Minuscule chips for NMR spectroscopy promise portability, parallelization

The small chips could be used in a portable spectrometer for on-demand applications in the field. Alternatively, they could be assembled in parallel to perform high-throughput NMR spectroscopy, dramatically accelerating molecular analysis in the laboratory. Credit: Dongwan Ha, Harvard SEAS

http://phys.org/news/2014-08-minuscule-chips-nmr-spectroscopy-portability.html

A team of engineers at the Harvard School of Engineering and Applied Sciences (SEAS), Schlumberger-Doll Research Center in Cambridge, Mass., and the University of Texas, Austin, have created a truly portable device for nuclear magnetic resonance (NMR) 
NMR spectroscopy is a technique that perturbs protons within a molecule to glean important clues about its structure. It can identify unknown substances, detect very slight variations in chemical composition, and measure how molecules interact, making it an essential tool in organic chemistry, structural biology, and drug discovery, as well as for quality control in many industries.

Led by Donhee Ham, Gordon McKay Professor of Electrical Engineering and Applied Physics at Harvard SEAS, and his student Dongwan Ha, Ph.D. '14, the team has dramatically shrunk the electronic spectrometer components, fitting them on a silicon chip smaller than a sesame seed. Combined with a compact permanent magnet, this minuscule spectrometer represents the smallest device that can presently perform multidimensional NMR spectroscopy—a process Ham calls "one of the most powerful analytical tools to determine molecular structures at atomic resolution."

Significantly reducing both the size and cost of the device—while also preserving the broad functionality of much larger spectroscopy setups—now enables the development of portable NMR spectrometers that could travel to remote sites for online, on-demand applications or simply to laboratories where massive, state-of-the-art systems would be prohibitively expensive. The chips can also operate accurately over a wide temperature range.

A paper demonstrating the use of this silicon-based chip with a compact permanent magnet will be published online this week in Proceedings of the National Academy of Sciences (PNAS).

"State-of-the-art NMR systems use very large superconducting magnets, and they are indeed necessary for probing the structure of complex molecules like proteins," says Ham. "But in many circumstances—for example, many experiments in biochemistry or organic chemistry, quality control in production lines, or chemical reaction monitoring—you're doing NMR on smaller molecules, and for those applications the big superconducting magnets may be avoided."

Permanent magnets, which have been made much smaller in recent years, are weaker than superconducting magnets but still adequate to resolve small-to-medium size hydrocarbons, drug compounds, and biomolecules such as metabolites and amino acids. The advent of these smaller magnets motivated Ham's team to try to miniaturize the electronic components of the spectrometer. Those components include the transmitter and receiver for radio-frequency signals that orchestrate complex proton motions and monitor the telltale responses that reveal the quantum-mechanical details of molecular structure.

In comparison to superconducting magnets, however, permanent magnets are far less stable. With slight changes in temperature, the magnetic field fluctuates and drifts—a severe challenge that accompanies the system miniaturization. Ha, who is the main architect of the silicon spectrometer chip and lead author of the paper in PNAS, overcame the thermal problem with a distinctly modern tactic.

"Not only did Dongwan design the chip, but he also came up with a way to use statistical distance minimization and entropy minimization to estimate the magnetic field drift and calibrate out its effect," explains Ham. "This signal-processing method obviates the need for physical thermal regulation for the permanent magnet, which would have added hardware and increased the power consumption. That would have defeated our aim of achieving portability."

While Ham and Ha demonstrated the tiny spectrometer chips for portable applications with the permanent magnet, they also see potential for a completely different application in conjunction with a larger superconducting magnet. The chips, they say, could one day be assembled into a massively parallel array in a superconducting magnet bore to tremendously accelerate analysis of complex molecules by performing many NMR spectroscopy experiments at once.

"An individual NMR spectroscopy experiment is inherently slow, taking several minutes to hours," says Ham. "Using a hundred of these cheap and small spectrometer chips in parallel within a superconducting magnet bore could counter the intrinsic slowness of NMR spectroscopy, enabling a high-throughput paradigm for pharmaceutical screening and structural biology. One year of testing could be completed in a few days. We have already started investigating this angle."

The research team has filed for a provisional patent on the miniature NMR spectrometer, and they are exploring avenues for commercialization with Harvard's Office of Technology Development (OTD).

"We see a strong opportunity to commercialize the IP that's emerged from this work," says Sam Liss, Director of Business Development in OTD. "The feedback has been very positive from pharmaceutical companies involved in drug discovery, as well as from companies poised to deliver next-generation instrumentation for spectroscopy applications."

