Using Musical Chords To Analyze And Illustrate Hydrogen Molecule's Response To Laser Pulses

Daily Science Journal (Feb. 10, 2008) — For Kansas State University physics professor Uwe Thumm, confirmation of a theory about the behavior of small molecules became music to his ears -- literally. He and colleagues in Heidelberg, Germany, have shown how a hydrogen molecule responds to laser pulses by using the changing musical chord created by the molecule's vibrational motion.

Researchers in Heidelberg visualized the development over time of molecular resonance. The distance between the two nuclei (R) in the heavy hydrogen (deuterium) ion D2+ is plotted against the time. After approximately 100 femtoseconds, the wave packet, i.e. the location of the nuclei, starts to become hazy, after 400 femtoseconds there is a "revival" and the wave packet is put back together again. (Credit: Max Planck Institute for Nuclear Physics)

Thumm is a member of K-State's J.R. Macdonald Laboratory, where he is among several researchers who work on the properties and behavior of atoms and small molecules.

For decades, researchers had used the Macdonald Laboratory to make atoms and molecules collide with particles. Thumm said much of what scientists know about atoms and molecules is based on such collision experiments. To predict and explain what happens in these collisions, a large group of experimental physicists works closely with Thumm and two other theorists. The theorists use computers, make models and crunch numbers with the hope of producing results that are compatible with what experiments show.

Thanks to improvements in laser technology, around 1999 the Macdonald Laboratory researchers realized that they could transfer a lot of their expertise in atomic collisions to study in detail what happens when atoms and molecules get irradiated by very intense laser light. The new laser systems in the laboratory offer some advantages over the big particle accelerators, Thumm said. The laser pulses offer more control and can be made so short that the researchers now routinely observe the motion of nuclei inside small molecules in time. In addition, the laser pulses' peak intensity is enormous and would equal all of the sun's light focused onto a small spot of the size of a postage stamp or smaller.

Motivated by these opportunities, Thumm and his colleagues became curious about figuring out what would happen if the smallest and simplest molecule, hydrogen, were exposed to such ultra short and intense laser pulses. Together with his postdoctoral collaborator Bernold Feuerstein, Thumm developed a model and did calculations to determine how laser pulses influence the motion of the two protons in the hydrogen molecule.

"The short answer is that the laser pulse either makes the molecules vibrate more violently or blows them apart," Thumm said. He said this wasn't surprising because in the hydrogen molecule, two protons are connected by two electrons that function like a spring. When hit with the laser pulses, the protons oscillate back and forth.

Although this model may be easy to imagine on a large scale, Thumm said particles behave differently at the quantum level. This means that determining the locations of these oscillating protons isn't easy. Thumm described determining the protons' movements after being hit with the laser like what happens if you drop a marble in a bathtub. Looking at the circular ripples of water in the center of the tub, it's pretty easy to tell where the marble was dropped in. But when those ripples bounce off the sides of the tub, the wave pattern changes shape, and it becomes harder to tell where the marble was dropped. The wave gets delocalized. Thumm said the same thing happens to the protons not in a matter of seconds, but in a matter of femtoseconds -- that's a billionth of a millionth of a second. After about 60 femtoseconds, it's impossible to tell where the protons are.

"You quickly loose track of what the distance between the two protons is," Thumm said." All you can say is that they have a certain likelihood of being at a certain distance. This is in agreement with the bathtub experiment: Seconds after the marble was dropped, you can't tell where exactly it plunged in."

But things work differently at the quantum level, and the researchers were surprised that about 600 femtoseconds after being hit with the laser, the distance between the protons again becomes well defined. "We call this a revival of the original motion of the protons," Thumm said. "It's not going to happen in the bathtub, but it happens at the quantum level."

Thumm and Feuerstein published their theoretical prediction in 2003. Thumm said that they were pleasantly surprised when experiments at the Max-Planck Institute in Heidelberg, Germany, in 2006 confirmed the revival described in their model. "The agreement between the new experiments and our model was almost perfect and exceeded our expectations," Thumm said.

