Atomic interdiffusion and charge transfer in ordered arrays of plasmonic nanoparticles in interaction with molecules
Résumé
Understanding the interaction of molecules with nanoparticles is the key to control charge transfers for molecular electronics or energy production. The main difficulty lies in the need to probe at the scale of the individual molecule, otherwise having a system that is poorly dispersed in size to reduce the inhomogeneous broadening of the observables. In this context, we carry out ordered hybrid nano-assemblies where organic molecules functionalize metallic or plasmonic nanoparticles epitaxied on an alumina bilayer on Ni3Al(111). We combine non-linear/linear spectroscopy and microscopy, to reveal structural, chemical and plasmonic properties as well as the impact of charge transfer in those hybrid assemblies [1-5]. The mechanical stress in the bilayer induced by the substrate periodically modulates the surface reactivity, which ensures the ordered growth of Pd metal clusters [1]. The correlation of geometry to the reactivity of long-range, narrow size distributed Pd NPs containing from few atoms to several hundred are revealed using CO molecule as a probe of the surface structure [2]. This nanostructured surface allows producing ordered assemblies of NP weakly coupled with organic molecules (perylene) [4]. By evaporating gold or silver on the Pd core, plasmonic properties arise above two atomic layer thick shell, giving an additional control of photophysical properties. Pd/Ag core/shell NPs show a better long-range ordering and a reduced atomic interdiffusion at the core-shell interface compared to Pd/Au NPs [3] leading to a stronger plasmonic response [5]. When fullerene is evaporated on NPs, we follow in real-time the strong change of optical, vibronic and plasmonic properties. Charge transfer from NP to C60 affects the optical response and the vibronic structure and reduces the plasmonic response. This work paves the way for future assemblies, where charge transfer can be induced and followed in real-time at sub-ps timescale using ultrafast laser.