As large deflections subject the sample to strong and potentially damaging forces, it is desirable to minimize cantilever deflections while operating the microscope. The SFM can be operated in three ways to produce different types of images. The topographic information contained in these images is displayed as distance or applied force. The signal used to control the feedback loop is calibrated and displayed as true height. 2 Three ways by which SFM is operated to produce different types of images.
Details see text above.
To make use of this property, samples have to be immobilized on a suitable support so that they cannot be displaced by the scanning tip. Often electrostatic interactions between the biological material and the support are strong enough to warrant stable imaging conditions. This has been achieved with large, charged or polar supramolecular structures such as the purple membrane and gap junctions. Immobilization of uncharged biomacromolecules usually requires a different approach. In this case, chemically modified coverslips can be used to couple biological samples covalently to this substrate via photoreactive crosslinkers that have been bound to the chemically modified glass surface.