Multicomponent or high-entropy oxide films are of interest due to their remarkable structure and properties. Here, energetic ion irradiation is utilized for controlling the phase formation and structure of AlCrNbTi oxide at growth temperature of 500 degrees C. The ion acceleration is achieved by using a high-power impulse magnetron sputtering (HiPIMS) discharge, accompanied by a 10 & mu;s-long synchronized substrate bias (Usync), to minimize the surface charging effect and accelerate early-arriving ions, mainly Al+, O+, Ar2+, and Al2+. By increasing the magnitude of Usync from-100 V to-500 V, the film structure changes from amorphous to single-phase corundum, followed by the formation of high-number-density stacking faults (or nanotwins) at Usync =-500 V. This approach paves the way to tailor the high-temperature-phase and defect formation of oxide films at low growth temperature, with prospects for use in protective-coating and dielectric applications.

Noble-gas implantation was used to introduce defects in n-type degenerate ScN thin films to tailor their transport properties. The electrical resistivity increased significantly with the damage levels created, while the electron mobility decreased regardless of the nature of the ion implanted and their doses. However, the transport property characterizations showed that two types of defects were formed during implantation, named point-like and complex-like defects depending on their temperature stability. The point-like defects changed the electrical conduction mode from metallic-like to semiconducting behavior. In the low temperature range, where both groups of defects were present, the dominant operative conduction mechanism was the variable range hopping conduction mode. Beyond a temperature of about 400 K, the point-like defects started to recover with an activation energy of 90 meV resulting in a decrease in resistivity, independent of the incident ion. The complex-like defects were, therefore, the only remaining group of defects after annealing above 700 K. These latter, thermally stable at least up to 750 K, introduced deep acceptor levels in the bandgap resulting in an increase in the electrical resistivity with higher carrier scattering while keeping the metallic-like behavior of the sample. The generation of both types of defects, as determined by resistivity measurements, appeared to occur through a similar mechanism within a single collision cascade.

c-TiAlN/h-Cr2N multilayer thin films, with modulation period lambda of 10 nm, 20 nm, and 30 nm and different Cr2N/lambda thickness ratios (25 %, 50 % and 75 %), were deposited on c-plane sapphire using reactive DC magnetron sputtering. All multilayers exhibited preferred orientation [Cr2N(0001)/ TiAlN(111)](x), regardless of the modulation period and thickness ratios. X-ray diffraction f-scans revealed an influence of the Cr2N layer thickness on the overall orientation quality of the multilayer, where the thicker the Cr2N layer the higher orientation quality. Atomically resolved high-angle annular dark-field scanning transmission electron microscopy revealed well defined and homogeneous atom stacking in the Cr2N layers. In contrast, the cubic TiAlN layer was found to be composed of coherent cubic AlN-rich and TiN-rich regions. Additionally, the TiAlN layers were found with a higher density of grain boundaries compared to the Cr2N layers. Mechanical properties evaluation revealed that the film with a 20 nm period and 75 % Cr2N thickness ratio exhibited the highest hardness of 27.11 +/- 0.72 GPa and an reduced elastic modulus of 349.1 +/- 6.84 GPa. The hardness increased as the thickness of Cr2N increased, until reaching 10 nm, after which it remained at a high level (similar to 25 GPa).

Phase formation, morphology, and optical properties of Ti(O,N) thin films with varied oxygen-to- nitrogen ration content were investigated. The films were deposited by magnetron sputtering at 500 & DEG;C on Si(100) and c-plane sapphire substrate. A competition between a NaCl B1 structure TiN1-xOx, a rhombohedral structure Ti-2(O1-yNy)(3), and an anatase structure Ti(O1-zNz)(2) phase was observed. While the N-rich films were composed of a NaCl B1 TiN1-xOx phase, an increase of oxygen in the films yields the growth of rhombohedral Ti-2(O1-yNy)(3) phase and the oxygen-rich films are comprised of a mixture of the rhombohedral Ti-2(O1-yNy)(3) phase and anatase Ti(O1-zNz)(2) phase. The optical properties of the films were correlated to the phase composition and the observation of abrupt changes in terms of refractive index and absorption coefficient. The oxide film became relatively transparent in the visible range while the addition of nitrogen into films increases the absorption. The oxygen rich-samples have bandgap values below 3.75 eV, which is higher than the value for pure TiO2, and lower than the optical bandgap of pure TiN. The optical properties characterizations revealed the possibility of adjusting the band gap and the absorption coefficient depending on the N-content, because of the phases constituting the films combined with anionic substitution.

A common design of sputtering systems is to integrate many magnetron sources in a tilted closed-field configuration, which can drastically affect the magnetic field in the chamber and thus plasma characteristics. To study this effect explicitly, multicomponent TiZrNbTaN coatings were deposited at room temperature using direct current magnetron sputtering (DCMS) and high-power impulse magnetron sputtering (HiPIMS) with different substrate biases. The coatings were characterized by x-ray diffraction, scanning electron microscopy, nano-indentation, and energy dispersive x-ray spectroscopy. Magnetic field simulations revealed ten times higher magnetic field strengths at the substrate in single-magnetron configuration when compared to the closed-field. As a result, the substrate ion current increased similar to 3 and 1.8 times for DCMS and HiPIMS, respectively. The film microstructure changed with the discharge type, in that DCMS coatings showed large sized columnar structures and HiPIMS coatings show globular nanosized structures with (111) orientation with a closed-field design. Coatings deposited from a single source showed dense columnar structures irrespective of the discharge type and developed (200) orientation only with HiPIMS. Coatings deposited with closed-field design by DCMS had low stress (0.8 to -1 GPa) and hardness in the range from 13 to 18 GPa. Use of HiPIMS resulted in higher stress (-3.6 to -4.3 GPa) and hardness (26-29 GPa). For coatings deposited with single source by DCMS, the stress (-0.15 to -3.7 GPa) and hardness were higher (18-26 GPa) than for coatings grown in the closed-field design. With HiPIMS and single source, the stress was in the range of -2.3 to -4.2 GPa with a similar to 6% drop in the hardness (24-27 GPa).

Growth temperature (Ts) and ion irradiation energy (Ei) are important factors that influence film growth as well as their properties. In this study, we investigate the evolution of crystal structure and residual stress of TiNb-CrAlHfN films under various Ts and Ei conditions, where the latter is mainly controlled by tuning the flux of sputtered Hf ions using bipolar high-power impulse magnetron (BP-HiPIMS). The results show that TiNbCrAlHfN films exhibit the typical FCC NaCl-type structure. By increasing Ts from room temperature to 600 degrees C, the film texture changes from high-surface-energy (111) to low-surface-energy (100) accompanied by a higher crystal-linity in the out-of-plane direction and a more disordered growth tilt angle to the surface plane. In addition, compressive stress decreases with increasing Ts, which is ascribed to changes in the film growth both in the early and post-coalescence stages and more tensile thermal stress at elevated Ts. In contrast, a clear texture transition window is seen under various Ei of Hf+ ions, i.e., high-surface-energy planes change to low-surface-energy planes as Ei exceeds-110 eV, while low-surface-energy planes gradually transform back to high-surface-energy planes when Ei increases from 210 to 260 eV, indicating renucleation events for Ei > 210 eV. Compressive stress in-creases with increasing Ei but is still lower than that of a reference series with DC substrate bias UDC =-100 V. The study shows that it is possible to tailor properties of FCC-structured high-entropy nitrides by varying Ts and Ei in a similar fashion to conventional transition metal nitrides using the approach of unipolar and bipolar HiPIMS co-sputtering.

