Scanning Probe Techniques Measure Different Interactions

2007-03-08 10:33:40

( Technology )



Probe microscopy refers to a group of technologies that enable scientists to observe objects on infinitesimally tiny scales from one-millionth of a meter (micron) to one-billionth of one meter (nanometer). There are several techniques involved, but the common element among them all is the interaction of the scanning probe tip with the surface.

In all of these techniques, you have a scanning probe tip affixed to a flexible cantilever. The cantilever moves along the surface and responds to interactive forces between the scanning probe and the target surface under examination. Sensors detect and measure these movements, which convert into images displayed in a scanning probe microscope.

You will find several modes of operation for the scanning probe: contact, non-contact, intermittent contact, lateral force, magnetic force and thermal scanning. In the contact mode and its variations, the scanning probe tip either keeps a constant force as the cantilever moves, or the tip vibrates up and down with an oscillator. In lateral force mode, frictional forces torque the cantilever. In magnetic force mode, the scanning probe maps the magnetic fields on the object, while the probe images surface thermal conductivity in thermal scanning mode.

Your choice of analytic mode in probe microscopy depends on the surface characteristics you want to study and on the sample's hardness. For instance, hard surfaces usually require contact mode, although your scanning probe tip easily erodes with this technique. Soft biological samples are perfectly suited to the vibrating-tip techniques.

You may wonder whether scanning probes are subject to image distortions. That is possible, because the imaging technique and scanning probe tip geometry will influence the quality of the scanned image. You thus need to know the probe tip's geometry to enable you to interpret properly the image presented in the scanning probe microscope. If you are imaging high-relief surfaces, the sharpness of the tip becomes important.


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