J.C. Sánchez-López

Bonding structure in amorphous carbon nitride: A spectroscopic and nuclear magnetic resonance study

Since the prediction of Liu and Cohen [Science 245, 841 (1989)] of the potential extraordinary mechanical properties of crystalline β-C3N4, many authors have attempted its synthesis. However, in most cases, the obtained materials are amorphous phases with a complex bonding structure. Their characterization is complicated due to the absence of a reference compound, the lack of long-range order, and the poor knowledge about their bonding structure. In this article, we present 1H, 13C, and 15N solid-state nuclear magnetic resonance (NMR) measurements for the determination of the bonding types in amorphous CNx films. NMR measurements do not require long-range order and are able to clearly identify the signals from the sp2- and sp3-bonded phases. The analysis of the data obtained by other characterization techniques, such as infrared spectroscopy, x-ray photoelectron spectroscopy, electron energy-loss spectroscopy, and x-ray absorption near-edge spectroscopy on the same sample, based on the information acquired by NMR, enables the description of a structure model for the studied amorphous-CNx phase prepared by dc-magnetron sputtering and to revise the interpretation found in the literature.Since the prediction of Liu and Cohen [Science 245, 841 (1989)] of the potential extraordinary mechanical properties of crystalline β-C3N4, many authors have attempted its synthesis. However, in most cases, the obtained materials are amorphous phases with a complex bonding structure. Their characterization is complicated due to the absence of a reference compound, the lack of long-range order, and the poor knowledge about their bonding structure. In this article, we present 1H, 13C, and 15N solid-state nuclear magnetic resonance (NMR) measurements for the determination of the bonding types in amorphous CNx films. NMR measurements do not require long-range order and are able to clearly identify the signals from the sp2- and sp3-bonded phases. The analysis of the data obtained by other characterization techniques, such as infrared spectroscopy, x-ray photoelectron spectroscopy, electron energy-loss spectroscopy, and x-ray absorption near-edge spectroscopy on the same sample, based on the information acquire...

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.

Evidence of spin disorder at the surface–core interface of oxygen passivated Fe nanoparticles

Hysteresis, thermal dependence of magnetization, and coercivity of oxide coated ultrafine Fe particles prepared by inert gas condensation and oxygen passivation have been studied in the 5–300 K range. The results are found to be consistent with a spin-glasslike state of the oxide layer inducing, through exchange interaction with the ferromagnetic core, a shift of the field cooled hysteresis loops at temperatures below the freezing at approximately 50 K.

Mechanical behavior and oxidation resistance of Cr(Al)N coatings

Nanocrystalline chromium nitride and ternary chromium aluminium nitride thin films were deposited by reactive magnetron sputtering of Cr and Al targets in argon/nitrogen atmosphere varying the sputtering power and gas composition. The coatings were characterized in terms of crystal phase, chemical composition, microstructure, and mechanical properties by x-ray diffraction, x-ray photoelectron spectroscopy, including x-ray-induced Auger electron spectroscopy, transmission electron microscopy, selected-area electron diffraction, electron energy-loss spectroscopy, cross-sectional scanning electron microscopy, and ultramicrohardness tester. The incorporation of Al in the composition of the films produces an increase in the mechanical properties (hardness and reduced Young’s modulus) and an increased thermal resistance against oxidation in comparison to the pure CrN composition. The hardness behavior was attributed mainly to a reduction of the CrN crystallite size according to a Hall–Petch relationship. The ox...

Doping and Alloying Effects on DLC Coatings

Doped or alloyed diamond-like carbon (DLC) coatings is an important category of DLC characterized by the incorporation of different elements in their structure to achieve multifunctionality and improved properties in respect to pure DLC films. By controlling the nature, content and distribution of the dopants, tailored synthesis of doped-DLC with properties adapted to a desired value for specific applications can be obtained. Common dopants are light elements (B, Si, N, O or F), metals and combinations thereof to modify properties such as hardness, tribological properties, internal stress, adhesion, electrical conductivity or biocompatibility. The purpose of this chapter is to provide an overview of the different alloyed-DLC and more novel nanostructured coatings reported in the literature in relation with the property of interest. The tribological properties will be discussed in light of their chemical composition and microstructure trying to obtain general trends or correlation between them when possible due to the high number of parameters influencing their practical tribological response.

