Search

Hard Ti1-xAlxN thin films are of importance for metal-cutting applications. The hardness, thermal stability, and oxidation resistance of these coatings can be further enhanced by alloying with TaN. We use a hybrid high-power pulsed and dc magnetron co-sputtering (HIPIMS/DCMS) technique to grow dense and hard Ti0.41Al0.51Ta0.08N alloys without external heating (Ts<150 °C). Separate Ti and Al targets operating in the DCMS mode maintain a deposition rate of ~50 nm/min, while irradiation of the growing film by heavy Ta+/Ta2+ ions from the HIPIMS-powered Ta target, using dc bias synchronized to the metal-ion-rich part of each HIPIMS pulse, provides effective near-surface atomic mixing resulting in densification. The substrate is maintained at floating potential between the short bias pulses to minimize Ar+ bombardment, which typically leads to high compressive stress. Transmission and scanning electron microscopy analyses reveal dramatic differences in the microstructure of the co-sputtered HIPIMS/DCMS films (Ta-HIPIMS) compared to films with the same composition grown at floating potential with all targets in the DCMS mode (Ta-DCMS). The Ta-DCMS alloy films are only ~70% dense due to both inter- and intra-columnar porosity. In contrast, the Ta-HIPIMS layers exhibit no inter-columnar porosity and are essentially fully dense. The mechanical properties of Ta-HIPIMS films are significantly improved with hardness and elastic modulus values of 28.0 and 328 GPa compared to 15.3 and 289GPa for reference Ta-DCMS films. [ABSTRACT FROM AUTHOR]

The quest for lowering energy consumption during thin film growth, as by magnetron sputtering, becomes of particular importance in view of sustainable development goals. A recently proposed solution combining high power impulse and direct current magnetron sputtering (HiPIMS/DCMS) relies on the use of heavy metal-ion irradiation, instead of conventionally employed resistive heating, to provide sufficient adatom mobility, in order to obtain high-quality dense films. The major fraction of process energy is used at the sputtering sources rather than for heating the entire vacuum vessel. The present study aims to investigate the W+ densification effects as a function of increasing Al content in (Ti1-yAly)1-xWxN films covering the entire range up to the practical solubility limits (y ~ 0.67). Layers with high Al content are attractive to industrial applications as the high temperature oxidation resistance increases with increasing Al concentration. The challenge is, however, to avoid precipitation of the hexagonal wurtzite AlN phase, which is softer. We report here that (Ti1-yAly)1-xWxN layers with y = 0.66 and x = 0.05 grown by a combination of W-HiPIMS and TiAl-DCMS with the substrate bias Vs synchronized to the W+-rich fluxes (to provide mobility in the absence of substrate heating) possess single-phase NaCl-structure, as confirmed by XRD and SAED patterns. The evidence provided by XTEM images and the residual oxygen content obtained from ERDA analyses reveals that the alloy films are dense without discernable porosity. The nanoindentation hardness is comparable to that of TiAlN films grown at 400–500 °C, while the residual stresses are very low. We established that the adatom mobility due to the heavy ion W+ irradiation (in place of resistive heating) enables the growth of high-quality coatings at substrate temperatures not exceeding 130 °C provided that the W+ momentum transfer per deposited metal atom is sufficiently high. The benefit of this novel film growth approach is not only the reduction of the process energy consumption by 83%, but also the possibility to coat temperature-sensitive substrates. [ABSTRACT FROM AUTHOR]

Nanocrystalline films with high hardness have attracted increasing interest for wear resistant applications. Specifically, nanocrystalline Ti–B–N layers have been demonstrated to exhibit enhanced hardness and thermal stability. Here, we show that Ti–B–N films grown at 300 °C and consisting of a high volume fraction, ∼50%, of a fully percolated disordered phase encapsulating 2–3 nm wide TiN and TiB2 grains, have a hardness of 37 GPa and an elastic modulus of 332 GPa which increase with annealing to 43 and 362 GPa, respectively, at Ta=800 °C. The structural rearrangement which occurs during annealing results in the formation of compact interface boundaries which lead, in turn, to the observed hardness increase. Annealing at Ta>900 °C decreases the hardness, although the elastic modulus continues to increase, due to the combination of grain growth and B loss via the formation of volatile boron oxides and hydroxides. These conclusions, obtained based upon a combination of x-ray diffraction, nanoindentation, electron probe microanalysis, and transmission electron microscopy, are corroborated by calorimetric investigations. The overall results provide insight toward developing “design rules” for high-temperature superhard nanoscale based coatings. [ABSTRACT FROM AUTHOR]

