Regensburg 2007 – wissenschaftliches Programm

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O: Fachverband Oberflächenphysik

O 17: Poster Session I (Nanostructures at Surfaces; Metal Substrates: Epitaxy and Growth; Methods: Scanning Probe Techniques; Phase Transitions)

O 17.56: Poster

Montag, 26. März 2007, 17:30–20:30, Poster C

Higher harmonics and frequency mixing in electrical force microscopy (EFM) — •Benjamin Graffel¹, Falk Müller², Anne-Dorothea Müller², and Michael Hietschold¹ — ¹Chemnitz University of Technology, Institute of Physics, 09107 Chemnitz, Germany — ²Anfatec Instruments AG, 08606 Oelsnitz (V), Germany

Electrical force microscopy (EFM) in the dynamic non-contact mode is a suitable technique to measure local distributions of surface potentials on electronic devices as well as to detect different doping concentrations in semiconductors. The electrical force between tip and sample is proportional to the derivative of the capacitance of the tip-sample arrangement with respect to the tip-sample distance z and proportional to the potential difference U squared. In our experiments this voltage consists of a direct voltage and an additional alternating voltage with the frequency f_el. While the capacitance of a completely metallic tip-sample arrangement only depends on z, it also depends on U in the case of a semiconductive sample.

In this work we show that these nonlinear effects lead to further signals at higher harmonics of f_el and at frequencies that arise from mixing with the mechanical excitation frequency of the oscillating cantilever. The frequency spectrum of the cantilever was measured for different parameters such as various set points and different values of U. Detailed studies of the distance dependencies in connection with imaging indicate that the lateral resolution can be improved by detecting signals at mixed frequencies.