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The system is mounted in a large cryogenic cooler, an enclosed container with a helium-3 cooling system, an isotope of a helium molecule-which is brought down to 300 milli-Kelvin, or 1000 times below room temperature, about one-half a degree above absolute zero. The cooler has a vacuum jacket around it so the heat can't transmit in, and it prevents the cold from being mitigated by the ambient room temperature.The AFM tip is on a cantilever. Normally, with the AFM, one moves the cantilever along the surface and then notes the change in position as it goes over topography on the surface. Dr. Ferry's group is utilizing a process called a piezo-electric sensor in which they metalicize the AFM cantilevered tip with a very thin layer of metal so they can apply a voltage to it. They then use that voltage to perturb the structure they are looking at. As the tip moves it creates a voltage across the plane, which is measured to determine certain mechanical property values. This is a technique that was developed four or five years ago at Harvard University. High Level of Vibration Isolation Required When measuring a very few angstroms or nanometers of displacement, an absolutely stable surface upon which to rest your instrument is critical. If not, any of the vibration coupled into the mechanical structure of the instrument will cause vertical noise and fundamentally an inability to measure these kinds of high resolution features.
"The entire system had to be isolated, not just the cantilever," continues Dr. Ferry. "We required an extremely high level of vibration isolation given our research parameters. We are deriving modern electronic devices from our experiments. Future electronic devices are our interest. What we are doing is looking at the conductivity of materials and then seeing how quantum mechanics fits into this. We study basic physics, which has a real application-engineering-particularly in the semiconductor industry." Dr. Ferry's Research Covers: (1) Electron beam lithography of quantum dots and quantum devices, with applications such as quantum ballistic transport at very low temperatures and high magnetic fields, as well as the quantum-classical transition and the role of quantum effects in real devices at room temperature.
(2)
Magneto-transport studies used to probe the nature of
electron dynamics in semiconductor quantum dots, which are
quasi-zero-dimensional structures whose size is comparable
to the Fermi wavelength of the electrons themselves. Magneto-transport
studies may be used to probe these phenomena and to determine
the factors which limit electron phase coherence within the
structures. Current interest in these devices is motivated
by their potential application in new areas of technology,
such as quantum computing and ultra high frequency signal
processing.
He has also developed a nitrogen chamber coupled directly to a UHV STM/AFM facility for CEVE processing of silicon dioxide resists, and their use in semiconductor device fabrication. Within the nitrogen chamber there is a processing system for the actual CEVE development.
Compared to other laboratory research instrumentation, the growth of AFM usage has been quite extensive over the past 10 years. AFM equipment placement has gone through a doubling phase pretty much every year during the last decade. Since its inception in 1988, it has continuously proven to be a key tool in moving nanotechnology research forward. "More
than half of the universities in the United States, and worldwide,
are engaging in nanotechnology research," says Dr. Ferry.
"In the electronic area, the nanoelectronic side of it
has been going since the late 1960s. This is driven by the
fact that in the semiconductor industry all things are getting
smaller and smaller.
Today, the
transistors have critical dimensions down around 25 nanometers.
And the most critical dimension is the oxide thickness, which
is 1 nanometer. When you consider that you have to control
one nanometer vertical thickness over 300 millimeters of lateral
dimension, that is a difference of 10 to the 8th power. That
defines what modern manufacturing technology produces. The
need for effective vibration isolation has never been greater,
and will continue to become more demanding as the nano-industry
progresses."
For more information contact Steve Varma at Minus K Technology, Inc at sales@minuk.com or by phone at 310-348-9656.
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