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Non-equilibrium states of molecules or solids play crucial roles across a broad range of fields such as the photovoltaics, chemical reactions, phase transition, quantum sensing and quantum computation, etc. The detection and control of non-equilibrium states are extremely crucial for understanding and tuning many basic processes involving electron and energy transfer, but they remain a great challenge to date. Optical methods with the ultrafast laser have proven to be very powerful in detecting various non-equilibrium states, but they suffer from a poor spatial resolution which is about half the wavelength due to the optical diffraction limit. Scanning probe microscopies such as the scanning tunneling microscope (STM) and atomic force microscope (AFM) have the advantage of ultrahigh spatial resolution down to atomic level [1, 2]. However, they are usually only accessible to the equilibrium ground states due to their poor temporal resolution (ms-us). Here I will show how we broke this constraint by developing a novel electronic pump-probe AFM technique, which allows us to probe the lifetimes of molecular excited states (triplet states) at atomic scale for the very first time [3]. The unique power of our technique was shown via demonstrating the triplet quenching induced by single oxygen molecules. In the end, I will show how the temporal resolution was further improved by combining the STM with ultrashort optical or terahertz pulses, realizing the atomic spatial resolution and femtosecond temporal resolution simultaneously [4, 5]. Such a technique will make it possible to track various ultrafast dynamics at atomic scale such as molecular vibrations and rotations, phonons, carrier dynamics, spin dynamics, phase transitions, etc.
[1] Peng et al., Nature communications 9, 122(2018).
[2] Peng et al., Nature 557, 701 (2018).
[3] Peng et al., Science 373, 452 (2021).
[4] Terada et al., Nature Photonics 4, 869 (2010).
[5] Cocker et al., Nature Photonics 7, 620 (2013).
Dr. Jinbo Peng got his Phd degree in the group of Prof. Ying Jiang at Peking University in 2017. He focused on the probing of interfacial water with ultrahigh spatial resolution by combined STM and AFM techniques. After graduation, he joined the group of Prof. Jascha Repp and Prof. Rupert Huber in the University of Regensburg as a postdoc and a Humboldt fellow. He focused on the detection of ultrafast dynamics by developing the cutting-edge THz-STM technique and the pump-probe AFM technique. From November 2020, he continued the postdoc (later as a JSPS fellow) research in the group of Prof. Hidemi Shigekawa and Prof. Shoji Yoshida in the University of Tsukuba who are the pioneers of ultrafast-STM technique. Now he works with the ultrafast STM to study ultrafast carrier dynamics and phase transitions with atomic resolution.
Tencent Meeting link: https://meeting.tencent.com/dm/9287FEjlOnvI Meeting ID: 695 254 040 No password