Invited Paper SP+AS+BI+ET+MI+NS-TuA1
Molecules Investigated with Atomic Resolution using Scanning Probe Microscopy with Functionalized Tips

Tuesday, October 30, 2012, 2:00 pm, Room 16

Single organic molecules 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 terminated tips, atomic resolution on molecules has been demonstrated and the contrast mechanism was assigned to the Pauli repulsion [1]. On the other hand, by using STM the molecular frontier orbitals, i.e., the highest occupied and the lowest unoccupied molecular orbitals (HOMO and LUMO), were mapped [2]. Using a CO terminated tip for orbital imaging with the STM, the resolution can be increased and the images correspond to the gradient of the molecular orbitals due to the p-wave character of the tip states [3]. Finally, KPFM reveals information about the distribution of charges within molecules by measuring the z-component of the electrostatic field above the molecule, as demonstrated on the hydrogen tautomerization switch naphthalocyanine [4].

[1] L. Gross et al. Science 325, 1110 (2009).

[2] J. Repp et al. Phys. Rev. Lett. 94, 026803 (2005).

[4] F. Mohn et al. Nature Nanotechnol. 7, 227 (2012).