Denis Music

Ion-assisted physical vapor deposition for enhanced film properties on nonflat surfaces

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.

Influence of the Al distribution on the structure, elastic properties, and phase stability of supersaturated Ti1−xAlxN

Ti1−xAlxN 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 configuration...

Ab initio calculated binodal and spinodal of cubic Ti1−xAlxN

During annealing, metastable NaCl-structured (c) Ti1−xAlxN films initially exhibit spinodal decomposition which results in age hardening. Based on ab initio calculations, we show that the chemical requirement for spinodal decomposition in the quasibinary c‐TiN–c‐AlN system is fulfilled over a wide composition and temperature range. The enthalpy change for the decomposition of c‐Ti0.34Al0.66N is ∼26.4kJmol−1, which is in good agreement with previously reported experiments. The obtained results enable materials design of Ti1−xAlxN-based coating systems for high-temperature applications.

Low temperature deposition of α-Al2O3 thin films by sputtering using a Cr2O3 template

A description about low temperature deposition of a-Al2O3 thin films by sputtering was presented. Cr2O3 thin layer was used as a template. Nanoindentation was used to study the mechanical propertie ...

Experimental and computational study on the phase stability of Al-containing cubic transition metal nitrides

The phase stability of Al-containing cubic transition metal (TM) nitrides, where Al substitutes for TM (i.e. TM1−xAlxN), is studied as a function of the TM valence electron concentration (VEC). X-ray diffraction and thermal analyses data of magnetron sputtered Ti1−xAlxN, V1−xAlxN and Cr1−xAlxN films indicate increasing phase stability of cubic TM1−xAlxN at larger Al contents and higher temperatures with increasing TM VEC. These experimental findings can be understood based on first principle investigations of ternary cubic TM1−xAlxN with TM = Sc, Ti, V, Cr, Y, Zr and Nb where the TM VEC and the lattice strain are systematically varied.However, our experimental data indicate that, in addition to the decomposition energetics (cubic TM1−xAlxN → cubic TMN + hexagonal AlN), future stability models have to include nitrogen release as one of the mechanisms that critically determine the overall phase stability of TM1−xAlxN.

Elastic properties of Fe–Mn random alloys studied by ab initio calculations

We have studied the influence of the Mn content on the elastic properties of Fe-Mn random alloys (space group of Fm (3) over barm) using ab initio calculations. The magnetic effects in Fe-Mn alloys ...

Experimental and ab initio study of the mechanical properties of hydroxyapatite

The authors have studied the elastic properties of radio frequency sputtered phase pure, stoichiometric, and dense hydroxyapatite films by nanoindentation. The measured elastic modulus values have been compared to ab initio calculated data. The calculation technique was based on the determination of all elastic constants. The calculated and measured elastic modulus values differ by ∼10%. The good agreement indicates that the elasticity of hydroxyapatite can be described using ab initio calculations, establishing the elastic modulus thereof.

Elastic properties of MFe3N (M=Ni, Pd, Pt) studied by ab initio calculations

Using ab initio calculations, we have studied the correlation between the electronic structure and elastic properties of MFe3N phases (M=Ni, Pd, Pt). These ternary nitrides possess a bulk-modulus-to-C44 ratio from 2.3 to 2.9, a rather unusual ratio for nitrides. This may be understood based on the electronic structure: Predominantly covalent-ionic Fe–N layers are interleaved with predominantly metallic Fe–M layers. We propose that the unusually large bulk-modulus-to-C44 ratio is a consequence of weak coupling between the Fe–N and Fe–M layers (giving rise to a low C44) as well as strong coupling within Fe–N layers (giving rise to a large bulk modulus).

A proposal for an unusually stiff and moderately ductile hard coating material: Mo2BC

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 Youngs 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.

Phase stability and elastic properties of Tan+1AlCn (n = 1–3) at high pressure and elevated temperature

We have studied the electronic structure of Tan+1AlCn (space group P63/mmc,n = 1?3) under uniform compression from 0 to 60?GPa and at temperatures from 0 to 1500?K using ab initio calculations. These phases can be characterized by alternating layers of high and low electron density and are referred to as nanolaminates. At 0?K we observe similar compressibilities in both the a and c directions for all phases investigated. This is unusual for nanolaminates. Based on the density of states analysis, we propose that these similar compressibilities may be caused by an increase in Ta?Al and Ta?Ta bonding strength as well as a stronger long-range interaction between TaC?TaC layers. No evidence of a phase transition is observed as the pressure is increased to 60?GPa. However, as the temperature is increased to approximately 1000?K without applying pressure, a first-order phase transition occurs in Ta3AlC2. These results are relevant for applications of Tan+1AlCn at elevated temperature and pressure.