Y. Pauleau

Characterization of magnesium fluoride thin films produced by argon ion beam-assisted deposition

Abstract Magnesium fluoride thin films have been deposited on silica glass and single crystal silicon substrates by argon ion beam-assisted deposition (IBAD). The structure, composition, mass density of films deposited at ambient temperature were investigated as functions of the flux and kinetic energy of argon ions striking the film surface. The residual stresses in the films calculated from the change of the radius of curvature of silicon substrates, were studied as functions of the normalized momentum ( P N ) transferred from incident argon ions to deposited atoms. The respective contributions of thermal, intrinsic and extrinsic stresses in residual stresses were also determined. Thin films produced with a P N value of approximately 55 g 1/2 mol −1/2 eV 1/2 exhibited appropriate characteristics for optical applications.

Silver thin films deposited by magnetron sputtering

Abstract Silver thin films have been deposited on various substrates by d.c. and r.f. sputtering from a silver magnetron target and argon plasma. The deposition rate of metal films was investigated as a function of the sputtering power, argon pressure and r.f. bias voltage applied to substrates. The structure of sputter-deposited films was analysed by the X-ray diffraction technique. The composition of films was determined by Rutherford backscattering spectroscopy. The morphology of the cross-sections of films was examined by scanning electron microscopy. Very low tensile residual stresses in these silver films were measured from the change in the radius of the curvature of silicon substrates induced by the films. The Knoop hardness and electrical resistivity of films determined by four-point probe measurements were investigated as functions of the sputtering gas pressure. The properties of silver films produced by d.c. and r.f. sputtering of the silver magnetron target are discussed and compared in this paper.

Properties of Silver Films Sputter‐Deposited on Biased Substrates

Silver thin films have been deposited on various self-biased substrates by radio frequency sputterring of a magnetron silver target in pure argon plasma using a load-lock deposition equipment. The properties of these metal films were investigated as functions of the negative self-bias voltage applied to substrates. The composition and crystallographic structure of silver films were determined by Rutherford backscattering spectroscopy and x-ray diffraction techniques, respectively. Pure silver films having electrical resistivities nearly equal to the bulk resistivity were produced on substrates at the floating potential. Argon atoms were incorporated in silver films deposited on biased substrates

Mechanical behaviour of hard PVD multilayered coatings

Abstract The aim of this work was to investigate the cracking behaviour and adhesion of tungsten–carbon-based multilayered coatings deposited on steel substrates by magnetron sputtering. Three-point bending experiments were performed on the coating-on-substrate systems until failure of the film. The systems were also strained uniaxially with a microtensile device adapted to a scanning electron microscope. The mechanical response is analysed from the evolution of the crack density in the coating and the fracture toughness. The results show that the rupture properties of the multilayered coatings are correlated to the film thickness and arrangement of the elementary layers. Scratch experiments on the systems revealed a strong adhesion of the multilayered coatings on steel substrates, and delamination at layer interfaces. Thus, graded coatings appear to be more attractive for mechanical applications.

Failure and adhesion characterization of tungsten-carbon single layers, multilayered and graded coatings

Abstract Hard multilayered and graded coatings based on a stacking arrangement of ductile layers and hard layers appear to be promising wear- or erosion-resistant coatings. To optimize the architecture of the protective coatings, the mechanical behaviour of the films has to be first investigated through basic mechanical tests before being subjected to specific tests. This paper reports a qualitative and comparative study of the adhesion and failure mechanisms of tungsten–carbon single layers, multilayered and graded coatings by means of scratch tests.

Structure and physical properties of nickel films deposited by microwave plasma-assisted cathodic sputtering

Nanocrystalline nickel films have been deposited by microwave plasma-assisted sputtering from pure argon discharges on steel and (100)-oriented single crystal silicon wafers mounted on a water-cooled substrate holder biased to various direct current voltages ranging from 0 to −120 V. The crystallographic structure and surface morphology of films were determined by x-ray diffraction techniques and atomic force microscopy, respectively. The magnitude of compressive residual stresses (intrinsic stress) calculated from the radius of curvature of Si substrates reached a maximum value of −250 MPa in films deposited on grounded substrates and decreased with increasing negative substrate bias voltage. The hardness of films was determined by nanoindentation as a function of the substrate bias voltage. Alumina ball-on-disk tribological tests of films deposited on steel substrates were conducted in room air at 20 °C under a load of 1 N with a sliding speed of 50 mm s−1. The value of the stabilized friction coefficient was in the range 0.35–0.45 for 5000 cycles. Beyond 5000 cycles, the films were worn and the friction coefficient increased rapidly. The electrical resistivity of films deduced from the thickness and sheet resistance of films determined by four point probe measurements was approximately equal to 13 µΩ cm.

