Vibrational fingerprints of molecules and low-dimension materials can be traced with subnanometer resolution by performing Tip-enhanced Raman spectroscopy (TERS) in a scanning tunneling microscope (STM). Strong atomic-scale localization of light in the plasmonic nanocavity of the STM enables high spatial resolution in STM-TERS; however, the temporal resolution is so far limited. Here, we demonstrate stable TERS measurements from subphthalocyanine (SubPc) molecules excited by ∼500 fs long laser pulses in a low-temperature (LT) ultrahigh-vacuum (UHV) STM. The intensity of the TERS signal excited with ultrashort pulses scales linearly with the increasing flux of the laser pulses and exponentially with the decreasing gap-size of the plasmonic nanocavity. Furthermore, we compare the characteristic features of TERS excited with ultrashort pulses and with a continuous-wave (CW) laser. Our work lays the foundation for future experiments of time-resolved femtosecond TERS for the investigation of molecular dynamics with utmost spatial, temporal, and energy resolutions simultaneously.

中文翻译：

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分子中的超短脉冲激发尖端增强拉曼光谱

通过在扫描隧道显微镜 (STM) 中执行尖端增强拉曼光谱 (TERS)，可以以亚纳米分辨率追踪分子和低维材料的振动指纹。STM 等离子体纳米腔中光的强原子级定位使 STM-TERS 具有高空间分辨率；然而，到目前为止，时间分辨率是有限的。在这里，我们展示了在低温 (LT) 超高真空 (UHV) STM 中由约 500 fs 长激光脉冲激发的次酞菁 (SubPc) 分子的稳定 TERS 测量。用超短脉冲激发的 TERS 信号的强度随着激光脉冲通量的增加呈线性比例变化，并随着等离子体纳米腔间隙尺寸的减小呈指数变化。此外，我们比较了用超短脉冲和连续波 (CW) 激光激发的 TERS 的特征。我们的工作为时间分辨飞秒TERS的未来实验奠定了基础，以同时研究具有最大空间、时间和能量分辨率的分子动力学。