Single-crystal TiN(111) layers, 45 nm thick, were grown on MgO(111) by ultrahigh vacuum reactive magnetron sputter deposition in pure N[sub 2] discharges at T[sub s]=700 °C. Epitaxial Al(111) overlayers, 160 nm thick, were then deposited at T[sub s]=100 °C in Ar without breaking vacuum. Interfacial reactions and changes in bilayer microstructure due to annealing at 620 and 650 °C were investigated using x-ray diffraction and transmission electron microscopy (TEM). The interfacial regions of samples annealed at 620 °C consist of continuous =7-nm-thick epitaxial wurtzite-structure AlN(0001) layers containing a high density of stacking faults, with =22 nm thick tetragonal Al[sub 3]Ti(112) overlayers. Surprisingly, samples annealed at the higher temperature are more stable against Al[sub 3]Ti formation. TEM analyses of bilayers annealed at 650 °C (10 °C below the Al melting point!) reveal only the self-limited growth of an =3-nm-thick interfacial layer of perfect smooth epitaxial wurtzite-structure AlN(0001) which serves as an extremely effective deterrent for preventing further interlayer reactions. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Reports that polycrystalline bcc W layers were grown on amorphous-SiO2/Si(001) substrates by ultrahigh vacuum magnetron sputter deposition. As-deposited Al/W bilayers; Annealed Al/W bilayers; Interfacial reaction pathway during the annealing of polycrystalline Al/W bilayers; Role of W surface orientation and grain boundaries on Al/W bilayer interaction kinetics.

Examines the effect of self-ion energy E[subi] on the surface morphology and the orientation distribution of crystallites. Factors associated with thin film deposition methods; Description of an experiment which analyzes metal film growth on an amorphous substrate; Procedure for the measurement of the statistical properties of the surface roughness; Significant aspects of heteroepitaxial film growth.

[Display omitted] • (Ti 1- y Al y) 1- x W x N coatings are grown by W-HiPIMS/TiAl-DCMS under industrial conditions. • Conventional resistive heating can be replaced by high-mass metal ion irradiation. • The densification of the coatings controlled by the W ion energy and W ion dose per deposited metal atom. • The energy consumption during the pre-heating and coating stage is lowered by 70 % and 62 %, respectively. Decreasing the growth temperature to lower energy consumption and enable deposition on temperature-sensitive substrates during thin film growth by magnetron sputtering is crucial for sustainable development. High-mass metal ion irradiation of the growing film surface with ion energy controlled by metal-ion-synchronized biasing, allows to replace conventionally-used resistive heating, as was recently demonstrated in experiments involving a hybrid high-power impulse and dc magnetron co-sputtering (HiPIMS/DCMS) setup and stationary substrates. Here, we report the extension of the method to industrial scale conditions. As a model-case towards understanding the role of one-fold substrate rotation on Ti 0.50 Al 0.50 N film growth employing W+ irradiation, we investigate the effect of two parameters: W ion energy (controlled in the range 45 ≤ E W+ ≤ 630 eV by the amplitude of synchronized substrate bias voltage) and W ion dose per deposited metal atom (determined by the target power). We show that the efficient densification of coatings grown without external heating can be achieved by minimizing the thickness of DCMS-deposited Ti 0.50 Al 0.50 N layer that is exposed to an W+ ion flux, or by increasing E W + at a given Ti 0.50 Al 0.50 N thickness. [ABSTRACT FROM AUTHOR]

Energy Dispersive X-ray and X-ray Photoelectron (XPS) spectroscopies show that SiO x films deposited by reactive r.f. magnetron sputtering at partial pressure ratios R between oxygen and argon in a wide range (1–0.005) have compositions close to the stoichiometric one. For these films high temperature annealing at 1,000 °C shifts the band in the Fourier Transform-Infrared spectrum due to the Si–O–Si stretching vibration to values typical of stoichiometric SiO2. Further decrease of R leads to splitting of the Si 2p XPS line indicating increase of the Si content and formation of a second phase in a SiO2 matrix. The electrical properties of test MOS structures with SiO x gate dielectric, regarding defect density in the oxide and at the SiO x/c-Si interface, degrade with the decrease of R. High temperature annealing at 1,000 °C strongly improves the properties of all films regarding leakage current and properties of the interface. [ABSTRACT FROM AUTHOR]

CrN films were prepared on steel substrates by a hybrid method utilizing filtered cathodic arc for Cr ion pretreatment and magnetron sputtering for coating deposition. During pretreatment the substrates were biased to -1200 V and exposed to filtered chromium plasma. The substrate-coating interface formed during the pretreatment contained a Cr-enriched modified layer with composition that was strongly influenced by the temperature of the substrate as observed by scanning transmission electron microscopy—energy dispersive spectroscopy. The modified layer had a nanocrystalline morphology and thickness of 15 nm. The path of formation of the layer is linked to the combined action of implantation, diffusion, and resputtering. The resulting adhesion of 3 μm thick CrN films was very high with scratch test critical load values of 83 N. The morphology of the films was smooth without large scale defects and the microstructure was columnar. The coatings behaved well in dry sliding tests with very low wear coefficients of 2.3×10-16 m3 N-1 m-1, which can be linked to the high adhesion and defect-free microstructure. The smooth coatings also had a high resistance to corrosion as demonstrated by potentiodynamic tests with particularly high pitting potentials of +800 mV. [ABSTRACT FROM AUTHOR]

