When graduate student Pengpeng Zhang successfully imaged a piece of silicon just 10 nanometers-or a millionth of a centimeter-in thickness, she and her University of Wisconsin-Madison co-researchers were puzzled. According to established thinking, the feat should be impossible because her microscopy method required samples that conduct electricity.
"After she did it, we realized, Hey, this silicon layer is really thin-its much thinner than what people normally use," says UW-Madison physicist Mark Eriksson. "In fact, its thin enough that it should be very hard to run a current through it. So we began asking, Why is this working?"
A team led by College of Engineering professors Paul Evans, Irena Knezevic and Max Lagally and physics professor Eriksson has now answered that question. Writing in the Feb. 9 issue of the journal Nature, they have shown that when the surface of nanoscale silicon is specially cleaned, the surface itself facilitates current flow in thin layers that ordinarily wont conduct. In fact, conductivity at the nanoscale is completely independent of the added impurities, or dopants, that usually control silicons electrical properties, the team reports.
Paul Evans | EurekAlert!
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