Multi-mode spectroscopy uses the simultaneous data collection of several signals. In the case of the UHV AFM/STM with standard preamplifier tunneling current, normal force, lateral force, and frequency shift signals are available simultaneously; furthermore, external inputs can be selected in order to obtain useful multi-mode spectroscopy combinations.
The choice of the appropriate feedback regulation channel is independent of the combination of different channels for data acquisition. Hence a number of different phenomena including local conductivity, adhesive properties and surface elasticity can be investigated on conducting and non-conducting surfaces.
The typical force/distance curve used for force calibration can also be applied in a spectroscopic manner, yielding information on local adhesion properties and surface composition. The slope of the force/distance curve in the contact region gives information on the local surface elasticity, and the position of the break-off point a measure of local adhesion properties.
A wealth of possibilities is opened up by the combination of AFM measurements with tunneling current detection. An example is the spectroscopic differentiation between conducting, semiconducting or non-conducting molecules by measuring I(V)-curves during an AFM experiment (conductivity mapping). By applying an electric field between tip and sample more physical properties of the sample, e.g. piezoelectricity or electrostriction, can be investigated.
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