Determination of the NDR and Electron Transport Properties of Self-Assembled Nitro-Benzene Monolayers Using UHV-STM

Abstract

We investigated the negative differential resistance (NDR) property of self-assembled 4,4-di(ethynylphenyl)-2'-nitro-l-(thioacetyl)benzene (nitro-benzene), which has been well known as a conducting molecule [1]. Self-assembly mono layers (SAMs) were prepared on Au (111), which had been thermally deposited onto pre-treated (H₂SO₄: H₂O₂=3:1) Si. The Au substrate was exposed to a 1 mM solution of l-dodecanethiol in ethanol for 24 hours to form a monolayer. After thorough rinsing of the sample, it was exposed to a 0.1 μM solution of nitro-benzene in dimethylformamide (DMF) for 30 min and kept in the dark during immersion to avoid photo-oxidation. Following the assembly, the samples were removed from the solutions, rinsed thoroughly with methanol, acetone, and CH₂Cl₂, and finally blown dry with N₂. Under these conditions, we measured the electrical properties of SAMs using ultra high vacuum scanning tunneling microscopy (UHV-STM) and scanning tunneling spectroscopy (STS) [2]. As a result, we confirmed the properties of NDR in between the positive and negative region.