VALLEY RESEARCH

Research News is a digest of science and technology news items arising from research and development magazines, newspapers, trade magazines, newsletters, and other news sources that Valley Research processes daily for the benefit of its customers everywhere. It is provided freely to our customers who are free in turn to post or transmit it to other interested researchers provided only that credit to Valley Research is given. Research News is updated approximately once a week.

Rodolfo Carrera, Editor

WEEK OF MARCH 8, 2010 [No. 835]

A step closer to the exaflop (10¹⁸ flops) computer level:   researchers at the IBM Watson Research Center in New York have built an array of Ge nanophotonic APDs (avalanche photodetector) on a Si chip that converts optical to electronical signals at a record speed of 40 Gps operating at just 1.5 v. That compares with 10 GHz at 25 v of previous devices. The APD has built-in Si/Ge waveguides that concentrate incoming light at the Ge detector (30 nm thick, holding very high electric fields at 1.5v biases). The avalanche is produced much faster and over shorter distances than before with a 70% reduction in noise caused by random fluctuations.

For more information: Physicsworld, March 4 (2010); Wall Street Journal, March 4 (2010) page B8; Nature, March 4 (2010) page 80.

A transistor with no doping gradient in the source-drain interface:   Irish researchers at the University College Cork have made a transistor consisting of a Si nanowire in which current flow is perfectly controlled by a Si gate that is separated from the nanowire by a thin insulating layer. There is no need to alter the doping over very short distances. Instead, the entire Si nanowire is heavily n-doped, making it an excellent conductor. However, the gate is p-doped and its presence has the effect of depleting the number of electrons in the region under the nanowire. If a voltage is simply applied along the nanowire, current cannot flow through this depleted region. If a voltage is applied to the gate, the squeezing effect is reduced and current can flow.

For more information: Physicsworld, March 1 (2010); Nature Nanotechnology, March (2010) page 225.

WEEK OF MARCH 1, 2010 [No. 834]

Stimulated sound amplification by stimulated emission of phonons:   two separate groups at Caltech and the University of Nottingham have created the first phonon lasers that emit coherent sound waves (sasers). The idea of extending the laser process to phonons have stumbled against the difficulty of finding materials in which stimulated emission, rather than random spontaneous emission, is the dominant decay process. The Caltech group has used two silica 6µ-diameter microwave resonators separated by 1 µ gap to form a two-state quantum system coupled by light waves. The system is pumped to a higher energy state by a laser and MHz phonons are emitted that stimulate further emission of phonons. Sound in a narrow frequency range is emitted only after a pumping energy threshold is past. The Nottingham device is made of alternating layers of the semiconductor GaAs and the insulator AlAs. Applying a voltage between layers, electrons hop between GaAs quantum wells across the AlAs barrier emitting a phonon in the process that is capable of stimulating another hop. The layer interdistance resonates with the phonon wavelength so that the process is sustained. A femtosecond laser is used to initiate the stimulated emission. The intensity of coherent phonons is increased by increasing the bias voltage up to 160 mV where the photon wavelength (~400 GHz) resonates with the device configuration. A Terahertz saser with phonons ~1 nm wavelength would allow for 3D probing of nanostructures.

For more information: Physicsworld, February 25 (2010); Phys. Rev. Lett., to be published (2010).

WEEK OF FEBRUARY 22, 2010 [No. 833]

Optical clock with Al ion beats time accuracy record:   researchers at NIST in Colorado have built a single Aluminum optical clock that remains accurate to within one second over 3.7 Byrs (precision 8.6 x 10^-18).The previous record was held by a clock with a single Hg ion which is good to one second in 1.7 Byrs. The team begins by trapping an Mg ion using electric fields and then cooling it using a laser. They then introduce the Al ion into the chamber, which interacts with the Mg via electrical forces. These interactions allow the team to chill the Al ion. The local-oscillator laser is then fired at the Al ion (QLS, quantum logic spectroscopy, is used to determine the absorption efficiency) that tunes the laser frequency which is then precisely measured.

For more information: Physicsworld, February 12 (2010); Phys. Rev. Lett., to be published (2010).

Gamma rays become relativistic long after emission from blazars:   an international group lead by scientists at SLAC have used the Fermi Gamma-ray Space Telescope and other telescopes to measure the radiation emitted from a supermassive black hole that fires an intense beam of radiation directly at Earth. They conclude that the beam has to travel several light years before being accelerated to nearly the speed of light. They spotted a big change in polarization which they think occurs as a huge blob of ejected material encounters a bend in the jet located at 10 light-years from the black hole (a thousand times further away than previously thought).

For more information: Physicsworld, February 18 (2010); Nature, February 18 (2010) pages 919 and 886.

