Measurements of Currents through Single Molecules of Alkanedithiols by Repeated Formation of Break Junction in Scanning Tunneling Microscopy under Ultrahigh Vacuum

摘要

We measured currents through the single molecules of 1,6-hexanedithiol and 1,8-octanedithiol using a scanning tunneling microscope (STM) under ultrahigh vacuum (UHV). Self-assembled monolayers (SAMs) of alkanedithiols were formed on Au(111) surfaces of gold films deposited on mica by dipping them in each 1 mM ethanol solution of alkanedithiols for 1 min. The sample with each SAM was introduced into the UHV-STM chamber. The current was recorded as a bare Au STM tip was repeatedly pushed against and drawn away from the sample surface. In this way, the single molecules of each alkanedithiol compound bridged a gap between the Au(111) surface and the Au STM tip apex by forming S-Au bonds at both ends of the molecules. The single-molecular conductivities G_(m6) and G_(m8) of alkanedithiols (N = 6, 8) in this break junction were found to be approximately 9.4 x 10~(-5)G_0 and 1.3 x 10~(-5)G_0 (G_0: quantum conductance), respectively.