A LCAO-LDF Study of CO and NH3 Chemisorption on ZnO(0001)

The coordination of CO and NH3 to ZnO(0001) has been studied by the LCAO-LDF molecular-cluster approach. A realistic description of the electronic structure of the Lewis acid site has been found to be the most important point of the chemisorption simulation. An excellent agreement between experiment and theory has been obtained by considering the dangling bonds of ZnO(0001) to be empty. The bonding of CO to the surface is dominated by a covalent interaction involving a donation from the CO HOMO into the empty AOs of the Zn surface ions. The same kind of mechanism is active for the NH3 chemisorption, even if the electrostatic interaction between the NH3 dipole moment and the Lewis acid site is at least as important as the covalent one

CVD Cu2O and CuO nanosystems characterized by XPS

In the present investigation, X-ray photoelectron and X-ray excited Auger electron spectroscopy analyses of the principal core levels (O 1s, Cu 2p, and Cu LMM) of Cu2O and CuO nanosystems are proposed. The samples were obtained by chemical vapor deposition starting from a novel second-generation copper(II) precursor, Cu(hfa)2\ub7TMEDA (hfa1,1,1,5,5,5-hexafluoro- 2,4-pentanedionate; TMEDA=N,N,N\u2019,N\u2019- tetramethylethylenediamine), under a dry O2 atmosphere. The obtained route led to pure, homogeneous and single-phase Cu(I) and Cu(II) oxide nanosystems at temperatures of 300 and 500 \ub0C, respectively, whose chemical nature could be conveniently distinguished by analyzing the Cu 2p band shape and position, as well as by evaluating the Auger parameters. The samples were characterized by O/Cu atomic ratios greater than the expected stoichiometric values, due to marked interactions with the outer atmosphere attributed to their high surface-to-volume ratio

Metal/oxide interfaces in inorganic nanosystems: what's going on and what's next?

Metal/oxide nanosystems with different spatial organizations have attracted a remarkable interest for their unique features and multi-functional properties, which can be finely tuned by controlling the interplay between their structure, morphology and composition. Their assembly and ultimate utilization depend indeed on the nature of metal/oxide interfaces, the birthplaces of a multitude of fascinating phenomena. A detailed insight into interfacial chemical/physical properties by advanced experimental techniques would thus deliver significant advantages from both a fundamental and an applicative point of view

Gold nanotubes by template-directed synthesis

Gold nanotubes were prepared by radiofrequency-sputtering through a template-directed synthesis in porous alumina substrates. The resulting composite material was subsequently treated in acidic or alkaline aqueous solutions in order to selectively remove the membrane, thus resulting in the obtainment of self-supporting Au nanotubules. The adopted strategy allows the preparation of both composites and free-standing metal nanostructures with an aspect ratio tunable as a function of the synthesis conditions and the membrane pore size

Amorphous WO3 Films via Chemical Vapor Deposition from Metallorganic Precursors Containing Phosphorus Dopant.

Amorphous WO3 films, doped with phosphorus, have been synthesized by chemical vapor deposition of volatile, low-melting P-substituted tungsten carbonyls. The presence of a small quantity of dopant released by the precursor during its decomposition is sufficient to inhibit the crystallization of the tungsten oxide on the matrix (P/W 2-4 atom % on Si(100) and ca. 10 atom % on KGlass). The nature of the film is scarcely affected by the experimental conditions of deposition (namely p(O2) partial pressure) and the quantity of the P dopant is properly tuned by an appropriate choice of the molecular precursor, being in the order W(CO)(4)[P(OEt)(3)](2) (P/W 1/1) > W-2(mu-PR2)(2)(CO)(8) (P/W 1/4) > W(CO)(4)(PEt3)(2) (P/W 1/10 on KGlass, 1/30 on Si). The films on KGlass exhibit interesting electrochromic properties with a maximum efficiency of 66 cm(2)/C

A Molecular Cluster Approach to the Study of the Bonding of CO and NH3 to a d10 ion on ZnO(0001) and CuCl(111)

The local-density-functional approximation coupled to the molecular cluster approach is used here to compare the electronic structure of CO and NH3 molecules chemisorbed on the ZnO(0001) and CuCl(111) polar surfaces. For both substrates the interaction with the adsorbate is strongly dependent on the charge carried by the atom representative of the Lewis acid site. In particular, a realistic description of the surface-adsorbate bonding scheme is only obtained by forcing the partially occupied dangling bonds on ZnO(0001)/CuCl(111) to be empty. The bonding of CO to CuCl(111) looks similar to that present in metal-carbonyl complexes, with a donation from the CO 5\u3c3 HOMO into the empty levels of the coordinatively unsaturated Cu surface ions assisted by a significant backdonation from the fully occupied Cu 3d orbitals into the CO 2\u3c0* LUMO. At variance to that, the bonding of CO to ZnO(0001) is limited to a donation from the CO HOMO into the empty levels of the surface Zn2+ ions. The surface-molecule electrostatic interaction, negligible for CuCl(111), plays for ZnO(0001) an important role in determining the relative energy position of CO based MOs. As far as the bonding of NH3 to CuCl(111) and ZnO(0001) is concerned, it has been found to be characterized in both cases by a donation from the NH3 3a1 HOMO into the empty levels of the unsaturated metal sites. Any backbonding from the 3d orbitals of the Lewis acid sites is prevented by the high energy of the NH3 2e LUMO. Finally, for NH3 on ZnO(0001), the electrostatic interaction between the permanent NH3 dipole moment and the high value of the Lewis acid site effective charge plays a leading role in determining the binding energy