  In this communication we study the transport properties of two-dimensional
assemblies of [Fe(Htrz)2(trz)](BF4) spin-crossover nanoparticles (NPs) with two
different morphologies. The NPs have been synthesized made in a similar manner
than in our previous study in which single NPs were measured. We prepared
free-standing self-assembled monolayer sheets of both SCO NPs formed at the
air/liquid interface on holey carbon TEM grids to extract their global
arrangement and NP size distributions by STEM-HAADF technique. The SCO NP
systems present a rod-like shape and possess two different volumes,
corresponding to lengths of 25 nm and 44 nm along the rod direction and average
diameters of 10 nm and 6 nm respectively. In a similar manner, sheets of SCO
NPs with the two different morphologies were electrically measured by
contacting them on pre-patterned gold electrodes substrates. For both NP
morphologies, a thermal hysteresis loop in the electrical conductance near room
temperature was observed, which was correlated to their morphologies and 2D
organization. The most remarkable result was the observation of an
unprecedented large change in the electrical conductance of the two spin
states, increasing by up to two orders of magnitude in the 2D assemblies of
spin-crossover NPs. This value is significantly larger than that obtained in
single-NP measurements (~ 3). Although such large conductance changes are not
fully understood, our results point at important contributions from its
size/morphology-dependence at the nanoscale.
