Polyferrocenylsilanes as Protective Charge Migration Coatings for Dielectrics
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Polyferrocenylsilanes [Fe(η-C5H4)2SiMePh] n (3) and [Fe(η-C5H4)2SiMe2] n (4) were prepared by transition metal-catalyzed ring-opening polymerization (ROP) and thin films of these materials were studied to investigate their potential utility as protective charge migration coatings for dielectrics. Films ( \(>\)15 μm) of 3 or 4 cast from a concentrated toluene solution coated on Mylar did not experience any arc discharging when exposed to a beam of low energy (20 keV) electrons for a 1 h time period. In order to further investigate the charge migration properties of polyferrocenylsilanes, thick shapes and films of 3 were prepared by mold-extrusion and solution-casting onto a Teflon substrate, respectively. Charge accumulation measurements on 3 using a nonintrusive electrostatic probe showed that even after a 1 h exposure to a 25 keV electron flux, no appreciable charge accumulation existed. The direction of current flow was explored by constructing a device consisting of a film (thickness ca. 100–130 μm) of polymer 3 coating a layer of copper. When positioned beneath a circular mask and exposed to a low energy electron flux (5–25 keV), measurements of the current at the surface of the polymer film either exposed to or not exposed to the electron flux were not significantly different, and the current recorded from the bare copper connection to the ground was significantly (100–1000 times) higher. Although the mechanism of charge migration in polyferrocenylsilanes is not fully understood, these experiments indicated it may arise from a conduction mechanism, however electron scattering may also be involved.
KeywordsPolyferrocenylsilanes charge migration negative charge accumulation arc discharge
This research was supported by the Centre for Research in Earth and Space Technology (CRESTech) and Materials Manufacturing Ontario (MMO). A. B-S. is grateful to the Ontario Government for a graduate scholarship (2004–2005) and A. Be. and R.R. are grateful to NSERC for postgraduate scholarships. In addition, I.M. is grateful to NSERC for an E.W.R. Steacie Fellowship (1997–1999), the University of Toronto for a McLean Fellowship (1997–2003), the Ontario Government for a PREA award (1999), and the Canadian Government for a Canada Research Chair (2001–2008) for the duration of the work described.
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