SELECTIVE FUNCTIONALIZATION OF GOLD MICROSTRUCTURES WITH FERROCENYL DERIVATIVES VIA REACTION WITH THIOLS OR DISULFIDES - CHARACTERIZATION BY ELECTROCHEMISTRY AND AUGER-ELECTRON SPECTROSCOPY

Auger electron spectroscopy and electrochemistry show that ferrocenyl thiols or disulfides can be used to modify selectively the Au microelectrodes (approximately 2-mu-m X 90-mu-m X 0.1-mu-m) on a Si3N4 substrate. The Auger technique shows the selectivity of chemisorption of thiol (-SH) or disulfide (-SS-) groups on Au relative to their physisorption on Si3N4 to be at least 100:1. Immersion of Au electrodes into solutions containing (1-mercapto-3,6-dithiaheptanyl) octamethylferrocene (I), 11-mercaptoundecanoylferrocene (II), or bis[10-(ferrocenylcarbonyl)decyl] disulfide (III) yields modified Au electrodes showing about one monolayer of a reversibly redox active ferrocene reagent. Compound I yields an E1/2 about 550 mV more negative than that for II or III (which both have the same E1/2 values). The electroactive layer from I on Au is far more labile than that from II or III. Loss of I takes place with a t1/2 of approximately 2 h at 298 K in a hexane solution; little or no loss of electroactive material derived from II or III occurs on the same time scale. When Au electrodes modified with I are immersed in hexane solutions of II, replacement of I by II occurs cleanly and at a rate that is the same as loss of I in hexane only. Detailed procedure for Auger element mapping of organic monolayers at high lateral resolution (approximately 0.1-mu-m) are presented, and such maps give a reliable image of the distribution of molecules on the surface.