Technology Trends

It’s an antenna, it’s a nanomachine, and it’s a macroscopic quantum system. This antenna, made of 50 billion atoms, is so far the largest structure to display quantum mechanical movements. It’s also the fastest device of its kind in the world, oscillating about 1.5 billion times per second. Such technology might soon be used in our cell phones. But more importantly, this nanomechanical device bridges classic and quantum physics. Such ”mechanical/quantum mechanical hybrids could be used for quantum computing” in the future. Read more…

Here is the introduction from this Boston University news release.

A team of Boston University physicists led by Assistant Professor Pritiraj Mohanty developed the nanomechanical oscillator. Operating at gigahertz speeds, the technology could help further miniaturize wireless communication devices like cell phones, which exchange information at gigahertz frequencies. But, more important to the researchers, the oscillator lies at the cusp of classic physics, what people experience everyday, and quantum physics, the behavior of the molecular world.

Please note that this is the second appearance of Mohanty’s team in this space. I already mentioned their works back in October 2004 in “Nanomechanical Memory Outstrips Chip Technology.”

Now, let’s look at some — impressive — numbers.

Comprised of 50 billion atoms, the antenna built by Mohanty’s team is so far the largest structure to display quantum mechanical movements.

“It’s a truly macroscopic quantum system,” says Alexei Gaidarzhy, a graduate student in the BU College of Engineering’s Department of Aerospace and Mechanical Engineering. The device is also the fastest of its kind, oscillating at 1.49 gigahertz, or 1.49 billion times a second, breaking the previous record of 1.02 gigahertz achieved by a nanomachine produced by another group.

The above image shows different views of this nanomechanical structure. The center, (a), is a scanning electron micrograph of the suspended antenna oscillator. The nanomechanical antenna consists of a central silicon beam, 10.7 microns long and 400 nm wide, that bears a “paddle” array 500 nm long and 200 nm wide along each side. In (b), you can see a modal simulation of the antenna structure, showing the low frequency fundamental resonance mode. And in the high order collective mode (c), the paddles vibrate at their own natural frequency. (Credit: Pritiraj Mohanty, Boston University)

The research work has been published in a recent issue of Physical Review Letters on January 25, 2005 under the name “Evidence for Quantized Displacement in Macroscopic Nanomechanical Oscillators.” Here is a link to the abstract.

We report the observation of discrete displacement of nanomechanical oscillators with gigahertz-range resonance frequencies at millikelvin temperatures. The oscillators are nanomachined single-crystal structures of silicon, designed to provide two distinct sets of coupled elements with very low and very high frequencies. With this novel design, femtometer-level displacement of the frequency-determining element is amplified into collective motion of the entire micron-sized structure. The observed discrete response possibly results from energy quantization at the onset of the quantum regime in these macroscopic nanomechanical oscillators.

And here is a link to the full article (PDF format, 4 pages, 955 KB). The above illustration comes from this article.

Finally, for explanations written in — almost — plain English, you might read the news release quoted above.

Sources: Boston University, via EurekAlert!, February 9, 2005; and various websites

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• Nanotechnology
  
  
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• Science
  

Many teams of nanoscientists around the world want to be the first one to build quantum computers. To achieve this goal, they’re using artificial atoms — also known as ‘quantum dots.’ But even if they’re able to use them, not a single team has been able to consistently control their quantum mechanical states — or their properties — at the nanoscale. Now, a team from Ohio University claims it found a flaw in quantum dot construction and proposes a solution. And guess what? As it happens often in research, this new finding is based on a very simple fact: an interference between two physical phenomena. Read more…

[For example,] experimental scientists in Germany had blasted the quantum dots with light to create the quantum mechanical state needed to run a quantum computer. But they couldn’t consistently control that state, explained Sergio Ulloa, an Ohio University professor of physics and astronomy. Jose Villas-Boas, a postdoctoral fellow at Ohio University, Ulloa and Associate Professor Alexander Govorov developed theoretical models to learn what went wrong.

The problem, they argued, happens during the creation of the type of quantum dots under study. Using a molecular beam epitaxy chamber, scientists spray paint a surface with atoms under high temperatures, creating an atomic coating. As more layers are added, the quantum dots bead up on the surface like droplets of water, Ulloa said.

But a fine residue left behind on the surface that Ulloa calls the “wetting layer” can cause problems during experiments. When experimental scientists blasted the quantum dots with a beam of light in previous studies, the wetting layer caused interference, instead of allowing the light to enter the dot and trigger the quantum state, he explained.

The illustration above “shows a quantum dot (blue central bulge) bombarded from the top with laser light. The laser produces excitations (called excitons) inside the dot, and the electric fields generated by the top and bottom gold contacts pull the electrons (yellow) and holes (red) away. Other electrons/holes are undesirably produced instead on the wetting layer, causing interference. The semiconductor compounds used in these experiments are Gallium Arsenide (GaAs) and Indium Gallium Arsenide (InGaAs).” (Credit for image and legend: Jose Villas-Boas) Here is a link to a larger version.

