There are three main techniques to excite an AFM cantilever: though thermally, acoustically and magnetically. In a liquid environment the response of the cantilever strongly depends on the excitation technique. In the case thermal excitation [7, 8], the cantilever response or thermal noise is the result of random collisions from the Brownian motion of the surrounding fluid selleck inhibitor molecules. In this technique, the cantilever is excited directly and consequently a smooth Inhibitors,Modulators,Libraries vibration response, related only to the properties of the cantilever and the fluid, is observed. In the magnetic excitation technique [9], a microcantilever magnetized either by attaching a magnetic particle [10] or coating Inhibitors,Modulators,Libraries with a magnetic material [11] is excited by an external magnetic field.

This is another direct excitation method providing a Inhibitors,Modulators,Libraries smooth vibration response.

In comparison, the acoustic technique [4] is not a direct method. In this technique, the cantilever is excited through movement of its base by a piezoelectric Inhibitors,Modulators,Libraries actuator. The actuator is usually placed directly under the cantilever chip in the tip holder used in air Inhibitors,Modulators,Libraries or vacuum, while it is usually located away from the cantilever Inhibitors,Modulators,Libraries base in the fluid cell which is used for liquid media. As will be explained in detail later, the response of the cantilever to Inhibitors,Modulators,Libraries acoustic excitation, in a liquid environment, contains many spurious peaks which do not correspond to the natural frequencies of the cantilever and are rather Inhibitors,Modulators,Libraries related to the design of the fluid cell.

It should also Brefeldin_A be noted that there are some other techniques [12, 13] for excitation of the AFM cantilever, which are not as common as the techniques discussed AV-951 above.

Although the thermal and magnetic driving techniques produce smoother cantilever responses, they have some drawbacks which make working with acoustic excitation desirable. Firstly, these techniques require additional sellectchem hardware such as a signal conditioner, a data acquisition system, special cantilevers, and a magnetic field system making these techniques more complex and costly. Secondly, in the magnetic technique, the fluid is heated by the electromagnetic field and the magnetic coating changes the vibrational properties and bending angle of the cantilever.

For these reasons, many studies have been aimed at understanding and removing the redundant peaks in the response of the cantilever no to acoustic excitation.Putman et al. [4], who were the pioneers in introducing tapping mode atomic force microscopy in liquid media, were the first faced with these extra frequency peaks. They realized that any changes in the liquid cell system, such as changing its geometry, its material, the working liquid, and more importantly the amount of liquid, affect the positions and amplitudes of the resonances. Schaffer et al.