Ru(II) polypyridine complexes: photophysics, photochemistry, eletrochemistry, and chemiluminescence

Ferrous (Fe2+) and ferric (Fe3+) compounds were investigated by XPS to determine the usefulness of calculated multiplet peaks to fit high-resolution iron 2p3/2 spectra from high-spin compounds. The multiplets were found to fit most spectra well, particularly when contributions attributed to surface peaks and shake-up satellites were included. This information was useful for fitting of the complex Fe 2p3/2 spectra for Fe3O4 where both Fe2+ and Fe3+ species are present. It was found that as the ionic bond character of the iron —ligand bond increased, the binding energy associated with either the ferrous or ferric 2p3/2 photoelectron peak also increased. This was determined to be due to the decrease in shielding of the iron cation by the more increasingly electronegative ligands. It was also observed that the difference in energy between a high-spin iron 2p3/2 peak and its corresponding shake-up satellite peak increased as the electronegativity of the ligand increased. The extrinsic loss spectra for ion oxides are also reported; these are as characteristic of each species as are the photoelectron peaks. Copyright © 2004 John Wiley & Sons, Ltd.

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Investigation of multiplet splitting of Fe 2p XPS spectra and bonding in iron compounds

The isolation of various two-dimensional (2D) materials, and the possibility to combine them in vertical stacks, has created a new paradigm in materials science: heterostructures based on 2D crystals. Such a concept has already proven fruitful for a number of electronic applications in the area of ultrathin and flexible devices. Here, we expand the range of such structures to photoactive ones by using semiconducting transition metal dichalcogenides (TMDCs)/graphene stacks. Van Hove singularities in the electronic density of states of TMDC guarantees enhanced light-matter interactions, leading to enhanced photon absorption and electron-hole creation (which are collected in transparent graphene electrodes). This allows development of extremely efficient flexible photovoltaic devices with photoresponsivity above 0.1 ampere per watt (corresponding to an external quantum efficiency of above 30%).

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Strong light-matter interactions in heterostructures of atomically thin films.

Surface Science Studies of the Photoactivation of TiO2New Photochemical Processes

Atomic-layered MoS(2) is synthesized directly on SiO(2) substrates by a scalable chemical vapor deposition method. The large-scale synthesis of an atomic-layered semiconductor directly on a dielectric layer paves the way for many facile device fabrication possibilities, expanding the important family of useful mono- or few-layer materials that possess exceptional properties, such as graphene and hexagonal boron nitride (h-BN).

Large-area vapor-phase growth and characterization of MoS(2) atomic layers on a SiO(2) substrate.

Concepts of inorganic photochemistry

Fundamental aspects of the electronic structure, materials properties and lubrication performance of sputtered MoS2 films

Photochemistry of transition-metal coordination compounds

Lubricating films of MoS2 have been prepared by sputter deposition onto steel substrates maintained at different temperatures. The surface chemical compositions and bulk structural properties of the films before and after rubbing for various periods of time in dry nitrogen gas were determined by x-ray photoelectron spectroscopy and X-ray diffraction, respectively. Film thickness, density, and morphology measurements were also made. Differences in these properties for the films prepared under different conditions provide some insight into the mechanism(s) of lubrication and failure of the films. On the basis of the reported results, it is proposed that lubrication by MoS2 films occurs through a process of intercrystallite slip and that there is an optimum crystallite size that provides maximum wear life under any particular set of application (use) conditions. Methods for improving film performance based on particle/crystallite size and lattice spacing arguments and on the electronic properties of MoS2 and...

Chemical and structural effects on the lubrication properties of sputtered MoS2 films

The use of solid (dry) lubricants, particularly solid lubricant thin films, in space systems, including satellites and launch vehicles, is reviewed. Various types of satellites and their generic mechanical requirements are outlined. Mechanisms that use solid lubricant films are described. The types of solid lubricant films available, including burnished, bonded, and sputter-deposited, are reviewed and their properties assessed relative to application requirements. Future opportunities for insertion of solid lubricants as replacements for liquid or grease lubricants are identified.

Paul D. Fleischauer

Papers

Concepts of inorganic photochemistry

Fundamental aspects of the electronic structure, materials properties and lubrication performance of sputtered MoS2 films

Photochemistry of transition-metal coordination compounds

Chemical and structural effects on the lubrication properties of sputtered MoS2 films

Applications of solid lubricant films in spacecraft