子操纵的测量得到了阐明。值得注意的是，当光比被探测的正常模式更局域时，分子内的振动斯塔克调谐（反映分子内电荷分布）变得可行。CoTPP 的斯塔克图像表明它是鞍形的，并且这种变形伴随着通过两个锚定吡咯向金的电荷转移。
