Molecular graphene heralds new era of 'designer electrons'

Researchers from Stanford University and the U.S. Department of Energy's SLAC National Accelerator Laboratory have created the first-ever system of "designer electrons" -- exotic variants of ordinary electrons with tunable properties that may ultimately lead to new types of materials and devices.

"The behavior of electrons in materials is at the heart of essentially all of today's technologies," said Hari Manoharan, associate professor of physics at Stanford and a member of SLAC's Stanford Institute for Materials and Energy Sciences, who led the research. "We're now able to tune the fundamental properties of electrons so they behave in ways rarely seen in ordinary materials."

Their first examples, recently reported in Nature, were hand-crafted, honeycomb-shaped structures inspired by graphene, a pure form of carbon that has been widely heralded for its potential in future electronics. Initially, the electrons in this structure had graphene-like properties; for example, unlike ordinary electrons, they had no mass and traveled as if they were moving at the speed of light in a vacuum. But researchers were then able to tune these electrons in ways that are difficult to do in real graphene.

To make the structure, which Manoharan calls molecular graphene, the scientists use a scanning tunneling microscope to place individual carbon monoxide molecules on a perfectly smooth copper surface. The carbon monoxide repels the free-flowing electrons on the copper surface and forces them into a honeycomb pattern, where they behave like graphene electrons.

To tune the electrons' properties, the researchers repositioned the carbon monoxide molecules on the surface; this changed the symmetry of the electron flow. In some configurations, electrons acted as if they had been exposed to a magnetic or electric field. In others, researchers were able to finely tune the density of electrons on the surface by introducing defects or impurities. By writing complex patterns that mimicked changes in carbon-carbon bond lengths and strengths in graphene, the researchers were able to restore the electrons' mass in small, selected areas.

"One of the wildest things we did was to make the electrons think they are in a huge magnetic field when, in fact, no real field had been applied,"Manoharan said. Guided by the theory developed by co-author Francisco Guinea of Spain, the Stanford team calculated the positions where carbon atoms in graphene should be to make its electrons believe they were being exposed to magnetic fields ranging from zero to 60 Tesla, more than 30 percent higher than the strongest continuous magnetic field ever achieved on Earth. The researchers then moved carbon monoxide molecules to steer the electrons into precisely those positions, and the electrons responded by behaving exactly as predicted -- as if they had been exposed to a real field.

"Our new approach is a powerful new test bed for physics," Manoharan said. "Molecular graphene is just the first in a series of possible designer structures. We expect that our research will ultimately identify new nanoscale materials with useful electronic properties."

Additional authors included Kenjiro K. Gomes, Warren Mar and Wonhee Ko of the Stanford Institute for Material and Energy Sciences. Francisco Guinea is a researcher at the Madrid Materials Science Institute. The research was supported by the U.S. Department of Energy's Office of Basic Energy Sciences, the National Science Foundation and the Spanish Ministry of Science & Innovation.

Story Source:

The above story is reprinted from materials provided by DOE/SLAC National Accelerator Laboratory.

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

Journal Reference:

Kenjiro K. Gomes, Warren Mar, Wonhee Ko, Francisco Guinea, Hari C. Manoharan. Designer Dirac fermions and topological phases in molecular graphene. Nature, 2012; 483 (7389): 306 DOI: 10.1038/nature10941

Tests to catch the makers of dangerous 'legal high' designer drugs

Urgently needed tests which could help identify the manufacturers of designer 'legal high' drugs are being developed in research led at the University of Strathclyde in Glasgow.

The drugs, known by names such as 'ivory wave' and NRG-1" and sold labelled as bath salts, plant food and incense, mimic the effects of illegal drugs such as amphetamine, cocaine and ecstasy. Although these so-called 'designer drugs' can be dangerous, many have not yet been made illegal and are difficult to detect with current drug tests.

A means of potentially tracing the source of the raw materials, and consequently providing information as to who is making the 'bath salts,' is being developed by scientists at Strathclyde and The James Hutton Institute.

The bath salts drug can cause euphoria, paranoia, anxiety and hallucinations. It often contains mephedrone, a synthetic compound structurally related to methcathinone, which is found in Khat - a plant which, like mephedrone itself, is illegal in many countries.

The bath salts drug is labelled as being not for human consumption and is not illegal in the UK but its import has been banned. The term 'bath salts' is used by those who sell the drug as a way of circumventing legislation when supplying it.