Feuerstein had since moved to Heidelberg, where he and his group of researchers continued to collaborate with Thumm's group at K-State. Excited about the success of their model, they began to analyze the molecule's vibrational motion by breaking it down into its various frequencies. Each frequency being like a note in a chord, the frequencies told researchers how the protons were behaving. However, the frequency of these molecular vibrations is way above the audible range. The two researchers share an interest in music and had collaborated musically before. So when it came time to illustrate the revival, they decided the best way to do it was to scale the frequencies down to 1,000 Hertz, which is in the range at which the human ear hears best. "This way you can listen to the vibrations and hear the revival. In the same way sound is analyzed and decomposed, we decomposed the vibration with regard to the frequencies," Thumm said. Their result, a changing musical chord coupled with a movie illustrating the protons' vibrations can be heard and viewed at http://www.mpg.de/video/FilmundoAudio-KdM.wmv

Thumm said researchers hope to be able to do the same thing for more complex molecules like water or methane. Just as a C Major chord sounds different from a d minor chord, Thumm said other molecules also would have their own unique sound. Thumm and Feuerstein's most recent work was first published last fall in the Physical Review Letters. Their research was supported by the National Science Foundation, the U.S. Department of Energy and the Max-Planck Society. Thumm said such basic research supports the long-term goal of applying lasers to steer chemical reactions. The hope is to largely increase the efficiency of chemical reactions by enhancing desired reaction pathways with lasers, he said.

Adapted from materials provided by Kansas State University.

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Particle Accelerator May Reveal Shape Of Alternate Dimensions

Daily Science Journal (Feb. 6, 2008) — When the world's most powerful particle accelerator starts up later this year, exotic new particles may offer a glimpse of the existence and shapes of extra dimensions.

A new particle accelerator, the Large Hadron Collider, is scheduled to begin operating later this year near Geneva, Switzerland. (Credit: CERN)

Researchers from the University of Wisconsin-Madison and the University of California-Berkeley say that the telltale signatures left by a new class of particles could distinguish between possible shapes of the extra spatial dimensions predicted by string theory.

String theory, which describes the fundamental particles of the universe as tiny vibrating strings of energy, suggests the existence of six or seven unseen spatial dimensions in addition to the time and three space dimensions that we normally see.

Much as the shape of a musical instrument determines its sound, the shape of these dimensions determines the properties and behavior of our four-dimensional universe, says Gary Shiu, lead author of a paper appearing in the Jan. 25 issue of Physical Review Letters.

"The shape of the dimensions is crucial because, in string theory, the way the string vibrates determines the pattern of particle masses and the forces that we feel," says the UW-Madison physics professor.

Zeroing in on that shape should further our understanding and predictions of our four-dimensional world, Shiu says. "There are myriad possibilities for the shapes of the extra dimensions out there. It would be useful to know a way to distinguish one from another and perhaps use experimental data to narrow down the set of possibilities."

Such experimental evidence could appear in data from a new particle accelerator, the Large Hadron Collider, scheduled to begin operating later this year near Geneva, Switzerland.

In an accelerator, smashing atomic nuclei head-on at nearly the speed of light can briefly create new high-energy and highly unstable particles, which quickly decay into a shower of detectable lower energy ones. Characteristic patterns of decay serve as fingerprints of the fleeting exotic particles and, possibly, the shape of the unseen dimensions.

With colleagues Bret Underwood and Kathryn Zurek at UW-Madison and Devin Walker at UC-Berkeley, Shiu shows in the new study that the signature patterns from particles called Kaluza-Klein (KK) gravitons can distinguish between different proposed extra-dimensional geometries.

How" Shiu compares the effect to a darkened room in which patterns of sound resonating off the walls can reveal the shape of the room. Similarly, KK gravitons are sensitive to the extra-dimensional shape and, through their behavior and decay, may reveal clues to that shape.

The current study shows that, in simulations, even small geometric variations lead to visible differences in KK graviton signatures, Underwood says.

Based on these results, Shiu says, "At least in principle, one may be able to use experimental data to test and constrain the geometry of our universe."

