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The quest for lowering energy consumption during thin film growth by magnetron sputtering techniques becomes of particular importance in view of sustainable development goals. As large fraction of the process energy is consumed in substrate heating for the purpose of providing high adatom mobility necessary to grow dense films, the most straightforward strategy toward more environment-friendly processing is to find alternatives to thermally activated surface diffusion. One possibility is offered by high mass metal ion irradiation of the growing film surface, which has been recently shown to be very effective in densification of transition metal nitride layers grown with no external heating, such that Zone 2 microstructures of the structure-zone model are obtained in the substrate temperature Ts range otherwise typical for Zone 1 growth. The large mass difference between the incident ion and the atoms constituting the film results in effective creation of low energy recoils, which leads to film densification at low Ts. Due to their high mass, metal ions become incorporated at lattice sites beyond the near-surface region of intense recoil generation leading to further densification, while preventing the buildup of residual stress. The practical implementation of this technique discussed in this Perspective employs heavy metal targets operating in the high-power impulse magnetron sputtering (HiPIMS) mode to provide periodic metal-ion fluxes that are accelerated in the electric field of the substrate to irradiate layers deposited from direct current magnetron sputtering (DCMS) sources. A key feature of this hybrid HiPIMS/DCMS configuration is the substrate bias that is synchronized with heavy metal ion fluxes for selective control of their energy and momentum. As a consequence, the major fraction of process energy is used at sputtering sources and for film densification, rather than for heating of the entire vacuum vessel. Model material systems include TiN and metastable NaCl-structure Ti1−yAlyN films, which are well-known for challenges in stoichiometry and phase stability control, respectively, and are of high relevance for industrial applications. This Perspective provides a comprehensive overview of the novel film growth method. After presenting basic concepts, time-resolved measurements of ion fluxes at the substrate plane, essential for selective control of metal ion energy and momentum, are discussed. The role of metal ion mass, energy, momentum, and concentration is described in more detail. As some applications require substrate rotation for conformal coating, a section is devoted to the related complexity in the implementation of metal-ion-synchronized growth under industrial conditions. [ABSTRACT FROM AUTHOR]

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]

Energy and time-dependent mass spectrometry is used to determine the relative number density of singly- and multiply-charged metal-ion fluxes incident at the substrate during high-power pulsed magnetron sputtering (HIPIMS) as a function of the average noble–gas ionization potential. Ti is selected as the sputtering target since the microstructure, phase composition, properties, and stress-state of Ti-based ceramic thin films grown by HIPIMS are known to be strongly dependent on the charge state of Ti n+ ( n = 1, 2, …) ions incident at the film growth surface. We find that the flux of Ti n+ with n > 2 is insignificant; thus, we measure the Ti 2+ /Ti + integrated flux ratio J T i 2 + / J T i + at the substrate position as a function of the choice of noble gas–Ne, Ar, Kr, Xe, as well as Ne/Ar, Kr/Ar, and Xe/Ar mixtures -- supporting the plasma. We demonstrate that by changing noble–gas mixtures, J T i 2 + varies by more than two orders of magnitude with only a small change in J T i + . This allows the ratio J T i 2 + / J T i + to be continuously tuned from less than 0.01 with Xe, which has a low first-ionization potential IP 1 , to 0.62 with Ne which has a high IP 1 . The value for Xe, I P X e 1 = 12 . 16 eV , is larger than the first ionization potential of Ti, I P T i 1 = 6 . 85 eV , but less than the second Ti ionization potential, I P T i 2 = 13 . 62 eV . For Ne, however, I P N e 1 = 21 . 63 eV is greater than both I P T i 1 and I P T i 2 . Therefore, the high-energy tail of the plasma-electron energy distribution can be systematically adjusted, allowing J T i 2 + / J T i + to be controllably varied over a very wide range. [ABSTRACT FROM AUTHOR]

