Speaker
Description
The ultrafast dynamics of electrons and phonons in solid state matter can be of crucial importance for a variety of fundamental processes such as chemical reactions and ultrafast phase transitions. Tracing the ultrafast relaxation out of equilibrium after impulsive optical excitation provides valuable insight into microscopic coupling mechanisms and energy transfer processes. Whereas pump–probe techniques are generally established to trace ultrafast dynamics in real time, complementary real-space observation of photoinduced ultrafast dynamics on the atomic scale remains a challenging task. In order to image the nonequilibrium state of a sample in real time and space, various approaches combining femtosecond laser excitation with scanning tunneling microscopy (STM) have been developed and new approaches such as lightwave-driven STM are currently emerging [1]. We discuss recent progress and current status in the development of femtosecond pump–probe STM within the department of physical chemistry. First, the implementation and characterization [2] of a lightwave-driven STM using broadband single-cycle THz pulses (THz-STM) is presented, and its application to study the ultrafast relaxation of photoexcited hot electrons on THz sub-cycle time scales is discussed. Second, we demonstrate optical pump–probe STM that utilizes atomically-confined plasmonic fields generated at the apex of nanoscopically sharp tip produced by focused-ion beam. This approach allows us to access the local dynamics of coherent lattice vibrations in ultrathin ZnO films with 1-nm spatial resolution. In the poster, we discuss current challenges, future directions and the emergence of new approaches in the field of lightwave- and photon-driven time-resolved STM.
References
[1] T. Cocker et al., Nature 539, 236 (2016).
[2] M. Müller et al., ACS Phot. 7, 8, 2046 (2020).
