Bilayer Graphene Works as an Insulator: Research Has Potential Applications in Digital and Infrared Technologies

ScienceDaily  — A research team led by physicists at the University of California, Riverside has identified a property of "bilayer graphene" (BLG) that the researchers say is analogous to finding the Higgs boson in particle physics.

BLG is formed when two graphene sheets are stacked in a special manner. Like graphene, BLG has high current-carrying capacity, also known as high electron conductivity. The high current-carrying capacity results from the extremely high velocities that electrons can acquire in a graphene sheet.Graphene, nature's thinnest elastic material, is a one-atom thick sheet of carbon atoms arranged in a hexagonal lattice. Because of graphene's planar and chicken wire-like structure, sheets of it lend themselves well to stacking.

The physicists report online Jan. 22 in Nature Nanotechnology that in investigating BLG's properties they found that when the number of electrons on the BLG sheet is close to 0, the material becomes insulating (that is, it resists flow of electrical current) -- a finding that has implications for the use of graphene as an electronic material in the semiconductor and electronics industries.

"BLG becomes insulating because its electrons spontaneously organize themselves when their number is small," said Chun Ning (Jeanie) Lau, an associate professor of physics and astronomy and the lead author of the research paper. "Instead of moving around randomly, the electrons move in an orderly fashion. This is called 'spontaneous symmetry breaking' in physics, and is a very important concept since it is the same principle that 'endows' mass for particles in high energy physics."

Lau explained that a typical conductor has a huge number of electrons, which move around randomly, rather like a party with ten thousand guests with no assigned seats at dining tables. If the party only has four guests, however, then the guests will have to interact with each other and sit down at a table. Similarly, when BLG has only a few electrons the interactions cause the electrons to behave in an orderly manner.

New quantum particle

Allan MacDonald, the Sid W. Richardson Foundation Regents Chair in the Department of Physics at The University of Texas at Austin and a coauthor on the research paper, noted that team has measured the mass of a new type of massive quantum particle that can be found only inside BLG crystals.

"The physics which gives these particles their mass is closely analogous to the physics which makes the mass of a proton inside an atomic nucleus very much larger than the mass of the quarks from which it is formed," he said. "Our team's particle is made of electrons, however, not quarks."

MacDonald explained that the experiment the research team conducted was motivated by theoretical work which anticipated that new particles would emerge from the electron sea of a BLG crystal.

"Now that the eagerly anticipated particles have been found, future experiments will help settle an ongoing theoretical debate on their properties," he said.

Practical applications

An important finding of the research team is that the intrinsic "energy gap" in BLG grows with increasing magnetic field.

In solid state physics, an energy gap (or band gap) refers to an energy range in a solid where no electron states can exist. Generally, the size of the energy gap of a material determines whether it is a metal (no gap), semiconductor (small gap) or insulator (large gap). The presence of an energy gap in silicon is critical to the semiconductor industry since, for digital applications, engineers need to turn the device 'on' or conductive, and 'off' or insulating.

Single layer graphene (SLG) is gapless, however, and cannot be completely turned off because regardless of the number of electrons on SLG, it always remains metallic and a conductor.

"This is terribly disadvantageous from an electronics point of view," said Lau, a member of UC Riverside's Center for Nanoscale Science and Engineering. "BLG, on the other hand, can in fact be turned off. Our research is in the initial phase, and, presently, the band gap is still too small for practical applications. What is tremendously exciting though is that this work suggests a promising route -- trilayer graphene and tetralayer graphene, which are likely to have much larger energy gaps that can be used for digital and infrared technologies. We already have begun working with these materials."

Lau and MacDonald were joined in the research by J. Velasco Jr. (the first author of the research paper), L. Jing, W. Bao, Y. Lee, P. Kratz, V. Aji, M. Bockrath, and C. Varma at UCR; R. Stillwell and D. Smirnov at the National High Magnetic Field Laboratory, Tallahassee, Fla.; and Fan Zhang and J. Jung at The University of Texas at Austin.

The research was supported by grants from the National Science Foundation, Office of Naval Research, FENA Focus Center, and other agencies.

Story Source:

The above story is reprinted from materials provided by University of California - Riverside.

Note: Materials may be edited for content and length. For further information, please contact the source cited above.

---

Journal Reference:

1. J. Velasco, L. Jing, W. Bao, Y. Lee, P. Kratz, V. Aji, M. Bockrath, C. N. Lau, C. Varma, R. Stillwell, D. Smirnov, Fan Zhang, J. Jung, A. H. MacDonald. Transport spectroscopy of symmetry-broken insulating states in bilayer graphene. Nature Nanotechnology, 2012; DOI:10.1038/nnano.2011.251

X-ray camera makes A-grade particle detector

ScienceDaily (Oct. 11, 2011) — In the particle identification business, two pieces of information are vital: energy and spatial location. By measuring its energy you can work out the mass of your mystery particle. From its spatial location on the surface of a detector, you can work out where the particle came from -- and therefore how big the event was that produced the particle in the first place.

