The formation of organic compounds in the atmosphere of Titan is an ongoing process of the generation of complex organics from the simplest hydrocarbon, methane. Solar radiation and magnetosphere electrons are the main energy sources that drive the reactions in Titan's atmosphere. Since energy from solar radiation is 200 times greater than that from magnetosphere electrons, we have investigated the products formed by the action of UV radiation (185 and 254 nm) on a mixture of gases containing nitrogen, methane, hydrogen, acetylene, ethylene, and cyanoacetylene, the basic gas mixture (BGM) that simulates aspects of Titan's atmosphere using a flow reactor [Tran, B.N., Ferris, J.P., Chera, J.J., 2003a. Icarus 162, 114–124; Tran, B.N., Joseph, J.C., Force, M., Briggs, R.G., Vuitton, V., Ferris, J.P., 2005. Icarus 177, 106–115]. The present research extends these studies by the addition of carbon monoxide and hydrogen cyanide to the BGM. Quantum yields for the loss of reactants and the formation of volatile products were determined and compared with those measured in the absence of the hydrogen cyanide and carbon monoxide. The GCMS analyses of the volatile photolysis products from the BGM, with added hydrogen cyanide, had a composition similar to that of the BGM while the photolysis products of the BGM with added carbon monoxide contained many oxygenated compounds. The infrared spectrum of the corresponding solid product revealed the absorption band of a ketone group, which was probably formed from the reaction of carbon monoxide with the free radicals generated by photolysis of acetylene and ethylene. Of particular interest was the observation that the addition of HCN to the gas mixture only resulted in a very small change in the C/N ratio and in the intensity of the CN frequency at 2210 cm−1 in the infrared spectrum suggesting that little HCN is incorporated into the haze analog. The C/N ratio of the haze analogs was found to be in the 10–12 range. The UV spectra of the solid products formed when HCN or CO added to the BGM is similar to the UV absorption formed from the BGM alone. This result is consistent with absence of additional UV chromophores to the solid product when these mixtures are photolyzed. The following photoproducts, which were not starting materials in our photochemical studies, have been observed on Titan: acetonitrile, benzene, diacetylene, ethane, propene, propane, and propyne.

The photochemical flow reactor (D.W. Clarke et al., 2000, Icarus 147, 282–291) has been modified to minimize the incorporation of oxygen and other impurities in the photoproducts. A mixture of gases that approximate their mixing ratios on Titan (N2, CH4, H2, C2H2, C2H4, and HC3N) (0.98, 0.018, 0.002, 3.5 × 10−4, 3 × 10−4, 1.7 × 10−5, respectively) was irradiated in the flow photochemical reactor using a 185-nm source to give a Titan haze analog as a solid product. X-ray photoelectron spectroscopy (XPS) gave a composition of 93.3% C, 5.3% N, and 1.4% O. Of the 93.3% carbon, high-resolution XPS revealed that 81.2% was present as CH, CC, and CC groups, 12.1% may be CO, CN, CN, CN, and/or CN groups, 5.3% as a CN group. The peak for N was symmetrical and was assigned to the CN while that for oxygen was assigned to the CO and/or the CO group. Some of these assignments were confirmed by FTIR spectroscopy. The polymeric product had a C:N ratio of 17.6, which is significantly greater than that for Titan haze analogs prepared in discharge reactions. When the polymer was exposed to air for seven days the oxygen content increased by 6% along with an increase in the infrared absorption at 1710 cm−1 assigned to the CO group of a ketone. The oxidation is attributed to the reaction of oxygen with free radicals trapped in the polymer matrix. It is proposed that the photochemical initiation of Titan haze formation from compounds formed from starting materials formed high in Titan’s atmosphere is a more plausible model than haze formed in reactions initiated by solely by discharges. These data will be helpful in the interpretation of the data returned from the Huygens probe of the Cassini mission.

The passivity behavior of Alloy 22 and Grade 7 titanium has been studied at 95°C in a high pH salt environment characteristic of concentrated Yucca Mountain groundwater. Measurements of corrosion potential (CP) versus time, potentiostatic polarization (PP) and cyclic potentiodynamic polarization (CPP) behavior were conducted to evaluate the passivity of these alloys. The characterization of passive films was also analyzed by x-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM) to obtain the chemical composition and cross-sectional view of the metal, interface, and oxide layers. It was observed that the oxide layer responsible for passivity of Alloy 22 consisted of chromium oxide (Cr2O3) containing Ni. The surface analysis showed that the passive films formed on Alloy 22 at high anodic potentials (> 0 mV vs. SCE) contained more Mo and W than ones formed at lower anodic potentials (< 0 mV vs. SCE). However, no visual evidence of localized corrosion on Alloy 22 after potentiostatic polarization measurements was observed.