WEEK OF FEBRUARY 15, 2010 [No. 823]

First Germanium laser fabricated:   researchers at MIT have made an important next step in the quest for a useful (low cost optoelectronics integration) electrically pumped laser on silicon by creating the first infrared-emitting Ge laser. They have shown that lasers can be made that exploit direct-gap transitions in Ge by overcoming the energy difference between indirect and direct bandgap with doping and thermal strain. The group stimulated light emission at room temperature with a separate pulsed 1064 nm pump laser. Lasing around 1600 nm occurred with pumping power over 6 µJ / pulse. The group has developed an electrically pumped laser too.

For more information: Physicsworld, February 10 (2010); Optics Letters, to be published (2010).

Mass of a trans-uranium element directly measured:   European researchers at the GSI in Darmstadt have for the first time made direct mass measurements of an element heavier than Uranium. They produced Nobelium (102 protons) by firing isotopes of Ca at a Pb target whose fusion process produces No isotopes. They slowed down the energetic No ions through a cloud of He atoms and guided them into a magnetic Penning trap. After the ions were picked up in the magnetic field lines their masses were determined from their orbital rotational frequencies. Results are accurate to a precision of 0.05 ppm and confirm previous indirect evaluations.

For more information: Physicsworld, February 11 (2010); Nature, February 11 (2010) pages 785 and 740.

WEEK OF FEBRUARY 8, 2010 [No. 831]

Test of synchronous neural interactions diagnoses PTSD:   researchers at the University of Minnesota have been able to diagnose post-traumatic stress disorder (PTSD) using a magnetoencephalograpy (MEG) technique to analyze patterns of neural interactions. It is particularly difficult to tell whether someone has the condition or not because this disease has no clear pathology that other psychiatric diseases have and is a purely functional brain disorder instead. MEG data were acquired within an electromagnetically shielded chamber in just a minute using a 248-channel axial gradiometer system. The near-real time non-invasive measurements are done using superconducting LHe-cooled quantum interference device sensors (SQUID) capable of measuring the femtoTesla magnetic fields created by currents flowing in and around neurons. A significant difference between people with a disorder and healthy controls is found in the interaction between the different signals. The idea is that MEG can diagnose brain diseases from patterns of neural interactions. The technique could be used both for initial diagnosis and for monitoring of evolution and remission of the disorder. It allows to identify genuine PTSD sufferers and without the need for patients to relive painful past memories.

For more information: Physicsworld, February 2 (2010); Journal of Neural Engineering, January 20 (2010).

WEEK OF FEBRUARY 1, 2010 [No. 830]

Single organic transistor behaves like a brain synapse:   CNRS and CEA researchers have made the first transistor that mimics connections in the human brain. They added Au nanoparticles to the interface between an insulating layer (dielectric gate) and an organic transistor made of pentacene. A nanoparticle organic memory field effect transistor (NOMFET) was built by fixing 5, 10 and 20 nm diameter particles into the source-drain channel of the device and covering the structure with a 35 nm thick film of pentacene. The transistor mimics the short-term plasticity of synaptic junctions. Previous neural nets required at least 7 transistors to build just one electronic-based synapse. In the NOMFET the pre-synaptic signal is the pulse voltage applied to the device and the output signal is the drain current. The holes are trapped in the nanoparticles and act like the neurotransmitters. A certain number of holes are trapped for each incoming voltage spike and in the absence of pulses, the holes escape in a matter of seconds. The time delay is precisely adjusted by the researchers by optimizing the nanoparticle number and the device geometry. Depending on the frequency of the applied voltage spikes, the output of the NOMFET reproduces either the decreasing or the amplifying behavior typical of a synapse.

For more information: Physicsworld, January 28 (2010); Advanced Functional Materials (2010), to be published.

WEEK OF JANUARY 25, 2010 [No. 829]

Color e-paper using in-plane electrophoresis made:   researchers at Philips have designed an electronic paper that can change color and does not require backlights. Present e-paper is black and white (it reflects ambient light with no need for backlight as needed in LCDs). They apply a voltage across two electrodes on the face of the e-paper rather than into the display as in conventional top-down electrophoresis. Different colored pigments are combined in each pixel (cyan, magenta, yellow, and black all stacked away in the corner of each pixel site leaving a transparent display) and a third electrode controls the spread of the particles across the display.

For more information: Physicsworld, January 20 (2010); J. Soc. Information Display (2010), to be published.

Spin polarization controlled by an electric field alone:   a group lead by scientists of the CNRS has controlled the polarization of a spin current by applying an electric field across an insulator. The electric-only control has been demonstrated in a hybrid material made by coupling a ferroelectric to a ferromagnet. They made tunnel junctions that combine two ferromagnetic electrodes (iron and the ferromagnetic oxide LSMO) separated by a layer of ferroelectric BaTiO₃ just 1 nm thick. The technique requires much less energy than previous schemes for flipping spin. This opens the way to controlling all spintronics devices by purely electric means.

