Sum frequency generation from Langmuir-Blodgett multilayer films on metal and dielectric substrates.
Sum frequency generation (SFG) vibrational spectra of cadmium arachidate multilayer films adsorbed on a substrate with high nonresonant susceptibility, i.e., gold, and on a low nonresonant susceptibility substrate, i.e., fused quartz, have been investigated in the C-H stretching region in air. The films were formed by Langmuir-Blodgett (LB) deposition and their spectra recorded using SFG spectrometers employing both 532-nm nanosecond and 800-nm femtosecond lasers, with counter-propagating and co-propagating beam geometries, respectively. Both kinds of substrate were rendered hydrophobic by coating them with per-deuterated octadecanethiol (gold) or per-deuterated cadmium arachidate (fused quartz) monolayers. Single per-protonated arachidate layers in otherwise per-deuterated 10-layer films were used to show that the SFG resonances arise only from the topmost and lowermost layers in a LB film comprised of an even number of per-protonated layers, although the SFG spectra from the two hydrophobic substrates are different from each other. The differences in the spectra from the same ten-layer per-protonated films deposited on the two types of hydrophobic substrate have been explained in terms of a simple model that accounts for resonant and nonresonant contributions.
Holman
Jasper
J
Department of Chemistry, University of Cambridge, Lensfield Road, Cambridge, CB2 1EW, UK.
Davies
Paul B
PB
Nishida
Takuma
T
Ye
Shen
S
Neivandt
David J
DJ
D000327:Adsorption; D002104:Cadmium / Q000737:chemistry*; D004537:Eicosanoic Acids / Q000737:chemistry*; D006046:Gold / Q000737:chemistry*; D057927:Hydrophobic and Hydrophilic Interactions; D008567:Membranes, Artificial; D011791:Quartz / Q000737:chemistry*; D013057:Spectrum Analysis / Q000379:methods; D013499:Surface Properties; D014732:Vibration
D004537:Eicosanoic Acids; D008567:Membranes, Artificial; D002104:Cadmium; D011791:Quartz; D006046:Gold; C094477:arachidic acid