 Explore further: Producing hyperpolarized xenon gas on a microfluidic chip

More information: Scalable NMR spectroscopy with semiconductor chips, PNAS, www.pnas.org/cgi/doi/10.1073/pnas.1402015111

Read more at: http://phys.org/news/2014-08-minuscule-chips-nmr-spectroscopy-portability.html#jCp

OT-Measuring the mass of 'massless' electrons

Hosang Yoon, Ph.D. '14, and Prof. Donhee Ham have measured the collective mass of electrons in graphene. (Photo by Eliza Grinnell, SEAS Communications.)


http://www.seas.harvard.edu/news/2014/06/measuring-mass-of-massless-electrons

TAMING GRAPHENE, HARVARD-LED RESEARCHERS SUCCESSFULLY MEASURE COLLECTIVE MASS OF ‘MASSLESS’ ELECTRONS IN MOTION

Cambridge, Mass. – June 23, 2014 – Individual electrons in graphene are massless, but when they move together, it’s a different story.

Graphene, a one-atom-thick carbon sheet, has taken the world of physics by storm—in part, because its electrons behave as massless particles. Yet these electrons seem to have dual personalities. Phenomena observed in the field of graphene plasmonics suggest that when the electrons move collectively, they must exhibit mass.

After two years of effort, researchers led by Donhee Ham, Gordon McKay Professor of Electrical Engineering and Applied Physics at the Harvard School of Engineering and Applied Sciences (SEAS), and his student Hosang Yoon, Ph.D.’14, have successfully measured the collective mass of ‘massless’ electrons in motion in graphene.

By shedding light on the fundamental kinetic properties of electrons in graphene, this research may also provide a basis for the creation of miniaturized circuits with tiny, graphene-based components.

The results of Ham and Yoon’s complex measurements, performed in collaboration with other experts at Columbia University and the National Institute for Materials Science in Japan, have been published online in Nature Nanotechnology.

“Graphene is a unique material because, effectively, individual graphene electrons act as though they have no mass. What that means is that the individual electrons always move at a constant velocity,” explains Ham. “But suppose we apply a force, like an electric field. The velocity of the individual electrons still remains constant, but collectively, they accelerate and their total energy increases—just like entities with mass. It’s quite interesting.”

Without this mass, the field of graphene plasmonics cannot work, so Ham’s team knew it had to be there—but until now, no one had accurately measured it.

“One of the greatest contributions of this work is that it is actually an extremely difficult measurement,” says Ham.

Prof. Donhee Ham and his student Hosang Yoon in the laboratory at the Harvard School of Engineering and Applied Sciences. (Photo by Eliza Grinnell, SEAS Communications.)

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As Newton’s second law dictates, a force applied to a mass must generate acceleration. Yoon and Ham knew that if they could apply an electric field to a graphene sample and measure the electrons’ resulting collective acceleration, they could then use that data to calculate the collective mass.

But the graphene samples used in past experiments were replete with imperfections and impurities—places where a carbon atom was missing or had been replaced by something different. In those past experiments, electrons would accelerate but very quickly scatter as they collided with the impurities and imperfections.

“The scattering time was so short in those studies that you could never see the acceleration directly,” says Ham.

To overcome the scattering problem, several smart changes were necessary.

First, Ham and Yoon joined forces with Philip Kim, a physics professor at Columbia who will join the Harvard faculty on July 1 as Professor of Physics and of Applied Physics. A Harvard graduate (Ph.D. ’99), Kim is well known for his pioneering fundamental studies of graphene and his expertise in fabricating high-quality graphene samples. The team was now able to reduce the number of impurities and imperfections by sandwiching the graphene between layers of hexagonal boron nitride, an insulating material with a similar atomic structure. By also collaborating with James Hone, a professor of mechanical engineering at Columbia, they designed a better way to connect electrical signal lines to the sandwiched graphene. And Yoon and Ham applied an electric field at a microwave frequency, which allows for the direct measurement of the electrons’ collective acceleration in the form of a phase delay in the current.

“By doing all this, we translated the situation from completely impossible to being at the verge of either seeing the acceleration or not,” says Ham. “However, the difficulty was still very daunting, and Hosang [Yoon] made it all possible by performing very fine and subtle microwave engineering and measurements—a formidable piece of experimentation.”

“To me, it was a victorious moment that finally justified a long-term effort, going through multiple trials and errors,” says Yoon, lead author of the paper in Nature Nanotechnology. “Until then, I wasn’t even sure if the experiment would really be possible, so it was like a ‘through darkness comes light’ moment.”

A schematic of the experimental setup. Ham and Yoon measured the change in phase of a microwave signal sent through the graphene. (Image courtesy of Hosang Yoon, Harvard SEAS.)

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Collective mass is a key aspect of explaining plasmonic behaviors in graphene. By demonstrating that graphene electrons exhibit a collective mass and by measuring its value accurately, Yoon says, “We think it will help people to understand and design more sophisticated plasmonic devices with graphene.”

