Stretching silicon: A new method to measure how strain affects semi...( MADISON: University of Wisconsin-Mad...)

MADISON: University of Wisconsin-Madison engineers and physicists have developed a method of measuring how strain affects thin films of silicon that could lay the foundation for faster flexible electronics.

Silicon is the industry standard semiconductor for electronic devices. Silicon thin films could be the basis for fast, flexible electronics. Researchers have long known that inducing strain into the silicon increases device speed, yet have not fully understood why.

Developed by a team of researchers led by Max Lagally, the Erwin W. Mueller and Bascom Professor of Materials Science and Engineering at UW-Madison, the new method enables the researchers to directly measure the effects of strain on the electronic structure of silicon. The group published its findings in the October 10 online edition of Physical Review Letters, and the paper will soon appear in the print edition of the journal.

Standard strained silicon has so many dislocations and defects that strain measurements aren╒t accurate, so the research team starts with its own specially fabricated silicon nanomembranes. The team can induce uniform strain in these extremely thin, flexible silicon sheets.

"Imagine if you were to attach a ring and a hook on all four corners and pull equally on all four corners like a trampoline, it stretches out like that," says Lagally.

As a result, the researchers avoid the defects and variations that make it difficult to study standard strained silicon. Uniform strain allows accurate measurement of its effect on electronic properties.

The researchers drew on the powerful X-ray source at the UW-Madison Synchrotron Radiation Center (SRC), which allowed them to measure conduction bands in strained silicon. To study the energy levels, the researchers needed a wavelength-tunable X-ray source. The SRC also houses a monochromator, a device that enabled the team to choose a precise wavelength, giving thei
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