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.     

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.     

Mechanical properties of high-density diamond like carbon (HD-DLC) films prepared using filtered arc deposition

Because high density DLC (HD-DLC) films prepared using filtered arc deposition (FAD) systems possess high hardness, low friction coefficients, and a smooth surface, they have been good candidates for use in tribological applications. The aim of present work is the investigation of the mechanical and structural properties of HD-DLC films.The experimental conditions were the following: arc current, 50 A; base pressure, less than 3 × 10^− 3 Pa; substrate bias, DC-100 V; substrate temperature, less than 100 °C. The HD-DLC films were formed on silicon wafers and tungsten carbide (WC) substrates. The film properties of hardness, composition, structure, and friction were analyzed.The film hardness is high, 80-90 GPa, with a low friction coefficient of less than 0.1.     

Hexagonal diamond formation on steel substrates by negative bias microwave plasma enhanced chemical vapor deposition

This paper reports for the first time the synthesis of hexagonal diamond thin films on high-speed steel substrates by multi-mode microwave plasma enhanced chemical vapor deposition. Before deposition of the films, the substrate surface was treated by scratching with diamond powder. The deposited films were characterized by X-ray diffraction (XRD), Raman spectroscopy and scanning electron microscopy. The XRD patterns of (100) and (101) planes and the Raman peaks at ~ 1317-1322 cm^− 1 were observed, confirming the formation of hexagonal diamond phase in the prepared films. The effects of voltage bias on the phase formation, microstructure and hardness of the films were also studied by setting the voltage to 0, − 70, − 150 and − 190 V. The highest hardness of 23.8 GPa was found in the film having clusters of size about 550 nm deposited under a bias voltage of − 150 V. These clusters were built up of grains of size about 14 nm.     

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.     

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.     

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.     

Study on nanocrystalline Cr2O3 films deposited by arc ion plating: I. composition, morphology, and microstructure analysis

Nanocrystalline Cr₂O₃ thin films were deposited on silicon wafers with (100) orientation by arc ion plating (AIP) technique at various negative bias voltages. By virtue of X-ray diffraction analysis, scanning electron microscope, and high-resolution transmission electron microscope, the influence of substrate bias voltage on the film growth process, microstructure, and characteristics was investigated systematically, including the phase constituents, grain size, lattice constant, chemical compositions, as well as surface and cross-section morphologies. With increasing the bias voltage, the grain size and lattice constant of AIP Cr₂O₃ films first decreased slightly, and then increased gradually again. Both reached the minimum (35 nm and 13.57 Å) when the bias voltage was − 100 V. However, the bias voltage had little effect on the phase constituents and chemical compositions of AIP Cr₂O₃ films. During the film growth process, the surfaces of Cr₂O₃ films were getting smoother with the negative bias voltage increase, in the meantime, their microstructures evolved from coarse columnar grains to fine columnar grains, short columnar recrystallized grains, and fine columnar grains again.     

Study on nanocrystalline Cr2O3 films deposited by arc ion plating: II. Mechanical and tribological properties

In this work, the influence of substrate bias voltage on the microhardness, adhesive strength, friction coefficient, and wear rate of AIP Cr₂O₃ films deposited on AISI 304 stainless steel substrates was investigated systematically. In the meantime, the wear failure mechanism of AIP Cr₂O₃ films in dry sliding contact was also analyzed and discussed. The results showed that the mechanical properties, adhesive behaviors, and tribological performance of AIP Cr₂O₃ films were greatly altered by applying a negative bias voltage. With increasing the bias voltage, the hardness, critical load, and tribological performance of AIP Cr₂O₃ films first were improved gradually, and then were impaired slightly again. When the bias voltage is − 100 V, the Cr₂O₃ film possessed the highest hardness, the strongest adhesion, and the best wear resistance. The essence of above phenomena was attributed to the variations of microstructure and defect density in the films induced by the substrate bias voltage increase. The main wear failure mechanism of AIP Cr₂O₃ films is crack initiation and propagation under the high contact stresses, inducing the local film with small area to flake off gradually, and eventually leading to the formation of a wear scar.     

