Studying nanoparticle-induced structural changes within fatty acid multilayer films using sum frequency generation vibrational spectroscopy

The nonlinear optical technique of sum frequency generation (SFG) vibrational spectroscopy has been used for the first time to study CdS nanoparticle/arachidic acid multilayer structures. Using a combination of per-deuterated and per-protonated arachidic acid, it is possible to study individual layers anywhere within the film, buried or on the surface. Before reaction with H2S all layers are highly ordered, but after the reaction the layers become highly disordered, except for the surface layer, which remains well ordered. This sheds new light on the structure and stability of these films and shows that SFG can provide unique structural information.