ZANG group research

department of chemistry and biochemistry SIU

Scanning Probe Microscopy (SPM)

Scanning probe microscopy (SPM) represents a new class of microscopy technique, sharing the concept of scanning an extremely sharp tip (3-50 nm radius). The tip is mounted on a flexible cantilever, allowing the tip to scan the surface without ever quite touching it. As the tip passes over the sample surface, the distance between the tip and the surface is kept constant by a so-called feedback system. For different SPM techniques, such as STM and AFM, the feedback mechanisms are different. For STM, the feedback is based on electrical interaction between the tip and the surface atoms (tunneling effect), while for AFM the mechanical force (typically, van der Waals force) between the tip and surface is used to maintain feedback. To keep the constant distance from the surface, the feedback system controls the tip to scan exactly following the surface profile (topography). The vertical movements of the tip are continuously recorded by a computer, which then uses the data to construct an digital image of the surface --- just like a pen-and-ink drawing of rippling waves on the ocean. This is completely different from the ideas of the conventional optical and electron microscopies, which work through bouncing a beam (either light or electrons) from a surface. One advantage of using SPM is that it readily supplies the vertical dimensions of an object's surface, the height and depth of the surface features, which are generally not available from the optical or electron microscopies..

The first member of SPM family, scanning tunneling microscopy (STM), was developed in 1980s since Gerd Binnig and Heinrich Rohrer at IBM in Zurich created the ideas in 1982 (Phys. Rev. Lett., 1982, vol 49, p57). Both of the two people won 1986 Nobel prize in physics for their brilliant invention. Since then, the themes of STM have been extended and applied to some other feedback mechanisms based on using different types of tips, from where the atomic force microscopy (AFM), near-field scanning optical microscopy (NSOM) and scanning confocal microscopy (SCM) have been developed in recent years. Nowadays, SPM means a whole family of related microscopy technologies for imaging and measuring surfaces at nanometer and even atomic scale. 

As a highly versatile and tunable imaging technique for nanoscale structures and heterogeneous systems, SPM has been extensively exploited in the research of materials, surfaces, electronic devices, and biological systems.

(updated on june 22, 2004)