Franz Josef Giessibl Academic Affiliation: University of Regensburg Title: The character of chemical bonds to natural and artificial atoms revealed
Franz Josef Giessibl
Academic Affiliation: University of Regensburg
Title: The character of chemical bonds to natural and artificial atoms revealed by atomic force microscopy
Abstract: Atomic force microscopy with CO terminated tips has demonstrated outstanding spatial resolution on organic molecules , metallic clusters  and many other samples. Experimental evidence and calculations show that the CO tip is chemically inert and probes organic molecules mainly by Paulirepulsion . Thus, images of organic molecules, graphene, etc. observed with a CO tip can be interpreted as a map of the absolute charge density of the sample. The total charge density of a single adatom is approximately given by a Gaussian peak. While single silicon adatoms appear similar to a Gaussian peak when imaged by AFM with a CO terminated tip, copper and iron adatoms adsorbed on Cu(111) and Cu(110) appear as tori [2,4]. Experiments and DFT calculations show that the total charge density of Cu and Fe adatoms is approximately Gaussian–in contrast to a hypothesis that proposes 4spz hybridization of Cu and Fe adatoms on a Cu surface. The bonding strength between the AFM tip and the atoms of the sample depends not only on the chemical identity but also on the coordination-corner atoms in clusters are more reactive than center atoms . Progress in force resolution  opens up the fN-regime, enabling to study engineered surface structures such as quantum corrals  that can be viewed as artificial atoms. Surprisingly, these artificial atoms interact in a similar way with AFM tips as natural atoms, yet with a force of only 1/1000of what is experienced in natural atoms .
 L. Gross et al.,Science325, 1110 (2009).
 M. Emmrich et al.,Science348, 308 (2015).
 N. Moll et al.,New Journal of Physics12, 125020 (2010).
 F. Huber et al.,Science366, 235 (2019).
 J. Berwanger et al.,Phys.Rev. Lett.124, 096001 (2020).
 A. Liebig et al.,New Journal of Physics22, 063040 (2020).
M.F. Crommie, C.P. Lutz, D.M. Eigler,Science262, 218(1993).
 F. Stilp, et al.,Science372, 1196 (2021).
Date: June 17, 11:00 (KST)
Location: B1 Jupiter, Center for Quantum Nanoscience
(Friday) 11:00 am - 12:00 am