Monolayer doping of germanium by phosphorus-containing molecules.

The DPP (diethyl 1-propylphosphonate) and ODPA (octadecylphosphonic acid) molecules are studied as precursors for the monolayer doping (MLD) of germanium. Their adsorption behaviour is investigated, revealing different physicochemical interactions between the phosphorus-containing molecules and the Ge surfaces. It is discovered that DPP adsorption occurs after the oxidation of Ge surface, while the ODPA undergoes chemisorption on -H terminated surfaces. Quantitative phosphorus analysis demonstrates that in the first case more than one monolayer is formed (from 2 to 4), while in the second a single monolayer is formed. Moreover, the analysis of phosphorus diffusion from the surface layers into the Ge matrix reveals that conventional thermal annealing processes are not suitable for Ge injection due to a higher activation energy of the process in comparison with silicon. On the contrary, pulsed laser melting is effective in forming a doped layer, owing to the precursor's decomposition under UV light.

AMnO3 (A = Sr, La, Ca, Y) Perovskite Oxides as Oxygen Reduction Electrocatalysts.

A series of perovskite-type manganites AMnO3 (A = Sr, La, Ca and Y) particles were investigated as electrocatalysts for the oxygen reduction reaction. AMnO3 materials were synthesized by means of an ionic-liquid method, yielding phase pure particles at different temperatures. Depending on the calcination temperature, particles with mean diameter between 20 and 150 nm were obtained. Bulk versus surface composition and structure are probed by X-ray photoelectron spectroscopy and extended X-ray absorption fine structure. Electrochemical studies were performed on composite carbon-oxide electrodes in alkaline environment. The electrocatalytic activity is discussed in terms of the effective Mn oxidation state, A:Mn particle surface ratio and the Mn-O distances.

Indium selenide: an insight into electronic band structure and surface excitations.

We have investigated the electronic response of single crystals of indium selenide by means of angle-resolved photoemission spectroscopy, electron energy loss spectroscopy and density functional theory. The loss spectrum of indium selenide shows the direct free exciton at ~1.3 eV and several other peaks, which do not exhibit dispersion with the momentum. The joint analysis of the experimental band structure and the density of states indicates that spectral features in the loss function are strictly related to single-particle transitions. These excitations cannot be considered as fully coherent plasmons and they are damped even in the optical limit, i.e. for small momenta. The comparison of the calculated symmetry-projected density of states with electron energy loss spectra enables the assignment of the spectral features to transitions between specific electronic states. Furthermore, the effects of ambient gases on the band structure and on the loss function have been probed.

A multi-technique comparison of the electronic properties of pristine and nitrogen-doped polycrystalline SnO2.

Nitrogen doped tin(iv) oxide (SnO2) materials in the form of nanometric powders have been prepared by precipitation with ammonia. Their properties have been compared with those of undoped materials obtained in a similar way using various physical techniques such as photoelectron spectroscopies (XPS and UPS), UV-Vis-NIR spectroscopy and electron paramagnetic resonance (EPR). Nitrogen doping leads to the formation of various nitrogen containing species, the more relevant of which is a nitride-type ionic species, based on the substitution of a lattice oxygen atom with a nitrogen atom. This species exists in two forms, paramagnetic (hole centre, formally N(2-)) and diamagnetic (N(3-)). The mutual ratio of the two species varies according to the oxidation state of the material. The doped solid, like most of the semiconducting oxides, tends to lose oxygen forming oxygen vacancies upon annealing under vacuum and leaving an excess of electrons in the solid. The stoichiometry of the solid can thus be markedly changed depending on the external conditions. Excess electrons are present both as itinerant electrons in the conduction band and as Sn(ii) states lying close to the valence band maximum. The presence of nitride-type centres, which are low energy states located below the top of the valence band, decreases the energy cost for the formation of oxygen vacancies by O2 release from the lattice. This particular feature of the doped system represents a severe limit to the preparation of a p-type SnO2via nitrogen doping.

The nature of the Fe-graphene interface at the nanometer level.

The emerging fields of graphene-based magnetic and spintronic devices require a deep understanding of the interface between graphene and ferromagnetic metals. This paper reports a detailed investigation at the nanometer level of the Fe-graphene interface carried out by angle-resolved photoemission, high-resolution photoemission from core levels, near edge X-ray absorption fine structure, scanning tunnelling microscopy and spin polarized density functional theory calculations. Quasi-free-standing graphene was grown on Pt(111), and the iron film was either deposited atop or intercalated beneath graphene. Calculations and experimental results show that iron strongly modifies the graphene band structure and lifts its π band spin degeneracy.

Optoelectrochemical biorecognition by optically transparent highly conductive graphene-modified fluorine-doped tin oxide substrates.

Both optical and electrochemical graphene-based sensors have gone through rapid development, reaching high sensitivity at low cost and with fast response time. However, the complex validating biochemical operations, needed for their consistent use, currently limits their effective application. We propose an integration strategy for optoelectrochemical detection that overcomes previous limitations of these sensors used separately. We develop an optoelectrochemical sensor for aptamer-mediated protein detection based on few-layer graphene immobilization on selectively modified fluorine-doped tin oxide (FTO) substrates. Our results show that the electrochemical properties of graphene-modified FTO samples are suitable for complex biological detection due to the stability and inertness of the engineered electrodic interface. In addition, few-layer immobilization of graphene sheets through electrostatic linkage with an electrochemically grafted FTO surface allows obtaining an optically accessible and highly conductive platform. As a proof of concept, we used insulin as the target molecule to reveal in solution. Because of its transparency and low sampling volume (a few microliters), our sensing unit can be easily integrated in lab-on-a-chip cell culture systems for effectively monitoring subnanomolar concentrations of proteins relevant for biomedical applications.