For the range of energies close to one million electron volts (1 MeV) -- a popular energy range to probe, with uses in a variety of fields from cancer treatment research to astrochemistry -- there are currently two leading methods of detecting particles. But both are limited in the types of molecules they can detect, and both sacrifice one type of information -- spatial location or energy measurements -- for the other.

Now a group of nuclear physicists and molecular scientists from the Université Paris Sud and Hamamatsu Photonics have demonstrated a new type of detector that can do both of these jobs at the same time. Their device uses the CCD image sensor chip in a particular off-the-shelf X-ray camera. In the study, described in a paper accepted to the AIP's Review of Scientific Instruments, the experimenters accelerated charged atoms (or ions) of carbon at various energies above 1 MeV, then "caught" those atoms with the camera. A single ion impact with the camera produced a bright spot on the image sensor.

They also accelerated molecules containing carbon and hydrogen. Unfortunately, these bigger particles overwhelmed the CCD chip, wiping out the details.

To avoid saturating the sensor, the researchers came up with the solution of putting a piece of thin carbon foil in front of it. The foil breaks up the projectile molecules that collide with it and sends them, like shrapnel, to the sensor to be counted. The foil also allowed them to separate different types of molecules from one another when the molecules' signatures would otherwise have overlapped.

The researchers say they hope their new detector will open the door to a new class of tools in the study of complex molecules using high-energy accelerators.

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The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by American Institute of Physics, via EurekAlert!, a service of AAAS.

Journal Reference:

M. Chabot, G. Martinet, K. Be´roff, T. Pino, S. Bouneau, B. Genolini, X. Grave, K. Nguyen, C. le Gailliard, P. Rosier, G. Fe´raud, H. Friha, B. Villier. Detection of atomic and molecular mega-electron-volt projectiles using an x-ray charged coupled device camera. Review of Scientific Instruments, 2011; 82 (10): 103301 DOI: 10.1063/1.3640411

Note: If no author is given, the source is cited instead.

Disclaimer: Views expressed in this article do not necessarily reflect those of ScienceDaily or its staff.

View the original article here

X-ray camera makes A-grade particle detector

ScienceDaily (Oct. 11, 2011) — In the particle identification business, two pieces of information are vital: energy and spatial location. By measuring its energy you can work out the mass of your mystery particle. From its spatial location on the surface of a detector, you can work out where the particle came from -- and therefore how big the event was that produced the particle in the first place.

For the range of energies close to one million electron volts (1 MeV) -- a popular energy range to probe, with uses in a variety of fields from cancer treatment research to astrochemistry -- there are currently two leading methods of detecting particles. But both are limited in the types of molecules they can detect, and both sacrifice one type of information -- spatial location or energy measurements -- for the other.

Now a group of nuclear physicists and molecular scientists from the Université Paris Sud and Hamamatsu Photonics have demonstrated a new type of detector that can do both of these jobs at the same time. Their device uses the CCD image sensor chip in a particular off-the-shelf X-ray camera. In the study, described in a paper accepted to the AIP's Review of Scientific Instruments, the experimenters accelerated charged atoms (or ions) of carbon at various energies above 1 MeV, then "caught" those atoms with the camera. A single ion impact with the camera produced a bright spot on the image sensor.

They also accelerated molecules containing carbon and hydrogen. Unfortunately, these bigger particles overwhelmed the CCD chip, wiping out the details.

To avoid saturating the sensor, the researchers came up with the solution of putting a piece of thin carbon foil in front of it. The foil breaks up the projectile molecules that collide with it and sends them, like shrapnel, to the sensor to be counted. The foil also allowed them to separate different types of molecules from one another when the molecules' signatures would otherwise have overlapped.

The researchers say they hope their new detector will open the door to a new class of tools in the study of complex molecules using high-energy accelerators.

Recommend this story on Facebook, Twitter,
and Google +1:

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Story Source:

The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by American Institute of Physics, via EurekAlert!, a service of AAAS.

Journal Reference:

M. Chabot, G. Martinet, K. Be´roff, T. Pino, S. Bouneau, B. Genolini, X. Grave, K. Nguyen, C. le Gailliard, P. Rosier, G. Fe´raud, H. Friha, B. Villier. Detection of atomic and molecular mega-electron-volt projectiles using an x-ray charged coupled device camera. Review of Scientific Instruments, 2011; 82 (10): 103301 DOI: 10.1063/1.3640411

Note: If no author is given, the source is cited instead.

