Damien RIEDEL
Institut des Sciences Moléculaires d’Orsay (ISMO), CNRS, Univ. Paris Sud, Université Paris-Saclay, F-91405 Orsay, France.
Abstract:
Understanding how light interacts with matter at the atomic scale is a major challenge for nanoscience, as many key optoelectronic and quantum processes occur locally at defects, molecules, or individual atoms adsorbed at surfaces or embedded in solid-state environments. Conventional optical spectroscopies, however, are fundamentally limited by diffraction and typically require ensembles of emitters. Scanning probe techniques such as scanning tunneling microscopy (STM) and atomic force microscopy (AFM) offer atomic spatial resolution but traditionally lack direct optical access to excited electronic states. Both techniques also suffer from a low electronic sampling frequency that is intrinsically incompatible with the ultrafast electronic dynamics of atomic and molecular adsorbates.
During this talk, after a brief introduction to nanodevices, I will focus on two different examples of how combining specific optical excitation at the STM junction allows the control of characteristic processes.
By coupling UV laser excitation to the STM junction, we were able to locally engineer the optical field at the STM tip with nanometer precision, enabling controlled light–matter interaction far below the diffraction limit [1]. Using a hydrogen-passivated Si(100):H surface, we mapped the local optical field at the surface by selectively desorbing individual H atoms in regions where the local laser field is strongly enhanced.
In a second approach, using a tunable supercontinuum laser, we investigated the optoelectronic readout of individual lanthanide atom excited states when adsorbed on semiconductor surfaces [2]. For erbium adatoms on the bare Si(100) surface at cryogenic temperature, laser-driven STM photocurrent spectroscopy reveals distinct signatures associated with intra-atomic optical transitions and exciton mediated relaxation processes.
The ensuing photocurrent spectroscopy reveals distinct signals associated with both the silicon substrate and the Er adatoms, allowing the identification of several optically driven processes at the single-atom level. In particular, additional photocurrent peaks are observed that originate from relaxation pathways of the Er adatom followed by the dissociation of nearby trapped excitons. Density functional theory calculations including spin–orbit coupling allow us to assign these features to specific intra-atomic transitions involving 4f → 4f and 4f → 5d electronic excitations.
These findings open exciting new avenues for investigating quantum emitters, excitonic processes, and atomically precise optoelectronic functionalities relevant for nanoscale photonics and quantum information technologies.
[1] Nano Lett. 2010, 10, 10, 3857–3862 [2] ACS Nano 2024, 18, 13, 9656–9669