The scanning tunneling microscope (STM) and atomic force microscope (AFM) provide pictures of atoms on or in surfaces. A system that uses variations of the principles used by an STM or AFM to image surfaces is often called a scanning probe microscope (SPM).

The AFM works by scanning a fine ceramic or semiconductor tip over a surface much the same way as a phonograph needle scans a record (for those of you that remember what a record player was!). The tip is positioned at the end of a cantilever beam shaped much like a diving board. As the tip is repelled by or attracted to the surface, the cantilever beam deflects. The magnitude of the deflection is captured by a laser that reflects at an oblique angle from the very end of the cantilever. A plot of the laser deflection versus tip position on the sample surface provides the resolution of the hills and valleys that constitute the topography of the surface. The AFM can work with the tip touching the sample (contact mode), or the tip can tap across the surface (tapping mode) much like the cane of a blind person.

Other measurements can be made using modifications of the SPM. These include variations in surface microfriction with a lateral force microscope (LFM), orientation of magnetic domains with a magnetic force microscope (MFM), and differences in elastic modulii on the micro-scale with a force modulation microscope (FMM). A very recent adaptation of the SPM has been developed to probe differences differences in chemical forces across a surface at the molecular scale. This technique has been called the chemical force microscope (CFM). The AFM and STM can also be used to do electrochemistry on the microscale.
 

A Digital Instruments   Nanoscope IIIa Scanning   Probe Microscope available   in the Macromolecular   Crystallization Laboratory.	Fluid cell attachment for   Nanoscope IIIa enabling crystal   growth studies to be conducted in situ.

 
AFM is being used to solve processing and materials problems in a wide range of technologies affecting the electronics, telecommunications, biological, chemical, automotive, aerospace, and energy industries. The materials being investigating include thin and thick film coatings, ceramics, composites, glasses, synthetic and biological membranes, metals, polymers, and semiconductors. The AFM is being applied to studies of phenomena such as abrasion, adhesion, cleaning, corrosion, etching, friction, lubrication, plating, and polishing. The publications related to the AFM are growing speedily since its birth.

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AFM in Protein Crystallization	Macromolecular Crystallization Laboratory	Chemical & Environmental Engineering	UT College of Engineering	The University of Toledo