Last year, Shiu and Underwood reported that clues to dimensional geometries might also be visible in patterns of cosmic radiation left over from the Big Bang. The new work complements the previous approach, they say.

"The more hints we get, the better idea we have about the underlying physics," says Shiu.

Adds Underwood, "If the cosmology and particle physics data agree, it's an indication we're on the right track."

The work was supported by the National Science Foundation, the U.S. Department of Energy, the Research Corporation, and a University of California Presidential Fellowship.

Adapted from materials provided by University of Wisconsin-Madison.

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Researchers Create Gold Aluminum, Black Platinum, Blue Silver Using Tabletop Laser

Daily Science Journal (Feb. 2, 2008) — Using a tabletop laser, University of Rochester optical scientists have turned pure aluminum, gold. And blue. And gray. And many other colors. And it works for every metal tested, including platinum, titanium, tungsten, silver, and gold.

Gold Aluminum, Blue Titanium, Gold Platinum. (Credit: Richard Baker, University of Rochester)

Chunlei Guo, the researcher who a year ago used intense laser light to alter the properties of a variety of metals to render them pitch black, has pushed the same process further in a paper in today's Applied Physics Letters. He now believes it's possible to alter the properties of any metal to turn it any color—even multi-colored iridescence like a butterfly's wings.

Since the process changes the intrinsic surface properties of the metal itself and is not just a coating, the color won't fade or peel, says Guo, associate professor of optics at the Institute of Optics at the University of Rochester. He suggests the possibilities are endless—a cycle factory using a single laser to produce bicycles of different colors; etching a full-color photograph of a family into the refrigerator door; or proposing with a gold engagement ring that matches your fiancée's blue eyes.

"Since the discovery of the black metal we've been determined to get full control on getting metals to reflect only a certain color and absorb the rest, and now we finally can make a metal reflect almost any color we wish," says Guo. "When we first found the process that produced a gold color, we couldn't believe it. We worked in the lab until midnight trying to figure out what other colors we could make."

Guo and his assistant, Anatoliy Vorobeyv, use an incredibly brief but incredibly intense laser burst that changes the surface of a metal, forming nanoscale and microscale structures that selectively reflect a certain color to give the appearance of a specific color or combinations of colors.

The metal-coloring research follows up on Guo's breakthrough "black metal" discovery in late 2006, when his research team was able to create nanostructures on metal surfaces that absorbed virtually all light, making something as simple as regular aluminum into one of the darkest materials ever created.

Guo's black metal, with its very high absorption properties, is ideal for any application where capturing light is desirable. The potential applications range from making better solar energy collectors, to more advanced stealth technology, he says. The ultra-brief/ultra-intense light Guo uses is produced by a femtosecond laser, which produces pulses lasting only a few quadrillionths of a second. A femtosecond is to a second what a second is to about 32 million years. During its brief burst, Guo's laser unleashes as much power as the entire electric grid of North America does, all focused onto a spot the size of a needlepoint.

The intense blast forces the surface of the metal to form nanostructures—pits, globules, and strands that response incoming light in different ways depending on the way the laser pulse sculpted the structures. Since the structures are smaller than the wavelength of light, the way they reflect light is highly dependent upon their specific size and shape, says Guo. Varying the laser intensity, pulse length, and number of pulses, allows Guo to control the configuration of the nanostructures, and hence control what color the metal reflects.

Guo and Vorobyev also achieve the iridescent coloring by creating microscale lines covered with nanostructures. The lines, arranged in regular rows, cause reflected light of different wavelengths to interfere differently in different directions. The result is a piece of metal that can appear solid purple from one direction, and gray from another, or multiple colors all at once.

To alter an area of metal the size of a dime currently takes 30 minutes or more, but the researchers are working on refining the technique. Fortunately, despite the incredible intensity involved, the femtosecond laser can be powered by a simple wall outlet, meaning that when the process is refined, implementing it should be relatively simple.

