Spectroscopy of Molecular Junction Networks Obtained by Place Exchange in 2D Nanoparticle Arrays

Well ordered nanoparticle arrays were prepared on Si/SiO2 surfaces from alkanethiol-coated Au nanoparticles via self-assembly and micro-contact printing. We study the insertion of conjugated molecular species within the nanoparticle arrays via spectroscopic and electrical transport measurements. Upon exchange of the alkanethiol chains with the conjugated oligomers, the conductance of the network increases by one to 3 orders of magnitude. In addition, the absorption spectra in the visible light range show a red-shift of the surface plasmon resonance (SPR). The latter shift, which is due to the difference in permittivity between alkanes and conjugated oligomers, can be understood within Mie and Maxwell−Garnett theory. Finally, infrared absorption spectra provide direct spectroscopic evidence that the conjugated oligomers can be not only inserted but also, subsequently, fully removed from the nanoparticle arrays via place-exchange. The reversibility of the exchange process demonstrates the potential of these structures as a platform for molecular electronics.