Disclaimer: Views expressed in this article do not necessarily reflect those of ScienceDaily or its staff.

View the original article here

Pocket Particle Accelerators Like This One Could Bring Safer Nuclear Power to Neighborhoods

Meet EMMA, the Electron Model of Many Applications
EMMA Installation Science and Technology Facilities Council-UK

A wee particle accelerator in the English countryside could be a harbinger of a safer, cleaner future of energy. Specifically, nuclear energy, but not the type that has wrought havoc in Japan and controversy throughout Europe and the U.S. It would be based on thorium, a radioactive element that is much more abundant, and much more safe, than traditional sources of nuclear power.

Some advocates believe small nuclear reactors powered by thorium could wean the world off coal and natural gas, and do it more safely than traditional nuclear. Thorium is not only abundant, but more efficient than uranium or coal — one ton of the silver metal can produce as much energy as 200 tons of uranium, or 3.5 million tons of coal, as the Mail on Sunday calculates it.

The newspaper took a tour of a small particle accelerator that could be used to power future thorium reactors. Nicknamed EMMA — the Electron Model of Many Applications — the accelerator would be used to jump-start fissile nuclear reactions inside a small-scale thorium power plant.

Thorium reactors would not melt down, in part because they require an external input to produce fission. Thorium atoms would release energy when bombarded by high-energy neutrons, such as the type supplied in a particle accelerator.

Providing that stimulus is one obstacle to building small thorium reactors — but a new generation of accelerators like EMMA, and someday potentially even smaller, luggage-sized ones — could do the job.

EMMA is the first non- scaling, fixed-field, alternating-gradient (NS-FFAG) accelerator, qualities that make it easier to operate and maintain, more reliable and compact, more flexible and more efficient, according to British researchers. Other particle accelerators use alternating electric fields, which require special safety measures to guard against microwave exposure, for instance. EMMA’s alternating magnetic field gradients are a more efficient and cheaper way to accelerate particles to higher energies. (Brookhaven National Laboratory explains in more detail here.)

EMMA operates at operates around 20 MeV, or 20 million electronvolts, a paltry amount for an atom accelerator. The Tevatron, for instance, accelerates particles to 1 tera-electron volts. The Large Hadron Collider is designed to speed them to 7 TeV. But thorium reactors would not need such high energies to initiate fusion.

British scientists are already working on a successor called PAMELA, the Particle Accelerator for Medical Applications, which will be used to treat cancer.

Click through to the Mail for a full tour of EMMA, its sister apparatus ALICE (Accelerators and Lasers In Combined Experiments), and a description of British efforts to produce thorium power.

[Mail on Sunday]

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Particle trap paves way for personalized medicine

ScienceDaily (May 24, 2011) — Sequencing DNA base pairs -- the individual molecules that make up DNA -- is key for medical researchers working toward personalized medicine. Being able to isolate, study and sequence these DNA molecules would allow scientists to tailor diagnostic testing, therapies and treatments based on each patient's individual genetic makeup.

But being able to isolate individual molecules like DNA base pairs, which are just two nanometers across -- or about 1/50,000th the diameter of a human hair -- is incredibly expensive and difficult to control. In addition, devising a way to trap DNA molecules in their natural aqueous environment further complicates things. Scientists have spent the past decade struggling to isolate and trap individual DNA molecules in an aqueous solution by trying to thread it through a tiny hole the size of DNA, called a "nanopore," which is exceedingly difficult to make and control.

Now a team led by Yale University researchers has proven that isolating individual charged particles, like DNA molecules, is indeed possible using a method called "Paul trapping," which uses oscillating electric fields to confine the particles to a space only nanometers in size. (The technique is named for Wolfgang Paul, who won the Nobel Prize for the discovery.) Until now, scientists have only been able to use Paul traps for particles in a vacuum, but the Yale team was able to confine a charged test particle -- in this case, a polystyrene bead -- to an accuracy of just 10 nanometers in aqueous solutions between quadruple microelectrodes that supplied the electric field.

Their device can be contained on a single chip and is simple and inexpensive to manufacture. "The idea would be that doctors could take a tiny drop of blood from patients and be able to run diagnostic tests on it right there in their office, instead of sending it away to a lab where testing can take days and is expensive," said Weihua Guan, a Yale engineering graduate student who led the project.

In addition to diagnostics, this "lab-on-a-chip" would have a wide range of applications, Guan said, such as being able to analyze how individual cells respond to different stimulation. While there are several other techniques for cell-manipulation available now, such as optical tweezers, the Yale team's approach actually works better as the size of the targets gets smaller, contrary to other approaches.

