Good vibrations: Metal–molecule–metal nanosystems are fabricated by the self‐assembly of gold and silver nanoparticles interconnected with 4‐aminothiophenol (PATP) molecules (see picture). The b2 vibrational modes of the PATP molecules are greatly enhanced by near‐infrared excitation, as a result of charge transfer between the metal nanoparticles coupled with the vibrations of the PATP molecules.

Assemblies consisting of nanosized silver particles, 4-aminothiophenol, and the smooth macroscopic surface of silver metal (Ag/PATP/Ag) were prepared and characterized by surface-enhanced Raman spectroscopy. The Raman spectrum of 4-aminothiophenol in the assemblies is similar to that obtained on the electrochemically roughened electrode, although spectral differences, including slight frequency shifts and changes in relative intensity of the characteristic bands, were observed. The enhancement of the spectrum of 4-aminothiophenol in the assemblies is ascribed to the electromagnetic coupling between the silver particles and the surface of the silver metal. The fact that only the SERS spectrum of 4-aminothiophenol was observed for the assembly, where 4-aminothiophenol is partially replaced with N,N‘-diphenylthiourea, demonstrates that the electromagnetic field is mainly localized in the region between the silver particles and the surface of the silver metal.

Surface properties of an assembled silver nanoparticle/ITO (AAgNP/ITO) electrode and an electrochemically roughened Ag electrode were studied by surface-enhanced Raman spectroscopy and electrochemical techniques. Methyl viologen (MV) and p-aminothiophenol (PATP) were used as the probing molecules. The electrochemical results show that MV can be strongly adsorbed on the surface of the roughened Ag electrode but not on the surface of the AAgNP/ITO electrode. The SERS spectra further indicate that the MV molecules are adsorbed with parallel orientation to the surface of the roughened Ag electrode. The fact that no SERS spectrum was observed on the AAgNP/ITO electrode may imply that there are no required active sites on the surface of the isolated Ag nanoparticle for the interaction between the ring plane of MV and Ag nanoparticle. On the other hand, the SERS spectra of PATP reveal that PATP molecules can be adsorbed on the surfaces of both electrodes, because of the perpendicular orientation of the adsorbed molecules relative to the surface of the Ag nanoparticle on the electrodes. Nevertheless, changes in relative intensities of several a1 and b2 modes also indicate that there are slight differences in the orientation of the adsorbed PATP and the chemical property of the electrode surfaces.

By introducing a coplanar fluorenone into the center of an azo molecule, the turn-on voltages of the ternary memory devices are significantly decreased to lower than -2 V due to the improved crystallinity and the reduced charge injection barrier. The resulting low-power consumption devices will have great potential applications in high-performance chips for future portable nanoelectronic devices.