The new process has worked on every metal Guo has tried, and the results are so consistent that he believes it will work for every metal known. His team is currently working to find the right tuning to create the rest of the rainbow for the solid-colored metal, including red and green.

Adapted from materials provided by University of Rochester.

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Scientists Propose Test Of String Theory Based On Neutral Hydrogen Absorption

Daily Science Journal (Feb. 1, 2008) — Ancient light absorbed by neutral hydrogen atoms could be used to test certain predictions of string theory, say cosmologists at the University of Illinois. Making the measurements, however, would require a gigantic array of radio telescopes to be built on Earth, in space or on the moon.

This image reveals the first galaxies to emerge from the so-called "dark ages," the time shortly after the big bang when the first stars reheated the cold, dark universe. A network of strings is predicted by string theory to have been produced in the early universe. (Credit: NASA/ESA/S. Beckwith(STScI) and The HUDF Team)

String theory -- a theory whose fundamental building blocks are tiny one-dimensional filaments called strings -- is the leading contender for a "theory of everything." Such a theory would unify all four fundamental forces of nature (the strong and weak nuclear forces, electromagnetism, and gravity). But finding ways to test string theory has been difficult.

Now, cosmologists at the U. of I. say absorption features in the 21-centimeter spectrum of neutral hydrogen atoms could be used for such a test.

"High-redshift, 21-centimeter observations provide a rare observational window in which to test string theory, constrain its parameters and show whether or not it makes sense to embed a type of inflation -- called brane inflation -- into string theory," said Benjamin Wandelt, a professor of physics and of astronomy at the U. of I.

"If we embed brane inflation into string theory, a network of cosmic strings is predicted to form," Wandelt said. "We can test this prediction by looking for the impact this cosmic string network would have on the density of neutral hydrogen in the universe."

Wandelt and graduate student Rishi Khatri describe their proposed test in a paper accepted for publication in the journal Physical Review Letters.

About 400,000 years after the Big Bang, the universe consisted of a thick shell of neutral hydrogen atoms (each composed of a single proton orbited by a single electron) illuminated by what became known as the cosmic microwave background.

Because neutral hydrogen atoms readily absorb electromagnetic radiation with a wavelength of 21 centimeters, the cosmic microwave background carries a signature of density perturbations in the hydrogen shell, which should be observable today, Wandelt said.

Cosmic strings are filaments of infinite length. Their composition can be loosely compared to the boundaries of ice crystals in frozen water.

When water in a bowl begins to freeze, ice crystals will grow at different points in the bowl, with random orientations. When the ice crystals meet, they usually will not be aligned to one another. The boundary between two such misaligned crystals is called a discontinuity or a defect.

Cosmic strings are defects in space. A network of strings is predicted by string theory (and also by other supersymmetric theories known as Grand Unified Theories, which aspire to unify all known forces of nature except gravity) to have been produced in the early universe, but has not been detected so far. Cosmic strings produce characteristic fluctuations in the gas density through which they move, a signature of which will be imprinted on the 21-centimeter radiation.

The cosmic string network predicted to occur with brane inflation could be tested by looking for the corresponding fluctuations in the 21-centimeter radiation.

Like the cosmic microwave background, the cosmological 21-centimeter radiation has been stretched as the universe has expanded. Today, this relic radiation has a wavelength closer to 21 meters, putting it in the long-wavelength radio portion of the electromagnetic spectrum.

To precisely measure perturbations in the spectra would require an array of radio telescopes with a collective area of more than 1,000 square kilometers. Such an array could be built using current technology, Wandelt said, but would be prohibitively expensive.

If such an enormous array were eventually constructed, measurements of perturbations in the density of neutral hydrogen atoms could also reveal the value of string tension, a fundamental parameter in string theory, Wandelt said. "And that would tell us about the energy scale at which quantum gravity begins to become important."

Funding was provided by the Alexander von Humboldt Foundation.

Adapted from materials provided by University of Illinois at Urbana-Champaign.

