H. Ljungcrantz

NANOINDENTATION STUDIES OF SINGLE-CRYSTAL (001)-, (011)-, AND (111)-ORIENTED TIN LAYERS ON MGO

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 increasin...

ION INDUCED STRESS GENERATION IN ARC-EVAPORATED TIN FILMS

The influence of Ti ion bombardment on the intrinsic stress and microstructure of TiN films during deposition by arc evaporation of Ti in pure N2 has been investigated. Ions with an average charge of +1.6 were accelerated from the arc discharge by a negative substrate bias Vs between 5 and 540 V which yielded a steady‐state substrate temperature between 300 and 600 °C, respectively. The compressive intrinsic stresses in the films, as determined by the x‐ray‐diffraction (XRD) sin2 ψ method after subtracting the thermal stress contribution at room temperature, changed abruptly from 1.9 to a maximum of 6.5 GPa as Vs increased from 5 to 100 V. The compressive stress then decreased monotonically to ∼1.6 GPa as Vs increased to 540 V. Broadening of XRD peaks (β) showed accompanying inhomogeneous strain with a maximum values for Vs=100 V. Cross‐sectional transmission electron microscopy showed a dense columnar film microstructure. Electron microdiffraction showed a distorted structure within the same columns for ...

Growth, microstructure, and mechanical properties of arc evaporated TiCxN1-x (0 <= x <= 1) films

TiCxN1-x films with x ranging from 0 to 1 were grown by arc evaporation by varying the flow ratio between the reactive gases. The substrates were cemented carbide inserts (WC-6 wt.% Co) which were negatively biased at 400 V, resulting in a deposition temperature of similar to 550 degrees C. The film composition, as measured by glow discharge optical emission spectroscopy, was found to vary almost linearly with the gas flow ratio. Cross-sectional transmission electron microscopy in combination with X-ray diffraction (XRD) showed that the films were of single-phase NaCl-structure with a dense columnar microstructure. The intrinsic stress analyzed using the XRD sin(2)psi method, was found to have a maximum of - 5.9 GPa in the composition range of 0.4 less than or equal to x less than or equal to 0.7 which correlated with a maximum in XRD peak broadening due to inhomogeneous strains. The hardness and Youngs modulus of the as-deposited TiCxN1-x films were measured by the nanoindentation technique. A maximum in hardness of 45 GPa was found at the same composition range (0.4 Ix I 0.7) as the intrinsic stress maximum. The hardness for x = 0 (TiN) and x = 1 (TiC) were found to be 28 and 36 GPa, respectively. The Youngs modulus was constant similar to 610 GPa for films with compositions up to x = 0.6, thereafter it decreased to 540 GPa at x = 1. The increase in intrinsic stress with increasing carbon content is suggested to be due to increased stability of defects created from the collision cascade or/and by a change in the defect structure itself. The fact that hardness showed a maximum at the same composition as residual stress and FWHM indicates that obstruction on dislocation movement has a major influence on the hardness of these films

Enhanced mechanical hardness in epitaxial nonisostructural Mo/NbN and W/NbN superlattices

Epitaxial Mo/NbN and W/NbN superlattices with modulation wavelengths Λ ranging from 1.3 to 120 nm were grown on MgO (001) substrates by dc reactive magnetron sputtering in Ar/N2 mixtures. The superlattices were shown to be epitaxial with nearly planar layers using high- and low-angle x-ray diffraction and transmission electron microscopy. Computer simulation fits of the x-ray data indicated that interface widths were ⩽0.3 nm. The epitaxial relationship between the layers was (001)metal∥(001)NbN and [110]metal∥[100]NbN. The nanoindenter microhardness values from W/NbN and Mo/NbN superlattices with 50 vol % metal were nearly identical. The largest hardnesses were 30 GPa, observed at superlattice periods Λ=2–3 nm, compared to rule-of-mixtures values of 10 GPa. The hardness decreased with increasing Λ above ≈3 nm, following the dependences H=10.3+26.70Λ−0.38 GPa for Mo/NbN and H=12.88+22.1Λ−0.3 GPa for W/NbN. Hardness versus metal volume fraction with Λ≈5 nm showed a flat-topped dependence. Brillouin scatteri...

Microstructural investigation of droplets in arc-evaporated TiN films

Abstract The microstructure and composition of macro particles (droplets) in TiN films deposited by arc evaporation on cemented-carbide substrates were investigated using a combination of scanning electron microscopy, cross-sectional transmission electron microscopy (TEM) including lattice resolution TEM, X-ray diffraction (XRD), energy-dispersive X-ray analysis and electron energy loss spectroscopy. The apparent surface number density of droplets, with diameters of 0.1–10 μm, was found to be about 10 7 cm −2 . Droplets were incorporated in the film at various distances from the substrate surface. In between the droplets, the TiN films exhibited a dense columnar microstructure. On top of the incorporated droplets, the TiN films grew in a pronounced columnar structure with a column diameter close to the droplet diameter. The core of the droplets consisted of equiaxed grains of an α-Ti superstructure containing approximately 3–5 at.% N whereas the rim of the droplets had increasing nitrogen content up to 50 at.% XRD showed evidence for the presence of Ti 2 N possibly at the rim of the droplets. Beneath each droplet a large voided region was observed with the shape of a flattened torus as a consequence of droplets being incorporated in the solid state and subsequent shadowing of the Ti flux to the film.

