C. Gómez-Aleixandre

Hydrogen quantification in hydrogenated amorphous carbon films by infrared, Raman, and x-ray absorption near edge spectroscopies

In this study, we have employed infrared (IR) absorption spectroscopy, visible Raman spectroscopy, and x-ray absorption near edge structure (XANES) to quantify the hydrogen (H) content in hydrogenated amorphous carbon (a-C:H) films. a-C:H films with a hydrogen content varying from 29 to 47 at. % have been synthesized by electron cyclotron resonance chemical vapor deposition at low substrate temperatures (<120 °C) applying a wide range of bias voltage, Vb, (−300 V<Vb<+100 V). With the application of high negative Vb, the a-C:H films undergo a dehydrogenation process accompanied by a sharp structural modification from polymer- to fullerenelike films. The trend in the H content derived from elastic recoil detection analysis (ERDA) is quantitatively reproduced from the intensity of the C–H bands and states in the IR and XANES spectra, respectively, as well as from the photoluminescence (PL) background drop in the Raman spectra. Using the H contents obtained by ERDA as reference data, semiquantitative expressi...

Optical emission characterization of CH4+H2 discharges for diamond deposition

Methane and hydrogen discharges has been studied at different discharge frequencies (35 kHz, 13.56 MHz, and 2.45 GHz) and feeding gas ratios (up to 100% of methane) during diamond and diamond‐like deposition by plasma chemical vapor deposition techniques. Optical emission spectroscopy shows that the intensity of atomic hydrogen line (Hα) is the highest at the microwave frequency (2.45 GHz). In addition, at this frequency and low methane concentrations (<7.5%) the emission of CH+ species is also detected, which has been associated to the presence of the diamond phase in the films. On the contrary, at the lower frequencies (35 kHz and 13.56 MHz), the emission spectra are dominated by neutral CH species that are supposed to be the precursor species in the diamond‐like films deposited at these frequencies.

Direct spectroscopic evidence of self-formed C60 inclusions in fullerenelike hydrogenated carbon films

The detection of self-formed C60 inclusions in hydrogenated carbon (C:H) with fullerenelike (FL) structure is reported. This material is synthesized by bias-enhanced electron cyclotron resonance chemical vapor deposition at low substrate temperatures (<120°C). The FL structure is identified by high-resolution transmission electron microscopy whereas the presence of C60 inclusions is derived from spectral signatures in the C(1s) x-ray absorption near edge structure. The formation of FL-C:H takes place for negative bias voltages higher than 100V, in parallel with dehydrogenation and drastic improvement of the tribomechanical film properties.

Carbon nitride thin films formation by N2+ ion implantation

Abstract Low energy (1–5 keV) N2+ ion irradiation of graphite and diamond surfaces has been investigated by angle resolved X-ray photoelectron spectroscopy (ARXPS). Analysis of the N 1s band indicates the existence of three bands that could be assigned to CN sp3, CN sp2 types of bonding and molecular nitrogen, respectively. Such an explanation is consistent with the analysis of C 1s band. The depth profiles of implanted nitrogen, recovered by inversion of the angle-dependent XPS data, revealed that ion-dose, ion-energy and angle between the ion beam and the surface normal are relevant parameters to control the composition and the thickness of the produced films.

The effect of nitrogen incorporation on the bonding structure of hydrogenated carbon nitride films

This work describes the composition and bonding structure of hydrogenated carbon nitride (a-CNx:H) films synthesized by electron cyclotron resonance chemical vapor deposition using as precursor gases argon, methane, and nitrogen. The composition of the films was derived from Rutherford backscattering and elastic recoil detection analysis and the bonding structure was examined by infrared (IR) spectroscopy and x-ray absorption near edge spectroscopy (XANES). By varying the nitrogen to methane ratio in the applied gas mixture, polymeric a-CNx:H films with N/C contents varying from 0.06 to 0.49 were obtained. Remarkably, the H content of the films (∼40 at. %) was rather unaffected by the nitrogenation process. The different bonding states as detected in the measured XANES C(1s) and N(1s) spectra have been correlated with those of a large number of reference samples. The XANES and IR spectroscopy results indicate that N atoms are efficiently incorporated into the amorphous carbon network and can be found in d...