Abstract: Epitaxial CoSi2 layers, which are phase pure but contain {111} twins, are grown on Si(001) at 700 °C by reactive deposition epitaxy. Transmission electron microscopy analyses show that the initial formation of CoSi2(001) follows the Volmer–Weber mode characterized by the independent nucleation and growth of three-dimensional islands whose evolution we follow as a function of deposited Co thickness t Co in order to understand the origin of the observed twin density. We find that there are two families of island shapes: inverse pyramids and platelets. The rectangular-based pyramidal islands extend along orthogonal 〈110〉 directions, bounded by four {111} CoSi2/Si interfaces, and grow with a cube-on-cube orientation with respect to the substrate: (001)CoSi2 ||(001)Si and [100]CoSi2 ||[100]Si. Platelet-shaped CoSi2 islands are bounded across their long 〈110〉 directions by {111} twin planes (i.e. {111}(001)CoSi2 ||{111}Si) and their narrow 〈110〉 directions by {511}CoSi2 ||{111}Si interfaces. The top and bottom surfaces are {22¯1}, with {22¯1}CoSi2 ||(001)Si, and {1¯1¯1}, with {1¯1¯1}CoSi2 ||{11¯1}Si, respectively. The early stages of film growth (t Co ≤13 Å) are dominated by the twinned platelets due to a combination of higher nucleation rates resulting from a larger number of favorable adsorption sites in the Si(001)2×1 surface unit cell and rapid elongation of the platelets along preferred 〈110〉 directions. However, at t Co ≥13 Å island coalescence becomes significant as orthogonal platelets intersect and block elongation along fast growth directions. In this regime, where both twinned and untwinned island number densities have saturated, further island growth becomes dominated by the untwinned islands. A continuous epitaxial CoSi2(001) layer, with a twin density of 2.8×1010 cm−2, is obtained at t Co =50 Å. [Copyright &y& Elsevier]

Abstract: Nickel composite coatings were prepared by a conventional electrodeposition method from a nickel-based electrolyte containing a narrow size fraction of detonation nanodiamond (DND) separated from a polydispersed DND powder. Our study demonstrates that the incorporation of nanodiamond particles significantly affects the microstructure, mechanical and tribological properties of the corresponding composites. [Copyright &y& Elsevier]

TiB2 thin films are well known for their high hardness which makes them useful for wear-resistant applications. Overstoichiometric TiB2 deposited at 300 °C by nonreactive sputtering has been shown to exhibit superhardness (H>=40 GPa), while the hardness of their bulk stoichiometric counterparts is ∼25 GPa. We show, using high-resolution transmission electron microscopy, that overstoichiometric TiB2.4 layers have a complex self-organized columnar nanostructure. The ∼20 nm wide columns, encapsulated in excess B and oriented along 0001, consist of a bundle of ∼5 nm diameter TiB2 subcolumns separated by an ultrathin B-rich tissue phase. The nanocolumnar structure, which is thermally stable to postannealing temperatures up to 700 °C, inhibits nucleation and glide of dislocations during hardness indentation measurements, while the high cohesive strength of the B-rich tissue phase prevents grain-boundary sliding. The combination of these effects results in the observed superhardness of ∼60 GPa. [ABSTRACT FROM AUTHOR]

We investigate the evolution of texture and grain morphology in fine-grained TiN thin films using cross correlation of dark-field images obtained using annular objective apertures with radii that correspond to different low index TiN reflections. This technique enables parallel analyses of the orientations of thousands of grains, with a spatial resolution of order 10 nm. Preferred grain orientations were determined for 40 and 100 nm thick TiN layers grown on SiO[sub 2] by magnetically unbalanced reactive magnetron sputter deposition. We find that no single orientation is dominant in the 40 nm films but that a <100> texture has developed by the time these films reach 100 nm in thickness. [ABSTRACT FROM AUTHOR]

Abstract: Ultrahigh-vacuum dual-target reactive magnetron sputtering, in a mixed Ar/N2 discharge was used to deposit epitaxial single-crystal MAX phase Ti2AlN(0001) thin films, without seed layers, onto Al2O3(0001) substrates kept at 1050°C. By varying the N2 partial pressure a narrow process window was identified for the growth of single-crystal Ti2AlN. The film microstructure was characterized by a combination of X-ray diffraction, spherical aberration (C s) corrected transmission electron microscopy (TEM), high-resolution image simulation and high-resolution scanning TEM. Nitrogen-depleted deposition conditions resulted in the concurrent formation of N-free Ti–Al intermetallics at the film/substrate interface and a steady-state growth of Ti2AlN together with N-free intermetallic phases. At higher N2 partial pressures the growth assumes a columnar epitaxial nature. 1Å resolution of the lattice enabling location of all elements in the Ti2AlN unit cell is demonstrated. [Copyright &y& Elsevier]

