Multi-flavoured nanowires can act as miniature bar-codes, diodes and light sources
Wires one-millionth of a millimetre wide change composition along their length.
Wires one-millionth of a millimetre wide that change chemical composition along their length, just as fruit pastilles change flavour along a packet, have been grown in the United States. These multi-flavoured nanowires can act as miniature bar-codes, diodes and light sources.
Conventional microelectronics components are etched into flat layers of semiconducting material. Charles Lieber and colleagues at Harvard University in Cambridge, Massachusetts, grow their wires - smaller than the thinnest wire on a commercial silicon chip - from vapours of the atomic ingredients.
Superlattice lines up
The team has made wires about 20 nanometres across that contain alternating sections of the semiconductors gallium arsenide and gallium phosphide. Microelectronic engineers often use structures like this, called superlattices, in electronic devices. They are currently made by carving up flat sandwiches of layered semiconductors.
Superlattices are used, for example, as mirrors in microscopic lasers, or as waveguides to capture and confine light. If electrons are trapped in a thin layer of a semiconductor sandwiched between barriers of a different semiconductor, quantum wells are created that emit light. The colour of the light can be tuned by varying the well thickness.
Nanowire superlattices could be used in all these applications. Their size means that many more could be packed onto a single chip than today’s microelectronics components. The researchers envisage making nanowire lasers, for example.
Up the junction
To demonstrate the wires’ potential, Lieber’s group made structures called p-n junctions. They grew silicon nanowires in two sections, each spiced with a different additive to fine-tune the electrical behaviour of the silicon. These nanowire p-n junctions behave like diodes - they let current flow in only one direction.
The team also made p-n junctions that act as light-emitting diodes. Because these glowing devices are so small, the researchers hope to make them expel light one photon at a time. This could be useful in a new type of ultra-powerful information processing called quantum computing.
PHILIP BALL | © Nature News Service
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