Biomedical Engineering Reference
In-Depth Information
Lateral deflection signal
Probe orientation
Scanning direction
Scanning direction
Scanning direction
Scanning direction
Fig. 3.18. Schematic of lateral force signals recorded on a sample with variations in topography only
(top) and in material friction only (bottom). Darker colours represent material with higher friction.
Note that in the case of topography changes (upper), the difference between the forward and back
lateral deflection signals is constant; for material contrast (lower), the difference changes.
between the tip and the sample [194-196], which depends on a number of factors,
including such features as viscoelasticity, adhesion and also contact area [197]. As contact
area is dependent on the slope of the sample, the phase image also contains topographic
contributions, so unambiguous interpretation of contrast in phase images is best left to flat
samples. Even in such cases, understanding of the contribution of the individual factors to
the phase shift is not trivial. For more details on this topic, the reader is recommended to
read the excellent and comprehensive reviews by Garcia [108, 197]. Despite the compli-
cations involved in interpretation, phase contrast is one of the most commonly used
techniques for 'mechanical' characterization of sample surfaces, probably due to the
