A scientist of Indian origin has created new ’superatoms’ with magnetic properties for the first time.

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London, June 27 (ANI): A team of researchers led by a scientist of Indian origin has created new ’superatoms’ with magnetic properties for the first time, a breakthrough that could be used to make “spintronic devices”, faster computer processors and denser memory storage.
According to a report in New Scientist, the research was led by Shiv Khanna from Virginia Commonwealth University.
Superatoms were discovered in the 1980s when Walter Knight and colleagues at the University of California, Berkeley, found that groups of sodium atoms can share electrons amongst themselves.
The electrons form a collective “supershell” that coats the cluster.
Until now, clusters that copy the magnetic properties of other elements have proved more difficult to design.
Magnetism is caused by the spin of an atom’s electrons, which are arranged in shells, or orbitals, around the atom’s nucleus.
Their net spin determines the strength of the atom’s magnetic “moment,” and because they tend to occur in pairs that cancel each other out, it is the atom’s unpaired electrons that contribute to its magnetic moment.
Unpaired electrons, however, will make an atom, or a superatom, more likely to react with others in an attempt to fill its orbitals and become stable.
As a result, stability and magnetism have long been thought to be mutually exclusive.
A team led by Shiv Khanna at Virginia Commonwealth University has come up with a way around the problem.
Khanna’s team worked out that encapsulating an atom of vanadium in a cage of eight caesium atoms would create a stable supershell of electrons around the entire cluster.
This would prevent the vanadium atom’s unpaired electrons from reacting with other atoms, maintaining its magnetism.
The arrangement would yield a magnetic moment of five Bohr magnetons, which is the same as an atom of manganese.
“What we have done is expand the range of possible magnetic materials,” said Khanna.
Khanna’s magnetic superatoms are only calculations at this point, but he has funding from the Department of Energy to make them a reality.
He hopes the clusters can be used to give researchers a new dimension of control in designing new materials.
For example, stable magnetic clusters could one day be used in new “spintronic” devices, which compute or store information using magnetic moments rather than simply electrical charge.
Encoding data in this way means the devices can be far smaller than those used to make conventional electronic components, potentially providing an overall boost in computing power. (ANI)

ATLAS (LHC,CERN) e-News: Cosmic shakedown

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For the last seven weeks, ATLAS has been going through the motions, practicing and problem-solving in preparation for beam.Like a choir rehearsing ahead of a concert, the first five weeks – so called ‘slice weeks’ – each focused on running different combinations of parts of the detector, to inspect how each performed and cooperated.Week 1, commencing April 13th, was all about the SCT, Pixels, and Beam Condition Monitor.

