Methods for Atomic Force and Scanning Tunneling Microscopies

Abstract

Scanning tunneling microscopy (STM) is a relatively new tool for examining surface topography on a subatomic scale. Watt (1) summarized the main principles of STM as follows (see Fig. 1): The scanning tunneling microscope utilizes a very fine stylus with an atomically sharp tip and does not require an ultrahigh vacuum. The tip is positioned 1 nm or thereabouts from a conducting specimen’ s surface (2) . When a small voltage is applied between the tip and the specimen, a limited but measurable tunneling current passes between the two. Watt (1) further explained that the tip and specimen are traversed relative to one another. Either the tip is kept at a constant height and the variation in tunneling current plotted or the tip is moved up and down to maintain a constant tunneling current. An impression of an area of the surface is compiled through oscillations of the tip tracing the surface topography. Welland and Taylor (2) pointed out that the interpretation of STM images is not straightforward, requiring comparison with other surface image technologies. A summary of the advantages and disadvantages of STM are

Table 1 Summary of the Advantages and Disadvantages of Scanning Tunneling Microscopy

presented in Table 1. Should the reader require additional information regarding principles, the reviews and monographs of Neddermeyer (3), Stroscio and Kaiser (4), Chiang and Wilson (5), Hansma and Tersoff (6), Park and Quate (7), Welland and Taylor (2), Wiesendanger and Gountherodt (8) and Cohen et al. (9) can be consulted. Sakurai et al. (10) consider STM instrumentation and resolution.