Although this method can be applied to a wide range of samples, statistical analysis is difficult because of low frequency of appearance of target molecules in an STM image in order to keep them in single molecule state. 4 Generally, in the method, apparent height difference is measured between self-assembled monolayers (SAMs) as a reference molecule and subject molecules confined in the SAMs on an Au substrate ( Fig. On the other hand, comparing apparent height in constant-current STM measurement is also effective for investigating molecular conductance. Therefore, undesired effects of anchoring groups and metal substrates cannot be ignored. However, the method is based on formation of a single molecular junction between the metal electrode and anchoring group of the molecule. 3 These methods offer statistical treatment of single molecular properties by repeating the measurements. In general, single molecular conductance can be measured by means of mechanically controllable break junction (MCBJ) 2 and scanning tunneling microscopy break junction (STM-BJ) techniques. 1 For developing single molecular electronics, it is a key issue to evaluate electric properties of various single molecular elements. The concept of single molecular electronics has attracted great interest for decades because it can minimize the size of electric elements to the single molecular level, realizing higher integration of electronic devices.
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