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Computer Scientist Makes Splash With Academy Award For Fluid Simulation

Daily Science Journal (Jan. 31, 2008) — The rushing floodwaters in Evan Almighty, the heaving seas of the latter two Pirates of the Caribbean movies and the dragon's flaming breath in Harry Potter and the Goblet of Fire all featured computer-generated fluids in spectacular action. The science behind those splashy thrills will be recognized Feb. 9 with an Academy Award for Ron Fedkiw, associate professor of computer science at Stanford, and two collaborators at the special effects firm Industrial Light and Magic (ILM).

A computer-generated scene shows off the fluid simulation technology developed by computer science Associate Professor Ron Fedkiw, former students, and collaborators at Industrial Light and Magic. (Credit: Frank Losasso, Jerry Talton, Nipun Kwatra, Ron Fedkiw / courtesy of Stanford University)

"The primary work started a few years ago when we developed a system designed for the female liquid terminator in Terminator 3," Fedkiw said. "Almost immediately after that it was used in the first Pirates of the Caribbean movie to simulate the wine that the pirate skeleton was drinking out of the bottle in the moonlight. Things like the sinking ship in Poseidon and the large water whirlpool in Pirates of the Caribbean 3 are good examples of the system in action."

The system, co-developed with ILM scientists Nick Rasmussen and Frank Losasso Petterson (a former doctoral student of Fedkiw's), uses a method of simulating low-viscosity fluids such as water and fire, as in the explosions in Star Wars: Revenge of the Sith.

Contributing to a Star Wars movie was a particular honor for Fedkiw.

"George Lucas made Star Wars and, well, that changed the world for a lot of us," he said. "It's amazing what a movie can do to a civilization. I can only be grateful that he made three more of them and that I started working with ILM just in time to get a screen credit on the last one."

Lifelike liquids

Computer graphics experts typically have used particles and complex blobs to represent water, but these can give rise to unrealistically lumpy or grainy surfaces. Alternatively, they have used a technique called "the level set method" that gives a smooth surface representation, but some water is "under-resolved" and simply disappears when it breaks down into small volumes, as in a crashing wave.

The key innovation behind Fedkiw and former doctoral student Douglas Enright's novel "particle level set method" was to mix the use of particles and level sets so that studios could maintain smooth surfaces wherever possible and still keep all the fluid via the particle representation.

"As an added bonus, the method automatically generates spray particles and bubbles in under-resolved regions where the level set [method] loses mass and volume," Fedkiw said.

Fedkiw gives a lot of the credit to his colleagues for the system used to make the movies: "Nick made the system and Frank made it rock."

The effect's power is clearly evident in a movie on Fedkiw's website. There, gigantic waves crash against a lighthouse and produce huge sprays. In addition to incorporating the particle level set method, the rendering also uses an additional method to simulate how the spray interacts with itself and the surrounding water.

Such integrations are indicative of a future direction of Fedkiw's computer graphics research.

"This year we built a system that allows two-way coupling between rigid and deformable bodies, so we can fully physically simulate bones moving around under flesh—interacting with the environment," he said. "Another main result is a two-way, solid-fluid coupling method that can be used with it, so the environment can be water; that is, we're going to be simulating people swimming."

Of course the more immediate future calls for a trip to the Beverly Wilshire Hotel in Beverly Hills for the Scientific and Technical Academy Awards presentation Feb. 9. Fedkiw says he'll probably go to pick up his plaque.

"After wearing sandals for the last two years—even in the Lake Tahoe snow— it's going to be tough to go black tie," he said.

Adapted from materials provided by Stanford University.

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New Kind Of Transistor Radios Shows Capability Of Nanotube Technology

Daily Science Journal (Jan. 30, 2008) — Carbon nanotubes have a sound future in the electronics industry, say researchers who built the world's first all-nanotube transistor radios to prove it.

Schematic exploded view of a radio-frequency transistor that uses parallel, aligned arrays of carbon nanotubes for the semiconductor. (Credit: Images courtesy John Rogers)

The nanotube radios, in which nanotube devices provide all of the active functionality in the devices, represent "important first steps toward the practical implementation of carbon-nanotube materials into high-speed analog electronics and other related applications," said John Rogers, a Founder Professor of Materials Science and Engineering at the University of Illinois.