Week 2 dealt with the Tile and Liquid Argon calorimeters, the L1 Calo trigger system, and some High Level Trigger (HLT) algorithms specific to the calorimeters. The third week concentrated on the suite of muon sub-systems.Week 4 took things up a notch, combining all of the above and focusing on testing HLT algorithms as much as possible with cosmics. Finally, week 5 was the first time that the forward detectors – LUCID and the Zero Degree Calorimeter – had been run together and integrated into the ATLAS data stream. Look out for articles reporting in more detail on these final two weeks in the next issue of e-News (June 15th).Due to ongoing work on the cooling for the silicon detectors, the SCT and Pixel detectors could not be switched on, and so week 1 involved only the off-detector part of Pixel and SCT electronics, with Monte Carlo data being 'plugged' into their readout devices. The rest of the slice weeks were full cosmic runs.The muon detectors with the largest surface areas can detect 1000 cosmic particles per second, but in LHC conditions, up to 100,000 ‘interesting’ events will be sent to the HLT per second. To simulate the stress on the HLT, ‘fake’ so-called random triggers were layered on top of the cosmic ones.“We’ve tested so far up to 80 kilohertz. The bulk of this is fake triggers, with about 1 kilohertz of real cosmic muons,” says Run Coordinator Christophe Clement. “The HLT can filter out the fake triggers, run algorithms on the real cosmic ones, and then write maybe 200 interesting ones per second to Tier 0.”According to Christophe, the slice weeks have been pretty successful, particularly considering how much the landscape has changed since the detectors were last run together, in Autumn 2008; the Detector Control System (DCS) which monitors the hardware has been upgraded, bits of the detectors have been replaced and repaired, the online software and HLT software have both been upgraded, and the whole detector has been opened and is now almost closed.“I think we can say now that we have upgraded all software for Data Acquisition and Trigger as well as the Detector Control System, and we’re more or less at the same level that we were last year in terms of stability,” says Christophe “and then we start to push more at the trigger rates.”Stability tests, where the system is left to run unhampered for extended periods, were performed on the weekends of the slice weeks. “It’s like a test-program for a plane,” explains Christophe, “they’re going to do all possible things: fly it into a storm, try to land it when it’s snowing. That’s what we do during the week. Then on the Friday evening, we say ‘OK, now we’ll just try to fly straight for the weekend, without touching anything, and see if it works for a long flight’.”Most of the sub-systems were able to run well for extended periods, although there were some unexpected instabilities at high rate. This week and next, experts from the calorimeters and L1 Calo will meet in Geneva to try to get to the bottom of those problems.Weekend tests were also run using a simulated beam schedule, to give groups a better sense of how they will need to work during beam time – stopping and starting and reconfiguring between LHC fills. “We were quite positively surprised at how well we were able to do this,” says Christophe, reporting crude data-taking efficiency calculations of 91 per cent during the long muon weekend. Ignoring a glitch on the general power grid on a certain Sunday morning at 3 a.m., the figure for the calorimeter weekend would have been 97 per cent.Since the slice weeks, more tests have been done with the muon system and the TRT, as ATLAS works towards a two-week combined magnet run, due to begin on June 22nd.“For these two weeks, we hope to run cosmics with less debugging,” says Christophe. “The weeks we had so far were really to try to address technical issues. Hopefully [the combined run] will be much smoother, and we can calculate our data taking efficiency much better.”The data taken so far will be analysed for weeks to come, and used to perfect the calibration, alignment, and synchronisation of ATLAS. Over 40 million cosmic events were triggered in the muon slice week alone, and there is now a big push to bring trigger timings for different parts of the detector and different types of triggers into alignment. When real collision particles start shooting through the different layers of the detector, all the electronics must be synchronised and shouting their findings in unison, a choir hitting its notes in time. “We’re fine-tuning this now,” says Christophe. “If we can get everything within 25 to 50 nanoseconds on the cosmics before the beam it would be a great success. And then we can improve with the collisions.”

Ceri Perkins
ATLAS e-News

Particles, Molecules Prefer Not To Mix

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ScienceDaily (May 11, 2009) — In the world of small things, shape, order and orientation are surprisingly important, according to findings from a new study by chemists at Washington University in St. Louis.

Lev Gelb, WUSTL associate professor of chemistry, his graduate student Brian Barnes, and postdoctoral researcher Daniel Siderius, used computer simulations to study a very simple model of molecules on surfaces, which looks a lot like the computer game "Tetris." They have found that the shapes in this model (and in the game) do a number of surprising things.
WUSTL chemists headed by Lev Gelb simulated the motions and behavior of particles on a lattice and found "birds of a feather flock together." It's plainly evident that, in this four-component mixture of squares, rods, S shapes and Z shapes, the shapes all make little clusters, rather than completely mixing together. Tetris, anyone?
"First, different shapes don't mix very well with each other; each shape prefers to associate with others of the same kind," Gelb says. "When you put a lot of different shapes together, they separate from each other on microscopic scales, forming little clusters of nearly pure fluids. This is true even for the mirror-image shapes.
"Second, the structures of the pure (single-shape) fluids are quite complex and not what we might have predicted. There is a very strong tendency for some of the shapes, like rods and S- and Z- shapes, to align in the same direction. Finally, how `different looking' the shapes are isn't a good predictor for how well they mix; it turns out that the hard-to-predict characteristic structures of the fluids are more important than the shapes themselves, in this regard."
The researchers used Monte Carlo computer simulations of a simple lattice model (think of the lattice as a checkerboard), on which are placed "tetrominoes," which are S-, Z-, L-, J-, T-, rod- and square-shaped pieces.
Gelb and his colleagues use simulations to develop an atomic-scale understanding of the behavior of complex systems. They want to understand how molecules and nanoparticles of different shapes interact with each other to gain a better understanding of self-assembly, which is important in the development of new, strong materials for one, and designed catalysts for another.
Lining up
Gelb says that there has long been interest in self-assembly and in designing things that will assemble into predictable structures. Most researchers try to hold simple shapes together energetically, using some sort of chemical lock and key, such as DNA or hydrogen bonds. But if the particles have more shape to them, surprising things can happen.
"People have known for a long time when you make round nanoparticles and deposit them on a surface and you do it well, they make a nice, crystalline lattice," Gelb says. "If you do mixtures of two sizes you can get a number of different patterns with them. But if the particles aren't round, if they are short rods or things with more structure, it gets much more complicated quickly, and there's much less known about that."
The chemists also studied all 21 mixtures of two different shapes, as well as many combinations of three or more shapes.
"In all of the binary mixtures you get small-scale phase separation, which is counterintuitive," Gelb says. "It's not that the shapes repel each other. When there's no special repulsion between things or no stronger interaction between things of the same shape, you expect things to mix really well. In fact, that's not what happens."
Using ideas from classical thermodynamics and solution theory, the team was able to understand this separation using two different quantities. One is the virial coefficient, which measures the overlap between two shapes. They found that the shapes adopt alignments that minimize this overlap. Another is the volume of mixing. If you mix two liquids together, the volume of the mixture isn't necessarily the same as the volume of pure liquids you started with. In a mixture of water and ethanol, for instance, the volume of the mixture is smaller by about five percent than the sum of the original volumes. They found that in this model the volume always goes up when mixing different shapes.
Small world
"That's another indication that they don't mix well," Gelb says. "They take up more space when you mix them than when you allow them to be separate."
The model provides information on a very small world.
"If you think of the shapes as molecules sticking to a crystalline surface they would be a few Angstroms wide," says Barnes. "If you relate the model to nanoparticles, the shapes would be much larger, on the scale of tens of nanometers across."
In explaining the alignment phenomenon, Siderius offers the analogy of a roomful of people trying to circulate among each other.
"If they're all randomly placed, they'd bump shoulders frequently," he says. "But if they aligned a bit, everyone could move around more freely, which increases the entropy. In the past, we'd think of an ordered system as being low in entropy, but in this case the ordered state is high entropy."
Does it have anything to do with Tetris?
"Well, it suggests that one of the reasons the game is difficult is that the shapes don't fit together as well as we might think," says Gelb. "That, and they come down too fast."
The results were published in the on-line edition of the journal Langmuir on April 27, 2009
Journal reference:
Barnes et al. Structure, Thermodynamics, and Solubility in Tetromino Fluids. Langmuir, 2009; 090427084503036 DOI: 10.1021/la900196b
Adapted from materials provided by Washington University in St. Louis.