NiO thin films with varied oxygen contents are grown on Si(100) and c-Al2O3 at a substrate temperature of 300 degrees C using pulsed dc reactive magnetron sputtering. We characterize the structure and optical properties of NiO changes as functions of the oxygen content. NiO with the cubic structure, single phase, and predominant orientation along (111) is found on both substrates. X-ray diffraction and pole figure analysis further show that NiO on the Si(100) substrate exhibits fiber-textured growth, while twin domain epitaxy was achieved on c-Al2O3, with NiO(111) k Al2O3(0001) and NiO[1 (1) over bar0]k Al2O3[10 (1) over bar0] or NiO[(1) over bar 10]k Al2O3[2 (1) over bar(1) over bar0] epitaxial relationship. The oxygen content in NiO films did not have a significant effect on the refractive index, extinction coefficient, and absorption coefficient. This suggests that the optical properties of NiO films remained unaffected by changes in the oxygen content.

The epitaxial growth of boron rich hexagonal zirconium diborides (h-ZrB2+delta) thin films on Si(111) substrates using the magnetron co-sputtering technique with elemental zirconium and boron is reported. The effect of process temperature (700-900 degrees C) on the compositions and epitaxy quality was investigated. The chemical composition of the films was found to have a higher boron to zirconium ratio than the ideal stoichiometric AlB2-type ZrB2 and was observed to be sensitive to process temperature. Films deposited at 700 degrees C exhibited intense diffraction peaks along the growth direction corresponding to (000l) of h-ZrB2 using both lab and synchrotron-based x-ray diffractograms. The thermal and compositional stability of the epitaxial h-ZrB2+delta film was further evaluated under a nitrogen-rich environment through isothermal annealing which showed a reduction in in-plane misorientation during thermal annealing. The relative stability of deviating compositions and the energetics of impurity incorporations were analyzed using density functional theory simulations, and the formation of native point defects or impurity incorporation in h-ZrB2 was found to be endothermic processes. Our experimental results showed that an epitaxial thin film of h-ZrB2+delta can be grown on Si(111) substrate using a magnetron co-sputtering technique at a relatively low processing temperature (700 degrees C) and has the potential to be used as a template for III-nitride growth on Si substrates.

Thin films of BaZr1-xScxO3-x/2, (0 ≤ x ≤ 0.64), well known as proton conducting solid electrolytes for intermediatetemperature solid oxide fuel cell, were deposited by magnetron sputtering. X-ray diffraction analysis of theas deposited films reveals the presence of single-phase perovskite structure. The films were deposited on fourdifferent substrates (c-Al2O3, LaAlO3〈100〉, LaAlO3〈110〉, LaAlO3〈111〉) yielding random, (110)- or (100)-orientedfilms. The stability of the as-deposited films was assessed by annealing in air at 600 ◦C for 2 h. Theannealing treatment revealed instabilities of the perovskite structure for the (110) and randomly oriented films,but not for (100) oriented film. The instability of the coating under heat treatment was attributed to the lowoxygen content in the film (understoichiometry) prior annealing combined with the surface energy and atomiclayers stacking along the growth direction. An understoichiometric (100) oriented perovskite films showedhigher stability of the structure under an annealing in air at 600 ◦C.

Low-temperature epitaxial growth of multicomponent alloy-based thin films remains an outstanding challenge in materials science and is important for established fundamental properties of these complex materials. Here, Cantor nitride (CrMnFeCoNi)N thin films were epitaxially grown on MgO(100) substrates at low deposition temperature by magnetic-field-assisted dc-magnetron sputtering, a technique where a magnetic field is applied to steer the dense plasma to the substrate thereby influencing the flux of Ar-ions bombarding the film during growth. Without ion bombardment, the film displayed textured growth. As the ion flux was increased, the films exhibited epitaxial growth. The epitaxial relationship between film and substrate was found to be cube on cube (001)film parallel to(001)MgO, [100]film parallel to[100]MgO. The epitaxy was retained up to a thickness of approximately similar to 100 nm after which the growth becomes textured with a 002 out-of-plane orientation. The elastic constants determined by Brillouin inelastic light scattering were found to be C-11 = 320 GPa, C-12 = 125 GPa, and C-44 = 66 GPa, from which the polycrystalline Youngs modulus was calculated as 204 GPa and Poissons ratio = 0.32, whereas available elastic properties still remained very scarce. (c) 2023 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/).

Realizing stress-free inorganic epitaxial films on weakly bonding substrates is of importance for applications that require film transfer onto surfaces that do not seed epitaxy. Film-substrate bonding is usually weakened by harnessing natural van der Waals layers (e.g., graphene) on substrate surfaces, but this is difficult to achieve in non-layered materials. Here, we demonstrate van der Waals epitaxy of stress-free films of a non-layered material VO2 on mica. The films exhibit out-of-plane 010 texture with three inplane orientations inherited from the crystallographic domains of the substrate. The lattice parameters are invariant with film thickness, indicating weak film-substrate bonding and complete interfacial stress relaxation. The out-of-plane domain size scales monotonically with film thickness, but the in-plane domain size exhibits a minimum, indicating that the nucleation of large in-plane domains supports subsequent island growth. Complementary ab initio investigations suggest that VO2 nucleation and van der Waals epitaxy involves subtle polarization effects around, and the active participation of, surface potassium atoms on the mica surface. The VO2 films show a narrow domain-size-sensitive electrical-conductiv ity-temperature hysteresis. These results offer promise for tuning the properties of stress-free van der Waals epitaxial films of non-layered materials such as VO2 through microstructure control (C) 2023 The Author(s). Published by Elsevier Ltd. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).

Thin films of CrMoVN are deposited on c-plane sapphire (Al2O3 (0001)) by direct current reactive magnetron sputtering, to investigate the effects of Mo and V addition to CrN-based films. All films grow epitaxially, but Mo incorporation affects the crystal structure and nitrogen content. All films in the CrMoVN series are understoichiometric in nitrogen, but largely retain the NaCl B1 structure of stoichiometric CrN films. Addition of vanadium increases the phase-stability range of the cubic phase, allowing for higher solubility of Mo than what has previously been reported for cubic CrN. The Seebeck coefficient and electrical resistivity are greatly affected by the alloying, showing a decrease of the Seebeck coefficient along with a decrease in resistivity. Cr0.83Mo0.11V0.06Nz shows a 70% increase in power factor (S2 sigma = 0.22 mW m-1 K-2) compared to the reference CrNz (S2 sigma = 0.13 mW m-1 K-2). Thermoelectric (TE) materials are in use in several applications, but often have too low efficiency. For more widespread use of these materials, fundamental research on TE material system is necessary. In this work, alloying in CrN, with the hope of pushing a material with great promise closer to applications, is investigated.image (c) 2023 WILEY-VCH GmbH

As a single-phase alloy, CrFeCoNi is a face centered cubic (fcc) material related to the archetypical highentropy Cantor alloy CrFeCoNiMn. For thin films, CrFeCoNi of approximately equimolar composition tends to assume an fcc structure when grown at room temperature by magnetron sputtering. However, the single-phase solid solution state is typically not achieved for thin films grown at higher temperatures. The same holds true for Cantor alloy-based ceramics (nitrides and oxides), where phase formation is extremely sensitive to process parameters such as the amount of reactive gas. This study combines theoretical and experimental methods to understand the phase formation in nitrogen-containing CrFeCoNi thin films. Density functional theory calculations considering three competing phases (CrN, Fe-Ni and Co) show that the free energy of mixing, Delta G of (CrFeCoNi)(1-x)N-x solid solutions has a maximum at x = 0.20-0.25, and AG becomes lower when x < 0.20 and x > 0.25. Thin films of (CrFeCoNi)1-xNx (0.14 >= x <= 0.41) grown by magnetron sputtering show stabilization of the metallic fcc when x <= 0.22 and the stabilization of the NaCl B1 structure when x > 0.33, consistent with the theoretical prediction. In contrast, films with intermediate amounts of nitrogen (x = 0.22) grown at higher temperatures show segregation into multiple phases of CrN, Fe-Ni-rich and Co. These results offer an explanation for the requirement of kinetically limited growth conditions at low temperature for obtaining single-phase CrFeCoNi Cantor-like nitrogen-containing thin films and are of importance for understanding the phase-formation mechanisms in multicomponent ceramics. The results from the study further aid in making correlations between the observed mechanical properties and the crystal structure of the films.

