Power is nothing without control

Abstract

A great deal of technological progress occurs by chance. In 1985 Harold Kroto and his colleagues at Rice University were working on experiments to understand the mechanisms by which long-chain carbon molecules are formed in interstellar space and circumstellar shells. What they found was the remarkably stable C60 molecule now referred to as Buckminster fullerene or 'bucky balls' [1]. Six years later, using an arc-discharge evaporation method similar to that used for fullerene synthesis at NEC Corporation in Japan, Sumio Ijima synthesised carbon nanotubes [2]. The extraordinary properties of these carbon nanostructures have since sparked the imagination of researchers in fields ranging from photonics and electronics to biology and medicine. But these properties depend greatly on geometrical factors, such as the chirality, length, diameter and whether they are single- or multi-walled. While it is possible to discover these fascinating materials by chance, it takes a great deal of curiosity and scientific ingenuity to reveal their unusual qualities, and their potential can only be harnessed by careful design. In this issue, Journet et al from Lyon University in France describes how far the field has come in exacting control in carbon nanotube synthesis [3]Morphological control has become key to nanotechnology synthesis. In2O3 nanowires have generated considerable interest for potential applications in thin film transistors and optoelectronic devices. But the morphology significantly affects the performance of these devices. Synthesising high-quality crystalline nanowires is crucial. Researchers in Singapore have investigated factors affecting the resulting products in vapour transport, a dominant technique for In2O3 nanowire synthesis. They successfully synthesised In2O3 nanowires, nanotowers and ultralong layered nanorods with uniform diameter, high aspect ratio and high yield by controlling the synthesis conditions [4]. A collaboration of researchers in Korea and China have shown that they can fabricate well aligned arrays of ZnO nanorods as long as 10 μm by using a preheating hydrothermal treatment [5.] The dimensions and orientations of the nanorod arrays are particularly well suited to technological applications. Researchers in the US have enhanced the gas-sensing performance of SnO2 single-crystal nanostructures by fabricating nanowires with a segmented morphology [6]. The low-diameter sections allow an optimum ratio of the radius to the Debye length. At the same time, the structures are sufficiently robust to avoid the problems associated with manipulating extremely narrow nanowires.It has been suggested that differences in fabrication methods such as annealing parameters can affect the photoluminescence from silicon quantum dots. Hao and Shen from Shanghai Jiao Tong University in China combined their data on silicon dots annealed in oxygen with that of silicon dots annealed in hydrogen and argon and used analysis of the results to identify the photoluminescence mechanism [7]. The work shows how annealing can be used to control photoluminescence properties by modifying the defect density through annealing treatment.Defects play an important role in tailoring the properties of graphene to maximise the materials potential in electronics and spintronics. Atomistic simulations of these sorts of systems can face problems due to the shear size of the calculations. Researchers in Brazil integrated a number of modelling approaches to propose a true spin filter based on realistic boron-doped zigzag singly hydrogen passivatedgraphene nanoribbons up to 450 nm in length [8]. The authors explain the excellent spin filtering performance in terms of different scattering probabilities at the impurity site for majority and minority spins, which consequently leads to different localization lengths. Carbon-based nanomaterials have catalysed enormous activity in nanoscale science and technology research. As Journet et al describe in their review, synthesis of these materials is now a refined art allowing considerable control over the parameters. The mechanisms behind the growth using different techniques is also understood, making the alchemy of creating these prized nanostructures into an advanced science. With these new nanomaterials researchers in nanoscale science and technology now have the power to create devices with performance attributes previously unimagined, and the advancing fine art of controlled synthesis allows these devices to be made on demand.