The researchers developing tests for the drug are using a technique known as isotope ratio mass spectrometry (IRMS) to reveal the course of a drug's manufacture.

The research is being carried out by Dr Oliver Sutcliffe, at the Strathclyde Institute of Pharmacy and Biomedical Sciences, and Professor Niamh Nic Daeid and Dr Katy Savage at the Centre for Forensic Science in the Department of Pure and Applied Chemistry, in collaboration with Dr Wolfram Meier-Augenstein at The James Hutton Institute.

Dr Sutcliffe said: "The legal status of designer drugs varies around the world but they present many dangers to users and these are borne out by the Home Office's decision to ban the import of 'bath salts.'

"The new method we have used has enabled us to work backwards and trace the substances back to their starting materials. IRMS measures the relative amounts of an element's different forms- it is successful because these relative amounts are transferred like a fingerprint through the synthesis of the drug."

Provided by University of Strathclyde

New tests for 'legal marijuana,' 'bath salts' and other emerging designer drugs

 

Scientists today reported development of much needed new tests to help cope with a wave of deaths, emergency room visits and other problems from a new genre of designer drugs sold legally in stores and online that mimic the effects of cocaine, ecstasy and marijuana. They spoke at the 242nd National Meeting & Exposition of the American Chemical Society (ACS).

The reports, among more than 7,500 on the ACS agenda, focus on drugs sold as "bath salts," "plant food," "incense" and other products with colorful names, such as "Ivory Wave," "Red Dove" and "legal marijuana." They provide users with a high, but many have not yet been made illegal and are undetectable with current drug tests. In one presentation on these "legal highs," a United Kingdom researcher reported a new method to trace the source of the substances in "bath salts." In the other, a U.S. researcher discussed the challenges facing law enforcement and policy makers in regulating synthetic versions of marijuana.

Oliver Sutcliffe, Ph.D., and his collaborators reported the successful use of a method called isotope ratio mass spectrometry (IRMS) to determine who is making bath salts — drugs that can cause euphoria, paranoia, anxiety and hallucinations when snorted, smoked or injected — and which chemical companies supplied the raw materials. He and his co-workers are based at the University of Strathclyde and the James Hutton Institute in the U.K.

"With the new method, we could work backwards and trace the substances back to the starting materials," said Sutcliffe. IRMS measures the relative amounts of an element's different forms, or isotopic ratio. "This method was successful because the isotopic ratio of the starting material is transferred like a fingerprint through the synthesis," he explained.

"Bath salts" first garnered major media attention in the U.K. in early 2010, and then became a problem in the U.S. These products are not in the supermarket soap aisle — they are sold on the Internet, on the street and in stores that sell drug paraphernalia. They are sold in small individual bags for as low as $20 each for the real purpose of providing a cheap, legal high.

The powders often contain mephedrone, which is a synthetic compound, structurally related to methcathinone, which is found in Khat — a plant that is illegal in many countries, including the U.K. and the U.S. Usually, that would mean that these compounds (and derivatives thereof) would be illegal in those countries too, but because the bath salts are labeled "not for human consumption," they get around this restriction and other legislation governing the supply of medicines for human use. However, Florida and Louisiana — two hotspots of bath salts abuse — specifically banned the substances. U.K. officials banned the import of bath salts, which may lead some in the drug trade to set up clandestine labs on U.K. soil, said Sutcliffe. The new method provides law enforcement with a tool to track down these bath salts manufacturers.

In previous work, Sutcliffe developed the first pure reference standard for mephedrone, as well as the first reliable liquid chromatography test for the substance, which could be easily run in a typical law enforcement lab. The team is also developing a color-change test kit for mephedrone, which he estimates may be available by the end of the year.

In another presentation, Robert Lantz, Ph.D., from the Rocky Mountain Instrumental Laboratories, described another high that is legal in most of the U.S. — synthetic cannabinoids marketed as incense, a spice product or "legal marijuana" that give a high similar to marijuana without showing up in conventional drug tests.

"We can detect synthetic cannabinoids with modern analytical chemistry techniques, such as liquid or gas chromatography coupled to mass spectrometry, but these assays are too expensive for the 5,000-10,000 urine samples that most drug testing labs receive each day," said Lantz. Most labs screen for drugs with less expensive antibody assays, but because the structures of these substances are so dissimilar, different antibodies would likely be required for many of them, driving up the cost of a more comprehensive test.

