Scientists at the Lawrence Berkeley National Laboratory in California, USA, have discovered that nanocrystals of germanium embedded in silica glass don't melt until the temperature rises almost 200 degrees Kelvin above the melting temperature of germanium in bulk. What's even more surprising, these melted nanocrystals have to be cooled more than 200 K below the bulk melting point before they resolidify. Such a large and nearly symmetrical "hysteresis" -- the divergence of melting and freezing temperatures above and below the bulk melting point -- has never before been observed for embedded nanoparticles.

An egg-shaped fullerene, or "buckyball egg" has been made and characterized by chemists in America at UC Davis (California), Virginia Tech, and Emory and Henry College in Virginia. They were trying to encapsulate terbium atoms within fullerenes but instead encapsulated terbium nitride within an egg-shaped fullerene.

The compound Tb₃N@C₈₄ was synthesized using an arc-discharge generator by vaporizing composite graphite rods containing a mixture of Tb₄O₇, graphite, and iron nitride as catalyst in a low-pressure He/N₂atmosphere. This gave a complex mixture of products and chromatography gave seven terbium-containing fractions, the fourth fraction of which contained two isomers of Tb₃N@C₈₄. Crystallographc studies show the compound from one angle in particular seems very egg shaped! Remarkable! The Tb₃N unit is clearly visible (terbium in green and nitrogen in blue).

Until the publication of this work it was normally accepted that no two pentagons can touch in a fullerene and are always surrounded by hexagons. However in this case there are two pentagons (the 8 atoms at the pointy part of the egg at the top of the attached image) linked as a bent pentalene fragment.

References

1. "Tb₃N@C₈₄: An Improbable, Egg-Shaped Endohedral Fullerene that Violates the Isolated Pentagon Rule", C.M. Beavers, T. Zuo, J.C. Duchamp, K. Harich, H.C. Dorn, M.M. Olmstead, and A.L. Balch, J. Am. Chem. Soc., 2006, 128, 11352.
2. UC Davis News Service

Workers at The University of Wisconsin-Madison in the USA have managed to release thin membranes of semiconductors from a substrate and transfer them to new surfaces. The freed membranes which are just tens of nanometers thick retain all the properties of silicon in wafer form but the nanomembranes are flexible. By varying the thicknesses of the silicon and silicon-germanium layers composing them, membrane shapes are possible ranging from flat to curved to tubular.

Potential applications include flexible electronic devices, faster transistors, nano-size photonic crystals that steer light, and lightweight sensors for detecting toxins in the environment or biological events in cells.

The scientists made a three-layer nanomembrane composed of a thin silicon-germanium layer sandwiched between two silicon layers of similar thinness. The membrane sat upon a silicon dioxide layer in a silicon-on-insulator substrate. The nanomembranes may be etched away from the oxide layer with hydrofluoric acid.

Although the Wisconsin team grew their nanomembranes on silicon-on-insulator substrates, the method should apply to many substances beyond semiconductors, such as ferroelectric and piezoelectric materials. The key requirement is a layer, like an oxide, that can be removed to free the nanomembranes.

Nobel laureate Richard Smalley, the Rice University professor who helped discover buckyballs (buckminsterfullerene, C₆₀, the football (soccer) ball shaped form of carbon, died at the age of 62. Richard Smalley shared the 1996 Nobel Prize in chemistry with Sir Harold Kroto (Sussex) and Robert Curl (also Rice) for the identification of the new form of carbon known as buckminsterfullerene because of its similarity to Buckminster Fuller's geodesic domes. Further information: Nanotubes and Buckyballs and Smalley Research Group.

Molecules that can act as rotors could be the key to making sub-microscopic machines, according to nanotechnologists. Now, John Gladysz and colleagues at the Friedrich Alexander University of Erlangen-Nurenberg have developed a new class of molecular rotor that resembles a toy gyroscope and reveal details of its X-ray structure. Read the full story from David Bradley in X-factors webzine.

Like blowing bubbles, making persistent micelles could soon be child's play thanks to researchers in Germany. Their new technique for producing these hollow nanoscopic spheres could revolutionise model studies of cell membranes and other systems. Their work might also lead to novel nano-scale reaction vessels, new catalysts, sensor components, and biocompatible drug-delivery capsules. Read the full article by David Bradley Science Writer in Issue 36 of Spectral Lines, the spectroscopy webzine.

The Science Blog reports here that researchers at Penn State in the USA are developing self-cleaning titania nanotube hydrogen sensors. The hydrogen sensors are titania nanotubes coated with a discontinuous layer of palladium.

"The photocatalytic properties of titania nanotubes are so large - a factor of 100 times greater than any other form of titania - that sensor contaminants are efficiently removed with exposure to ultraviolet light, so that the sensors effectively recover or retain their original hydrogen sensitivity in real world application"

"The photocatalytic properties of titania nanotubes are so large - a factor of 100 times greater than any other form of titania - that sensor contaminants are efficiently removed with exposure to ultraviolet light, so that the sensors effectively recover or retain their original hydrogen sensitivity in real world application"

"By doping the titania nanotubes with trace amounts of different metals such as tin, gold, silver, copper, niobium and others, a wide variety of chemical sensors can be made.