Rogers is a corresponding author of a paper* that describes the design, fabrication and performance of the nanotube-transistor radios, which were achieved in a close collaboration with radio frequency electronics engineers at Northrop Grumman Electronics Systems in Linthicum, Md.

"These results indicate that nanotubes might have an important role to play in high-speed analog electronics, where benchmarking studies against silicon indicate significant advantages in comparably scaled devices, together with capabilities that might complement compound semiconductors," said Rogers, who also is a researcher at the Beckman Institute and at the university's Frederick Seitz Materials Research Laboratory.

Practical nanotube devices and circuits are now possible, thanks to a novel growth technique developed by Rogers and colleagues at the U. of I., Lehigh and Purdue universities, and described last year in the journal Nature Nanotechnology.

The growth technique produces linear, horizontally aligned arrays of hundreds of thousands of carbon nanotubes that function collectively as a thin-film semiconductor material in which charge moves independently through each of the nanotubes. The arrays can be integrated into electronic devices and circuits by conventional chip-processing techniques.

"The ability to grow these densely packed horizontal arrays of nanotubes to produce high current outputs, and the ability to manufacture the arrays reliably and in large quantities, allows us to build circuits and transistors with high performance and ask the next question," Rogers said. "That question is: 'What type of electronics is the most sensible place to explore applications of nanotubes"' Our results suggest that analog RF (radio frequency) represents one such area."

As a demonstration of the growth technique and today's nanotube analog potential, Rogers and collaborators at the U. of I. and Northrop Grumman fabricated nanotube transistor radios, in which nanotube devices provided all of the key functions.

The radios were based on a heterodyne receiver design consisting of four capacitively coupled stages: an active resonant antenna, two radio-frequency amplifiers, and an audio amplifier, all based on nanotube devices. Headphones plugged directly into the output of a nanotube transistor. In all, seven nanotube transistors were incorporated into the design of each radio.

In one test, the researchers tuned one of the nanotube-transistor radios to WBAL-AM (1090) in Baltimore, to pick up a traffic report.

"We were not trying to make the world's tiniest radios," Rogers said. "The nanotube radios are a demonstration, an important milestone toward building the technology into a form that ultimately would be commercially competitive with entrenched approaches."

*The paper has been accepted for publication in the Proceedings of the National Academy of Sciences, and is to be published in PNAS Online Early Edition in the first week in February, 2008.

The work was funded by the National Science Foundation and the U.S. Department of Energy.

Adapted from materials provided by University of Illinois at Urbana-Champaign.

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First Fully-functional Radio From A Single Carbon Nanotube Created

Daily Science Journal (Oct. 31, 2007) — Make way for the real nanopod and make room in the Guinness World Records. A team of researchers with the U.S. Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab) and the University of California at Berkeley have created the first fully functional radio from a single carbon nanotube, which makes it by several orders of magnitude the smallest radio ever made.

This image, taken by a transmission electron microscope, shows a single carbon nanotube protruding from an electrode. This nanotube is less than a micron long and only 10 nanometers wide, or 10,000 times thinner than the width of a single human hair. When a radio wave of a specific frequency impinges on the nanotube, it begins to vibrate vigorously. An electric field applied to the nanotube forces electrons to be emitted from its tip. This electrical current may be used to detect the mechanical vibrations of the nanotube, and thus listen to the radio waves. (The waves shown in this image were added for visual effect, and are not part of the original microscope image.) (Credit: Courtesy Zettl Research Group, Lawrence Berkeley National Laboratory and University of California at Berkeley)

Wielding a single carbon nanotube 10,000 times smaller than a human hair, this is definitely the smallest radio yet. The nanotube vibrates at radio frequencies to receive the signal, then acts as both amplifier and demodulator. With only a battery and sensitive earphones, it can pick up AM or FM. With such a small receiver or transmitter, you could put a tracking collar on a bacterium.

