Thermochromic nanocrystalline Au-VO2 composite thin films prepared by radiofrequency inverted cylindrical magnetron sputtering

Highly crystalline Au-VO₂ nanocomposite thin films were prepared on Corning glass substrates by reactive radiofrequency inverted cylindrical magnetron sputtering (ICMS). It is a low cost potential coating technology for the production of large area uniform nanocomposite thin films exhibiting plasmonic properties. This paper reports the synthesis and feasibility of reliably reproduced high quality of Au-VO₂ by ICMS. Structural, morphological, interfacial analysis and optical properties of synthesized Au-VO₂ nanocomposite thin films are reported.     

Investigation of antiperovskite Mn3CuNx film prepared by DC reactive magnetron sputtering

Antiperovskite Mn₃CuN_x film was prepared by dc reactive magnetron sputtering. It is the first time to report an antiperovskite ternary nitride film. The composition and crystal structure were characterized by energy dispersive spectroscope (EDS), X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD). From the XRD pattern, it displays a (1 0 0) preferential orientation. A comparative study on the properties of Mn₃CuN_x film and the bulk sample was presented. The film exhibits an antiferromagnetic to paramagnetic transition around 135 K, similar with the bulk sample. With temperature, the resistivity of the film shows semiconductor-like behavior throughout the measured temperature region, whereas there is an abrupt drop around the magnetic transition for the bulk. The variable temperature XRD results indicate that the film did not display any structure transition and shows a normal linear thermal expansion property around the magnetic transition.     

Low friction CrN/TiN multilayer coatings prepared by a hybrid high power impulse magnetron sputtering/DC magnetron sputtering deposition technique

High power impulse magnetron sputtering (HIPIMS) has gained increasing scientific and industrial attention as it allows high plasma densities without the drawback of droplet formation. Recently, we showed that by a combination of HIPIMS with dc magnetron sputtering the properties of the coatings are comparable to those prepared solely with HIPIMS, but with the advantage of increased deposition rate.Here, we show that for CrN_HIPIMS/TiN_DCMS multilayered coatings the friction coefficient µ decreases from 0.7 to 0.35 (with an almost constant hardness H around 25 GPa, and modulus of indentation around 375 GPa) when decreasing the bilayer period λ from 7.8 to 6.4 nm, while keeping the CrN_HIPIMS layer thickness constant at 3.2 nm. A further reduction of the friction coefficient at room temperature dry-sliding testing to ∼ 0.25 or 0.05 is obtained when an additional HIPIMS cathode equipped with a Cr or Ti target material, respectively, is added to the process. Contact angle measurements of distilled water drops on as deposited film surfaces were carried out to investigate their wettability. The measurements show, that with increasing contact angle from 70° to 90°, for the individual coatings prepared, also their friction coefficient increases from ∼ 0.05 to ∼ 0.8. The depositions of all coatings were achieved with two- and threefold substrate rotation, which meet the industrial requirements of uniform deposition on complex shaped specimens.     

Synthesis and tribological properties of WSex films prepared by magnetron sputtering

WSe_x films with variable Se/W ratio were deposited by non-reactive r.f. magnetron sputtering from WSe₂ target changing the applied d.c. pulsed bias conditions and substrate temperature. The structural and chemical properties were measured by cross-sectional scanning electron microscopy (X-SEM), energy dispersive analysis (EDX), X-ray diffraction (XRD), Raman and X-ray photoelectron spectroscopy (XPS). The tribological properties were measured in ambient air (RH = 30–40%) and dry nitrogen by means of a reciprocating ball-on-disk tribometer. A clear correlation was found between the Se/W ratio and the measured friction coefficient displaying values below 0.1 (in ambient air) and 0.03 (in dry N₂) for ratios Se/W ≥ 0.6 as determined by electron probe microanalysis (EPMA). The results demonstrated that notable tribological results could be obtained even in ambient air (friction ≤ 0.07 and wear rate ≈10⁻⁷ mm³ Nm⁻¹) by controlling the film microstructure and chemical composition. By incorporating carbon, wear and chemical resistance can be gained by formation of non-stoichiometric carbides and/or alloying into the defective WSe_x hexagonal structure. The existence of a WSe₂ rich interfacial layer (either on the ball scar or embedded in the film track) was evidenced by Raman in low friction conditions. The improvement in tribological performance is therefore obtained by means of layered WSe_x, the formation of gradient composition from metallic W (hard) to WSe₂ (lubricant) and carbon incorporation.     

