Reactivity, modification and adsorption properties of carbon based surfaces and thin films

To better understand the role that phosphorous atoms play in protecting polymers under extreme environments, I have studied the surface reactions of carbon-phosphide films exposed to atomic oxygen (AO). Results showed that the film's surface carbon atoms were volatilized during AO exposure, producing a higher concentration of surface phosphorous atoms. Ultimately, a highly oxidized, phosphate surface layer developed that was resistant to further AO-mediated erosion below 500 K.;Atomic hydrogen (AH) is a ubiquitous component of plasma reactors, but its surface reactions with organic films are poorly understood. To better understand AH mediated surface processes, I investigated its reactivity towards two types of self-assembled monolayers (SAMs): alkanethiolate SAMs and semi-fluorinated SAMs (CF-SAMs). AH reactions with alkanethiolate SAMs (CH3(CH 2)nS-Au) adsorbed on Au were studied as a function chain length, and results from these studies highlighted the role that film thickness plays in thin film modification. For example, with short-chain SAMs (n=8,11) the sulfur and carbon atoms desorbed at the same rate indicating complete chain removal upon AH exposure. However, with long-chain SAMs (n=15,17) AH diffusion rates to the film-substrate interface were slower, and the loss of carbon and sulfur was uncorrelated. AH reactions with CF-SAMs adsorbed on SiO2 (CF3(CF2)7(CH2)Si≡) were markedly different than those observed for alkanethiolates. Initially, AH abstracts a hydrogen atom from a C-H bond forming a carbon-centered radical. Subsequent reactions of these radicals with AH led to desorption of the CF-SAM's fluorocarbon component (CF3(CF2)5). By controlling the surface concentration of C-F species with AH, the CF-SAM's wettability could be tuned over a wide range of values.;To model the effects of naturally occurring macromolecules on activated carbon in aquatic environments, I have used AFM to characterize the adsorption of natural organic matter (NOM) onto highly ordered pyrolytic graphite (HOPG). NOM adsorption increased under acidic conditions and increasing electrolyte concentration. These results indicated that reduced electrostatic repulsions between NOM macromolecules increased aggregation onto HOPG. The presence of Ca2+ was particularly effective in increasing NOM surface adsorption due to its intermolecular complexation capabilities.