Deposition of nanolayered CrN/AlBN thin films by cathodic arc deposition: Influence of cathode arc current and bias voltage on the mechanical properties

Thin films of CrAlBN were deposited on SKD 11 tool steel substrate using Cr and AlB cathodes in a cathodic arc plasma deposition system. The influence of AlB cathode arc current and substrate bias voltage on the mechanical and the structural properties of the films was investigated. The CrAlBN thin films had a multilayered structure in which the nano-crystalline CrN layer alternated with the amorphous AlBN layer. The hardness of the films increased as the AlB cathode arc current was raised from 35 to 45 A, and then decreased with further increase of the current. The hardness of the films increased rapidly with the increase of the bias voltage from − 50 to − 150 V. Further increase in the bias voltage decreased the hardness. The maximum hardness of 48 GPa was obtained at the bias voltage of − 150 V. With the increase of bias voltage, a good correlation between the residual stress and the hardness of the films was observed.     

Deposition of dense and smooth Ti films using ECR plasma-assisted magnetron sputtering

We report high quality Ti films grown in a novel electron cyclotron resonance (ECR) plasma-assisted magnetron sputtering (PMS) deposition system. The films are compared with films deposited by conventional direct current (DC) magnetron sputtering. Using ECR-PMS, the argon plasma bombardment energy and Ti film deposition rate can be controlled separately, with the substrate bias voltage under feedback control. Results from SEM, AFM, XRD and PAS (scanning electron microscopy, atomic force microscopy, X-ray diffraction and positron annihilation spectroscopy) show that the properties of Ti films prepared by ECR-PMS are greatly improved compared with conventional sputtering. SEM and AFM confirmed that ECR-PMS Ti films have a dense, smooth, mirror-like surface. Increasing the substrate bias of the ECR plasma from − 23 V to − 120 V while keeping a fixed sputtering bias voltage of − 40 V, the intensity of the (100) reflection of Ti film was a little strengthened, but (002) remained strongly preferred orientation. The XRD peak broadening of ECR-PMS Ti films is more than for conventional magnetron sputtering, due to grain refinement induced by Ar ion bombardment. Doppler broadening of PAS analysis reveals that the Ti films have fewer vacancy defects compared with films prepared by the conventional magnetron.     

Cathodic arc plasma deposition of nano-multilayered ZrN/AlSiN thin films

Thin films of ZrN/AlSiN were deposited on SKD 11 tool steel substrate using Zr and AlSi cathodes in an Ar/N₂ gas mixture in a cathodic arc plasma deposition system. The influence of the AlSi cathode arc current and the substrate bias voltage on the mechanical and structural properties of the films was investigated. X-ray diffraction, electron probe micro-analysis, high resolution transmission electron microscopy, nanoindentation and profilometry were used to characterize the films. The ZrN/AlSiN thin films had a multilayered structure by rotating the substrate in which nano-crystalline ZrN layers alternated with amorphous AlSiN layers. The hardness of the films increased as the AlSi cathode arc current was raised from 35 to 40 A, and then decreased with a further increase of the current. The hardness of the films increased with the increase of the bias voltage from − 50 to − 100 V. Further increase in the bias voltage decreased the hardness. The films exhibited a maximum hardness of 38 GPa. With the increase of bias voltage, the residual stress of the films correlated well with the hardness.     

Influence of substrate bias, deposition temperature and post-deposition annealing on the structure and properties of multi-principal-component (AlCrMoSiTi)N coatings