Tribological and mechanical behaviors of TiN/CNx multilayer films deposited by magnetron sputtering

TiN/CN_x multilayer films with bilayer periods of 4.5-40.3 nm were deposited by direct-current magnetron sputtering. Layer morphology and structure of the multilayered films were characterized by X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy and transmission electron microscopy. The TiN/CN_x multilayers exhibited coherent epitaxial growth due to the mutual growth-promoting effect at small bilayer period and some crystalline regions going through the interface of TiN/CN_x. Nanoindentation tests showed that the hardness of the multilayers varied from 12.5 to 31 GPa, with the highest hardness being obtained with a bilayer period of 4.5 nm. The tribological properties of the films were investigated using a ball-on-disk tribometer in humid air, and the TiN/CN_x multilayer with a bilayer period of 4.5 nm also exhibited the lowest friction coefficient and the highest wear resistance.     

Corrosion behavior of nanolayered TiN/NbN multilayer coatings prepared by reactive direct current magnetron sputtering process

TiN, NbN and TiN/NbN multilayer coatings were deposited on tool steel substrates using a reactive DC magnetron sputtering process. The coatings were characterized using X-ray diffraction, nanoindentation, atomic force microscopy, scanning electron microscopy (SEM) and energy-dispersive X-ray analysis. The corrosion behavior of TiN/NbN multilayer coatings was studied in 0.5 M HCl and 0.5 M NaCl solutions using potentiodynamic polarization and compared with single layered TiN and NbN coatings. Approximately 1.5 μm thick coatings of TiN, NbN and TiN/NbN multilayers showed good corrosion protection of the tool steel substrate and multilayer coatings performed better than single layered coatings. The corrosion behavior of the multilayers improved with total number of interfaces in the coatings. In order to conclusively demonstrate the positive effect of layering, corrosion behavior of 40-layer TiN/NbN multilayers was studied at lower coating thicknesses (32–200 nm) and compared with single layer TiN coatings of similar thicknesses. The polarization data and SEM studies of these coatings indicated that the corrosion behavior improved with coating thickness and multilayers showed better corrosion resistance as compared to the single layer coatings. Other studies such as intrinsic corrosion, effects of Ti interlayer and post-deposition annealing on the corrosion behavior of the multilayer coatings are also presented in this paper. The results of this study demonstrate that nanolayered multilayers can effectively improve the corrosion behavior of transition metal nitride hard coatings.     

Annealing temperature effects on ferromagnetism and structure of Si1−xMnx films prepared by magnetron sputtering

Si_1−xMn_x diluted magnetic semiconductor films were deposited on the p-Si (100) single crystal wafer using magnetron sputtering method. Post-rapid thermal annealing treatments were performed at temperatures of 700 °C, 800 °C, and 900 °C in an argon atmosphere for approximately 5 min. Alternating gradient magnetometer, scanning electron microscope, atomic force microscope, X-ray diffraction and X-ray absorption near-edge structure spectra were employed to characterize magnetic properties and structure of the as-grown and annealed films. The films were about 2.8 μm thick and the RMS roughness of the surface was about 5-10 nm. All samples exhibit ferromagnetism at room temperature and the saturation magnetization reaches at the maximum value for the sample annealed at 700 °C. The silicide MnSi_1.7 was observed in the annealed samples. X-ray absorption near-edge structure spectra indicated that Mn atoms preferred to occupy substitutional or interstitial sites instead of precipitating to form silicide when annealing at 700 °C. It is inferred that the observed ferromagnetism is attributed to the interstitial and substitutional Mn dimers, which existed mostly in the sample annealed at 700 °C. The weaker ferromagnetism of the 900 °C annealed sample was closely related to the increased content of Mn₄Si₇ compound.     

