One of the greatest issues of nanoelectronics today is how to control the heating of the components. Graphene is a promising material in this area, and it is essential to study its thermal properties. Here, the effect of heating a bilayer structure was investigated using in situ Raman spectroscopy. In order to observe the effects on each individual layer, an isotopically labeled bilayer graphene was synthesized where the two layers were composed of different carbon isotopes. Therefore, the frequency of the phonons in the Raman spectra was shifted in relation to each other. This technique was used to investigate the influence of different stacking order. It was found that in bilayer graphene grown by chemical vapor deposition (CVD), the two layers behave very similarly for both Bernal stacking and randomly oriented structures, while for transferred samples, the layers act more independently. This highlights a significant dependence on the sample preparation procedure.

The electromechanical properties of arrays of vertically aligned multiwalled carbon nanotubes were studied in a parallel plate capacitor geometry. The electrostatic actuation was visualized using both optical microscopy and scanning electron microscopy, and highly reproducible behaviour was achieved for actuation voltages below the pull-in voltage. The walls of vertically aligned carbon nanotubes behave as solid cohesive units. The effective Young's modulus for the carbon nanotube arrays was determined by comparing the actuation results with the results of electrostatic simulations and was found to be exceptionally low, of the order of 1-10 MPa. The capacitance change and Q-factor were determined by measuring the frequency dependence of the radio-frequency transmission. Capacitance changes of over 20% and Q-factors in the range 100-10 were achieved for a frequency range of 0.2-1.5 GHz.

Post-print of a peer-reviewed article published by Inderscience Publishers.

Ambient room temperature growth of aligned multi-walled carbon nanotube arrays on micrometer scale local heaters is demonstrated. High growth rates of up to 8.8 microm per second have been achieved and the growth has been monitored in situ using optical microscopy. The growth starts and ends abruptly over the length of the local heater. The terminal length of the nanotubes shows a clear dependence on growth temperature and small inhomogeneities in temperature across the heater are seen to lead to interesting microstructure of the arrays. The activation energy for growth was seen to be consistent with earlier reports for acetylene growth of nanotubes on iron catalysts.

Arrays of carbon nanotubes were reversibly actuated by applying a bias voltage. The actuation results in a variable capacitance between the arrays, which can be used to build a varactor. The capacitances were evaluated by simulating the scattering parameters in an equivalent electrical circuit while using the capacitance between the arrays as a fitting parameter. These simulations were compared with radio-frequency (RF) measurements on devices. A very good agreement between measurement and model was obtained. The capacitance could be varied by more than 20 per cent before the arrays were pulled into contact.

Using electron microscopy and in situ Raman spectroscopy we investigate carbon nanotube growth from ethylene on iron catalyst islands patterned on top of Mo electrodes, using a highly localized resistive on-chip-heating technique. A clear transition is observed between multi-walled and single-walled nanotube growth as the local temperature of the heater is increased. This can be rationalized in terms of the balance between incoming carbon flux and diffusion through the catalyst particle. The observed changes in heater performance on exposure to the hydrocarbon gas are explored and related to the formation of molybdenum carbide, leading to a rapid change in resistivity and heating power that increases the local temperature of the heater by up to 100 °C. This provides optimum conditions for nanotube growth after an incubation time that depends on the carbon flux.

The initial stages of graphene chemical vapor deposition at very low pressures (<10−5 Torr) were investigated. The growth of large graphene domains (∼up to 100 μm) at very high rates (up to 3 μm2 s−1) has been achieved in a cold-wall reactor using a liquid carbon precursor. For high temperature growth (>900 °C), graphene grain shape and symmetry were found to depend on the underlying symmetry of the Cu crystal, whereas for lower temperatures (<900 °C), mostly rounded grains are observed. The temperature dependence of graphene nucleation density was determined, displaying two thermally activated regimes, with activation energy values of 6 ± 1 eV for temperatures ranging from 900 °C to 960 °C and 9 ± 1 eV for temperatures above 960 °C. The comparison of such dependence with the temperature dependence of Cu surface self-diffusion suggests that graphene growth at high temperatures and low pressures is strongly influenced by copper surface rearrangement. We propose a model that incorporates Cu surface self-diffusion as an essential process to explain the orientation correlation between graphene and Cu crystals, and which can clarify the difference generally observed between graphene domain shapes in atmospheric-pressure and low-pressure chemical vapor deposition.

Carbon-based nanoelectromechanical devices are approaching applications in electronics. Switches based on individual carbon nanotubes deliver record low off-state leakage currents. Arrays of vertically aligned carbon nanotubes or nanofibers can be fabricated to constitute varactors. Very porous, low density arrays of quasi-vertically aligned arrays of carbon nanotubes behave mechanically as a single unit with very unusual material properties.