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UD researchers put 'spin' in silicon, advance new age of electronics
May 21, 2007Electrical engineers from the University of Delaware and Cambridge NanoTech have demonstrated for the first time how the spin properties of electrons in silicon--the world's most dominant semiconductor, used in electronics ranging from computers to cell phones--can be measured and controlled.
The discovery could dramatically advance the nascent field of spintronics, which focuses on harnessing the magnet-like "spin" property of electrons instead of solely their charge to create exponentially faster, more powerful electronics such as quantum computers.
The experiment, conducted in the laboratory of Ian Appelbaum, assistant professor of electrical and computer engineering at UD, with doctoral student Biqin Huang, and in collaboration with Douwe Monsma, co-founder of Cambridge NanoTech in Cambridge, Mass., is reported in the May 17 issue of the prestigious scientific journal Nature.
In commenting on the UD team's research findings in the "News and Views" section, which also was published in the Nature edition, Igor Zutic of the Department of Physics at the State University of New York at Buffalo, and Jaroslav Fabian, of the Institute of Theoretical Physics at the University of Regensburg in Germany, note, "Modern computers present serious challenges for conventional, silicon-based electronics. Ever-increasing demands on processor speed, memory storage and power consumption--the era of the laptop that can keep us warm in winter is fast upon us--are forcing researchers to explore unfamiliar territory in the quest for increased performance. In these endeavours, Appelbaum and colleagues report a possibly decisive development: the first demonstration of the transport and coherent manipulation of electron spin in silicon."
While manipulating electron charge is the basis of the present-day electronics industry, researchers in academia and industry over the past decade have been exploring the capability of electron spin to carry, process and store information. A major goal in spintronics is to reach the precise level of control over electron spin that modern electronics has executed over electron charge.
"An electron has intrinsic angular momentum called spin," Appelbaum noted. "The first step to making spintronic devices and circuits is to inject more spins of one direction than in the opposite direction into a semiconductor."
Silicon has been the workhorse material of the electronics industry, the transporter of electrical current in computer chips and transistors. Silicon also has been predicted to be a superior semiconductor for spintronics, yet demonstrating its ability to conduct the spin of electrons, referred to as "spin transport," has eluded scientists--until now.
To provide conclusive evidence of spin transport in silicon, Appelbaum and Huang fabricated small, silicon semiconductor devices using a custom-built, ultra-high vacuum chamber for silicon-wafer bonding.
After spin injection, electrons in the silicon were then subjected to a magnetic field, which caused their spin direction to "precess" or gyrate (much like gravity's effect on a rotating gyroscope), producing tell-tale oscillations in their measurement.
"The processes of precession and dephasing, or decay, are the most unambiguous hallmarks for spin transport. Our work is the first time anyone has shown this effect in silicon," Appelbaum said.
"It's an important problem to solve because silicon is the most important semiconductor for electronics," Appelbaum noted. "However, methods that worked for spin detection in other semiconductors failed in silicon."
Appelbaum said that pursuing the research was a risk worth taking. He credits Monsma with introducing him to hot-electron spin transport and applying it to the problem of spin detection in silicon several years ago when they were postdoctoral fellows together at Harvard University.
Originally, when Appelbaum entered college as an undergraduate at Rensselaer Polytechnic Institute, he thought he wanted to become a physician. But a professor there, Stephen Nettel, turned him on to physics and electrical engineering, and now Appelbaum is teaching his UD students using Nettel's textbook.
So while Appelbaum decided not to become a medical doctor, in some circles he might now be considered, literally, a "spin" doctor.
"We hope we're with spintronics where Bell Labs was with semiconductor electronics in 1948," Appelbaum said.
That year, Bell announced the invention of the transistor, which laid the foundation for modern electronics.
Appelbaum's research was supported by grants from the U.S. Office of Naval Research and by the Microsystems Technology Office of the Defense Advanced Research Projects Agency (DARPA), which is the central research and development organization for the U.S. Department of Defense.
University of Delaware
In commenting on the UD team's research findings in the "News and Views" section, which also was published in the Nature edition, Igor Zutic of the Department of Physics at the State University of New York at Buffalo, and Jaroslav Fabian, of the Institute of Theoretical Physics at the University of Regensburg in Germany, note, "Modern computers present serious challenges for conventional, silicon-based electronics. Ever-increasing demands on processor speed, memory storage and power consumption--the era of the laptop that can keep us warm in winter is fast upon us--are forcing researchers to explore unfamiliar territory in the quest for increased performance. In these endeavours, Appelbaum and colleagues report a possibly decisive development: the first demonstration of the transport and coherent manipulation of electron spin in silicon."
