Imaging and modification of redox active structures with scanning probe microscopy techniques

Scanning probe microscopies (SPM) and electrochemical techniques have been applied to the study of surfaces modified with macromolecular assemblies. The intent was to develop a basic understanding the interactions between an SPM tip, an adsorbate and a surface that might allow for the assembly of nanostructures of deliberate architecture. Three different cases are presented.;In the first, the interfacial reaction of terpyridyl-pendant dendrimers and of terpyridine containing bridging ligands with Fe2+ or Co2+ was shown to give rise to film formation on HOPG surfaces. Molecularly-resolved STM images reveal that these films form highly ordered 2-D trigonal arrays which appear to be composed of one-dimensional polymeric strands. An extensive study with ligands of tailored architecture has provided insight on the relation between the ligand's molecular details and the structure of the resulting films. In all cases, the films were electrochemically active and exhibited a metal based reversible wave at a formal potential that corresponded to that for the respective [M(tpy)2]2+ complex.;In the second, four generations of redox active ferrocene and cobaltocenium functionalized dendrimers were characterized. The thermodynamics and kinetics of adsorption of these redox active dendrimers were studied using electrochemical techniques. These materials adsorb onto Pt surfaces and the coverage is dependent on their redox state. Using tapping mode atomic force microscopy (TMAFM) molecularly resolved images of these dendrimers adsorbed onto a Pt(111) surface were obtained. In-situ electrochemical AFM (ECAFM) was employed to study the electrodeposition process. ECAFM and electrochemical quartz microbalance (EQCM) results could be correlated with the film's morphology and their redox state.;In the last case, a lithographic application of a technique which we have developed an termed redox probe microscopy, RPM, in which an AFM tip is modified with redox active materials is presented. In this application, an RPM tip is used to "expose" a pH-sensitive block co-polymer in what we have termed the pH-stylus. In the pH-stylus, an RPM tip is modified with a hydroquinone monolayer which upon oxidation releases protons. By scanning such a modified tip over a pH sensitive block-copolymer and controlling the electrode potential, the polymer film can be exposed to generate desired patterns.