P.E. Schmid

High-temperature oxidation resistance of Cr1−xAlxN thin films deposited by reactive magnetron sputtering

The thermal stability against oxidation of Cr1−xAlxN films with 0≤x≤0.63 has been investigated by isochronal (15 min) heating in air at various temperatures up to 1173 K. Cr1−xAlxN thin films were deposited by reactive magnetron sputtering from Cr and Al targets in a mixed Ar/N2 atmosphere at a substrate temperature of 573 K. All the films crystallize in the pseudo binary, rocksalt-type cubic structure, showing a (111) preferential orientation. Oxidation proceeds by de-nitridation and the formation of a pseudo binary, mixed, Cr/Al oxide with the corundum structure. The degree of film oxidation was evaluated by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and Rutherford backscattering spectroscopy (RBS). The substitution of Cr atoms by Al atoms leads to two oxidation behaviors. Cr1−xAlxN films with low Al content (x 0.2) are more resistant to high temperatures compared to pure CrN. Films with the highest Al content (x=0.63) are stable up to 1173 K due to the formation of an amorphous, aluminum-rich oxide which blocks oxygen diffusion and prevents further film oxidation.

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.

Electrical and optical properties of TiOx thin films deposited by reactive magnetron sputtering

The present study of the electronic properties of titanium monoxide thin films is centered on the electrical and optical properties of nano-grain material. TiOx thin films with x ranging from 0.75 to 1.45 have been deposited by r.f. reactive magnetron sputtering in a mixed Ar/O2 or Ar/H2O atmosphere. All films show a negative temperature coefficient of the resistivity. Spectroscopic ellipsometry measurements were performed in the Vis-UV spectral range. The free carrier and interband contributions to the dielectric function have been sorted out. The most striking feature of the free carrier optical response is the very short scattering time of the order of 10−15 s. Such an intense impurity scattering is beyond the validity range of the semi-classical Boltzmann equation and remains an open problem.

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.

Optical and electronic properties of magnetron sputtered ZrNx thin films

The optical properties of sputtered ZrNx films with 0.81≤x≤1.35 have been investigated and interpreted in terms of stoichiometry-related defects and crystal structure. The optical properties were determined by optical reflectivity, transmission and spectroscopic ellipsometry. As x increases from 0.81 to 1.35, the optical properties continuously change from metallic to semiconducting behavior. The experimental results have been fitted with a model dielectric function based on a set of Drude–Lorentz oscillators in order to separate the contributions due to free carriers and interband transitions. The effective density N* of conduction electrons decreases from N*=4.9×1022 cm−3 to N*=2.9×1021 cm−3 as x is increased from 0.81 to 1.29. The charge carrier scattering time increases from 4.9×10−16 to 2.6×10−15 s for 0.81 1.3 are poorly crystallized. In this composition range, the compounds exhibit a crystal structure close to orthorhombic Zr3N4; they are insulating with optical absorption coefficients in the range of 2×104 cm−1 below 2 eV and an optical absorption onset at 2.3 eV.

Electronic properties of Cr1-xAlxN thin films deposited by reactive magnetron sputtering

X-Ray photoelectron spectroscopy (XPS) and electrical resistivity measurements have been performed to investigate the electronic properties of Cr1−xAlxN films. The films, deposited by reactive magnetron sputtering, crystallize in the fcc rocksalt type of structure (B1-type) in a wide composition range of 0≤x≤0.63. The electrical resistivity was measured from 50 to 320 K. The electrical resistivity at 320 K increases with increasing Al content, and the temperature coefficient of the resistivity is always negative. A detailed study of XPS valence band (VB) spectra shows that the substitution of Cr atoms by Al atoms leads to local modifications of covalent-ionic bonds between N 2p and Cr 3d orbitals. The variations of the VB structure due to the changes in the chemical composition correlate with the electrical and mechanical properties.

Morphology and electrical properties of titanium oxide nanometric multilayers deposited by DC reactive sputtering

Abstract Thin films of titanium oxides TiO x ( x =0.7…2) can be produced by DC reactive magnetron sputtering with O 2 and/or H 2 O as a reactive gas. In this work we investigate the deposition of nanometric multilayers and thin films of modulated composition. Samples are characterized by electrical resistivity measurements, optical measurements, X-ray diffraction and atomic force microscopy. The influence of the sputtering parameters on the morphology and on the electrical properties of the multilayers is reported. The analysis of the electrical and optical properties of the TiO 2 –TiO x multilayer system will contribute to a better understanding of the doping mechanism of nano-crystalline titanium dioxide by the grain boundaries.

Structural and optical properties of Pd1−xInx thin films

Pd 1-x In x (0.4 < x < 0.56) thin films have been prepared by RF sputtering from a multi-zone target. Their structural and optical properties have been studied by X-ray diffractometry, near normal incidence optical reflectivity and ellipsometry. both structural and optical properties exhibit composition dependent characteristics. Indium-deficient films include Pd in antisite positions. Indium-rich films incorporate Pd vacancies. The optical spectrum shows both free electron-like properties and interband transitions giving rise to absorption peaks around 2.7 and 4.8 eV. A rigid band model is not sufficient to explain the optical properties of the alloys. The effects of Pd antisite atoms and Pd vacancies on the band structure must be lien into account to explain the evolution of the optical parameters.

The effect of ammonia/dimethylamine ratio in deposition of hydrogenated CNx films by PE-HF-CVD

Abstract We have investigated the influence of ammonia (NH 3 ) and dimethylamine ((CH 3 ) 2 NH or DA) precursors on the deposition of carbon nitride films in a plasma enhanced-hot filament-chemical vapor deposition process. We found that using C and N directly bonded into precursor, as in DA, notably enhanced the N incorporation and film compactness, as compared to CH 4 precursor or CH 4 /NH 3 mixtures. The optical properties of films prepared with DA were investigated by IR and Raman spectroscopy, while the film hardness was investigated by nanoindentation. We found that introducing small amounts of ammonia (NH 3 /DA=0.2) during deposition improves film density and N incorporation, but a further increase of ammonia content (0.2 3 /DA 3 during deposition prevails over N incorporation in the films.

Role of point defects on the optical properties of Pd-based Hume-Rothery alloys

Cubic Pd 1-x In x and Pd 1-x Al x (0.4 <x< < 0.56) intermetallic compound films have been deposited on oxidized silicon wafers by r.f. sputtering using either a multizone target or two independent targets. The actual composition was determined by electron-probe microanalysis. The characterizations by X-ray diffraction show that the films crystallize in a β-CsCl structure. This is the structure prescribed by the Hume-Rothery rule for an electron concentration of 1.5 valence electrons per atom. In non-stoichiometric compounds, constitutional point defects keep the rule enforced. The optical properties have been studied by normal incidence reflectivity and ellipsometry and have been interpreted in terms of a Lorenz-Drude model. The analyzed results show that the variations of the optical properties can be assigned to changes in the electronic density of states. These changes are caused by the point defects imposed by the deviation from stoichiometry.