Nitride films are deposited from a single equiatomic AlCrMoSiTi target by reactive DC magnetron sputtering. The influence of the substrate bias and deposition temperature on the coating structure and properties are investigated. The bias is varied from 0 to − 200 V while maintaining a substrate temperature of 573 K. And the temperature is changed from 300 to 773 K whilst maintaining a substrate bias of − 100 V. From X-ray diffraction analysis, it is found that all the as-deposited coatings are of a single phase with NaCl-type FCC structure. This is attributed to the high mixing entropy of AlN, CrN, MoN, SiN, and TiN, and the limited diffusion kinetics during coating growth. Specific aspects of the coating, namely the grain size, lattice constant and compressive stress, are seen to be influenced more by substrate bias than deposition temperature. In fact, it is possible to classify the deposited films as large grained (~ 15 nm) with a reduced lattice constant (~ 4.15 Å) and low compressive residual stresses for lower applied substrate biases, and as small grained (~ 4 nm) with an increased lattice constant (~ 4.25 Å) and high compressive residual stresses for applied biases of − 100 V or more. A good correlation between the residual stress and lattice constant under various deposition conditions is found. For the coatings deposited at − 100 V, and at temperatures above 573 K, the hardness could attain to the range of 32 to 35 GPa.Even after annealing in vacuum at 1173 K for 5 h, there is no notable change in the as-deposited phase, grain size or lattice constant of the coatings but an increase in hardness. The thermal stability of microstructure is considered to be a result of the high mixing entropy and sluggish diffusion of these multi-component coatings. For the anneal hardening it is proposed that the overall bonding between target elements and nitrogen is enhanced by thermal energy during annealing.     

Effect of bias voltage on microstructure and properties of Ti-doped graphite-like carbon films synthesized by magnetron sputtering

Ti-doped graphite-like carbon (GLC) films with different microstructures and compositions were fabricated using magnetron sputtering technique. The influence of bias voltages on microstructure, hardness, internal stress, adhesion strength and tribological properties of the as-deposited GLC films were systemically investigated. The results showed that with increasing bias voltage, the graphite-like structure component (sp² bond) in the GLC films increased, and the films gradually became much smoother and denser. The nanohardness and compressive internal stress increased significantly with the increase of bias voltage up to −300 V and were constant after −400 V. GLC films deposited with bias voltages in the range of -300--400 V exhibited optimum adhesion strength with the substrates. Both the friction coefficients and the wear rates of GLC films in ambient air and water decreased with increasing voltages in the lower bias range (0--300 V), however, they were constant for higher bias values (beyond −300 V) . In addition, the wear rate of GLC films under water-lubricated condition was significantly higher for voltages below −300 V but lower at high voltage than that under dry friction condition. The excellent tribological performance of Ti-doped GLC films prepared at higher bias voltages of −300--400 V are attributed to their high hardness, tribo-induced lubricating top-layers and planar (2D) graphite-like structure.     

Deposition of BN films on metal substrates from a fluorine-containing plasma

Boron nitride (BN) films were deposited on Mo, W, Ni, Ti and Zr substrates by DC arc jet chemical vapor deposition using a gas mixture of Ar-N₂-BF₃-H₂ at 50 Torr, a substrate temperature of 850-1150 °C, and a − 85 V substrate bias. Cubic BN (c-BN) films showing clear c-BN Raman peaks were obtained on Mo and W, but they did not adhere well to the substrates. Hexagonal or turbostratic BN was deposited predominantly on Ni substrates, which is similar to the preferable deposition of graphitic carbons in diamond CVD. High quality c-BN films with good adhesion were obtained on Ti and Zr. The reasons for these differences among metal substrates are discussed.     