Mg3Bi2-based compounds are of great interest for thermoelectric applications near room temperature. Here, undoped p-type Mg3SbxBi2-x thin films were synthesized using magnetron sputtering (three elemental targets in Ar atmosphere) with a growth temperature of 200 ? on three different substrates, namely, Si as well as c- and r-sapphire. The elemental composition was measured with energy-dispersive x-ray spectroscopy and the structure by x-ray diffraction. The electrical resistivity and the Seebeck coefficient were determined under He atmosphere from room temperature to the growth temperature. All samples are crystalline exhibiting the La2O3-type crystal structure (space group P-3m1). The observed thermoelectric response is consistent with a semiconductive behavior. With increasing x, the samples become more electrically resistive due to the increasing bandgap. High Bi content (x < 1) is thus beneficial due to lower resistivity and a higher power factor near room temperature. Thermoelectric thin films synthesized at low temperatures may provide novel pathways to enable flexible devices on polymeric and other heat-sensitive substrates.

Refractory high-entropy protective coatings are of interest for nuclear fuel cladding applications due to their corrosion resistant properties and irradiation resistance at elevated temperature. Here, TiZrNbTaV metallic and (TiZrNbTaV)N films were deposited by magnetron co-sputtering. The metal elemental contents of both films were nearly equiatomic. These films were irradiated by Xe ions at room temperature and 500 degrees C, and examined by X-ray diffraction and transmission electron microscopy. The as-deposited (TiZrNbTaV)N film showed a single NaCl-type fcc phase and a pronounced columnar growth structure, which could remain intact after irradiation treatments. In contrast, the as-deposited TiZrNbTaV film exhibited an amorphous structure and formed a bcc phase structure after irradiation at 500 degrees C. The TiZrNbTaV film after irradiation at 500 degrees C composed of depth -dependent size of grains. This distribution of grain size is consistent with simulated displacement damage. The stable structure of (TiZrNbTaV)N film under high temperature irradiation indicates that these materials have potential for use as protective coatings for nuclear fuel claddings.

Conducting polymer poly(3,4-ethylenedioxythiophene) nanowires(PEDOTNWs) were synthesized by a modified self-assembled micellar soft-templatemethod, followed by fabrication by vacuum filtration of self-supportingexfoliated WSe2-nanosheet (NS)/PEDOT-NW composite films.The results showed that as the mass fractions of WSe2 NSsincreased from 0 to 20 wt % in the composite films, the electricalconductivity of the samples decreased from & SIM;1700 to & SIM;400S cm(-1), and the Seebeck coefficient increased from12.3 to 23.1 & mu;V K-1 at 300 K. A room-temperaturepower factor of 44.5 & mu;W m(-1) K-2 was achieved at 300 K for the sample containing 5 wt % WSe2 NSs, and a power factor of 67.3 & mu;W m(-1) K-2 was obtained at 380 K. The composite film containing5 wt % WSe2 NSs was mechanically flexible, as shown byits resistance change ratio of 7.1% after bending for 500 cycles ata bending radius of 4 mm. A flexible thermoelectric (TE) power generatorcontaining four TE legs could generate an output power of 52.1 nWat a temperature difference of 28.5 K, corresponding to a power densityof & SIM;0.33 W/m(2). This work demonstrates that the fabricationof inorganic nanosheet/organic nanowire TE composites is an approachto improve the TE properties of conducting polymers.

Chromium-based nitrides are used in hard, resilient coatings and show promise for thermoelectric applications due to their combination of structural, thermal, and electronic properties. Here, we investigate the electronic structures and chemical bonding correlated to the thermoelectric properties of epitaxially grown chromium-based multicomponent nitride Cr(Mo,V)Nx thin films. The small amount of N vacancies causes Cr 3d and N 2p states to appear at the Fermi level and reduces the band gap in Cr0.51N0.49. Incorporating holes by alloying of V in N-deficient CrN results in an enhanced thermoelectric power factor with marginal change in the charge transfer of Cr to N compared with Cr0.51N0.49. Further alloying of Mo, isoelectronic to Cr, increases the density of states at the Fermi level due to hybridization of the (Cr, V) 3d and Mo 4d-N 2p states in Cr(Mo,V)Nx. This hybridization and N off-stoichiometry result in more metal-like electrical resistivity and reduction in Seebeck coefficient. The N deficiency in Cr(Mo,V)Nx also depicts a critical role in reduction of the charge transfer from metal to N site compared with Cr0.51N0.49 and Cr0.50V0.03N0.47. In this paper, we envisage ways for enhancing thermoelectric properties through electronic band engineering by alloying and competing effects of N vacancies.

Thin-film Ni-Ca3Co4O9 and Ni-Mo thermocouples were prepared by stepwise magnetron-sputtering/annealing synthesis using masks. Compared with Ni-Mo thin film thermocouples, Ni-Ca3Co4O9 thin film thermocouples have higher output voltage due to large positive Seebeck voltage (153 mu V/K for single thermocouple and 912 mu V/ K for 6-series thermocouple). The maximum output voltage from the thermocouple is 70 mV was obtained for a hot-end temperature of 105 degrees C for Ni-Ca3Co4O9 for a 6-series thermocouple. The stability of Ca3Co4O9 films and the ability to make free-standing films, together with the high Seebeck coefficient, show that these thin-film oxides can be used as p-type leg in thermocouples, with implications for use in free-standing and flexible thermoelectric devices.

Motivated by frequently reported deviations from stoichiometry in cubic transition metal nitride (TMNx) thin films, the effect of N-vacancy concentration on the elastic properties of cubic TiNx, ZrNx, VNx, NbNx, and MoNx (0.72 & LE; x & LE; 1.00) is systematically studied by density functional theory (DFT) calculations. The predictions are validated experimentally for VNx (0.77 & LE; x & LE; 0.97). The DFT results indicate that the elastic behavior of the TMNx depends on both the N-vacancy concentration and the valence electron concentration (VEC) of the transition metal: While TiNx and ZrNx exhibit vacancy-induced reductions in elastic modulus, VNx and NbNx show an increase. These trends can be rationalized by considering vacancy-induced changes in elastic anisotropy and bonding. While introduction of N-vacancies in TiNx results in a significant reduction of elastic modulus along all directions and a lower average bond strength of Ti-N, the vacancy-induced reduction in [001] direction of VNx is overcompensated by the higher stiffness along [011] and [111] directions, resulting in a higher average bond strength of V-N. To validate the predicted vacancy-induced changes in elasticity experimentally, close-to-singlecrystal VNx (0.77 & LE; x & LE; 0.97) are grown on MgO(001) substrates. As the N-content is reduced, the relaxed lattice parameter a0, as probed by X-ray diffraction, decreases from 4.128 & ANGS; to 4.096 & ANGS;. This reduction in lattice parameter is accompanied by an anomalous 11% increase in elastic modulus, as determined by nanoindentation. As the experimental data agree with the predictions, the elasticity enhancement in VNx upon N-vacancy formation can be understood based on the concomitant changes in elastic anisotropy and bonding.

