Press releases
Please quote Nature Materials as the source of these items.
July 2007
Graphene senses single molecules
A single graphene sheet can be used to detect gas with single-molecule resolution, according to a report online this week in Nature Materials.
Kostya Novoselov and colleagues have demonstrated that the resistance of a graphene flake placed in a chamber of dilute nitrogen dioxide gas at room temperature changes in well-defined steps. Calculations show that each step corresponds to absorption (for increasing conductivity) or desorption (for decreasing conductivity) of single gas molecules. This demonstrates that graphene can be used as a sensor with the ultimate resolution, that is, the quantum — or smallest unit — of the measured physical entity.
Detection of individual gas molecules adsorbed on graphene
F. Schedin, A. K. Geim, S. V. Morozov, E. W. Hill, P. Blake, M. I. Katsnelson & K. S. Novoselov
Published online: 29 July 2007 | doi 10.1038/nmat1967
The shape of a Möbius strip
The classic problem of predicting the shape of a Möbius strip - the famous band that is closed with a half-twist, and which therefore has only one side - can be resolved using a set of equations, as suggested online this week in Nature Materials.
Gert van der Heijden and Eugene Starostin used a recently developed mathematical approach that enabled them to derive a numerically solvable set of equations that describe this problem. Thus they were able to confirm that the ratio of the width of the band to its length essentially determines its shape. Writing in an accompanying News & Views article, John H. Maddocks suggests that the mathematical approach developed by the researchers can be used for related problems such as the modelling of biological molecules, or to explain why a telephone handset cord frequently exhibits regions of both left- and right-handed helices.
The shape of a Möbius strip
E. L. Starostin & G. H. M. van der Heijden
Published online: 15 July 2007 | doi 10.1038/nmat1929
Mathematics: Around the Möbius band
John H. Maddocks
Published online: 15 July 2007 | doi 10.1038/nmat1960
A solid base for nitride semiconductors
High-quality gallium nitride (GaN) blocks, which can be used as substrates for optoelectronic devices, can be grown at low cost, as suggested in a report online this week in Nature Materials.
Tadao Hashimoto and colleagues succeeded in growing up to 180 layers of micrometre-thick single-crystalline layers of GaN on a seed of the same material by ammonothermal growth. This method is based on immersing both the source material — polycrystalline GaN in this case — and the seed in ammonia. The grown material contained only a small number of defects and dislocations.
Solid-state structures based on GaN and other nitride semiconductors are very promising for optoelectronics devices, but the absence of high-quality and low-cost substrates has been a great obstacle to large-scale production — these results represent a definite leap towards resolving this problem.
A GaN bulk crystal with improved structural quality grown by the ammonothermal method
Tadao Hashimoto, Feng Wu, James S. Speck & Shuji Nakamura
Published online: 8 July 2007 | doi 10.1038/nmat1955
Nanocrystal shape control
The shape of metal nanocrystals can be accurately controlled by using a small particle of a different metal as a seed, as reported in an article online this week in Nature Materials.
Peidong Yang and co-authors reacted a platinum nanocube (~13 nanometres each side) with a palladium-based compound to produce core–shell Pt/Pd nanocrystals. By varying the reaction environment, and in particular the amount of NO2, the researchers were able to obtain three different shapes — cubes, cuboctahedra and octahedra.
Many of the physical and chemical properties of nanocrystals depend strongly on their morphology. The authors show, for example, that the catalytic activity of the cubes is quite different from that of the other two types of nanocrystals. The use of seeds represents a clear step towards the development of nanocrystals with well-defined shapes.
