  Metallic nanoparticles offer possibilities to build basic electric devices
with new functionality and improved performance. Due to the small volume and
the resulting low self-capacitance, each single nanoparticle exhibits a high
charging energy. Thus, a Coulomb-energy gap emerges during transport
experiments that can be shifted by electric fields, allowing for charge
transport whenever energy levels of neighboring particles match. Hence, the
state of the device changes sequentially between conducting and non-conducting
instead of just one transition from conducting to pinch-off as in
semiconductors. To exploit this behavior for field-effect transistors, it is
necessary to use uniform nanoparticles in ordered arrays separated by
well-defined tunnel barriers. In this work, CoPt nanoparticles with a narrow
size distribution are synthesized by colloidal chemistry. These particles are
deposited via the scalable Langmuir-Blodgett technique as ordered, homogeneous
monolayers onto Si/SiO2 substrates with pre-patterned gold electrodes. The
resulting nanoparticle arrays are limited to stripes of adjustable lengths and
widths. In such a defined channel with a limited number of conduction paths the
current can be controlled precisely by a gate voltage. Clearly pronounced
Coulomb oscillations are observed up to temperatures of 150 K. Using such
systems as field-effect transistors yields unprecedented oscillating current
modulations with on/off-ratios of around 70 %.