Mechanical properties of superhard TiB2 coatings prepared by DC magnetron sputtering

Superhard titanium diboride (TiB₂) coatings (H_v> 40 GPa) were deposited in Ar atmosphere from stoichiometric TiB₂ target using an unbalanced direct current (d. c.) magnetron. Polished Si (0 0 1), stainless steel, high-speed steel (HSS) and tungsten carbide (WC) substrates were used for deposition. The influence of negative substrate bias, U_s, and substrate temperature, T_s, on mechanical properties of TiB₂ coatings was studied. X-ray diffraction (XRD) analysis showed hexagonal TiB₂ structure with (0 0 01) preferred orientation. The texture of TiB₂ coatings was dependent upon the ion bombardment (U_s increased from 0 to −300 V) and the substrate heating (T_s increased from room temperature (RT) to 700 °C). All TiB₂ coatings were measured using microhardness tester Fischerscope H100 equipped with Vickers and Berkovich diamond indenters and exhibited high values of hardness H_v up to 34 GPa, effective Young's modulus E*=E/(1-ν) ranging from 450 to 600 GPa; here E and ν are the Young's modulus and Poisson's ratio, respectively, and elastic recovery W_e≈80%. TiB₂ coating with a maximum hardness H_v≈73 GPa and E*≈580 GPa was sputtered at U_s=−200 V and T_s=RT. Macrostresses of coatings σ were measured by an optical wafer curvature technique and evaluated by Stoney equation. All TiB₂ coatings exhibited compressive macrostresses.     

A comparative study of CrNx coatings Synthesized by dc and pulsed dc magnetron sputtering

Chromium nitride (CrN_x) coatings were prepared by reactively sputtering chromium metal target with various nitrogen flow rate percentages (f_N2) using a closed field unbalanced magnetron sputtering system operated in dc and middle frequency pulsed condition (100 kHz and 50% duty cycle). In this study, plasma examination proved that a large amount of ions with a wide range of ion energies (up to 65 eV and mainly from 10-30 eV region) was identified in the pulsed plasma compared to the low ion flux and energy (0-10 eV) in a dc discharged plasma. The results showed that the phase structure of CrN_x coatings was changed from nitrogen doped Cr(N) to pure β-Cr₂N, and to a mixture of β-Cr₂N and c-CrN and then to pure c-CrN phases with an increase in the f_N2 in both dc and pulsed conditions. However, the pulsed CrN_x coatings exhibit lower N concentrations than dc CrN_x coatings prepared under the same f_N2, which leads to the existing of β-Cr₂N phase within a wide range of f_N2 (30-50%). In comparison with the typical large columnar structure in the dc sputtered coatings, the pulsed CrN_x coatings exhibit dramatic microstructure improvements which benefited from the improved plasma density and ion bombardment from the pulsed plasma, where the super dense and nearly equi-axial structures were observed in a wide range of f_N2. The microstructure improvements contributed to the enhancements in the hardness and wear resistance of pulsed CrN_x coatings. In the pulsed CrN_x coatings, the hardness values were above 30 GPa when the f_N2 is in the range of 30-40%, which is related to the formation of the β-Cr₂N phase. With the formation of a mixture of β-Cr₂N and c-CrN phases in the coatings deposited with 40-50% f_N2, a low COF of 0.36 and wear rate of 1.66 × 10^− 6 mm³ N^− 1 m^− 1 can be achieved.     

Mo/SiO2 nanocomposite films for optical coatings prepared by vacuum magnetron sputtering

The embedding of metallic nanoparticles in the traditional optical materials (e.g. SiO₂) gives us the possibility to create new optical materials. Metallic particles of nanometric dimensions can be transparent in wide spectral ranges of light. The incorporation of nanocrystal inclusions in such nanocomposites provides the benefit of targeted manipulations of their macroscopic optical response. In this paper we present the possibility to create, using vacuum deposition methods, the nanocomposite coatings with fairly small refractivity.     

