Recently, research on conducting molecules containing thiol functional groups, such as benzenethiol has been progressing. This conducting molecule is applicable to the study of NDR and switching properties of logic devices. The 4,4 '-di(ethynylphenyl)-2 '-nitro1-(thioacetyl)benzene molecule contains a thiol functional group as in benzenethiol. Thus, we measured the property of NDR by using the self-assembly method in STM. An substrate was exposed to a I mM solution of 1-dodecanethiol in ethanol for 24 h to form a monolayer. After thoroughly rinsing the sample, it was exposed to a 0.1 mM 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 assembly, we measured the electrical properties of self-assembly monolayers (SAMs) by using ultra-high-vacuum scanning tunneling microscopy (UHV-STM) and scanning tunneling spectroscopy (STS) [LA. Bumm, J.J. Arnold, M.T. Cygan, T.D. Dunbar, T.P. Burgin, L. Jones 11, D.L. Allara, J.M. Tour, P.S. Weiss, Science 271 (1996) 1705]. As a result, we confirmed the property of NDR in a positive region between negative regions. The energy gap (E,) obtained by using differential conductance (dI/dV-V) was verified through UV/visible. This molecule is applicable to the fabrication of molecular junctions. (C) 2006 Elsevier B.V. All rights reserved.