AFM Part II

There are two primary methods for measuring the force between a probe and a sample:

Contact mode and vibrating mode.Contact mode entails a direct quasi-static force versus distance measurement, that is, a rather intimate contact between probe and surface.While producing accurate results, it tends to rapidly damage both probe and surface. Vibrating mode may be either large amplitude,in which the probe contacts the surface on every cycle, or small amplitude non-contact.The latter is generally less stressful on both the probe and surface, and tends to give superior results. It measures more subtle properties ofthe surface.

Non-contact: It is desirable because it provides a means for measuring sample topography with little or no contact between the tip and the sample. Like contact AFM, non-contact AFM can be used to measure the topography of insulators and semiconductors as well as electrical conductors. The total force between the tip and the sample in the non-contact regime is very low, generally about 10­12N. This low force is advantageous for studying soft or elastic samples. A further advantage is that samples like silicon wafers are not contaminated through contact with the tip.

Because the force between the tip and the sample in the non-contact regime is low, it is more difficult to measure than the force in the contact regime, which can be several orders of magnitude greater. In addition, cantilevers used for NC-AFM must be stiffer than those used for contact AFM because soft cantilevers can be pulled into contact with the sample surface. The small force values in the non-contact regime and the greater stiffness of the cantilevers used for NC-AFM are both factors that make the NC-AFM signal small, and therefore difficult to measure. Thus, a sensitive, detection scheme is used for NC-AFM operation.

 Application in Pharmacy and Bio-related systems

 With immense knowledge of Scanning probe microscopy (SPM) many researchers  exploited the application of AFM apart from imaging in many science and technical fields which includes Drug interaction,Drug Discovery by means pulling,tapping and probing,Drug delivery,Gene therapy,Microbilogical studies,Metrological and Mechanobiological characterization,Forensic studies,Cell and macromolecule research, Nanomanipulation,Nanomedicine and huge Nanobiofabrication for biosensor and biochip technology.Hope the application of AFM in pharmaceutical Nanotechnology will revolutionize the existing barriers of other probing microscopes.