Spatially and temporally resolved studies of electron transfer reactions in solutions and thin organic surfaces

Understanding electron transfer (ET) on the nanoscale is important to both the frontier of fundamental science and to applications in molecular electronics. Ultrafast infrared spectroscopy and conducting probe atomic force microscopy (CP-AFM) are valuable tools in studies of temporally and spatially resolved ET reactions in solutions and surfaces. Static optical metal-metal charge transfer spectra, infrared absorption spectra at different temperatures, resonance Raman spectra, and polarized light transient spectra are employed to reveal the solvent and vibrational coupling to reverse ET in transition metal complex [(CN)5OsCNRu(NH3)5]-. Experimental evidence that the non-totally symmetric vibrational mode is populated after reverse electron transfer is presented.An electrical conduction study of nanocontacts between gold-grafted polythiophene film and conductive tip under different applied load using CP-AFM is presented. The importance of the adhesion force between a conducting probe and a conductive surface for characterization of electrical properties is demonstrated.A method to measure localized charge within a molecular circuit that shows negative differential resistance via CP-AFM is presented. The voltage region over which conduction through Au-supported 11-ferrocenylundecanethiol self-assembled monolayer (SAM) was enhanced was found to strongly correlate with the region over which the scanning probe tip experienced capacitive attraction to the surface. A mechanism involving two-step resonant hole transfer via sequential oxidation and subsequent reduction is proposed.Single-molecule electrical conduction studies are presented to evaluate how the molecular linking unit influences the tunneling efficiency in metal-Molecule-metal (m-M-m) junctions. CP-AFM was employed to compare the molecular conduction of two ð-bonded molecules, one with a single thiol linker and another with a conjugated double thiol linker at both ends of the molecules. The results demonstrating that the molecule with the conjugated double thiol linkers displays higher conduction than the non-conjugated single thiol-Au contacts are presented.The electrical conduction studies of m-M-m junctions formed between Au-supported SAMs of 1-hexanethiol, 11-ferrocenylundecanethiol, and a Pt-coated AFM tip under different compressing forces using CP-AFM are presented. The observed junction resistance had two distinct power law scaling changes with compressing force. Different scaling regions were described through the change in the area of contact, tunneling distance and structure of the film under compression