Specifics for some SPM techniques

Judgments about the quality and merits of STM tips need to be made on the basis of a number of requirements  

In practice, only two materials are in common use. A Pt-Ir (typically 80 20) alloy wire tends to be used for STM scanning in air, while W wire is used as tip material for UHV operation. Electrochemical polishing is the preferred method in both cases for producing good tips with small radii of curvature (=10 nm) and high aspect ratios (better than 3 1). There are recipes to be found in the literature [26,27]. When W tips are used, it is essential that the tips be cleaned in UHV by field desorption/emission in order to remove the oxide layer and any other contamination. 

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