A new transistor concept exploits the colloidal synthesis of metal nanoparticles and their Coulomb charging energy.

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%.

ZnO is a promising catalyst for hydrogen and oxygen production due to the position of the conduction and valence bands. Nevertheless, there are some limitations to the efficiency due to its n-type character. Once in contact with the electrolyte, an extraction barrier for electrons is formed. The purpose of this work was to create an extraction site for electrons by synthesizing small pyramidally shaped ZnO nanocrystals (∼10 nm), which consist of a predefined site for the growth of a gold particle at the tip. Photoelectrochemical deposition of gold on ZnO was performed to yield the hybrid structure. Photoluminescence (PL) studies of the relative change of intensities of band gap versus defect state relaxation showed electron transfer from the conduction band of ZnO to Au. Using cyclic voltammetry, Aumediated charge extraction from Au−ZnO hybrids was demonstrated, which circumvents the electron extraction barrier in ZnO. Thus, this work demonstrates the nanoscale design of hybrid structures for photocatalytic applications.

Abstract:Colloidal lead sulfide is a versatile material with great opportunities to tune the bandgap by electronic confinement and to adapt the optical and electrical properties to the target application. We present a new and simple synthetic route to control size and shape of PbS nanoparticles. Increasing concentrations of explicitly added acetic acid are used to tune the shape of PbS nanoparticles from quasi-spherical particles via octahedrons to six-armed stars. The presence of acetate changes the intrinsic surface energies of the different crystal facets and enables the growth along the ⟨100⟩ direction. Furthermore, the presence of 1,2-dichloroethane alters the reaction kinetics, which results in smaller nanoparticles with a narrower size distribution.