Corrosion resistance and catalytic activity toward the oxygen reduction reaction (ORR) in an alkaline environment are two key properties for water recombination applications. In this work, CoCrFexNi (0 <= x <= 0.7) thin films were deposited by magnetron sputtering on polished steel substrates. The native passive layer was 2-4 nm thick and coherent to the columnar grains determined by transmission electron microscopy. The effect of Fe on the corrosion properties in 0.1 M NaCl and 1 M KOH and the catalytic activity of the films toward ORR were investigated. Electrochemical impedance spectroscopy and potentiodynamic polarization measurements indicate that CoCrFe0.7Ni and CoCrFe0.3Ni have the highest corrosion resistance of the studied films in NaCl and KOH, respectively. The high corrosion resistance of the CoCrFe0.7Ni film in NaCl was attributed to the smaller overall grain size, which leads to a more homogeneous film with a stronger passive layer. For CoCrFe0.3Ni in KOH, it was attributed to a lower Fe dissolution into the electrolyte and the build-up of a thick and protective hydroxide layer. Scanning Kelvin probe force microscopy showed no potential differences globally in any of the films, but locally, a potential gradient between the top of the columns and grain boundaries was observed. Corrosion of the films was likely initiated at the top of the columns where the potential was lowest. It was concluded that Fe is essential for the electrochemical activation of the surfaces and the catalytic activity toward ORR in an alkaline medium. The highest catalytic activity was recorded for high Fe-content films (x >= 0.5) and was attributed to the formation of platelet-like oxide particles on the film surface upon anodization. The study showed that the combination of corrosion resistance and catalytic activity toward ORR is possible for CoCrFexNi, making this material system a suitable candidate for water recombination in an alkaline environment.

A variety of bulk high-entropy alloy superconductors have been recently discovered; however, for thin films, only the TaNbHfZrTi highentropy alloy system has been investigated for its superconducting properties. Here, (TiZrNbTa)_1-xW_x and (TiZrNbTa)_1-xV_x superconducting films have been produced by DC magnetron sputtering at different growth temperatures. The phase formation and superconducting behavior of these films depend on the content of alloying x and deposition temperature. A single body-centered cubic (bcc) phase can be formed in the low x range with enough driving energy for crystallinity, but phase transition between amorphous or two bcc structures is observed when increasing x. The highest superconducting transition temperature T_c reaches 8.0 K for the TiZrNbTa film. The superconducting transition temperature T_c of these films deposited at the same temperature decreases monotonically as a function of x. Increasing deposition temperature to 400 °C can enhance T_c for these films while retaining nearly equivalent compositions. Our experimental observations suggest that T_c of superconducting high entropy alloys relate to the atomic radii difference and electronegativity difference of involved elements beyond the valence electron number.

Controlling nanoporosity to favorably alter multiple properties in layered crystalline inorganic thin films is a challenge. Here, we demonstrate that the thermoelectric and mechanical properties of Ca3Co4O9 films can be engineered through nanoporosity control by annealing multiple Ca(OH)(2)/Co3O4 reactant bilayers with characteristic bilayer thicknesses (b(t)). Our results show that doubling b(t), e.g., from 12 to 26 nm, more than triples the average pore size from similar to 120 nm to similar to 400 nm and increases the pore fraction from 3% to 17.1%. The higher porosity film exhibits not only a 50% higher electrical conductivity of sigma similar to 90 S cm(-1) and a high Seebeck coefficient of alpha similar to 135 mu V K-1, but also a thermal conductivity as low as kappa similar to 0.87 W m(-1) K-1. The nanoporous Ca3Co4O9 films exhibit greater mechanical compliance and resilience to bending than the bulk. These results indicate that annealing reactant multilayers with controlled thicknesses is an attractive way to engineer nanoporosity and realize mechanically flexible oxide-based thermoelectric materials.

Mg3Sb2-based thermoelectric materials attract attention for applications near room temperature. Here, Mg-Bi films were synthesized using magnetron sputtering at deposition temperatures from room temperature to 400 & DEG;C. Single-phase Mg3Bi2 thin films were grown on c-plane-oriented sapphire and Si(100) substrates at a low deposition temperature of 200 & DEG;C. The Mg3Bi2 films grew epitaxially on c-sapphire and fiber-textured on Si(100). The orientation relationships for the Mg3Bi2 film with respect to the c-sapphire substrate are (0001) Mg3Bi2||(0001) Al2O3 and [11 2 over bar 0] Mg3Bi2||[11 2 over bar 0] Al2O3. The observed epitaxy is consistent with the relatively high work of separation, calculated by the density functional theory, of 6.92 J m(-2) for the Mg3Bi2 (0001)/Al2O3 (0001) interface. Mg3Bi2 films exhibited an in-plane electrical resistivity of 34 mu omega m and a Seebeck coefficient of +82.5 mu V K-1, yielding a thermoelectric power factor of 200 mu W m(-1) K-2 near room temperature.

CaMnO3 is a perovskite with attractive magnetic and thermoelectric properties. CaMnO3 films are usually grown by pulsed laser deposition or radio frequency magnetron sputtering from ceramic targets. Herein, epitaxial growth of CaMnO3-y (002) films on a (112 over bar 0)-oriented LaAlO3 substrate using pulsed direct current reactive magnetron sputtering is demonstrated, which is more suitable for industrial scale depositions. The CaMnO3-y shows growth with a small in-plane tilt of <approximate to 0.2 degrees toward the (200) plane of CaMnO3-y and the (1 over bar 104) with respect to the LaAlO3 (112 over bar 0) substrate. X-ray photoelectron spectroscopy of the electronic core levels shows an oxygen deficiency described by CaMnO2.58 that yields a lower Seebeck coefficient and a higher electrical resistivity when compared to stoichiometric CaMnO3. The LaAlO3 (112 over bar 0) substrate promotes tensile-strained growth of single crystals. Scanning transmission electron microscopy and electron energy loss spectroscopy reveal antiphase boundaries composed of Ca on Mn sites along and , forming stacking faults.

Nowadays, making thermoelectric materials more efficient in energy conversion is still a challenge. In this work, to reduce the thermal conductivity and thus improve the overall thermoelectric performances, point and extended defects were generated in epitaxial 111-ScN thin films by implantation using argon ions. The films were investigated by structural, optical, electrical, and thermoelectric characterization methods. The results demonstrated that argon implantation leads to the formation of stable defects (up to 750 K operating temperature). These were identified as interstitial-type defect dusters and argon vacancy complexes. The insertion of these specific defects induces acceptor-type deep levels in the band gap, yielding a reduction in the free-carrier mobility. With a reduced electrical conductivity, the irradiated sample exhibited a higher Seebeck coefficient while maintaining the power factor of the film. The thermal conductivity is strongly reduced from 12 to 3 W.m(-1). K-1 at 300 K, showing the influence of defects in increasing phonon scattering. Subsequent high-temperature annealing at 1573 K leads to the progressive evolution of these defects: the initial dusters of interstitials evolved to the benefit of smaller dusters and the formation of bubbles. Thus, the number of free carriers, the resistivity, and the Seebeck coefficient are almost restored but the mobility of the carriers remains low and a 30% drop in thermal conductivity is still effective (k(total) similar to 8.5 Wm(-1).K-1). This study shows that control defect engineering with defects introduced by irradiation using noble gases in a thermoelectric coating can be an attractive method to enhance the figure of merit of thermoelectric materials.