Synthesis of luminescent 3D microstructures formed by carbon quantum dots and their self-assembly properties.

We report in this communication the synthesis of star-shaped carbon quantum dots-(poly-γ-benzyl-L-glutamate) conjugates that self-assemble into microstructures and retain the characteristic emission properties of the native dots. Dots were used either as an initiator to give a daisy-like peptide-polymer structure or as capping agents towards more elaborated hybrid nanostructures.

Surface functionalization of fluorine-doped tin oxide samples through electrochemical grafting.

Transparent conductive oxides are emerging materials in several fields, such as photovoltaics, photoelectrochemistry, and optical biosensing. Their high chemical inertia, which ensured long-term stability on one side, makes challenging the surface modification of transparent conductive oxides; long-term robust modification, high yields, and selective surface modifications are essential prerequisite for any further developments. In this work, we aim at inducing chemical functionality on fluorine-doped tin oxide surfaces (one of the most inexpensive transparent conductive oxide) by means of electrochemical grafting of aryl diazonium cations. The grafted layers are fully characterized by photoemission spectroscopy, cyclic voltammetry, and atomic force microscopy showing linear correlation between surface coverage and degree of modification. The electrochemical barrier effect of modified surfaces was studied at different pH to characterize the chemical nature of the coating. We showed immuno recognition of biotin complex built onto grafted fluorine-doped tin oxides, which opens the perspective of integrating FTO samples with biological-based devices.

Green synthesis and electrophoretic deposition of Ag nanoparticles on SiO2/Si(100).

Plasmonic substrates were prepared by electrophoretic deposition of Ag nanoparticles on SiO2/Si(100). The Ag nanoparticles were obtained using [Ag(NH3)2](+) as the Ag precursor and d-glucose as the reducing agent. Under optimized conditions, this simple and green synthesis method furnished a suspension of Ag nanoparticles with a narrow dimensional dispersion (centered around 27 nm) and a negative z-potential, suitable for electrophoretic deposition. Samples were chemically, optically and morphologically characterized by photoemission and UV-vis spectroscopy and electron microscopy, and tested as substrates for surface enhanced Raman spectroscopy. Despite being a very simple procedure, good enhancement factors were measured thanks to the formation of hot spots, formed by sandwiching the analyte (benzenethiol) between sequentially deposited Ag nanoparticles.

Growth and optical properties of silver nanostructures obtained on connected anodic aluminum oxide templates.

Ag nanostructures are grown by AC electrodeposition on anodic alumina oxide (AAO) connected membranes acting as templates. Depending on the thickness of the template and on the voltage applied during the growth process, different Ag nanostructures with different optical properties are obtained. When AAO membranes about 1 µm thick are used, the Ag nanostructures consist in Ag nanorods, at the bottom of the pores, and Ag nanotubes departing from the nanorods and filling the pores almost for the whole length. When AAO membranes about 3 µm thick are used, the nanostructures are Ag spheroids, at the bottom of the pores, and Ag nanowires that do not reach the upper part of the alumina pores. The samples are characterized by angle resolved x-ray photoelectron spectroscopy, scanning electron microscopy and UV-vis and Raman spectroscopies. A simple NaOH etching procedure, followed by sonication in ethanol, allows one to obtain an exposed ordered array of Ag nanorods, suitable for surface-enhanced Raman spectroscopy, while in the other case (3 µm thick AAO membranes) the sample can be used in localized surface plasmon resonance sensing.

High resolution photoemission and x-ray absorption spectroscopy of a lepidocrocite-like TiO2 nanosheet on Pt(110) (1 × 2).

The electronic structure of TiO(2) nanosheets on the Pt(110)-(1 × 2) surface has been investigated by using high resolution photoemission spectroscopy and x-ray absorption spectroscopy (XAS). The Ti 2p XAS spectra of the deposited TiO(2) films have been theoretically evaluated and, from the comparison with the experimental data, the assignment to a lepidocrocite-like structure is confirmed. Coexistence of TiO(2) islands with PtO(2) stripes for incomplete nanosheets is confirmed by high resolution photoemission data. The location of the valence and conduction band edges of the nanosheet has been experimentally determined allowing us to describe in details subtle electronic effects due to the interface with the substrate. The locations of the valence band maximum and the leading peak in the O 1s XAS spectrum indicate a band gap similar to anatase but with the Fermi level closer to mid-gap than found for bulk, n-type TiO(2).

Experimental and theoretical study of a surface stabilized monolayer phase of nickel oxide on Pd(100).

A surface stabilized monolayer phase of nickel oxide, c(4 x 2)-Ni(3)O(4), has been found to grow epitaxially under reactive deposition conditions on Pd(100), in the presence of other adsorbed phases and in competition with them. High-quality scanning tunneling microscopy data are reported and discussed, including a detailed analysis of the defects and of the border morphology of this new phase. The data are discussed in the light of ab initio simulations of the electronic, energetic, and geometric properties of such a phase. A hybrid-exchange density functional theory approach has been used, and a slab model is adopted where palladium is simulated by a thin film covered on both sides by regular epilayers. A growth model has been developed that explains both the unusual stoichiometry of the phase and the observed defects.