Proton Processes on the Surfaces of Semiconductors and Insulators

Spectroscopic and Photoluminescence Studies of a Wide Band Gap Insulating Material: Powdered and Colloidal ZrO2 Sols

“…Photoexcitation of band delocalized electronic states associated with regular lattice and intragap localized electronic states associated with lattice irregularities or defects in an insulating solid with a large band gap, e.g., ZrO 2 , gives rise to a variety of photophysical and photochemical processes, − the nature of which depends on the type of interaction between the incident light and the solid's subsystem and on the experimental approach used. Taking into consideration the types of initial and final electronic states involved in light-induced electronic transitions, three cases can be delineated: (i) intradefect transitions (both states are localized), (ii) band-to-band transitions (both states are delocalized), and (iii) defect-to-band transitions (initial state is localized, final state is delocalized) or band-to-defect transitions (initial state is delocalized, final state is localized) .…”

“…Extrinsic absorption by solids normally occurs at lower energies. Note that extrinsic surface absorption is at times red-shifted by a few electronvolts relative to the intrinsic fundamental absorption edge of wide band gap insulators. ,, …”

“…The first set of interactions between incident light and solids can display various photoexcitation pathways that yield a large number of subsequent, interconnected photochemical and photophysical events: 1-4,7 (i) photoluminescence associated with band-to-band recombination and with defect recombination centers and centers directly excited by light; (ii) photoconductivity; (iii) formation of defects by trapping of carriers by intrinsic defects and by impurities or by utilizing the type of electronic excitation that displaces lattice ions to irregular positions (e.g., formation of interstitials and vacancies by exciton annihilation); , and (iv) chemical reactions at the solid particle surface owing to the presence of the O •- radical species (a trapped hole after absorption of radiation) . ,, Moreover, zirconia finds pertinence in thermal catalysis implicating superacids in mixtures of several metal oxides. Of relevance to the present study, significant interest has focused on photocatalytic reactions in heterogeneous systems that yield intermediate delocalized excited states in solids: i.e., excitons (e o ), electrons (e), and holes (h).…”

Forms of adsorption and transition states of oxidation of carbon monoxide by molecular oxygen and dissociation of nitrogen monooxide, catalyzed by monovalent copper

“…The hydroxides of metals being rather simple of the aprotic centers of oxides' surface, were successfully observed for modeling complexation of metal oxide M(OH) n (M = Na, Mg, Al, Sc, Cu, Zn, Y) with carbon monoxide 12, 13. The studying of electronic effects of similar systems expediently and consequently, that active sites of a real heterogeneous surface of many catalysts contain group M‐O‐H 14, 15. At the beginning of the present work the results for molecular models of copper hydroxides: Cu(OH), where δ = −1, 0, +1; n = 1, 2, and 3 with molecules CO and NO are given at first.…”

X-ray photoelectron analysis of lead-silicate glass structure

“…Because the thickness of the analyzed layer is ≈5 nm, it should be considered that a layer with a structure that differs from the bulk structure by an increased content of small Si-O structures may form on the surface of the studied samples during preparation. The thickness of this destroyed layer is ≈1 nm [39]. Based on atomic-force microscopy, we determined the surface area of glassy and crystalline quartz chips and estimated the contribution of the destroyed layer to the x-ray-electron spectra.…”