The effect of X-ray irradiation on the chemical and physical properties of a semifluorinated self-assembled monolayer (CF-SAM) derived from 1H,1H,2H,2H-perfluorodecanethiol (CF3(CF2)7(CH2)2SH) adsorbed on gold and copper substrates was studied using X-ray photoelectron spectroscopy. During the initial period of irradiation, the effects of electron-stimulated C-F, C-C, and S-X (X ) Au, Cu) bond breaking are responsible for changes in the chemical composition of the CF-SAM. Furthermore, the evolution of the C(1s) X-ray photoelectron spectral region indicates that C-F rather than C-C bond cleavage dominates desorption within the CF-SAM. Except for fluorine desorption, irradiation-induced changes to the chemical and structural properties of the CF-SAM were most pronounced during the initial stages of irradiation, prior to the development of a highly cross-linked carbonaceous overlayer. X-ray irradiation of CF-SAMs adsorbed on Au also resulted in the production of new irradiation-induced sulfur species. A comparison with experiments carried out on a n-hexanedecanethiol (CH3(CH2)15SH)-based SAM revealed that the concentration and distribution of these irradiation-induced sulfur species were both sensitive to the SAM's initial chemical composition. On Cu substrates, native CF-SAMs formed an effective barrier to oxygen diffusion although the film's permeability to oxygen increased for CF-SAMs pre-exposed to X-ray irradiation.

The evolution of the metal-organic interface during iron-mediated metalization of fluorinated organic surfaces has been studied using X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM). Poly-(tetrafluoroethylene) (PTFE) and a semifluorinated self-assembled monolayer (CF 3 (CF 2 ) 7 (CH 2 ) 2 SH, CF-SAM) formed on Au were used as substrates, the latter serving as a model for the interfacial region of a fluorinated polymer. Reaction of Fe with both surfaces resulted in defluorination of the organic film, production of a carbonaceous overlayer, and exclusive formation of iron(II) fluoride. A metallic iron overlayer was formed concurrently with FeF 2 during deposition on CF-SAMs and following extended iron exposures with PTFE substrates. Terminal CF 3 groups produced during metalization of PTFE are postulated to arise from a chain rearrangement reaction involving transient -C ˙Fradicals. X-ray treatment of metalized PTFE was found to represent an effective means to increase the FeF 2 content in the metal-organic interface. Ex situ AFM measurements revealed that the frictional characteristics of the surface increased during the initial stages of metalization associated with defluorination and FeF 2 formation. At higher Fe exposures the surface friction decreased as a metallic overlayer evolved.

The chemistry of hydrazoic acid (HN 3 ) on polycrystalline gold and amorphous ice was studied as a function of HN 3 exposure, temperature, and X-ray irradiation using reflection absorption infrared spectroscopy (RAIRS) and X-ray photoelectron spectroscopy (XPS). On Au, HN 3 was found to adsorb molecularly at 100 K. In contrast, at 100 K the reaction of HN 3 with ice was dominated initially by deprotonation and the formation of azide ions (N 3 -). At higher HN 3 exposures on ice, RAIRS data was consistent with molecular adsorption, although a distinct, more strongly bound molecular state was also observed that is attributed to hydrogen bonding between H 2 O and HN 3 . Annealing HN 3 adsorbed on Au resulted in predominantly molecular HN 3 desorption while in the HN 3 /ice system molecular desorption was accompanied by the production of ammonium azide (NH 4 + N 3 -). In contrast, NH 4 + N 3was not observed on the Au surface during annealing experiments. The formation of NH 4 + N 3is postulated to derive from the reactions of NH radicals, formed as a result of NN-NH bond cleavage, within the adsorbate layer. In both the HN 3 /ice and HN 3 /Au systems, secondary electrons generated by X-ray irradiation induced NH 4 + N 3formation and nitrogen desorption, which are consistent with the following net reaction: 4HN 3(a) f NH 4 + N 3(a)-+ 4N 2(g) v