Dependence of tribological properties on deposition parameters for non hydrogenated amorphous carbon films produced by magnetron sputtering

Abstract Amorphous carbon films have been deposited on various substrates by direct current (DC) magnetron sputtering from a graphite target in an argon discharge. The composition and physical properties of films (mass density, morphology, electrical resistivity, residual stresses) were investigated as functions of the argon pressure and negative substrate bias voltage. The friction properties of 2 μm thick carbon films deposited on polished stainless steel substrates at various argon pressures and substrate bias voltages were determined by alumina ball-on-disk tribological tests performed in dry air under a load of 4.9 N with a sliding velocity of 10 m min −1 for 10 5 cycles. The tribological behavior and friction performance of carbon coated disks are discussed in connection with the deposition parameters and physical properties of non hydrogenated amorphous carbon films.

Tribological properties of thin silver films sputter-deposited on superalloy substrates

Abstract Thin silver films have been deposited on superalloy (alacrite) substrates with an average roughness of 0.2–0.3 micrometer by radio frequency magnetron sputtering of a silver target in argon atmosphere. The silver films, of 0.4–20 μm thickness, exhibited a crystallographic structure preferentially oriented in the (111) direction, with grain sizes of 150 nm. The compressive residual stresses in these films were as low as -0.05 GPa. Argon-free silver films deposited on silicon substrates at the floating potential possessed an electrical resistivity similar to the bulk-resistivity value. The tribological tests were carried out with an alumina ball-on-disk apparatus operating under loads of 9.8, 2.9 and 1 N at room temperature and 500 °C with a sliding velocity of 0.02 m s −1 for 5000 to 90 000 cycles, i.e. for an average sliding distance varying from 385 m to 7 km. After an initial stage of about 1000 cycles, the friction coefficient of silver-coated alacrite disks was essentially independent of the number of cycles. The average friction coefficient values were in the range 0.14 to 0.42, depending upon film thickness and test temperature. After 5000 cycles under loads of 2.9 and 1 N, the bottom of the wear tracks exhibited a periodic sequence of bumps and hollows. The periodicity of these undulations was dependent on the load and test temperature. The formation of these undulations probably resulted from the adhesive friction mechanism of silver films. Under a load of 9.8 N, the bottom of the wear tracks was flat and the wear of silver films was caused by a ploughing mechanism. The variation of the average friction coefficient of silver-coated alacrite disks with film thickness at room temperature was interpreted on the basis of a mechanism of friction proposed for soft metal films deposited on steel substrates when sliding against hard antagonists.

Tribological properties of calcium fluoride-based solid lubricant coatings at high temperatures

Abstract Silver, calcium fluoride (CaF x with x =1.85) and chromium–carbon (Cr 3 C 2 ) thin films have been deposited on various tribological test specimens by sputtering. The friction properties of sputter-deposited Ag and CaF x single layers as well as Ag/CaF x multilayer films were determined by ball-on-disk tribological tests conducted in room air under various experimental conditions. The tribological properties (friction coefficient and wear rate) of sputter-deposited CaF x films were also determined at 500°C by pin-on-disk tribological tests performed with pin specimens made of cobalt-based alloy (alacrite). Chromium–carbon films sputter-deposited on alacrite disk and counterfaces were found to be of interest to reduce the formation of alacrite wear debris in the wear tracks whereby reduced friction coefficient and wear rate values were obtained. The friction behavior of sputter-deposited CaF x /Cr 3 C 2 thin bilayer structures was also investigated by plane-on-plane tribological tests conducted in room air at 500°C and 700°C.

Residual stresses in physically vapor-deposited thin films

Publisher Summary This chapter deals with the effects of physically vapor-deposited (PVD) process parameters, including physical factors that are specific to the PVD process on residual stresses in continuous films—that is, with a thickness higher than that corresponding to a film formed by the simple coalescence of islands on flat substrate surfaces. The average value of residual stresses in continuous films is independent of the film thickness. In addition, PVD thin films can grow on various types of substrates. In general, three primary growth modes of PVD thin films can be distinguished on the basis of the bonding strength between depositing atoms and substrate atoms. This three-dimensional island growth referred to as the “Volmer-Weber growth mode” involves the nucleation of the condensed phase into distinct, small clusters directly on the substrate surface. Then, with elapsing time and the arrival of additional adatoms, the clusters grow into islands that begin to touch and finally coalesce to form a continuous film.