Solar UV is the principal energy source impinging the atmosphere of Titan while the energy from the electrons in Saturn's magnetosphere is less than 0.5% of the UV light. Titan haze analogs were prepared by the photolysis of a mixture of gases that simulate the composition of its atmosphere (nitrogen, methane, hydrogen, acetylene, ethylene, and cyanoacetylene). The real (n) and imaginary (k) parts of the complex refractive index of haze analogs formed from four different gas mixtures were calculated from the spectral properties of the solid polymer in UV-visible, near infrared and infrared wavelength spectral regions. The value of n was constant at 1.6 +/- 0.1 throughout the 0.2-2.5 mum region. The variation of k with wavelength for the values derived for Titan has a lower error than the absolute values of k so the more significant comparisons are with the slopes of the k(lambda) plots in the UV-VIS region. Three of the photochemical Titan haze analogs had slopes comparable to those derived for Titan from the Voyager data (Rages and Pollack, 1980, Icarus 41, 119-130; McKay and Toon, 1992, in: Proceedings of the Symposium on Titan, in: ESA SP, Vol. 338, pp. 185-190). The slopes of the k(lambda) plots for haze analogs prepared by spark discharge (Khare et al., 1984, Icarus 60, 127-137) and plasma discharge (Ramirez et al., 2002, Icarus 156, 515-529) were also comparable to Titan's. These finding show that the k(lambda) plots do not differentiate between different laboratory simulations of atmospheric chemistry on Titan in the UV-VIS near IR region (0.2-2.5 microns). There is a large difference between the k(lambda) in the infrared between the haze analogs prepared photochemically and analogs prepared using a plasma discharges (Khare et al., 1984, Icarus 60, 127-137; Coll et al., 1999, Planet. Space Sci. 47, 1331-1340; Khare et al., 2002, Icarus 160, 172-182). The C/N ratio in the haze analog prepared by discharges is in the 2-11 range while that of the photochemical analogs is in the 18-24 range. The use of discharges and UV light for initiating the chemistry in Titan's atmosphere is discussed. (C) 2003 Elsevier Inc. All rights reserved.

A spin cast film of polystyrene (PS) was analyzed by XPS using monochromatic Al Kα excitation. The XPS survey spectrum contained only a trace of oxygen, indicating a minimum of surface contamination. The high resolution spectrum of the C 1s peak is also reported.

A method is described for correcting the binding energy scale for specimen charging that occurs during XPS analysis of insulating samples, A small quantity of polymeric poly (dimethyl silicone) (PDMS) is deposited from solution onto the surface of a series of polymers. After XPS analysis, the binding energy scale is then adjusted to align the Si 2p signal of the adsorbed PDMS to the value observed on conducting samples. A model is proposed that shows that the binding energies of insulating specimens are measured with respect to the sample Fermi level. Using this method, the C Is binding energy for aliphatic hydrocarbon (-CH2)(x) in polyethylene is measured at 284.97 eV, in excellent agreement with previously reported values based on other correction schemes. Measured energies for 12 other materials are also presented. Copyright (C) 1999 John Whey & Sons, Ltd.

A spin cast film of poly(butadiene) (PBD) was analyzed by XPS using monochromatic Al Kα excitation. The XPS survey spectrum contained only carbon, as expected from the stoichiometry of the polymer. The high resolution spectrum of the C 1s peak is also reported.

A spin cast film of polyetherimide (Ultem® 1000, GE Plastics) was analyzed by XPS using monochromatic Al Kα excitation. The measured atomic composition closely matched the expected stoichiometry of the polymer. Peak positions of the individual chemically shifted C 1s, O 1s, and N 1s components are reported. The results are in general agreement with other reported spectra of polyetherimide polymers: experimental, C 83.0%, O 12.9%, and N 4.1%; theoretical, C 82.2%, O 13.3%, and N 4.3%.

A spin cast film of poly(hexamethylene adipamide) (Nylon 6,6) was analyzed by XPS using monochromatic Al Kα excitation. The measured atomic composition closely matched the expected stoichiometry of the polymer. Peak positions of the individual chemically shifted C 1s, O 1s, and N 1s components are reported. The results are in general agreement with other reported spectra of poly(hexamethylene) polymers: experimental, C 67.1%, O 17.6%, and N 11.1%; theoretical, C 75.0%, O 12.5%, and N 12.5%.

A spin cast film of poly(butylene terephthalate) (PBT) was analyzed by XPS using monochromatic Al Kα excitation. The measured atomic composition closely matched the expected stoichiometry of the polymer. Peak positions of the individual chemically shifted C 1s and O 1s components are reported. The results are in general agreement with other reported spectra of PBT polymers: experimental, C 74.8% and O 25.2%; theoretical, C 75% and O 25%.

