Emerging new properties at oxide interfaces

 Dr. Ariando of the National University of Singapore discovered a collective electronic state not seen before in the bulk of either two individual insulating oxides, thus demonstrating that electrons at their interface can now exhibit ferromagnetism.

In many ionic materials, including the oxides, surfaces created along specific directions can become electrically charged. By the same token, such electronic charging, or 'polarisation', can also occur at the interface of two connecting materials.

Theoretically, this could lead to the build-up of an ever increasing voltage in the materials in certain systems, a situation known as a 'polarity catastrophe'. Certainly this cannot occur in practical systems, for energy sake, and Nature deals with this situation by reconstructing the electronic configuration of the interface via a shifting of charges across the interface, or by structural reconstructions, namely, the displacement of atoms.

With oxide materials, a unique consequence of these reconstructions is that it provides a means to create novel electronic phases, stabilised by the interface, and which cannot exist in the bulk.

Dr. Ariando from the National University of Singapore's (NUS) Department of Physics and NUS Nanoscience and Nanotechnology-NanoCore, along with his co-workers, showed that at this interface, a remarkable combination of strong diamagnetism (superconductor like), paramagnetism and ferromagnetism can co-exist with the quasi two-dimensional electron gas when prepared under a more oxidising condition.

Past studies had shown that two-dimensional conducting planes, in the form of quasi two-dimensional electron gas, could emerge between otherwise non-magnetic insulating oxide, Lanthanum Alumniate (LaAlO3) and Strontium Titanate (SrTiO3).

Interestingly, Dr. Ariando's team had also shown that the ferromagnetic phase was stable even above room temperature and the diamagnetism below a relatively high temperature of 60 K.

Industrial applications

The results also indicate that the free surface of SrTiO3 could well be responsible for all these fascinating phenomena. The SrTiO3 resembles Silicon. This will have a significant impact on industry since Silicon has been used in semiconductor technology -- silicon has been the workhorse for oxide-based devices and electronics.

These multiple electronic and magnetic phases at oxide interfaces could yield interesting technological applications. That a variety of magnetic states can be produced close to the surface (< 10 nm) by changing the external stimulus to the SrTiO3 or the interface of LaAlO3/SrTiO3, be it change in oxygen pressure or magnetic field, thus proves that this is a very active interface, and that it can yield strong responses to external stimuli.

One could well consider building novel sensors out of these interfaces that could be used as, say, oxygen sensors, or even magnetic sensors. Still, where these applications are concerned, there is a need to further understand these phenomena and optimise the device configuration.

The research of Dr. Ariando and his co-workers in the oxide interface field is reminiscent of the times when two-dimensional electron gas in the semiconductor heterostructures first became available, and the quantum Hall effect and fractional quantum Hall effect were discovered, both resulting in Nobel prizes.

The physics of the oxide material systems is however richer, involving much stronger interaction between the electrons, mutually and within the crystal lattice. There is great interest in exploring these interfaces in the quest for new nano-electronic devices.

Story Source:

The above story is reprinted from materials provided by National University of Singapore, via AlphaGalileo.

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

Journal Reference:

Ariando, X. Wang, G. Baskaran, Z. Q. Liu, J. Huijben, J. B. Yi, A. Annadi, A. Roy Barman, A. Rusydi, S. Dhar, Y. P. Feng, J. Ding, H. Hilgenkamp, T. Venkatesan. Electronic phase separation at the LaAlO3/SrTiO3 interface. Nature Communications, 2011; 2: 188 DOI: 10.1038/ncomms1192

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.

Under pressure, sodium, hydrogen could undergo a metamorphosis, emerging as superconductor

In the search for superconductors, finding ways to compress hydrogen into a metal has been a point of focus ever since scientists predicted many years ago that electricity would flow, uninhibited, through such a material.

Liquid metallic hydrogen is thought to exist in the high-gravity interiors of Jupiter and Saturn. But so far, on Earth, researchers have been unable to use static compression techniques to squeeze hydrogen under high enough pressures to convert it into a metal. Shock-wave methods have been successful, but as experiments with diamond anvil cells have shown, hydrogen remains an insulator even under pressures equivalent to those found in Earth's core.

To circumvent the problem, a pair of University at Buffalo chemists has proposed an alternative solution for metallizing hydrogen: Add sodium to hydrogen, they say, and it just might be possible to convert the compound into a superconducting metal under significantly lower pressures.

The research, published June 10 in Physical Review Letters, details the findings of UB Assistant Professor Eva Zurek and UB postdoctoral associate Pio Baettig.

Using an open-source computer program that UB PhD student David Lonie designed, Zurek and Baettig looked for sodium polyhydrides that, under pressure, would be viable superconductor candidates. The program, XtalOpt <http://xtalopt.openmolecules.net>, is an evolutionary algorithm that incorporates quantum mechanical calculations to determine the most stable geometries or crystal structures of solids.

In analyzing the results, Baettig and Zurek found that NaH9, which contains one sodium atom for every nine hydrogen atoms, is predicted to become metallic at an experimentally achievable pressure of about 250 gigapascals -- about 2.5 million times Earth's standard atmospheric pressure, but less than the pressure at Earth's core (about 3.5 million atmospheres).

"It is very basic research," says Zurek, a theoretical chemist. "But if one could potentially metallize hydrogen using the addition of sodium, it could ultimately help us better understand superconductors and lead to new approaches to designing a room-temperature superconductor."

By permitting electricity to travel freely, without resistance, such a superconductor could dramatically improve the efficiency of power transmission technologies.

Zurek, who joined UB in 2009, conducted research at Cornell University as a postdoctoral associate under Roald Hoffmann, a Nobel Prize-winning theoretical chemist whose research interests include the behavior of matter under high pressure.

In October 2009, Zurek co-authored a paper with Hoffman and other colleagues in the Proceedings of the National Academy of Sciences predicting that LiH6 -- a compound containing one lithium atom for every six hydrogen atoms -- could form as a stable metal at a pressure of around 1 million atmospheres.

Neither LiH6 and NaH9 exists naturally as stable compounds on Earth, but under high pressures, their structure is predicted to be stable.

"One of the things that I always like to emphasize is that chemistry is very different under high pressures," Zurek says. "Our chemical intuition is based upon our experience at one atmosphere. Under pressure, elements that do not usually combine on the Earth's surface may mix, or mix in different proportions. The insulator iodine becomes a metal, and sodium becomes insulating. Our aim is to use the results of computational experiments in order to help develop a chemical intuition under pressure, and to predict new materials with unusual properties."

Story Source:

The above story is reprinted (with editorial adaptations ) from materials provided by University at Buffalo.