Robertino Zanoni

Self-assembled monolayers of silver nanoparticles firmly grafted on glass surfaces: Low Ag + release for an efficient antibacterial activity

A two-step, easy synthetic strategy in solution has been optimized to prepare authentic monolayers of silver nanoparticles (NP) on MPTS-modified glass surfaces, that were investigated by AFM imaging and by quantitative silver determination techniques. NP in the monolayers remain firmly grafted (i.e. not released) when the surfaces are exposed to air, water or in the physiological conditions mimicked by phosphate saline buffer, as UV-Vis spectroscopy and AFM studies demonstrate. About 15% silver release as Ag(+) ions has been found after 15days when the surfaces are exposed to water. The released silver cations are responsible of an efficient local microbicidal activity against Escherichia coli and Staphylococcus aureus bacterial strains.

Synchrotron radiation induced metal deposition on semiconductors: Mo(CO)6 on Si (111)

We found that unmonochromatized soft x‐ray synchrotron radiation stimulates the dissociation of molecular Mo(CO)6 adsorbed on silicon, producing a metallic overlayer. The process, which is interesting for potential applications, was studied using soft x‐ray photoemission spectroscopy.

Electrochemically deposited ZnO films: an XPS study on the evolution of their surface hydroxide and defect composition upon thermal annealing

Electrodeposition from ZnCl2 aqueous solution was performed to grow ZnO thin films on the surface of polycrystalline copper plates. Electrochemical parameters for deposition were optimized by means of cyclic voltammetry (CV). The morphology of the deposits was studied via scanning electron microscopy (SEM), and their chemical composition was ascertained by means of X-ray photoelectron spectroscopy (XPS). The effects of changing the deposition bath temperature (Tbath) and the role played by post-deposition treatments, such as temperature and time of annealing in air, were studied. SEM images of freshly deposited vs. annealed samples have shown that in the former case the films display a rough morphology with mixed grain/hexagonal platelets structures and in the latter smaller but more uniformly dispersed cubic grains. Tbath is found to be the key parameter to induce the different morphology in the deposited films, which reflects in a different chemical reactivity of surface species, as found on the basis of the binding energies and relative quantitative ratios between Zn 2p and O 1s peaks. In fact, a higher Tbath favours a more efficient desorption of OH groups upon annealing, the O 1s peak resulting to much more drastically modified oxide/hydroxide intensity ratio with respect to the case of the sample deposited at lower Tbath.

Ethylene and Acetylene Adsorption on Cleaved Si - a Photoemission-Study with Synchrotron Radiation

Abstract Our data reveal a close analogy between the adsorption states of ethylene and acetylene on cleaved silicon. The adsorption mechanisms confirm that the cleaved Si surface is a good π donor.

Organometallic adsorption on semiconductors: a synchrotron radiation photoemission study of ferrocene and nickelocene on Si(111)2×1

A synchrotron radiation photoemission study of the adsorption behaviours of ferrocene, Fe (C5H5)2, and nickelocene, Ni (CH5)2, on the Si (111) 2 X 1 surface is reported. The substrate temperature ranged between 80 and 300 K and the exposure range investigated was 1-1000 langmuir. For both species the adsorption is molecular over the entire temperature range, as demonstrated by the one-to-one correspondence between the valence photoemission spectra of the species adsorbed on Si and those of the corresponding free molecules. Exposure of the reacted surfaces saturated with metallocenes to unmonochromatized synchrotron light results in a partial desorption of the species. This result is at variance with the reactivity on Si shown by some Fe, W and Mo carbonyl analogues of the metallocenes, which readily decompose to metal under the same experimental conditions. The higher chemical stability on Si of the metallocenes discussed here with respect to carbonyls is consistent with the corresponding behaviour of the free molecules.

Metal-free and transition-metal tetraferrocenylporphyrins part 1: synthesis, characterization, electronic structure, and conformational flexibility of neutral compounds

H(2)TFcP [TFcP = 5,10,15,20-tetraferrocenyl porphyrin(2-)] was prepared by a direct tetramerization reaction between pyrrole and ferrocene carbaldehyde in the presence of a BF(3) catalyst, while the series of MTFcP (M = Zn, Ni, Co and Cu) were prepared by a metallation reaction between H(2)TFcP and respective metal acetates. All compounds were characterized by UV-vis and MCD spectroscopy, APCI MS and MS/MS methods, high-resolution ESI MS and XPS spectroscopy. Diamagnetic compounds were additionally characterized using (1)H and (13)C NMR methods, while the presence of low-spin iron(ii) centers in the neutral compounds was confirmed by Mössbauer spectroscopy and by analysis of the XPS Fe 2p peaks, revealing equivalent Fe sites. XPS additionally showed the influence on Fe 2p binding energies exerted by the distinct central metal ions. The conformational flexibility of ferrocene substituents in H(2)TFcP and MTFcP, was confirmed using variable-temperature NMR and computational methods. Density functional theory predicts that alpha,beta,alpha,beta atropisomers with ruffled porphyrin cores represent minima on the potential energy surfaces of both H(2)TFcP and MTFcP. The degree of non-planarity is central-metal dependent and follows the trend: ZnTFcP < H(2)TFcP approximately CuTFcP < CoTFcP < NiTFcP. In all cases, a set of occupied, predominantly ferrocene-based molecular orbitals were found between the highest occupied and the lowest unoccupied, predominantly porphyrin-based molecular orbitals. The vertical excitation energies of H(2)TFcP were calculated at the TDDFT level and confirm the presence of numerous predominantly metal-to-ligand charge-transfer bands coupled via configurational interaction with expected intra-ligand pi-pi* transitions.

