P. Hones

Sputter deposited chromium nitride based ternary compounds for hard coatings

Thin films of chromium based ternary transition metal nitrides Cr12xMexNy (CrMoN, CrTiN, CrWN and CrNbN) with 0 # x # 1 were deposited on silicon, glass and high speed steel substrates by reactive magnetron sputtering. The phase, texture and lattice parameter were determined by X-ray diffraction analysis. The surface morphology was examined by scanning tunneling microscopy. The chemical composition was measured by electron probe microanalysis. The cubic phase was the only phase observed for the ternary compounds. Thin films grown at 460 K substrate temperatures exhibit grain sizes of up to 25 nm. The core levels and the valence band were analyzed using X-ray photoelectron spectroscopy. Hardness values, obtained by nanoindentation, vary strongly with the dopant and the doping level. Similarities in changes of the mechanical properties and electronic structure indicate a strong correlation between these properties. q 1998 Elsevier Science S.A. All rights reserved.

Optical dispersion analysis of TiO2 thin films based on variable-angle spectroscopic ellipsometry measurements

Pure and doped TiO2 thin films, deposited by reactive r.f. sputtering onto glass substrates, have been investigated by spectroscopic ellipsometry in the wavelength range between 360 and 830 nm. Doping with Ce and Nb induces structural changes in TiO2 and modifies its optical constants. While undoped TiO2 films crystallize in a mixed rutile/anatase phase at a substrate temperature of 250°C, the doped films exhibit the anatase phase only. Using a polynomial and a single oscillator model dispersion function the spectral dependency of the refractive index and the extinction coefficient, as well as the optical band-gap have been determined. It turned out that even a moderate surface roughness in the range of 10 nm significantly influences the absolute value of the refractive index. Therefore, the surface roughness has been measured by atomic force microscopy and has been taken into account in the ellipsometric model.

Characterization of sputter-deposited chromium nitride thin films for hard coatings

Abstract CrN and Cr 2 N thin films were deposited on silicon, quartz, HSS-steel and carbon substrates by rf reactive magnetron sputtering. The phase and texture were determined by X-ray diffraction analysis. The chemical composition was measured by electron probe microanalysis. Atomic force microscopy revealed a finely grained morphology. The nitrogen content in the sputtering gas influences the film composition and morphology. At N 2 partial pressure below 20% (0.08 Pa) of the total pressure (0.67 Pa) the hexagonal Cr 2 N phase is present, while above 40%, the cubic CrN phase only is observed. Thin films grown at high substrate temperatures (T s ≥400 K) exhibit larger grain sizes of up to 20 nm. The real and imaginary parts of the dielectric function were determined by spectroscopic ellipsometry in the photon energy range of 1.5 to 5.0 eV. The core levels and the valence band were analyzed using X-ray photoelectron spectroscopy. The degree of ionicity of the Cr-N bonding increases continuously with the N 2 partial pressure promoting the CrN phase. Hardness values of 2950 HV for Cr 2 N films and 1800 HV for CrN films were obtained by microindentation,

Structural and mechanical properties of chromium nitride, molybdenum nitride, and tungsten nitride thin films

Cr–N, Mo–N, and W–N thin films are deposited on silicon by rf reactive magnetron sputtering. The crystallographic phase and residual stress are determined by x-ray diffraction analysis. In each of the three material systems, a hexagonal and a face-centred cubic (fcc) phase are observed. Plasma diagnostics using energy-resolved mass spectroscopy reveal that a significant fraction of the Cr+ ions exhibits a high flux and kinetic energy if the nitrogen partial pressure pN2 is low. These high-energy ions effectively bombard the growing film and a densely packed morphology results. In contrast, in absence of a significant amount of high-energy ions at higher pN2, a columnar crystal morphology is observed by scanning electron microscopy. The grain size strongly depends on the presence of a second phase and on the nitrogen content. The hardness, measured by nanoindentation, increases in every material system if the content of the hexagonal phase increases. Under overstoichiometric conditions, the hardness of fcc compounds decreases. The observed hardness differences are explained by morphological changes and by differences in the electronic structure of the compounds.

