C. Quirós

Friction mechanisms of amorphous carbon nitride films under variable environments: a triboscopic study

Abstract In this work, a carbon nitride film prepared by ion-beam-assisted deposition onto silicon was investigated using reciprocating sliding tests under different surrounding atmospheres (ambient air, dry air, dry nitrogen (DN), and ultra-high vacuum) and testing conditions (contact pressure, nature of the counterface). The carbon–nitrogen (CNx) coating provided a ‘superlow’ friction coefficient of 0.007–0.008 in DN atmosphere independently of the mating material (steel or sapphire balls). The build-up of a smooth transfer film onto the ball surface was detected by optical microscopy. The change in the friction coefficient was spatially recorded along the track as sliding progressed. This technique, called ‘triboscopy’, combined with variable amplitude tests performed on the same wear track, revealed that the nature of both counterfaces (ball and film) has to be modified during a short running-in period before achievement of the superlow friction regime. When other surrounding atmospheres are used, the superlow friction coefficient is not attained even if the counterfaces are previously rubbed in DN. This assembly of tools allowed the characterization of environmental influence on the tribological behavior of CNx coatings in terms of friction coefficient, material transfer, and chemistry of the sliding interface, and the comparison with that observed for diamond-like coatings.

CHARACTERIZATION OF CARBON NITRIDE THIN FILMS PREPARED BY DUAL ION BEAM SPUTTERING

Carbon nitride thin films obtained by dual ion beam sputtering have been investigated by electron energy‐loss spectroscopy (EELS), transmission electron microscopy, and Fourier transform infrared spectroscopy. The nitrogen content in the films depends on deposition conditions. A maximum value of N/C=0.8 has been achieved. A new peak at 286.7 eV energy loss in the C K‐edge EELS spectra has been assigned to C=N bonds with C in the sp2 hybridization state. In addition, experimental evidences are presented of the formation of β‐C3N4 crystallites embedded in a layer of a polymer like CNx amorphous phase. An evaluation of the experimental parameters that lead to the highest N content in the films is also included.

Correlation between N 1s core level x-ray photoelectron and x-ray absorption spectra of amorphous carbon nitride films

This work presents a comparative analysis of the N 1s core level spectra, as measured by x-ray photoelectron spectroscopy (XPS) and x-ray absorption spectroscopy (XAS), of amorphous CNx films which gives evidence of the existing correlation between the different components that constitute the respective spectra. After annealing, the contribution of XPS at 399.3 eV and the components of XAS at 399.6 and 400.8 eV are clearly enhanced. They are assigned to sp2 with two neighbors and to sp states of nitrogen. In addition, the XPS component at 401.3 eV is related to the XAS feature at 402.0 eV and has been assigned to sp2 nitrogen bonded to three carbon neighbors.

Bonding and morphology study of carbon nitride films obtained by dual ion beam sputtering

Thin carbon–nitrogen films (i.e., CNx) have been obtained by dual ion beam sputtering. The chemical composition and the type of bonding of the CNx material have been examined, as a function of the deposition parameters, by Fourier transform infrared spectroscopy, x-ray photoelectron spectroscopy (XPS), and electron energy loss spectroscopy (EELS). The high concentration of C≡N bonds present in some of the samples, as stated by FT-IR, allowed us to correlate this type of bonding with some of the features observed in the corresponding XPS and EELS spectra. Nitrogen concentrations of up to 45 at. %, depending on the deposition conditions, have been estimated by XPS and EELS. The films deposited at low energy were rather homogeneous, as demonstrated by Auger electron spectroscopy depth profiling, and show the highest C–N simple bonds concentration. On the contrary, the use of high energy assisting nitrogen ions leads to the formation of carbonitrile groups (i.e., C≡N), as well as resputtering effects that significantly reduce the thickness of the films and even hinder the growth of a film. The topography and morphology of the different films, as determined by atomic force microscopy, were also observed to depend on the conditions of assistance.Thin carbon–nitrogen films (i.e., CNx) have been obtained by dual ion beam sputtering. The chemical composition and the type of bonding of the CNx material have been examined, as a function of the deposition parameters, by Fourier transform infrared spectroscopy, x-ray photoelectron spectroscopy (XPS), and electron energy loss spectroscopy (EELS). The high concentration of C≡N bonds present in some of the samples, as stated by FT-IR, allowed us to correlate this type of bonding with some of the features observed in the corresponding XPS and EELS spectra. Nitrogen concentrations of up to 45 at. %, depending on the deposition conditions, have been estimated by XPS and EELS. The films deposited at low energy were rather homogeneous, as demonstrated by Auger electron spectroscopy depth profiling, and show the highest C–N simple bonds concentration. On the contrary, the use of high energy assisting nitrogen ions leads to the formation of carbonitrile groups (i.e., C≡N), as well as resputtering effects that sig...

