45901-AC5
Sum Frequency Generation Spectroscopic Imaging of Catalytic Surface Reactions
Sum frequency generation imaging (SFGIM) is used to monitor, in situ, the reaction of cyanide ions with gold surface. Spatial and chemical variations across the surface are observed as a function of time. The initial period resulted in the formation of linearly bound cyanide to gold and with continuous exposure of gold film to cyanide solution led to the presence of higher-coordinated gold-cyanide complexes. These species were identified by their specific position in the SFG vibrational spectrum (2105 cm-1, 2140 cm-1, 2170 cm-1, and 2225 cm-1). The relative amount of these gold-cyanide species varied across the surface as resolved by the sum frequency generation microscopy.
In order to control the spatial arrangement of molecules on surface and direct the chemical reaction microcontact printed surfaces have been created and studied. Vibrational spectroscopic imaging is demonstrated for a variety of organic monolayer- functionalized surfaces patterned using microcontact printing. The images from sum frequency generation imaging microscopy (SFGIM) are analyzed using different contrast mechanisms in the interpretation of the transition from stamped to backfilled regions of interest. For this experiment, microcontact printing is used to spatially control the surface monolayers by using a patterned stamp and by varying the terminal functional group of the backfilling solutions. Analysis by the three different methods suggests that significant mixing occurs between the stamped and backfilled regions, which influence the contrast in the images at the resonant peaks. In addition, the interference between the resonant peaks and non-resonant background also has an effect on the appearance of the image.
The development of a new vacuum/high pressure reaction chamber is being completed.
