More than a wire

Nanowires are the natural evolution of the connections in circuits when scaled down to nanometre sizes. On closer inspection, of course, the role of nanowires in developing new technologies is much more than just a current-bearing medium. By sizing the diameters of these objects down to the nanoscale, their properties become increasingly sensitive to factors such as the gas composition, temperature and incident light of their surrounding environment, as well as defects and variations in diameter. What becomes important in modern electronics innovations is not just what is connected, but how.Nanowires had already begun to attract the attention of researchers in the early 1990s as advances in imaging and measurement devices invited researchers to investigate the properties of these one-dimensional structures [1, 2]. This interest has sparked ingenious ways of fabricating nanowires such as the use of a DNA template. A collaboration of researchers at Louisiana Tech University in the US hs provided an overview of various methods to assemble conductive nanowires on a DNA template, including a summary of different approaches to stretching and positioning the templates [3]. Work in this area demonstrates a neat parallel for the role of DNA molecules as the building blocks of life and the foundations of nanoscale device architectures.Scientists at HP Labs in California are using nanowires to shrink the size of logic arrays [4]. One aspect of electronic interconnects that requires particular attention at nanoscale sizes is the effect of defects. The researchers at HP Labs demonstrate that their approach, which they name FPNI (field-programmable nanowire interconnect), is extremely tolerant of the high defect rates likely to be found in these nanoscale structures, and allows reduction in size and power without significantly sacrificing the clock rate. Another issue in scaling down electronics is the trend for an increasing resistivity with decreasing wire width. Researchers from the National Institute of Standards and Technology in the US tackle this challenge by demonstrating a top-down method for fabricating nickel mono-silicide (NiSi) nanowires or nanolines. The work demonstrates a constant room temperature electrical resistivity of the NiSi nanowires as the line widths are reduced to as low as 23 nm [5].The field effect transistor, the closest device under current research to that comprising the transistor first patented by physicist Julius Edgar Lilienfeld in Canada in 1925, has become the focus of a large proportion of research in nanoscale science and technology. Up to now, most devices have been based on natural n-type transition metal oxides, but synthesis of p-type metal oxide nanowires enables the development of novel complementary nanowire devices and circuits, including LEDs, electrically driven nanolasers and multiplexing biosensors. Doping is the most common means of producing p-type semiconductor nanowires but the stability and reproducibility of these structures are often poor. A collaboration of researchers in China and Singapore has demonstrated that CuO nanowires could be a promising candidate for a p-type field-effect transistor [6]. The sensitivity of nanowires to gases in their surroundings has stimulated considerable interest for applications in sensing, and the CuO nanowires in this report also exhibit a high response to CO gas in air at 200 °C.In this issue, researchers in Korea and the US provide an overview of the use of nanomaterials in memory technology [7]. The review provides details of the current status and future prospects of alternatives that may become available in the near future for phase-change RAM, ferroelectric RAM and magnetic RAM, as well as other novel architectures under investigation such as molecular memory and devices based on carbon nanotubes. Nanowires feature here as well. Although, as pointed out in the review the use of nanowires in phase-change RAM is still far from being at the commercial stages, these one-dimensional structures have a number of advantages including the lower melting point of materials at the nanoscale and the potential for further reductions in size and programming current and power requirements.Investigations of one-dimensional structures have provided an enduring stimulant to both fundamental and applied research in nanoscale science and technology research. William Plomer once described creativity as 'the ability to connect the apparently unconnected'. It could perhaps be said that nanowires bring creativity to the ability to connect.References[1] Joachim C, Rousset B, Schonenberger C, Kerrien A, Druet E and Chevalier J 1991 Nanotechnology 2 96[2] Brandbyge M, Schiotz J, Sorensen M R, Stpltze P, Jacobsen K W and Norskov J K 1995 Phys. Rev. B 52 8499–514[3] Dai K and Haynie D T 2006 Nanotechnology 17 R14–R25[4] Snider G S and Williams R S 2007 Nanotechnology 18 035204[5] Li B, Luo Z, Shi L, Zhou J, Rabenberg L, Ho P S, Allen R A and Cresswell M W 2009 Nanotechnology 20 085304[6] Liao L, Zhang Z, Yan B, Zheng Z, Bao Q L, Wu T, Li C M, Shen Z X, Zhang J X, Gong H, Li J C and Yu T 2009 Nanotechnology 20 085203[7] Chung A, Deen J, Lee J-S and Meyyappan M 2010 Nanotechnology 21 412001