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nanotimes News in Brief

came across this phenomenon. Such actuators are, for example, used in loudspeakers for ultrasonic frequencies undetectable by the human ear in the medical world. None of the mechanical techniques currently available are suitable for making a very compact loudspeaker of this kind and still achieving a ‘deflection’ of metres per second on this scale. Svetovoy thought, however, that it might be possi- ble by building up pressure with bubbles.

The problem was that the bubbles could be made very rapidly but that they did not disappear quickly enough. The combustion reaction that has now been demonstrated might solve this problem. But it causes other problems too, such as the damage to the electrodes. “That is what we now have to look at”, Svetovoy said.

This research was carried out by Prof. Miko Elwenspoek’s Transducer Science and Technology group of the University of Twente’s MESA+ Insti- tute for Nanotechnology.

Vitaly Svetovoy, Remko Sanders, Theo Lammerink and Miko Elwenspoek: Combustion of hydrogen-oxygen mix- ture in electrochemically generated nanobubbles, In: Physical Review E, Vol. 84(2011), Issue 3, September 22, 2011, Article 035302 [4 pages], DOI:10.1103/PhysRe- vE.84.035302: http://10.1103/PhysRevE.84.035302

http://www.utwente.nl/ewi/tst/

The method used by the Chalmers researchers to control the light by using asymmetric material com- position – such as silver and gold – is completely new. It is easy to build this kind of nanoantenna;

11-09 :: September 2011

Researchers at Chalmers University of Technology (SE) have built a very simple nanoantenna that directs red and blue colours in opposite direc- tions, even though the antenna is smaller than the wavelength of light. The findings can lead to optical nanosensors being able to detect very low concen- trations of gases or biomolecules.

A structure that is smaller than the wavelength of visible light (390 to 770nm) should not really be able to scatter light. But that is exactly what the new nanoantenna does. The trick employed by the Chalmers researchers is to build an antenna with an asymmetric material composition, creating optical phase shifts.

The antenna consists of two nanoparticles about 20nm apart on a glass surface, one of silver and one of gold. Experiments show that the antenna scatters visible light so that red and blue colours are di- rected in opposite directions.

“The explanation for this exotic phenomenon is optical phase shifts,” says Timur Shegai, one of the researchers behind the discovery. “The reason is that nanoparticles of gold and silver have different optical properties, in particular different plasmon resonances. Plasmon resonance means that the free electrons of the nanoparticles oscillate strongly in pace with the frequency of the light, which in turn affects the light propagation even though the anten- na is so small. “