Using single-crystal adsorption calorimetry, heat data have been measured for the adsorption of oxygen on the three low-index planes of Ni at 300 K along with corresponding sticking probabilities. New data are presented with coadsorbed potassium on each plane, and temperature-dependent data for O2/Ni{100}. The initial heats of adsorption of oxygen on Ni{100}, {110}, and {111} are 550, 475, and 440 kJ (mol O2)−1, respectively, at 300 K, and the heat is found to drop rapidly with coverage in the chemisorption regime, indicating strong interadsorbate interactions. However, this rapid decline is not seen with coadsorbed potassium, a difference discussed both in terms of electron availability and coadsorbate attractions. The integral heats of adsorption for oxide film formation are 220, 290, and 320 kJ mol−1, respectively. Corresponding sticking probability measurements show initial values, all less than unity, of 0.63, 0.78, and just 0.23, again for the {100}, {110}, and {111} surfaces in that order. The coverage dependence of the sticking probability is consistent in each case with a passivating oxide film four layers thick. Comparable data for Ni{100} obtained using a pyroelectric detector gave good agreement with the conventional results at 300 K. At 410 K, however, the heat-coverage curve was flat up to 0.25 monolayers. Data were also obtained at 90 K. Analysis and Monte Carlo simulation of the temperature-dependent adsorption heat curves indicates that the large drop in adsorption heat with coverage seen at room temperature is consistent with a local second-nearest neighbor adatom–adatom repulsion rather than a long-range electronic effect.
This article features macromolecular engineering via carbocationic polymerization, the focus of research of the recently established Macromolecular Engineering Research Centre (MERC) at the University of Western Ontario. The fundamental philosophy of MERC is interdisciplinary research with a strong industrial orientation, while emphasizing the quest for fundamental understanding of polymerization processes and polymer structure-property relationships. First, a brief overview of living polymerizations in general, and living carbocationic polymerizations in particular will be given. This latter technique is of interest because some monomers (e. g., isobutylene) can be polymerized by cationic techniques only, to yield polymers with unique properties (e. g., polyisobutylene with superior chemical and oxidative stability, low permeability and high damping). This will be followed by an overview of our research strategy and a summary of our latest results. These include the development of a fiber-optic mid-FTIR method for the real-time monitoring of low temperature polymerization processes, the discovery that selected epoxides initiate effectively the living carbocationic polymerization of isobutylene, fundamental studies into the mechanism and kinetics of living carbocationic polymerization, and the design and synthesis of various polymer architectures (e. g., branched homo- and block copolymers) with improved properties and nanostructured phase morphologies.
Selective and efficient transformation of a diazoketone monolayer on a Pt (110) metal surface has been achieved by irradiation using light with a wavelength of 300–400 nm. The monolayer loses nitrogen to give a remarkably stable ketene intermediate at the interface.
The adsorption of water on Ni(110) at 92-230 K has been studied by Fourier transform infrared reflection-absorption spectroscopy (FTIR-RAS) in the 200-2000 cm -l frequency range using a synchrotron radiation source. For water adsorbed at 90-180 K and coverage θ(0≤θ≤0.5 monolayers), two IR bands at frequencies of ~ 667 and 806 cm -1 can always be observed despite the absence of an O–H stretch band. For water adsorbed at 180 K followed by annealing to 230 K, two IR bands are again observed, at 767 and 947 cm -1 . In both cases we attribute the bands to water wagging and rocking modes. At 180 K, they are rather broad and indicative of interactions in the ordered c (2 × 2) water layer; long range dipole–dipole interactions could be important in stabilizing this 0.5 ML structure at 180 K. At 230 K the bands are believed to originate from the water molecules in water-hydroxyl complexes which occur in well-ordered 2 × 1 islands.
We have studied the mechanism of photoluminescence (PL) change in porous Si layers (PSLs) by gradually replacing the hydrogen-terminated surface with an oxygen-terminated surface by anodic oxidation at room temperature. The observed PL change did not follow the change in the silicon hydrides detected by transmission Fourier transform spectroscopy (FTIR). FTIR spectra show that the silicon hydrides decreased while the PL increased. The results of this study show that the polysilane species is not solely responsible for efficient luminescence from PSLs. In addition, an enhancement of PL intensities after laser exposure was observed from anodically oxidized PSLs.
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