Mechanical and tribological properties of multi-element (AlCrTaTiZr)N coatings

Multi-element (AlCrTaTiZr)N coatings are deposited onto Si and cemented carbide substrates by reactive RF magnetron sputtering in an Ar + N₂ mixture. The influence of substrate bias voltage, ranging from 0 to − 200 V, on the microstructural, mechanical and tribological properties of these nitride coatings is studied. A reduction in concentration of N and Al is observed with increasing substrate biases. The (AlCrTaTiZr)N coatings show the face-centered-cubic crystal structure (B1-NaCl type). The use of substrate bias changes the microstructure of the (AlCrTaTiZr)N coating from the columns with microvoids in boundaries to the dense and less identified columns. The compressive macrostress increases from − 0.9 GPa to − 3.6 GPa with an increase of substrate bias. The hardness and adhesion increase to peak values of 36.9 GPa and 60.7 N at the bias voltage of − 150 V, respectively. The tribological properties of the (AlCrTaTiZr)N coatings against 100Cr6 steel balls are evaluated by a ball-on-disc tribometer with a 10 N applied load. With an increase of substrate bias, the wear rate reduces while the friction coefficient almost keeps constant at 0.75. The lowest wear rate of 3.65 × 10^− 6 mm³/Nm is obtained for the (AlCrTaTiZr)N coating deposited at the bias voltage of − 150 V.     

Cathodic arc plasma deposition of nano-multilayered Zr-O/Al-O thin films

Thin films of Zr-O/Al-O were deposited on SKD 11 tool steel substrate using Zr and Al cathodes in a cathodic arc plasma deposition system. The substrates were mounted on a rotating holder which alternatively exposed them to plasma from the two cathodes. The influence of the Zr and Al cathode arc currents and the substrate bias on the mechanical and the structural properties of the films were investigated. Films with a nano-layered structure of alternating Al-rich and Zr-rich layers were obtained. The Zr layers contained nano-crystallites of (101) oriented t-ZrO structure. Crystallites with α-Al₂O₃ structure were observed only when the substrate was negatively biased in the 100-150 V range. The hardness of the film decreased with the increase of Zr cathode current from 60 to 80 A, increased when the Al cathode current increased from 25 to 30 A, and decreased when the Al cathode current increased from 30 to 35 A. The hardness of the film increased with the increase of bias voltage up to − 150 V and then decreased with further increase of the negative bias. The film structure was elucidated by HRTEM microscopy. Good correlation between the residual stress and the hardness enhancement of the films was observed.     

X-ray reflectivity studies on DLC films deposited by microwave ECR CVD: Effect of substrate bias

Diamond like carbon (DLC) films were deposited at room temperature on Si (111) substrates by microwave electron cyclotron resonance (ECR) plasma chemical vapor deposition (CVD) process using plasma of methane diluted with argon gas. During deposition, dc self bias (− 25 V to − 200 V) on substrate was varied by application of RF power to the substrate. The influence of substrate bias on density of the deposited films was studied by X-ray reflectivity (XRR). The results from these measurements are further correlated with the results from UV and visible Raman spectroscopy. DLC film is modeled as a structure having three different layers such as low density surface, bulk and interface with the substrate. This three-layer model is used to fit the measured XRR data to evaluate the surface, interface and interlayer roughness, thickness and density of these films. The surface roughness obtained from XRR is correlated with the results from Atomic Force Microscopy (AFM) measurements. The observed results are explained based on the subplantation model for DLC film growth.     

Density, stress, hardness and reduced Young's modulus of W-C:H coatings

Density, hardness and compressive stress of tungsten contained in an amorphous-hydrogenated-carbon matrix (W-C:H) have been studied as a function of composition and bias voltage. W-C:H coatings were deposited by reactive sputter deposition from a tungsten-carbide (WC) target on silicon substrate in an argon-acetylene plasma. W-C:H coatings obtained at different acetylene flow rates and substrate bias voltages, were characterized by scanning electron microscopy, X-ray diffraction, nanoindentation and substrate curvature method. It has been observed that compressive stress, hardness and reduced Young's modulus decrease when the acetylene flow is increased from 0 to 10 sccm. Also, compressive stress and hardness increases with the substrate bias voltage. In particular, for W-C:H coatings obtained at 5 sccm of acetylene flow, the compressive stress and hardness increase from − 1.6 GPa to − 3.2 GPa and from 19 GPa to 24 GPa, respectively, when increasing the substrate bias from 0 to 200 V. The variation of the internal stress, hardness and density of the coatings is discussed in terms of composition and structure of the W-C:H coatings.     