Fast and non-catalytic growth of transparent and conductive graphene-like carbon films on glass at low temperature

This article presents the synthesis and systematic study of graphene-like carbon thin films directly grown on commercial glass by using remote electron cyclotron resonance plasma-assisted chemical vapour deposition. The fabrication process is extremely rapid and performed on 2 inch scale dielectric substrate at relatively low temperature (<550 °C) without using metal catalyst. This method avoids damaging and expensive transfer processes of graphene based films and improves compatibility with current fabrication technologies. Nanostructural characterization by transmission electron microscopy indicates the formation of layered graphene-like carbon material. Raman spectroscopy shows that the film consists of nanocrystals with a mean domain size close to 2 nm, probably interconnected by amorphous material. These graphene-like carbon based films are transparent and conductive. Functional optoelectric characterization of these films confirms their high transparency over 95% and relative high conductivity around 5 kΩ, exceeding the properties of non-doped small domain graphene based films grown at low temperatures reported so far.

On the bonding structure of hydrogenated carbon nitrides grown by electron cyclotron resonance chemical vapour deposition: towards the synthesis of non-graphitic carbon nitrides

Abstract This work compares the composition and bonding structure of hydrogenated carbon nitride films (CN x :H) obtained by electron cyclotron resonance chemical vapour deposition (ECR-CVD) with those of hydrogen-free carbon nitrides (CN x ) obtained by nitrogen ion beam assisted deposition (IBAD) of graphite. The composition and structure of the films was analysed by ion scattering techniques well suited to the detection of hydrogen, in addition to the more conventional infrared spectroscopy. The bonding structure was examined by X-ray absorption spectroscopy (XANES). The typical IBAD CN x films are graphitic with a N/C content below 0.3. However, the ECR-CVD films show a less graphitic bonding structure. The ECR-CVD films were synthesised in a conventional microwave ECR reactor (2.25 GHz, 875 Gauss, 250 W) using as precursor gases N 2 and Ar in the reactor chamber, and CH 4 directly in the deposition chamber.

Study of the plasma discharges in diamond deposition with different O2 concentrations

Abstract The effect of the O2 concentration in the structure of diamond films deposited from CH4H2O2 gas mixtures by microwave chemical vapor deposition has been studied. For oxygen-to-methane ratios in the 0–0.75 range a strong increase in the diamond content in the films has been observed. At higher oxygen-to-methane ratios the diamond content in the film stabilizes and then decreases, resulting in no carbon deposition when the oxygen concentration exceeds the methane concentration in the discharge. The emission intensity corresponding to carbon-hydrogen species (CH + and CH), detected by optical emission spectroscopy slightly decreases with the oxygen concentration in the plasma. Only an increase in the 300–312 nm emission range has been measured, which can be related to the presence of activated CO and OH species in the discharge, in agreement with the results obtained by mass spectrometry. We have related the diamond content in the films with the CO mole fraction present in the discharge.

Crystallization and sintering characteristics of chemically vapor deposited silicon nitride powders

High purity silicon nitride powders have been obtained by Chemical Vapor Deposition (CVD), through the reaction of SiH 4 and NH 3 gas mixtures at 1000 °C in a quartz reactor. The crystallization characteristics of the powder have been followed by infrared and x-ray diffraction analysis. The material shows a transition from amorphous to the α-phase after a thermal treatment at about 1300 °C for 1 h, while the β-phase starts to appear at 1725 °C. The sintering properties of the amorphous and crystalline phases were evaluated by measuring the dilatometric curves of compacted powders.

Influence on the electrical characteristics of the -NH radicals incorporated into PECVD silicon nitride films

Abstract The electrical and structural properties of silicon nitride films deposited by plasma-enhanced chemical vapour deposition (PECVD) have been investigated. The films were grown using ammonia and silane diluted in nitrogen (2%) as reactants in a wide range of ammonia to silane flow ratios (between 3 and 35) and plasma powers (10–500 W). Only -NH species were found incorporated into the films. For the stoichiometric samples, a good correlation between the NH bond density and the positive charge density was observed.