Atomic Force Microscopy

Atomic Force Microscopy (AFM) is one of the most promising tools for characterization of surfaces at nanoscale. In the imaging mode, a sharp tip mounted on the end of a flexible cantilever probes the surface to obtain an image of sample surface. A laser beam is shown on the back of the cantilever and reflected onto a photodiode or a laser detector. The deflection of the cantilever is monitored by the photodetector by converting the voltage signal into distance (Fig. 8.23). As the tip approaches the surface, the interaction forces between the tip and the sample surface result in a deflection of the cantilever. Different types of adhesion forces (Sect. 8.2.1) can be responsible for the observed deflection.

The AFM can operate in three different modes: contact, non-contact, and tapping modes. In the contact mode, the tip stays in contact with the sample during scanning. For soft materials, it is likely that the AFM tip would damage the sample surface, so the non-contact modes are more desirable for these materials [51]. In the non-contact modes, on the other hand, the AFM tip is not in contact with the sample, and the change of resonance frequency of the cantilever is measured. The

Fig. 8.23 Schematic illustration of AFM

Photodiode

Photodiode

Cantilever

Cantilever

■» x y non-contact mode is suitable for studying many soft surfaces such as biological surfaces and polymers [73]. In the tapping mode, the cantilever is oscillated above the sample with high amplitude, and the tip contacts the surface at each oscillation cycle. The change of oscillation amplitude of the cantilever is used to measure the interaction force.

AFM is a powerful technique for surface characterization of polymeric surfaces. Surface topography can be visualized, and surface roughness can be measured. Compositional imaging for heterogeneous polymers can also be done with AFM. Individual components of a heterogeneous system can be detected as the AFM tip scans over the surface. This ability is due to the senility of tip to the variations in local properties, and has a potential application in characterization of semi-crystalline polymers, block copolymers, polymer blends, and polymers composites [13].

Renewable Energy Eco Friendly

Renewable Energy Eco Friendly

Renewable energy is energy that is generated from sunlight, rain, tides, geothermal heat and wind. These sources are naturally and constantly replenished, which is why they are deemed as renewable.

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