Regensburg 2010 – scientific programme

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O: Fachverband Oberflächenphysik

O 3: Methods: Scanning probe techniques I

O 3.4: Talk

Monday, March 22, 2010, 12:00–12:15, H32

Interaction of the STM/AFM tip with graphite and graphene surfaces - theoretical models — •Martin Ondráček, Vít Rozsíval, and Pavel Jelínek — Institute of Physics, Academy of Sciences of the Czech Republic, Praha

Although atomic resolution is routinely achieved on the graphite (0001) surface and graphene with scanning probe techniques (STM and AFM), there are still open questions with respect to the identification of the atomic-scale features in the images with the actual atomic and hollow sites on the surface. While it is generally agreed that the low-bias STM sees one of the two non-equivalent surface atoms of the graphite surface (the β-site atom), the interpretation of contrast in the AFM is not so simple. Depending on the experimental setup, the apparent height maxima may be located at the hollow sites or at the atomic sites. We show that any realistic modeling of the AFM must include the relaxation of the tip and surface atomic structure as well as the chemical composition of the tip. Furthermore, conductance calculations aiming to explain near-to-contact STM measurements cannot neglect multiple electron scattering. In order to meet these requirements, we combine accurate total energy DFT calculations in the PAW method with calculations of electron transport in the Green’s function approach. Such an approach allows us to analyze the relation between the chemical short-range force and the electric conductance in the range from the tunneling to the contact regime.