Chemistry Nexus

by WebElements: the periodic table on the web

Abstract:
The melting behavior of Ge nanocrystals embedded within SiO2 is evaluated using in situ transmission electron microscopy. The observed melting-point hysteresis is large (±17%) and nearly symmetric about the bulk melting point. This hysteresis is modeled successfully using classical nucleation theory without the need to invoke epitaxy.1

References

1. Xu, Q., I. D. Sharp, C. W. Yuan, D.
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December 15th, 2009

Posted In: Chemistry, Materials chemistry

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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.1 What’s even more surprising, these melted nanocrystals have to be cooled more than 200 K below the bulk melting point before they resolidify.

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October 9th, 2006

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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.1

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.

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June 2nd, 2006

Posted In: Chemistry, Materials chemistry, Nanoscience and nanotechnology

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Workers in Russia and Los Alamos, USA report in Nature1 superconductivity in boron-doped diamond synthesized at high pressure (nearly 100,000 atmospheres) and temperature (2500-2800 K). Electrical resistivity, magnetic susceptibility, specific heat and field-dependent resistance measurements show that boron-doped diamond (carbon) is a bulk, type-II superconductor below the superconducting transition temperature Tc 4 K.

Boron has one less electron than carbon and, because of its small atomic radius, is relatively easily incorporated into diamond.

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May 9th, 2004

Posted In: Chemistry, Materials chemistry

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