Direct In-junction Characterization of Molecular Switching Devices Based on Self-Assembled Monolayer Embedded in Nanowire Junction

In this paper, we report the direct in-junction characterization of OAn SAM embedded in the crossed-wire junction structure which is more reliable and available for spectroscopic analysis to reveal the origin of switching characteristics. The crossed-wire junction is prepared with the Au nano wire (diameter: ~300nm) aligned on OAn SAM on Au bottom wire (width: ~1mum) with Electric-field assisted assembly technique. The OAn SAM on planar substrate prepared by same preparation procedure for the crossed-wire junction is characterized by infrared reflection spectroscopy (IRS), x-ray photoelectron spectroscopy (XPS), and atomic force microscope (AFM) to avoid the unfavorable contamination or side reaction during the device preparation process. Inelastic electron tunneling spectroscopy (IETS) is applied to the electronically prepared high and low state of OAn junction to understand the molecular level phenomenon in the crossed-wire junction. The distinct spectra of high and low state of the junction are observed under temperature controlled condition (~4K). Surface Plasmon enhanced Raman spectroscopy (SERS) is utilized to the crossed-wire junction to reveal the chemical and conformational characteristics change in high and low state. According to obtained results, we believe that the origin of electrical conductance switching behavior is from conformation and redox state changes of embedded molecules.