Silicon Can Work For New-Age Spintronics Applications

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http://www.sciencedaily.com/releases/2007/10/071026162320.htm

ScienceDaily (Oct. 31, 2007) — In a rapid follow-up to their achievement as the first to demonstrate how an electron's spin can be electrically injected, controlled and detected in silicon, electrical engineers from the University of Delaware and Cambridge NanoTech now show that this quantum property can be transported a marathon distance in the world of microelectronics-- through an entire silicon wafer.

The finding confirms that silicon--the workhorse material of present-day electronics--now can be harnessed up for new-age spintronics applications.
The results mark another major steppingstone in the pioneering field of spintronics, which aims to use the intrinsic “spin” property of electrons versus solely their electrical charge for the cheaper, faster, lower-power processing and storage of data than present-day electronics can offer.
The research team included Ian Appelbaum, UD assistant professor of electrical and computer engineering, and his doctoral student, Biqin Huang, and Douwe Monsma, of Cambridge NanoTech in Cambridge, Mass. Huang was the lead author of the article.*
“Our new result is significant because it means that silicon can now be used to perform many spin manipulations both within the space of thousands of devices and within the time of thousands of logic operations, paving the way for silicon-based spintronics circuits,” Appelbaum said.
In Appelbaum's lab at UD, the team fabricated a device that injected high-energy, “hot” electrons from a ferromagnet into the silicon wafer. Another hot-electron structure (made by bonding two silicon wafers together with a thin-film ferromagnet) detected the electrons on the other side.
“Electron spin has a direction, like 'up' or 'down,' ” Appelbaum said. “In silicon, there are normally equal numbers of spin-up and -down electrons. The goal of spintronics is to use currents with most of the electron spins oriented, or polarized, in the same direction.”
In another recent paper published in the Aug. 13 issue of Applied Physics Letters, the team showed how to attain very high spin polarization, achieving more than 37 percent, and then demonstrated operation as the first semiconductor spin field-effect transistor.
“One hundred percent polarization means that all injected electrons are either spin-up or spin-down,” Huang explained. “High polarization will be necessary for practical applications.”
“In the future, spintronics may bring a great change to daily life,” Huang added.
“We're taking the first steps at the beginning of a new road,” Appelbaum said. “Before our initial work on spin transport in silicon, we didn't even know where the road was,” he said with a smile. “There's a lot of fundamental work to be done, which we hope will bring us closer to a new age of electronics.”
*The article was published in the Oct. 26 issue of the American Physical Society's journal Physical Review Letters.
Adapted from materials provided by University of Delaware.

Fausto Intilla

www.oloscience.com