Anthony J. Wagner

Reactivity of vapor-deposited metal atoms with nitrogen-containing polymers and organic surfaces studied by in situ XPS

The reactivity of vapor-deposited Fe, Ni, Cu and Au atoms with nylon 6 ([–NH(CH2)5CO–]n), a nitrogen ion beam-modified polyethylene substrate (N-PE) and a nitrile-terminated self-assembled monolayer (CN-SAM) have been investigated using in situ X-ray photoelectron spectroscopy (XPS). On nylon 6, Fe deposition produced Fe–O and Fe–N bonded species as well as an amorphous carbonaceous film at the metal/polymer interface. Metal–nitrogen bond formation was also observed during Ni and Cu deposition on nylon 6, although the C¼O functionality remained intact, and no evidence was found for the production of either Cu–O or Ni–O species. Deposition of Fe and Ni on N-PE and the CN-SAM also resulted in the production of metal– nitrogen bonds. In contrast, Cu exhibited little or no reactivity with N-PE and failed to activate CBN bond cleavage in the CNSAM, while the deposition of Au produced a purely metallic overlayer on all three substrates. The relative reactivity of different polymer functional groups in the present study was found to be largely determined by their respective bond strengths, while the overall metal reactivity trend (Fe > Ni > Cu > Au) can be correlated with the strength of metal–oxygen and metal–nitrogen bonds that can potentially form during metallization.

Surface reactions of vapor phase titanium atoms with halogen and nitrogen containing polymers studied using in situ X-ray photoelectron spectroscopy and atomic force microscopy

Abstract The surface reactions of vapor phase Ti with polytetrafluorethylene (PTFE), polyvinylchloride (PVC) and nitrogen-modified polyethylene (PE) have been studied using in situ X-ray photoelectron spectroscopy (XPS) and ex situ atomic force microscopy (AFM). Titanium reactions with PTFE and PVC surfaces lead to the simultaneous formation of a titanium halide salt and TiC. Titanium reactions with both PTFE and PVC also produced significant morphological changes at the polymer surface. During Ti metallization of PTFE, defluorination did not produce any CF or CF 3 species normally observed during defluorination reactions of metal atoms with PTFE. The amount of titanium fluoride present at the metal–polymer interface was enhanced by post-metallization X-ray irradiation. Results on the Ti surface reactions are also compared and contrasted with Fe and Cu reactivity with PTFE and PVC. The reactions of Ti with nitrogen-modified PE lead to the simultaneous formation of TiN and TiC. Experimental evidence, however, suggests that the different nitrogen containing functional groups present in the nitrogen-modified PE were not equally reactive towards Ti metallization.

Deposition of Au x Ag1 − x / Au y Ag1 − y Multilayers and Multisegment Nanowires

Au x Ag 1-x /Au y Ag 1-y multilayers and multisegment nanowires were deposited from a single solution containing KAu(CN) 2 , KAg(CN) 2 , and Na 2 CO 3 (pH 13). Cyclic voltammograms for deposition from solutions containing Au(CN) - 2 and Ag(CN) - 2 show the characteristic deposition peaks for gold and silver. The composition of the deposited alloys is dependent on the deposition potential (or current) and solution chemistry. Multisegment nanowires were prepared by sequential deposition at -0.7 and -1.2 V from solutions containing Au(CN)2 and Ag(CN) - 2 solution in porous Al 2 O 3 templates. The different segments deposited at -0.7 and -1.2 V are clearly distinguished by scanning electron microscopy and optical microscopy under blue light illumination.

Interaction of chlorine radicals with polyethylene and hydrocarbon thin films under vacuum conditions: a comparison with atomic oxygen reactivity