Electronic states and mechanical properties in transition metal nitrides

Abstract Thin films of hard materials are of prime importance for wear-resistant, protective and decorative coatings. Besides adhesion, hardness is the most often quoted requirement, even if doubts remain on the experimental determination of the hardness values of thin films, on their theoretical interpretation and on their significance for wear protection. Transition metal interstitial compounds are extensively used because of their broad range of functional properties in the fields of machining, microelectronics, decoration, etc. This article presents a summary of recent relevant results on the structural, mechanical, electronic and optical properties of fcc TiN, VN, CrN, NbN, W2N, hexagonal MoN, and some ternary nitrides in the form of sputtered thin films. The process parameters, e.g. the reactive gas partial pressure and the substrate bias, strongly influence the film properties. The composition and growth parameters influence the morphology, the stress state and other physical properties. The systematic investigation of the electronic density of states in valence and core states of comparable nitrides provides indications of the degree of covalency in the chemical bonding in relation to properties such as cohesive energy and hardness. For example, in molybdenum nitride the low stability of the cubic MoN phase is related to an increase in the charge transfer of Mo d electrons to nitrogen with increasing stoichiometric ratio N/Mo. Ellipsometric measurements of the dielectric function interpreted in relation to details of the band structure measure the variation of the density of conduction electrons. Vacancies and interstitials remove or add a specific number of electrons at the Fermi level. This analysis allows one to differentiate the types of defect at various compositions in, for example, TiNY films, for which the reported hardness values spread over a wide range.

Hexagonal nitride coatings: electronic and mechanical properties of V2N, Cr2N and δ-MoN

The electronic structure of hexagonal V 2 N, Cr 2 N and δ-MoN thin film nitrides, deposited by rf magnetron sputtering, have been investigated by X-ray photoemission spectroscopy. The binding energy values and the shape of the core level peaks are representative of the chemical bonding between the elements, and thus related to the mechanical properties. Comparing hexagonal and fcc structures, both V 2 N and Cr 2 N are more covalent than the cubic phases VN and CrN. In the case of molybdenum nitrides, the fcc and the hexagonal close-packed (hcp) structures exhibit comparable covalency level. The prominent covalent bonding in hexagonal Cr 2 N and V 2 N nitrides can be related with their higher hardness values compared to that of the fcc phases.

Mechanical and electrical properties of fcc TiO1+x thin films prepared by r.f. reactive sputtering

This paper reports on an investigation on fcc TiO1+x thin films with 0<x<1. The films were deposited by r.f. reactive sputtering and characterized by X-ray diffraction, electron probe microanalysis, X-ray photoelectron spectroscopy, atomic force microscopy, scanning tunneling microscopy, and electrical measurements. The films crystallized in the fcc phase with a lattice parameter a=0.419 nm, exhibit a gold like color, an electrical resistivity of about 400 μΩ cm at room temperature, and remarkable nanohardness values of about 23 GPa. The results of these experiments are discussed and compared to the archetypal fcc TiN coatings.

High rate and process control of reactive sputtering by gas pulsing: the Ti–O system

Abstract Titanium oxide thin films were deposited by dc reactive magnetron sputtering from a pure titanium target in a mixture of Ar+O 2 . The reactive gas was injected with a well-controlled pulsed technique. A constant pulsing period was used for every deposition whereas the O 2 injection time was changed systematically. Pulsing the reactive gas led to an increase of the deposition rate (up to 70% of the metallic rate) and an improvement of the electrical conductivity of the films (σ=21 S m −1 at 300 K) keeping an optical transmittance of 63% in the visible region. The influence of the modulated reactive gas flow rate on the crystallographic structure and composition was also investigated. Real time measurements of the electrical parameters of the titanium target and of the oxygen partial pressure by differential mass spectrometry show that the significant improvements of the reactive gas pulsing technique are due to the possibility to process alternately in metallic/compound mode.

MOCVD of thin ruthenium oxide films: properties and growth kinetics

Reference LPI-ARTICLE-2000-020doi:10.1002/1521-3862(200008)6:4 3.0.CO;2-QView record in Web of Science Record created on 2006-02-21, modified on 2017-05-12

Conducting Thin Films of Ruthenium Oxide Prepared by Mocvd

Reference LPI-CHAPTER-1998-031View record in Web of Science Record created on 2006-02-21, modified on 2017-05-12