Structure-property relations of arc-evaporated Al-Cr-Si-N coatings

The addition of silicon to the widely used aluminum-containing transition metal nitrides is promising for the synthesis of hard and thermally stable films with good oxidation resistance. For that reason, Al-Cr-Si-N coatings were deposited by reactive cathodic arc-evaporation under industrial conditions from Al₇₀Cr_30 − xSi_x (x = 0, 1, 2, 5 at.%) targets at substrate bias voltages ranging from − 40 V to − 150 V. The structure of the well adherent coatings was investigated by X-ray diffraction and Raman spectroscopy, which indicated at higher Al/Cr ratio > 1.9 an increased tendency of the metastable face-centered cubic solid solution of AlN in CrN to separate into a cubic-hexagonal phase mixture. At higher bias voltages, this effect is gradually inverted and the single cubic phase can be retained. X-ray photoelectron spectroscopy revealed dominant Si-N bonds suggesting either a substitutional solid solution or a separate Si-N phase. Mechanical properties, i.e. hardness and elastic modulus, measured by indentation together with stress evolution demonstrate the beneficial effect of the conservation of the metastable cubic phase.     

Composition and mechanical properties of AlC, AlN and AlCN thin films obtained by r.f. magnetron sputtering

Aluminum carbide (Al-C), aluminum nitride (Al-N), and aluminum carbonitride (Al-C-N) thin films were grown onto Si [100] substrates by r.f. reactive magnetron sputtering at 400 °C. The Al-N coatings were obtained by sputtering of Al (99.9%) target in Ar/N₂ atmosphere and the Al-C and Al-C-N by co-sputtering of a binary (50% Al, 50% C) target in argon and in Ar/N₂ mixture, respectively. The d.c. bias voltage was varied between 0 and − 150 V. The films were characterized by X-ray diffraction (XRD), energy dispersive X-ray spectroscopy (EDS), Fourier transformed infrared spectroscopy (FTIR) and the mechanical properties by nanoindentation. The structure of the films has been determined by XRD, which shows that amorphous films are formed in all cases. The variation of polarization bias voltage produced chemical differences in the films. As the bias voltage is increased, the Al content is reduced in all three materials. The nitrogen content also varied between 10 and 14 at.% for Al-N coatings, remaining practically constant (21 at.%) for the Al-C-N films. The Berkovich hardness results were 7.0, 17.2 and 9.2 GPa for Al-C, Al-N, and Al-C-N films, respectively.     

Magnetron reactively sputtered Ti-DLC coatings on HNBR rubber: The influence of substrate bias

In this study, Ti-containing diamond-like carbon (Ti-DLC) coatings have been deposited on HNBR (hydrogenated nitrile butadiene) rubber and also on Si wafer as reference via unbalanced magnetron reactive sputtering from a Ti target in C₂H₂/Ar plasma. The deposition rates of coatings on rubber and Si wafer were about the same. Columnar structures resulting from a rough interface were often observed in the coatings deposited on rubbers. Only at a high bias voltage of − 300 V the coating on HNBR rubber became column-free whereas a bias voltage of − 100 V could already restrain the columnar structure and thus produced dense and smooth coatings on Si wafer. A segmented morphology of the coatings on HNBR rubber is formed as a result of the large difference in thermal expansion between the coating and HNBR rubber. The crack network that separates the patches plays an important role in maintaining the coating flexibility. The size of the patches reduces with increasing bias voltage and thus the variation of deposition temperature. A high bias voltage enhances the hardness of Ti-coating and the rubber-coating adhesion, and guarantees a good tribological performance. When sliding against ø6 mm 100Cr6 steel ball counterpart, very low coefficients of friction were achieved (< 0.25 for the coated rubber versus > 1.3 for the uncoated). The Ti-DLC coating can be considered as a promising material for the enhancement of tribological performance of rubbers.     