The study suggests that scientists could tweak the process by re-focusing the beam of light or changing the duration of the light pulses to negate the effects of the wetting layer, Villas-Boas said. One experimental physicist already has used the theoretical finding to successfully manipulate a quantum dot in the lab, he added. “Now that they know the problem, they realize there are a few ways to avoid it,” Villas-Boas said.

The research work from these scientists at the Ohio University’s Nanoscale & Quantum Phenomena Institute has been published in a recent issue of Physical Review Letters on February 8, 2005 under the name “Decoherence of Rabi Oscillations in a Single Quantum Dot.” Here is a link to the abstract.

We develop a realistic model of Rabi oscillations in a quantum-dot photodiode. Based in a multiexciton density matrix formulation we show that for short pulses the two-level model fails and higher levels should be taken into account. This affects some of the experimental conclusions, such as the inferred efficiency of the state rotation (population inversion) and the deduced value of the dipole interaction. We also show that the damping observed cannot be explained using constant rates with fixed pulse duration. We demonstrate that the damping observed is in fact induced by an off-resonant excitation to or from the continuum of wetting layer states. Our model describes the nonlinear decoherence behavior observed in recent experiments.

And if you want to know more, but don’t want to buy the article, here is a link to the full article (PDF format, 5 pages, 221 KB), thanks to the invaluable arXiv.org website.

Finally, just in case you wouldn’t know anything about Rabi oscillations, please read Isidor Isaac Rabi’s biography. He won the Nobel Prize for Physics in 1944.

Sources: Andrea Gibson, Ohio University, via EurekAlert!, February 10, 2005; and various websites

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• Materials
  
  
• Nanotechnology
  
  
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• Quantum World
  

Researchers from the Netherlands, France and Portugal are working together on a European Union research project called H-Alpha Solar. And they have developed very thin flexible solar panels that can be woven into fabrics, reports the Scotsman in this article. In about three years, you’ll be able to wear jackets that will recharge your phones while you walk. Or you’ll become a very happy camper under a tent covered with flexible films of solar modules. No more batteries to carry! And there are even more good news. This will not empty your wallet. This technology is cheap, about $2 per watt. Read more… UPDATE (December 17, 2004): An alert reader named Julien posted a comment about this entry. A company based in Switzerland, Flexcell, is already selling flexible, custom-designed solar cells and modules. So you don’t have to wait for three years to buy some.

The Scotsman decided to start its article with a touch of humor.

Mobile phone users left talking to themselves when their battery runs out in the middle of a call could soon see an end to their frustration as scientists perfect a way to recharge electrical equipment while on the move.

Researchers are investigating ways flexible solar panels can be sewn into clothing and other textiles so electrical equipment can be recharged without being connected to a mains supply.

According to the New Scientist magazine, the project could soon lead to a tent whose flysheet charges batteries all day so campers can have light all night, or a roll-out plastic sheet which powers cells to operate a DVD player.

The European Union research project called H-Alpha Solar is at the origin of this technology.

For more information about the H-Alpha Solar project, you can read this EUROPA press release about “European research on photovoltaics and biomass” or this presentation named “H-Alpha Solar: Thin film, silicon based, plastic foil Solar Modules”(PDF format, 12 pages, 1.18 MB). Below are some pictures extracted from this presentation.

Now, let’s return to the Scotsman for some more details about the technology.

Gerrit Kroesen, a physicist at Eindhoven University of Technology in the Netherlands, who led the development team, said: “This technology will be a lot easier to handle than the old glass solar panels.”

His team has made its solar cells flexible simply by making them very thin, but the advance has also involved a degree of compromise in their ability to produce electricity efficiently. While cutting-edge solar panels now operate at an efficiency of about 20 per cent, the new flexible cells are only 7 per cent efficient. However, the manufacturers believe that the reduction in the generating capacity is worth accepting for a cell they believe will be more useful and robust.

So you’ll wear jackets with solar panels in three years. But will this be expensive? Not at all, according to the researchers.

A projected full-scale manufacturing plant would produce panels at a cost of under £1 per watt (about $1.94 or 1.45 euro). As such, an A4 sized panel sewn into the back of a jacket and costing less than £7 (about $13 or 10 euros)would charge a mobile phone during a summer stroll in the countryside. Provided mobile users kept within range of the transmitting masts that relay a call to the networks, phones would never again be out of action.

Is this good or bad? You’ll decide.

Sources: James Reynolds, The Scotsman, December 16, 2004; and various web sites

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• Energy
  
  
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This seems as a far-fetched idea, but scientists from the City University of New York think that “superfast trains of the future could glide over fluffy tracks like snowboarders over snow,” according to “Trains get fluffy,” an article published by Nature. They compared the lift forces experienced by red cell blood cells moving through our veins to the ones produced in snowboarding by skiers. And they concluded that the forces in presence were similar, and could be applied to high-speed trains. As long as you go fast enough, even a train can run on feathers, adds PhysicsWeb. The researchers think the future fluffy tracks, capable to support 50-ton trains, could be built by using goose feathers, like the ones found in pillows. So far, they don’t have a prototype for the tracks, but they already bought the pillows. Read more…

Let’s start with Nature.