Nanoporous Ca3Co4O9 exhibits high thermoelectric properties and low thermal conductivity and can be made mechanically flexible by nanostructural design. To improve the mechanical flexibility with retained thermoelectric properties near room temperature, however, it is desirable to incorporate an organic filler in this nanoporous inorganic matrix material. Here, double-layer nanoporous Ca3Co4O9/PEDOT:PSS thin films were synthesized by spin-coating PEDOT:PSS into the nanopores. The obtained hybrid films exhibit high Seebeck coefficient (~+130 mu V/K) and thermoelectric power factor (0.75 mu W cm(-1) K-2) at room temperature with no deterioration in electrical properties after cyclic bending tests (98% preservation of electrical conductivity after 1000 cycles bending to a bending radius of 3 mm). Compared with the nanoporous Ca3Co4O9 thin film, the mechanical flexibility of the hybrid film can be effectively improved after hybrid with PEDOT:PSS with only a slight decrease of the thermoelectric properties.

During direct current magnetron sputtering (dcMS) of thin films, the ion energy and flux are complex parameters that influence thin film growth and can be exploited to tailor their properties. The ion energy is generally controlled by the bias voltage applied at the substrate. The ion flux density however is controlled by more complex mechanisms. In this study, we look into magnetic-field-assisted dcMs, where a magnetic field applied in the deposition chamber by use of a solenoid coil at the substrate position, influences the energetic bombardment by Ar ions during deposition. Using this technique, CrFeCoNi multicomponent nitride thin films were grown on Si(100) substrates by varying the bias voltage and magnetic field systematically. Plasma diagnostics were performed by a Langmuir wire probe and a flat probe. On interpreting the data from the current-voltage curves it was confirmed that the ion flux at the substrate increased with increasing coil magnetic field with ion energies corresponding to the applied bias. The increased ion flux assisted by the magnetic field produced by the solenoid coil aids in the stabilization of NaCl B1 crystal structure without introducing Ar ion implantation.

We report the results of a combined experimental and theoretical study on nonstoichiometric CrN1+δ thinfilms grown by reactive magnetron sputtering on c-plane sapphire and MgO (100) substrates in an Ar/N2 gasmixture using different percentages of N2. There is a transition from n-type to p-type behavior in the layersas a function of nitrogen concentration varying from 48 to 52 at. % in CrN films. The compositional changefollows a similar trend for all substrates, with a N/Cr ratio increasing from approximately 0.7 to 1.06–1.11 byincreasing the percentage of N2 in the gas flow ratio. As a result of the change in stoichiometry, the latticeparameter and the Seebeck coefficient increase together with the increase of N in CrN1+δ ; in particular, theSeebeck value coefficient transitions from –50 μV K–1 for CrN0.97 to +75μV K–1 for CrN1.1. Density functionaltheory calculations show that Cr vacancies can account for the change in the Seebeck coefficient, since they pushthe Fermi level down in the valence band, whereas N interstitial defects in the form of N2 dumbbells are neededto explain the increasing lattice parameter. Calculations including both types of defects, which have a strongtendency to bind together, reveal a slight increase in the lattice parameter and a simultaneous formation of holesin the valence band. To explain the experimental trends, we argue that both Cr vacancies and N2 dumbbells,possibly in combined configurations, are present in the films. We demonstrate the possibility of controlling thesemiconducting behavior of CrN with intrinsic defects from n to p type, opening possibilities to integrate thiscompound in energy-harvesting thermoelectric devices.

Solid-state precipitation can be used to tailor material properties, ranging from ferromagnets and catalysts to mechanical strengthening and energy storage. Thermoelectric properties can be modified by precipitation to enhance phonon scattering while retaining charge-carrier transmission. Here, unconventional Janus-type nanoprecipitates are uncovered in Mg3Sb1.5Bi0.5 formed by side-by-side Bi- and Ge-rich appendages, in contrast to separate nanoprecipitate formation. These Janus nanoprecipitates result from local comelting of Bi and Ge during sintering, enabling an amorphous-like lattice thermal conductivity. A precipitate size effect on phonon scattering is observed due to the balance between alloy-disorder and nanoprecipitate scattering. The thermoelectric figure-of-merit ZT reaches 0.6 near room temperature and 1.6 at 773 K. The Janus nanoprecipitation can be introduced into other materials and may act as a general property-tailoring mechanism.

Controllable engineering of the nanoporosity in layered Ca3Co4O9 remains a challenge. Here, we show the synthesis of discontinuous films with islands of highly textured Ca3Co4O9, effectively constituting distributed nanoparticles with controlled porosity and morphology. These discontinuously dispersed textured Ca3Co4O9 nanoparticles may be a candidate for hybrid thermoelectrics.

Multicomponent as well as high-entropy-based nitrides have received increasing interest in the field of materials science and engineering. The structural characteristics of these compounds result in a mix of covalent, metallic, and ionic bonds that give rise to a number of attractive properties including high hardness, electrical and thermal conductivities as well as chemical stability. These properties render these materials promising candidates for various industrial applications involving harsh operating conditions. Herein, the corrosion resistances of dc magnetron sputtered nitrogen-containing TiZrTaNby thin films with Nb content ranging from 8.0 to 24.5 at% have been investigated to provide insights regarding the corrosion resistances of multicomponent systems containing more than one passive element. The corrosion resistances and anodic behavior of the films were examined by electrochemical means in 0.1 M H2SO4 and 0.1 M HCl solutions. The results demonstrate that despite the significant differences in the concentration of one of the two main passive elements in the films i.e., Nb, the corrosion resistance did not differ significantly between the films. To provide insights into this phenomenon, the surface chemical state and composition of the prepared films were probed using X-ray photoelectron spectroscopy. It was shown that all samples exhibited Ta-rich surfaces after positive polarization up to 3.0 V vs. Ag/AgCl (3 M NaCl) as a result of the anodic dissolution of Zr and Ti. The thickness of the oxide layer formed upon different anodic polarization was studied using transmission electron microscopy, while complementary electrochemical impedance studies were performed. The extent of Nb dissolution from the surface of the films was, on the other hand, found to be small. These findings highlight the dominant role of Ta in the passivation of the films and demonstrate the minor effect of Nb concentration on the corrosion resistances of the films. However, it was demonstrated that the presence of Nb was still important for the corrosion resistance of the films above 1.4 V vs. Ag/AgCl (3 M NaCl), when replacing Nb with Cr, due to transpassive dissolution of Cr. These results facilitate the design of highly corrosion resistant multicomponent nitrides containing more than one passive element.(c) 2022 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

The Cantor alloy CrFeCoMnNi is generally fcc structured, but moderate changes in the composition can have a large influence on the phase formation. The aim of this study was to understand the changes brought on in lownitrogen-containing (CrFeCo)1-yNy thin films with y = 0.19 on the addition of copper, an interesting metal in terms of atomic size and nitride formation enthalpy. (CrFeCoCux)1-yNy films were grown by reactive magnetron sputtering. The amount of copper in the films was increased from x = 0 to x = 0.15 to study competitive phase formation. Without Cu, two-phase fcc + bcc films were obtained. The addition of Cu was found to stabilize the bcc structure despite the fact that Cu as a pure metal is fcc. Nanoindentation tests showed slight increase in hardness with initial Cu addition from 11 GPa to 13.7 +/- 0.2 GPa. The occurrence of pile up as opposed to cracking is an indication of the films ductility.

