Ignacio Caretti

BCN films with controlled composition obtained by the interaction between molecular beams of B and C with nitrogen ion beams

Abstract Ternary BCN compounds with controlled composition have been synthesised by using independent molecular fluxes of B and C supplied from two different electron beam evaporators, and concurrent N2+ ions from a Kauffman ion gun fed with nitrogen gas. We have established experimentally the correspondence between the ratio of B/C/N atoms arriving at the substrate and the actual film composition measured by energy dispersive X-ray spectroscopy. The composition of the BCN films does not follow simply the ratio of the impinging B/C/N fluxes, but it is determined by the complex interplay of several factors, such as the reactivity between the different species, its sticking coefficient and the possibility of formation of volatile moieties.

Point defects in hexagonal BN, BC3 and BCxN compounds studied by x-ray absorption near-edge structure

The generation of point defects in highly oriented pyrolytic boron nitride (HOPBN) after Ar+ ion bombardment in ultrahigh vacuum and subsequent exposure to air was studied by angle-resolved x-ray absorption near edge structure (XANES). The pristine HOPBN showed well-oriented boron nitride (BN) basal planes parallel to the surface, with a negligible amount of defects. Amorphization of the BN structure took place after Ar+ sputtering, as indicated by the broadening of the XANES spectra and significant decrease of the characteristic π* states. Following air exposure, the XANES analysis revealed a spontaneous reorganization of the sample structure. The appearance of four new B1s π* excitonic peaks indicates an oxygen decoration process of the nitrogen vacancies created by ion bombardment. A core-level shift model is presented to support this statement. This model is successfully extended to the case of oxygen substitutional defects in hexagonal BC3 and BCxN (0 < x < 4) materials, which can be applied to any B...

Boron carbides formed by coevaporation of B and C atoms: Vapor reactivity, B{sub x}C{sub 1-x} composition, and bonding structure

Boron carbides (B{sub x}C{sub 1-x}) in thin film form have been synthesized in a high vacuum by coevaporation of B and C atoms from independent sources, allowing a study of the whole composition range from pure B films to pure C films. The relationship between the impinging B/C atomic fluxes and the film composition has been studied, providing information on the chemical reactivity between the B and C vapors. The composition was determined with x-ray emission energy dispersion spectroscopy and x-ray absorption near edge spectroscopy (XANES). Finally, the bonding structure of the films has been determined by XANES, showing a change from structures based on B{sub 12}-icosahedral units for the B-rich samples to hexagonal-like structures for the C-rich samples. The study shows that the structural transition takes place for x{approx}0.5.

Surface nanopatterning of metal thin films by physical vapour deposition onto surface-modified silicon nanodots

Nanostructuring of metallic and semiconductor surfaces in the sub-100 nm range is a key point in the development of future technologies. In this work we describe a simple and low-cost method for metal nanostructuring with 50 nm lateral and 6 nm vertical resolutions based on metal film deposition on a silane-derivatized nanostructured silicon master. The silane monolayer anti-sticking properties allow nanopattern transfer from the master to the deposited metal films as well as easy film detachment. The method is non-destructive, allowing the use of the derivatized master several times without damaging. Potential applications of the method are in the field of high-density data storage, heterogeneous catalysis and electrocatalysis, microanalysis (sensors and biosensors) and new optical devices.

Coordination chemistry of titanium and zinc in Ti(1−x)Zn2xO2 (0 ≤ x ≤ 1) ultrathin films grown by DC reactive magnetron sputtering

XANES and RBS were used to explore the structural phase and composition transitions of ultrathin films with Ti(1−x)Zn2xO2 stoichiometries, from very low (∼0.5 at.%) to high (∼25 at.%) titanium content. In this way, the coordination chemistry of Ti4+ and Zn2+ cations was examined for a wide range of oxide compositions.

X-ray emission by electron impact as a surface characterization tool for the light elements B, C, N and O: sensitivity factors and effective attenuation length

X-ray emission induced by electron impact is a common characterization technique associated to electron microscopy. The possibility of employing this technique for surface and thin film analysis arises from the low energy electrons required to excite the inner shell transitions of the light elements, and is a field not sufficiently explored. In this work, we have studied experimentally the X-ray emission intensities from h-BN, B4C and B2O3 bulk samples to determine the sensitivity factors (also known as k-factors) of the light elements C, N and O relative to B as a function of the incident electron beam energy. Furthermore, evaporated carbon thin films grown on Si(100) with thicknesses in the 20–200 nm range were used to derive the effective attenuation length λ(E) of the technique. In this way, and following a classical surface analysis approach, a fast and simple quantification procedure is presented to determine the composition of any compound of the B–C–N–O family in thin film form. These results have been compared with Monte Carlo simulations.

Influence of carbon content and nitrogen vacancies on the bonding structure and mechanical performance of graphite-like BCxN thin films

X-ray absorption near edge structure (XANES) was used to investigate two sets of graphite-like BCxN thin films with similar B:C:N ratios but different amounts of nitrogen vacancies, which become oxygen-filled in the surface-most region. The two sets of samples were grown on Si (100) at room temperature by ion beam assisted deposition using two different ion/atom ratios. Nitrogen vacancy defects were detected in the B1s XANES spectra due to an oxygen decoration mechanism taking place at the film surface, which is correctly described by a core-level shift model. Analysis of the O1s XANES spectra showed two different types of oxygen incorporation in the samples under study. The tribomechanical properties of the BCxN samples were tested by the pin-on-disk technique, revealing the substantial role played by both the carbon intake in the hexagonal BCN planes and the concentration of nitrogen vacancies generated during the growth.