  Self-assembled functionalized nano particles are at the focus of a number of
potential applications, in particular for molecular scale electronics devices.
Here we perform experiments of self-assembly of 10 nm Au nano particles (NPs),
functionalized by a dense layer of azobenzene-bithiophene (AzBT) molecules,
with the aim of building a light-switchable device with memristive properties.
We fabricate planar nanodevices consisting of NP self-assembled network
(NPSANs) contacted by nanoelectrodes separated by interelectrode gaps ranging
from 30 to 100 nm. We demonstrate the light-induced reversible switching of the
electrical conductance in these AzBT NPSANs with a record on/off conductance
ratio up to 620, an average value of ca. 30 and with 85% of the devices having
a ratio above 10. Molecular dynamics simulation of the structure and dynamics
of the interface between molecular monolayers chemisorbed on the nano particle
surface are performed and compared to the experimental findings. The properties
of the contact interface are shown to be strongly correlated to the molecular
conformation which in the case of AzBT molecules, can reversibly switched
between a cis and a trans form by means of light irradiations of well-defined
wavelength. Molecular dynamics simulations provide a microscopic explanation
for the experimental observation of the reduction of the on/off current ratio
between the two isomers, compared to experiments performed on flat
self-assembled monolayers contacted by a conducting cAFM tip.
