  The spontaneous assembly of particles in suspension provides a strategy for
inexpensive fabrication of devices with nanometer-scale control, such as
single-electron transistors for memory or logic applications. A scaleable and
robust method to form electrodes with the required nanometer-scale spacing,
however, remains a major challenge. Here, we demonstrate a straightforward
assembly approach in which metallic colloidal spheres serve as the electrodes.
The devices are formed by assembly in suspension followed by deposition onto a
patterned substrate. The key to this approach is that the inter-electrode
(inter-sphere) spacing is spontaneously set to allow tunneling contact with a
single layer of nanoparticles. The measured current exhibits the Coulomb
blockade owing to the small size and large electrostatic charging energy of the
nanoparticles. We show that the device resistance can be tuned by means of a
gate electrode. Our results demonstrate an altogether new approach to
inexpensive and large-scale fabrication of electronic devices such as
transistors with nanometer-scale features.