No abstract

Photoinduced polymerization of styrene monomer thin films condensed on a Ag(110) substrate has been studied using a combination of reflectance absorption infrared spectroscopy (RAIRS) and temperatureprogrammed desorption (TPD). At 100 K, styrene polymerizes upon ultraviolet irradiation. Postirradiation TPD indicates that several species form in the film. These species are identified as styrene dimer, trimer, and tetramer. RAIR spectra as a function of temperature provide evidence for the formation of polystyrene as well. A mechanism for the direct UV photopolymerization of styrene thin films is proposed. IntroductionRecently, there have been reports in the literature on the in-situ formation of polymer films on metal surfaces. Formation of thin polymer films on a metal substrate can be achieved by adsorbing a preformed polymer 1,2 or by forming the polymer in situ. [3][4][5][6][7][8][9][10][11] The motivation for these studies is the desire to form a polymer with a regular two-dimensional morphology that may have novel anisotropic properties. In-situ polymerization has been initiated by photon, electron, and γ-ray irradiation. Radiationinduced chemistry allows for select areas of the substrate to be polymerized, opening the way for the production of positive and negative resists. In addition to the interest in surface modification of metal substrates, in-situ methods for forming polymers in an ultrahigh vacuum allow for further study of the chemistry of the polymer surface and the metal-polymer interface using standard surface analysis techniques.There have been several studies on photoinduced polymerization of adsorbed monomers on metal surfaces. Laser-initiated (514 nm) polymerization of 1,4-dinitrobenzene on Ag colloids was studied by surface-enhanced Raman scattering (SERS). 4 Thick films of 1,4-and 1,3-dinitrobenzene were deposited onto Ag colloids from solution. SERS showed that 1,4-dinitrobenzene polymerized readily on the Ag surface upon CW Ar ion irradiation whereas 1,3-dinitrobenzene did not. Differences in molecular orientation of 1,4-dinitrobenzene compared to 1,3-dinitrobenzene were determined to be the cause of the difference in the photoreactivity of these two isomers on the metal substrate.Ford et al. used a self-assembled monolayer approach to form ordered polymer films by adsorbing 4-(mercap-

Articles you may be interested inElectromigration failure mechanisms for SnAg 3.5 solder bumps on Ti ∕ Cr -Cu ∕ Cu and Ni ( P ) ∕ Au metallization pads J. Appl. Phys. 96, 4518 (2004); 10.1063/1.1788837 Reactivity of Cu with poly(tetrafluoroethylene) and poly(vinyl chloride): Effect of pre-and post-metallization modification on the metal/polymer interface J. Vac. Sci. Technol. A 20, 1690 (2002); 10.1116/1.1497989X-ray photoelectron spectroscopy study of two nitrogen-containing polymer surfaces metallized by nickel Study of poly(ether sulfone)/metal interfaces by high energy x-ray photoelectron spectroscopy and x-ray absorption spectroscopyThe evolution of the metal-polymer interface during the physical vapor deposition of Fe, Ni, Cu, Ag, and Au on poly͑vinylchloride͒ ͑PVC͒ has been studied in situ using x-ray photoelectron spectroscopy. At low metal exposures, all of the metals studied reacted with PVC, forming a metal chloride. For those metals with more than one stable oxidation state, the salt produced corresponded to the metal's lowest stable oxidation state, e.g., CuCl instead of CuCl 2 . Higher metal exposures resulted in deposition of a metallic overlayer. For Fe, Ni, Cu, and Au the variation in the metal's reactivity ͑measured by the metal/metal-chloride ratio as a function of metal coverage͒, was observed to increase in the order FeϷNiϾCuϾAu.

No abstract

The reactivity of Cu with poly(tetrafluoroethylene) (PTFE) and poly(vinylchloride) (PVC) during thermal evaporation, as well as the effect of pre- and post-metallization Ar+ ion and x-ray mediated surface modification treatments on the metal/polymer interface, have been studied using in situ x-ray photoelectron spectroscopy (XPS) and ex situ atomic force microscopy (AFM). During thermal evaporation, copper was unreactive on PTFE but reacted with PVC to form CuCl. Pretreatment of PTFE or PVC surfaces by Ar+ ion or x-ray irradiation did not modify the chemical reactivity of the polymer surface during subsequent Cu deposition, although significant morphological changes were observed on PTFE by AFM. In contrast, post-metallization modification of the Cu/PTFE interface by Ar+ ion or x-ray irradiation lead to the production of CuF2, and increased the yield of CuCl in the Cu/PVC system. In either the Cu/PTFE or Cu/PVC systems, the maximum concentration of copper halide formed and dependence upon treatment time was found to be similar for either Ar+ ion or x-ray irradiation post-metallization treatment strategies, suggesting a common reaction mechanism.