| AVS 59th Annual International Symposium and Exhibition | |
| Scanning Probe Microscopy Focus Topic | Wednesday Sessions |
| Session SP+AS+BI+ET+MI+TF-WeA |
| Session: | Emerging Instrument Formats |
| Presenter: | FJ. Giessibl, University of Regensburg, Germany |
| Correspondent: | Click to Email |
Frequency-modulation AFM can be combined with scanning tunneling microscopy, yielding a simultaneous data set for current and average force gradient. Ternes et al. [1] have shown that for some metallic contacts, force and current are proportional. The interaction of a tungsten tip with a CO molecule adsorbed on Cu(111), however, yields a much different symmetry and distance dependence of tunneling current and force [2]. The tunneling current yields a gaussian dip over the CO molecule, while the forces show a strong angular dependence with force fields that vary strongly by distance and angle within the extent of the single front atom, displaying subatomic variations. While the simultaneous acquisition of current and force can reveal new information about the atomic and electronic structure of matter, the tunneling current can modify the atomic forces. This “phantom force” [3,4], a modification of the electrostatic attraction between tip and sample, originates in an alteration of the effective potential difference between tip and sample caused by strongly localized voltage drop induced by the tunneling current. The talk discusses the potential of combined STM/AFM as well as the challenges, in particular with respect to tip preparation and characterization.
[1] M. Ternes et al., Phys. Rev. Lett. 106, 016802 (2011).
[2] J. Welker, F. J. Giessibl, Science 326, 444 (2012).
[3] A.J. Weymouth et al. Phys. Rev. Lett. 106, 226801 (2011).
[4] T. Wutscher et al. Phys. Rev. B 85, 195426 (2012).