Vanadium oxide nanoparticles as optical sensors of cysteine.

We report on the synthesis of vanadium oxide nanoparticles using the laser ablation in solution technique. The particles were characterized by dynamic light scattering-DLS, transmission electron microscopy-TEM, X-ray diffraction-XRD, X-ray photoelectron spectroscopy-XPS and UV-Vis optical spectroscopy. The oxide nanoparticles are mainly composed of tetragonal V2O5, a semiconductor with a 2.2 eV band gap. The interaction of the nanoparticles with cysteine, a very important aminoacid present in proteins, was studied. Upon reaction with cysteine, the bandgap of the nanoparticles shifts to the ultraviolet region at 2.87 eV. This color change from yellow to transparent can be used for selective cysteine sensing. Additionally, the intervalence band of the optical absorption spectra shows capability for cysteine sensing in the microM range.

Morphology, structure, and magnetism of FeCo thin films electrodeposited on hydrogen-terminated Si(111) surfaces.

In this work we describe the fabrication of FeCo alloy (less than 10 at% Co) thin films from aqueous ammonium sulfate solutions onto n-type Si(111) substrates using potentiostatic electrodeposition at room temperature. The incorporation of Co into the deposits tends to inhibit Fe silicide formation and to protect deposits against oxidation under air exposure. As the incorporation of Co was progressively increased, the sizes of nuclei consisting of FeCo alloy increased, leading to films with a highly oriented body-centered cubic structure with crystalline texture, where (110) planes remain preferentially oriented parallel to the film surface.

Synthesis and characterization of disordered layered silica obtained by selective leaching of octahedral sheets from chrysotile and phlogopite structures.

Natural chrysotile fibers and pegmatitic phlogopite were acid-leached under controlled conditions. The resulting products were characterized by powder X-ray diffraction, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, (29)Si nuclear magnetic resonance, transmission electron microscopy, and selected area electron diffraction. The leached products derived of the two clays are similar, consisting of layered hydrated disordered silica with a "distorted" structure resembling the silicate layer existing in the original minerals. A simple model of the "disordered" silica structure is presented.

Application of Ni:SiO2 nanocomposite to control the carbon deposition on the carbon dioxide reforming of methane.

Stable Ni nanoparticles embedded in a mesoporous silica material were used as catalysts for the conversion of methane into synthesis gas. This catalyst has the singular properties of controlling the carbon deposition and deactivation of active sites. A comparative study of our nanocomposites with conventional catalysts showed that impregnation material presented a preferential encapsulation and growth of carbon nanotubes on the metal surface. The impregnated catalyst showed a higher tendency for carbon nanotube and whiskers formation.

Tuning protein GlnB-Hs surface interaction with silicon: FTIR-ATR, AFM and XPS study.

Herbaspirillum seropedicae GlnB (GlnB-Hs) is a signal transduction protein involved in the control of nitrogen, carbon and energetic metabolism. The adsorption of GlnB-Hs deposited by spin coating on hydrophilic and hydrophobic silicon forms a thin layer that was characterized using atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared attenuated total reflectance spectroscopy (FTIR-ATR). AFM allowed the identification of globular, face-up donut like array of protein on hydrophilic silicon substrate, favoring deprotonated residues to contact the silicon oxide surface. Over hydrophobic silicon, GlnB-Hs adopts a side-on conformation forming a filament network, avoiding the contact of protonated residues with silicon surface. XPS allowed us to determine the protonated and non-protonated states of nitrogen 1s (N 1s). The FTIR-ATR measurements provided information about protein secondary structure and its conservation, after surface adsorption.

Ferromagnetism induced by oxygen and cerium vacancies above the percolation limit in CeO2.

We studied the structural, chemical and magnetic properties of non-doped ceria (CeO(2)) thin films electrodeposited on silicon substrates. Experimental results confirm that the observed room temperature ferromagnetism is driven by both cerium and oxygen vacancies. We investigated ceria films presenting vacancy concentrations well above the percolation limit. Irradiation experiments with neon ions were employed to generate highly oxygen defective CeO(2-δ) structures. X-ray photoelectron spectroscopy and x-ray absorption near-edge structure spectroscopy were used to estimate the concentration of Ce(3+) sites in the films, which can reach up to 50% of Ce(3+) replacing Ce(4+), compared to a stoichiometric CeO(2) structure. Despite the increment of structural disorder, we observe that the saturation magnetization continuously increases with Ce(3+) concentration. Our experiments demonstrate that the ferromagnetism observed in ceria thin films, highly disordered and oxygen-deficient, preserving the fluorite-type structure only in a nanometer scale, remains intrinsically stable at room temperature.

Modification of the Interlayer Surface of Layered Copper(II) Hydroxide Acetate with Benzoate Groups: Submicrometer Fiber Generation.

We report on the functionalization of layered copper(II) hydroxide acetate with benzoic acid. The grafting of benzoate groups is characterized by thermogravimetry/differential scanning calorimetry, Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy. The submicrometer fiber generation of the grafted material is clearly demonstrated through scanning electron microscopy. Copyright 2001 Academic Press.