“A single carbon nanotube molecule serves simultaneously as all essential components of a radio — antenna, tunable band-pass filter, amplifier, and demodulator,” said physicist Alex Zettl, who led the invention of the nanotube radio. “Using carrier waves in the commercially relevant 40-400 MHz range and both frequency and amplitude modulation (FM and AM), we were able to demonstrate successful music and voice reception.”

Given that the nanotube radio essentially assembles itself and can be easily tuned to a desired frequency band after fabrication, Zettl believes that nanoradios will be relatively easy to mass-produce. Potential applications, in addition to incredibly tiny radio receivers, include a new generation of wireless communication devices and monitors. Nanotube radio technology could prove especially valuable for biological and medical applications.

“The entire radio would easily fit inside a living cell, and this small size allows it to safely interact with biological systems,” Zettl said. “One can envision interfaces with brain or muscle functions, or radio-controlled devices moving through the bloodstream.”

It is also possible that the nanotube radio could be implanted in the inner ear as an entirely new and discrete way of transmitting information, or as a radically new method of correcting impaired hearing.

Zettl holds joint appointments with Berkeley Lab's Materials Sciences Division (MSD) and the UC Berkeley Physics Department where he is the director of the Center of Integrated Nanomechanical Systems. In recent years, he and his research group have created an astonishing array of devices out of carbon nanotubes - hollow tubular macromolecules only a few nanometers (billionths of a meter) in diameter and typically less than a micron in length – including sensors, diodes and even a motor. The nanotube radio, however, is the first that – literally – rocks!

“When I was a young kid, I got a transistor radio as a gift and it was the greatest thing I could imagine - music coming from a box I could hold in my hand!” Zettl said. “When we first played our nanoradio, I was just as excited as I was when I first turned on that transistor radio as a kid.”

The carbon nanotube radio consists of an individual carbon nanotube mounted to an electrode in close proximity to a counter-electrode, with a DC voltage source, such as from a battery or a solar cell array, connected to the electrodes for power. The applied DC bias creates a negative electrical charge on the tip of the nanotube, sensitizing it to oscillating electric fields. Both the electrodes and nanotube are contained in vacuum, in a geometrical configuration similar to that of a conventional vacuum tube.

Kenneth Jensen, a graduate student in Zettl’s research group, did the actual design and construction of the radio.

“We started out by making an exceptionally sensitive force sensor,” Jensen said.“Nanotubes are like tiny cat whiskers.Small forces, on the order of attonewtons, cause them to deflect a significant amount.By detecting this deflection, you can infer what force was acting on the nanotube. This incredible sensitivity becomes even greater at the nanotube’s flexural resonance frequency, which falls within the frequencies of radio broadcasts, cell phones and GPS broadcasting. Because of this high resonance frequency, Alex (Zettl) suggested that nanotubes could be used to make a radio.”

Although it has the same essential components, the nanotube radio does not work like a conventional radio. Rather than the entirely electrical operation of a conventional radio, the nanotube radio is in part a mechanical operation, with the nanotube itself serving as both antenna and tuner.

Incoming radio waves interact with the nanotube’s electrically charged tip, causing the nanotube to vibrate. These vibrations are only significant when the frequency of the incoming wave coincides with the nanotube’s flexural resonance frequency, which, like a conventional radio, can be tuned during operation to receive only a pre-selected segment, or channel, of the electromagnetic spectrum.

Amplification and demodulation properties arise from the needle-point geometry of carbon nanotubes, which gives them unique field emission properties. By concentrating the electric field of the DC bias voltage applied across the electrodes, the nanotube radio produces a field-emission current that is sensitive to the nanotube’s mechanical vibrations. Since the field-emission current is generated by the external power source, amplification of the radio signal is possible. Furthermore, since field emission is a non-linear process, it also acts to demodulate an AM or FM radio signal, just like the diode used in traditional radios.

“What we see then is that all four essential components of a radio receiver are compactly and efficiently implemented within the vibrating and field-emitting carbon nanotube,” said Zettl. “This is a totally different approach to making a radio - the exploitation of electro-mechanical movement for multiple functions. In other words, our nanotube radio is a true NEMS (nano-electro-mechanical system) device.”

