M.P. Dariel

Structural analysis of (Ti1−xAlx)N graded coatings deposited by reactive magnetron sputtering

Abstract Graded (Ti1−xAlx)N coatings were prepared by reactive magnetron co-sputtering of Ti and Al on silicon and glass substrates in an Ar+N2 atmosphere. The N2 content was kept constant in the gas mixture and the composition of the (Ti1−xAlx)N film was controlled by the power applied to the targets. The composition of the graded films was determined by Auger electron spectroscopy (AES) depth profiling and by energy dispersive spectroscopy (EDS) of their cross sections. Phase determination was performed by X-ray diffraction (XRD) and by selected area electron diffraction (SAED). Transmission electron microscopy (TEM) of the cross sections was used to determine the microstructure of the graded films. Interfaces between the films and substrates and within the films were investigated by high resolution TEM (HRTEM). The microstructural observations as well as the composition analysis, performed by AES depth profile and by EDS measurements, show that the graded films are continuous. XRD patterns have shown a strong preferred orientation with the (111) planes parallel to the surface of the film. Splitting of the (111) peak or its broadening reflect reduction in the lattice parameter with increasing Al content. TEM images show that the films posses columnar structure with an average grain size of ∼50 nm. HRTEM images reveal randomly oriented grains near the Si substrate and semi-coherent grain boundary between neighboring columnar grains.

A tem study of the crystallization behavior in amorphous vacuum condensed Er—Cu thin films

Abstract The isothermal crystallization of amorphous, vacuum condensed Er 0.6 Cu 0.4 thin films was investigated in situ by transmission electron microscopy. Heterogeneous nucleation of ErCu crystallites was observed to occur on the thin rare-earth oxide layer which is inevitably formed on the external surface of the thin film exposed to the ambient atmosphere. The crystalline particles exhibited preferential growth in the direction parallel to the surface of the film. The crystallization process is interface controlled and characterized by a constant nucleation and constant growth rate. The kinetics of transformation were anslyzed in terms of Avramis equation. The kinetic exponent n in Avramis equation is equal to 2.9 in good agreement with the theoretical value for two-dimensional, interface-controlled growth. The experimental date allowed to derive the values of Δ E = 581 kJ.mole −1 for the overall activation energy of the crystallization reaction, Δ cr = 151 kJ.mole −1 for the energy of critical nucleus formation and Δ E m = 143 kJ.mole −1 for the activation energy of atomic motion.

Early stages of interface reactions between AlN and Ti thin films

The early stages of interface reactions between AlN and Ti thin films were investigated using x-ray diffractions, Auger electron spectroscopy, cross section transmission electron microscopy (XTEM), and high resolution XTEM. The AlN/Ti bilayers were deposited on a molybdenum substrate using reactive and nonreactive magnetron sputtering techniques. After deposition, the bilayers were heat treated for 1–10 h at 600 °C in a nitrogen atmosphere. Decomposition of the AlN layer took place at the AlN/Ti interface and its products, Al and N, reacted with Ti to produce a AlN/Al3Ti/Ti2N/Ti3Al/α-(Ti, Al)ss phase sequence. This phase sequence is not consistent with the Ti–Al–N phase diagram and is believed to be the outcome of the particular conditions that prevail in the thin film and correspond to a particular set of kinetic parameters. A model that explains the development of the phase sequence and predicts its evolution after prolonged heat treatments is put forward. The applicability of such a solid-state reactio...

Copper grain growth in thin film Cu-Cr multilayers

Abstract Copper-chromium multilayers with a 25 nm repeat distance were prepared by dual gun sequential magnetron sputtering. The mutual immiscibility of the two elements ensures that no interdiffusion or reaction takes place at the deposition temperature. High temperature X-ray diffraction runs were carried out in the 370–630°C temperature range, at constant time intervals. At elevated temperature, the Cu(111) reflection showed increasing intensity and decreasing line-width as a function of time. Analysis of the line narrowing as a function of the annealing time and temperature allowed deduction of the activation energy, 0.41 ± 0.05 eV per atom, associated with the atom mobility involved in the copper grain growth.

