Modification of Conducting Polymer Thin Film Interfaces Using Self-Assembled Monolayers Containing Transition Metal Comp
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Modification of Conducting Polymer Thin Film Interfaces Using Self-Assembled Monolayers Containing Transition Metal Complexes David M. Sarno, Sudhindra Prasad, Wayne E. Jones, Jr. Department of Chemistry, Institute for Materials Research, and Integrated Electronics and Engineering Center, State University of New York at Binghamton, Binghamton, NY 13902. Luis J. Matienzo IBM Microelectronics, Endicott, NY 13760. ABSTRACT Thin films of polyaniline (PANi) have been in-situ deposited onto fused silica plates modified with ruthenium porphyrin and polypyridyl complexes coordinated to self-assembled monolayers of pyridyl-terminated alkylsilanes. Based on UV-vis and AFM studies, PANi exhibits a slower deposition rate and an earlier onset of secondary nucleation on the metal complex-modified interfaces. Electrical conductivity of the HCl-doped emeraldine salt form of PANi is increased to as high as 40 S/cm, relative to 100°). [3] We therefore surmised a mechanism different from simple non-polar polymer-surface interactions. There is a great deal of π-density in both the immobilized metal complexes and the conjugated polymer, thus an opportunity exists for intermolecular π interactions among the aromatic ring systems. We hypothesize that the porphyrin macrocycle and the bipyridine ligands provide inherently more favorable interfaces for the deposition and adhesion of the conjugated polymer. Other metal complexes such as Zn-tetraphenylporphyrin and Ru-bis(dimethylbipyridine) have been similarly immobilized and their effects on film deposition are of current interest.
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Figure 2. AFM images of razor-scored PANi film after 5 min deposition onto bare silica (left) and Ru-bipyridine (right) surfaces. Z-scale is 300 nm.
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Electrical Conductivity The conductivity of HCl-doped PANi on bare silica ranged from ~0.3 to ~0.5 S/cm and has previously been reported as high as 2 to 6 S/cm. [1, 2, 13] Interestingly, the conductivities on the Ru-metalated surfaces were two orders of magnitude higher. Values ranging from ~14.5 S/cm to ~26 S/cm were obtained for PANi on Ru(bpy)2Cl2. On RuTPP(CO), the conductivity ranged from ~24.5 to ~40 S/cm. Significantly, this enhancement is observed in the absence of any secondary chemical or physical modification of the polymers. [13] Polymerization occurs at room temperature in aqueous acidic solution with HCl as the dopant, and there is no externally induced orientation to the films. In other words, our results are based on films deposited “as is.” The average four-probe data is compiled in Table II. There is no clear correlation between film thickness and conductivity. Bare silica and both Ru-metalated surfaces demonstrated essentially infinite resistance in the absence of PANi thin films. Whitesides and MacDiarmid previously reported substrate effects in which a 5 minute PANi deposition onto hydrophobic OTS-patterned glass resulted in a significant decrease in sheet resistivity from ~107 to ~5 x 103 Ω/□
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