When it comes to churning out electrons, metal glass beats plastics

ScienceDaily (Nov. 21, 2011) — Field emission devices, which produce a steady stream of electrons, have a host of consumer, industrial, and research applications. Recent designs based on nanotubes and other nanomaterials embedded in plastics show initial promise, but have a number of drawbacks that hinder their wide-scale application.

The embedded nanotubes, which serve as the source for the electrons, also enable the normally inert plastic to conduct electricity. This has the desired effect of producing a versatile and easily manufactured field emission device. But since plastics are, by nature, poor conductors of electricity, they require a high concentration of nanomaterials to function. Plastics also have low thermal stability and do not hold up well under the excess heat produced by prolonged operation.

A team of researchers from Monash University in Australia, in collaboration with colleagues from CSIRO Process Science and Engineering, has developed a promising and easily manufactured replacement for plastics: amorphous bulk metallic glass (ABM). These ABM alloys form amorphous materials as they cool, giving them more of a glass-like behavior. In a paper accepted for publication in the AIP's journal Applied Physics Letters, the researchers used an alloy made from magnesium, copper, and gadolinium.

This metallic glass has many of plastics' desirable features. It can conform to a variety of shapes, be produced in bulk, and serve as an effective matrix for the nanotubes. Besides its high conductivity, the metallic glass' highly robust thermal properties mean that it can withstand high temperatures and still retain its shape and durability. According to the researchers, these advantages, alongside excellent electron emission properties, make these composites one of the best reported options for electron emission applications to date.

Though other composites of bulk metallic glass and carbon nanotubes have been reported before, this is the first time that such a system is being used for a functional device, such as for field emission. Electron microscopes, microwave or X-ray generation, nano-electronics, and modern display devices are all examples of the potential applications of this technology, the researchers note.

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The above story is reprinted from materials provided by American Institute of Physics.

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Journal Reference:

Pejman Hojati-Talemi, Mark A. Gibson, Daniel East, George P. Simon. High performance bulk metallic glass/carbon nanotube composite cathodes for electron field emission. Applied Physics Letters, 2011; 99 (19): 194104 DOI: 10.1063/1.3659898

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Scientists play ping-pong with single electrons

ScienceDaily (Sep. 22, 2011) — Scientists at Cambridge University have shown an amazing degree of control over the most fundamental aspect of an electronic circuit, how electrons move from one place to another.

Researchers from the University's Cavendish Laboratory have moved an individual electron along a wire, batting it back and forth over sixty times, rather like the ball in a game of ping-pong. The research findings, published September 22 in the journal Nature, may have applications in quantum computing, transferring a quantum 'bit' between processor and memory, for example.

Imagine you are at a party and you want to get to the other side of a crowded room to talk to someone. As you walk you have to weave around people who are walking, dancing or just standing in the way. You may also have to stop and greet friends along the way and by the time you reach the person you wanted to talk to you have forgotten what you were going to say. Wouldn't it be nice to be lifted up above the crowd, and pushed directly to your destination?

In a similar way, electrons carrying a current along a wire do not go directly from one end to the other but instead follow a complicated zigzag path. This is a problem if the electron is carrying information, as it tends to 'forget' it, or, more scientifically, the quantum state loses coherence.

In this work, a single electron can be trapped in a small well (called a quantum dot), just inside the surface of a piece of Gallium Arsenide (GaAs). A channel leads to another, empty, dot 4 microns (millionths of a metre) away. The channel is higher in energy than the surrounding electrons. A very short burst of sound (just a few billionths of a second long) is then sent along the surface, past the dot. The accompanying wave of electrical potential picks up the electron, which then surfs along the channel to the other dot, where it is captured. A burst of sound sent from the other direction returns the electron to the starting dot where the process can be repeated. The electron goes back and forth like a ping-pong ball. Rallies of up to 60 shots have been achieved before anything goes wrong.

"The movement of electrons by our 'surface acoustic wave' can also be likened to peristalsis in the esophagus, where food is propelled from the mouth to the stomach by a wave of muscle contraction," explains Rob McNeil, the PhD student who did most of the work, helped by postdoc Masaya Kataoka, both at the University of Cambridge's Department of Physics, the Cavendish Laboratory.

"This is an enabling technology for quantum computers," Chris Ford, team leader of the research from the Semiconductor Physics Group in the Cavendish, says. "There is a lot of work going on worldwide to make this new type of computer, which may solve certain complex problems much faster than classical computers. However, little effort has yet been put into connecting up different components, such as processor and memory. Although our experiments do not yet show that electrons 'remember' their quantum state, this is likely to be the case. This would make the method of transfer a candidate for moving quantum bits of information (qubits) around a quantum circuit, in a quantum computer. Indeed, our theorist, Crispin Barnes, proposed using this mechanism to make a whole quantum computer a long time ago, and this is an important step towards that goal."

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The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by University of Cambridge. The original story is licensed under a Creative Commons license.

Journal Reference:

R. P. G. McNeil, M. Kataoka, C. J. B. Ford, C. H. W. Barnes, D. Anderson, G. A. C. Jones, I. Farrer, D. A. Ritchie. On-demand single-electron transfer between distant quantum dots. Nature, 2011; 477 (7365): 439 DOI: 10.1038/nature10444

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