Effect of the aluminium content and the bias voltage on the microstructure formation in Ti1 − xAlxN protective coatings grown by cathodic arc evaporation

The effect of aluminium contents and bias voltage on the microstructure of cathodic arc evaporated Ti_1 − xAl_xN coatings was investigated with the aid of X-ray diffraction experiments and transmission electron microscopy. The coatings were deposited from mixed Ti-Al targets with different Ti:Al ratios (60:40, 50:50, 40:60 and 33:67) at bias voltages ranging between − 20 V and − 120 V. The microstructure of the coatings was described in terms of the phase composition, crystallite size and residual stress and related to the indentation hardness. The microstructure features were found to be related to the uniformity of the local distribution of Ti and Al in (Ti,Al)N, which was controlled, for a certain overall chemical composition of the coatings, by the bias voltage. The consequences of large local fluctuations of the Ti and Al concentrations in Ti_1 − xAl_xN that occurred at higher bias voltages were the phase segregation, which was indicated through the formation of the fcc-(Ti,Al)N/fcc-AlN nanocomposites and the increase of the compressive residual stress in the face-centred cubic (Ti,Al)N. Concurrently, the increasing bias voltage contributed significantly to the reduction of the crystallite size. Higher residual stress and smaller crystallite size increased the hardness of the coatings. The overall chemical composition of the coatings influenced mainly their phase composition. The high concentration of Al in (Ti,Al)N led to the formation of wurtzitic AlN in the coatings.     

Filtered vacuum arc deposition of undoped and doped ZnO thin films: Electrical, optical, and structural properties

Filtered vacuum (cathodic) arc deposition (FVAD, FCVD) of metallic and ceramic thin films at low substrate temperature (50-400 °C) is realized by magnetically directing vacuum arc produced, highly ionized, and energetic plasma beam onto substrates, obtaining high quality coatings at high deposition rates. The plasma beam is magnetically filtered to remove macroparticles that are also produced by the arc. The deposited films are usually characterized by their good optical quality and high adhesion to the substrate. Transparent and electrically conducting (TCO) thin films of ZnO, SnO₂, In₂O₃:Sn (ITO), ZnO:Al (AZO), ZnO:Ga, ZnO:Sb, ZnO:Mg and several types of zinc-stannate oxides (ZnSnO₃, Zn₂SnO₄), which could be used in solar cells, optoelectronic devices, and as gas sensors, have been successfully deposited by FVAD using pure or alloyed zinc cathodes. The oxides are obtained by operating the system with oxygen background at low pressure. Post-deposition treatment has also been applied to improve the properties of TCO films.The deposition rate of FVAD ZnO and ZnO:M thin films, where M is a doping or alloying metal, is in the range of 0.2-15 nm/s. The films are generally nonstoichiometric, polycrystalline n-type semiconductors. In most cases, ZnO films have a wurtzite structure. FVAD of p-type ZnO has also been achieved by Sb doping. The electrical conductivity of as-deposited n-type thin ZnO film is in the range 0.2-6 × 10^− 5 Ω m, carrier electron density is 10²³-2 × 10²⁶ m^− 3, and electron mobility is in the range 10-40 cm²/V s, depending on the deposition parameters: arc current, oxygen pressure, substrate bias, and substrate temperature. As the energy band gap of FVAD ZnO films is ∼ 3.3 eV and its extinction coefficient (k) in the visible and near-IR range is smaller than 0.02, the optical transmission of 500 nm thick ZnO film is ∼ 0.90.     

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.     

Ar/O2 gas pressure dependences of a pulsed zirconium arc and extracted ion characteristics

A pulsed dc zirconium arc discharge is generated in an argon diluted oxygen gas by separating a pin electrode as an anode from the cathode. The arc is transiently generated, and its life time is approximately 3 ms for a series resistance of 1 Ω and a dc output of 33 V. The life is prolonged and the plasma becomes stable with increasing the arc current. A target with a diameter of 100 mm is set at 150 mm from the arc source, and is immersed in the plasma. A pulse voltage is applied to the target to extract ions from the plasma. The ion current is not detected after approximately 8 ms since the plasma initiation. When the plasma is generated in oxygen without argon, the plasma generation time is scattered, and the plasma is unstable. An ion density is estimated from the temporal behavior of the target voltage in the recovery region after the pulse voltage. The ion density at the target is approximately 2.5 × 10¹⁵ m^− 3 at a mixed gas pressure of 1.9 Pa, which corresponds to the plasma density of 1.1 × 10¹⁷ m^− 3 under an assumption of electron temperature of 1 eV.     