[Display omitted] • Near-stoichiometric in B content, Ti 1-x Al x B y films with 1.81≤y≤2.03 are designed by utilizing a hybrid HiPIMS/DCMS method. • The B/metal ratio decreases with increasing Al content due to changes between the angular distribution of Ti and Al atoms • A much higher ionization of the Al-DCMS flux also undercut the B/metal in grown TiB 2 -HiPIMS/AlB 2 -DCMS Ti 1-x Al x B y thin films. • A 15-times improvement in 800 °C-oxidation resistance of single-phase occurs with increased Al-alloying, from 0.36 to 0.74. • The best compromise between low O-scale thickness (90-180 nm) and high hardness (34-38 GPa) is presented within 0.58≤x≤0.67. Ti 1-x Al x B y films (0.40 ≤ x ≤ 0.76, and 1.81 ≤ y ≤ 2.03) combining good mechanical properties and high-temperature oxidation resistance are demonstrated. Layers are grown using a hybrid high-power impulse and dc magnetron co-sputtering employing two target configurations (AlB 2 -HiPIMS/TiB 2 -DCMS and TiB 2 -HiPIMS/AlB 2 -DCMS) and no external substrate heating. Near-stoichiometric B content are achieved by co-sputtering two diboride targets. Time-resolved ion mass spectrometry analyses reveal that the ionization of the DCMS flux (Al) is much higher during TiB 2 -HiPIMS/AlB 2 -DCMS. The effect is caused by the difference in the first ionization potentials and the ionization probabilities of sputtered metals and results in lower B/metal ratios in films grown in this configuration. The B/metal ratio in the single-phase Ti 1-x Al x B y decreases with increasing Al content, which is explained by the change between angular distribution of Ti and Al atoms. Alloying with Al improves the high-temperature oxidation resistance: the thickness of the oxide-scale forming after 1 h anneal at 800 °C decreases more than 15 times upon increasing x from 0.36 to 0.74. Ti 1-x Al x B y films with 0.58 ≤ x ≤ 0.67 offer the best compromise between high-temperature oxidation resistance and mechanical properties with an average oxide scale thickness 90–180 nm and the hardness of 34–38 GPa. [ABSTRACT FROM AUTHOR]

Over the past decades, enormous effort has been dedicated to enhancing the hardness of refractory ceramic materials. Typically, however, an increase in hardness is accompanied by an increase in brittleness, which can result in intergranular decohesion when materials are exposed to high stresses. In order to avoid brittle failure, in addition to providing high strength, films should also be ductile, i.e., tough. However, fundamental progress in obtaining hard-yet-ductile ceramics has been slow since most toughening approaches are based on empirical trial-and-error methods focusing on increasing the strength and ductility extrinsically , with a limited focus on understanding thin-film toughness as an inherent physical property of the material. Thus, electronic structure investigations focusing on the origins of ductility vs. brittleness are essential in understanding the physics behind obtaining both high strength and high plastic strain in ceramics films. Here, we review recent progress in experimental validation of density functional theory predictions on toughness enhancement in hard ceramic films, by increasing the valence electron concentration, using examples from the V 1-x W x N and V 1-x Mo x N alloy systems. [ABSTRACT FROM AUTHOR]

We report the first results on nanostructured N-doped bcc -Cr films exhibiting the unique combination of ceramic hardness with metallic toughness and electrical conductivity at unexpectedly low N concentrations, ~ 5 at.%. The Cr:N films are deposited at 200 °C in N 2 /Ar mixtures by high-power pulsed magnetron sputtering using tunable time-domain control of Cr + and Cr 2+ ion fluxes incident at the film growth surface. Subplanted N atoms impede annealing of metal-ion induced point defects and hinder bcc -Cr grain growth, resulting in a material with a nearly isotropic nanostructure and atomically smooth surface, rather than typical Cr:N solid solutions consisting of faceted microcolumns. [ABSTRACT FROM AUTHOR]

