Electron-spin resonance atomic force microscopy and tip-induced chemistry

Many phenomena in nature are governed by non-equilibrium properties. We developed two novel atomic force microscopy (AFM) spectroscopic methods to access properties of excited electronic states: electron-spin resonance (ESR)-AFM [1] on excited triplet states and electronic excited-state spectroscopy [2]. These methods rely on single-electron tunneling between a conductive AFM tip and a molecule adsorbed on an insulating surface (>20ML NaCl), steered by a pump-probe voltage pulse scheme. In this talk, an introduction to ESR-AFM and excited-state spectroscopy will be given. Our ESR-AFM spectra measured for single pentacene molecules feature a sub-nanoelectronvolt energy resolution, allowing distinguishing molecules only differing in their isotopic configuration. Moreo-ver, the electron spins of pentacene can be coherently manipulated over tens of microseconds [1]. Excited-state spectroscopy allows accessing many quantum transitions of different types, includ-ing radiative, non-radiative and charge-related transitions. It can thereby shed light on other scanning tunneling microscopy (STM)/AFM based measurements, such as STM luminescence [2]. In addition, I will discuss our recent investigations of cyclocarbons with both scanning tunneling microscopy (STM) and AFM. Cyclocarbons, molecular allotropes of carbon in which all carbon atoms are two-fold coordinated, have been synthesized on surface using tip-induced chemistry [3-5], and the formation of larger cyclocarbons by dimerization of precursors was shown [5]. This presentation will focus on the creation of larger cyclocarbons and the investigation of the proper-ties of cyclocarbons with both STM and AFM.

[1] L. Sellies et al., Nature, 624, 64-68 (2023) [2] L. Sellies et al., Nature Nanotechnology, 20, 27-35 (2025) [3] K. Kaiser et al., Science, 365, 1299-1301 (2019) [4] L. Sun et al., Nature, 623, 972-976 (2023) [5] F. Albrecht et al., Science, 384, 677-682 (2024)