ARCHIVED - Making a Very Fine Point
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November 06, 2006— Ottawa, Ontario
Researchers at the NRC National Institute for Nanotechnology (NINT) have developed the sharpest tip ever known – the size of a single atom.
The single atom tip needle will be used as a probe in scanning tunneling microscopy (STM). It was created by Drs. Mohamed Rezeq, Jason Pitters and Bob Wolkow whose paper about the achievement was recently published in the Journal of Chemical Physics.
NINT research: a team effort
Like most groups at NINT, the team behind this development included researchers from both NRC and the University of Alberta. Dr. Bob Wolkow is a principal investigator with NINT, a professor of physics at the University, and an NRC alumnus. Dr. Jason Pitters is a NINT Research Council Officer and Dr. Mohamed Rezeq is a Post-Doctoral Fellow.
Pointing out a new method for making probes
Previously, STM probes might have had single crystal tips measuring a few nanometres (a nanometre is one millionth of a millimetre), but these were usually formed accidentally. There existed no reliable way to produce tips that small. The method developed by the NINT team is the first to provide a well-controlled technique for making extremely sharp tips with a radius of curvature less than a nanometre – making it the sharpest probe tip ever created.
The tip is made with tungsten. Tungsten is a very hard metal with an extremely high melting point. It is used in microelectronics, light bulb filaments and very strong alloys for cutting and drilling tools.
Creating the tiny tip was no easy task. Such a small arrangement of tungsten atoms is very unstable and the atoms can simply shift out of position. As Dr. Wolkow describes, it's like a sand pile: "You can't make it arbitrarily pointy. If you try to pile on more sand, it flows down and makes a more blunt pile. Metal atoms do the same thing."
A single atom-thick coating of nitrogen near the peak of the atom pile stabilizes the pyramid-shaped tip. Once coated, the tip is quite stable and can withstand temperatures of 900°C and a full-day exposure to normal atmospheric pressure.
Improving the performance of microscopy probes
Scanning tunneling microscopy involves scanning an electrical probe over a surface to detect the electric current flowing between the point of the probe and the surface. This allows scientists to visualize the electron density of the object being scanned.
The nano-tips have been successfully tested in STM applications. The new tips may potentially be used in other microscopy techniques as well, including atomic force microscopes, magnetic force microscopes, or any scanning probe technique. The probe is also a potential electron source for scanning electron microscopes and transmission microscopes.
Dr. Wolkow believes this new probe could improve the performance of scanning and transmission electron microscopes: "If this works... it would be like taking a modest car and making it go like a race car by just changing its spark plugs. We would take a conventional electron microscope, put in one of our tips as the electron source and render the microscope instantly improved and capable of finer resolution."
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|NINT's sharp team: Dr. Rezeq (seated) with Drs. Pitter and Wolkow (from left to right)|
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