Morphological changes induced by thermal anneals in NiFe/Ag multilayers; their relation to the resistive and magnetoresistive properties

Abstract X-ray diffraction and simulation were used to characterize the morphological evolution that takes place in permalloy/silver (NiFe/Ag) multilayers as the result of thermal annealing. Auger spectroscopy, electron microscopy, resistivity and magnetoresistivity measurements were performed in order to obtain additional insight into the results. The results are consistent with the model of Ag grain boundary diffusion taking place along the columnar grains, leading to the creation of so-called ‘silver bridges’ between the permalloy grains. The initial stages of annealing (up to 633 K) result in formation of individual NiFe grains that leads to enhanced values of the magnetoresistivity. Annealing at higher temperatures causes the growth of relatively large Ag and NiFe agglomerates and results in breakup of the original multilayered structure.

The crystallization of amorphous Dy-Cu thin films☆

Abstract The crystallization of vacuum-deposited amorphous Dy-35at.%Cu thin films was studied by transmission electron microscopy and electron diffraction. The transmission electron micrographs allowed us to follow the nucleation and subsequent growth of DyCu crystals within the amorphous matrix. The crystallization process is characterized by its sharp onset at 150 °C. The temperature dependence of the nucleation rate agrees with simple models. The growth rate increases linearly with temperature. The characteristic exponent n in Avramis equation corresponds to a two-dimensional interface-controlled growth. The results allowed us to determine the free energy of critical nucleas formation (0.18 eV) and also the free energy associated with atomic migration (1 eV).

Functionally Graded Ti-TiC Multilayers: The Effect of a Graded Profile on Adhesion to Substrate

Thin Ti-TiC multilayer coatings on silicon substrates, when sputtered under bias, are in a state of compressive stress due to the incorporation of argon into the deposited layer. Under certain conditions, the compressive stresses lead to spontaneous delamination of the coating. The delamination process takes place by the propagation of a front of concentrated stress that produces local interface separation. The delamination process is characterized by outward buckling of the coating that propagates with relatively well-defined wavelengths of the order of 30 to 70 nm. Ultimately the delamination grows into a complex wrinkling pattern of the coating. The Ti-TiC graded multilayers were deposited with pre-designed composition profiles that affect the state of stress within the coating. The profile reflects the variation of the TiC/Ti ratio along the z-direction, perpendicular to the coating. Elementary composition profiles are characterized by one single parameter, k, that defines whether the TiC/Ti ratio is concave (for k 1) with respect to z. Graded multilayers with different values of k display delamination patterns that vary both by their kinetics and by the final morphology of the coating. In particular, graded multilayers with k≥3, display long term stability. The results illustrate the potential of graded coatings to reduce intrinsic stresses leading to delamination and failure.

Structural and magnetoresistive properties of NiFe/Ag multilayered system

Abstract X-ray diffraction and its theoretical simulation were used to characterize morphological evolution that takes place in permalloy—silver multilayers as the outcome of thermal annealing treatments. Resistivity and magnetoresistivity measurements were performed in order to obtain additional insight into the results.

The effect of a diffusion reaction on the elastic properties of thin films

Abstract We have obtained an approximate solution for the velocity of a surface acoustic wave (SAW) in a system consisting of an arbitrary number of plane parallel isotropic layers on an isotropic substrate. This solution is used for estimating the elastic properties of an Au/Al thin film diffusion couple. The changes in the phase velocity of the surface wave during annealing of an Au/Al diffusion couple were measured. The effective elastic parameter of the intermetallic compound Au 2 Al, formed during the diffusion anneal, is estimated on the basis of the experimental data. Using the experimentally measured variations in the velocity of the SAW we were able to calculate the changes in thickness of the intermetallic compound layer.