Special Issue on Nanodiamonds

DOI: 10.1002/cvde.200800001

Special Issue on Nanodiamonds Nanocarbon research has exploded (quite literally in some cases) over the last 15 years. The diversity of nanocarbon structures and allotropes has lead to a plethora of growth techniques, unique properties and has opened the door to a number of exciting applications. In the past, the addition of C60 to the diamond–graphite family generated substantial interest and expanded the carbon research field enormously. More recently the development of nanostructured carbon such as the nanotube, Diamond-Like-Carbon (DLC), nanocrystalline diamond films and diamond nanoparticles has driven the field with increased intensity. Taking nanocrystalline diamond films as a case in point, we find that what was initially thought of as a ‘‘poor man’s’’ diamond, has now evolved into a stateof-the-art material for MEMS, thermal management, and biological applications (to name a few). However, even this class of diamond is still too diverse to generalise under one title, prompting the community to subdivide it. We now distinguish between materials that grow using a suppression of re-nucleation, akin to conventional diamond growth, and materials grown using intentional enhancement of re-nucleation processes. These two approaches are complementary rather than competitive, and the review by Butler and Sumant in this Special Issue shows how nanocrystalline diamond may be considered a designer material, to be tailored to specific applications, rather than a ‘‘one size fits all’’ material. The evolution of complexity of observed in nanocarbons has resulted in the discovery of some intriguing properties, and lead to vast contrasts between materials initially presumed to be similar. For example, nanocrystalline diamond exhibits superconductivity at low temperatures when metallically doped, as we see from the paper by Chem. Vap. Deposition 2008, 14, 141

Maresˇ et al., whereas ultrananocrystalline diamond (a term used to describe diamond films with a grain size less than 10 nm) contains incredibly high concentrations of hydrogen, as shown by Hoffman et al. in this issue. As one attempts to predict the properties of nanocarbons a priori, particular attention must be given to the volume fraction (or critical grain size) in each case. One additional degree of complexity characteristic of carbon is the possibility of coexisting allotropes, leading to materials with mixed fractions of sp2 and sp3 bonding. The phase composition of sp2–sp3 composites (such as nanodiamond) is critical to their performance in a variety of situations, and understanding the relationship between phase composition and properties/performance is fundamental to nanodiamond research. In this Special Issue, a collection of studies from leading research groups from around the world are presented. We begin with an education in the role that various synthesis parameters play in the CVD growth of nanodiamond. A diagnostic study characterizing pulsed microwave plasmas used for nanocrystalline diamond growth is presented by Be´ne´dic et al., in the high temperature regime. The low temperature growth of nanodiamond is then presented by Kromka et al., with particular attention given to the early stages of film formation. Following this, a study of the bias enhanced nucleation of nanodiamond from plasma, and the formation of ultra-thin nanodiamond films is presented by Arnault et al. and an analysis of the relationship between grain size and hydrogen concentration then follows from Hoffman et al. These papers are accompanied by a similarly impressive selection of theoretical and computational studies. We receive new insights into the reactions of carbon and hydrogen containing molecular species at the nanodiamond

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surfaces from the molecular dynamics simulations of Eckert et al. and the role of nitrogen in containing species from the first principle simulations of Van Regemorter and Larsson. This is followed by a theoretical study of how the nucleation density of growth species affects the morphology of nanodiamond films by Sternschulte et al. Finally, CVD technology is used to create an array of exotic and beautiful diamond nanostructures that go beyond the formation of conventional thin films. The formation of nanodiamondnanotude composites is presented by Zheng et al., and a detailed study of the early stages of formation of these materials is given by Orlanducci et al. Rather than linear structures, the coating of conical tips with nanodiamond is then outlined by Sunkara et al., and finally a study of the CVD growth diamond nanoplatelets is outlined by Chen et al. As we can see, this Special Issue has been structured so as to incorporate as many of the important aspects of the CVD growth of nanodiamond as possible. It has been our pleasure to bring this issue together, and we would like to take this opportunity to thank all of the authors for their inspiring contributions. Each article has under gone the journal’s peer review process, and we would also like to thank the referees for their support. We hope that this issue will introduce readers to this remarkable area of research, and give them some appreciation of how intelligent and systematic control of synthesis parameters can allow us to produce high-performance CVD nanodiamond for specific applications. Amanda S. Barnard School of Chemistry, University of Melbourne Oliver A. Williams

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