X-ray photoelectron spectroscopy of an ethylene–tetrafluoroethylene copolymer

The electronic structure of a clean copolymer of ethylene and tetrafluoroethylene is investigated by measuring the ESCA spectra of the core and valence levels. The chemical composition and alternating (>95%) structure of the copolymer, characterized separately by classical methods, is verified by analyzing the C 1s core-level spectrum. The comparison of the experimental valence band with an original EHCO band-structure calculation, and with similar data for a model of polymer with block structure, shows that the combined methods allow us to distinguish between the two compounds through their valence-band spectra.     

Gas sensing properties of MWCNTs decorated with gold or tin oxide nanoparticles

Gas sensors based on oxygen plasma functionalised MWCNTs and plasma-treated nanotubes decorated either with gold nanoclusters or tin oxide nanoparticles were evaluated for the detection of NO₂, CO and ethylene. The sensor active layers were deposited by airbrushing onto micro-machined silicon transducers. Sensitivity, linearity, selectivity, response and recovery times and humidity effect were studied. XPS and TEM were employed to analyse the gas sensitive films. Among the different sensors tested, those based on tin oxide decorated MWCNTs showed the highest sensitivity to NO₂ (at ppb level) and the lowest humidity cross-sensitivity when operated at room temperature.     

Characterization of WO3:Ag films: ToF-SIMS studies of ammonia adsorption

In this work, the composition and morphology of WO₃ films loaded with different levels of Ag, prepared by screen-printing onto Si substrates and annealed in air were investigated. The TEM micrography showed that the films are grain-like; the grain size increases with the increase of the Ag loading level. The Raman spectroscopy showed the formation of a AgWO₃ bronze structure. XPS and ToF-SIMS results showed that while undergoing annealing, the Ag atoms migrate to the surface forming clusters. The molecular images obtained by ToF-SIMS showed that the NH₃ binds preferentially at the surface of the Ag clusters. No preferential binding site was found for hydrocarbon contamination.     

The NMR reciprocity theorem for arbitrary probe geometry

It is shown that the NMR reciprocity theorem is a variant of a problem considered by Lorentz in 1895. This formulation is quite general and applies to electric-dipole-based as well as coil-based or resonator-based magnetic resonance probes. The reasoning is related to, but different from, the proof of the reciprocity theorem for radiofrequency networks and for transmit/receive antenna systems in telecommunications. The signal-to-noise ratio of the NMR experiment is also discussed in very general terms.     

Electronic structure of Pd nanoparticles on carbon nanotubes

The effect of the oxygen plasma treatment on the electronic states of multi-wall carbon nanotubes (MWCNTs) is analyzed by X-ray photoemission measurements (XPS) and UPS, both using synchrotron radiation. It is found that the plasma treatment effectively grafts oxygen at the CNT-surface. Thereafter, the interaction between evaporated Pd and pristine or oxygen plasma-treated MWCNTs is investigated. Pd is found to nucleate at defective sites, whether initially present or introduced by oxygen plasma treatment. The plasma treatment induced a uniform dispersion of Pd clusters at the CNT-surface. The absence of additional features in the Pd 3d and C 1s core levels spectra testifies that no Pd-C bond is formed. The shift of the Pd 3d core level towards high-binding energy for the smallest clusters is attributed to the Coulomb energy of the charged final state.     

Electronic structure of fluoropolymers : Theory and esca measurements

Theoretical and experimental results for the band structure of fluoropolymers are presented. Original theoretical results are obtained from the extende Hückel method of the following polymers : (I) polyethylene, (II) polyvinyl fluoride, (III) polydifluoro (1,2) ethylene-cis, (IV) polydifluoro (1,2) ethylene-trans, (V) polyvinylidene fluoride, (VI) polytrifluoroethylene and (VII) polytetrafluoroethylene. Band structures schemes and density of state histograms are calculated. Results are compared with valence band structures as revealed by E.S.C.A. spectroscopy, using a flood gun to neutralize char effects on these compounds. In this work, accent is put on the substituent effect of fluorine. Correlation between theoretical and observed density of     

Electron spectroscopic characterization of oxygen adsorption on gold surfaces: II. Production of gold oxide in oxygen DC reactive sputtering

Gold oxide is produced by oxygen DC reactive sputtering in a UHV compatible chamber. It is subsequently characterized by High Resolution Electron Energy Loss, Auger and X-ray Photoelectron Spectroscopies. It is demonstrated that the oxide is of the Au₂O₃ type (auric oxide) and that it decomposes under thermal treatment. Au₂O (aurous oxide) is a possible intermediate of this reduction.     

Formation of dense self-assembled monolayers of (n-decyl)trichlorosilanes on Ta/Ta2O5

Tantalum pentoxide (Ta2O5) is a promising material for the realization of biological interfaces because of its high dielectric constant, its high chemical stability, and its excellent passivating properties. Nevertheless, the deposition of highly organized silane SAMs to realize well-defined and tailored Ta2O5-based (bio)interfaces, has not been studied in great detail as of yet. In this work, we have investigated the formation of a highly ordered, dense monolayer of trichlorosilanes on Ta2O5 surfaces. Specifically, two different cleaning procedures for Ta2O5 were compared and (n-decyl)trichlorosilane (DTS) was used to study the effect of both cleaning methods on the silanization of Ta2O5. Both types of cleaning allowed the formation of complete and crystalline DTS monolayers on Ta2O5, in contrast with the incomplete, disordered silane layer assembled on uncleaned Ta2O5. The deposited self-assembled monolayers were studied by means of contact angle goniometry, Brewster angle FTIR, X-ray photoelectron spectroscopy, cyclic voltammetry, and ellipsometry. Infrared analysis exhibited a highly ordered DTS silane film on Ta2O5 and indicated a larger tilt angle of the alkyl chains on this substrate by comparison to DTS on SiO2. Furthermore, with use of ellipsometry and XPS, the silane film thickness on Ta2O5 was determined to be substantially smaller than that reported in the literature for DTS on SiO2, supporting the observations of an increased tilt angle (approximately 45 degrees ) on Ta2O5 than on SiO2 (approximately 10 degrees ). By means of cyclic voltammetry, the formation of a dense, essentially pinhole-free, silane film was observed on the cleaned samples. In conclusion, the fully characterized and optimized procedure for the silanization of Ta2O5 surfaces with trichlorosilanes will allow the formation of well-defined, reproducible, and controllable chemical interfaces on Ta2O5.     

X-ray photoemission spectroscopy and secondary-ion mass spectroscopy applied to the compositional study of pre-colonial pottery from Pantanal,Brazil

X-ray photoemission spectroscopy (XPS) and time-of-flight (TOF) secondary-ion mass spectroscopy (SIMS) have been applied to investigate potsherd samples from Pantanal, Brazil. One of the potsherds presented burnt bone as an additive, which was characterized by XPS as carbonate hydroxyapatite. For shell-tempered ceramics the phase present in shells after firing was identified by X-ray diffraction. TOF-SIMS was used to study the distribution of quartz as temper in one of the sherds. XPS was also applied to the characterization of the finishing external layer of the ceramic vessels. In this case, based on the Fe 2p spectra of the sherd's interior and outermost layers, it was possible to prove that their difference in coloration is due to black heart formation. Hierarchical clustering analysis and principal component analysis of the XPS elemental data enabled the potsherds to be classified with respect to their clay composition.