Physical Society Colloquium

Individual Molecules Investigated by Scanning Probe Microscopy with Atomically Functionalized Tips

Leo Gross

IBM Research
Zurich Research Laboratory

Single organic molecules adsorbed on ultrathin insulating films were investigated using scanning tunnelling microscopy (STM), noncontact atomic force microscopy (NC-AFM), and Kelvin probe force microscopy (KPFM). With all of these techniques submolecular resolution was obtained due to tip functionalization by atomic manipulation. The techniques yield complementary information regarding the molecular structural and electronic properties.

Using NC-AFM with CO functionalized tips, atomic resolution on molecules was demonstrated [1]. Moreover, different bond orders of individual carbon-carbon bonds in polycyclic aromatic hydrocarbons and fullerenes were distinguished [2]. Using KPFM information about the distribution of charges within molecules was gained by measuring the z-component of the electrostatic field above the molecule, as demonstrated on the hydrogen tautomerization switch naphthalocyanine [3].

Recently, we investigated other tip functionalizations for AFM that also yielded atomic resolution on molecules, i.e., Cl, Br, Xe, Kr, and NO [4]. The tip dependence will be discussed. The prospects to use high resolution AFM for molecular structure identification [5] or adsorption geometry determination will be discussed.

References
[1] L. Gross, F. Mohn, N. Moll, P. Liljeroth, G. Meyer, Science 325, 1110 (2009)
[2] L. Gross, F. Mohn, N. Moll, B. Schuler, A. Criado, E. Guitian, D. Pena, A. Gourdon, G. Meyer, Science 337, 1326 (2012)
[3] F. Mohn, L. Gross, N. Moll, G. Meyer Nature Nanotechnol. 7, 227 (2012)
[4] F. Mohn, B. Schuler, L. Gross, G. Meyer, Appl. Phys. Lett. in print (2013)
[5] L. Gross, F. Mohn, N. Moll, G. Meyer, R. Ebel, W. M. Abdel-Mageed, M.  Jaspars, Nature Chem. 2, 821 (2010)