Stress-free Lattice Parameter Research Articles

Internal Stress In Sputtered Silver Nickel Thin Films And Multilayers: Sputtering Pressure And Thickness Effects

ABSTRACTNanometer thick films are often in a state of high residual stress. This may strongly influence physical properties such as magnetic anisotropy. The aim of our study is to investigate whether the overall stress in multilayers may be tailored via the control of the sputtering parameters or of the individual thicknesses. The coatings investigated were deposited at room temperature by magnetron sputtering on oxidised silicon substrates. Ag/Ni multilayers of superperiod between 4 to 20 nm and thin films (Ag or Ni) 200 nm thick have been deposited under a krypton partial pressure varying between 1 and 8 mTorr. Internal stress measurements were performed by curvature method and x-ray diffraction sin2ψ method. The latter one allows the determination of the stress and of the stress-free lattice parameter in the Ag or the Ni layers whereas the first one gives rise to a measure of the average stress in the coating. The main results are the followings: (i) The stress in Ni thin films changes from compressive to tensile at a pressure between 2 and 5 mTorr whereas Ag thin films are sligthly tensile whatever the pressure; (ii) The stress in multilayers is tensile in Ag and Ni and decreases with sublayer thickness; (iii) The stress free lattice parameter of Ag in thin films or multilayers is independent of the Kr pressure and of the layer thickness and is equal to the bulk value; (iv) On the opposite, the stress-free lattice parameter of nickel decreases with the layer thickness in multilayers and is equal to the bulk value in thin films. These results are discussed in terms of the respective influence of interfacial intermixing and atomic peening mechanism.

Structure characterization of metallic multilayers by symmetric and asymmetric X-ray diffraction

Results of the structure characterization of Au/Ni multilayers are presented. The analysis is based on symmetric and asymmetric X-ray diffraction (XRD). Particular attention is paid to interplanar distances and composition profiles of studied multilayers. Symmetric XRD profiles are interpreted using the model of non-ideal superlattice structure based on a Monte Carlo simulation. The model allows to fit experimental profiles starting within a wide range of interplanar distances and avoiding any local minima. Asymmetric XRD measurements were performed for different hkl reflections. A stress analysis was done using sin 2 Ψ method. Both asymmetric and symmetric XRD measurements confirm that perpendicular interplanar distances in Au and Ni are larger than the bulk ones. These interplanar distances are discussed in terms of a stress free lattice parameter and a strained one.

Influence of the plasma current to Ti-melt on the plasma parameters and microstructure of TiN coatings in the triode ion plating system

TiN coatings have been deposited by triode ion plating in a mixture of Ar and N 2 with a varying total current through the melt. The observed energy spectra of ions and neutrals are discussed with respect to the plasma parameters measured with Langmuir probes. The current I Pm from the plasma to the Ti-melt in the crucible was modified from 0 A up to 100 A. As I pm is increased, major effects on the plasma and on the film microstructure (preferred orientation, stress-free lattice parameter, residual stress, thickness and microhardness) were observed. The positive voltage of the melt UR with respect to the ground increased from 0.1 to 29 V. The plasma potential (positive voltage with respect to ground) of the main plasma body increased from 4 to 16 V, while the electron temperature ranged from 2.5 to 4 eV. Plasma density and floating potential is also discussed. A high energy tail appeared in the energy distribution function of some neutral and ionic species, especially for neutral and ionized evaporated Ti. At high values of I pm the energy distribution of both highly energetic Ti + and neutral Ti goes up to 25 eV and 30 eV. At low values of I pm the majority of the Ti + ions are thermalized. The microstructure of the deposited TiN films develops from porous structures, with low compressive or even tensile stresses at I pm =0 A, up to dense structures, with high compressive stresses of more than 15 GPa at the highest value of I pm . Possible explanations of the observed effects are discussed, based on plasma ionization processes close to the melt and in the plasma body.

