We are interested in the spatio-temporal response of solid state surfaces, nanostructures, and molecules following ultrafast laser excitation. Our goal is to obtain an atomistic understanding of photoinduced processes on (sub-) nanometer length and femtosecond time scales by employing novel pump-probe schemes for ultrafast scanning probe microscopy (SPM). We envision to study, drive and control solid state matter in highly non-equilibrium states on ultrashort length und ultrafast time scales.

To achieve this goal, we are putting efforts into the development of ultrafast scanning probe methods, with a strong focus on broadband THz-gated STM combined with femtosecond optical excitation and all-optical plasmon-assisted femtosecond STM. For more information please check our research page and follow our news below.

d

Exciting! Femtosecond laser-excited STM allows us to excite and probe coherent phonons with few nanometer spatial resolution. This work brings us a big step closer to our research goal of understanding the coupling between microscopic degrees of freedom – such as electrons and phonons – in spatially inhomogeneous crystalline solids at the nanoscale. One of our open questions has been: Can we use STM to probe lattice vibrations in real-time? In this collaborative study, we demonstrate that femtosecond laser-excited STM can measure coherent phonons in ultrathin ZnO films with ~2 nm spatial resolution. Our work introduces a new approach to locally probe the ultrafast structural response and electron-phonon coupling in a photoexcited solid with STM. For more details read our work: DOI: 10.1126/sciadv.abq5682.

Since September we are happy to welcome Henrik as a new member of the light-driven STM team. Henrik is a master student from the Freie Universität Berlin with interest in physical chemistry. In his master project he will explore the light-matter interaction of ultrathin semiconductor films inside plasmonic nanojunctions with STM. Welcome Henrik!

Is hot electron tunneling from a femtosecond laser-excited STM tip thermal or nonthermal? (How) do the femtosecond dynamics of hot electrons inside the tip affect the ultrafast photocurrent response in STM? We have addressed this fundamental question using a THz-gated STM and are pleased that our results are now being published in ACS Nano. (DOI: 10.1021/acsnano.2c04846)

We had a closer look into the nonequilibrium dynamics of hot electrons inside
a photoexcited STM tip, and were curious about the question: does the tunneling of photo-generated hot electrons in STM have thermal or nonthermal character? THz sampling inside the photoexcited STM junction can answer this question, have a closer look at our preprint: https://doi.org/10.48550/arXiv.2205.08248.