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A new class of x-ray photoelectron spectroscopic microscope has been developed at the U.S. Department of Energy?s Brookhaven National Laboratory (Upton, New York) and will be used for advanced research on a wide range of technologically important materials systems.
A new class of x-ray photoelectron spectroscopic microscope has been developed at the U.S. Department of Energy’s Brookhaven National Laboratory (Upton, New York) and will be used for advanced research on a wide range of technologically important materials systems.
A prototype of the new instrument, a vector potential photoelectron microscope (VPPEM), has been built in collaboration with the National Institute of Standards and Technology (NIST) Synchrotron Light Source (NSLS) (Gaithersburg, Maryland). The microscope was invented by Raymond Browning of R. Browning Consultants.
The new microscope uses a unique imaging method, and opens up many novel experimental possibilities. According to Browning, VPPEM potentially has a thousand times greater spatial resolution than current technology can provide, and is expected to be the world’s most advanced general purpose x-ray photoelectron microscope when combined with NIST’s beamline at Brookhaven’s new light source, NSLS-II. Currently under construction, NSLS-II will be the most advanced synchrotron light source in the world when it begins operating by 2015.
VPPEM uses x-ray photoelectron spectroscopy to image the composition and chemistry of surfaces. These chemical properties determine the technologically valuable properties of a material, such as resistance to corrosion, usefulness in fuel cells, as well as strength and hardness. Such information obtained from VPPEM images can be used for semiconductor device defect analysis, inspection of surfaces used in medical practice, organic photovoltaic materials characterization, novel materials development, and general materials surface and interface analysis.
The VPPEM is unique because it uses a strong vector potential field created by a superconducting coil rather than a traditional lens system to magnify a sample. The vector potential field, which is a consequence of the electrical current flowing in the coil, forms a symmetric circular field in the center of the coil. VPPEM uses this symmetric field as a two-dimensional map, or spatial reference, for imaging samples.
“Unlike other microscopes, VPPEM does not ‘focus’ on the sample with a lens system, but magnifies the effects of the vector potential field on the photoelectrons emitted from the sample,” explained Browning in a statement. “When a sample’s surface is irradiated with synchrotron-generated x-rays, the characteristic photoelectron energies emitted from the surface atoms give a wealth of information about the type of atoms, chemical bonding, and, to a certain extent, the atomic structure of a material.” So far, he said, the VPPEM has successfully imaged uncoated silk, magnetic steel wool, gold mesh, and micron-sized tungsten wires.
The VPPEM’s magnifying action has several advantages over conventional electron microscopy. For instance, the sample can be located at different places in the vector potential field and still be imaged. The sample is always in focus because there is no imaging lens to adjust. Relatively large, uneven samples can be imaged in this way, with little sample preparation.
The development of the VPPEM was funded by NIST Small Business Innovation and Research contracts. Browning, who holds three patents and has another three patents pending on the VPPEM, said he is seeking an industrial partner to develop the microscope and commercialize it.