Recent Advances In The Depth-resolved X-rayAnalysis Of Residual Stresses And Stress-free Lattice Parameters In Ti(C-N)-gradient Coatings

Thin hard coatings are widely employed in order to improve the efficiency of cutting and forging processes through an increased wear and corrosion resistance of the respective tools. Therefore, the coatings are more and more refined. In recent investigations. PVD-gradient coatings of Ti(C-N) on cutting edges of cemented carbide have shown a significantly higher wear resistance than conventional TiC- or TiN coatings. However, the residual stress states in the coatings strongly influence the in-service properties of the coatings and of the entire components. In order to understand the influences of the residual stress states. X-ray residual stress analyses were performed. A special approach was developed which allows the non- destructive depth-resolved determination of the residual stress states and stress-free lattice parameters of the coatings. As a consequence of the Ti(C-N)-gradient, the residual stresses and stress-free lattice parameters varied linearely over the thickness of the coatings.

Energy-resolved mass spectra of ions and neutrals in triode ion plating of Ti(C,N) coatings

Ti(C,N) coatings have been deposited by triode ion plating in a mixture of Ar, N 2 and C 2H 2. The energy spectra of selected ions and neutrals during deposition were measured by an energy-resolved mass spectrometer. The observed energy spectra of ions and neutrals are discussed. The energy spectra of neutral species were measured as the energy spectra of ions produced by crossed-beam electron ionization in the mass spectrometer. Both the energy spectra of Ti + ions and Ti atoms show wide energy spectra, ranging to about 40 eV, Properties of the Ti(C,N) coatings are reported, especially the stress-free lattice parameter and the residual macroscopic stress measured by X-ray diffraction. It is observed that the compressive stress varies from −6 to −21 GPa with the different deposition conditions used. Effects of the total pressure, the substrate voltage and the current in the low voltage arc on the energy spectra of ions and neutrals are discussed.

Stress and microstructure in YBaCuO thin films on MgO and SrTiO 3 substrates studied by X-ray diffraction and bending tests

Stress-strain tensors and stress-free lattice parameters related to the microstructure is studied in YBCO thin films deposited by pulsed-laser ablation on MgO and SrTiO 3 substrates by means of X-ray diffraction and bending test measurements. The results show that the lattice of the thin film deposited on SrTiO 3 is under compression in the ( a,b) plane and the stress-free lattice parameters of this film are always lower than the parameters of the bulk material.

Stabilization of Cubic AlN in Epitaxial AlN/TiN Superlattices

The high-pressure rocksalt structure of AlN was stabilized in epitaxial AlN/TiN(001) superlattices with AlN layer thickness $\ensuremath{\le}2.0\mathrm{nm}$. The AlN layers were shown to be pure rocksalt-structure AlN, with a stress-free lattice parameter of $0.408\ifmmode\pm\else\textpm\fi{}0.002\mathrm{nm}$, using x-ray diffraction, transmission electron microscopy, and electron energy loss spectroscopy. The stable hexagonal phase was observed for AlN layer thickness $g2\mathrm{nm}$. The rocksalt structure formed at small layer thicknesses since it provided lower AlN/TiN interfacial energy than the hexagonal or zinc-blende structures.

Small Lattice Mismatches in Highly Imperfect Single Crystals: A Probe into Phase Specific Strains and Stresses

A formalism is proposed for the evaluation of phase specific strains and stresses in I-hardened single crystal nickel-based superalloys using volume-resolved constrained lattice parameters, which can be determined by a procedure as discussed in the first part of this contribution. Taking mechanical equilibrium conditions into consideration, the stress-free lattice parameters of both phases can be calculated so that absolute values of strains and stresses can be given. Using the data obtained from the calculation of the stress-free lattice parameters, the influence of diffusion controlled variations of the stress-free lattice parameters can be quantified and separated from dislocation-induced effects on the stress values. This way, distributions of phase specific strains and stresses in the monocrystalline nickel-based superalloy SC 16 have been determined. The investigations by means of X-ray and neutron diffraction methods have been performed on the initial material state and material after uniaxial plastic high-temperature deformation (tensile and creep deformation). All strain distributions exhibit a strong overlap of phase and orientation dependent contributions, which are evaluated by a model based on the microstructural properties and local mechanical equilibrium conditions. Coherency stresses in the initial material state and the unconstrained misfit are evaluated. Stress distributions after high-temperature deformation are interpreted using a model from literature with an extended combined gliding and climbing mechanism.