Density changes with substrate negative bias for ta-C films deposited by filter cathode vacuum arc

Specular X-ray reflectivity (XRR) measurements were used to study the density and cross-section information of tetrahedral amorphous carbon (ta-C) films deposited by filter cathode vacuum arc(FCVA) system at different substrate bias. According to the correlation between density and substrate negative bias, it is found that the value of density reaches a maximum at -80 V bias. As the substrate bias increases or decreases, the density tends to lower gradually. Based on the density of diamond and graphite, sp3 bonding ratio of ta-C films was obtained from their corresponding density according to a simple equation between the two. And a similar parabolic variation was observed for ta-C films with the sp3 content changes with substrate negative bias. The mechanical properties such as hardness and elastic modulus were also measured and compared with the corresponding density for ta-C films. From the distribution of data points, a linear proportional correlation between them was found, which shows that the density is a critical parameter to characterize the structure variation for ta-C films.     

Layer formation by resputtering in Ti-Si-C hard coatings during large scale cathodic arc deposition

This paper presents the physical mechanism behind the phenomenon of self-layering in thin films made by industrial scale cathodic arc deposition systems using compound Ti-Si-C cathodes and rotating substrate fixture. For the as-deposited films, electron microscopy and energy dispersive X-ray spectrometry reveals a trapezoid modulation in Si content in the substrate normal direction, with a period of 4 to 23 nm dependent on cathode configuration. This is caused by preferential resputtering of Si by the energetic deposition flux incident at high incidence angles, when the substrates are facing away from the cathodes. The Ti-rich sub-layers exhibit TiC grains with sizes up to 5 nm, while layers with high Si-content are less crystalline. The nanoindentation hardness of the films increases with decreasing layer thickness.     

Al and Zn film deposition using a vacuum arc plasma source with a refractory anode

The radially expanding plasma plume generated in a Hot Refractory Anode Vacuum Arc was used to deposit thin Al and Zn films on glass substrates. The electrode separation was 10 mm, arc time varied up to 165 s, and current (I) was 100-225 A. The cathode was a water-cooled Al or Zn cylinder. A graphite anode with 9 or 30 mm height was used with the Al cathode, and 10 or 30 mm height Mo anode was used with the Zn cathode. A mechanical shutter controlled the substrate exposure onset and duration (15 s) to the anodic plasma. The distance from the arc axis to the substrate (L) was varied between 80 and 165 mm. The film thickness was measured with a profilometer, and macroparticle (MP) presence on the coating surface was examined by optical microscopy.It was found that the deposition rate increased as a function of time to a peak, and then decreased to a steady-state value. The peak occurred sooner using the 9 mm anode than with the 30 mm anode. The peak deposition rate increased and the peak time decreased with I. The steady-state deposition rate was larger for Zn (~ 2 μm/min) than for Al cathodes (~ 1 μm/min) at I = 225 A and L = 110 mm. The arc voltage for Al was ~ 20-22 V and for Zn it was 11 V. The deposition rate peak appeared due to MPs evaporating from the hot anode, where they had initially condensed during the conventional arc stage when the anode was still cold. This effect was significant with low melting temperature Al and Zn cathodes, and negligible with Cu and Ti cathodes studied previously.     

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.     

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|.     

Zirconium vacuum arc operation in a mixture of Ar and O2 gases: Ar effect on the arcing characteristics,deposition rate and coating properties

The effect of oxygen and argon partial pressures (P_O2, P_Ar) in a Zr vacuum arc on plasma ion current density J_p, arc voltage V_arc, deposition rate v_d, and selected coating properties was determined. A d.c. arc current of I_arc = 100 A was initiated between a Zr cathode and a grounded anode. Cathode spots produced a plasma jet, which entered a 1/8 torus macroparticle (MP) filter. The plasma was guided by a d.c. magnetic field through an aperture to a glass substrate or a flat disk probe, mounted on a rotatable holder. J_p was measured with the probe, negatively biased to V_b = − 60 V. Coating thickness was measured using a profilometer, and coating properties were investigated using optical microscopy, energy dispersive X-ray spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), nano-indentation and optical analysis.     

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.