초록
The characteristic of negative differential resistance(NDR) is decreased current when the applied voltage is increased. The NDR is potentially very useful in molecular electronics device schemes. Here, we investigated the NDR characteristic of self-assembled 4,4'-di(ethynylphenyl)-2'-nitro-1-benzenethiolate, which has been well known as a conducting molecule. Self-assembly monolayers(SAMs) were prepared on Au(111), which had been thermally deposited onto $pre-treatment(H_2SO_4:H_2O_2=3:1)$ Si. The Au substrate was exposed to a 1 mM/1 solution of 1-dodecanethiol in ethanol for 24 hours to form a monolayer. After thorough rinsing the sample, it was exposed to a 0.1 ${\mu}M/l$ solution of 4.4'-di(ethynylphenyl)-2'-nitro-1-(thioacetyl)benzene in dimethylformamide(DMF) for 30 min and kept in the dark during immersion to avoid photo-oxidation. After the assembly, the samples were removed from the solutions, rinsed thoroughly with methanol, acetone, and $CH_2Cl_2,$ and finally blown dry with N_2. Under these conditions, we measured electrical properties of self-assembly monolayers(SAMs) using ultra high vacuum scanning tunneling microscopy(UHV-STM). The applied voltages were from -2 V to +2 V with 298 K temperature. The vacuum condition was $6{\time}10^{-8}$ Torr. As a result, we found the NDR voltage of the 4,4'-di(ethynylphenyl)-2'-nitro-1-benzenethiolate were $-1.61{\pm}0.26$ V(negative region) and $1.84{\pm}0.33$ V(positive region). respectively.
