APS Physics Tip Sheet – May 13, 2014
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The Growth of Metal Whiskers
A new theory explains the formation of metal whiskers—tiny hairlike protrusions that can cause short circuits in electronic components.
Metals widely used in electronics, such as tin and zinc, often show hairlike protrusions on their surfaces. These “whiskers” can cause current leakages and short circuits in electronic equipment and are responsible for billion-dollar losses in the auto, aviation, and space industries. But their formation mechanism has remained a mystery. Now, a researcher at the University of Toledo, Ohio has proposed a theory that provides, for the first time, quantitative predictions of whisker nucleation, growth rates, and length distributions based on the presence of defects and impurities on the surface.
* Victor G. Karpov (contact author), “Electrostatic theory of metal whiskers,” Physical Review Applied (expected publication date: May 15)
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The Perfect Wave for Attosecond Generation
Researchers have found new ways to generate extremely short laser pulses, achieving higher frequencies and larger intensities than previously possible.
Intense and short laser pulses can be used to generate, through a process known as high-harmonic generation (HHG), electromagnetic pulses that last for only a few billionths of a billionth of a second – or attoseconds. These pulses can be used to measure ultrafast phenomena like the movement of electrons in solids and molecules. But HHG is inefficient at the extreme-ultraviolet or x-ray wavelengths, which would be useful to probe tightly bound core-level electrons of atoms or to carry out experiments with high spatial resolution. Now, a team of researchers from Austria, the UK and Germany has generated HHG starting from a “perfect waveform”: a carefully chosen combination of laser beams that can produce higher frequencies and photon fluxes than were previously possible.
* Stefan Haessler (contact author) et al., “Optimization of quantum trajectories driven by strong-field waveforms,” Physical Review X (expected publication date: May 14)
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Why Heat Moves Molecules in Water
Thermophoresis is a phenomenon by which different particles in solution move differently in response to a temperature difference. The effect has a number of practical applications, in particular in the test of how drugs bind to proteins. But a satisfactory molecular-level thermophoresis theory that could guide such binding experiments is still lacking. Now researchers in Germany have developed a complete theory for thermophoresis that includes previously neglected effects due to the presence of local electric fields in the liquid. The new model was able to successfully reproduce a number of lab tests on DNA and RNA strands carried out under a wide range of conditions.
* M. Reichl, M. Herzog, A. Götz and Dieter Braun (contact author), “Why charged molecules move across a temperature gradient,” Physical Review Letters (expected publication date: May 13)
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Journal articles and preprints are available to journalists on request.
Matteo Rini, PhD
Deputy Editor, Physics