In snow, this lift is created by air between the tiny ice crystals. When the snow is compressed by the weight of a board, the air is pushed out from the porous snow, exerting an upwards pressure on the board. This cushion of air means that there is very little friction slowing the snowboarder’s motion.

The same forces allow red blood cells to glide smoothly along our capillaries. A loose mesh of sugar-coated proteins on the vessel walls gets squeezed by the passage of a red blood cell, pushing out fluid from between the protein strands.

But why applying red cells blood and snowboarders’ behaviors to a high-speed train?

To find out whether the forces generated would be enough to support a whole train, team leader Sheldon Weinbaum, of the City University of New York, and his colleagues measured the lift force created when snow inside a cylinder is compressed by a piston.

During the first one and a half seconds or so of squeezing, there was a surge in upwards pressure as air was pushed out of the porous snow. Within a couple of seconds, this pressure dropped virtually to zero, as most of the air had drained away. This is why light, fluffy snow can support the heavy load of a snowboarder, provided that she doesn’t linger for longer than about a second.

It’s time to turn to PhysicsWeb for more technical details.

To measure the pressures that develop during snowboarding, Weinbaum and colleagues used a piston cylinder apparatus that was capable of reproducing the dynamic forces experienced by a moving snowboard. They calculated that the air trapped in the snow can easily support the weight of a 70-kg snowboarder. They also found that the pore pressure underneath a snowboard with a surface area of 5000 square centimetres is about 1.4 kilopascals.

Extrapolating these results to the case of a 50-ton high-speed train, Weinbaum and co-workers calculated that 9.8 kilopascals of pore pressure would be needed to support a train that was 25 metres long and 2 metres wide. According to the scientists, a porous material with a permeability of 10^-8 metres squared or smaller — such as goose down — could be used as a track that was capable of supporting the weight of the moving train.

You’ll find additional diagrams in the PhysicsWeb article. But the conclusion belongs to Nature.

The track would consist of two side walls, filled by fluffy material with the same bouncy properties as goose down. Goose down itself would be too costly for filling miles of track; but there are plenty of synthetic substitutes, like those used to fill cheap pillows.

Because the train would only be supported when travelling at high speed, so Weinbaum and colleagues suggest that the vehicles should have retractable wheels that run along the track side walls when the train slows down or as it gathers speed from a standing start.

Will we ever see such trains? As the researchers admit,  ”It’s a far-out idea.” But they do have the pillows.

For more information, the research work has been published by Physical Review Letters under the title “From Red Cells to Snowboarding: A New Concept for a Train Track.” Here is a link to the abstract.

Sources: Philip Ball, Nature, November 10, 2004; Belle Dumé, PhysicsWeb, November 10, 2004

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Biologists and physicists from the University of California, Santa Barbara (UCSB), have discovered living nanoscale ‘necklaces’. They were studying “microtubules from the brain tissue of a cow to understand the mechanisms leading to their assembly and shape.” And unexpectedly, they found that some divalent cations pushed these microtubules, which are nanotubes derived from cell cytoskeleton, to assemble into ‘necklaces’ of different shapes. Now they think their discovery could be used to deliver drugs or genes. These ‘necklaces’ also could be used to build biosensors or new optical nanomaterials. Read more…

Here is the description of the discovery.

The scientists studied microtubules from the brain tissue of a cow to understand the mechanisms leading to their assembly and shape. Microtubules are nanometer-scale hollow cylinders derived from cell cytoskeleton. In an organism, microtubules and their assembled structures are critical components in a broad range of cell functions — from providing tracks for the transport of cargo to forming the spindle structure in cell division. Their functions include the transport of neurotransmitters in neurons. The mechanism of their assembly within an organism has been poorly understood.

the researchers report the discovery of a new type of higher order assembly of microtubules. Positively-charged large, linear molecules (tri-, tetra- and penta-valent cations) resulted in a tightly bundled hexagonal grouping of microtubules — a result that was predicted. But unexpectedly, the scientists found that small, spherical divalent cations caused the microtubules to assemble into a “necklace.” They discovered distinct linear, branched and loop shaped necklaces.

And what can we expect from these living necklaces?

The scientists envision applications based on both the tight bundle and living necklace phases. For example, metallization of necklace bundles with different sizes and shapes would yield nanomaterials with controlled optical properties.

A more original application is in the area of using the assemblies — encased by a lipid bilayer — as drug or gene carriers where each nanotube may contain a distinct chemical, as noted by the team. In delivery applications the shape of the bundle determines its property. For example, the linear necklace phase with its higher surface to volume ratio would have a larger contact area and a faster delivery rate compared to the tight bundle phase.

The research work has been published online by the Proceedings of the National Academy of Sciences under the intriguing title “Higher-order assembly of microtubules by counterions: From hexagonal bundles to living necklaces.” It should appear in the printed version on November 16, 2004. Here is a link to the abstract of the paper.

For more information, you can visit the Materials Research Laboratory website at UCSB, and more specifically, the Biomaterial Microstructures page.

Sources: UCSB news release, via EurekAlert!, November 8, 2004; and various other websites

You also can read previous entries on this blog in the following categories.

• Biotechnology
  
  
• Materials
  
  
• Nanotechnology
  
  
• Physics