The team’s experiments also revealed that, in graphene, kinetic inductance (the electrical manifestation of collective mass) is several orders of magnitude larger than another, far more commonly exploited property called magnetic inductance. This is important in the push toward smaller and smaller electronic circuitry—the main theme of modern integrated circuits—because it means the same level of inductance can be achieved in a far smaller area. Furthermore, Ham and Yoon say that this miniature graphene-based kinetic inductor could enable the creation of a solid-state voltage-controlled inductor, complementary to the widely used voltage-controlled capacitor. It could be used to substantially increase the frequency tuning range of electronic circuits, which is an important function in communication applications.

For now, the challenge remains to improve the quality of graphene samples so that the detrimental effects of electron scattering can be further reduced.

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Hosang Yoon is lead author of the paper in Nature Nanotechnology, with corresponding authors Donhee Ham at Harvard SEAS and Philip Kim at Columbia. Additional coauthors include Columbia professor James Hone, Columbia graduate students Carlos Forsythe and Lei Wang; Nikolaos Tombros, a former member of the Kim lab at Columbia, now at the University of Groningen in the Netherlands; Kenji Watanabe, chief researchers in optoelectronic materials at the National Institute for Materials Science (NIMS) in Japan; and Takashi Taniguchi, group leader in the Ultra-high Pressure Processes Group at NIMS.

This research was supported by the Air Force Office of Scientific Research, the Office of Naval Research, the National Science Foundation, and the Samsung Advanced Institute of Technology and its Global Research Opportunity program. Additional support was provided by the Nano Material Technology Development Program through the National Research Foundation of Korea funded by the Ministry of Science, ICT and Future Planning; the Columbia Optics and Quantum Electronics IGERT; and the Netherlands Organisation for Scientific Research.

Scientists bend light the ‘wrong’ way

Fiber optic cables carry light -- and Cornell scientists have managed to hide a flash of light in such a cable by making it "temporally invisible." (NIST.gov)

By Jesse Emspak

http://www.foxnews.com/scitech/2012/08/02/scientists-bend-light-wrong-way/
Materials that bend light in unnatural ways are often touted as the path to futuristic technologies such as cloaking devices and super-powered lenses. But such materials are hard to make, but scientists have now discovered a simpler way using electrons.
At Harvard University's School of Engineering and Applied Sciences, a team of researchers led by Hosang Yoon and Donhee Ham showed that using ordinary semiconductors and confining electrons to a two-dimensional plane they could make a material with a so-called negative refractive index that bends radio waves the “wrong” way, and does so a hundred times better than other methods.
A refractive index is a measure of how much a material bends light. An index of 1 means no bending at all. Diamonds have that nice prism effect because they have an index of about 2.42, whereas air bends light hardly at all. Light – and that includes radio waves – bends because as it travels through anything other than a vacuum it slows down. Most materials always have a positive refractive index. That means that if light is approaching a denser, higher-index material from a lower-index one it gets bent to the right if the denser stuff is on that same side.
This all changes if the material has a negative index – as metamaterials do. In that case, the bend would be to the left. An object surrounded by a metamaterial would scatter the light away from it, making it invisible.
The Harvard team’s radio-wave metamaterial itself won't make you invisible, but it could be used to make a kind of "superlens" for radio waves, boosting signals. Or it could divert radar away from a target.
['Invisibility Cloak' Renders Objects Hidden to the Naked Eye]
The researchers set up one micrometer-wide strips of aluminum-gallium-arsenide (a common semiconductor) parallel to each other. They then cooled the device to a few degrees above absolute zero and ran a current through it, while simultaneously applying an electric field to one end.
The electric field accelerates the electrons in one of the strips. Those accelerating electrons couple to those in the strip next to it, and so on. That creates an effect like people in a stadium doing the wave – the electrons don't move but they do couple with others.
This differs from other methods of coupling electrons, which use magnetic fields. In this case, it's an electric field, and the coupling is due to the acceleration of the electrons themselves, a phenomenon called kinetic inductance.
Yoon and Ham then fired a beam of microwaves at frequencies of 1-50 gigahertz at the accelerating electrons. They found that the beam was refracted the "wrong" way, with an index of refraction at up to -700. For comparison, diamond, one of the most refractive materials known for visible light, has an index of 2.42. Most metamaterials developed so far have indexes of between -1 and -5.
Ham told InnovationNewsDaily that the wave of electrons is a key piece of the effect. The electric field applied to the strips creates an effective wave of a specific frequency, so the electrons will refract radio waves in a certain range. But that range can be adjusted by simply raising or lowering the frequency of the field.
This system wouldn't work for visible light, as the semiconductors used aren't transparent. So the technology won’t lead to the creation of invisibility cloaks. But that doesn't mean it won't be possible later on.
Ham said future experiments will look at proving that the apparatus works with higher frequencies, in the terahertz and far infrared range.


Read more: http://www.foxnews.com/scitech/2012/08/02/scientists-bend-light-wrong-way/#ixzz22gf7XOIW