Analysis of simultaneous STM/AFM measurements with atomic resolution

Abstract:
Fast development of real space local probe techniques such as Scanning Probe Microscope (SPM) has allowed the precise control and the modification of surfaces at the atomic scale. While standard STM image procedures operate mostly at so called the tunneling regime, more and more applications take place in the near-to-contact regime (see e.g. [1]) during last years. In this regime, the probe proximity strongly modifies the surface structure making the precise interpretation of experimental results more complicated.
From an elementary quantum mechanics course we learned that the tunneling current grows exponentially with the decrease of the length of the tunneling barrier or, in context of STM measurements, to the tip-sample distance. However, this basic assumption has to be carefully re-examined at distance where the onset of short-range chemical interaction between the probe apex and the surface adatoms takes place [2,3].
In this work, we will discus key effects playing an important role during the formation of the atomic contact between tip and sample and the electron transport through the contact. Here, we combine STM/AFM measurements, first principle DFT total energy methods and calculations of the electron currents based on Green's function techniques [2]. First, we will discus the mechanism of the resonant tunneling through 'dangling bond' states of Si adatoms on the Si(111)-(7x7) surface. In the near-to-contact regime, the substantial decrease of the current, almost to zero, is both experimentally and theoretically observed. We will also present recent results on metal surfaces [5].

[1] F.J. Giessibl Mod. Phys. 75 (2003) 949.
[2] J.M. Blanco et al Phys. Rev. B 70 (2004) 085405.
[3] Y. Sugimoto et al 2006 Phys. Rev. B 73 (2006) 205329.
[4] P. Jelínek et al Phys. Rev. Lett. 101 (2008) 176101.
[5] M. Ternes et al (in preparation)