Residual stresses and fracture properties of magnetron sputtered Ti films on Si microelements

The influence of different deposition parameters on the microstructure, the residual stress, and the mechanical properties of thin Ti films has been investigated. Ti films were deposited onto Si (001) wafers with a native oxide layer, held at a temperature <250 °C, by dc magnetron sputtering. The film thickness was 1 μm. The microstructure of the films, as determined by x‐ray diffraction (XRD) and transmission electron microscopy (TEM), was varied by changing the Ar sputtering pressure PAr between 0.8 and 8.3 mTorr, and by applying a negative substrate bias Vs between 0 and 300 V. The residual stresses in the films were determined by both a beam curvature technique and the XRD sin2 ψ method. For Vs=0, the residual stress in the films changed abruptly from tensile to compressive as PAr decreased below 2.5 mTorr. A maximum tensile stress of 0.4 GPa was obtained at 3 mTorr. The compressive stress reached at PAr=0.8 mTorr was 0.4 GPa. TEM showed accompanying structural changes from columnar structure with a h...

Corrosion behaviour of monocrystalline titanium nitride

The corrosion behaviour of monocrystalline and highly textured TiN films deposited onto single crystalline MgO has been investigated. It was found that films with high defect concentrations and elements of polycrystallinity had a reduced corrosion resistance. These films had low corrosion potentials and high critical and passive current densities. For high quality films the [110]- and [111]-orientations generally displayed better corrosion properties than films with [100]-orientation. Corrosion had different effects on films of different orientations: On [100]-oriented films loose rectangularly shaped flakes were observed. [110]-oriented films cracked because of compressive stresses, which in many cases caused the films to peel off during corrosion. On [111]-oriented films, finally, triangular pits were detected after corrosion. Films with high corrosion potentials had low values of critical and passive current densities. Non-destructive electrochemical analysis in combination with defect analysis can thus be used to predict the behaviour of these films on anodic polarisation.

Influence of ionization degree on film properties when using high power impulse magnetron sputtering

Chromium thin films are deposited by combining direct current magnetron sputtering and high power impulse magnetron sputtering (HiPIMS) on a single cathode in an industrial deposition system. While maintaining a constant deposition rate and unchanged metal ion energy distribution function, the fraction of the total power supplied by either deposition technique is altered, and thereby also the metal ion to metal neutral ratio of the deposition flux. It is observed that the required total average power needed to be proportionally increased as the HiPIMS fraction is increased to be able to keep a constant deposition rate. The influence on microstructure, electrical, and electrochemical properties of the films is investigated and shows improvements with the use of HiPIMS. However, considerable influence of the studied properties occurs already when only some 40% of the total power is supplied by the HiPIMS technique. Further increase of the HiPIMS power fraction results in comparatively minor influence of the studied properties yet significant deposition rate efficiency reduction. The results show that the degree of ionization can be controlled separately, and that the advantages associated with using HiPIMS can be obtained while much of the deposition rate reduction, often reported for HiPIMS, can be avoided.

Effects of nitrogen pressure on arc-evaporated TiN coatings

Abstract This article addresses both fundamentals, such as the generation of metal ions and macroparticles (droplets), as well as more practical aspects, e.g. how different process parameters affect microstructure and mechanical properties of TiN films grown on powder metallurgical steel substrates by reactive arc evaporation. A commercially available Multi-Arc equipment has been used to deposit coatings using different nitrogen pressures, substrate-source distances and bias voltages during the growth stage. The microstructural characterisation, regarding droplet number density, surface roughness, changes in the strain and grain size of the deposited coatings, have been performed by scanning and transmission electron microscopy and X-ray diffraction. The influence of the nitrogen pressure on the growth rate, surface roughness and mechanical properties, such as adhesion and scratch resistance, have also been studied by using standard techniques. Only minor changes in the grain size, compressive strain, preferred orientation and adhesion were observed while varying the nitrogen pressure by a factor of ten. In this large process window, general trends such as an increased growth rate and a decreased droplet number density with increasing nitrogen pressure has been established, although these variations are different depending on the substrate-source distances. The increasing nitrogen pressure results in higher deposition rates for the TiN film but in lower ion current densities extracted by the negative substrate bias. This increase in growth rate is discussed in terms of a decreased resputtering effect owing to the observed decrease in ion current density. The major part of the droplets can be concluded to be created during the initial etching/heating stage and their number density decreases linearly with film thickness. An initial discussion regarding the results obtained and a phenomenological explanation of the possible reasons for the dependencies found is proposed.

Growth and electronic properties of epitaxial TiN thin films on 3C-SiC(001) and 6H-SiC(0001) substrates by reactive magnetron sputtering

Epitaxial TiN films were grown on cubic (3C)-SiC(001) and hexagonal (6H)-SiC(0001) substrates by ultrahigh vacuum reactive magnetron sputtering from a Ti target in a mixed Ar and N 2 discharge at a substrate temperature of 700 °C. Cross-sectional transmission electron microscopy, including high-resolution imaging, showed orientational relationships TiN(001)‖3C-SiC(001), and TiN[110]‖3C-SiC[110], and TiN(111)‖6H-SiC(0001) and . In the latter case, twin-related TiN domains formed as the result of nucleation on SiC terraces with an inequivalent stacking sequence of Si and C. The TiN/SiC interface was locally atomically sharp for both SiC polytypes. Defects in the TiN layers consisted of threading double positioning domain boundaries in TiN(111) on 6H-SiC. Stacking faults in 3C-SiC did not propagate upon growth of TiN. Room-temperature resistivity of TiN films was ρ = 14 μΩ cm for 6H-SiC(0001) and ρ = 17 μΩ cm for 3C-SiC(001) substrates. Specific contact resistance of TiN to 6H-SiC(0001) was 1.3 3 10 −3 Ω cm 2 for a 6H-SiC substrate with an n -type doping of 5 × 10 17 cm −3 .