Plasma-assisted Physical Vapour Deposition Research Articles

Characterisation and applications of Cr–Al–N coatings

There is an increasing number of applications for hard coatings in engineering where both high oxidation resistance and hot hardness are required. One way to address this problem is to use hard ceramic coatings which are a combination of more than one metal so that the coating performance will benefit from the combined mechanical properties of the metals present. In this study, chromium aluminium nitride (Cr–Al–N), titanium nitride (Ti–N), titanium aluminium nitride (Ti–Al–N) and chromium nitride (Cr–N) coatings were deposited on 6.35 mm HSS drills and on hardened and polished AISI M2 steel test discs by means of electron beam plasma-assisted physical vapour deposition. For all depositions, the coating temperature was below 500 °C. Laboratory tests were performed to characterise the mechanical and tribological properties of the coatings. Along with the laboratory tests, accelerated drilling tests and actual industrial applications (punching and gear-shaping) were also used to evaluate the performance of the coatings. The results from the laboratory characterisation, drill tests and industrial applications all showed that Cr–Al–N performs exceptionally well compared to the industry “standards” of Ti–N, Ti–Al–N and titanium carbo-nitride (Ti–C–N). The exceptional performance of Cr–Al–N compared to the other coatings is considered with reference to the coatings’ characteristics.

Generation and Characterization of Multilayer Systems Consisting of Au55(PPh3)12Cl6 Double Layers and SiO2 Barrier Films

AbstractMultilayer systems, consisting of Au55(PPh3)12Cl6 double layers and SiO2 barrier films of different thickness, have been generated and characterised. The formation of the double layer between the barrier films was carried out by using spin‐coating techniques. For the generation of the SiO2 films, a plasma‐assisted physical vapour deposition (PAPVD) procedure has been applied, based on an anodic plasma arc process. Samples of up to nine cluster/SiO2 combinations have been produced and have been characterised by AFM and SEM. Impedance measurements showed that there is a characteristic thermally activated frequency dependence of the capacitance of the different systems. The cluster layers interact by dipoles formed in the double layers at low frequencies. It has also been shown that multilayer systems with SiO2 films thicker than 15 nm tend to spontaneously crystallise. Furthermore, wetting problems during the spin‐coating processes have been investigated. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)

Influence of plasma nitriding and PAPVD Cr 1 − x N x coating on the cavitation erosion resistance of an AISI 1045 steel

Carbon steels are often used in engineering components that are subjected to a cavitation erosion phenomenon. An attempt to improve the cavitation erosion resistance of an AISI 1045 carbon steel was made by carrying out two surface treatments: plasma nitriding and Plasma-Assisted Physical Vapour Deposition (PAPVD) coating. The cavitation erosion resistance of four systems was investigated, as follows: (i) AISI 1045 steel; (ii) plasma nitrided AISI 1045 steel; (iii) PAPVD Cr 1 − x N x coating on AISI 1045 steel (non-duplex) and (iv) PAPVD Cr 1 − x N x coating on plasma nitrided AISI 1045 steel (duplex). Cavitation erosion tests were performed according to the ASTM G 32-85 standard. Mass loss plots were obtained as a function of time and statistical analyses (piecewise linear regressions) were performed in order to evaluate the cavitation erosion wear rates. The plasma nitrided AISI 1045 steel exhibited three distinctive wear regimes, with an intermediate stage characterised by a low cavitation erosion rate (2.0 mg h − 1 ) between the incubation period (first regime) and accelerated stage (third regime); this intermediate regime could be associated with the wear of the nitrided layer. For the duplex system, an additional wear regime could be detected in comparison to those of the plasma nitrided steel. This additional regime, which exhibited a cavitation erosion rate of 1.3 mg h − 1 , followed the first regime (incubation period) and was associated with the intrinsic wear of the PAPVD Cr 1 − x N x coating. The previous results were corroborated by SEM examination of eroded surface areas. The plasma nitriding treatment, whether or not combined with PAPVD coating, significantly increased the incubation period and was able to provide lower cavitation erosion rates for longer times. The Cr 1 − x N x deposition onto the AISI 1045 steel (non-duplex coating) led to localised erosion and the substrate was reached in the early stages of the cavitation process. The duplex system exhibited the lowest erosion rates over extended cavitation times; its superior performance in vibratory cavitation tests indicates that a combination of plasma nitriding + PAPVD coating should be used in applications where cavitation erosion resistance is a property of prime importance.

