F. Bouillon

Synthesis and characterization of thin-film molybdenum nitrides

Abstract The action of ammonia on Mo(bcc)/MgO, obtained by thermal evaporation, leads to the formation of a mixture of γ-Mo2N and γ-MoN phases. Their experimental conditions of separation and stability are determined and a structural discussion is presented. It was also found that MgO(100) is suitable for epitaxial growth of nitrides of cubic symmetry at high temperature (T > 1073 K), owing to the thermal stability of magnesium oxide. The coatings are characterized by transmission high-energy electron diffraction (THEED), transmission electron microscopy (TEM), and Auger electron spectroscopy (AES).

Deposition parameter effects on the composition and the crystalline state of reactively sputtered molybdenum nitride

Abstract Using d.c. reactive sputtering of a molybdenum target, we have studied the effect of discharge power, substrate temperature and nitrogen pressure on molybdenum nitride formation. The crystallographic structure and composition of the deposited Mo-N film surfaces were investigated by reflection high energy electron diffraction and Auger electron spectroscopy. It was found that the deposits consist of the cubic Mo 2 N 1± x (f.c.c.), the tetragonal β-Mo 2 N and the hexagonal δ-MoN phases. By controlling the substrate temperature and the deposition rate, which is strongly dependent on the discharge power, during the reactive sputtering, the stability domains of different phases were established and it has been possible to produce the f.c.c. nitride with a composition near 48.5 at.% N.

Preparation and characterization of epitaxial films of silver, palladium and Ag-Pd alloys deposited by glow discharge sputtering I: Onto NaCl single-crystal substrates

The experimental conditions to condense epitaxial films of silver, palladium and Ag-Pd alloys onto (100) air-cleaved rocksalt faces by glow discharge sputtering are described. The orientation (100)d‖(100)s (where d indicates deposit and s substrate) is observed for all the systems studied. A simple experiment demonstrates that by simultaneous sputtering of silver and palladium we obtain an effective monophasic alloy. The films are characterized by transmission and reflection high energy electron diffraction, selected area diffraction, transmission electron microscopy, Auger electron spectroscopy and grazing angle X-ray diffraction. The relative concentrations of silver and palladium in the alloy films can be determined by grazing angle X-ray diffraction with good accuracy.

Structure and purity of epitaxial films of copper and rhodium deposited onto MgO single-crystal substrates by glow discharge sputtering

The structure and surface purity of epitaxial films of rhodium deposited by thermal evaporation and ion sputtering onto MgO(100), air cleaved and chemically polished, and onto epitaxial films of Cu(100) are compared. The orientation (100)d//(100)s (where d indicates deposit and s indicates substrate) is always predominant and only this orientation occurs on the (100)Cu//(100)MgO substrate. Electron diffraction and Auger spectroscopy show that the best results are obtained by glow discharge sputtering onto the last substrate.

C-growth of d.c.-sputtered Mo and W thin films

Abstract Molybdenum and tungsten thin films were deposited onto MgO(100) and amorphous substrates (silica, glass) by d.c.-sputtering in argon. Although the gas used is neutral, the deposits realized for both metals with low deposition rates ν d ( −1 ) presented an f.c.c. structure. The occurence of this structure was independent of the substrate nature. A detailed study concerning molybdenum showed that for ν d >6 nm min −1 , Mo systematically appeared in the bulk b.c.c. structure. It is proposed that the f.c.c. structure is stabilized by metalloid impurities (C, N, O) present in the residual atmosphere. Special care was given to the orientation of the Mo and W f.c.c. layers on MgO(100), and a (100) orientation was observed. It was found that these deposits exhibit, under certain conditions, the same orientation on amorphous substrates, which is characteristic of a fiber of 〈100〉 axis. The crystallographic structure of the coatings was explored by X-ray, RHEED and THEED techniques. Surface composition was determined by AES.

Surface segregation study of Ib-VIII single-crystal alloys

Abstract Surface segregation of AgPd, CuPd and CuRh single crystals was studied by AES. The samples were either massive alloys or epitaxial thin films deposited on MgO. A weak surface segregation of silver was detected in AgPd alloys while the surfaces of CuPd and CuRh alloys were enriched in copper. The diffusion of copper and silver to the surface during heat treatments can be easily shown by looking at the behaviour of the Auger low-energy peaks. Our results were compared with previously published data and with theoretical models. The element with the lower surface energy segregates but not as strongly as suggested by the ideal solution model.

Composition and structure of reactively sputter-deposited molybdenum-carbon films

Abstract MoC x films were grown by d.c. reactive sputtering in an ArCH 4 atmosphere onto MgO (001) single-crystal surfaces. The crystallographic structure of the films was revealed by reflection and transmission high-energy electron diffraction. The microstructure was studied by transmission electron microscopy and the composition of the films was determined by Auger electron spectroscopy. Under the used processing conditions, the electron diffraction shows that only MoC with the B 1 structure (NaCl-type) was formed. The carbon content of the films was found to increase with increasing CH 4 partial pressure and the lattice parameter of the B 1 phase was also found to vary in the same direction as a consequence of an increase of incorporated carbon in the B 1 lattice. The determined values for lattice parameters and carbon contents, in the carbon-richer side, were somewhat greater than the highest ones reported for the rapidly quenched B 1 phase. This fact was related to an extension of the homogeneity range of this phase. The results may be attributed to lower deposition rates which seem to play a prominent role. In agreement with previous studies performed on analogous reactively sputtered MC systems, the grain size was found to decrease when the concentration of reactive gas is increased. This behavior may be interpreted in terms of carbon location at the grain boundaries as well as in terms of a reduction of the mean migration paths of adatoms caussed by an increase of the substrate impinging flux resulting from more CH n radical formation.

Structural behavior of direct-current sputtered and thermally evaporated molybdenum thin films

Mo films were deposited on sintered polycrystalline MgO. These films exhibited, depending on deposition conditions, two different structures, namely the normal body-centered cubic and an abnormal face-centered cubic. The analysis performed by electron diffraction and Auger electron spectroscopy indicated that the fcc structure assumed by molybdenum is an impurity-stabilized phase rather than a simple polymorphic transformation or dimolybdenum nitride (γMo2N) as previously stated by some authors.

Enrichment in molybdenum carbides and nitrides during Ar+ bombardment

Abstract α-Mo2C, δ-MoN and MoO3 interstitial compounds, obtained by direct metal-gas interaction, were investigated by coupled Auger electron spectroscopy (AES) and ionic erosion with Ar+. It was found that, when the energy EAr+ varies from 3.5 to 1 keV, the relative AES signal hx(KL2, 3L2, 3)/hMo(M4, 5N2, 3N4, 5) (X ≡ C and N in the case of the MoC and MoN systems respectively) is attenuated. It indicates a preferential enrichment in molybdenum on the film surface at a low energy (less than 1.5 keV). The observed behaviour was interpreted in terms of preferential reimplantation and sputtering of C and N. The relative sensitivity coefficients of carbon, nitrogen and oxygen compared with molybdenum were also determined.

Solidification of silver-palladium single crystals

Abstract This paper describes the preparation of Ag-Pd alloy single crystals by the vertical Bridgman method. Solidification structures were detected for all the alloys studied. The solute distribution was examined using scanning Auger microscopy and microindentation and was in good agreement with theoretical models. Homogeneous samples could be obtained after annealing.