New Imaging Method Uses Helium Atoms
EUGENE, Ore., Aug. 1, 2006 -- 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.
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 US Department of Education, was the first to capture speckle diffraction patterns using atomic de Broglie waves. France's Louis de Broglie won the Noble Prize in physics 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 ionization detector.
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 his colleagues wrote. "This atom optical experiment would benefit from developing an 'atom camera,' that would measure the entire speckle pattern in one exposure."
Co-authors of the study with Kevan were doctoral students Forest S. Patton and Daniel P. Deponte, both of the University of Oregon's department of physics, and Greg S. Elliott, a physicist at the University of Puget Sound in Tacoma, Wash. For more information, visit: www.uoregon.edu
- As a wavefront of light passes by an opaque edge or through an opening, secondary weaker wavefronts are generated, apparently originating at that edge. These secondary wavefronts will interfere with the primary wavefront as well as with each other to form various diffraction patterns.
- An instrument consisting essentially of a tube 160 mm long, with an objective lens at the distant end and an eyepiece at the near end. The objective forms a real aerial image of the object in the focal plane of the eyepiece where it is observed by the eye. The overall magnifying power is equal to the linear magnification of the objective multiplied by the magnifying power of the eyepiece. The eyepiece can be replaced by a film to photograph the primary image, or a positive or negative relay...
- The use of atoms, molecules and molecular-scale structures to enhance existing technology and develop new materials and devices. The goal of this technology is to manipulate atomic and molecular particles to create devices that are thousands of times smaller and faster than those of the current microtechnologies.
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