Single-crystal ZrN films, 830 nm thick, are grown on MgO(001) at 450 °C by magnetically unbalanced reactive magnetron sputtering. The combination of high-resolution x-ray diffraction reciprocal lattice maps, high-resolution cross-sectional transmission electron microscopy, and selected-area electron diffraction shows that ZrN grows epitaxially on MgO(001) with a cube-on-cube orientational relationship, (001)ZrN|(001)MgO and [100]ZrN|[100]MgO. The layers are essentially fully relaxed with a lattice parameter of 0.4575 nm, in good agreement with reported results for bulk ZrN crystals. X-ray reflectivity results reveal that the films are completely dense with smooth surfaces (roughness = 1.3 nm, consistent with atomic-force microscopy analyses). Based on temperature-dependent electronic transport measurements, epitaxial ZrN/MgO(001) layers have a room-temperature resistivity ρ300K of 12.0 μΩ-cm, a temperature coefficient of resistivity between 100 and 300 K of 5.6 × 10-8 Ω-cm K-1, a residual resistivity ρo below 30 K of 0.78 μΩ-cm (corresponding to a residual resistivity ratio ρ300Κ/ρ15K = 15), and the layers exhibit a superconducting transition temperature of 10.4 K. The relatively high residual resistivity ratio, combined with long in-plane and out-of-plane x-ray coherence lengths, ξ| = 18 nm and ξ⊥ = 161 nm, indicates high crystalline quality with low mosaicity. The reflectance of ZrN(001), as determined by variable-angle spectroscopic ellipsometry, decreases slowly from 95% at 1 eV to 90% at 2 eV with a reflectance edge at 3.04 eV. Interband transitions dominate the dielectric response above 2 eV. The ZrN(001) nanoindentation hardness and modulus are 22.7 ± 1.7 and 450 ± 25 GPa. [ABSTRACT FROM AUTHOR]

Nanoscale multilayer TiAlCN/VCN coatings with bilayer thickness Δ=2·2 nm were deposited by the combined high power impulse magnetron sputtering (HIPIMS)/unbalanced magnetron sputtering technology. The V+ HIPIMS etching produced atomically clean interface and V implantation resulting in enhanced coating adhesion LC=58 N. High resolution transmission electron microscopy and electron energy loss spectroscopy revealed that in TiAlCN/VCN, carbon forms a lateral phase between the nanolayers, producing low shear strength interfaces. This results in a well defined nanometre scale layer by layer wear mechanism, which is the key for prevention of tribofilm and consequently thick built up layer formation. In dry milling of Al 7010-T 7651 alloy, TiAlCN/VCN outperformed state of the art diamond like carbon, Cr/WC/a-CH coated and uncoated end mills by factors of 4 and 8 respectively. In turning of Ti alloys (Ti0·90Al0·06V0·04) the TiAlCN/VCN coated cemented carbide inserts produced two to three times more components (orthopaedic implants), as compared to uncoated tools. [ABSTRACT FROM AUTHOR]

V0.6W0.4N alloys are grown on MgO(001) by ultrahigh vacuum reactive magnetron sputtering from V and W targets in 10 mTorr pure-N2 atmospheres at temperatures Ts ranging from 600 to 900 °C. Based on x-ray diffraction and transmission electron microscopy results, all films have the B1-NaCl crystal structure and grow with a cube-on-cube epitaxial relationship to the substrate, (001)VWN|(001)MgO and [100]VWN|[100]MgO. Rutherford backscattering spectrometry analyses show that the N content in V0.6W0.4Nx alloys decreases with increasing Ts from overstoichiometric with x = 1.13 at 600 °C, to approximately stoichiometric with x = 1.08 at 700 °C, to understoichiometric at 800 °C (x = 0.80) and 900 °C (x = 0.75). High-resolution scanning transmission electron microscopy, Z-contrast, and selected-area electron diffraction investigations of V0.6W0.4N(001) alloys grown at 600 and 700 °C reveal the onset of W ordering on adjacent 111 planes of the metal sublattice; no ordering is observed for understoichiometric films grown at higher temperatures. [ABSTRACT FROM AUTHOR]