A spin cast film of poly(2,6 dimethyl-1,4-phenylene oxide) [PPO, also known as PPE, poly(phenylene ether)] was analyzed by XPS using monochromatic Al Kα excitation. The measured atomic composition closely matched the expected stoichiometry of the polymer. Peak positions of the individual chemically shifted C 1s and O 1s components are reported. The results are in general agreement with other reported spectra of polyphenylene polymers: experimental, C 98.2% and O 10.8%; theoretical, C 88.90% and O 11.1%.

Interfacial characteristics such as chemical reaction. metal diffusion, and morphology were investigated for Cu/BCB, Cr/BCB and Ti/BCB structures. Using Auger and XPS depth profiling, the formation of titanium carbide and chromium oxide was confirmed at the metal/BCB interface. Annealing at 250-degrees-C for extended periods resulted in the diffusion of Cu, Cr and Ti into the BCB and subsequent formation of Cu-Si, CrSi2 and Ti-Si compound precipitates. The reaction is a thermal diffusion controlled process which is dependent on time and temperature. Ar sputtering treatment of BCB film before metallization was found to roughen the surface, resulting in metal spikes which penetrate into the roughened BCB film. However, the peel strength of metals on BCB was only about 177 g cm-1 presumably due to the brittleness of the BCB film.The etch rates of the BCB film in a reactive ion etcher (RIE) and a plasma etcher were measured using Ar, O2, O2 + CF4, and O2 + SF6 gas mixtures. Faster etch rates were obtained when CF4 and SF6 were added to oxygen, since the presence of atomic fluorine enhances the etch rate of organics, while also etching Si and SiO2 formed by exposure of Si-containing BCB film to oxygen gas. Surface compositional changes on the BCB film were observed by XPS after plasma modification. Pure O2 and O2 + CF4 plasmas oxidized the carbo-siloxane linkage (C-Si-O) of the BCB, resulting in the formation of SiO2 on the surface. The O2 + SF6 plasma, however, did not produce the surface SiO2, because of its faster Si and SiO2 etch rates.

The surface composition and morphology of a series of thermoplastic elastomers based on polyester (PBT)–polyether (PPG) copolymers have been studied using x-ray photospectroscopy (XPS) and static secondary-ion-mass spectroscopy (SIMS). In all cases, an enrichment of the polyether soft block at the surface is observed. The degree of preferential surface adsorption is greater for molded specimens compared ot the solvent cast films. The enrichment factor (surface content/bulk content) is greater for speciment of highest PBT content. Angle-dependent XPS measurements are fit with an enriched overlayer model and a continuous profile model. Static SIMS measurements are consistent with the XPS results for molded versus solvent cast films, but indicate that some PBT is present at the outer surface of all specimens analyzed.

The etch rates of BCB film in a reactive ion etcher(RIE) were measured using Ar, O2, O2+CF4, and O2+SF6 gas mixtures. Faster etch rates were obtained when CF4 and SF6 were added to oxygen, since the presence of atomic fluorine enhances the etch rate of organics, while also etching Si and SiO2 formed by exposure to oxygen gas. Surface compositional changes on the BCB film were observed by XPS after plasma modification. Pure O2 and O2+CF4 plasma oxidized the carbo-siloxane linkage (C-Si-O) of the BCB, resulting in the formation of SiO2 on the surface. The O2 +SF6 plasma, however, did not produce the surface SiO2, because of its faster Si and SiO2 etch rates. Ar ion sputtering following the plasma modification, restored the surface chemical composition to a state similar to the initial BCB surface.

Thin films of polyimide were prepared by spin coating the poly(amide–acid) precursor onto copper and aluminum substrates, followed by the usual heat treatment to promote imidization (curing) of the film. Films prepared on aluminum substrates were completely cured during the heat treatment, as shown by x-ray photoelectron spectroscopy and infrared measurements. On copper substrates, the thinnest films (2000 Å or less) showed considerable intermixing of copper ions in the polymer layer. This prevented the films from curing completely during heat treatment. The formation of a copper carboxylate at the acid site in the polyimide precursor is postulated.

Polymeric coatings on copper surfaces are known to degrade at a faster rate than identical materials on other metals such as aluminum, particularly during thermal aging. We have studied the interfacial reactions occurring at copper surfaces coated with poly(esterimide) and polyimide wire enamels. Thin coatings (100 Å–1 μm) were heat treated at temperatures from 200 to 240 °C. Interfacial reactions were studied by x-ray photoelectron spectroscopy (XPS), Auger profiling, and reflectance infrared spectroscopy. In addition to copper oxide growth at the interface, thermal oxidative degradation of the polymer leads to thinning of the coating. This reaction is catalyzed by the copper (oxide) surface and material loss occurs primarily at the polymer/copper (oxide) interface. Migration of mobile copper species into the bulk of the coating is observed by its appearance at the surface and by depth profiling. For polyimide films prepared from poly(amide-acid) precursors, an interfacial reaction occurs during initial contact, prior to curing or aging, and infrared and XPS measurements show incomplete curing of the film. The formation of a copper carboxylate is postulated.