Characterisation of Pristine and Recoated electron beam evaporation plasma-assisted physical vapour deposition Cr–N coatings on AISI M2 steel and WC–Co substrates

This paper is focussed on the characterisation of electron beam evaporation plasma-assisted physical vapour deposition Cr–N coatings deposited on AISI M2 steel and hardmetal (K10) substrates in two different conditions: Pristine (i.e., coated) and Recoated (i.e., stripped and recoated). Analytical methods, including X-ray diffraction (XRD), scanning electron microscopy, scratch adhesion and pin-on-disc tests were used to evaluate several coating properties. XRD analyses indicated that both Pristine and Recoated coatings consisted of a mixture of hexagonal Cr 2N and cubic CrN, regardless of substrate type. For the M2 steel substrate, only small differences were found in terms of coating phases, microstructure, adhesion, friction and wear coefficients between Pristine and Recoated. Recoated on WC–Co (K10) exhibited a less dense microstructure and significant inferior adhesion compared to Pristine on WC–Co (K10). The wear coefficient of Recoated on WC–Co was 100 times higher than those exhibited by all other specimens. The results obtained confirm that the stripping process did not adversely affect the Cr–N properties when this coating was deposited onto M2 steel substrates, but it is clear from the unsatisfactory tribological performance of Recoated on WC–Co that the stripping process is unsuitable for hardmetal substrates.

Single chamber PVD/PECVD process for in situ control of the catalyst activity on carbon nanotubes growth

In this paper, we studied the effect of oxygen on the catalyst activity and related influence on the nanotubes (CNTs) growth by low-pressure/high-density plasma. CNTs were prepared using a novel single vacuum chamber reactor combining (i) plasma assisted physical vapour deposition (PVD) for catalyst deposition under O2, NH3 or Ar atmosphere with (ii) electron cyclotron resonance (ECR) C2H2/NH3 plasma enhanced chemical vapour deposition (PECVD) process for carbon nanotubes growth. The substrates are in situ prepared by controlled PVD allowing the deposition of sub-nanometric catalyst (Fe, Ni, Pd) films followed by ECR-PECVD CNTs growth. Transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS) analysis of CNTs show that the volume oxidation of the nanometric catalyst particles partially inhibits the CNTs growth while the catalyst surface oxidation can be reduced by the atomic nitrogen during the PECVD process. The specially designed PVD/PECVD process preserves the catalyst from moisture contamination, reducing walls nanotube defects.

Study of TiN/BN bilayers produced by pulsed arc plasma

Bilayers of TiN/BN were produced by using a PAPVD (Plasma Assisted Physical Vapor Deposition) pulsed vacuum arc system. The equipment is formed by a reactor composed by a vacuum chamber with two face-to-face electrodes and an RLC circuit to produce the arc discharge. To obtain the BN coating a target of h-BN was used placed on the cathode and a substrates of silicon placed on the anode. The work gas was nitrogen at a pressure of 4.4×10 −1 mbar and a voltage of 240 V. In order to improve the adherence of the BN film, an interlayer of TiN was grown. In this case the chamber was filled with N 2 to produce the TiN coating, with a pressure of 1.7 mbar and a voltage of 300 V. By means of XRD (X-ray diffraction), the existence of TiN was determined finding different crystalline orientation in FCC phase. An FTIR (Fourier Transform Infrared Spectroscopy) was employed to determine sp 3/sp 2 bonding ratio in the BN film. By plotting I– V curves the electrical properties of the bilayer were studied, observing a semiconductor behavior and this result was compared to the silicon substrate without coating.