High-power impulse magnetron sputtering (HiPIMS) of materials systems with metal/gas-atom mass ratios m Me / m g near, or less than, unity presents a challenge for precise timing of synchronous substrate-bias pulses to select metal-ion irradiation of the film and, thus, reduce stress while increasing layer density during low-temperature growth. The problem stems from high gas-ion fluxes F g + ( t ) at the substrate, which overlap with metal-ion fluxes F Me + ( t ). We use energy- and time-dependent mass spectrometry to analyze F Me + ( t ) and F g + ( t ) for Group IVb transition-metal targets in Ar and show that the time-and energy-integrated metal/gas ion ratio N Me + / N Ar + at the substrate can be controlled over a wide range by adjusting the HiPIMS pulse length τ ON , while maintaining the peak target current density J T,peak constant. The effect is a consequence of severe gas rarefaction which scales with J T ( t ). For Ti-HiPIMS, terminating the discharge at the maximum J T ( t ), corresponding to τ ON = 30 μs, there is an essentially complete loss of Ar + ion intensity, yielding N Ti + / N Ar + ~ 60. With increasing τ ON , J T ( t ) decreases and N Ti + / N Ar + gradually decays, due to Ar refill, to ~ 1 with τ ON = 120 μs. Time-resolved ion-energy distribution functions confirm that the degree of rarefaction depends on τ ON : for shorter pulses, τ ON < 60 μs, the original sputtered-atom Sigmund-Thompson energy distributions are preserved long after the HiPIMS pulse, which is in distinct contrast to longer pulses, τ ON ≥ 60 μs, for which the energy distributions collapse into narrow thermalized peaks. Thus, optimizing the HiPIMS pulse width minimizes the gas-ion flux to the substrate independent of m Me / m g . [ABSTRACT FROM AUTHOR]

2.5 μm thick TiAlCN/VCN coatings were deposited by a reactive high power impulse magnetron sputtering (HIPIMS) process. Cross-sectional TEM showed gradual evolution of the structure of the coating with thickness. The initial structure is a nanoscale multilayer with sharp interlayer interfaces. This transforms to nanocomposite of TiAlCN and VCN nanocrystalline grains surrounded by a C-rich tissue phase and finally changes to an amorphous carbon rich Me-C phase. In contrast deposition in similar conditions using standard magnetron sputtering produces a well-defined nanoscale multilayer structure. Depth profiling by AES showed that the carbon content in the HIPIMS coating gradually increased from 25% at the coating substrate interface to 70% at the top thus supporting the TEM observations. Energy-resolved mass spectrometry revealed that HIPIMS plasma is a factor of 10 richer in C 1 + ions, and therefore more reactive, as compared to the plasma generated by standard magnetron discharge at the same conditions. The peculiar structure evolution in HIPIMS is discussed in relation to target poisoning effect and carbon outward diffusion during coating growth. Highly abrasive AlSi9Cu1 alloy was dry machined using TiAlCN/VCN coated 25 mm diameter end mills to investigate the coating-work piece material interaction. Green (532 nm excitation) and ultraviolet (325 nm excitation) Raman spectroscopy was employed to identify the phase composition of the built up material on the cutting edge and chip (swarf) surfaces produced during machining. These analyses revealed formation of lubricious Magnèli phases namely V 2 O 5 and graphitic carbon as well as highly abrasive SiO 2 and mixed (AlSi)O thus shedding light on the wear processes and coating tribological behavior during machining. [ABSTRACT FROM AUTHOR]

[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]

