Welcome to the Geiger Laboratories

for Nonlinear Optics at Interfaces

at Northwestern University

in Focus 
Zinc Ion-Hydroxyl Interactions at Undecanol-Functionalized Fused Silica/Water Interfaces Quantified Using the Eisenthal chi(3) Technique
Ehow H. Chen, Sarah A. Saslow, SonBinh T. Nguyen, and Franz M. Geiger
JPC C, 116, 7016-7020 (2012) 











The interaction of Zn2+ ions with undecanol-functionalized fused silica/water interfaces was studied directly at the aqueous/solid interface. We characterized the surface functionalization using X-ray photoelectron spectroscopy (XPS), where changes in the binding energies of the C1s region are indicative of the presence of hydroxyl group associated with undecanol at the functionalized surface. We then employed the SHG χ(3) technique to determine the degree of silane functionalization, track Zn2+ adsorption directly at the hydroxyl-terminated undecanol silane-functionalized fused silica/aqueous interface at pH 7 and 10 mM NaCl concentration, determine the electrostatic and thermodynamic binding parameters, quantify the change in interfacial potential upon zinc ion adsorption, and compare these values to our previous work with glucosamine-functionalized and bare fused silica/water interfaces. The results from the calculated adsorption free energy suggest that 2:1 hydroxyl:metal coordination complexes, which have not been observed with natural carbohydrates in the bulk aqueous phase, are possible in interfacial environments, with direct implications for controlling and predicting coordination chemistry.




http://pubs.rsc.org/en/content/articlelanding/2011/cp/c1cp20428a
Hydrocarbon on Carbon: Coherent Vibrational Spectroscopy of Toluene on Graphite
Jennifer L. Achtyl, Avram M. Buchbinder, and Franz M. Geiger
JPC Letters, 3, 280-282 (2012)








The ability to study the interactions of hydrocarbons on carbon surfaces is an integral step toward gaining a molecular level understanding of the chemical reactions and physical properties occurring on them. Here, we apply vibrational sum frequency generation (SFG) to determine the tilt angle of toluene, a common organic solvent, on millimeter-thick highly oriented pyrolytic graphite (HOPG). The combination of a time-delay technique, which results in the successful suppression of the nonresonant SFG response, and a null angle method is shown to overcome the “strong optical absorber” problem posed by macroscopically thick carbon samples and yields a molecular tilt angle of toluene in the range of 37° to 42° from the surface normal. The implications of this approach for determining the orientation of organic species adsorbed on carbon interfaces, which are important for energy-relevant processes, are discussed.