Because carbon nanotubes are so much smaller than the wavelengths of visible light, they cannot be viewed with even the highest powered optical microscope. Therefore, to observe the critical mechanical motionof their nanotube radio, Zettl and his research team, which in addition to Jensen, also included post-doc Jeff Weldon and graduate student Henry Garcia, mounted their nanotube radio inside a high resolution transmission electron microscope (TEM). A sine-wave carrier radio signal was launched from a nearby transmitting antenna and when the frequencies of the transmitted carrier wave matched the nanotube resonance frequency, radio reception became possible.

“To correlate the mechanical motions of the nanotube to an actual radio receiver operation, we launched an FM radio transmission of the song Good Vibrations by the Beach Boys,” said Zettl. “After being received, filtered, amplified, and demodulated all by the nanotube radio, the emerging signal was further amplified by a current preamplifier, sent to an audio loudspeaker and recorded. The nanotube radio faithfully reproduced the audio signal, and the song was easily recognizable by ear.”

When the researchers deliberately detuned the nanotube radio from the carrier frequency, mechanical vibrations faded and radio reception was lost. A “lock” on a given radio transmission channel could be maintained for many minutes at a time, and it was not necessary to operate the nanotube radio inside a TEM. Using a slightly different configuration, the researchers successfully transmitted and received signals across a distance of several meters.

“The integration of all the electronic components of a radio happened naturally in the nanotube itself,” said Jensen. “Within a few hours of figuring out that our force sensor was in fact a radio, we were playing music!”

Added Zettl, “Our nanotube radio is sophisticated and elegant in the physics of its operation, but sheer simplicity in technical design. Everything about it works perfectly, without additional patches or tricks.”

Berkeley Lab’s Technology Transfer Department is now seeking industrial partners to further develop and commercialize this technology.

A paper on this work is now on-line at the Nano Letters Website. It will also be published in the November 2007 print edition of Nano Letters. The paper is entitled “Nanotube Radio” and the co-authors are Zettl, Jensen, Weldon and Garcia. In that same print edition, there appears a paper by Peter Burke and Chris Rutherglen of UC Irvine, reporting on the use of a carbon nanotube as a demodulator.

The nanotube radio research was supported by the U.S. Department of Energy and by the National Science Foundation within the Center of Integrated Nanomechanical Systems.

Berkeley Lab is a U.S. Department of Energy national laboratory located in Berkeley, California. It conducts unclassified scientific research and is managed by the University of California.

Adapted from materials provided by DOE/Lawrence Berkeley National Laboratory.

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You Thought Your Nano Was Small: Nano-sized Detector Turns Radio Waves Into Music

Daily Science Journal (Oct. 19, 2007) — Researchers in California report development of the world's first working radio system that receives radio waves wirelessly and converts them to sound signals through a nano-sized detector made of carbon nanotubes.

The "carbon nanotube radio" device is thousands of times smaller than the diameter of a human hair. The development marks an important step in the evolution of nano-electronics and could lead to the production of the world's smallest radio, the scientists say.

Peter Burke and Chris Rutherglen developed a carbon nanotube "demodulator" that is capable of translating AM radio waves into sound. In a laboratory demonstration, the researchers incorporated the detector into a complete radio system and used it to successfully transmit classical music wirelessly from an iPod to a speaker several feet away from the music player.

Although other researchers have developed nano-sized radio wave detectors in the past, the current study marks the first time that a nano-sized detector has been demonstrated in an actual working radio system, the scientists say. The study demonstrates the feasibility of making other radio components at the nanoscale in the future and may eventually lead to a "truly integrated nanoscale wireless communications system," they say. Such a device could have numerous industrial, commercial, medical and other applications.

Their findings appeared online October 17 and are scheduled for publication in the Nov. 14 print edition of ACS' Nano Letters.

Adapted from materials provided by American Chemical Society, via EurekAlert!, a service of AAAS.

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