Cr-N based materials, including stoichiometric CrN and Cr:N with a wide range of nitrogen contents, are commonly used as hard and corrosion-resistant coatings. Cr-rich films in this materials system can retain the bcc structure of metallic Cr with few percent of dissolved nitrogen, which can be used for tailoring the mechanical, thermal, and electrical properties. Here, we investigated low nitrogen containing Cr thin films deposited by high ion assisted magnetron sputtering with a substrate temperature of 200 degrees C. With the gas flow ratio maintained at f(N2/Ar) = 0.02, the substrate bias and the target power allows for control of the film composition (0.03 < N/Cr < 0.34). The films comprise a mixture of bcc-Cr and hexagonal Cr2N1-delta phases. The mechanical properties studied by nanoindentation and Brillouin inelastic light scattering revealed a hardening effect due to the multiphase nanostructure. The mechanical properties of the Cr:N films depend on the residual stress, on the amount of h-Cr2N1-delta phase and on the nanostructuring nature of the coatings. A maximum hardness of 37 GPa was achieved for a dense film with a Youngs modulus of 340 GPa, a shear modulus of 118 GPa, and a relatively low thermal conductivity of 7 W/mK.

Multilayers of high entropy alloys (HEA) are picking up interest due to the possibility of altering material properties by tuning crystallinity, thickness, and interfaces of the layers. This study investigates the growth mechanism and mechanical properties of CrFeCoNi/TiNbZrTa multilayers grown by magnetron sputtering. Multilayers of bilayer thickness (A) from 5 nm to 50 nm were grown on Si(1 0 0) substrates. Images taken by transmission electron microscopy and energy-dispersive X-ray spectroscopy mapping revealed that the layers were well defined with no occurrence of elemental mixing. Multilayers with A < 20 nm exhibited an amorphous structure. As A increased, the CrFeCoNi layer displayed a higher crystallinity in comparison to the amorphous TiNbZrTa layer. The mechanical properties were influenced by the crystallinity of the layers and stresses in the film. The film with A = 20 nm had the highest hardness of approximately 12.5 GPa owing grain refinement of the CrFeCoNi layer. An increase of A >= 30 nm resulted in a drop in the hardness due to the increase in crystal domains of the CrFeCoNi layer. Micropillar compression induced shear in the material rather than fracture, along with elemental intermixing in the core of the deformed region of the compressed micropillar.

The study aims to understand the irradiation behavior of multilayer coatings composed of high-entropy materials. Here, we report the structural stability and elemental segregation of high-entropy TiNbZrTa/CrFeCoNi metallic and nitride multilayer coatings under 3-MeV Xe20+ ion-irradiation at room temperature and 500 degrees C, respectively. Transmission electron microscopy analysis shows that the microstructure of nanocrystalline CrFeCoNi high-entropy-alloy sublayers are not stable and readily transforms into amorphous state at 500 degrees C and/or under irradiation conditions. The elemental distribution, acquired by energy-dispersive X-ray spectroscopy under scanning transmission electron microscopy mode, shows preferential diffusion of Co and Ni into TiNbZrTa sublayers, while Fe and Cr preferentially remain within the previous CrFeCoNi sublayers. TiNbZrTaN/CrFeCoNiNx nitride multilayers exhibit a higher crystallinity and structural stability as well as resistance to diffusion at high-temperature and/or irradiation conditions than their TiNbZrTa/CrFeCoNi metallic multilayer counterparts. These findings are explained by atomic size differences, the difference in Gibbs free energy of the mixing system, and interstitial-solute-induced chemical heterogeneity. Our findings thus provide a design strategy of high entropy nitride for nuclear fuel cladding. (C) 2022 The Author(s). Published by Elsevier Ltd.

Magnetron sputtering is a widely used physical vapor deposition technique. Reactive sputtering is used for the deposition of, e.g, oxides, nitrides and carbides. In fundamental research, versatility is essential when designing or upgrading a deposition chamber. Furthermore, automated deposition systems are the norm in industrial production, but relatively uncommon in laboratory-scale systems used primarily for fundamental research. Combining automatization and computerized control with the required versatility for fundamental research constitutes a challenge in designing, developing, and upgrading laboratory deposition systems. The present article provides a detailed description of the design of a lab-scale deposition chamber for magnetron sputtering used for the deposition of metallic, oxide, nitride and oxynitride films with automated controls, dc or pulsed bias, and combined with a coil to enhance the plasma density near the substrate. LabVIEW software (provided as Supplementary Information) has been developed for a high degree of computerized or automated control of hardware and processes control and logging of process details.

Introducing porosity is attractive for tailoring electronic, thermal, and mechanical properties of inorganic materials. Nanoporosity is typically either inherent in crystallographic channels in the structure or obtained by external templating during synthesis and sintering. However, controllably engineering porosity in materials with laminated crystal structures without channels remains a challenge. Here, we demonstrate the realization of faceted and oriented nanopores in textured Ca3Co4O9-a laminated ceramic with a misfit-layered structure of importance for thermoelectric applications-from chemical reactions in CaO/Co3O4 multilayers. We show that CaO conversion to Ca(OH)(2) and the cobalt oxide stoichiometry are key determinants of nanoporosity. Adjusting the unreacted CaO fraction alters the nanopore size and fraction and the thermoelectric properties of Ca3Co4O9. The preferred orientation of Ca3Co4O9 is underpinned by the texture of the reactant multilayers and reactant-product crystallographic relationships and density difference. Oriented pore formation is attributed to basal plane removal driven by local densification of textured Ca3Co4O9 nuclei through growth and impingement. These findings point to possibilities for controllably engineering nanoporosity and properties in a variety of inorganic materials with laminated crystal structures.

The layered cobaltates A(x)CoO(2) (A = Li, Na, Ca, Ba, Sr) are of interest for energy applications such as thermoelectrics and batteries. However, it is challenging to obtain these phases in pure from as thin films. Here, phase-pure CaxCoO2 (x similar to 0.5) thin films were obtained by annealing of Ca(OH)(2)/Co3O4 multilayers made by moisture treatment of sputter-deposited CaO/Co3O4 multilayer films. The pure CaxCoO2 thin films exhibit an average optical transmittance of approximately 36% in the visible region and greater than 70% in the near-infrared (NIR) region. In addition, the electrical conductivity can be increased by incorporating a secondary Ca3Co4O9 phase into the CaxCoO2 thin film without large changes in optical properties and Seebeck coefficient. (C) 2021 The Authors. Published by Elsevier Ltd.

Chromium-nitride based materials have shown unexpected promise as thermo-electric materials for, e.g., wasteheat harvesting. Here, CrN and (Cr,V)N thin films were deposited by reactive magnetron sputtering. Thermoelectric measurements of pure CrN thin films show a low electrical resistivity between 1.2 and 1.5 x 10(-3) Omega cm and very high values of the Seebeck coefficient and thermoelectric power factor, in the range between 370-430 mu V/K and 9-11 x 10(-3) W/mK(2), respectively. Alloying of CrN films with small amounts (less than 15 %) of vanadium results in cubic (Cr,V)N thin films. Vanadium decreases the electrical resistivity and yields powerfactor values in the same range as pure CrN. Density functional theory calculations of sub-stoichiometric CrN1-delta and (Cr,V)N1-delta show that nitrogen vacancies and vanadium substitution both cause n-type conductivity and features in the band structure typically correlated with a high Seebeck coefficient. The results suggest that slight variations in nitrogen and vanadium content affect the power factor and offers a means of tailoring the power factor and thermoelectric figure of merit.

