Measurement of Tunneling Current of Self-Assembled Viologen Derivative Molecules Using Scanning Tunneling Microscopy

Abstract

The electrical properties of viologen derivatives with various lengths were studied using self-assembly and ultrahigh-vacuum scanning tunneling microscopy (UHV-STM). In addition, in this study, we produced the vertical junction structure of an STM tip/molecule/Au(111) substrate using an STM tip. We used Au(111) as the base substrate. Also, the current-voltage (I-V) and differential conductance (dI=dV{V) characteristics were measured while the electrical properties of the selfassembled viologen derivatives were scanned by scanning tunneling spectroscopy (STS). We investigated electron movement, which is caused by height variation, because we can observe height variation between the barrier height of organic materials and the STM tip from the energy gap (E g ) of organic materials. The effective barrier heights of viologen derivative N-methyl-N 0 -(8-mercaptooctyl)-4,4 0 -bipyridinium (VC 8 SH), N-methyl-N 0 -(10-mercaptodecyl)-4,4 0 -bipyridinium (VC 10 SH), N-methyl-N 0 -di(8-mercaptooctyl)-4,4 0 -bipyridinium (HSC 8 VC 8 SH), and N-methyl-N 0 -di(10-mercaptodecyl)-4,4 0 -bipyridinium (HSC 10 -VC 10 SH) self-assembled monolayers (SAMs) were calculated from the decay constant () to be 0.81, 0.46, 0.28, and 0.26 A ˚À1 , respectively.