研究领域

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Sampling materials on the nano-scale (with the least amount of material, good signal-to-noise in order to obtain important structural information) is a continuous venture that has lead to novel devices. A research program has been developed that uses the unique optical transmission properties of metallic microarray meshes with subwavelength holes to study and understand several interesting chemical problems. This phenomenon, involves transmitting more light than that incident on the holes. This work primarily involves working in the mid-infrared region of the electro-magnetic spectrum which leads to vibrational and orientation information. Light incident upon the metal excites the conducting electrons at the metal surface as surface plasmon (SP) polaritons. They can: propagate along the metal until a hole is reached, tunnel through the hole, and reemerge as light again. Three types of enhancements have been attributed to enhanced IR absorption. The 1st type is simply being on metal which when absorbed molecules are oriented on a metal surface there are metal surface selection rules that can enhance or cancel the molecular vibration of interest. The enhancement factor for being on metal is 100-300 in absorption. The 2nd type is a pathlength effect of 8 µm (16 µm by both the front and back of the mesh) along the metal just as in Beer’s Law (A=εbc) given an enhancement factor of 100-1000 in absorption. Finally, the 3rd type is due to the interaction of a surface plasmon with excited molecular vibrations, which is similar in the shift as observed in Stark Effect experiments with an applied electric field of 1 MV/cm. The enhancement factor for the interaction of a SP with a molecular vibration is about 30-100 in absorption. The infrared extraordinary transmission of metallic microarrays (which involves transmitting more light than that incident on the holes) is used to investigate self-assembled monolayers (SAMs), bilayer lipid membranes, catalytic reactions, thin films of nanocoatings, and the interaction of a molecular vibration with a surface plasmon resonance.