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Nanotube Photonics Cell Imaging with Liquid Crystals Erratum Measuring RESEARCH NEWS Nanotube photonics Measuring spin decay Periodic arrays of carbon Spintronic devices,such as magnetic random access memories and spin nanotubes can be grown transistors,rely on the manipulation of non-equilibrium spin.So device operations from catalytic dots must be performed within the spin relaxation time — the characteristic time taken deposited on a surface by for the non-equilibrium spin to decay.Usually,this spin relaxation time is measured electron-beam by using optical techniques or electron spin resonance.In Applied Physics Letters lithography,but this is an (82, 221–223; 2003),Sankar Das Sarma and colleagues at the University of expensive and slow Maryland report an all-electrical method of determining the spin relaxation time in process.Zhifeng Ren and chemical-vapour inhomogeneously doped magnetic semiconductors.The researchers make use of colleagues have developed deposition.As well as the spin-voltaic effect,in which the injected non-equilibrium spin gives rise to a an ingenious new displaying bright colours measurable spin-voltaic current that is highly sensitive to the spin relaxation time. technique for growing — owing to their strong In magnetic semiconductor p–n junctions,the spin relaxation time can then be periodic nanotube arrays reflection and diffraction determined by measuring the I–V characteristics of the device. (see images),which can be of visible light — the developed into photonic honeycomb arrays of bandgap crystals.As they nanotubes can also act Cell imaging with liquid crystals report in Nano Letters as two-dimensional (http://dx.doi.org/10.1021 photonic bandgap Liquid crystals (LCs) are crucial to advanced display technologies, nl0258271),the authors crystals.Previous studies but biocompatible LCs may find other uses.Any small imperfection first generate self- have shown that a in a surface in contact with LCs perturbs the orientational order of assembled arrays of honeycomb array of rods, these systems.You can easily experience this effect by pressing a polystyrene nanospheres embedded in a material finger against an LC computer screen.Jiyu Fang and colleagues at on a silicon substrate. with a different dielectric the Naval Research Laboratory in Washington make a virtue out of The nanosphere arrays are constant,produces a these LC defects,and exploit them as an optical amplification then used as a mask during photonic crystal structure, medium to look at features of biological surfaces.In Langmuir deposition of the nickel which perfectly reflects (http://dx.doi.org/10.1021/la0264062) they report the imaging of catalyst.Once the light at the frequency three types of human cell immobilized on a microscope slide and nanospheres have been of the bandgap. covered with liquid crystals.Each of the cell types used — muscle chemically removed,they Although they have yet to cells,fat cells and neurons — have very different shapes,which are clearly distinguishable through leave behind a honeycomb do so,the authors are the cross-polarized light of a common optical microscope (see image).By assuming perpendicular pattern of nickel dots. confident that they will be anchoring of the liquid crystals on the cell surface,the authors explain how the muscle and fat cells alter the alignment of the liquid crystals and how this is related to what is observed.So far,this theory American Chemical Society Growth of carbon able to demonstrate nanotubes from these dots photonic bandgaps in the fails to explain the images of neurons,suggesting more complex interactions between neural takes 10–15 min,using the visible frequency range by surfaces and the LCs.Understanding such interactions may shed light on the structure and behaviour Images: established technique of using their carbon of cell surfaces. plasma-enhanced nanotube arrays. ELECTRICALLY DRIVEN NANOWIRE LASERS There is much interest in the optical properties of semiconducting nanowires because their cylindrical geometry Composites by numbers and two-dimensional confinement of electrons and photons Computer simulations optimal microstructure maximizing both makes them attractive building blocks for nanoscale electronics play an essential role in for two-phase composites conductivities turns and optoelectonic devices,including lasers.This is particularly understanding the that are good at out to be a bicontinuous true for electrically driven semiconductor lasers as the defect- microstructure of many conducting heat and composite with a triply free nanowire structures exhibit improved electrical transport materials,and are electricity.Of course, periodic minimal surface. and optical properties.Charles Lieber and colleagues (Nature growing more important there are many materials These complex structures 421,241–245; 2003) have now investigated the properties of in the area of material that are good at both these occur naturally during single-crystal cadmium sulphide nanowires and show that design.Salvatore tasks,but the Princeton self-assembly processes these structures can function as optical cavities (a property that Torquato and colleagues researchers chose to involving block is crucial for lasing).They also demonstrate lasing by using at Princeton University make 50:50 composites copolymers,micelles or optical and electrical pumping.Their fabrication approach can (Phys.Rev.Lett.89, from two phases that excel nanocomposites,and be extended to other semiconductors and used to produce 266601; 2002) use at either one or the other. can be generated using lasers of many colours that could be integrated directly with topology optimization The way the two different sol–gel processing. existing microelectronic technologies.The authors believe that techniques to show the materials mix at the The authors believe their these nanowire lasers could be further developed for effect of optimizing two microscopic scale is approach is a general one applications as diverse as data storage,chemical and biological competing properties on therefore a direct and can be used to sensing,and medical therapeutics and diagnostics. the microstructure of consequence of the optimize other composite materials. competition between combinations of Previously,such the two properties,as competing functions to Erratum techniques have been both need to be guide the design of In the Research News of the November issue (Nature Materials 1, used to maximize a single maximized to produce a multifunctional materials 142; 2002),in the piece ‘Materials get plugged in’,the cation was material property.In their true multifunctional with desirable mechanical, mistakenly referred to as rubidium terpyridil (second column,line paper,Torquato and material.The best three- optical,chemical or 1) and rubidium terbipyridil (second column,line 13).In both colleagues calculate the dimensional structure for flow properties. places this should read ruthenium bipyridyl. 70 nature materials | VOL 2 | FEBRUARY 2003 | www.nature.com/naturematerials.
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