Friday, January 6, 2012

Ohm’s Law Extends to the Atomic Level - And Moore’s Law May Get a Reprieval.


""Moore’s Law, the cornerstone rule of the semiconductor industry, may get a reprieve from its predicted demise, according to a group of scientists in Australia and the United States. Their unexpected findings show that a well-understood law of classical physics—and a pillar of electrical engineering—holds for some objects that are just four atoms wide, a size where quantum effects should rule instead.

Michelle Simmons and her colleagues at the University of New South Wales, in Australia, together with collaborators at the University of Melbourne and Purdue University, in Indiana, have built low-resistance silicon wires that show that Ohm’s Law works at the atomic level. Ohm’s Law, an empirical rule discovered by the German physicist Georg Ohm in 1827, says that the current through a conductor is directly proportional to the potential difference across the conductor. Introducing the concept of resistance, the law is a mainstay of circuit theory and is taught to high school and college students in physics and engineering classes.""

""In an accompanying commentary in Science, where the research is being reported Friday, Arizona State University’s David Ferry called the finding "surprising." Scientists expected that classical behavior like Ohm’s Law would break down at the atomic level. "The pointlike electron motion of the classical world would be replaced by the spread-out quantum waves. These quantum waves would lead to very different behavior," the IEEE Fellow adds.

Simmons and her collaborators built fine nanowires out of silicon that were just one atom tall, four atoms wide (about 1.5 nanometers), and 106 nm long. They used scanning tunnel microscopy to pattern the wires on a silicon surface and then silicon crystal growth to bury the wires and protect them from surfaces and interfaces that could suck up any free electrons and interfere with Ohm’s Law–like behavior, Simmons says.

Previous experiments had shown that at widths less than 10 nm, the resistivity of silicon nanowires increased exponentially (Ohm’s Law, by contrast, is linear). The researchers were able to get around this exponential increase and follow Ohm’s Law, in effect, by heavily doping the silicon nanowires with phosphorus.""

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