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The preferred orientation of polycrystalline TiN films grown by ultrahigh-vacuum reactive-magnetron sputter deposition on amorphous SiO2 at 350 °C in pure N2 discharges was controllably varied from (111) to completely (002) by varying the incident ion/metal flux ratio Ji/JTi from 1 to ≥5 with the N+2 ion energy Ei maintained constant at ≂20 eV (≂10 eV per incident accelerated N). All samples were slightly over-stoichiometric with N/Ti=1.02±0.03. Films deposited with Ji/JTi=1 initially exhibit a mixed texture with competitive columnar growth which slowly evolves into a nearly complete (111) texture at film thicknesses greater than 1 μm. However, films grown with Ji/JTi≥5 exhibit an essentially complete (002) preferred orientation from the earliest observable stages. The normalized XRD (002) intensity ratio in thick layers increased from ≂0 to 1 as Ji/JTi was varied from 1 to ≥5. Both (111) and (001) interplanar spacings remained constant as a function of film thickness yielding a lattice constant of 0.4240±0.0005 nm, equal to that of unstrained bulk TiN. Contrary to previous models, the present results establish that TiN preferred orientation can be controlled without introducing large in-plane compressive stress and/or changes in the strain energy as a function of layer thickness.

Metastable single-phase, NaCl-structure, polycrystalline Ti0.5Al0.5N alloy films have been shown to exhibit much better high-temperature (750–900 °C) oxidation resistance than polycrystalline TiN films grown under similar conditions. The Ti0.5Al0.5N alloys, ≂3 μm thick, were deposited at temperatures between 400 and 500 °C on stainless-steel substrates by dc magnetron sputter deposition in mixed Ar+N2 discharges with an applied negative substrate bias Vs of either 0 or 150 V. Oxidation in pure O2 initially occurred at a rate that varied parabolically with time. The oxide overlayers consisted of two partially crystalline sublayers, the upper one Al-rich and the lower one Ti-rich, with no measurable N concentrations in either. Inert-marker transport experiments showed that oxidation proceeded by the simultaneous outward diffusion of Al to the oxide/vapor interface and inward diffusion of O to the oxide/nitride interface. The oxidation rate constant K increased with oxidation temperature Tox at a rate much higher than would be predicted from a simple exponential dependence due to changes in the oxide microstructure (increased crystallinity) with increasing Tox. At Tox ≥850 °C, O transport became the rate-limiting step. After oxidation times, ranging from 6 h at 750 °C to 7 min at 900 °C, oxide crystallites, exhibiting a tetragonal rutile TiO2 structure, were observed in Vs=0 samples to grow at an accelerated rate up through cracks in the oxide overlayer. The formation of these crystallites was postponed until a much later stage in oxide-overlayer development for samples grown with Vs=150 V.

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Articles you may be interested inThermoelectric properties of epitaxial ScN films deposited by reactive magnetron sputtering onto MgO(001) substrates J. Appl. Phys. 113, 153704 (2013); 10.1063/1.4801886 Growth of fullerene-like carbon nitride thin solid films by reactive magnetron sputtering; role of low-energy ion irradiation in determining microstructure and mechanical properties J. Appl. Phys. 93, 3002 (2003); 10.1063/1.1538316 Growth of single-crystal CrN on MgO(001): Effects of low-energy ion-irradiation on surface morphological evolution and physical properties Microstructure and electronic properties of the refractory semiconductor ScN grown on MgO(001) by ultra-highvacuum reactive magnetron sputter depositionScN layers, 345 nm thick, were grown on MgO͑001͒ substrates at 750°C by ultrahigh-vacuum reactive magnetron sputter deposition in pure N 2 discharges at 5 mTorr. The N 2 ϩ to Sc ratio incident at the substrate and growing film was maintained constant at 14, while the ion energy E N 2 ϩ was varied from 13 to 50 eV. All films were stoichiometric with N/Sc ratios of 1.00Ϯ0.02. However, microstructural and surface morphological evolution were found to depend strongly on E N 2 ϩ . The nucleation and initial growth stages of ScN films deposited with E N 2 ϩϭ 13 eV are dominated by the formation of 111-and 002-oriented islands, but preferred orientation rapidly evolves toward a purely 111 texture by a film thickness of Ӎ50 nm as 002 grains grow out of existence in a kinetically limited competitive growth mode. In distinct contrast, films deposited with E N 2 ϩ ϭ20 eV grow in a cube-on-cube epitaxial relationship with the substrate and exhibit no indication of 111-oriented grains, even in the earliest stages. Increasing E N 2 ϩ to 50 eV still results in epitaxial layers, but with high in-plane compressive stress and the presence of N 2 gas bubbles. All epitaxial layers contain rectangular nanopipes Ӎ1 nm wide and aligned along the growth direction. The nanopipes result from atomic shadowing near the bottom of a periodic array of surface cusps which form along orthogonal ͗100͘ directions due to kinetic roughening during growth. The hardness H and elastic modulus E of the epitaxial ScN͑001͒ layer grown with E N 2 ϩϭ 20 eV are 21.1Ϯ1.1 and 356Ϯ18 GPa, respectively. H and E increase ͑decrease͒ with increasing ͑decreasing͒ E N 2 ϩ .

The mechanical properties of (001)-, (011)-, and (111)-oriented MgO wafers and 1-μm-thick TiN overlayers, grown simultaneously by dc magnetron sputter deposition at 700 °C in a mixed N2 and Ar discharge, were investigated using nanoindentation. A combination of x-ray-diffraction (XRD) pole figures, high-resolution XRD analyses, and Auger electron spectroscopy was used to show that all TiN films were single crystals with N/Ti ratios of 1.0±0.05. The nanoindentation measurements were carried out using a three-sided pyramidal Berkovich diamond indentor tip operated at loads ranging from 0.4 to 40 mN. All three orientations of MgO substrates, as-received, exhibited identical hardness values as determined using the Oliver and Pharr method. After a 1 h anneal at 800 °C, corresponding to the thermal treatment received prior to film growth, the measured hardness of MgO(001) was 9.0±0.3 GPa. All TiN films displayed a completely elastic response at low loads. Measured hardness values, which decreased with increasing loads, increased in the order (011)<(001)<(111). After a 30 s postdeposition anneal at 1000 °C, however, hardness was found to be independent of load except at displacements >100 nm where substrate effects were apparent. TiN(001) and (111) films had hardnesses of 20±0.8 and 21±1 GPa, respectively, while data obtained from (011) layers exhibited large scatter due to surface roughness effects. Young’s moduli for annealed samples, calculated from the elastic unloading curves, were found to be 307±15 GPa for MgO (001) and 445±38 and 449±28 GPa for TiN (001) and TiN (111), respectively.