Residual stresses and microstructure in tungsten thin films analyzed by x-ray diffraction-evolution under ion irradiation

Microstructure and residual stresses have been studied in 100 nm tungsten thin films deposited by ion beam sputtering on silicon substrates. Residual stresses, stress-free lattice parameter, crystal microdistortions, and average length of the coherently diffracting domains have been deduced from x-ray diffraction measurements. The as-deposited film is strongly compressed (−5.2 GPa) and its microstructure is very far from the bulk tungsten one: the coherently diffracting domain size is nanometric (about 5 nm), the stress-free lattice parameter is larger than the bulk one (about 0.6%), and microdistortions are considerable (0.6%). The ‘‘atomic peening’’ model is proposed to explain the mechanical state of these films. Diffraction analysis, correlated with impurity concentration measurement, evidences the main role played by backscattered Ar ions in stress genesis. Nevertheless, the contribution of the most energetic W particles to the stress generation process cannot be neglected. We have equally studied Ar+ ion (340 KeV) irradiation effects. We have found that irradiation induces a total stress relaxation, a return of the stress-free lattice parameter to the bulk one, a strong decrease of the microdistortions, and an increase of the coherently diffracting domain sizes. A thermal irradiation effect seems appropriate to explain residual stresses and microstructure modifications induced by ion irradiation. These features are in agreement with the interpretation proposed in the case of as-deposited films.

Influence of microstructure on residual stress in tungsten thin films analyzed by X-ray diffraction

Microstructure and residual stresses have been studied in 100 nm thin tungsten films deposited by ion beam sputtering on silicon substrates. Residual stresses, the stress-free lattice parameter, crystal microdistortions and the average length of the coherently diffracting domains (CDD) have been measured by X-ray diffraction. The as-deposited film is strongly compressed (−5.2 GPa) and its microstructure is very far from that of bulk tungsten: the size of the CDD is nanometric (about 5 nm), the stress-free lattice parameter is larger than in the bulk (about 0.6%) and microdistortions are considerable (0.6%). Our diffraction data are in agreement with the “atomic peening” model usually admitted to explain the compressive stresses in sputtered films. These features are also confirmed by irradiations with Ar + ions (340 keV). They induce simultaneously a total stress relaxation, a return of the stress-free lattice parameter to the bulk value and a strong decrease of the microdistortions.

Residual stresses influence on the structural evolution of CuMo solid solutions studied by X-ray diffraction

Metastable CuMo thin films have been deposited on quartz substrates by ion beam Sputtering. The structural and mechanical state characterisation in these as-deposited films have been performed using X-ray diffraction. The size of the coherently diffracting domains is small (1.5 – 2.0 nm) and the micro-strains are very large (0.3 – 1.9%). The value of these parameters depends on the Mo concentration. The sin 2 Ψ method was applied to extract stresses and the stress-free lattice parameter a 0 in the Cu 30 Mo 70 films. In-plane stress is compressive and its amplitude is very high (4.5 GPa). The presence of such high intrinsic compressive stresses is related to lattice distortions induced by an ‘atomic peening’' effect and Ar interstitials during the deposition process. After thermal annealing, one observes the demixing of the solid solution ( a 0 evolution) and an inversion of stress sign (compressive to tensile).

Intergranular thermal stresses in zirconium — effects on X-rays macrostress measurements

Thermal intergranular residual stresses in a textured Zr sheet were evaluated using a self-consistent formulation and compared with experimental results obtained using X-ray diffraction techniques. Results show that intergranular thermal residual stresses can affect macrostresses measurements by approximately 20% of the yield stress of the material. The self-consistent formulation was also used in the reverse way to determine the stress free lattice parameters of the Zr sheet, their values being a = 3.2325Åandc = 5.1464Å.

Microstructure and residual stresses in (111) [formula omitted] multilayers

(111) AuNi multilayers have been deposited by molecular beam epitaxy on a (100) Cu buffer on (100) Si. At constant composition (1:1) and total thickness, the substrate interaction stress deduced from wafer curvature measurements is increasing with the superperiod (9–52 Å). It is tensile and varies between 200 and 400 MPa. The largest period sample has been studied in detail. Wavy interfaces are evidenced by transmission electron microscopy. A detailed stress analysis by X-ray diffraction shows that Au is under compressive stress (−1.25 GPa) and Ni under tensile stress (+1.43 GPa). Whereas the stress-free lattice parameter for Au is found to be the bulk one, a tensile expansion is found in Ni. This is tentatively attributed to Au intermixing.