V 0.5 Mo 0.5 N x /MgO(001) alloys with the B1-NaCl structure are grown by ultra-high-vacuum reactive magnetron sputter deposition in 5 mTorr mixed Ar/N 2 atmospheres at temperatures T s between 100 and 900 °C. Alloy films grown at T s ≤ 500 °C are polycrystalline with a strong 002 preferred orientation; layers grown at T s ≥ 700 °C are epitaxial single-crystals. The N/Metal composition ratio x ranges from 1.02 ± 0.05 with T s = 100–500 °C to 0.94 ± 0.05 at 700 °C to 0.64 ± 0.05 at T s = 900 °C. N loss at higher growth temperatures leads to a corresponding decrease in the relaxed lattice parameter a o from 4.212 Å with x = 1.02 to 4.175 Å at x = 0.94 to 4.120 Å with x = 0.64. V 0.5 Mo 0.5 N x nanoindentation hardnesses H and elastic moduli E increase with increasing T s from 17 ± 3 and 323 ± 30 GPa at 100 °C to 26 ± 1 and 370 ± 10 GPa at 900 °C. Both polycrystalline and single-crystal V 0.5 Mo 0.5 N x films exhibit higher toughnesses than that of the parent binary compound VN. V 0.5 Mo 0.5 N x films deposited at higher T s also exhibit enhanced wear resistance. Valence-band x-ray photoelectron spectroscopy analyses reveal an increased volume density of shear-sensitive d-t 2g – d-t 2g metallic states for V 0.5 Mo 0.5 N x compared to VN and the density of these orbitals increases with increasing deposition temperature, i.e., with increasing N-vacancy concentration. [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]

Ti 1− x Si x N (0 ≤ x ≤ 0.26) thin films are grown in mixed Ar/N 2 discharges using hybrid high-power pulsed and dc magnetron co-sputtering (HIPIMS/DCMS). In the first set of experiments, the Si target is powered in HIPIMS mode and the Ti target in DCMS; the positions of the targets are then switched for the second set. In both cases, the Si concentration in co-sputtered films, deposited at T s = 500 °C, is controlled by adjusting the average DCMS target power. A pulsed substrate bias of − 60 V is applied in synchronous with the HIPIMS pulse. Depending on the type of pulsed metal-ion irradiation incident at the growing film, Ti + /Ti 2+ vs. Si + /Si 2+ , completely different nanostructures are obtained. Ti + /Ti 2+ irradiation during Ti-HIPIMS/Si-DCMS deposition leads to a phase-segregated nanocolumnar structure with TiN-rich grains encapsulated in a SiN z tissue phase, while Si + /Si 2+ ion irradiation in the Si-HIPIMS/Ti-DCMS mode results in the formation of Ti 1− x Si x N solid solutions with x ≤ 0.24. Film properties, including hardness, modulus of elasticity, and residual stress exhibit a dramatic dependence on the choice of target powered by HIPIMS. Ti-HIPIMS/Si-DCMS TiSiN nanocomposite films are superhard over a composition range of 0.04 ≤ x ≤ 0.26, which is significantly wider than previously reported. The hardness H of films with 0.13 ≤ x ≤ 0.26 is ~ 42 GPa; however, the compressive stress is also high, ranging from − 6.7 to − 8.5 GPa. Si-HIPIMS/Ti-DCMS films are softer at H ~ 14 GPa with 0.03 ≤ x ≤ 0.24, and essentially stress-free ( σ ~ 0.5 GPa). Mass spectroscopy analyses at the substrate position reveal that the doubly-to-singly ionized metal-ion flux ratio during HIPIMS pulses is 0.05 for Si and 0.29 for Ti due to the difference between the second ionization potentials of Si and Ti vs . the first ionization potential of the sputtering gas. The average momentum transfer to the film growth surface per deposited atom per pulse 〈 p d 〉 is ~ 20 × higher during Ti-HIPIMS/Si-DCMS, which results in significantly higher adatom mean-free paths (mfps) leading, in turn, to a phase-segregated nanocolumnar structure. In contrast, relatively low 〈 p d 〉 values during Si-HIPIMS/Ti-DCMS provide near-surface mixing with lower adatom mfps to form Ti 1− x Si x N solid solutions over a very wide composition range with x up to 0.24. Relaxed lattice constants decrease linearly, in agreement with ab-initio calculations for random Ti 1− x Si x N alloys, with increasing x . [ABSTRACT FROM AUTHOR]