Thin films consisting of TiN nanocrystallites encapsulated in a fully percolated SiN y tissue phase are archetypes for hard and superhard nanocomposites. Here, we investigate metastable SiN y solid solubility in TiN and probe the effects of surface segregation during the growth of TiSiN films onto substrates that are either flat TiN(001)/MgO(001) epitaxial buffer layers or TiN(001) facets of length 1–5 nm terminating epitaxial TiN(111) nanocolumns, separated by voids, deposited on epitaxial TiN(111)/MgO(111) buffer layers. Using reactive magnetron sputter deposition, the TiSiN layers were grown at 550 °C and the TiN buffer layers at 900 °C. On TiN(001), the films are NaCl-structure single-phase metastable Ti 1 − x Si x N(001) with N/(Ti + Si) = 1 and 0 ≤ x ≤ 0.19. These alloys remain single-crystalline to critical thicknesses h c ranging from 100 ± 30 nm with x = 0.13 to 40 ± 10 nm with x = 0.19. At thicknesses h > h c , the epitaxial growth front breaks down locally to form V-shaped polycrystalline columns with an underdense feather-like nanostructure. In contrast, the voided epitaxial TiN(111) columnar surfaces, as well as the TiN(001) facets, act as sinks for SiN y . For Ti 1 − x Si x N layers with global average composition values 〈x〉 = 0.16, the local x value in the middle of Ti 1 − x Si x N columns increases from 0.08 for columns with radius r ⋍ 2 nm to x = 0.14 with r ⋍ 4 nm. The average out-of-plane lattice parameter of epitaxial nanocolumns encapsulated in SiN y decreases monotonically with increasing Si fraction 〈x〉, indicating the formation of metastable (Ti,Si)N solid solutions under growth conditions similar to those of superhard nanocomposites for which the faceted surfaces of nanograins also provide sinks for SiN y . [ABSTRACT FROM AUTHOR]

We use classical molecular dynamics and the modified embedded atom method formalism to investigate the dynamics of atomic-scale transport on a low-index model compound surface, TiN(OOl). Our simulations, totaling 0.25 µs for each case study, follow the pathways and migration kinetics of Ti and N adatoms, as well as TiNj complexes with x = 1-3, which are known to contribute to the growth of TiN thin films by reactive deposition from Ti, N2, and N precursors. The simulations are carried out at 1000 K, within the optimal range for TiN(OOl) epitaxial growth. We find Ti adatoms to be the highest-mobility species on TiN(OOl), with the primary migration path involving jumps of one nearest-neighbor distance dNN between adjacent fourfold hollow sites along in-plane (100) channels. Long jumps, 2dNN, are also observed, but at much lower frequency. N adatoms, which exhibit significantly lower migration rates than Ti, diffuse along in-plane 〈110〉 directions and, when they intersect other N atoms, associatively form N2 molecules, which desorb at kinetic rates. As expected, TiN and TiN3 complexes migrate at even lower rates with complex diffusion pathways involving rotations, translations, and rototranslations. TiN2 trimers, however, are shown to have surprisingly high diffusion rates, above that of N adatoms and almost half that of Ti adatoms. TiN3 motion is dominated by in-place rotation with negligible diffusion. [ABSTRACT FROM AUTHOR]

Abstract: The AlN incorporation probability in single crystal Hf1− x Al x N(001) layers is controllably adjusted between ∼0% and 100% by varying the ion energy (E i) incident at the growing film over a narrow range, 10–40eV. The layers are grown on MgO(001) at 450°C using ultrahigh vacuum magnetically unbalanced reactive magnetron sputtering from a Hf0.7Al0.3 alloy target in a 5%-N2/Ar atmosphere at a total pressure of 20mTorr (2.67Pa). The ion to metal flux ratio incident at the growing film is constant at 8. Epitaxial film compositions vary from x =0.30 with E i =10eV, to 0.27 with E i =20eV, 0.17 with E i =30eV, and ⩽0.002 with E i ⩾40eV. Thus, the AlN incorporation probability decreases by greater than two orders of magnitude. This extraordinary range in real-time manipulation of film chemistry during deposition is due to the efficient resputtering of deposited Al atoms (27 amu) by Ar+ ions (40 amu) neutralized and backscattered from heavy Hf atoms (178.5 amu) in the film. This provides a new reaction pathway to synthesize, at high deposition rates, compositionally complex heterostructures, multilayers, and superlattices with abrupt interfaces from a single alloy target by controllably switching E i. For multilayer and superlattice structures, the choice of E i value determines the layer composition and the switching periods control the individual layer thickness. [ABSTRACT FROM AUTHOR]

Abstract: The composition, structure and mechanical properties of pulsed-DC unbalanced magnetron sputtered Ti–Si–B thin films—hard coatings with the potential for excellent thermal stability and oxidation resistance—are investigated and reported in this paper. Fully dense, hard (19–37GPa) Ti–Si–B coatings were deposited at substrate bias voltages (V s) ranging from floating potential to −150V which resulted in substrate temperatures of ∼90–135°C. We found that variation of substrate biasing conditions critically affected film composition, structure and resultant mechanical properties. For instance, concentration of Si in films decreased from 18.4at.% to 3.8at.% as V s was increased from floating potential to −150V; composition profile analysis of the near-surface region of films (0–10nm) revealed them to be rich in Si with significant differences among specimens produced at different substrate bias conditions. Variation of substrate biasing conditions provided coating structures that ranged from completely amorphous at floating substrate potential to nanocrystalline at V s =−50 to −100V and crystalline nanocolumnar at V s =−150V. We found that each of the structures obtained exhibited different specific values of hardness and elastic modulus, which is also in a good agreement with results reported for other coatings possessing similar micro- and nano-structures. Film structure was analyzed in detail by conventional and analytical transmission electron microscopy. Coatings that exhibited the highest values of hardness (37GPa) were found to possess features such as crystalline nanocolumnar grains a few nanometres in diameter and disordered intergranular regions of different chemical composition, thus qualifying as nanocomposite films. Results of this work allowed relationships to be drawn between deposition parameters and Ti–Si–B coating composition, structure and mechanical properties. Qualitatively similar relationships are also expected for other biased plasma-assisted physical vapour deposited transition-metal-based ceramic coatings alloyed with Si (e.g. Ti–Si–N, Cr–Si–N, Cr–Al–Si–N). [Copyright &y& Elsevier]