Residual stresses and microstructure of Ag-Ni multilayers

A direct determination of residual stresses in very-low-period Ag-Ni multilayers has been performed by x-ray diffraction using the sin2ψ method. Stresses in silver layers as thin as three atomic planes and in nickel layers as thin as four atomic planes could be determined. They range from −3.07 to 0.522 GPa, and their genesis excludes any interfacial coherency relationship. The variation of the multilayer microstructure with respect to the period has been studied by measurement of the stress free lattice parameter and microdistortions. Important deviations with respect to the bulk microstructure have been observed and discussed.

Residual Stress and Microstructure of CU/W Multilayers

ABSTRACTWe have determined residual stresses and the layer microstructure in as-prepared Cu/W multilayers of different periods ranging from 5.2 to 20 nm by both X-ray diffraction and the curvature radius method. The magnitude of the principal in-plane stress is large in the W layers (around - 6 GPa) and small in the Cu layers (-0.5 - + 0.5 GPa). The stress state is independent of the multilayer period. Under the compressive stress, the W cubic unit cell becomes monoclinic-like. The stress-free lattice parameter is found higher than the bulk one.We also studied the stress relaxation and the layer microstructure modification in W layers induced by Kr ion irradiation., the relaxation is almost achieved after only low fluence irradiations and the decrease of the stress-free lattice parameter in W layers observed for higher fluences is attributed to the formation of a sursaturated solid solution W(Cu).

Structural analysis of tin films by Seemann-Bohlin X-ray diffraction

The accuracy of the Seemann-Bohlin method has been improved by usinginternal standards and a new calibration function. Experimental results illustrated by four typical examples show that the stress and stress-free lattice parameter values determined by this method are crystallographically averaged quantities convenient for an overall characterization of lattice distortions. Combination of the method with the Bragg-Brentano technique and with sample annealing or substrate dissolution can be used for the separation of particular structural effects on the properties of TiN hard films.

Surface stress effects on the critical film thickness for epitaxy

An analysis of the critical thickness dependence on misfit for epitaxy is presented including effects due to surface stresses. It is shown that these surface stress effects, which have not been included in previous theories of epitaxy, can have a major influence on the critical thickness, especially for relatively large misfits. A simple model incorporating effects due to compressive surface stresses is given which, compared to previous theories, predicts significantly larger (smaller) critical thicknesses when the stress-free lattice parameter of the film is greater (less) than the lattice parameter of the substrate.

Elastic state and thermodynamical properties of inhomogeneous epitaxial layers: Application to immiscible III-V alloys

The elastic strain and stress fields and the elastic energy of the system composed of a crystalline epitaxial layer of finite thickness coherently grown on a bulk substrate are calculated, when the intrinsic stress-free lattice parameter of the layer is modulated along directions parallel to the substrate surface. When the modulation has components with spatial periods of the same order as the thickness of the layer, the elastic energy is considerably reduced with respect to the same modulation occurring in a bulk sample. There exists an optimal period of elementary sinusoidal modulation, proportional to the layer thickness. Consequently, for immiscible alloys where changes of composition induce changes of intrinsic lattice parameter, the critical temperature (below which they become thermodynamically unstable with respect to composition modulations) is much higher (and the domain of instability larger) if the material is in the epitaxial layer form than in the bulk form. This extends Cahn’s theory of spinodal decomposition to epitaxial layers. It is also pointed out that if a modulation has started to occur in a growing layer, the elastic deformation induced near the free surface should have important consequences on the subsequent growth of this layer. These results are applied to III-V semiconductors immiscible alloys, such as InxGa1−xAsyP1−y, where such composition modulations are known to exist. New values of the critical temperatures for these alloys are calculated and compared with lower former estimates. The mode of development of these modulations is discussed in light of previous experimental results and these new calculations.

Elastic strain effects in coherent perthitic feldspars

For coherent cryptoperthites, the compositions inferred from X-ray spacing curves are incorrect due to elastic distortions of the structure; a method is described for correcting these apparent compositions. This method uses the elastic compliances and stress-free lattice parameters to calculate the change in a * due to the coherency strain, and thus the corresponding compositional correction; this method applies only to cases in which both phases are monoclinic The magnitude of the correction depends on the bulk composition, but is typically on the order of 2 to 10 mol % Or. Compositional corrections calculated using this model are roughly half as large as those obtained using Smith's (1961) less rigorous constant volume method.