Niobia and silica–niobia catalysts from sol–gel synthesis: an X-ray photoelectron spectroscopic characterization

Abstract An X-ray photoelectron spectroscopy study of distinct series of niobia and silica–niobia mixed oxides, prepared via sol–gel at 1:2, 1:10 and 1:20 Nb/Si atomic ratios, is reported. The values of Nb 3d binding energy and the peak shapes for all the investigated samples exclude the presence of oxidation states other than Nb(V) at the surface. In the mixed oxides, the progressive Nb dilution in silica results in an increase in the values of the full width at half peak maximum of Nb 3d, which is particularly relevant on passing from the 1:10 to the 1:20 sample, while the symmetric shape of the 3d spin-orbit components is preserved even at the higher dilution. This is interpreted as due to a dramatic increase in Nb dispersion in the same sequence, which is further evidenced by a combination of XPS and X-ray-excited Auger results. While a progressive Nb dilution in silica would be expected to result in the narrowing of both the Si 2p and the Si KLL Auger peaks as the Si environment approaches that of pure silica, the effect experimentally observed by means of XPS is surprisingly the opposite. It is proposed that an unexpectedly growing fraction of Si atoms in a distinct environment from silica results at the higher Nb dilution. This fraction is assigned to the Si atoms engaged in Si–O–Nb bridging bonds, on the basis of XPS findings. The dramatic increase in the surface area values experimentally observed on passing from the 1:10 to the 1:20 silica–niobia sample, is therefore proposed to be due to a very high Nb dispersion.

Synthesis and properties of ZnTe and ZnTe/ZnS core/shell semiconductor nanocrystals

We report the synthesis of spherical ZnTe nanocrystals and the successive coating with a ZnS shell to afford core/shell quantum dots. These nanocrystals can represent alternatives to cadmium-based quantum dots but their preparation and properties are challenging and relatively unexplored. The effect of various synthetic parameters on the reaction outcome was investigated, and the resulting nanocrystals were characterized by TEM, EDX, XPS, and spectroscopic measurements. The optical data indicate that these core/shell quantum dots belong to type I, i.e., both the electron and the hole are confined within the ZnTe core. Both the ZnTe core and ZnTe/ZnS core/shell quantum dot samples absorb in the visible region and are not luminescent. The ZnS shell preserves the optical properties of the core and improves the chemical and photochemical stability of the nanoparticles in air equilibrated solution, whereas they appear to be quite fragile in the solid state. XPS results have evidenced the distinct nature of core and core/shell QDs, confirming the formation of QDs with shells of different thicknesses and their evolution due to oxidation upon air exposure. Anodic photocurrent generation was observed when an ITO electrode functionalized with ZnTe/ZnS nanocrystals was irradiated in the visible region in a photoelectrochemical cell, indicating that the quantum dots perform spectral sensitization of the electron injection into the ITO electrode. Conversely, cathodic photocurrent generation was not observed; hence, the QD-modified electrode performs electrical rectification under a photon energy input.

SILICON METALLIZATION BY SYNCHROTRON-RADIATION-INDUCED W(CO)6 SURFACE REACTION

Abstract We produced metal overlayers on cleaved Si(111) at low temperature, by exposing to white synchrotron radiation in situ molecularly adsorbed W(CO)6. We show for the first time that the overlayer produced at low temperature remains stable at room temperature, thereby enhancing the possibility of practical use of this class of processes.

Mo(CO)6 on Si(111)2 × 1: a synchrotron radiation-excited photoemission study

A synchrotron radiation-excited photoemission study of the adsorption behaviour of Mo(CO)6 on Si(111)2 × 1 is reported. The compound has been investigated in the temperature range 50 K-room temperature (RT), and in the exposure range 0.1-200 L (1 Langmuir = 10-6 Torr s-1). Both core (Mo 3d, C 1s, Si 2p, O 1s) and valence levels were investigated. At T ≤ 100 K and exposures ≥0.5 L, the adsorption of Mo(CO)6 on cleaved Si is molecular, as clearly indicated by a 1: 1 correspondence of the features in the valence band (VB) spectrum with those already reported for free Mo(CO)6, at the same photon energy. At T < 100 K and very low exposures (0.1 L) we found evidence of a decomposition process taking place. At T ≥ 150 K, the adsorption is dissociative at exposures < 120 L and molecular at higher exposures. As the temperature increases up to 200 K, only dissociative processes are detected, also at high exposures. At RT, no adsorption at all was detected. Reacted surfaces were exposed to zero-order light to promote metal deposition on Si. A metal layer on top of Si was obtained after short exposures. CO adsorbs on this layer and is partially dissociated. Molecular CO is removed by further exposure to zero-order light. The presence of atomic C and O from CO partial dissociation and of carbide species was detected.