Multicomponent or high-entropy ceramics show unique combinations of mechanical, electrical, and chemical properties of importance in coating applications. However, generalizing controllable thin-film processes for these complex materials remains a challenge. Here, understoichiometric (TiZrTaMe)N1–x (Me = Hf, Nb, Mo, or Cr, 0.12 ≤ x ≤ 0.30) films were deposited on Si(100) substrates at 400 °C by reactive magnetron sputtering using single elemental targets. The influence of ion energy during film growth was investigated by varying the negative substrate bias voltage from ∼10 V (floating potential) to 130 V. The nitrogen content for the samples determined by elastic recoil detection analysis varied from 34.9 to 43.8 at. % (0.12 ≤ x ≤ 0.30), and the metal components were near-equimolar and not affected by the bias voltage. On increasing the substrate bias, the phase structures of (TiZrTaMe)N1–x (Me = Hf, Nb, or Mo) films evolved from a polycrystalline fcc phase to a (002) preferred orientation along with a change in surface morphology from faceted triangular features to a dense and smooth structure with nodular mounds. All the four series of (TiZrTaMe)N1–x (Me = Hf, Nb, Mo, or Cr) films exhibited increasing intrinsic stress with increasing negative bias. The maximum compressive stress reached ∼3.1 GPa in Hf- and Cr-containing films deposited at −130 V. The hardness reached a maximum value of 28.0 ± 1.0 GPa at a negative bias ≥100 V for all the four series of films. The effect of bias on the mechanical properties of (TiNbZrMe)N1–x films can thus guide the design of protective high-entropy nitride films.

Multicomponent TixNbCrAl nitride films were deposited on Si(100) substrates by reactive direct current magnetron sputtering (dcMS) and high power impulse magnetron sputtering (HiPIMS) in the absence of substrate heating and bias. Three single Ti, Nb, and Cr50Al50 targets were either driven by three de or three HiPIMS power supplies. The Ti content in the films was varied by tuning the power applied to the Ti target. The composition was determined by ion beam analysis. The nitrogen content is nearly stoichiometric (48-50 at.%) in the HiPIMS series, while the dcMS are understoichiometric (39-45 at.%). The crystal structure, stress and density of the studied film were investigated by X-ray techniques and the microstructure was examined by scanning electron microscopy. All the Ti-containing films for both series exhibit an fcc NaCl-type phase structure. In particular, the dcMS series shows a (111) preferred orientation, resulting in a faceted surface morphology compared to a dense and smooth microstructure of the HiPIMS films. The compressive stress of the HiPIMS series (> 2.0 GPa) is significantly larger than the values of the dcMS series (<0.5 GPa). Nanoindentation measurements show a maximum hardness of 29.9 GPa and Youngs modulus of 304 GPa were obtained in the HiPIMS series. The results may promote HiPIMS techniques for the synthesis of complex multicomponent films for the application aspect to protective and hard coatings.

The Cantor alloy (CoCrFeMnNi) and its variants, in bulk as well as thin films, have been extensively studied. They are known to exhibit cubic crystal structures and thermodynamic stability regardless of their complex chemical composition. Therefore, they may find use as hard, wear-resistant, corrosion and oxidation-resistant coatings. The addition of light elements, such as nitrogen, is known to help improve these properties further through processes such as amorphization and nitride compound formation. Here, we investigate the ternary CrFeCo system to study the effects of nitrogen addition. (CrFeCo)N_y multicomponent thin films are grown on silicon substrates by DC magnetron sputtering. Changes in crystal structure, morphology, mechanical and electrical properties with gradual increases of nitrogen in the film are described and discussed. Increased addition of nitrogen from 14 at.% to 28 at.% in the film leads to a transformation from an fcc to a bcc crystal structure, affects both the mechanical and electrical properties. XPS analysis shows the tendency of nitrogen to bond with Cr over other metals. The films display hardness values between 7 and 11 GPa with resistivities values ranging between 28 and 165 μΩ cm.

(Ti-0.5, Mg-0.5)N thin films were synthesized by reactive dc magnetron sputtering from elemental targets onto c-cut sapphire substrates. Characterization by theta-2 theta X-ray diffraction and pole figure measurements shows a rock-salt cubic structure with (111)-oriented growth and a twin-domain structure. The films exhibit an electrical resistivity of 150 m omega center dot cm, as measured by four-point-probe, and a Seebeck coefficient of -25 mu V/K. It is shown that high temperature (similar to 800 degrees C) annealing in a nitrogen atmosphere leads to the formation of a cubic LiTiO2-type superstructure as seen by high-resolution scanning transmission electron microscopy. The corresponding phase formation is possibly influenced by oxygen contamination present in the as-deposited films resulting in a cubic superstructure. Density functional theory calculations utilizing the generalized gradient approximation (GGA) functionals show that the LiTiO2-type TiMgN2 structure has a 0.07 eV direct bandgap.

Catalysts and electmcatalysts are crucial for energy production and storage. To develop cost-efficient systems taking advantage of functionalized surfaces, the catalysts can be synthesized as nanomaterials or thin films. In this work, cobalt thin films were deposited on low-alloyed steel using magnetron sputtering. The films are uniform with a smooth surface and a thickness of similar to 400 nm. The films were electrochemically oxidized via anodization to a mix of cobalt oxides, one of them being Co3O4, at room temperature in an alkaline solution. The electrocatalytic performances of the anodized films were evaluated in 1 M KOH electrolyte saturated with oxygen. Cathodic currents in -0.5 mA/cm(2) range, corresponding to oxygen reduction reaction (ORR) activity, were measured with cyclic voltammetry. The catalytic activity of the films was evaluated as a function of time. The anodized Co coating exhibited three times higher activity than the steel substrate. The kinetics for the ORR were evaluated through Tafel plots and a slope of 226 mV/decade was found. Post-ORR characterization of the films revealed hexagonal plate-like oxide particles on the surface. After 50 cyclic voltammograms, the film was further oxidized, indicating that the ORR activity also affects the overall surface state of the film. This study demonstrates that thin films, after electrochemical modification, can be electrocatalysts for the oxygen reduction reaction and potentially used for applications in energy production and storage.

Multicomponent (TiNbZrTa)N_x films were deposited on Si(100) substrates at room temperature using magnetron sputtering with a nitrogen flow ratio f_N [f_N = N₂/(Ar + N₂)], which was varied from 0 to 30.8%. The nitrogen content in the films varied between 0 and 45.2 at.%, i.e., x = 0 to 0.83. The microstructure was characterized by X-ray diffraction and electron microscopy. The metallic TiNbZrTa film comprised a dominant bcc solid-solution phase, whereas a single NaCl-type face-centred cubic structure was observed in all nitrogen-containing films (TiNbZrTa)N_x. The mechanical, electrical, and electrochemical properties of these films varied with nitrogen content. The maximum hardness was achieved at 22.1 ± 0.3 GPa when N = 43.0 at.%. The resistivities increased from 95 to 424 μΩcm with increasing nitrogen content. A detailed study of the variation of morphology and chemical bonding with nitrogen content was performed and the corrosion resistance of the TiNbZrTa nitride films was explored in 0.1 M H₂SO₄. While all the films had excellent corrosion resistances at potentials up to 2.0 V vs. Ag/AgCl, the metallic film and the films with low nitrogen contents (x < 0.60) exhibited an almost stable current plateau up to 4.0 V vs. Ag/AgCl. For the films with higher nitrogen contents (x ≥ 0.68), the current plateau was retained up to 2.0 V vs. Ag/AgCl, above which a higher nitrogen content resulted in a higher current. The decrease in the corrosion resistance at these high potentials indicate the presence of a potential-dependent activation effect resulting in an increased oxidation rate of the nitrides (present under the passive oxide film) yielding a release of nitrogen from the films. TEM results indicate that the oxide layer formed after this corrosion measurement was thick and porous for the film with x = 0.76, in very good agreement with the increased corrosion rate for this film. The results demonstrate that an increased nitrogen content in (TiNbZrTa)N_x system improves their mechanical properties with retained high corrosion resistance at potentials up to 2.0 V vs. Ag/AgCl in 0.1 M H₂SO₄. At even higher potentials, however, the corrosion resistance decreases with increasing nitrogen concentration for films with sufficiently high nitrogen contents (i.e. x ≥ 0.68).

