Metal nanoparticle film-based room temperature Coulomb transistor.

Single-electron transistors would represent an approach to developing less power-consuming microelectronic devices if room temperature operation and industry-compatible fabrication were possible. We present a concept based on stripes of small, self-assembled, colloidal, metal nanoparticles on a back-gate device architecture, which leads to well-defined and well-controllable transistor characteristics. This Coulomb transistor has three main advantages. By using the scalable Langmuir-Blodgett method, we combine high-quality chemically synthesized metal nanoparticles with standard lithography techniques. The resulting transistors show on/off ratios above 90%, reliable and sinusoidal Coulomb oscillations, and room temperature operation. Furthermore, this concept allows for versatile tuning of the device properties such as Coulomb energy gap and threshold voltage, as well as period, position, and strength of the oscillations.

Coulomb blockade based field-effect transistors exploiting stripe-shaped channel geometries of self-assembled metal nanoparticles.

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%.

Group 8 metallocenes as bulky functional groups in glucopyranosides.

The functionalization of methyl D-glucopyranosides at positions 4 and 6 with bulky moieties was carried out by using ferrocenyl and ruthenocenyl substituents. The synthesis succeeded by reaction of the methyl D-glucopyranosides with the corresponding metallocene monocarbaldehyde dimethyl acetal catalysed by iodine in acetonitrile. The resulting compounds methyl 4,6-O-(metallocenylmethylidene)-α-D-glucopyranoside (M=Fe (1) and M=Ru (3)) and methyl 4,6-O-(metallocenylmethylidene)-ß-D-glucopyranoside (M=Fe (2) and M=Ru (4)) were characterized by (1)H and (13)C NMR spectroscopy, by crystal structure determination as well as elemental analysis.

Adhesion and size dependent friction anisotropy in boron nitride nanotubes.

The frictional properties of individual multiwalled boron nitride nanotubes (BN-NTs) synthesized by chemical vapour deposition (CVD) and deposited on a silicon substrate are investigated using an atomic force microscope tip sliding along (longitudinal sliding) and across (transverse sliding) the tube's principal axis. Because of the tube's transverse deformations during the tip sliding, a larger friction coefficient is found for the transverse sliding as compared to the longitudinal sliding. Here, we show that the friction anisotropy in BN-NTs, defined as the ratio between transverse and longitudinal friction forces per unit area, increases with the nanotube-substrate contact area, estimated to be proportional to (L(NT)R(NT))(1/2), where L(NT) and R(NT) are the length and the radius of the nanotube, respectively. Larger contact area denotes stronger surface adhesion, resulting in a longitudinal friction coefficient closer to the value expected in the absence of transverse deformations. Compared to carbon nanotubes (C-NTs), BN-NTs display a friction coefficient in each sliding direction with intermediate values between CVD and arc discharge C-NTs. CVD BN-NTs with improved tribological properties and higher oxidation temperature might be a better candidate than CVD C-NTs for applications in extreme environments.