The team, whose findings appear in the May 23 Early Edition of the Proceedings of the National Academy of Sciences, used charged polystyrene beads rather than actual DNA molecules, along with a two-dimensional trap to prove that the technique worked. Next, they will work toward creating a 3-D trap using DNA molecules, which, at two nanometers, are even smaller than the test beads. They hope to have a working, 3-D trap using DNA molecules in the next year or two. The project is funded by a National Institutes of Health program that aims to sequence a patient's entire genome for less than $1,000.

"This is the future of personalized medicine," Guan said.

The project was directed by Mark Reed (Yale University) and Predrag Krstic (Oak Ridge National Laboratory). Other authors of the paper include Sony Joseph and Jae Hyun Park (Oak Ridge National Laboratory).

Story Source:

The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by Yale University, via EurekAlert!, a service of AAAS.

Journal Reference:

Weihua Guan, Sony Joseph, Jae Hyun Park, Predrag S. Krstic, Mark A. Reed. Paul trapping of charged particles in aqueous solution. Proceedings of the National Academy of Sciences, 2011; DOI: 10.1073/pnas.1100977108

Note: If no author is given, the source is cited instead.

Disclaimer: This article is not intended to provide medical advice, diagnosis or treatment. Views expressed here do not necessarily reflect those of ScienceDaily or its staff.

View the original article here

Particle trap paves way for personalized medicine

ScienceDaily (May 24, 2011) — Sequencing DNA base pairs -- the individual molecules that make up DNA -- is key for medical researchers working toward personalized medicine. Being able to isolate, study and sequence these DNA molecules would allow scientists to tailor diagnostic testing, therapies and treatments based on each patient's individual genetic makeup.

But being able to isolate individual molecules like DNA base pairs, which are just two nanometers across -- or about 1/50,000th the diameter of a human hair -- is incredibly expensive and difficult to control. In addition, devising a way to trap DNA molecules in their natural aqueous environment further complicates things. Scientists have spent the past decade struggling to isolate and trap individual DNA molecules in an aqueous solution by trying to thread it through a tiny hole the size of DNA, called a "nanopore," which is exceedingly difficult to make and control.

Now a team led by Yale University researchers has proven that isolating individual charged particles, like DNA molecules, is indeed possible using a method called "Paul trapping," which uses oscillating electric fields to confine the particles to a space only nanometers in size. (The technique is named for Wolfgang Paul, who won the Nobel Prize for the discovery.) Until now, scientists have only been able to use Paul traps for particles in a vacuum, but the Yale team was able to confine a charged test particle -- in this case, a polystyrene bead -- to an accuracy of just 10 nanometers in aqueous solutions between quadruple microelectrodes that supplied the electric field.

Their device can be contained on a single chip and is simple and inexpensive to manufacture. "The idea would be that doctors could take a tiny drop of blood from patients and be able to run diagnostic tests on it right there in their office, instead of sending it away to a lab where testing can take days and is expensive," said Weihua Guan, a Yale engineering graduate student who led the project.

In addition to diagnostics, this "lab-on-a-chip" would have a wide range of applications, Guan said, such as being able to analyze how individual cells respond to different stimulation. While there are several other techniques for cell-manipulation available now, such as optical tweezers, the Yale team's approach actually works better as the size of the targets gets smaller, contrary to other approaches.

The team, whose findings appear in the May 23 Early Edition of the Proceedings of the National Academy of Sciences, used charged polystyrene beads rather than actual DNA molecules, along with a two-dimensional trap to prove that the technique worked. Next, they will work toward creating a 3-D trap using DNA molecules, which, at two nanometers, are even smaller than the test beads. They hope to have a working, 3-D trap using DNA molecules in the next year or two. The project is funded by a National Institutes of Health program that aims to sequence a patient's entire genome for less than $1,000.

"This is the future of personalized medicine," Guan said.

The project was directed by Mark Reed (Yale University) and Predrag Krstic (Oak Ridge National Laboratory). Other authors of the paper include Sony Joseph and Jae Hyun Park (Oak Ridge National Laboratory).

Story Source:

The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by Yale University, via EurekAlert!, a service of AAAS.

Journal Reference:

Weihua Guan, Sony Joseph, Jae Hyun Park, Predrag S. Krstic, Mark A. Reed. Paul trapping of charged particles in aqueous solution. Proceedings of the National Academy of Sciences, 2011; DOI: 10.1073/pnas.1100977108

Note: If no author is given, the source is cited instead.

Disclaimer: This article is not intended to provide medical advice, diagnosis or treatment. Views expressed here do not necessarily reflect those of ScienceDaily or its staff.

View the original article here