Abstract The surface reactions of atomic chlorine and oxygen with hydrocarbon-based polymers and organic thin films under vacuum conditions have been investigated with in situ X-ray photoelectron spectroscopy (XPS). The interaction of chlorine radicals (Cl( 2 P)) with polyethylene (PE) under vacuum conditions produces a partially chlorinated layer containing both CCl and CCl 2 groups whose concentration was maximized at the surface. Compared to higher-pressure photochlorination experiments where the flux of chlorine atoms is higher, the maximum extent of PE chlorination as measured by the C:Cl XPS ratio and the evolution of the C(1s) region was reduced in the present study while the surface selectivity of the reaction was enhanced. This influence of chlorine atom flux on the extent of chlorination and surface selectivity can be rationalized by a simple stochastic model of the PE chlorination process that incorporates steric effects associated with the production of mono and dichlorinated carbon atoms as well as cross-linking reactions between carbon-containing radicals. During the reaction of PE with atomic oxygen (O( 3 P)), a concentration gradient of oxygen-containing carbon functionality is also observed in the near surface region. Experiments carried out on hydrocarbon thin films based on self-assembled monolayers (SAMs) reveal that chlorination proceeds without erosion. In contrast, the incorporation of new carbon containing-oxygen functionalities during reactions of hydrocarbon films with atomic oxygen occurs in competition with carbon erosion.

Electron stimulated C–F bond breaking kinetics in fluorine-containing organic thin films

Abstract By monitoring the variation in the fluorine content and the distribution of CF x (x=0–3) species in a semifluorinated self-assembled monolayer (CF-SAM) upon prolonged X-ray irradiation, the electron stimulated C–F bond breaking kinetics in fluorine-containing organic films has been determined. At short irradiation times, X-ray irradiation induced changes in the films chemical composition are consistent with the presence of C–F, C–C and S–Au bond cleavage events. In contrast, C–F bond breaking is identified as the dominant kinetic process for longer X-ray exposures. The kinetics of X-ray induced defluorination are consistent with a first-order decay process mediated by a series of consecutive C–F bond breaking events (e.g., CF→C) whose rate constants are in excellent agreement with a stochastic model of defluorination.

Effect of chemical composition on the neutral reaction products produced during electron beam irradiation of carbon tetrachloride/water (ice) films

The neutral reaction products formed during electron beam irradiation of carbon tetrachloride/water (ice) films have been studied as a function of the films initial CCl4 ∶ H2O ratio using a combination of reflection absorption infrared spectroscopy, mass spectrometry and X-ray photoelectron spectroscopy. When the initial CCl4 ∶ H2O ratio was high, the dominant reaction products in the film were C2Cl4 and a partially chlorinated carbonaceous film (CClx) formed as the result of carbon–carbon coupling reactions in the film. In these CCl4 rich films, chlorine is partitioned mainly into the gas phase while CO is the dominant carbon-containing gas phase species. As the CCl4 ∶ H2O ratio decreases, CO2 becomes an increasingly important reaction product at the expense of species generated from carbon–carbon coupling reactions, while chlorine is increasingly partitioned as HCl in the film, producing H3O+ and Cl−. The production of both H2 and O2 from electron stimulated reactions associated with H2O are suppressed in CCl4/H2O films, although oxygen is more efficiently quenched in the presence of CCl4.

CF3(CF2)7(CH2)2SH Self-Assembled on Au and Subsequent Degradation Under the Influence of Ionizing Radiation as Measured by XPS

X-ray photoelectron spectra are shown for a semifluorinated self-assembled monolayer basd on 1H,1H,2H,2H-perfluorodecanethiol [CF3(CF2)7(CH2)2SH] absorbed on a polycrystalline gold substrate. The effect of x-ray irradiation on the defluorination of the film, studied by following the time dependent variation in the C 1s spectral region, is also shown. This information has been used to elucidate the mechanism and kinetics of the elementary reaction steps that comprise defluorination.

Self-Assembled Monolayers as Models for Polymeric Interfaces

Surface modification techniques are widely used to tailor a polymer’s interfacial properties such as permeability, wettability, adhesion, and biocompatibility, transforming inexpensive raw materials into highly valuable finished products.1–3 These surface modification processes most commonly involve either wet chemical or vacuum based treatment strategies. Over the past decade, vacuum based methods, which include plasma based processing, 4–8 noble gas sputtering and metallization9 have become the preferred pathway to modification. Compared to wet chemical processes, vacuum based technologies are fast, easily controlled and environmentally benign.10 Despite their technological importance, a molecular level understanding of vacuum based surface modification processes at polymeric interfaces is not well understood. This lack of mechanistic understanding can be ascribed to the complexity of the typical reaction medium coupled with the heterogeneity of polymeric substrates.