Title: Plasmo-electronic properties of self-organised nanoparticles

Abstract

The coupling between charge transport and surface plasmons in metal nanostructures is the driving force of the emerging “plasmo-electronics” field, which may lead to a new class of light responsive nano-devices. Exploiting such a field need the conversion of light into charge carriers flowing through self-assembled NPs that requires the understanding of quite complex phenomena involving several interaction steps (plasmon-photon, electron-electron, electron-phonon). Here, we report on the plasmo-electronic properties of self-assembled monolayers of colloïdal gold nanoparticles (NPs) formed on a polyimide flexible substrate and on freestanding membranes. In these studies, impedance spectroscopy measurements were used to investigate the electrical properties of the NP assemblies in terms of an equivalent macroscopic electrical circuit, describing the overall self-assembled NPs, and composed of a resistance, a capacitance and a photoconductance (Figure 1a). The NP assemblies deposited on a flexible polyamide substrate were submitted to a uniaxial strain which allows to monitor the interparticle distance in the sub 10nm regime and hence to probe their plasmo-electro-mechanical properties. In particular, the dependence of the photo-capacitance on laser irradiation intensity and wavelength is measured, and the role of the surface plasmon resonance was pointed out. In the case of NP assembly deposited on freestanding membranes, we show that the photo-current generation and charge transport are due to a bolometric phenomenon involving laser induced temperature heating up to 40 degrees combined with trapping/detrapping of the charges at defect sites. On the basis of these experiments, the electrical equivalent macro-circuit was found to be directly connected to a local nano-circuit composed of a local inter-particles resistance Rij, a capacitance Cij and a photo-conductance gij-1(Figure 1b) which depend on the NP size, nature of the ligands, distance between nanoparticles, and spatial arrangement of both the ligands and the NPs within the assembly. Actually, the mechanisms at the different characteristic scales still need to be understood in terms of relation-ship between the local opto-electronic properties at the nanoparticle scale and the macroscopic characteristics of the photo-conductance (spectral dependence and positive or negative) properties of the NP assembly. We thus report on the development of the nano-circuit junction model to bridge the gap between the nano and the macro-circuit.