Iron and Superconductors

About 100 years ago, scientists discovered materials that could conduct electrons without losing energy to resistance, but, these "superconductors" had to be very cold. The electron-electron repulsion in these low-temperature superconductors was so weak that electrons could overcome it, pair up and move freely.

In 1986, scientists discovered new materials that became superconductors at temperatures above 100K. These high-temperature superconductors were made of layers of copper alloys sandwiched between layers of nonconducting material that were doped with trace amounts of material that could contribute a few extra electrons to the mix. If these materials were not doped with insulating material they did not conduct electricity as the electrons locked themselves at a distance from their neighbours. This locked pattern was named the "Mott localization".

In 2008 a second class of high-temperature superconductors was discovered. These pnictides are iron-based superconductors which are also layered and need to be doped. However, undoped pnictides are not Mott insulators.

Early in 2010, scientists replaced arsenic atoms in one of the intervening layers of a pnictide with slightly smaller phosphorous atoms. This brought the iron atoms a little closer together and further away from the Mott tipping point.

Rice University researchers are now using iron oxychalcogenides which are layered materials like pnictides, but with greater distance between the iron atoms, and this greater distance is enough to push the system into a Mott insulating state.

A better understanding of the behaviour of high-temperature superconductors is essential to future improvements in electric generators, MRI scanners, high-speed trains and other devices.

Reference:
Jian-Xin Zhu, Rong Yu, Hangdong Wang, Liang L. Zhao, M. D. Jones, Jianhui Dai, Elihu Abrahams, E. Morosan, Minghu Fang, and Qimiao Si. Band Narrowing and Mott Localization in Iron Oxychalcogenides La₂O₂Fe₂O(Se,S)₂. Physical Review Letters, 2010; 104 (21): 216405 DOI: 10.1103/PhysRevLett.104.216405

Graphane and Quantum Dots

Graphene is a honeycomb-like form of carbon that is just one atom thick. Graphane is produced when hydrogen atoms are added to both sides of the graphene matrix, making graphane an insulator.

Rice University scientists have discovered that the strategic extraction of hydrogen atoms from a two-dimensional sheet of graphane opens up hexagonal spaces of pure graphene that look and act like quantum dots. Quantum dots interact with light and magnetic fields in unique ways and can be used for chemical sensors, solar cells, medical imaging and nanoscale circuitry.

Reference:
Abhishek K. Singh, Evgeni S. Penev, Boris I. Yakobson. Vacancy Clusters in Graphane as Quantum Dots. ACS Nano, 2010; : 100513111745088 DOI: 10.1021/nn1006072

MALDI-MSI and Fingerprints

A fingerprint is made up of material from the surface of the skin and from gland secretions, which can be detected and analysed. Fingerprints found at a crime scene are often lifted using a powder, and compared with prints on a database to identify a suspect.

Matrix-Assisted Laser Desorption/Ionisation Mass Spectrometry Imaging (MALDI-MSI) is usually used to map different molecules within tissue sections, but, scientists at Sheffield Hallam University have just used the technique to analyse and produce images of fingerprints. Fingerprints analysed this way provided a wider range of information, eg, the technique can detect the presence of drugs and medication, and can provide information about a person's diet.

Reference:
Rosalind Wolstenholme, Robert Bradshaw, Malcolm R. Clench, Simona Francese. Study of latent fingermarks by matrix-assisted laser desorption/ionisation mass spectrometry imaging of endogenous lipids. Rapid Communications in Mass Spectrometry, 2009; 23 (19): 3031 DOI: 10.1002/rcm.4218

Organic Chemicals in Smoker's Breath

The Chemistry Department of the University of Girona (UdG) has been investigating the chemicals present in the breath of smokers. They analysed some volatile organic compounds such as benzene, 2,5-dimethylfurane, toluene, o-xylene and p-xylene, which could be used as bio-indicators of the condition of a smoker, and have shown that only 2,5-dimethylfuran provides effective results for breath samples. 2,5-dimethylfuran can also be present in the breath of passive smokers if they have had direct contact with tobacco smoke over a prolonged period.

Benzene is only useful as a bio-indicator when tobacco consumption is relatively high and when testing takes place 1-2 hours after a smoking a cigarette.