For more information: Physicsworld, January 15 (2010); Science, to be published (2010).

WEEK OF JANUARY 18, 2010 [No. 828]

Precise neural silencing on behaviorally relevant time scales shown:   MIT researchers have shown that members of the class of light-driven outward proton pumps can mediate powerful, safe, multiple-color silencing of neural activity. The gene archaerhodopsin-3 from Halorubrum sodomense enables near-100% silencing of neurons in the awake brain when virally expressed in the mouse cortex and illuminated with yellow light. This ability to silence the activity of genetically specified neurons in a temporally precise fashion should allow investigation of the causal role of specific cell classes in neural computations, behaviors, and pathologies.

For more information: Nature, January 7 (2010) page 98.

Superluminal speeds observed in space:   researchers at the University of Texas at Brownsville have witnessed anomalous dispersion in radio pulses that have traveled from a distant pulsar. They used the Arecibo Observatory in Puerto Rico to take radio data of the pulsar PSR B1937+21 at 1,420.4 MHz (resonance of H₂) with a 1.5 MHz bandwidth for three days. The pulses close to the center frequency value arrived earlier than would be expected given the pulsar's normal timing, and therefore appeared to have traveled faster than the speed of light.

For more information: Physicsworld, January 11 (2010); Astrophys. J., to be published (2010).

Fish-tetrapod transition reassessed:   scientists from Warsaw University have presented well-preserved and securely dated tetrapod tracks from Polish marine tidal flat sediments of early Middle Devonian (Eifelian stage) age that are approximately 18 Myrs older than the earliest tetrapod body fossils and 10 Myrs earlier than the oldest elpistostegids. They force a significant reassessment of the timing, ecology, and environmental setting of the fish-tetrapod transition.

For more information: Nature, January 7 (2010) page 43.

WEEK OF JANUARY 11, 2010 [No. 827]

Particle quantum trembling observed:   European researchers have observed for the first time zitterbewegung, the violent trembling motion of an elementary particle predicted by Schrodinger in 1930. It is currently impossible to detect the quivering of a free electron, which has amplitude of just 10^-13m and a frequency of 10²¹ Hz. Instead the team simulated the behavior of a free electron with a single, visible wavelength laser manipulated Ca ion trapped in an electrodynamic trap. When the right conditions are met, the Schrodinger equation that describes this ion as a quantum system looks identical to the Dirac equation of the free electron.

For more information: Physicsworld, January 6 (2010); Nature, January 7 (2010) pages 68, 37, and 5

Darwinian evolution active on non-living prions:   scientists at the Scripps Research Institute in Florida have shown that prion proteins, devoid of all genetic materials, can change to suit their environment and go on to develop drug resistance. They transferred prion populations from brain cells to other cells in culture and observed the prions that adapted to the new cellular environment out-competed their brain-adapted counterparts by natural selection. When returned to the brain cells, the brain-adapted prions again took over the population. They found the same process of mutation and adaptive change in prions (and protein folding) as one sees in viruses.

For more information: BBC News, January 1 (2010); ScienceDaily, January 3 (2010); Science, to be published.

WEEK OF JANUARY 4, 2009 [No. 826]

Single-molecule solid state transistor using orbital gating shown:   Korean researchers have fabricated transistors from single molecules, where the flow of electrons is controlled by modulating the energy of the molecular orbitals of the molecule. Their technique is based purely on electrostatic modulation of the molecular-orbital energy of a single molecule. This is the first demonstration of a single molecule being electrically connected to two electrodes. Each device consists of a fractured Au nanowire overlaid on a strip of Al₂O₃. They coated Au nanowires with alkane and aromatic dithiol molecules, then broke the wire (through electromigration) producing a nanogap filled by a single dithiol molecule through which electrons can tunnel. The broken ends form the source and drain electrodes connected by a single molecule and the dielectric strip forms the gate electrode. The electric field created by the gate electrode modulates the energies of molecular orbitals in the dithiol, which in turn control the amount of current that flows through the source and drain electrodes. In situ spectroscopy firmly shows that the IV curves are caused by the single molecule transistor as intended (and are not caused by either impurities or defects in the system) and a steep linear relationship between gate voltage and molecular-orbital energy.

For more information: Nature, December 31 (2009) pages 1039 and 994.

NOTE: previous Research News (since WEEK OF MARCH 1, 1994 [No. 1], around the time when the Quantum Cascade Lasers were demonstrated at AT&T Bell Laboratories in Murray Hill, N.J., as promising MIR solid-state room temperature sources that would enable laser spectroscopy in the spectral region where fundamental rotational-vibrational transitions of most molecules take place) not posted.