M. Ducarroir

Nanoindentation of Si, GaP, GaAs and ZnSe single crystals

We present a systematic study of the mechanical properties of bulk Si, GaP, GaAs and ZnSe semiconducting materials. Nanoindentation tests have been performed on the (001) surface of single crystals and their interpretation has been supported by AFM imaging of the indented surface. For all four materials, hardness and Young’s modulus appear to be independent of the orientation of the Berkovich nanoindenter tip relative to the [100] direction. In contrast, hardness varies significantly with the applied load for ZnSe, which is the only material exhibiting large creep. All mechanical properties—plasticity, hardness, Young’s modulus—depend on both the interatomic distance and the ionicity of the materials. Si and ZnSe are, respectively, the hardest and the softest materials of the series, the hardness of ZnSe being comparable to that of soft metals.

Theoretical approach to chemical vapour deposition in the atomic system Ti-Si-C-CI-H

Etude du diagramme de phase du systeme Ti-Si-C et estimation des energies libres de formation des composes solides de ce systeme

Nanoindentation study of Zn1−xBexSe heteroepitaxial layers

We present a study of the nanoindentation behaviour of Zn1−xBexSe heteroepitaxial layers grown onto (001)-oriented GaP and GaAs substrates in the whole composition range 0≤x≤1. The alloy composition, applied peak load and orientation of the Berkovich indenter have been found to significantly affect the nanoindentation response of these films. In particular, the Youngs modulus increases relatively steadily with beryllium composition (though discontinuities are observed at x0.2 and 0.7–0.9), whilst hardness reaches a maximum at x0.7–0.9. Hardness is anisotropic, as it depends upon the orientation of the side of the Berkovich pyramid relative to the [100] direction. The variation of hardness and Youngs modulus are related to the percolative behaviour of Zn1−xBexSe. Our results show that the mechanical properties of ZnSe (in which the type of bonding is essentially ionic) are greatly improved by alloying with BeSe (in which the bonding is essentially covalent), though they remain well below those of usual III–V compounds such as GaAs or GaP.

An experimental approach to the analysis of the adhesion properties of SiC coatings deposited on steel substrates

SiC coatings were deposited by a plasma-assisted chemical vapour deposition technique (r.f. coupled) on steel substrates from Si(CH3)4-Ar mixtures. Different atomic compositions (Si:C ratios) were obtained vs. deposition parameters, and the adhesive properties were semiquantitatively established. By three-point bending tests, different steps in the damage evolution were observed and were discussed; they are related to the deposition pressure and the ion cleaning of the substrate. From the occurrence of adhesion loss and the corresponding critical strain at the interface, apparent adhesion parameters were calculated through an analytical formulation. The results tend to indicate that the layers obtained are strongly adherent.

Coating of steel by plasma-activated metal-organic chemical vapour deposition in the Si-C system

Abstract In order to obtain a surface modification of 35CD4 steel (4135 steel) for tribilogical applications, experiments have been carried out in a tubular reactor by r.f. glow discharge (inductive process) from tetramethylsilane diluted in an argon flow. The influence of deposition parameters was investigated using statistically designed experiments and then parametric studies regarding deposition temperature and total pressure were carried out. The effects of these parameters on deposition rate and coating composition are presented and discussed in terms of basic phenomena in the plasma. Characterization of the coatings with various spectroscopic methods is presented.

SiCTiC multiphased materials obtained by CVD

Abstract Carbide composite structures have been prepared by thermal chemical vapour deposition under atmospheric pressure from an input gaseous mixture composed of SiH2Cl2C4H10TiCl4H2. Their morphologies are strongly dependent on the composition of the input gases leading to either micro- or nanostructures. The latter were investigated by transmission electron microscopy. High resolution observations have revealed the microstructural arrangement of phases. On the basis of these characterizations, a spatial arrangement of the components which fits the composition variations in the deposits is proposed.

Gas and plasma nitriding pretreatments of steel substrates before CVD growth of hard refractory coatings

Abstract Vapor phase nitriding pretreatments compatible with subsequent deposition processes of representative metallurgical coatings have been investigated. Thus, gas nitriding treatments of two steel substrates (38 CD 4 and 30 NCD 14) have been achieved in an MOCVD reactor using NH 3 /H 2 /He as reactive gas mixtures. The composition, the structure and the thickness of the nitride layers have been characterized by metallography, SEM, XRD, EPMA, XPS, SIMS and nano-indentation as a function of the main conditions, e.g., nitriding potential and duration. Such a pretreatment has been performed prior to the MOCVD of V–C–N type coatings. Similarly microwave-plasma nitriding by N 2 /Ar mixtures of these steel substrates has been studied and was applied prior to the deposition of silicon carbide based films by microwave-plasma CVD. The nitriding pretreatment enhances the adhesion of both plasma-CVD SiC(H) and MOCVD V(C,N) coatings unlike the MOCVD VN-type films. These different mechanical behaviors are discussed from features of the interface.

The evolution of the translational energy of hydrogen atoms in a 2 MHz inductively coupled plasma deposition reactor

The analysis of the Balmer H and H emission line shapes in a 2 MHz radiofrequency Ar- glow discharge, used in a plasma-assisted CVD reactor, reveals anomalous Doppler profiles which indicate that atomic hydrogen has two kinds of average kinetic energies. These energies vary with the distance z to the grounded substrate and are -0.4 eV for the slow (low-energy) hydrogen and 6-24 eV for the other. Moreover, the Doppler broadenings observed for Ar, and lines lead always to energy values lower than 0.15 eV. From the optical emission signals and a relevant discussion, it is established that would be the origin of the fast hydrogen. Its energy would be limited by charge transfer between and whereas the slow molecular hydrogen would give rise to slow hydrogen by a dissociative excitation mechanism.

Propriétés mécaniques des films minces : Problématiques et moyens de mesure

Summary The aim of this work is the characterization of the mechanical behaviour of a couple consisting of a substrate and of a ceramic coating with a few micrometer thickness. We review here the related quantities and the measurement methods with particular emphasis on the significant factors which influence these quantities. With the choosen testing techniques we discuss the various approaches and the constitutive equations of multilayer systems. Specific papers will describe in more details the results related to coatings composed of carbides or nitrides manufactured by dry routes.

Modification de la tenue mécanique d'un dépôt type Si - C sur acier par incorporation d'une intercouche métallique

Abstract SiC based coatings were deposited on a steel substrate by PACVD from TMS-Ar mixtures. The influence of a metallic interlayer between deposit and substrate on the mechanical stability has been studied through interface analysis and several mechanical tests (scratch, indentation, microbending in a SEM). The deposit adhesion is enhanced by a tantalum interlayer and is a function of its thickness. Micro-bending tests allowed to characterize the damage evolution and to obtain experimental parameters linked with the intrinsic properties of the coatings.