26, 2006 ---Eugene,
OR--- A newly devised nozzle fitted
with a pinhole-sized capillary has allowed researchers
to distribute helium atoms with X-ray-like waves
on randomly shaped surfaces. The technique could
power the development of a new microscope for nanotechnology,
allowing for a non-invasive, high-resolution approach
to studying both organic and inorganic materials.
All that is needed is a camera-like detector, which is now being pursued, to
quickly capture images that offer nanometer resolution, said principal investigator
Stephen Kevan, a physics professor at the University of Oregon. If successful,
he said, the approach would build on advances already achieved with emerging
X-ray-diffraction techniques. Reporting in the July 7 issue of Physical Review
Letters, Kevan's four-member team described how they sent continuous beams
of helium atoms and hydrogen molecules precisely onto material with irregular
surfaces and measured the speckle diffraction pattern as the wave-like atoms
scattered from the surface.
The research, funded by the National Science Foundation and U.S. Department
of Education, was the first to capture speckle diffraction patterns using atomic
de Broglie waves. The Nobel Prize in physics went to France's Louis de Broglie
in 1929 for his work on the properties of matter waves.
"The approach of using the wave nature of atoms goes back 100 years to the founding
of quantum mechanics," Kevan said. "Our goal is to make atomic de Broglie waves
that have very smooth wave fronts, as in the case in laser light. Usually atom
sources do not provide wave fronts that are aligned coherently, or nice and orderly."
The nozzle used in the experiments is similar to one on a garden hose. However,
it utilizes a micron-sized glass capillary, borrowed from patch-clamp technology
used in neuroscience. The capillary, smaller than a human hair, provides very
small but bright-source atoms that can then be scattered from a surface. This
distribution of scattered atoms is measured with high resolution using a field
The helium atoms advance with de Broglie wavelengths similar to X-rays, but
are neutral and non-damaging to the surface involved. Kevan's team was able
to measure single-slit diffraction patterns as well as speckle patterns made
on an irregularly shaped object.
Getting a timely image remains the big obstacle, Kevan said. Images of diffraction
patterns produced pixel-by-pixel in the study required hours to accumulate
and suffer from thermal stability limitations of the equipment. "We'd like
to measure the speckle diffraction patterns in seconds, not a day," he said.
"Given its simplicity, relative low cost, continuous availability, and the unit
probability for helium scattering from surfaces, our source will be very competitive
in some applications," Kevan and colleagues wrote.
"This atom optical experiment would benefit from developing an 'atom camera,'
that would measure the entire speckle pattern in one exposure," they wrote.
Co-authors of the study with Kevan were doctoral students Forest S. Patton
and Daniel P. Deponte, both of the department of physics at the University
of Oregon, and Greg S. Elliott, a physicist at the University of Puget Sound
in Tacoma, Wash.
Source: Stephen Kevan, professor of physics, 541-346-4742, email@example.com
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