Low-temperature cotunneling electron transport in photoswitchable molecule-nanoparticle networks.
Résumé
We report the temperature-dependent (4.2 - 300 K) electron transport properties (current-voltage) of photo-switchable two-dimensional arrays of gold nanoparticles (10 nm in diameter) functionalized by azobenzene derivatives. Under UV-light irradiation at 4.2 K, the azobenzene moieties are switched from the trans to cis isomers, leading to an increase of the current. In both conformations, at low temperature (< 77 K) and low voltage (< 1 V) the voltage- and temperature-dependent current behaviors show that electron cotunneling is the dominant transport mechanism. The number of cotunneling events Ncot slightly increases from ≈ 1. 4 to 1.7 upon trans-to-cis isomerization of the azobenzenes. The nanoparticle Coulomb charging energy is not significantly modified (≈ 15 meV) by the azobenzene isomerization. This weak increase of Ncot is explained by the modest cis/trans current ratio (≤ 10) and the limited numbers of nanoparticle-molecule-nanoparticle junctions inserted between the two nanoscale electrodes (< 50 nm apart) connecting the network.
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