Synthetic cannabinoid abuse rose sharply in 2010, according to U.S. poison control centers, up to 2,863 compared to only 14 in 2009. About 200 synthetic cannabinoids exist, but the U.S. Drug Enforcement Agency (DEA) banned only five of those. A handful of states, such as Washington, Georgia and Colorado, banned five of them, but they are not always the same five that the DEA banned. "The states banned several specific compounds without a particular basis for their choices," Lantz pointed out.

Colorado recently passed a law banning any substance that binds to a cannabinoid receptor in the human body. "The bill was well-intentioned, but technically, the new law not only covers synthetic cannabinoids, but also endocannabinoids, which are naturally occurring substances that the human body produces to regulate many normal processes," said Lantz.

Provided by American Chemical Society (news : web)

New tests for dangerous 'legal marijuana,' 'bath salts' and other emerging designer drugs

 Scientists report the development of much needed new tests to help cope with a wave of deaths, emergency room visits and other problems from a new genre of dangerous designer drugs sold legally in stores and online that mimic the effects of cocaine, ecstasy and marijuana.

They spoke at the 242nd National Meeting & Exposition of the American Chemical Society (ACS), being held in Denver.

The reports, among more than 7,500 on the ACS agenda, focus on drugs sold as "bath salts," "plant food," "incense" and other products with colorful names, such as "Ivory Wave," "Red Dove" and "legal marijuana." They provide users with a high, but many have not yet been made illegal and are undetectable with current drug tests. In one presentation on these "legal highs," a United Kingdom researcher reported a new method to trace the source of the substances in "bath salts." In the other, a U.S. researcher discussed the challenges facing law enforcement and policy makers in regulating synthetic versions of marijuana.

Oliver Sutcliffe, Ph.D., and his collaborators reported the successful use of a method called isotope ratio mass spectrometry (IRMS) to determine who is making bath salts -- drugs that can cause euphoria, paranoia, anxiety and hallucinations when snorted, smoked or injected -- and which chemical companies supplied the raw materials. He and his co-workers are based at the University of Strathclyde and the James Hutton Institute in the U.K.

"With the new method, we could work backwards and trace the substances back to the starting materials," said Sutcliffe. IRMS measures the relative amounts of an element's different forms, or isotopic ratio. "This method was successful because the isotopic ratio of the starting material is transferred like a fingerprint through the synthesis," he explained.

"Bath salts" first garnered major media attention in the U.K. in early 2010, and then became a problem in the U.S. These products are not in the supermarket soap aisle -- they are sold on the Internet, on the street and in stores that sell drug paraphernalia. They are sold in small individual bags for as low as $20 each for the real purpose of providing a cheap, legal high.

The powders often contain mephedrone, which is a synthetic compound, structurally related to methcathinone, which is found in Khat -- a plant that is illegal in many countries, including the U.K. and the U.S. Usually, that would mean that these compounds (and derivatives thereof) would be illegal in those countries too, but because the bath salts are labeled "not for human consumption," they get around this restriction and other legislation governing the supply of medicines for human use. However, Florida and Louisiana -- two hotspots of bath salts abuse -- specifically banned the substances. U.K. officials banned the import of bath salts, which may lead some in the drug trade to set up clandestine labs on U.K. soil, said Sutcliffe. The new method provides law enforcement with a tool to track down these bath salts manufacturers.

In previous work, Sutcliffe developed the first pure reference standard for mephedrone, as well as the first reliable liquid chromatography test for the substance, which could be easily run in a typical law enforcement lab. The team is also developing a color-change test kit for mephedrone, which he estimates may be available by the end of the year.

In another presentation, Robert Lantz, Ph.D., from the Rocky Mountain Instrumental Laboratories, described another high that is legal in most of the U.S. -- synthetic cannabinoids marketed as incense, a spice product or "legal marijuana" that give a high similar to marijuana without showing up in conventional drug tests.

"We can detect synthetic cannabinoids with modern analytical chemistry techniques, such as liquid or gas chromatography coupled to mass spectrometry, but these assays are too expensive for the 5,000-10,000 urine samples that most drug testing labs receive each day," said Lantz. Most labs screen for drugs with less expensive antibody assays, but because the structures of these substances are so dissimilar, different antibodies would likely be required for many of them, driving up the cost of a more comprehensive test.

