Regensburg 2007 – scientific programme

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O: Fachverband Oberflächenphysik

O 8: Methods: Scanning Probe Techniques I

O 8.2: Talk

Monday, March 26, 2007, 11:30–11:45, H41

Dispersion relation of field emission states — •Michael Fechner, Christian Heiliger, Peter Zahn, Ingrid Mertig, Stephan Großer, Christian Hagendorf, and Wolf Widdra — Martin-Luther-Universität, Institut f. Physik D06099 Halle,Germany

Scanning tunneling microscopy (STM) and scanning tunneling spectroscopy (STS) have been applied to investigate field emission states on Ag(001) surfaces. The STS measurements have been performed in constant current mode where the distance z(V) between tip and sample as a function of the applied voltage is controlled by the tunneling current. Field emission states cause strong changes in z(V) which indicates their energetic position [1]. Combining STM and STS the dispersion relation of the field emission states have been measured as has been demonstrated earlier on Cu(001) [2]. The previous study on Cu(001) found a free electron dispersion with an effective electron mass smaller than the free electron mass. For Ag(001) we observe a free electron like dispersion with the band bottom shifted with respect to the energy of the field emission state. A theoretical model based on the finite-difference method has been developed to reproduce the z(V) characteristics and to simulate the combination of STS and STM experiments to obtain the dispersion relation. Our results emphasize that the effective mass found in previous studies is an artifact of the operation modus whereas the band offset is the consequence of the energy uncertainty of the field emission state.

[1] G. Binnig et al., Phys. Rev. Lett. 55, 991 (1985).

[2] P. Wahl et al., Phys. Rev. Lett. 91, 106802 (2003).