UNISOKU Co., Ltd., Osaka, 573-0131, Japan.
Faculty of Pure and Applied Sciences, University of Tsukuba, Ibaraki, 305-8573, Japan.
Sci Rep. 2023 Jan 25;13(1):818. doi: 10.1038/s41598-023-27383-z.
Photoinduced carrier dynamics of nanostructures play a crucial role in developing novel functionalities in advanced materials. Optical pump-probe scanning tunneling microscopy (OPP-STM) represents distinctive capabilities of real-space imaging of such carrier dynamics with nanoscale spatial resolution. However, combining the advanced technology of ultrafast pulsed lasers with STM for stable time-resolved measurements has remained challenging. The recent OPP-STM system, whose laser-pulse timing is electrically controlled by external triggers, has significantly simplified this combination but limited its application due to nanosecond temporal resolution. Here we report an externally-triggerable OPP-STM system with a temporal resolution in the tens-picosecond range. We also realize the stable laser illumination of the tip-sample junction by placing a position-movable aspheric lens driven by piezo actuators directly on the STM stage and by employing an optical beam stabilization system. We demonstrate the OPP-STM measurements on GaAs(110) surfaces, observing carrier dynamics with a decay time of [Formula: see text] ps and revealing local carrier dynamics at features including a step edge and a nanoscale defect. The stable OPP-STM measurements with the tens-picosecond resolution by the electrical control of laser pulses highlight the potential capabilities of this system for investigating nanoscale carrier dynamics of a wide range of functional materials.
纳米结构的光致载流子动力学在开发先进材料的新型功能方面起着至关重要的作用。光泵浦-探测扫描隧道显微镜（OPP-STM）代表了以纳米级空间分辨率对这种载流子动力学进行实空间成像的独特能力。然而，将超快脉冲激光的先进技术与 STM 相结合以进行稳定的时间分辨测量仍然具有挑战性。最近的 OPP-STM 系统，其激光脉冲定时由外部触发器电控制，大大简化了这种组合，但由于纳秒时间分辨率限制了其应用。在这里，我们报告了一种具有数十皮秒时间分辨率的外部触发 OPP-STM 系统。我们还通过将由压电执行器驱动的可移动的非球面透镜直接放置在 STM 台上，并采用光束稳定系统，实现了针尖-样品结的稳定激光照明。我们在 GaAs(110)表面上进行了 OPP-STM 测量，观察到[Formula: see text] ps 的衰减时间的载流子动力学，并揭示了包括台阶边缘和纳米级缺陷在内的特征处的局部载流子动力学。通过激光脉冲的电控制进行的具有数十皮秒分辨率的稳定 OPP-STM 测量突出了该系统在研究各种功能材料的纳米级载流子动力学方面的潜在能力。
