NCAFM2023 Programme Booklet

Wednesday 1140 - 1200

REAL SPACE IMAGING OF CHARGE DISTRIBUTIONS BY MEANS OF KELVIN PROBE FORCE MICROSCOPY.

A. Gallardo a,* , B. Mallada b,c , K. Biswas a , J. I. Urgel a , D. Écija a , P. Jelínek b

a IMDEA Nanoscience, C/Faraday, 9, Campus Universitario de Cantoblanco, Madrid, 28049, Spain b Institute of Physics, Academy of Sciences of the Czech Republic, Prague, Czech Republic. c Regional Centre of Advanced Technologies and Materials, Czech Advanced Technology and Research Institute (CATRIN), Palacký University Olomouc, Olomouc, Czech Republic. Email: aurelio.gallardo@imdea.org Anisotropic charge distributions on individual atoms are crucial for the structural properties of certain systems. Nevertheless, the existence of some of them has only been demonstrated indirectly, either observing the interaction between molecules or by theoretical calculations. We show that Kelvin probe force microscopy (KPFM) with a properly functionalized tip can provide a direct visualization of the anisotropic charge distributions. [1-2] The KPFM contrast at macroscopic tip-sample distances is well understood as the difference between the work functions of tip and sample. On the other hand, at close tip sample distances we found the local contact potential difference (LCPD) to be given by an interplay of different interactions between intrinsic charges and polarizations on the tip-sample junction. When an external bias is applied between the metallic tip and the sample, it creates an electric field between them. This electric field will induce dipoles in both the molecules that form the sample and the tip. (See Fig. 1) We demonstrate here that the interaction between these polarizations and the intrinsic charges of both the tip and the sample are the main source of contrast on the LCPD measurements.

Fig. 1 Scheme of the dipoles induced in the tip-sample junction by an external potential in the case of (A) negative bias and (B) positive bias for the case of a KPFM system with the ground set on the tip.

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