Anny Sigaran

Atomic force microscopy (AFM)


Basic Description

A silica optical fiber was imaged using an atomic force microscope (AFM) in both contact and tapping mode. The fiber surface contains fragments of low-modulus, viscoelastic polymer after the coating was mechanically removed. While scanning in the contact mode resulted in tip-induced irreversible damage of the polymer, the tapping mode AFM generated reproducible images of the surface topography. It is used to examine any type of surface from polymers, ceramics, composites, glass and biological samples. It is a contact mode technique that uses high resolution type scanning probe microscopy. The machine can show resolution to fractions of a nano meter. A tip is very close to the sample, which measure with a mean value of 10-9 N which is set by the pushing of the cantilever against the sample surface. It can also be set to a DC feedback amplifier at a desired value in order to obtain an image. By collection height data from a sample a three dimensional map of the surface is created.

Purpose of Technique

The purpose of this technique is to give a three dimensional image of a sample. It also can measure local resistivity, elasticity, temperature, capillary forces, chemical bonding, magnetic force, chemical bonding, van der Waals forces, and others. This can give you more information on a sample that could not be always being obtained before. AFM provides information about flake thickness, presence of impurities and defects, structural uniformity, etc.

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Figure 1: Atomic force microscope topographical scan of a glass surface. The micro and nano-scale features of the glass can be observed, portraying the roughness of the material.

Origin and History

The AFM was created in 1986 by Beinnig, Quate and Gerber in a collaboration between IBM and Stanford University. It was invented to put a feeling to the surface of samples. It began with the development of the scanning tunneling microscope (STM) in 1982. The AFM was developed to help increase the array of this type of microscopy. If helps to provide nanometer to sub angstrom resolution.

Recent Research

One research article uses AFM to help analyze DNA under a high resolution imaging. This provides an image with proteins, small ligands in absence of stains, complexes of linear DNA with nucleoprotein complexes, super coiled DNA and states of double helical DNA can be assessed. This helped to show that DNA dynamics, not static DNA structures, plays more of a role than expected. It was found that DNA dynamics plays a role in controlled gene expression, recombination, replication and repair. If this techniques was not implied these new findings would never be discovered. (Lyubchenko, 2011)

Another research article used AFM to assess mechanical performance for phase separation polyurethanes. This was to show the molecular structures as a quantitative function. Nanoscale resolution of the surface elastic moduli was determined with AFM. This helped to enable the study of surface stiffness in a quanitative way via nanoscale resolution. HarmoniX material mapping and Peak Force Tapping were used as well. Varying stoichiometric ratios involving isocyanate and hydroxyl groups were investigated due to AFM. This helped to resolve the elastic moduli of stiff and soft segments. The fingerprint phase images shown helped to identify the sample. There is a fundamental need for quantitative characterization of separated polymeric structures by mechanical performance that can be obtained by AFM. The structure and morphology of polymers can be studied at nanoscale resolution. AFM provides height and phase contrast of solid polymers. (Schon et al, 2011)

A final research article uses AFM to study natural occurring mineralization to post new ideas around bone analogues. Dual membrane diffusion system (DMDS) is how mineralization behavior of collagen will be studied. The findings showed that over time the hardness of collagen fibers would increase during mineralization. It would decrease in adhesion factors over time too. A step by step assembling process of mineralization was determined to be the collagen-mineralization. It also provided more information on collagen fibers providing mechanisms of collagen mineralization. This can help to provide new functional material surrounding bone analogues and/or tissue engineering in scaffolds. (Zhao et al, 2010)