Toluene and xylene levels are only significant for those who smoke a lot and when little time has passed since smoking the last cigarette.

Reference:
Monica Alonso, Mar Castellanos, Juan M. Sanchez. Evaluation of potential breath biomarkers for active smoking: assessment of smoking habits. Analytical and Bioanalytical Chemistry, 2010; 396 (8): 2987 DOI: 10.1007/s00216-010-3524-z

Uniqueness of Helium

Helium. He, is used to fill balloons, in lasers for eye surgery, as a cooling agent in nuclear reactors, and as a pressurizing agent for liquid fuel rockets in space exploration.

Helium has a number of characteristics that make it special. It is the most stable of all the elements and has the lowest boiling point. It becomes a fluid at temperatures close to absolute zero (0K) while most other materials are solid. In fact, helium is a liquid even at 0K and becomes a solid only under high pressure, and, helium is the only substance to exhibit superfluidity.

Of all the elements, helium is closest to the ideal gas. Two helium atoms form the weakest bound diatomic molecule, or dimer. All the properties of temperature, a measure of the kinetic energy of particles in matter, can be modeled if the force acting between a pair of helium atoms is known.
University of Delaware scientists have now predicted that the average separation between the helium atoms is 47 angstroms, compared to a typical bond length of 1 angstrom (one ten billionth of a meter or 0.0001 micron), and that the binding energy is 6,790 times smaller than the potential depth.

Reference:
M. Przybytek, W. Cencek, J. Komasa, G. %u0141ach, B. Jeziorski, K. Szalewicz. Relativistic and Quantum Electrodynamics Effects in the Helium Pair Potential. Physical Review Letters, 2010; 104 (18): 183003 DOI: 10.1103/PhysRevLett.104.183003

Silver Isotopes to Date the Earth

The Earth is depleted in some elements, such as hydrogen, carbon, nitrogen and silver, compared to the Solar System as a whole. What scientists can not tell us is when this depletion occurred. Carnegie Institute scientists have used the isotopic ratios of silver in primitive meteorites and rocks from the Earth's mantle to determine the history of Earth's volatiles relative to the formation of Earth's iron core.

Silver has two stable isotopes of which silver-107 was produced in the early Solar System by the rapid nuclear decay of palladium-107, which is so unstable that virtually all of it decayed within the first 30 million years. Silver is more volatile than palladium, while palladium is more likely to bond with iron. The silver isotope evidence suggests that the core formed between 5 and 10 million years after the origin of the Solar System.

Studies using hafnium and tungsten isotopes indicate that the core formed between 30 and 100 million years after the origin of the Solar System.

These apparently contradictory results support the "Heterogeneous Accretion" model of planetary growth in which the Earth's building block's changed composition as the planet accreted. So, at first the Earth accreted volatile-depleted material until it reached about 85% of its final mass and then accreted volatile-rich material in the last stages of its formation, about 26 million years after the Solar System's origin.

Reference:
Carnegie Institution (2010, May 14). Water was present during birth of Earth, study of silver suggests. ScienceDaily. Retrieved May 17, 2010, from http://www.sciencedaily.com­ /releases/2010/05/100513143457.htm

Killer Seaweed in Coral Reefs

Studies have shown that several species of seaweed common in both the Pacific and Caribbean Oceans can kill corals upon contact using chemical means.

The study used racks of transplanted coral placed next to different types of common seaweed as well as plastic plants to simulate the effects of shading and mechanical damage. For comparison, other coral racks had neither seaweed not plastic plants near them. In as little as two days the corals in direct contact with the some seaweeds bleached and died.

Chemicals were extracted from the seaweeds causing death. These chemicals were applied to the corals in a gel matrix. As a control, the gel without the chemicals was added to a different group of corals. The results confirmed that these chemicals were responsible for the death of corals in contact with the killer seaweeds.

Overfishing of herbivorous fishes has resulted in more seaweeds being present amongst corals, and some of these seaweeds are responsible for the death of coral. The less coral there is, the fewer fish will be recruited into the area to feed, so the number of seaweeds increase, more coral dies.

Reference:
Douglas B. Rasher, Mark E. Hay. Chemically rich seaweeds poison corals when not controlled by herbivores. Proceedings of the National Academy of Sciences, 2010; DOI: 10.1073/pnas.0912095107