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O: Fachverband Oberflächenphysik
O 77: Scanning Probe Techniques: Method Development II
O 77.6: Talk
Thursday, March 30, 2023, 11:45–12:00, REC C 213
Field-emission resonances at exceptional large voltages: Consequences for determining work functions — •Anika Schlenhoff1, Gerassimos C. Kokkorakis2, and John P. Xanthakis2 — 1Institute of Physics, University of Münster, Germany — 2Electrical and Computer Engineering Department, National Technical University of Athens, Greece
In a scanning tunneling microscopy (STM) setup, a series of unoccupied electronic states evolve in the vacuum gap between the probe tip and the surface. Due to limited bias voltage ranges, so far only a small number (typically 4 - 8) of these so-called field-emission resonances (FERs) have been detected.
Here, we report a combined experimental and theoretical study of FERs over an exceptional range of energy and number, typically tens of an eV and over thirty in order n [1]. Unlike commonly assumed, the triangular potential well is not found to be a good approximation for the high-n states. Although the spectroscopy mode assures a constant electric field at the tip apex, this leads only for the intermediate FERs (approx. 2<n<6) to reside in a linear potential between the tip and the surface. At higher tip-sample distances d and bias voltages U(d), the quantum well is no longer triangular but attains a curvature, which is d-dependent. Each high-n state resides in its own well that can be well-approximated by a polynomial of second order. Hence, the range of Un to be analyzed in terms of spectroscopic positions needs to be chosen with great care when deducing surface work functions.
[1] A. Schlenhoff et al., Appl. Phys. Lett. 120, 261601 (2022).