Using a combination of experiments and density functional theory (DFT), we demonstrate the first example of vacancy-induced toughening, in this case for epitaxial pseudobinary NaCl-structure substoichiometric V0.5Mo0.5Nx alloys, with N concentrations 0.55≼x≼1.03, grown by reactive magnetron sputter deposition. The nanoindentation hardness H(x) increases with increasing vacancy concentration from 17GPa with x=1.03 to 26GPa with x=0.55, while the elastic modulus E(x) remains essentially constant at 370GPa. Scanning electron micrographs of indented regions show ductile plastic flow giving rise to material pile-up, rather than cracks as commonly observed for hard, but brittle, transition-metal nitrides. The increase in alloy hardness with an elastic modulus that remains constant with decreasing x, combined with the observed material pile-up around nanoindents, DFT-calculated decrease in shear to bulk moduli ratios, and increased Cauchy pressures (C12-C44), reveals a trend toward vacancy-induced toughening. Moreover, DFT crystal orbital overlap population analyses are consistent with the above results. [ABSTRACT FROM AUTHOR]

Abstract: A hybrid deposition process consisting of reactive high-power pulsed and dc magnetron cosputtering (HIPIMS and DCMS) from Ti and Al targets is used to grow Ti1−x Al x N alloys, with x ~0.6, on Si(001) at 500°C. Two series of films are deposited in which the energy and momentum of metal ions incident at the growing film are individually varied. In both sets of experiments, a negative bias Vs ranging from 20 to 280V is applied to the substrate in synchronous, as determined by in-situ mass spectrometry, with the metal-ion-rich part of the HIPIMS pulse. Ion momentum is varied by switching the HIPIMS and dc power supplies to change the mass m and average charge of the primary metal ion. Al-HIPIMS/Ti-DCMS layers grown under Al+ (mAl =26.98amu) bombardment with 20≤ Vs ≤160V are single-phase NaCl-structure alloys, while films deposited with Vs >160V are two-phase, cubic plus wurtzite. The corresponding critical average metal-ion momentum transfer per deposited atom for phase separation is 〈p d ⁎〉≥135 [eV-amu]1/2. In distinct contrast, layers deposited in the Ti-HIPIMS/Al-DCMS configuration with Ti+/Ti2+ (mTi =47.88amu) ion irradiation are two-phase even with the lowest bias, Vs =20V, for which 〈p d ⁎〉>135 [eV-amu]1/2. Precipitation of wurtzite-structure AlN is primarily determined by the average metal-ion momentum transfer to the growing film, rather than by the deposited metal-ion energy. Ti-HIPIMS/Al-DCMS layers grown with Vs =20V are two-phase with compressive stress σ =−2GPa which increases to −6.2GPa at Vs =120V; hardness H values range from 17.5 to 27GPa and are directly correlated with σ. However, for Al-HIPIMS/Ti-DCMS, the relatively low mass and single charge of the Al+ ion permits tuning properties of metastable cubic Ti0.38Al0.62 N by adjusting Vs to vary, for example, the hardness from 12 to 31GPa while maintaining σ ~0. [Copyright &y& Elsevier]

Abstract: Metastable Ti1-x Al x N (0.4≤ x ≤0.76) films are grown using a hybrid approach in which high-power pulsed magnetron sputtering (HIPIMS) is combined with dc magnetron sputtering (DCMS). Elemental Al and Ti metal targets are co-sputtered with one operated in HIPIMS mode and the other target in DCMS; the positions of the targets are then switched for the next set of experiments. In both cases, the AlN concentration in the co-sputtered films, deposited at T s =500°C with R =1.5–5.3Å/s, is controlled by adjusting the average DCMS target power. Resulting films are analyzed by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, atomic force microscopy, elastic recoil detection analysis, and nanoindentation. Mass spectroscopy is used to determine ion energy distribution functions at the substrate. The distinctly different flux distributions obtained from targets driven in HIPIMS vs. DCMS modes allow the effects of Al n+ and Ti n+ (n =1, 2) ion irradiation on film growth kinetics, and resulting properties, to be investigated separately. Bombardment with Al n+ ions (primarily Al+ in the Al-HIPIMS/Ti-DCMS configuration) during film growth leads to NaCl-structure Ti1-x Al x N (0.53≤ x ≤0.60) films which exhibit high hardness (>30GPa) with low stress (0.2–0.7GPa tensile). In contrast, films with corresponding AlN concentrations grown under Ti n+ metal ion irradiation (with a significant Ti2+ component) in the Ti-HIPIMS/Al-DCMS mode have much lower hardness, 18–19GPa, and high compressive stress ranging up to 2.7GPa. The surprisingly large variation in mechanical properties results from the fact that the kinetic AlN solubility limit x max in Ti1-x Al x N depends strongly on, in addition to T s and R, the target power configuration during growth and hence the composition of the ion flux. AlN with x max ~64mol% can be accommodated in the NaCl structure under Al n+ ion flux, compared with ~40mol% for growth with Ti n+ flux. The strong asymmetry in film growth reaction paths is due primarily to the fact that the doubly-ionized metal ion flux is approximately two orders of magnitude higher from the Ti target, than from Al, powered with HIPIMS. This asymmetry becomes decisive upon application of a moderate substrate bias voltage, −60V, applied synchronously with HIPIMS pulses, during growth. [Copyright &y& Elsevier]

