Atomic scale modification of metal surfaces to impact the surface-catalyzed growth of polymethylene films.

摘要

This dissertation focuses on the preparation of highly insulating ultrathin films of polymethylene [-(CH₂)_n-; PM] onto metal surfaces. The work develops a new surface-catalyzed method to grow linear PM films directly from a gold surface modified at the atomic level by the underpotential deposition (upd) of a highly ordered metal (sub)monolayer. Modification of the gold surface with upd provides a convenient strategy for tailoring the catalytic properties of the metal surface and therefore, altering the kinetics of polymer film growth and the properties of the surface-catalyzed PM films. For example, the upd of copper enhances the polymer growth over that on an unmodified gold surface while the effect of silver depends greatly on the upd coverage with >0.9 of a silver monolayer completely preventing PM growth.; This work develops a new strategy to pattern metal surfaces with highly insulating, chemically inert polymer films by exploiting the selectivity of upd metals toward the polymer growth. We have demonstrated the ability to direct the growth of PM into well-defined patterns at the micron-scale by first patterning upd layers on the gold surface through a process that involves microcontact printing.; Kinetics studies of PM formation on Cu(upd)/Au show an exponential growth trend for the polymer chains at short times and a linear growth trend at long times, suggesting two types of propagating chains, those that terminate and those that are living or resistant to termination. A possible mechanism in which copper adatoms catalyze living PM growth has been proposed. This “living” character enables an unprecedented control over film thickness and uniformity. Micron-thick PM films formed through this living mechanism provide excellent barrier protection toward the underlying metal substrate as measured by electrochemical impedance spectroscopy (EIS).; The final part of this work explores the use of sequential upd to design a new type of bimetallic catalytic surface. Through the sequential upd of copper and silver, we can produce metal surfaces with well-controlled surface compositions of both catalytically active and inactive metals that enable a fine tuning of the thickness and properties of PM films.