Oleg Nerushev

Carbon nanotube films obtained by thermal chemicalvapour deposition

Films of carbon nanotubes are interesting for technical applications such as cold cathodes in field emission devices. We discuss experiments in which nanotube films are grown by a simple thermal chemical vapour deposition method from hydrocarbon molecules, employing the catalytic activity of deposited iron particles. Using an in situ catalyst preparation method starting from gaseous Fe(CO)5, films of vertically aligned and non-aligned multi-wall carbon nanotubes can be synthesised. Nanotube film growth is discussed as a function of the growth conditions. Steps towards the formation of horizontally aligned nanotube films and nanotube patterns are presented. Field emission measurements demonstrate the high electron emission efficiency of the as-grown films.

Determination of the Bending Rigidity of Graphene via Electrostatic Actuation of Buckled Membranes

Classical continuum mechanics is used extensively to predict the properties of nanoscale materials such as graphene. The bending rigidity, κ, is an important parameter that is used, for example, to predict the performance of graphene nanoelectromechanical devices and also ripple formation. Despite its importance, there is a large spread in the theoretical predictions of κ for few-layer graphene. We have used the snap-through behavior of convex buckled graphene membranes under the application of electrostatic pressure to determine experimentally values of κ for double-layer graphene membranes. We demonstrate how to prepare convex-buckled suspended graphene ribbons and fully clamped suspended membranes and show how the determination of the curvature of the membranes and the critical snap-through voltage, using AFM, allows us to extract κ. The bending rigidity of bilayer graphene membranes under ambient conditions was determined to be 35.5−15.0 +20.0 eV. Monolayers are shown to have significantly lower κ than bilayers.

Particle size dependence and model for iron-catalyzed growth of carbon nanotubes by thermal chemical vapor deposition

The catalytic particle size dependence of chemical vapor deposition growth of multiwall carbon nanotubes was systematically investigated using two different molecules, C2H2 and C60, as carbon feedstock gases. In the particle size range between 25 and 500 nm, the use of C2H2 leads exclusively to growth of carbon nanotubes. The nanotube diameters increase with increasing catalytic particle sizes but do not scale 1:1. In contrast, nanotube formation from C60 is observed only if the particle sizes are sufficiently small with an optimum between 20 and 30 nm. For catalyst samples with considerably larger diameters, C60 is transformed into a nontubular deposit. A growth model is given that explains the different behavior.

Plasma-enhanced chemical vapour deposition growth of carbon nanotubes on different metal underlayers

One important requirement for future applications of carbon nanotube electronic devices is the ability to controllably grow carbon nanotubes on metal electrodes. Here we show that it is possible to grow small diameter (<10 nm) vertically aligned carbon nanotubes on different metal underlayers using plasma-enhanced chemical vapour deposition. A crucial component is the insertion of a thin silicon layer between the metal and the catalyst particle. The electrical integrity of the metal electrode layer after plasma treatment and the quality of the metals as interconnects are also investigated.

The temperature dependence of Fe-catalysed growth of carbon nanotubes on silicon substrates

Abstract The catalytic particle size (Fe) and temperature dependence of multi-walled nanotubes growth from C2H2 and C60 precursor molecules is studied. The structure and density of the carbon nanotubes produced is critically dependent on the particle size, the growth temperature and the carbon flux rate. Under certain conditions, bundles of single-walled nanotubes, where the bundles appear to consist of nanotubes with the same diameters, can be produced. The nanotubes are characterised by electron microscopy and Raman spectroscopy. Field emission properties of aligned films are studied and the electron emission is correlated with light emission measurements.

Blackbody radiation from resistively heated multiwalled carbon nanotubes during field emission

We report the observation of blackbody radiation from aligned multiwalled carbon nanotubes undergoing field emission. The light intensity correlates with fluctuations in the emission current. The onset of light emission occurs at an emission current of 1 mA/cm2 and corresponds to a temperature on the order of 1550 K. Beyond this critical current irreversible changes occur in the nanotube film. The correlation between light intensity and emission current provides convincing evidence for Joule heating and stable operation for nanotube temperatures up to at least 2000 K and emission current densities on the order of 10 mA/cm2.