Abstract: The paper discusses the effect of ion irradiation on a new type of nanoscale multilayer structure in C/Cr PVD coatings formed by a self-organisation mechanism. C/Cr coatings were deposited by the combined steered cathodic arc/unbalanced magnetron sputtering technique, at wide range of bias voltages, U b from −65 to −550 V. Plasma diagnostics carried out by electrostatic probe measurements revealed that C/Cr films grow under conditions of intensive ion bombardment with ion-to-neutral ratio exceeding J i/J n =6. Under these conditions the high diffusion mobility and the reactivity of the C leads to distinct changes in the coatings microstructure and phase composition. Raman spectroscopy and XPS (X-ray photoelectron spectrometer) analysis of the chemical bonding in the films showed that the phase composition of the films gradually transforms from more graphite like (sp2 C–C bonded) to more Me-carbon (Cr–C bonded), where the content of the carbide phase increases with increase of the bias voltage to U b =−350 V and higher. In parallel HRTEM (high-resolution transmission electron microscopy) employing HAADF (high-angle annular dark field) imaging revealed that the microstructure evolved from columnar with carbon accumulated at the column boundaries (U b =−65 V, −95 V) to a structure dominated by onion like C–Cr clusters (U b =−120 V), which than converts to a distinct nanoscale layered structure (U b =−350 V, −450 V), finally transforming to a uniform fine grain structure at U b =−550 V. The new nanoscale layered structure forms via ion irradiation induced self-organisation mechanism. It is characterized by an abnormally large values for the bi-layer thickness of 20 nm and 25 nm, which are not related to substrate rotation, for films grown at U b =−350 V and U b =−450 V, respectively. ADF (annular dark field) STEM (scanning TEM) imaging and quantitative EELS (electron-energy loss spectroscopy) analysis showed that the nanoscale multilayer structure comprises of alternating layers of Me-carbide phase (48%C, 52%Cr) and almost pure C (91.34%C), where the bias voltage defines the bi-layer thickness. A coating growth model is proposed accounting for the irradiation-induced ion mixing, re-sputtering, condensation surface temperature effects, nucleation and kinetic segregation process, as well as the diffusivity of the coating elements to explain the phase separation and formation of the self-organised layered nanostructure observed in C/Cr coatings. [Copyright &y& Elsevier]

Abstract: C/Cr coatings were prepared by the combined steered cathodic arc/unbalanced magnetron sputtering technique with a wide range of bias voltages, U b from −65 to −350 V. The paper focuses on the microstructure evolution and phase transformations in the coatings and their influence on the tribological performance of C/Cr coatings as a function of the bias voltage. Raman spectroscopy on the surface of the as deposited coatings and in the wear track generated in pin-on-disc tests has been carried out in conjunction with TEM and SEM studies of coatings microstructure and XPS analysis of the chemical bonding in the films. The Raman spectra from the surface of the C/Cr coatings consists of two main Raman features on a strong photoluminescence background: broad bands around ∼1380 cm−1 and ∼1572 cm−1, which are designated to D (disorder) and G (graphitic) peaks, respectively. The broad D and G bands further confirm the TEM-selected area diffraction (SAD) analysis, which shows an amorphous character of the coating. The downshift of the G-band by ∼2–10 cm−1 from the planar graphite (1582 cm−1) is ascribed as the shell curvature of the carbon plane, which could be due to the presence of Cr. We assume the D-band position has a close dependence on the stress in the coating, which results in shifting of the D-band to higher wave number as the stress in the coatings increases. The Raman spectra show better resolution of the D and G peaks for samples deposited at low bias voltage (U b =−65 to U b =−75 V). However, these peaks become more diffused and difficult to resolve, with a much lower intensity as the applied bias voltage increases and completely disappears at U b =−350 V, which suggests formation of metal carbides in the coating. This interpretation was further confirmed by the XRD, TEM and SAD pattern observations. The I D/I G ratio correlates well with the friction behaviour of the films. The friction coefficient decreases and reaches its minimum of μ =0.16 at U b =−95 V due to the increase in the sp2 content in the film, which is accompanied by a maximum I D/I G ratio of 7.15. [Copyright &y& Elsevier]