Abstract: We demonstrate, for the first time, the growth of metastable single-phase NaCl-structure high-AlN-content Ti1−x Al x N alloys (x ≤ 0.64) which simultaneously possess high hardness and low residual stress. The films are grown using a hybrid approach combining high-power pulsed magnetron (HPPMS/HIPIMS) and dc magnetron sputtering of opposing metal targets. With HIPIMS applied to the Al target, Al n+ ion irradiation (dominated by Al n+) of the growing film results in alloys 0.55 ≤ x ≤ 0.60 which exhibit hardness H ∼ 30 GPa and low stress σ = 0.2–0.7 GPa, tensile. In sharp contrast, films with corresponding AlN concentrations grown with HIPIMS applied to the Ti target, giving rise to Ti n+ ion irradiation (with a significant Ti2+ component), are two-phase – cubic (Ti,Al)N and hexagonal AlN – with low hardness, H = 18–19 GPa, and high compressive stress ranging up to 2.7 GPa. Annealing alloys grown with HIPIMS applied to the Al target results in age hardening due to spinodal decomposition; the hardness of Ti0.41Al0.59N increases from 30 to 33 GPa following a 900 °C anneal. [Copyright &y& Elsevier]

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: Epitaxial TiN layers, 0.3μm thick, are grown on MgO(001) in the absence of applied substrate heating using very high flux, low-energy (below the lattice atom displacement threshold), ion irradiation during reactive magnetron sputter deposition in pure N2 discharges. High-resolution x-ray diffraction, reciprocal lattice maps, and transmission electron microscopy analyses reveal that the TiN(001) films grow with an (001)TiN||(001)MgO and [100]TiN||[100]MgO orientation relationship to the substrate. The layers are fully coherent with no detectable misfit dislocations. For comparison, TiN/MgO(001) films grown at temperatures of 700–850°C under similar conditions, but with no intentional ion irradiation, are fully relaxed with a high misfit dislocation density. Thus, the present results reveal that intense low-energy ion irradiation during film growth facilitates high adatom mobilities giving rise to low-temperature epitaxy, while the low growth temperature quenches strain-induced relaxation and suppresses misfit dislocation formation. [Copyright &y& Elsevier]

Abstract: Epitaxial metastable Hf1− x Al x N alloys with 0≤ x ≤0.50 were grown on MgO(001) substrates at 600 °C by ultrahigh vacuum reactive magnetron sputtering from Hf and Al targets in 90% Ar+10% N2 discharges at 7 mTorr. X-Ray diffraction and cross-sectional transmission electron microscopy show that Hf1− x Al x N alloys are single crystals with the B1–NaCl structure. Rutherford backscattering spectroscopy investigations reveal that all films are slightly overstochiometric with N/(Hf+Al)=1.05±0.05. The relaxed lattice parameter decreased linearly from 0.4519 nm with x =0 to 0.4438 nm with x =0.50, compared to 0.4320 nm expected from the linear Vegard''s rule. We find a metastable single phase field that is remarkably broad given the large lattice mismatch (≃9%) between the two alloy components. Alloying HfN with AlN leads to an increase in hardness (≃30% to 32.4±0.7 GPa), as well as nanostructured compositional modulations due to the onset of spinodal decomposition. [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]

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]

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]