Influence of EDTA concentration on the structure and properties of SnS films prepared by electro-deposition

Tin sulfide (SnS) thin films were deposited onto indium tin oxide (ITO) glass substrates by cathodic electro-deposition from aqueous solution containing ethylene diamine tetraacetate acid (EDTA). Because EDTA can slow the deposition rate of Sn through formation of Sn chelates, it is possible to obtain stoichiometric SnS films with good quality by adding EDTA to the deposition bath. The deposited films were characterized with X-ray diffraction (XRD), atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), Raman spectroscopy (Raman), and ultraviolet-visible-near infrared (UV-VIS-NIR) spectrophotometer. The as-deposited films are mainly polycrystalline SnS with orthorhombic crystalline structure, and they show good uniformity and surface coverage with root mean square (RMS) roughness of 45.36-62.39 nm and grain sizes of 100-300 nm. Raman microscopy shows that the films have bands at around 190 and 218 cm^− 1 belonging to A_g mode of SnS. The concentration ratio of EDTA and Sn²⁺ (EDTA/Sn²⁺) has some influence on the structure, phase, Raman shift and optical properties of the deposited films. When the EDTA/Sn²⁺ is less than 0.5, the films have a Raman shift at around 306 cm^− 1 due to Sn₂S₃. XPS analysis also shows that there exists a Sn₂S₃ phase in the deposited films. When the EDTA/Sn²⁺ equals 1/1, there is only the SnS phase in the deposited films. With an increase of the EDTA/Sn²⁺ from 0.1 to 1, the direct band gap of the films is decreased from 1.75 eV to 1.43 eV. Therefore EDTA/Sn²⁺ = 1/1 is good for depositing SnS films.     

The effect of nitrogen pressure on cathodic arc deposited NbN thin films

NbN thin films were deposited on non-standard grade high speed steel (HSS) (79.90 wt.% Fe, 0.71 wt.% C, 6.09 wt.% W, 4.52 wt.% Mo, 3.95 wt.% Cr, 1.82 wt.% Co, 1.75 wt.% V and a hardness of 65 HRC) using cathodic arc deposition at 0.125, 0.5, 1.0 and 1.5 Pa nitrogen pressures (P_N2), with a bias voltage of − 150 V. X-ray diffraction (XRD), Scanning Electron Microscope (SEM), Nanoindentation and Rockwell C analysis were used to characterize the thin films in order to identify the NbN phases and to investigate the influence of P_N2 on mechanical properties. Hexagonal β-Nb₂N, ε-NbN and δ′-NbN_0.95 are identified in XRD analysis. Hardness values derived by nanoindentation technique are 20 GPa for β-Nb₂N, ε-NbN and 40 GPa for δ'-NbN_0.95. Due to the complexity of phase system special attention was focused on identification of NbN phases by deconvolating the XRD peaks especially at 0.5 Pa in which both ε-NbN and β-Nb₂N were found. Rockwell C analysis revealed that the film adhesion is found to be poor at lower P_N2, due to the brittle nature of β-Nb₂N.     

Effect of substrate bias in amorphous carbon films having embedded nanocrystallites

The effect of substrate bias on the structural, morphological, electrical and mechanical properties of amorphous carbon (a―C) films having embedded nanocrystallites deposited by filtered cathodic jet carbon arc technique has been investigated. X-ray diffraction exhibits predominantly an amorphous nature of the film. High resolution transmission electron microscope investigations reveal largely an amorphous structure. However, an ultra-fine nanograined microstructure with the average grain size between 20 and 50 nm was observed throughout the entire film and the majority of the individual grains were single crystallites with the preferred interplanar spacing of about 0.2 nm. All the parameters evaluated were seen to depend strongly on the negative substrate bias and exhibit maxima or minima in the properties of the films deposited at − 150 V substrate bias. These a-C films having embedded nanocrystallites act as hard coating materials.     

