Torbjörn Joelsson

Single-crystal Ti2AlN thin films

We have produced pure thin-film single-crystal Ti2AlN(0001), a member of the Mn+1AXn class of materials. The method used was UHV dc reactive magnetron sputtering from a 2Ti:Al compound target in a mixed Ar–N2 discharge onto (111) oriented MgO substrates. X-ray diffraction and transmission electron microscopy were used to establish the hexagonal crystal structure with c and a lattice parameters of 13.6 and 3.07A, respectively. The hardness H, and elastic modulus E, as determined by nanoindentation measurements, were found to be 16.1±1GPa and 270±20GPa, respectively. A room-temperature resistivity for the films of 39μΩcm was obtained.

Deformation structures under indentations in TiN/NbN single-crystal multilayers deposited by magnetron sputtering at different bombarding ion energies

Abstract Work elsewhere has suggested that multilayer films with layer thicknesses of a few nanometres can be much harder than monolithic films, although there is considerable variation in the observed magnitude of this effect. To investigate this, multilayer TiN/NbN films have been deposited by reactive magnetron sputtering on to MgO single crystals. The hardnesses measured were similar to those of the TiN and NbN alone, which is consistent with the observation by transmission electron microscopy (TEM) that deformation across the interfaces was not prevented. Varying the electrical potential at which the film was grown from -10 to -200V and the corresponding ion energy from 10 to 200eV increased the hardness from 19 to 25GPa; further decreases in the potential caused the hardness to decrease. Using TEM, deformation was observed to occur along the apparent columnar boundaries within the films, suggesting that the effect of the electrical potential on the measured hardness was caused by changes in the appa...

Phase stability tuning in the NbxZr1-xN thin-film system for large stacking fault density and enhanced mechanical strength

The phase stability of hexagonal WC-structure and cubic NaCl-structure 4d transition metal nitrides was calculated using first-principles density functional theory. It is predicted that there is a multiphase or polytypic region for the 4d transition metal nitrides with a valence electron concentration around 9.5 to 9.7 per formula unit. For verification, epitaxial NbxZr1−xN (0⩽x⩽1) was grown by reactive magnetron sputter deposition on MgO(001) substrates and analyzed with transmission electron microscopy (TEM) and x-ray diffraction. The defects observed in the films were threading dislocations due to nucleation and growth on the lattice-mismatched substrate and planar defects (stacking faults) parallel to the substrate surface. The highest defect density was found at the x=0.5 composition. The nanoindentation hardness of the films varied between 21GPa for the binary nitrides, and 26GPa for Nb0.5Zr0.5N. Unlike the cubic binary nitrides, no slip on the preferred ⟨11¯0⟩{110} slip system was observed. The inc...

Deposition of single-crystal Ti2AlN thin films by reactive magnetron sputtering from a 2Ti:Al compound target

Single-crystal Ti2AlN (0001) thin films were grown on (111) oriented MgO substrates kept at 830°C by ultrahigh vacuum dc reactive magnetron sputtering from a compound 2Ti:Al target in a mixed Ar∕N2 discharge. The effects of variations in the nitrogen partial pressure on the phase composition of the films were studied. Results from transmission electron microscopy, x-ray diffraction, and elastic recoil detection analysis show a narrow region for growth of Ti2AlN MAX phase with respect to the nitrogen content in the discharge. Perovskite Ti3AlN and intermetallic Ti3Al and TiAl phases dominate at nitrogen depletion. For overstoichiometric deposition conditions with respect to Ti2AlN, a phase mixture with NaCl-structured TiN is obtained. Epitaxial growth is observed with a layer-by-layer mode on the 0001 basal planes for all phases. A superstructure in the TiN phase is also observed along [111] with the repetition distance of 7.34A, most likely related to Al segregation. Nanoindentation shows that the film ha...

Residual stress formation in multilayered TiN/TaNx coatings during reactive magnetron sputter deposition

Multilayered physical vapor deposited TiN/TaNx coatings were deposited on cemented carbide substrates using a dual target magnetron sputtering system. The coatings were investigated with respect to the influence of nitrogen partial pressure during deposition on the residual stress developed in the coatings. Furthermore, the fracture strength of the material, i.e., the magnitude of the tensile stress that the coating can support without cracking, was evaluated. It was found that, by increasing the nitrogen partial pressure, it is possible to change the stress from compressive to tensile. The highest tensile stress was about 3.6 GPa. Despite this high stress, the coating displayed no cracking. This implies that it is possible to grow TiN/TaNx multilayered coatings with high tensile fracture strength using dual magnetron sputtering and a high deposition temperature (about 680 °C).

The Effect of Thermal Gradients on SiC Wafers

An in-situ curvature measurement equipment has been used to measure the curvature change of 4H-SiC 8degrees off-axis wafers, both with and without a CVD grown epitaxial layer, under beat treatments ...