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We have synthesized Ta thin films on Si substrates placed along a wall of a 2-cm-deep and 1-cm-wide trench, using both a mostly neutral Ta flux by conventional dc magnetron sputtering (dcMS) and a mostly ionized Ta flux by high-power pulsed magnetron sputtering (HPPMS). Structure of the grown films was evaluated by scanning electron microscopy, transmission electron microscopy, and atomic force microscopy. The Ta thin film grown by HPPMS has a smooth surface and a dense crystalline structure with grains oriented perpendicular to the substrate surface, whereas the film grown by dcMS exhibits a rough surface, pores between the grains, and an inclined columnar structure. The improved homogeneity achieved by HPPMS is a direct consequence of the high ion fraction of sputtered species.

Ti 1 − x Al x N films and/or their alloys are employed in many industrial applications due to their excellent mechanical and thermal properties. Synthesized by plasma-assisted vapor deposition, Ti1−xAlxN is reported to crystallize in the cubic NaCl (c) structure for AlN mole fractions below 0.4–0.91, whereas at larger Al contents the hexagonal ZnS-wurtzite (w) structure is observed. Here we use ab initio calculations to analyze the effect of composition and Al distribution on the metal sublattice on phase stability, structure, and elastic properties of c-Ti1−xAlxN and w-Ti1−xAlxN. We show that the phase stability of supersaturated c-Ti1−xAlxN not only depends on the chemical composition but also on the Al distribution of the metal sublattice. An increase of the metastable solubility limit of AlN in c-Ti1−xAlxN from 0.64 to 0.74 is obtained by decreasing the number of Ti–Al bonds. This can be understood by considering the Al distribution induced changes of the electronic structure, bond energy, and configurational entropy. This may in part explain the large variation of the metastable solubility limit reported in the literature.

The elastic properties of Mo2BC were studied using ab initio calculations. The calculated bulk modulus of 324 GPa is 45% larger than that of Ti0.25Al0.75N and 14% smaller than that of c-BN, indicating a highly stiff material. The bulk modulus (B) to shear modulus (G) ratio is 1.72 at the transition from brittle to ductile behaviour. This, in combination with a positive Cauchy pressure (c12 − c44), suggests moderate ductility. When compared with a typical hard protective coating such as Ti0.25Al0.75N (B = 178 GPa; B/G = 1.44; negative Cauchy pressure), Mo2BC displays considerable potential as protective coating for metal cutting applications. In order to test this proposal, Mo2BC thin films were synthesized using dc magnetron sputtering from three plasma sources on Al2O3(0 0 0 1) at a substrate temperature of ∼900 °C. The calculated lattice parameters are in good agreement with values determined from x-ray diffraction. The measured Young's modulus values of ∼460 ± 21 GPa are in excellent agreement with the 470 GPa value obtained by calculations. Scanning probe microscopy imaging of the residual indent revealed no evidence for crack formation as well as significant pile-up, which is consistent with the moderate plasticity predicted. The apparent contradiction between moderate ductility on the one hand and indentation hardness values of 29 GPa can be understood by considering the electronic structure particularly the extreme anisotropy. The presence of stiff Mo–C and Mo–B layers with metallic interlayer bonding enables this intriguing and unexpected property combination.

We have investigated the elastic properties of nanolayered M 2 AC, with M = Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W and A = Al, Ga, Ge, Sn, by ab initio calculations. We suggest that M 2 AC can be classified into two groups: One where the bulk modulus of the binary MC is conserved and another group where the bulk modulus is decreased. This classification can be understood in terms of coupling between MC and A layers, which is defined by the valence electron population. These results may have implications for the understanding of properties and the performance of this class of solids.Transition-metal carbides are suitable for many technological applications due to their high hardness, high melting point, and excellent electrical conductivity. However, the intrinsic brittleness of these carbides hinders their broader applications as structural materials. Owing to a combination of both metallic and ceramic properties, nanolayered ternary metal carbides of M n+1 AC n type (space group P6 3 / mmc) represent an exception, where n =1-2, M is an early transition metal, and A is mostly a IIIA or a IVA group element. 1 For example, Ti 3 SiC 2 , the most studied M n+1 AC n phase, exhibits an elastic modulus of more than 330 GPa, 1 fully reversible plasticity, 2 and negligible thermopower. 3 Also, M 2 AC phases have been investigated both experimentally 1,4-16 and theoretically. [17][18][19][20][21][22] It is reported that these ternary carbides exhibit improved ductility, 1,15 oxidation resistance, 1,7,9,10 and electrical conductivity. 1,11 They also demonstrate good damage tolerance and thermal shock resistance. 1 However, a systematic correlation between the electronic structure and properties of M n+1 AC n has not been explored in the literature. Here, we discuss the correlation between the chemical bonding and the elastic properties of M 2 AC by ab initio calculations.The VASP code 23,24 is used for the present calculations, wherein the generalized-gradient projector-augmented wave potentials are employed. 25 The following parameters were applied: 1 ϫ 10 −4 eV relaxation convergence for ions, 1 ϫ 10 −5 eV electronic relaxation convergence, conjugate gradient optimization of the wave functions, reciprocal-space integration with a Monkhorst-Pack scheme, 26 energy cutoff of 500 eV, k-points grid of 9 ϫ 9 ϫ 9, and the tetrahedron method with Blöchl corrections 27 for the energy. Spinpolarized configurations were not considered since no significant changes in structures and elastic properties were previously identified for Cr 2 AlC (Ref. 28). The equilibrium volume and the bulk modulus were calculated by a leastsquare fit of the volume-energy curves using the third-order Birch-Murnaghan's equations of states. 29 These volumeenergy curves stem from the relaxation of both the lattice parameter a and the hexagonal c / a ratio. The partial density of states and charge-density distributions are obtained using the relaxed structures at the equilibrium volumes. The input lattice parameters of the M 2 AC studied are taken from Ref. 1 and t...