In-situ electrical characterization of ultrathin TiN films grown by reactive dc magnetron sputtering on SiO2

Ultrathin TiN films were grown by reactive dc magnetron sputtering on thermally oxidized Si (100) substrates. The electrical resistance of the films was monitored in-situ during growth in order to determine the minimum thickness of a continuous film. The coalescence thickness has a minimum of 1 nm at a growth temperature of 400 °C after which it increases with growth temperature. The minimum thickness of a continuous film decreases with increasing growth temperature from 2.9 nm at room temperature to 2.2 nm at 650 °C. In-situ resistivity measurements show that films grown at 500 °C and above are resistant to oxidation indicating high density. X-ray photoelectron spectroscopy and X-ray diffraction measurements show that the TiN grain stoichiometry and grain size increases with increasing growth temperature.     

Photo-fixation of SO2 in nanocrystalline TiO2 films prepared by reactive DC magnetron sputtering

We report on photo-fixation of SO₂ onto nanostructured TiO₂ thin films prepared by reactive DC magnetron sputtering. The films were exposed to 50 ppm SO₂ gas mixed in synthetic air and illuminated with UV light at 298 and 473 K. The evolution of the adsorbed SO_x species was monitored by in situ Fourier transform infrared specular reflection spectroscopy. Significant photo-fixation occurred only in the presence of UV illumination. The SO₂ uptake was dramatically enhanced at elevated temperatures and then produced strongly bonded surface-coordinated SO_x complexes. The total SO_x uptake is consistent with Langmuir adsorption kinetics. The sulfur doping at saturation was estimated from X-ray photoelectron spectroscopy to be ~ 2.2 at.% at 473 K. These films were pale yellowish and had an optical absorption coefficient being ~ 3 times higher than in undoped film. The S-doped films exhibit interesting oleophobic properties, exemplified by the poor adherence of stearic acid. Our results suggest a new method for sulfur doping of TiO₂ to achieve combined anti-grease and photocatalytic properties.     

Synthesis and characterization of zirconium oxynitride ZrOxNy coatings deposited via unbalanced DC magnetron sputtering

A study of structure, morphology, and corrosion resistance was performed on zirconium oxynitride thin films deposited on 304 and 316 stainless steels by the DC sputtering magnetron unbalance technique. Structural analysis was carried out using X-ray diffraction (XRD), while morphological analysis was performed by scanning electron microscopy (SEM), atomic force microscopy (AFM), and transmission electron microscopy (TEM). These studies were performed as a function of deposition time via DC sputtering at room temperature (287 K) with an Ar/air flow ratio of 3.0 and a total deposition time of 30 min. The oxynitride films were grown with cubic crystalline structures Zr₂ON₂ and preferentially oriented along the (222) plane. Chemical analysis determined that in the last 5.0 nm, the Zr coatings present the following spectral lines: Zr3d_3/2 (184.6 eV) and 3d_5/2 (181.7 eV), O1s (531.3 eV), and N1s (398.5 eV).     

Depth redistribution of components of SiOx layers prepared by magnetron sputtering in the process of their decomposition

The process of thermal decomposition of SiO_x layers prepared by magnetron co-sputtering of Si and SiO₂ on Si and quartz substrates is studied by Auger and secondary ion mass spectroscopies. It is found that high temperature annealing of the layers causes a Si-depleted region near the layer/substrate interface. It is shown that the formation of this region does not depend on the type of substrate but depends on the content of excess Si and is observed at high content of excess Si. When the excess Si content decreases, the Si-depleted region at first smears and then disappears. The mechanism of SiO_x decomposition and possible reasons for the appearance of the Si-depleted region are discussed.     

Structural studies of ZnS thin films grown on GaAs by RF magnetron sputtering

X-ray diffraction (XRD) studies of ZnS thin films grown on GaAs (001) substrates at different temperatures by rf magnetron sputtering have been carried out using CuKα radiation. XRD analysis reveals that deposited films below 335 °C, assumed the zinc blend structure. Samples annealed at above 335 °C showed mixed phases of the zinc blend and wurzite structures. Information about crystallite size is obtained from (001), (111) and (104) diffraction peaks. The average crystallite size of the film was determined to be ∼ 32 nm using the Scherrer formula.     

