Research background
I studied physics at the Georg-August University of Göttingen, where I started working with scanning tunnelling microscopy (STM) and optical excitation already during my Bachelor’s and Master’s studies, focusing on GaAs and related semiconductor systems.
For my PhD, I moved to IBM Research in Zurich, joining the team of Leo Gross. There, I worked on the synthesis and characterization of individual molecules using STM and high-resolution atomic force microscopy (AFM), investigating their structural and electronic properties at the single-molecule level.
I subsequently joined the IPCMS in Strasbourg as a Marie Skłodowska-Curie fellow, where I focused on scanning tunnelling microscope-induced luminescence (STML) and tip-enhanced photoluminescence (TEPL). My work included investigating excitation dynamics in electroluminescence as well as developing sub-molecularly resolved TEPL on individual and coupled molecules.
Since September 2026, I have been a CNRS researcher (Chaire de Professeur Junior, CPJ) in the STM team in Strasbourg. My current research focuses on tip-enhanced optical spectroscopy of individual molecules on insulating substrates, with the aim of achieving optical excitation and spectroscopy of fully decoupled molecules at the sub-molecular scale.
Selected publications
- K. Kaiser, A. Rosławska, M. Romeo, F. Scheurer, T. Neuman, G. Schull. Electrically driven cascaded photon emission in a single molecule, Phys. Rev. X 15, 021072 (2025). (DOI: 10.1103/PhysRevX.15.021072)
We demonstrated – for the first time – cascaded photon emission from a single molecule quantum light source in a precisely controlled atomic environment. We revealed complex electroluminescence dynamics involving several quantum states, clarified the nanosecond-scale dynamics in STM-induced luminescence, and identified the role of dark states (e.g., triplets) in mediating correlated emission. - K. Kaiser, S. Jiang, M. Romeo, F. Scheurer, G. Schull, A. Rosławska. Gating single-molecule fluorescence with electrons, Phys. Rev. Lett. 133, 156902 (2024). (DOI: 10.1103/PhysRevLett.133.156902)
We demonstrated controlled quenching of single-molecule TEPL by resonant charging. Our study shows, for the first time, that molecular fluorescence can be modulated through precise control of single-electron tunneling, having potential implications for controlling energy transfer, dipole coupling, and collective optical responses in molecular assemblies. - A. Roslawska, K. Kaiser, M. Romeo, E. Devaux, F. Scheurer, S. Berciaud, T. Neuman, G. Schull. Submolecular-scale control of phototautomerization, Nat. Nanotechnol. 19, 738-743 (2024). (DOI: 10.1038/s41565-024-01622-4)
In this work, we used the picocavity below the tip of a scanning tunnelling microscope to drive and control a phototautomerization reaction with submolecular precision. Such atomic-scale control over a reversible chemical reaction can be extended to control other photochemical processes, and serves as a milestone in understanding and controlling photochemistry at the sub nanometer scale. - K. Kaiser, L. A. Lieske, J. Repp, L. Gross. Charge-state lifetimes of single molecules on few monolayers of NaCl, Nat. Commun. 14, 4988 (2023) (DOI: 10.1038/s41467-023-40692-1)
We measured lifetimes of transiently charged states in single molecules on thin insulating films, showing that the energetic alignment of the molecule’s ion resonances with respect to the substrate plays a critical role, and that charge-state lifetimes govern key dynamics in single-molecule electroluminescence. Our findings provide a quantitative basis for transient charge dynamics in molecular optoelectronics. - K. Kaiser, L. Scriven, F. Schulz, P. Gawel, L. Gross, H. Anderson. An sp-hybridized molecular carbon allotrope, cyclo[18]carbon, Science 365, 1299-1301 (2019) (DOI: 10.1126/science.aay1914)
We demonstrated the first synthesis and structural characterization of an isolated purely sp-hybridized carbon allotrope, setting the long-standing debate over its structure. Using atom manipulation, we could form and characterize cyclo[18]carbon (C18) by AFM, revealing a polyynic geometry with alternating triple and single bonds. The intrinsic reactivity of C18 enabled controlled covalent coupling via atom manipulation. This work demonstrates that highly reactive molecules can be generated, stabilized, and studied at the single-molecule level, and highlights the ability of AFM to detect minute changes in the geometry of a molecule with atomic precision. - M. Commodo, K. Kaiser, G. De Falco, P. Minutolo, F. Schulz, A. D’Anna, L. Gross. On the early stages of soot formation: molecular structure elucidation by high-resolution atomic force microscopy, Combust. Flame 205, 154-164 (2019) (DOI: 10.1016/j.combustflame.2019.03.042)
We used high-resolution AFM to investigate molecular structures from early stages of soot formation. By analyzing model compounds alongside soot samples, we could identify structural motifs and reactive species involved in soot particle formation. Linking specific molecular architectures to early soot growth, our findings contribute to a deeper understanding of combustion chemistry, which may help to improve technologies for cleaner combustion and reduced pollutant formation. - K. Kaiser, L. Gross, F. Schulz. A single-molecule chemical reaction studied by high-resolution atomic force microscopy and scanning tunneling microscopy induced light emission, ACS Nano 13, 6947-6954 (2019) (DOI: 10.1021/acsnano.9b01852)
In this proof of concept study we combined for the first time high-resolution AFM and STML to investigate the structural and optoelectronic properties of single vanadyl-phthalocyanine (VOPc) molecules. We selectively generated vanadium-phthalocyanine (VPc) by atom manipulation, confirmed by AFM. While VOPc shows luminescence in STML, VPc remains dark, demonstrating the possibility to directly correlate chemical structure and optoelectronic properties at the single molecule level. - B. Schröder, O. Bunjes, L. Wimmer, K. Kaiser, G. A. Traeger, T. Kotzott, C. Ropers, M. Wenderoth. Controlling photocurrent channels in scanning tunneling microscopy, New. J. Phys. 22, 033047 (2020) (DOI: 10.1088/1367-2630/ab74ac)
We investigated photocurrents driven by femtosecond laser excitation of a (sub)-nanometer tunnel junction in an STM. We found that photo-excited electrons see a reduced effective barrier height in tunneling. Power-dependent measurements suggest that multiphoton absorption excites electrons to levels hundreds of meV around the barrier maximum. In addition, stable STM imaging with photoelectrons is demonstrated.