In the past decade, an unconventional approach to large-scale fabrication of carbon-nanotube and graphene devices has emerged, namely, dielectrophoretic (DEP) assembly. This technique has now been demonstrated in wafer-scale assembly of nano-carbon electronic devices, sensors, opto-electronic devices and even suspended structures. It has also served as an enabling tool for a number of experiments which might otherwise not be possible. A detailed review of developments in DEP assembly of nano-carbons is presented as a Feature Article by Aravind Vijayaraghavan (pp. 2505–2517). The cover image is an artist's concept of some typical carbon-nanotube and graphene devices assembled by DEP (image courtesy N. Clark).

On the back cover, a single wall carbon nanotube is displayed (thin black line in the sketch) that is grown across a trench and contact electrodes (green), cooled to milli-Kelvin temperatures, and then characterized in electronic transport measurements. A quantum dot forms within the suspended segment at these temperatures. The typical Coulomb “diamond” pattern of differential conductance displays distinct signatures of electromechanical feedback and self-excitation (background measurement, yellow arrows). Using a radio-frequency cw source, driven mechanical resonances of the nanotube can be detected in dc transport - as exemplified by the red line, a measurement of time-averaged dc current as a function of the driving frequency. Stiller et al. (pp. 2518–2522) find higher harmonic resonances at integer multiples of the fundamental frequency, indicating that the nanotube is a string under tension. Applying a finite gate voltage to the highly doped chip substrate (light blue), the mechanical resonance strongly shifts to lower frequencies. This can be explained by electrostatic softening of the vibration mode.

This Feature Article reviews the development and applications of dielectrophoresis (DEP) towards carbon nanotube (CNT) and graphene devices. DEP was first used to separate metallic and semiconducting CNTs, but has since then emerged as a leading route to large-scale directed assembly of nano-carbons. In addition to field-effect transistors, DEP-assembled devices have been demonstrated for sensors, optoelectronics and resonators. DEP is a bottom-up assembly route, and could pose a challenge to conventional top-down fabrication for nano-carbon electronics.

Stiller et al. measured the electronic and mechanical properties of a high-quality factor carbon nanotube vibrational resonator at cryogenic temperatures. Both quantum dot behavior and multiple driven mechanical resonances are observed. A sequence of higher harmonics occurs approximately at multiple integers of a base frequency, indicating that the nanotube resonator is under tension. The gate voltage dependence of the resonance frequency is successfully modelled by electrostatic softening.

The interaction of atomic hydrogen at the graphene/SiC(0001) interface is addressed here using model interfaces characterized by negligible graphene strains and two different graphene/SiC rotation angles. The threefold coordinated C atoms in the buffer layer display an increased chemical reactivity compared to free-standing graphene, resulting in two--to-four times larger binding energies of hydrogen.

Piao et al. explored a more economical source of thermopower by investigating expanded graphite (ExG) composite thin films. They demonstrate that ExG can be sufficiently dispersed in polymer solution to form stable suspensions. Thin composite films were prepared by casting and drying the suspension. Electrically and thermally insulating polymers, PC and PVA, and an intrinsically conductive polymer PEDOT:PSS served as a matrix material in this study. The authors also demonstrate that the thermoelectric properties of ExG in polymers can be easily modified by chemical functionalization.