Probing Polymer Adsorption Using an Emissive Semiconductor Substrate: Adsorption of Poly(acrylic acid) onto Cadmium Selenide

摘要

Quenching of the photoluminescence (PL) intensity of single-crystal CdSe by adsorption of poly(acrylic acid) (PAA) from methanol solutions is introduced as a sensitive probe of polymer interactions with a semiconductor surface. Comparison with the influence on CdSe PL of methanol solutions of acrylic acid (AA), propionic acid (PrA), and methyl acrylate (MA), along with IR data, indicate that surface binding leading to PL quenching involves the carboxylic acid proton. Over the range of PAA molecular weights studied in methanol (2K-100K), the dependence of PL quenching on concentration is found to be insensitive to PAA chain length, indicating that the same fraction of CdSe surface sites are used. The PL profile of a surface COOH-derivatized dendrimer (PAMAM-COOH) differs markedly, suggesting that PAA chains uncoil upon adsorption. The time dependence of the PL decay for the PAA/methanol system indicates diffusion-controlled adsorption kinetics. Implications of the use of this methodology for characterizing semiconductor-polymer interfaces are discussed.