A series of (TiNbZrTa)Nx coatings with a thickness of similar to 1.1 mu m were deposited using reactive magnetron sputtering with segmented targets. The deposition temperature was varied from room temperature to 700 degrees C resulting in coatings with different microstructures. The coatings were characterized by electron microscopy, atomic force microscopy, compositional analysis, and X-ray diffraction. Effects of the deposition temperature on the electrical, mechanical and corrosion properties were studied with four-point probe, nanoindentation and potentiodynamic polarization measurements, respectively. X-ray photoelectron spectroscopy (XPS) analyses reveal a gradual change in the chemical state of all elements with increasing growth temperature from nitridic at room temperature to metallic at 700 degrees C. A NaCl-type structure with (001) preferred orientation was observed in the coating deposited at 400 degrees C, while an hcp structure was found for the coatings deposited above 400 degrees C. The resistivities of the TiNbZrTa nitride coatings were found to be around 200 mu Ocm. In 0.1 M H2SO4 aqueous solution, a corrosion current density of 2.8 x 10(-8) A/cm(2) and a passive behaviour up to 1.5 V vs. Ag/AgCl were found for the most corrosion resistant coating. The latter corrosion current is about two orders of magnitude lower than that found for a reference hyper-duplex stainless steel.

CaMn1-xNbxO3 (x = 0, 0.5, 0.6, 0.7 and 0.10) thin films have been grown by a two-step sputtering/annealing method. First, rock-salt-structured (Ca,Mn1-x,Nb-x)O thin films were deposited on 11 & x304;00 sapphire using reactive RF magnetron co-sputtering from elemental targets of Ca, Mn and Nb. The CaMn1-xNbxO3 films were then obtained by thermally induced phase transformation from rock-salt-structured (Ca,Mn1-xNbx)O to orthorhombic during post-deposition annealing at 700 degrees C for 3 h in oxygen flow. The X-ray diffraction patterns of pure CaMnO3 showed mixed orientation, while Nb-containing films were epitaxially grown in [101] out of-plane-direction. Scanning transmission electron microscopy showed a Ruddlesden-Popper (R-P) secondary phase in the films, which results in reduction of the electrical and thermal conductivity of CaMn1-xNbxO3. The electrical resistivity and Seebeck coefficient of the pure CaMnO3 film were measured to 2.7 omega cm and -270 mu V K-1 at room temperature, respectively. The electrical resistivity and Seebeck coefficient were reduced by alloying with Nb and was measured to 0.09 omega cm and -145 mu V K-1 for x = 0.05. Yielding a power factor of 21.5 mu W K-2 m(-1) near room temperature, nearly eight times higher than for pure CaMnO3 (2.8 mu W K-2 m(-1)). The power factors for alloyed samples are low compared to other studies on phase-pure material. This is due to high electrical resistivity originating from the secondary R-P phase. The thermal conductivity of the CaMn1-xNbxO3 films is low for all samples and is the lowest for x = 0.07 and 0.10, determined to 1.6 W m(-1) K-1. The low thermal conductivity is attributed to grain boundary scattering and the secondary R-P phase.

Heteroepitaxial c-(Ti-0.37,Al-0.63)N thin films were grown on MgO(001) and MgO(111) substrates using reactive magnetron sputtering. High resolution high-angle annular dark-field scanning transmission electron micrographs show coherency between the film and the substrate. In the as-deposited state, x-ray diffraction reciprocal space maps show a strained epitaxial film. Corresponding geometric phase analysis (GPA) deformation maps show a high stress in the film. At elevated temperature (900 degrees C), the films decompose to form iso-structural coherent c-Al- and c-TiN-rich domains, elongated along the elastically soft amp;lt;100amp;gt; directions. GPA analysis reveals that the c-TiN domains accommodate more dislocations than the c-AlN domains. This is because of the stronger directionality of the covalent bonds in c-AlN compared with c-TiN, making it more favorable for the dislocations to accumulate in c-TiN. The defect structure and strain generation in c-(Ti,Al)N during spinodal decomposition is affected by the chemical bonding state and elastic properties of the segregated domains.

ScN is an emerging semiconductor with an indirect bandgap. It has attracted attention for its thermoelectric properties, use as seed layers, and for alloys for piezoelectric application. ScN and other transition metal nitride semiconductors used for their interesting electrical properties are sensitive to contaminants, such as oxygen or fluorine. In this present article, the influence of depositions conditions on the amount of oxygen contaminants incorporated in ScN films were investigated and their effects on the electrical properties (electrical resistivity and Seebeck coefficient) were studied. Epitaxial-like films of thickness 125 +/- 5 nm to 155 +/- 5 nm were deposited by DC-magnetron sputtering on c-plane Al-2, O-3(111) and r-plane Al2O3 at substrate temperatures ranging from 700 degrees C to 950 degrees C. The amount of oxygen contaminants in the film, dissolved into ScN or as an oxide, was related to the adatom mobility during growth, which is affected by the deposition temperature and the presence of twin domain growth. The lowest values of electrical resistivity of 50 mu Omega cm were obtained on ScN(1 1 1)/ MgO(111) and on ScN(001)/r-plane Al2O3 grown at 950 degrees C with no twin domains and the lowest amount of oxygen contaminant. At the best, the films exhibited an electrical resistivity of 50 mu Omega cm with Seebeck coefficient values maintained at -40 mu V K-1, thus a power factor estimated at 3.2 x 10(-3) W m(-1) K-2 (at room temperature).

A two-step synthesis approach was utilized to grow CaMnO3 on M-, R- and C-plane sapphire substrates. Radio-frequency reactive magnetron sputtering was used to grow rock-salt-structured (Ca, Mn)O followed by a 3-h annealing step at 800 degrees C in oxygen flow to form the distorted perovskite phase CaMnO3. The effect of temperature in the post-annealing step was investigated using x-ray diffraction. The phase transformation to CaMnO3 started at 450 degrees C and was completed at 550 degrees C. Films grown on R- and C-plane sapphire showed similar structure with a mixed orientation, whereas the film grown on M-plane sapphire was epitaxially grown with an out-of-plane orientation in the [202] direction. The thermoelectric characterization showed that the film grown on M-plane sapphire has about 3.5 times lower resistivity compared to the other films with a resistivity of 0.077cm at 500 degrees C. The difference in resistivity is a result from difference in crystal structure, single orientation for M-plane sapphire compared to mixed for R- and C-plane sapphire. The highest absolute Seebeck coefficient value is -350 mu VK-1 for all films and is decreasing with temperature.