While manipulating electron charge is the basis of the present-day electronics industry, researchers in academia and industry over the past decade have been exploring the capability of electron spin to carry, process and store information. A major goal in spintronics is to reach the precise level of control over electron spin that modern electronics has executed over electron charge.
"An electron has intrinsic angular momentum called spin," Appelbaum noted. "The first step to making spintronic devices and circuits is to inject more spins of one direction than in the opposite direction into a semiconductor."
Silicon has been the workhorse material of the electronics industry, the transporter of electrical current in computer chips and transistors. Silicon also has been predicted to be a superior semiconductor for spintronics, yet demonstrating its ability to conduct the spin of electrons, referred to as "spin transport," has eluded scientists--until now.
To provide conclusive evidence of spin transport in silicon, Appelbaum and Huang fabricated small, silicon semiconductor devices using a custom-built, ultra-high vacuum chamber for silicon-wafer bonding.
After spin injection, electrons in the silicon were then subjected to a magnetic field, which caused their spin direction to "precess" or gyrate (much like gravity's effect on a rotating gyroscope), producing tell-tale oscillations in their measurement.
"The processes of precession and dephasing, or decay, are the most unambiguous hallmarks for spin transport. Our work is the first time anyone has shown this effect in silicon," Appelbaum said.
"It's an important problem to solve because silicon is the most important semiconductor for electronics," Appelbaum noted. "However, methods that worked for spin detection in other semiconductors failed in silicon."
Appelbaum said that pursuing the research was a risk worth taking. He credits Monsma with introducing him to hot-electron spin transport and applying it to the problem of spin detection in silicon several years ago when they were postdoctoral fellows together at Harvard University.
Originally, when Appelbaum entered college as an undergraduate at Rensselaer Polytechnic Institute, he thought he wanted to become a physician. But a professor there, Stephen Nettel, turned him on to physics and electrical engineering, and now Appelbaum is teaching his UD students using Nettel's textbook.
So while Appelbaum decided not to become a medical doctor, in some circles he might now be considered, literally, a "spin" doctor.
"We hope we're with spintronics where Bell Labs was with semiconductor electronics in 1948," Appelbaum said.
That year, Bell announced the invention of the transistor, which laid the foundation for modern electronics.
Appelbaum's research was supported by grants from the U.S. Office of Naval Research and by the Microsystems Technology Office of the Defense Advanced Research Projects Agency (DARPA), which is the central research and development organization for the U.S. Department of Defense.
University of Delaware
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Nano-sandwich Triggers Novel Electron Behavior
A material just six atoms thick in which electrons appear to be guided by conflicting laws of physics depending on their direction of travel has been discovered by a team of physicists at the University of California, Davis. Working with computational models, the team has found that the electrons in a thin layer of vanadium dioxide sandwiched between insulating sheets of titanium dioxide exhibit one set of properties when moving in forward-backward directions, and another set when moving left to right.
Keep On Spinning
By controlling the collective spin state of highly mobile electrons in semiconductors, researchers in the Materials Sciences Division (MSD) at the U.S. Department of Energy's Lawrence Berkeley National Laboratory have taken a major step forward in the technology of spintronics.
SPRING "BLOCKBUSTER" MOVIE NOW SHOWING: Berkeley Scientists Produce First Live Action Movie of Individual Carbon Atoms in Action
Science fiction fans still have another two months of waiting for the new Star Trek movie, but fans of actual science can feast their eyes now on the first movie ever of carbon atoms moving along the edge of a graphene crystal.
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Spintronics, Volume 82 (Semiconductors and Semimetals) by Tomasz Dietl (Editor), David D. Awschalom (Editor), Maria Kaminska (Editor), Hideo Ohno (Editor) This new volume focuses on a new, exciting field of research: Spintronics, the area also known as spin-based electronics. The ultimate aim of researchers in this area is to develop new devices which exploit the spin of an electron instead of, or in addition to, its electronic charge. In recent years many groups worldwide have devoted huge eforts to research of spintronic materials, from their technology through characterization to modeling. The resultant explosion of papers in this field and the sold scientific results achieved justify the publication of this volume. Its goal is to summarize the current level of understanding and to highlight some key results and milestones that have been achieved to date. Semiconductor spintronics is expected to lead to a new generation of... |
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