Synthetic cannabinoid abuse rose sharply in 2010, according to U.S. poison control centers, up to 2,863 compared to only 14 in 2009. About 200 synthetic cannabinoids exist, but the U.S. Drug Enforcement Agency (DEA) banned only five of those. A handful of states, such as Washington, Georgia and Colorado, banned five of them, but they are not always the same five that the DEA banned. "The states banned several specific compounds without a particular basis for their choices," Lantz pointed out.

Colorado recently passed a law banning any substance that binds to a cannabinoid receptor in the human body. "The bill was well-intentioned, but technically, the new law not only covers synthetic cannabinoids, but also endocannabinoids, which are naturally occurring substances that the human body produces to regulate many normal processes," said Lantz.

Story Source:

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

Shining a light on the elusive 'blackbody' of energy research: Designer material has potential applications for thermophotovoltaics

 A designer metamaterial has shown it can engineer emitted "blackbody" radiation with an efficiency beyond the natural limits imposed by the material's temperature, a team of researchers led by Boston College physicist Willie Padilla report in the current edition of Physical Review Letters.

A "blackbody" object represents a theorized ideal of performance for a material that perfectly absorbs all radiation to strike it and also emits energy based on the material's temperature. According to this blackbody law, the energy absorbed is equal to the energy emitted in equilibrium.

The breakthrough reported by Padilla and colleagues from Duke University and SensorMetrix, Inc., could lead to innovative technologies used to cull energy from waste heat produced by numerous industrial processes. Furthermore, the human-made metamaterial offers the ability to control emissivity, which could further enhance energy conversion efficiency.

"For the first time, metamaterials are shown to be able to engineer blackbody radiation and that opens the door for a number of energy harvesting applications," said Padilla. "The energy a natural surface emits is based on its temperature and nothing more. You don't have a lot of choice. Metamaterials, on the other hand, allow you to tailor that radiation coming off in any desirable manner, so you have great control over the emitted energy."

Researchers have long sought to find the ideal "blackbody" material for use in solar or thermoelectric energy generation. So far, the hunt for such a class of thermal emitters has proved elusive. Certain rare earth oxides are in limited supply and expensive, in addition to being almost impossible to control. Photonic crystals proved to be inferior emitters that failed to yield significant efficiencies.

Constructed from artificial composites, metamaterials are designed to give them new properties that exceed the performance limits of their actual physical components and allow them to produce "tailored" responses to radiation. Metamaterials have exhibited effects such as a negative index of refraction and researchers have combined metamaterials with artificial optical devices to demonstrate the "invisibility cloak" effect, essentially directing light around a space and masking its existence.

Three years ago, the team developed a "perfect" metamaterial absorber capable of absorbing all of the light that strikes it thanks to its nano-scale geometric surface features. Knowing that, the researches sought to exploit Kirchoffs's law of thermal radiation, which holds that the ability of a material to emit radiation equals its ability to absorb radiation.

Working in the mid-infrared range, the thermal emitter achieved experimental emissivity of 98 percent. A dual-band emitter delivered emission peaks of 85 percent and 89 percent. The results confirmed achieving performance consistent with Kirchoff's law, the researchers report.

"We also show by performing both emissivity and absorptivity measurements that emissivity and absorptivity agree very well," said Padilla. "Even though the agreement is predicted by Kirchoff's law, this is the first time that Kirchoff's law has been demonstrated for metamaterials."

The researchers said altering the composition of the metamaterial can results in single-, dual-band and broadband metamaterials, which could allow greater control of emitted photons in order to improve energy conversion efficiency.

"Potential applications could lie in energy harvesting area such as using this metamaterial as the selective thermal emitter for thermophotovoltaic (TPV) cells," said Padilla. "Since this metamaterial has the ability to engineer the thermal radiation so that the emitted photons match the band gap of the semiconductor -- part of the TPV cell -- the converting efficiency could be greatly enhanced.

In addition to Padilla, the research team included BC graduate student Xianliang Liu, Duke University's Nan Marie Jokerst and Talmage Tyler and SensorMetrix, Inc., researchers Tatiana Starr and Anthony F. Starr.

Story Source:

The above story is reprinted (with editorial adaptations ) from materials provided by Boston College, via EurekAlert!, a service of AAAS.

Journal Reference:

Xianliang Liu, Talmage Tyler, Tatiana Starr, Anthony Starr, Nan Jokerst, Willie Padilla. Taming the Blackbody with Infrared Metamaterials as Selective Thermal Emitters. Physical Review Letters, 2011; 107 (4) DOI: 10.1103/PhysRevLett.107.045901