Tribological and mechanical properties of diamond-like carbon prepared by high-density plasma

Abstract Diamond-like carbon films (DLC) have been deposited by plasma-enhanced chemical vapor deposition using a commercial r.f. high-density plasma (HDP). The hardness and elastic modulus have been determined from force–displacement curves using a nanoindentation instrument. The friction coefficients and wear rates have been measured using a pin-on-flat tribometer in ambient air and UHV at maximum Hertzian contact pressure of 1.09 GPa. It was found that the hardness, Youngs modulus, and wear resistance of the films increased with decreasing hydrogen content of the films. A viscoplastic behavior has been observed for films with hydrogen content higher than 30% indicating that these films have a softer ‘polymer-like’ structure. The unbound hydrogen present in the HDP films contributes to the enhancement of the viscoplastic behavior of the film and to the decrease of the friction in UHV. The correlation between viscoplastic properties, film structure and tribological behavior of the HDP films is presented and compared to those obtained with samples prepared by d.c. PECVD.

The melting behavior of passivated nanocrystalline aluminum

Abstract A nanocomposite Al 2 O 3 Al material has been prepared by consolidation of nanocrystalline aluminum particles which have been passivated with an alumina overlayer prior to the compaction step. Nanostructured Al has been prepared by the gas phase condensation method. The material has been characterized by XPS (X-ray photoelectron spectroscopy). DSC (differential scanning calorimetry), TEM (transmission electron microscopy) and AFM (atomic force microscopy). This study allowed us to demonstrate that the consolidated Al 2 O 3 Al material, although showing a metallic shine and an ohmic electrical resistivity, presents a microstructure constituted by Al grains interconnected by a very thin alumina network, which prevents the material from falling apart when heated at temperatures above the melting point of aluminum.

Diamond-like carbon prepared by high density plasma

Abstract This paper will present physical and tribological properties of diamond-like carbon (DLC) films deposited by plasma-enhanced chemical vapor deposition using a commercial RF high density plasma (HDP). The films have been prepared from acetylene or acetylene+hydrogen mixtures using a range of HDP conditions. The composition and optical properties of the DLC films have been characterized by forward recoil elastic scattering (FRES) and Fourier transform infrared spectroscopy (FTIR). The tribological properties have been measured in ambient air and in dry nitrogen using a pin-on-flat tribometer. While the friction coefficients in air (

A General Perspective of the Characterization and Quantification of Nanoparticles: Imaging, Spectroscopic, and Separation Techniques

This article gives an overview of the different techniques used to identify, characterize, and quantify engineered nanoparticles (ENPs). The state-of-the-art of the field is summarized, and the different characterization techniques have been grouped according to the information they can provide. In addition, some selected applications are highlighted for each technique. The classification of the techniques has been carried out according to the main physical and chemical properties of the nanoparticles such as morphology, size, polydispersity characteristics, structural information, and elemental composition. Microscopy techniques including optical, electron and X-ray microscopy, and separation techniques with and without hyphenated detection systems are discussed. For each of these groups, a brief description of the techniques, specific features, and concepts, as well as several examples, are described.

Tailored synthesis of TiC∕a-C nanocomposite tribological coatings

Composite coatings made of nanocrystalline TiC (nc-TiC) particles and amorphous carbon (a-C) have been prepared in a double magnetron sputtering system using graphite and titanium targets under Ar bombardment. Chemical composition and microstructure of coatings were studied by transmission electron microscopy (TEM), electron energy loss spectroscopy (EELS), and x-ray diffraction (XRD) for a set of samples prepared varying the ratio and intensity of power applied to each magnetron. Changes in coatings microstructure, from a quasipolycrystalline TiC to a nanocomposite formed by nanocrystals of TiC embedded in an amorphous matrix of carbon (nc-TiC∕a-C), are observed depending on the synthesis conditions. Tribological and mechanical properties of coatings were tested using a pin-on-disk tribometer and an ultramicrohardness indenter, respectively. Coatings with moderate hardness (7–27GPa), low friction (0.1–0.2), and low wear rates (k∼10−7mm3∕Nm) were obtained. A percentage between 15% and 30% of TiC is found ...