Tracing the Origin of the HSC Hierarchy Reveals an SCF-Dependent, IL-3-Independent CD43− Embryonic Precursor

Summary Definitive hematopoietic stem cells (HSCs) develop in the aorta gonad mesonephros (AGM) region in a stepwise manner. Type I pre-HSCs express CD41 but lack CD45 expression, which is subsequently upregulated in type II pre-HSCs prior to their maturation into definitive HSCs. Here, using ex vivo modeling of HSC development, we identify precursors of definitive HSCs in the trunk of the embryonic day 9.5 (E9.5) mouse embryo. These precursors, termed here pro-HSCs, are less mature than type I and II pre-HSCs. Although pro-HSCs are CD41+, they lack the CD43 marker, which is gradually upregulated in the developing HSC lineage. We show that stem cell factor (SCF), but not interleukin-3 (IL-3), is a major effector of HSC maturation during E9–E10. This study extends further the previously established hierarchical organization of the developing HSC lineage and presents it as a differentially regulated four-step process and identifies additional targets that could facilitate the generation of transplantable HSCs from pluripotent cells for clinical needs.

Highly efficient electron field emission from decorated multiwalled carbon nanotube films

The field emission properties of films of aligned multiwalled nanotubes produced by plasma-enhanced chemical vapor deposition are studied as a function of their length. The measured turn-on and threshold electric fields decrease strongly with increasing nanotube length, reaching values of below 1 V∕μm for the longest nanotubes investigated (170 μm). The field enhancement factors are discussed and the remarkable performance of the longest nanotube films is attributed to secondary thornlike growth at the tips.

Fabrication of individual vertically aligned carbon nanofibres on metal substrates from prefabricated catalyst dots

Carbon nanofibres (CNFs) of controlled diameter and length were grown on different metal substrates using plasma-enhanced chemical vapour deposition (PECVD). The diameter control of catalyst dots (and hence CNF diameter) was obtained by using the shot modulation technique in electron beam lithography. Catalyst dots of different sizes within arrays of different pitch were prepared and the dependence of the growth of vertically aligned CNFs on these parameters was studied for different metal underlayers. Good quality vertically aligned CNFs with a narrow length distribution were grown on Mo and W substrates. The structures grown on Nb substrates were significantly shorter for identical growth conditions and showed a lower nucleation rate. We demonstrate that through the shot modulation technique it is possible to control the diameter variation of CNFs from a single design geometry for the catalyst deposition. Individual VACNFs can be grown down to a pitch within the range 100–500 nm.

Synthesis of carbon nanotube films by thermal CVD in the presence of supported catalyst particles. Part I: The silicon substrate/nanotube film interface

The interface between the silicon substrate and a carbon nanotube film grown by thermal CVD with acetylene (C2H2) and hydrogen at 750 or 900 °C has been characterized by high resolution and analytical transmission electron microscopy, including electron spectroscopic imaging. Silicon (0 0 2) substrates coated with a thin (2.8 nm) iron film were heat treated in the CVD furnace at the deposition temperature in a mixture of flowing argon and hydrogen whereby nanosized particles of (Fe,Si)3O4 formed. These particles were reduced to catalytic iron silicides with the α–(Fe, Si), α2–Fe2Si and α1–Fe2Si structures during CVD at 900 °C, and multi-wall carbon nanotubes grew from supported particles via a base-growth mechanism. A limited number of intermediate iron carbides, hexagonal and orthorhombic Fe7C3, were also present on the substrate surface after CVD at 900 °C. The reduction of the preformed (Fe, Si)3O4 particles during thermal CVD at 750 °C was accompanied by disintegration leading to the formation of a number of smaller (<5 and up to 10 nm) iron and silicon containing particles. It is believed that the formation of these small particles is a prerequisite for the growth of aligned multi-wall carbon nanotube films.