Electronic interaction at the TiO2–Al2O3 interface as observed by X-ray absorption spectroscopy

The electronic structure of the TiO 2 -Al 2 O 3 interface has been studied using X-ray absorption spectroscopy. Special attention has been paid to the early stages of growth, i.e. the sub-monolayer regime (τ < 1). The Ti 2p spectra for coverages below I ML show significant changes with respect to those for large coverages and bulk TiO 2 indicating the presence of interfacial states. The spectra have been compared with atomic multiplet calculations reported in the literature. From this comparison it is concluded that strong electronic interactions occur at the interface, as deduced from the significant lowering of the crystal field of the Ti atoms at the interface (1.0 eV) as compared with bulk TiO 2 (1.8 eV). It is suggested that the important covalent character of the bonding of the Al 2 O 3 substrate is the responsible of this crystal field lowering.

The role of CN chemical bonding on the tribological behaviour of CNx coatings

Abstract The tribological performance of CN x coatings depends strongly on both the environmental conditions and the nature of the coating, in relation to the deposition process. In this paper, we present and discuss friction results in relation to the nature, crystal structure, chemical composition and hybridization state of CN x coatings prepared by dual ion beam sputtering under various conditions. The films were characterized by infrared spectroscopy, X-ray photoelectron spectroscopy and electron energy loss spectroscopy. By increasing the polarization of the substrate, an increase of the N/C atomic ratio, together with a decrease of the CN/CN and CN/CC bonding ratios are observed. The concentration of CN triple bond is negligible. Reciprocating pin-on-plane friction tests have been carried out in humid ambient air and in ultrahigh vacuum. Steady-state friction in ambient air has been found to be in the range of 0.14–0.25, increasing slightly with the increase of the substrate polarization during deposition. The presence of CN double bond is associated with a lower friction coefficient. The steady-state friction of the film exhibiting the lowest friction in ambient air is near 0.6 in ultrahigh vacuum. The chemical composition of the topmost surfaces both inside and outside the UHV wear tracks of the plane and the pin was investigated by in situ XPS and AES performed at the completion of the friction test in the analytical tribometer. The high friction in UHV is associated with a significant transfer of the iron oxide top layers from the pin as wear particles inside the wear track of the plane, without any CN transfer onto the steel pin.

Carbon nitride films synthesized by dual ion beam sputtering

Abstract Carbon nitride films CNx have been obtained in a dual ion beam sputtering system using Ar+ to deposite graphite and low energy (i.e.

Dielectric Properties of Ti, TiO2 and TiN from 1.5 to 60 eV Determined by Reflection Electron Energy Loss Spectroscopy (REELS) and Ellipsometry

The dielectric properties of metallic Ti and thin films of TiO2 and TiN in the energy range from 1.5 to 60 eV have been determined by quantitative analysis of the respective electron energy loss spectra in the reflection mode (REELS). The energy loss function (ELF) of every material, that is proportional to Im {1/e}, is obtained by trial and error until a good quantitative agreement between the simulated and experimental inelastic electron scattering cross-sections at three different primary electron energies (i.e. 0.5, 1 and 1.5 keV) is achieved. Kramers-Kronig transformation is then used to obtain real and imaginary parts of the dielectric function e(ω). In addition, spectroscopic ellipsometry was used to improve the ELF in the 1.5 to 4.5 eV energy range where it is strongly affected by the experimental energy resolution and the presence of the elastic peak. The characteristic differences among the spectra of the particular compounds are discussed in terms of different electronic properties.

Thin BN films obtained by dual-ion-beam sputtering: an FT-IR and spectroscopic ellipsometry characterization

Abstract Thin BN films (100–250 nm) have been deposited on Si(100) substrates in a double-ion-beam sputtering system from a h-BN target. The films have been characterized by FT-IR spectroscopy and spectroscopic phase-modulated ellipsometry as a function of the deposition and irradiation parameters. Assistance with Ar+ ions result in boron rich films with refraction indexes above 2 or even higher as the deposited energy of the assisting ions increases. N2+-bombardment causes stoichiometric and even nitrogen-rich BN films characterized by refraction indexes around 1.85. The stability of the films is enhanced when the deposited energy of the N2+ ions is above 30 eV/atom and/or the deposition is performed on substrates at temperatures above 100°C.

Characterization of Zr thin films grown by dual ion-beam sputtering

Abstract Zr thin films (100–600 nm) have been deposited on pyrex substrates at different temperatures (50–200°C) in a double ion beam sputtering system (residual pressure −7 torr) using Ar + ions for both sputtering and irradiation of the growing film. The films have been characterized by XRD, resistivity measurements and optical microscopy. The results show that, depending on the flux and energy of the ions impinging the growing film, the films develop compressive and tensile stresses which clearly influence their adherence and consequently their stability against exposure to the atmosphere.