Abstract: Nanoscale multilayer C/Cr coatings have been deposited by utilising the combined steered cathodic arc/unbalanced magnetron sputtering technique. The coating microstructure and tribological performance have been investigated as a function of the bias voltage, ranging from Ub=−65 to −350 V. The XRD results revealed that C/Cr coatings are amorphous at low Ub, but became more crystalline when the Ub increased to −350 V. High-resolution XTEM analysis indicated coating densification and smoothening as well as formation of novel amorphous nanostructure, in which carbon-rich clusters are surrounded by a Cr-rich matrix, leading to the formation of self-organised multilayer structure as the bias voltage was increased from −65 to −350 V. An increase of the bias voltage from −65 to −350 V resulted in an increase in the hardness from 8 to 25 GPa and Young''s modulus, E from 186 to 319 GPa. A pin-on-disc test showed that the friction coefficient was reduced from 0.22 to 0.16 when the bias voltage was increased from −65 to −95 V. However, a further increase in the bias voltage to −350 V led to an increase in the friction coefficient to 0.31. The lowest wear coefficient Kc∼6.25×10−17 m3 N−1 m−1 was achieved at Ub=−120 V. Standard HSS drills, 8 mm in diameter, coated with C/Cr have been tested using solution annealed AISI 304 stainless steel as the work piece material. An improvement of the lifetime by a factor of ∼9 has been achieved as compared to the uncoated tools. In this test, the C/Cr coating outperformed a number of commercially available PVD coatings, such as TiCN, TiAlCrN and showed similar performance to TiAlCrYN. [Copyright &y& Elsevier]

Abstract: (Al2O3)x(TiO2)1-x thin films obtained from sol solutions by spin coating technique have been studied. The chemical composition and stoichiometry of the films have been determined by X-ray photoelectron spectroscopy (XPS) and Rutherford backscattering spectroscopy (RBS). The peaks at 461.48eV for Al2p and Ti2p at 74.4eV are characteristic for the respective metal oxides and indicate the presence of Al2O3 and TiO2. The refractive index, dielectric constant and optical band gap for direct transitions have been determined for varying Al:Ti ratios in the starting solution. [Copyright &y& Elsevier]

Nanoscale multilayer C/Cr coatings (bilayer thickness ∼2 nm) were produced by the combined steered cathodic arc/unbalanced magnetron deposition technique. The mirror-polished M2 substrates were treated by Cr+ ion etching/implantation followed by the deposition of a 0.25 μm thick CrN base layer. A 1.6 μm thick C/Cr multilayer coating was then deposited by non-reactive unbalanced magnetron sputtering while rotating the substrates in front of three graphite and one Cr targets. During the multilayer deposition, a bias potential between −65 and −95 V was applied to the substrates. The ion flux measured by a flat electrostatic probe was 1.2 mA cm−2 and the deposition rate was 0.4 μm h−1, which resulted in ion-to-neutral ratio of Ji/Jn=5.2. Cross-sectional transmission electron microscopy diffraction and Z-contrast imaging investigations revealed a novel nanostructure in which the basic nano-lamellae obtained as a result of substrate rotation in front of the C and Cr targets were modified by ion-irradiation-induced nanocolumnar structure. The intense ion-irradiation of the immiscible film components caused local enrichment of Cr and C that propagated in the growth direction resulting in Cr-rich nanocolumns separated by C-rich boundaries in an overall amorphous structure. Tribological studies of the composite C/Cr coatings were conducted using a pin-on-disk apparatus under a load of 5 N, at velocities of 0.13–0.15 m s−1 and for distances of ∼500 m in dry nitrogen (∼0% humidity) and open air (30% relative humidity). Results indicated that the C/Cr composite coatings provided friction coefficients of 0.7–0.8 in dry nitrogen, while the values were significantly lower in open air, 0.21–0.24, during sliding against both the coated and uncoated balls for coatings deposited at bias voltage of −75 V. The friction coefficient decreases to 0.16 when the bias voltage of −95 V was used. [Copyright &y& Elsevier]

We report here on ferromagnetic/superconductor FM/SC and SC/FM double layers deposited without a buffer layer between FM and SC. Thin films of La0.7Sr0.3MnO3 (LSMO) are used for the FM, and YBa2Cu3O7−x (YBCO) for the SC. Both films can grow crystalline on SrTiO3 (STO) or LaAlO3 (LAO) substrates in high temperature and in oxygen atmosphere conditions. Magnetic and transport measurements and X-ray diffraction analysis are used to characterise film quality and properties. It is shown that off-axis magnetron sputtering can be used for high-quality double layer deposition. A prerequisite for this is the suppression of the interdiffusion process. This is achieved by lowering the deposition temperature and shortening the deposition time for the top layer. Lattice relaxation for LSMO films deposited on LAO substrates is seen. It is demonstrated that post-deposition annealing or additional top layer deposition enlarges the relaxed part of the lower LSMO film. LSMO films are smooth and free of imperfections and the stress is partly relieved by the formation of misfit dislocations. For YBCO films, SEM, XRD, EDX and magnetisation characterisations show that film lattice relaxation starts when single-element-oxide crystals start to grow into the film. Many experiments give evidence of a critical thickness of about 30 nm of a strained layer, after which the top part of the YBCO film relaxes. Despite the small compositional deviation due to the interdiffusion, the YBCO/LSMO double films demonstrate high enough transport and magnetic properties to allow their application in the investigation of the injection of spin-polarised quasiparticles from FM to SC film. The critical current for YBCO film is Jc∼0.7×106 A/cm2 if it is a bottom layer, and Jc∼1.7×106 A/cm2 if YBCO is a top layer, whilst our optimal single-layer YBCO films have Jc∼(2.5–5)×106 A/cm2 at 77 K. [Copyright &y& Elsevier]