Effect of applied dc bias voltage on composition, chemical bonding and mechanical properties of carbon nitride films prepared by PECVD

Carbon nitride films were deposited on Si (100) substrates using plasma-enhanced chemical vapor deposition (PECVD) technique from CH4 and N2 at different applied dc bias voltage. The microstructure, composition and chemical bonding of the resulting films were characterized by Raman spectroscopy, Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD). The mechanical properties such as hardness and elastic modulus of the films were evaluated using nano-indentation. As the results, the Raman spectra, showing the G and D bands, indicate the amorphous structure of the films. XPS and FTIR measurements demonstrate the existence of various carbon-nitride bonds in the films and the hydrogenation of carbon nitride phase. The composition ratio of N to C, the nano-hardness and the elastic modulus of the carbon nitride films increase with increasing dc bias voltage and reach the maximums at a dc bias voltage of 300 V, then they decrease with further increase of the dc bias voltage. Moreover, the XRD analyses indicate that the carbon nitride film contains some polycrystalline C3N4 phase embedded in the amorphous matrix at optimized deposition condition of dc bias voltage of 300 V.     

Influence of bias voltage on morphology and structure of MgO thin films prepared by cathodic vacuum arc deposition

MgO thin films with high optical transmittance were prepared by cathodic vacuum arc deposition technique. Rutherford backscattering spectroscopy, atomic force microscopy and X-ray diffraction were used to investigate the influences of the negative pulse bias voltage on the composition, the morphology and the crystal structure of MgO thin films, respectively. AFM images show that the grain growth is influenced by high energy ions under bias voltage and that the grains deposited at the pulse bias voltage with set value of |V_p| = 600 V stack densely and look the largest as compared to those prepared at different set V_p. The RBS spectra indicate that the Mg/O ratio is about 0.95-1.00 in MgO thin films which is nearly the stoichiometric composition of bulk MgO. The Mg/O ratio increases with set |V_p| until |V_p| is 450 V, and then keeps almost unchanged with set |V_p| up to 750 V. The MgO thin films have a combined orientation of (100) and (110). Below − 150 V, the (100) orientation is predominant and the intensity ratio of I₂₂₀/I₂₀₀ increases with set |V_p|.     

Characteristics of copper oxide films deposited by PBII&D

Copper oxide films were deposited by plasma based ion implantation and deposition using a copper antenna as rf sputtering ion source. A gas mixture of Ar + O₂ was used as working gas. During the process, copper that was sputtered from the rf antenna reacted with oxygen and was deposited on a silicon substrate. The composition and the chemical state of the deposited films were analyzed by XPS. The structure of the films was detected by XRD. It is observed that Cu₂O film has been prepared on the Si substrate. It is found that the microstructure of the deposited film is amorphous for the applied voltage of − 5 kV. The surface layer of the deposited films is CuO. This is because the surface layer absorbs the oxygen from ambient air after the treated sample was removed from the vacuum chamber. An appropriate applied voltage, 2 kV under the present conditions, brings the lowest resistance. It is also seen that the maximum absorbance of the deposited films moves to a lower wavelength with increased applied voltage.     

The effect of substrate bias voltage on PbTe films deposited by magnetron sputtering

The PbTe films were deposited onto ITO glass substrate by radio frequency magnetron sputtering. Effect of external direct current electrical field applied between substrate and target on the quality of films was investigated. Stylus surface profile, X-ray diffraction (XRD), atomic force microscope (AFM) and Fourier transform infrared spectroscopy (FTIR) were used to characterize the films. The film thickness was measured by a conventional stylus surface profile. The crystal structure and lattice parameters of films were determined by using XRD. The surface morphology of the films was measured by AFM. The absorption coefficients and optical band gaps of films were found from FTIR. The sheet resistance of the samples was measured with a four-point probe and the resistivity of the film was calculated. All the obtained films were highly textured with a strong (2 0 0) orientation. With increasing bias voltage to −30 V, the property of crystal structure, surface morphology and absorption coefficients and resistivity were improved. However, further increase of substrate bias leads to transformation of the property.