Objects smaller than 1 micron in size are too small to see with conventional light microscopes. Researchers often use electron microscopes to look at smaller features, but electron microscopes are limited to objects that conduct electricity or have been coated with a conducting material.They can't be used to study non-conducting materials in their natural state. This includes things such as molecules in living cells, other biomaterials, ceramics, glasses, and insulators.
Some researchers recently have gained access to this tiny world of non-conducting materials through the newly developed Near-Field Scanning Optical Microscope (NSOM).
Scientists and engineers at the University of Arizona now are among them, thanks to a NSOM lab being built in the Materials Science and Engineering Department. The lab is being funded through a $300,000 NSF grant, matching funds from the university and $150,000 in in-kind donations from corporations.
Professor Srini Raghavan, co-principal investigator on the project, explains that the NSOM gathers light through a tiny aperture at the end of a probe, which is placed within less than a wavelength of an object's surface. This allows the probe to gather the near-field light that hangs around the surfaces of objects but decays exponentially as it leaves the surface.
Common light microscopes that use lenses and mirrors sense only far-field light that travels through space. The NSOM's light-gathering tip scans across the surface and produces both 3-D topographic and 2-D light intensity images based on components of near-field light that have higher frequencies (shorter wavelengths) than far-field light.
In addition, the lab has acquired an Atomic Force Microscopy (AFM) system that produces high-resolution images of objects down to and including individual atoms.
To get this kind of resolution, the AFM sweeps a probe across the surface of a specimen. A laser/diode sensor records the force needed to deflect the probe. Tall features deflect the probe more and produce more force, while smaller features produce less deflection. As the probe sweeps, the laser/diode sends data to a computer. The computer records the height at each point and assembles the points into an image.
"We want to make this a campus-wide facility, available to researchers across campus for a minimum fee," Raghavan says. "It will have many uses in optical materials, biology, and semiconductors." Discoveries of material properties made in the lab will have applications in medicine, telecommunications, aviation, automobiles, chemicals and energy production, he adds.
Professor Joseph Simmons, head of the UA Materials Science and Engineering Department, is the other co-principal investigator on the project. He is in charge of setting up the NSOM lab and Raghavan is in charge of the AFM system.
[Contact: Srini Raghavan, Joseph Simmons]
01-Nov-2001
