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Homework 6 - Jacob Sutker ENGRI 111 Homework#6 Due Monday...

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Jacob Sutker ENGRI 111 Homework #6 Due Monday, Nov. 20, 2006 1. Compare and contrast the STM with the AFM. Include a) operating principle, b) type of materials appropriate for analysis, and c) ambient conditions required for analysis. In comparing the STM with the AFM there are many similarities as well as differences. In most cases, the resolution of STM is better than AFM because of the exponential dependence of the tunneling current on distance. The force-distance dependence in an AFM is much more complex when characteristics such as tip shape and contact force are considered. STM is generally applicable only to conducting samples while AFM is applied to both conductors and insulators. The AFM is much more versatile than the STM. The AFM offers the advantage that the writing voltage and tip- to-substrate spacing can be controlled independently, whereas with STM the two parameters are integrally linked. In comparing their operating principles, the STM, when approaching two-biased conductors, the current increases exponentially by a factor of 10 for each 0.1nm reduction in distance before finally making contact. The AFM is very similar but the attractive forces between the tip and
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