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CeNS Colloquium

Place: Kleiner Physik-Hörsaal, Geschwister-Scholl-Platz
Date: 11.02.11, Time: 15:30 h

Using a combined scanning tunneling and atomic force microscope to probe atomic and molecular structures

Dr. Markus Ternes
MPI for Solid State Research, Stuttgart, Nanoscale Science Department

 

The control of the geometric, electronic, magnetic, and mechanical properties of atomic-scale nanostructures is a prerequisite for the thorough understanding and fabrication of new materials and devices. The combination of a scanning tunneling and atomic force microscope is therefore advantageous because it allows detecting simultaneously electronic properties and short-range forces between the atomically sharp tip and atomic or molecular structures on a surface.

In the first part of my talk I will present measurements and simulations of the electrical conductance and forces during the formation of a prototypical chemical bond between the tip apex atom and adsorbed atoms on a surface. We found that conductance and attractive short-range force increase exponentially and are proportional to each other as the tip approached the adsorbate1. In the transition regime between tunneling and point-contact structural relaxations and changes in the electronic states are crucial for the detailed understanding of the force and conductance. Furthermore, we address the question: “How much force does it take to manipulate atoms and molecules on surfaces?”2 Measuring the forces during atom manipulation yield the full potential energy landscape of the tip-sample interaction which is surprisingly close to the diffusion barriers, which are obtained in the absence of a probe tip.

In the second part of my talk I will present results where we probe magnetic structures on thin insulators. In these structures, the spin of individual atoms and single molecular magnets as well as their magnetocrystalline anisotropy can be determined quantitatively.3 Systems with half-integer spin have always a degenerated ground state at zero field due to Kramers theorem. If these states differ by an orbital momentum of Δm = ±1 the localized spin is Kondo screened by the surrounding conducting electrons of the non-magnetic host and form a many-electron spin-singlet at sufficiently low temperature.4

 

1 M. Ternes et al., Phys. Rev. Lett. 106, 016802 (2011).
2 M. Ternes et al., Science 319, 1066 (2008).
3 C. F. Hirjibehedin et al., Science 317, 1199 (2007).
4 A. F. Otte et al., Nature Physics 4, 874 (2008).