11-01 :: December 2010 / January 2011

nanotimes News in Brief

Researchers at Columbia University, USA, and University of Electronic Science and Technology of China, China, report radio frequency (rf) elec- trical readout of graphene mechanical resonators.

The mechanical motion is actuated and detected directly by using a vector network analyzer, emplo- ying a local gate to minimize parasitic capacitance. A resist-free doubly clamped sample with resonant frequency ~34 MHz, quality factor ~10 000 at 77 K, and signal-to-background ratio of over 20 dB is demonstrated. In addition to being over two orders of magnitude faster than the electrical rf mixing method, this technique paves the way for use of graphene in rf devices such as filters and oscillators. © text APL Yuehang Xu, Changyao Chen, Vikram V. Deshpande, Frank A. DiRenno, Alexander Gondarenko, David B. Heinz, Shuaimin Liu, Philip Kim, James Hone: Radio frequency electrical transduction of graphene mechani- cal resonators, In: Applied Physics Letters, Vol. 97(2010), Issue 24, December 13, 2010, Article 243111 [3 pages], DOI:10.1063/1.3528341: http://dx.doi.org/10.1063/1.3528341 http://hone.mech.columbia.edu/

Srikanth Sastry at Jawaharlal Nehru Centre for Advanced Scientific Research, India, studied in PNAS the possibility of a liquid-liquid transition for silicon, germanium, water, silica, carbon, hydrogen. Srikanth Sastry: Illuminating liquid polymorphism in sili- con, In: PNAS, Vol. 107(2010), No. 40, October 5, 2010, Pages 17063-17064, DOI:10.1073/pnas.1012192107: http://dx.doi.org/10.1073/pnas.101219210

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Physicists from the Max Born Institute in Berlin, Germany, have now returned to the use of elec- trons in holography. A special element in their approach is that the electrons that image the object are made from the object itself using a strong laser.

Marc Vrakking describes what happens: “In our experiment, the strong laser field rips electrons from the Xe atoms and accelerates them, before turning them around. It is then as if one takes a catapult and shoots an electron at the ion that was left be- hind. The laser creates the perfect electron source for a holographic experiment.”

Some of the electrons re-combine with the ion, and produce extreme ultra-violet (XUV) light, thereby producing the attosecond pulses that are the ba- sis for the new attosecond science program that is under development at MBI. Most electrons pass the ion and form the reference wave in the holographic experiment. Yet other electrons scatter off the ion, and form the object wave. On a two-dimensional detector the scientists could observe holographic in- terference patterns caused by the interaction of the object wave with the Coulomb potential of the ion.

In order to successfully carry out the experiments, certain conditions had to be met. In order to create the conditions for holography, the electron source had to be put as far away as possible from the ion, ensuring that the reference wave was only mini- mally influenced by the ion. The experiments were therefore carried out in the Netherlands, making use of the mid-infrared free electron laser FELICE, in a collaboration that encompassed – among others – the FOM Institutes AMOLF and Rijnhuizen. At FELICE, the Xe atoms where ionized using laser light