5 research outputs found
Distance dependence of the phase signal in eddy current microscopy
Atomic force microscopy using a magnetic tip is a promising tool for
investigating conductivity on the nano-scale. By the oscillating magnetic tip
eddy currents are induced in the conducting parts of the sample which can be
detected in the phase signal of the cantilever. However, the origin of the
phase signal is still controversial because theoretical calculations using a
monopole appoximation for taking the electromagnetic forces acting on the tip
into account yield an effect which is too small by more than two orders of
magnitude. In order to determine the origin of the signal we used especially
prepared gold nano patterns embedded in a non-conducting polycarbonate matrix
and measured the distance dependence of the phase signal. Our data clearly
shows that the interacting forces are long ranged and therefore, are likely due
to the electromagnetic interaction between the magnetic tip and the conducting
parts of the surface. Due to the long range character of the interaction a
change in conductivity of m can be
detected far away from the surface without any interference from the
topography
Temperature dependence of the energy dissipation in dynamic force microscopy
The dissipation of energy in dynamic force microscopy is usually described in
terms of an adhesion hysteresis mechanism. This mechanism should become less
efficient with increasing temperature. To verify this prediction we have
measured topography and dissipation data with dynamic force microscopy in the
temperature range from 100 K up to 300 K. We used
3,4,9,10-perylenetetracarboxylic-dianhydride (PTCDA) grown on KBr(001), both
materials exhibiting a strong dissipation signal at large frequency shifts. At
room temperature, the energy dissipated into the sample (or tip) is 1.9
eV/cycle for PTCDA and 2.7 eV/cycle for KBr, respectively, and is in good
agreement with an adhesion hysteresis mechanism. The energy dissipation over
the PTCDA surface decreases with increasing temperature yielding a negative
temperature coefficient. For the KBr substrate, we find the opposite behaviour:
an increase of dissipated energy with increasing temperature. While the
negative temperature coefficient in case of PTCDA agrees rather well with the
adhesion hysteresis model, the positive slope found for KBr points to a
hitherto unknown dissipation mechanism