Electrical properties of single nitro oligophenylene ethynylene (OPE) molecule by using UHV STM

Self-assembled monolayers (SAMs) are ordered molecular structures formed by the adsorption of an active surfactant on a solid surface. A SAM film can be deposited on a substrate surface simply by exposing the surface to an environment containing surface-active molecular species for a certain period of time (solution or vapor phase deposition). The molecules will be spontaneously oriented toward the substrate surface and form an energetically favorable ordered layer. During this process, the surface-active head group of the molecule chemically reacts with and chemisorbs onto the substrate. In this paper, we confirmed the electrical properties of 4′4-di(ethynylphenyl)-2′-nitro-1-benzenethiolate, which have been well known as a conducting molecule having possible application to molecular level negative differential resistance (NDR) device. To deposit the self-assembly monolayers onto the gold electrode, we transfer the prefabricated Au(1 1 1) substrates into 0.5 mM self-assembly molecule in THF solution. Then, we measured electrical properties and surface morphologies 4′4-di(ethynylphenyl)-2′-nitro-1-benzenethiolate using ultra-high vacuum scanning tunneling microscopy (UHV STM). Current–voltage curves also showed several peaks between negative and positive region.