The Self-Assembly of Lipophilic Guanosine Derivatives - Molecular Self-Assembly: Advances and Applications - page 109

(Bio)molecular electronics is gaining an increasing attention
worldwide due to the appealing possibility of realizing cheap
and easy-to-fabricate devices that exploit the self-assembly, self-
recognition, and self-repairing capability of engineered organic or
bio-inspired molecules.
Nanoribbons formed from LG units are promising candidates
for the fabrication of molecular electronic nanodevices [28]. Self-
assembled nanoribbons obtained by drop casting were used to
interconnect gold nanoelectrodes fabricated by electron beam
lithography. As the typical length of the oriented arrays of ribbons (a
“nanocrystal”) is approximately 100 nm, for a contact gap of 60 nm
or less, only one nanocrystal of the ribbon-like assembly is probed.
Under these conditions, the plot of current intensity vs. voltage (I-V)
shows a clear diode-like behavior, with currents on the order of

µ

A
for positive bias and nA for negative bias. This rectifying feature is
related to the existence, in each nanocrystal, of a strong dipole that
originates from the ordering of molecular dipoles in the ribbon-like
structure of type A (see Fig. 4.12A). If an analogous three-terminal
device is prepared (Fig. 4.14), the system behaves as a field-effect
transistor (FET) when the guanosine nanoribbons are used to
interconnect the drain and source terminals [28b].

Figure 4.14 Left: cast deposition of LG on the three-terminal device

(FET transistor), consisting of two arrow-shaped Cr/Au
electrodes on a SiO2 substrate and a third Ag back electrode
(not to scale). Right: dependence of the drain-source current
(

I ) on the voltage ( V ) at discrete gate voltages ( V ). The

ds ds G

), indicating the onset of conduction,
can be modulated by tuning the control gate voltage

voltage threshold ( V T

V .

G

When the gap in the two-terminal device is increased to 120 nm
the situation drastically changes. In this case, a few nanocrystals of
self-assembled LG are probed by the electrodes and the total dipole
of the sample between the electrodes averages to zero because