Hybrid high power impulse/direct current magnetron sputtering (HiPIMS/DCMS) film growth technique with metal-ion-synchronized substrate bias allows for significant energy savings as compared to conventional PVD methods. For carefully selected type of metal ion irradiation, taking into account ion mass, ionization potential, and reactivity towards working gas, fully dense and hard films can be obtained with no intentional substrate heating. The thermally-driven adatom mobility, which is an essential densification mechanism in conventional film growth that takes place at elevated temperatures, is replaced with that supplied by effective low-energy recoil creation. In this contribution we explore effects of the high-mass W+ irradiation, which has proven to be the most efficient in densifying Ti 0.50 Al 0.50 N layers, serving here as a model system, grown with no substrate heating. We study the effects of two essential parameters: W+ energy E W + and W concentration x , on film porosity, phase content, nanostructure, and mechanical properties. E W + varies from ~90 to ~630 eV (controlled by substrate bias voltage amplitude V s) and x from 0.02 to 0.12 (controlled by the HiPIMS pulse length), while the HiPIMS peak target current is kept constant. Results reveal that a strong coupling exists between the W+ incident energy and the minimum W concentration required to grow dense layers. • The effect of W+ irradiation on densification of TiAlN films is studied. • Films are grown by W-HiPIMS/TiAl-DCMS with W+-synchronized bias. • No external heating is applied and substrate temperature is lower than 130 °C. • The effect of W+ energy E W + and W concentration x on film properties is studied. • Fully-dense films can be obtained with low E W + without high residual stress. [ABSTRACT FROM AUTHOR]

In view of the increasing demand for achieving sustainable development, the quest for lowering energy consumption during thin film growth by magnetron sputtering becomes of particular importance. In addition, there is a demand for low-temperature growth of dense, hard coatings for protecting temperature-sensitive substrates. Here, we explore a method, in which thermally-driven adatom mobility, necessary to obtain high-quality fully-dense films, is replaced with that supplied by effective low-energy recoil creation resulting from high-mass metal ion irradiation of the growing film surface. This approach allows the growth of dense and hard films with no external heating at substrate temperatures T s not exceeding 130 °C in a hybrid high-power impulse and dc magnetron co-sputtering (HiPIMS/DCMS) setup involving a high mass (m > 180 amu) HiPIMS target and metal-ion-synchronized bias pulses. We specifically investigate the effect of the metal ion mass on the extent of densification, phase content, nanostructure, and mechanical properties of metastable cubic Ti 0.50 Al 0.50 N based thin films, which present outstanding challenges for phase stability control. Ti 0.50 Al 0.50 N based thin films are irradiated by group VIB transition metal (TM) target ions generated by Me-HiPIMS discharge, in which Me = Cr (m Cr = 52.0 amu), Mo (m Mo = 96.0 amu), and W (m W = 183.8 amu). Three series of (Ti 1- y Al y) 1- x Me x N films are grown with x = Me/(Me+Al+Ti) varied intentionally by adjusting the DCMS powers, while y = Al/(Al+Ti) also varies as a result of Me+ ion irradiation. Results reveal a strong dependence of film properties on the mass of the HiPIMS-generated metal ions. All layers deposited with Cr+ irradiation exhibit porous nanostructure, high oxygen content, and poor mechanical properties. In contrast, (Ti 1- y Al y) 1- x W x N films are fully-dense even with the lowest W concentration, x = 0.09, show no evidence of hexagonal AlN precipitation, and exhibit state-of the-art mechanical properties typical of Ti 0.50 Al 0.50 N grown at 500 °C. The process energy consumption is lowered by 64% with no negative impact on the coating quality. TRIM simulations provide an insight into the densification mechanisms. • (Ti 1- y Al y) 1- x Me x N (Me = Cr, Mo, W) thin films are grown by Me-HiPIMS/TiAl-DCMS. • The effect of the metal ion mass on the Ti 0.50 Al 0.50 N densification is studied. • No external heating is applied during coating and substrate temperature is lower than 130 °C. • Dense films are achieved with W ions resulting in hardness of 32 GPa. • Process energy consumption can be decreased by 64%. [ABSTRACT FROM AUTHOR]