Synthesis, microstructural evolution, and properties of polycrystalline and epitaxial metastable titanium tungsten nitride alloy layers.

摘要

Phase composition, microstructural evolution, and physical properties of Ti_1−xW_xN alloys with 0:5 ≤ x ≤ 1.0 and superlattice layers grown by ultra-high vacuum (UHV) reactive magnetron sputtering were investigated using a combination of x-ray diffraction (XRD), high-resolution reciprocal lattice map (HR-RLM), transmission electron microscopy (TEM), Rutherford backscattering spectroscopy (RBS), Auger electron spectroscopy (AES), wavelength-dispersive electron probe microanalysis (EMPA), x-ray photoelectron spectroscopy (XPS), and Hall measurements.; Polycrystalline Ti_1−xW_xN alloys were grown on SiO₂ at 500°C. Alloys with 0 ≤ x ≤ 0.70 were single-phase B1-NaCl crystal structure with a nitrogen-to-metal ratio N/(Ti+W) ranging from slightly overstoichiometric to understoichiometric. The relaxed lattice constant a_o initially increased slightly with increasing W and then decreased below the stoichiometric TiN value for understoichiometric alloys (x > 0.50). TiN-rich alloys have a columnar microstructure exhibiting strong 111 preferred orientation with underdense column boundaries. The irradiation by energetic N backscattered from the W target resulted in WN-rich alloys having 002 preferred orientations with denser microstructures. The normalized room-temperature resistivity increased linearly at a rate dρ/ρ _TiNdx = 3.5.; Epitaxial B1-NaCl structure Ti_1−xW_xN alloys with 0 ≤ x ≤ 0.6 were grown on MgO(001) substrates at 500°C. Alloys with x ≥ 0.05 are slightly overstoichiometric. The alloy lattice parameter a_⊥ along the film growth direction is 4.251 Å for x ≤ 0.41 and decreases slightly at higher concentrations. Ti_0.5W _0.5N alloy exhibits long-range CuPt-type atomic ordering on the cation sublattice. The room-temperature resistivity increases linearly due primarily to alloy scattering, while the temperature coefficient of resistivity (TCR), switches from positive for x ≤ 0.21 to negative because of weak charge carrier localization. The superconducting critical temperature T_c initially increases with x reaching a maximum of 6.67 K at x = 0.21 and decreasing for larger x values.; Epitaxial TiN/Ti_0.53W_0.47N superlattices with periods Λ ranging from 16 to 205 Å were also grown on MgO(001) substrates at 600°C. The superlattices were single crystals exhibiting coherent interfaces and nearly fully strained. All samples showed metallic behavior while resistivities decrease with period Λ, reaching the level expected for bulk parallel layers at Λ ≥ 70 Å. TCR decreased with Λ but remained positive. T_c is 7.8 K at Λ = 16 Å, decreasing to 5.4 K at Λ = 205 Å.