Scanning electron microscope images of single crystal structures fabricated using template-assisted selective epitaxy. For better visibility, the silicon is coloured in green, and the compound semiconductor in red
SPIN NOT CHARGE One promising approach to developing new technologies is to exploit the electron’s tinymagnetic moment, or ‘spin’. Electrons have two properties – charge and spin – and although current technologies use charge, it is thought that spin-based technologies have the potential to outperformthe charge-based technology of semiconductors for the storage and processing of information. Scientists fromUniversity College London (UCL)
have discovered a newmethod to efficiently generate and control currents based on themagnetic nature of electrons in semi-conductingmaterials, offering a radical way to develop a new generation of electronic devices. In order to utilise electron spins for electronics, or
“spintronics”, themethod of electrically generating and detecting spins needs to be efficient so the devices can process the spin information with low power consumption. One way to achieve this is by the spin-Hall effect, which is being researched by scientists who are keen to understand the mechanisms of the effect, but also whichmaterials optimise its efficiency. If research into this effect is successful, it will open the door to new technologies. Meanwhile, researchers at Cambridge University
have built aminiature electro-optical switch which can change the spin – or angularmomentum– of a liquid formof light by applying electric fields to a semiconductor device amillionth of ametre in size. Their results demonstrate a way to bridge the gap between light and electricity, which could enable the
A cell (container) where the electrons on liquid helium experiments are conducted: copper mirrors direct and focus microwave photons in electrons on the liquid helium system. The focusing mirror (on the left) is made by pressing a hard stainless steel ball (also shown in the picture) into a soft piece of copper. The flat mirror (on the right) shows two concentric circular electrodes (aka a Corbino pair) that are used to measure electron conductivity
development of ever faster and smaller electronics. There is a fundamental disparity between the way
in which information is processed and transmitted by current technologies. To process information, electrical charges aremoved around on semiconductor chips; and to transmit it, light flashes are sent down optical fibres. Currentmethods of converting between electrical and optical signals are both inefficient and slow, and researchers have been searching for ways to incorporate the two. University of Cambridge researchers, led by
Professor Jeremy Baumberg fromthe NanoPhotonics Centre, in collaboration with researchers fromMexico and Greece, have built a switch which utilises a new state ofmatter called a polariton Bose-Einstein condensate in order tomix electrical and optical signals, while usingminiscule amounts of energy. Polariton Bose-Einstein condensates are
generated by trapping light betweenmirrors spaced only a fewmillionths of ametre apart, and letting it interact with thin slabs of semiconductormaterial, creating a half-light, half-mattermixture known as a polariton. Putting lots of polaritons in the same space can
induce condensation – similar to the condensation of water droplets at high humidity – and the formation of a light-matter fluid which spins clockwise (spin-up) or anticlockwise (spin-down). By applying an electrical field to this system, the researchers were able to control the spin of the condensate and switch it between up and down states. The polariton fluid emits light with clockwise or anticlockwise spin, which can be sent through optical fibres for communication, converting electrical to optical signals. While the prototype device works at cryogenic
temperatures, the researchers are developing other materials that can operate at roomtemperature, so that the devicemay be commercialised. EE
April 2017 /// Environmental Engineering /// 49
PICTURE: H SCHMID/IBM
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