Atomic force microscopy basic principles

Atomic Force Microscopy Atomic force microscopy is a direct descendant of STM and was first described in 1986 [254], The basic principle behind AFM is straightforward. An atomically sharp tip extending down from the end of a cantilever is scanned over the sample surface using a piezoelectric scanner. Built-in feedback mechanisms enable the tip to be maintained above the sample surface either at constant force (which allows height information to be obtained) or at constant height (to enable force information to be obtained). The detection system is usually optical whereby the upper surface of the cantilever is reflective, upon which a laser is focused which then reflects off into a dual-element photodiode, according to the motion of the cantilever as the tip is scanned across the sample surface. The tip is usually constructed from silicon or silicon nitride, and more recently carbon nanotubes have been used as very effective and highly sensitive tips. 

A new alternative to solve this problem is atomic force microscopy (AFM) which is an emerging surface characterization tool in a wide variety of materials science fields. The method is relatively easy and offers a subnanometer or atomic resolution with little sample preparation required. The basic principle involved is to utilize a cantilever with a spring constant weaker than the equivalent spring between atoms. This way the sharp tip of the cantilever, which is microfabricated from silicon, silicon oxide or silicon nitride using photolithography, mechanically scans over a sample surface to image its topography. Typical lateral dimensions of the cantilever are on the order of 100 pm and the thickness on the order of 1 pm. Cantilever deflections on the order of 0.01 nm can be measured in modem atomic force microscopes. 

Describe the basic principles of atomic force microscopy and optical trapping... 

Within the numerous proximal probe techniques developed in the years following the breakthrough inventions of the STM (1) and AFM (5), scanning force microscopy (8) represents a family of scanning probe techniques that rely in their contrast mechanism on various forces between probe tip and sample (9-12) (see Atomic Force Microscopy). In order to provide a basis for an understanding and appreciation of the SFM work on polymers (13-18), as presented in this review, the basic principles of SFM, as well as selected imaging modes, are briefly discussed. 

This chapter describes the basic principle, recent developments, and selected applications of some commonly used experimental techniques (i.e., optical microscopy, electron microscopy, atomic force microscopy, nuclear magnetic resonance, diffraction and scattering (X-ray, neutron, and light), and differential scanning calorimetry) for characterization of semicrystalline polymers. Many excellent reviews for each technique and their usage exist, and the listed references only represent the exem-... 

The basic principles of scanning probe microscopy are founded in the quantum mechanical prop>-erties of atoms. The methods use the measurement of electronic properties (current, voltage, or atomic force ) as the means of observing the nature of surfaces and surface phenomena. 

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