Reactive pulse magnetron sputtered SiOxNy coatings on polymers

Amorphous SiO₂, Si₃N₄ and SiO_xN_y single layers have been deposited on silicon, glass and glycol modified polyethylene terephthalate substrates by reactive pulse magnetron sputtering. Apart from the expected correlation between refractive index, coating density and nitrogen content in the reactive gas mixture further results have been found regarding mechanical stress and the humidity barrier property of these thin films. The lowest compressive stress was observed in the coatings deposited with nitrogen contents of around 30% to 50% in the reactive gas mixture. The humidity barrier effect of the thin films already begins to increase significantly at low nitrogen contents of below 20% in the reactive gas. Additional investigations regarding chemical composition, coating adhesion and environmental stability complement this work with the main focus on optimizing these materials for optical multilayer systems on polymer substrates.     

Characterization of Mo-Al-N nanocrystalline films synthesized by reactive magnetron sputtering

Mo-Al-N films were deposited by a dc reactive magnetron sputtering technique. The effects of N₂ partial pressure, substrate temperature, and aluminum content on the phase composition, microstructure, hardness and oxidation resistance of the films were studied. The MoAlN films as prepared are fcc Mo₂N structure where partial Mo sites were substituted by Al, and the grain size of the crystallites increased from 8 to 30 nm when the Al concentration was increased from 6% to 33%. In the Mo_0.94Al_0.06N film, the hardness can reach 29 GPa, which is much higher than that in binary Mo-N systems. The oxidation resistance temperature of Mo-Al-N film with an Al content of 6% was higher than that of Mo-N films, and with further addition of Al content, the oxidation resistance temperature increased slightly.     

Optical and electrical properties of hydrogenated amorphous Si1-xGex alloy thin films prepared by planar magnetron sputtering

Thin films of hydrogenated amorphous Si_1-xGe_x were prepared by the r.f. diode planar magnetron sputtering method using composite targets of silicon and germanium in an atmosphere of H₂ diluted with argon. The optical absorption coefficient, d.c. conductivity, photoconductivity and IR transmission spectra were measured, and the dependence of these characteristics on the germanium content x was investigated. For films with x ≈ 0.1, it is found that the dark conductivity decreases and the ratio of the photoconductivity to the dark conductivity increases by about one order of magnitude compared with those for hydrogenated amorphous silicon. This phenomenon seems to be caused by a reorganization of the tetrahedrally bonded structure. Films of this composition are considered to be of interest as an opto-electronic material requiring a high resistance. Photoconductive effects are not observed for films with x > 0.3. This is considered to be due to an alloying effect. The decrease in the amount of bonded hydrogen in the films becomes appreciable for the films with x > 0.6.     

Optical properties of nanocrystalline ZnS films prepared by high pressure magnetron sputtering

Nanocrystalline ZnS films with different thickness (10–40 nm) were deposited onto quartz and NaCl substrates by magnetron sputtering of a ZnS target in argon plasma. All the films showed a zinc blende structure and the photoluminescence peak positions depended on the surface to volume ratio of the films. The optical absorption in these films could be explained by the combined effects of phonon and inhomogeneity broadening along with optical loss due to light scattering at the nanocrystallites.     

Microstructure and hardness of SiC-TiC nanocomposite thin films prepared by radiofrequency magnetron sputtering

Silicon carbide-titanium carbide (SiC-TiC) nanocomposite thin films were prepared by radiofrequency magnetron sputtering using SiC-TiC composite targets fabricated by spark plasma sintering. The SiC thin films were amorphous at substrate temperatures below 573 K and crystallized in the cubic crystal system (3C) at substrate temperatures greater than 773 K. Cubic SiC-TiC nanocomposite thin films, which contain a mixture of 3C-SiC and B1-TiC phases, were obtained at a TiC content of greater than 20 mol%. The amorphous films possessed a dense cross-section and a smooth surface. The morphology of the SiC-TiC nanocomposite thin films changed from granular to columnar with increasing substrate temperature. The SiC-TiC nanocomposite thin films prepared at TiC content of 70-80 mol% and substrate temperature of 573 K showed the highest hardness of 35 GPa.