Cornell researchers collaborate on a major advance in microfabrication

University of Arizona (UA) scientists and their colleagues at Cornell have become the first researchers to engineer molecules that efficiently absorb two particles of light, or photons, at the same time and trigger acid production at any point in three dimensions in the materials. The researchers say that success at making these molecules demonstrates a new strategy that is broadly applicable in microfabrication, medicine and optical information technology.

In the May 10 issue of the journal Science, the researchers illustrate how the new materials could dramatically change microfabrication. They made networks of microchannels, as well as free-standing microstructures, by exposing solid resins of the new materials to near-infrared laser light.

For the past few years, Seth R. Marder and Joseph W. Perry and colleagues in the UA chemistry department and Optical Sciences Center have been developing new "two-photon" absorbing molecules. These are molecules that each simultaneously absorb two photons. Now the team has developed molecules that once excited, efficiently activate chemical reactions by transferring electrons to another part of the molecule.

In the Science article, Marder, Perry, Christopher Ober, the Francis Bard Professor of Materials Engineering at Cornell, and their colleagues describe how they have synthesized two-photon-absorbing molecules that are efficient "photoacid generators."

Ober's graduate student, Tianyue Yu, who is supported by the Nanobiotechnology Center at Cornell, designed and synthesized the photopolymer used with the UA photoactive compounds in the experiments and went to Arizona to use Perry's specialized equipment. Said Ober, "Along with nanobiotechnology where we are focusing our Cornell efforts, microphotonics is going to greatly benefit from this new invention." Ober also is director of the Department of Materials Science and Engineering at Cornell.

Beyond microfabrication, the new two-photon-activated photoacid technology has broad and far-reaching potential applications in medicine and information technology, scientists say. The process could be used for photodynamic therapy, three-dimensional photolithography, fast optical switching or any number of applications. In photodynamic therapy, for example, two intersecting infrared laser beams could trigger the release of a drug capsule.

Until now, so-called "photoacid generators," materials that generate acid when exposed to laser light, did not efficiently absorb by a two-photon process. As a result, photoacid generators haven't been widely practical. Conventional photoacid generators typically excite a one-photon absorption process with ultraviolet light. They thus require long exposure times and high-powered beams that often degrade or destroy materials used in the process.

In their Science article, the authors describe using new polymer materials that are between 20 to a few hundred times more sensitive for two-photon 3D microfabrication because they incorporate the new UA-developed two-photon-absorbing compounds. The researchers demonstrate how the new materials can be used to make three-dimensional microstructures of any desired shape, simply by focusing the laser anywhere acid is to be produced.

The joint research project was funded by the U.S. Air Force Office of Scientific Research and the National Science Foundation.

This report was prepared by Lori Stiles, University of Arizona News Services.