Study of multilayer coatings of Ti/TiN/TiC produced by pulsed arc discharge

This work presents a study of multilayered Ti/TiN/TiC thin films obtained using a PAPVD (Plasma Assisted Physical Vapor Deposition) system by pulsed-arc discharge. For this purpose, a titanium target and a stainless steel substrate were used, placed on the cathode and on the anode, respectively, inside a vacuum chamber. To grow these films, different gases and concentrations were required. Ti is obtained with argon gas, TiN with nitrogen, and TiC with methane, at 2.5 mbar and 5 mm distance between electrodes. By means of X ray diffraction (XRD), the phases present in the film were determined, observing (111), (200), and (100) orientations for both, TiN and TiC. Also, by employing XRD techniques, Titanium Atoms Distance (DTA) was calculated at the interface of TiN and TiC, in order to study the crystallographic match. Energy Dispersive Spectroscopy (EDS) was employed in order to carry out elemental analyses in the materials. These analyses were obtained for 12 keV and 30 keV, observing the effects in the results. Taking advantage of defects generated during the growth of the multilayer, chemical composition maps were carried out, probing the combination of Ti and N in one layer and Ti and C in the other layer. Scanning Electron Microscopy (SEM) technique allowed observing the presence of the multilayer, as well as the measurement of the thicknesses of each layer, which are in the order of nanometers.

Corrosion–erosion behavior of TiN-coated stainless steels in aqueous slurries

The corrosion–erosion resistance of TiN-coated AISI 304 and AISI 420 stainless steels in aqueous slurries was studied. TiN films with a thickness of 0.6 μm were obtained by using the pulsed-arc plasma-assisted physical vapour deposition technique. The corrosion–erosion experiments were performed in a test machine in which the impingement velocity, impact angle, concentration of solids and pH of the solution were controlled. Polarization curves were simultaneously obtained to relate the electrochemical effects to the erosive wear mechanisms. The slurry used consists of quartz particles suspended in a mixture of sulphuric acid solution and 3.5% NaCl, with a pH value of 0.2. Measurement of critical and passive current densities showed that the behavior of coated materials differed according to substrate, but in a general way increasing impact velocity and changing from normal to grazing incidence led to a reduction in resistance to corrosion–erosion and liquid impingement corrosion. Surface analysis by SEM revealed formation of cracks in the coating and plastic deformation in both the substrate and the coating, especially when the mean impact velocity exceeded a critical value between 6.9 and 8.6 ms −1. Additionally, intergranular corrosion was observed in some specimens.

Crystallization behavior of arc-deposited ceramic barrier coatings

Al 2O 3 and Er 2O 3 were deposited by plasma-assisted physical vapor deposition using a filtered vacuum arc device. Varying the deposition conditions with respect to the substrate temperature and bias voltage, the crystallization behavior of these films was investigated by X-ray diffraction. In the case of alumina, when a bias voltage of −200 V is applied, crystallization of metastable crystal phases starts around 500 °C; the growth of the thermodynamically stable α-phase starts above 600 °C. This has to be compared with the thermodynamic phase transformation temperature of 1100 °C. For erbia, crystallization of the cubic crystal phase occurs at room temperature, when a bias voltage of −100 V is applied. Without exceeding the upper service limit, structural low activation materials can therefore be coated with stable ceramic barrier coatings. Deuterium permeation experiments performed with these types of coatings yield a permeation reduction factor of 40 in the case of alumina and 200 for erbia, respectively.

Gas scattering effects and microstructural evaluation of electron beam evaporated titanium coatings in neon and argon at different gas pressures

Titanium coatings were deposited on stainless steel and glass substrates by electron beam evaporation in vacuum (4×10 −4 Pa) and at different neon and argon gas pressures (from 0.33 to 2.00 Pa). The effect of background gas pressure and type on film microstructure was evaluated by scanning electron microscopy (SEM). Since it was not feasible to maintain a constant evaporation rate for all runs, the ‘deposition efficacy’, a parameter defined as the ratio between coating thickness and mass of material evaporated, was statistically modelled using non-linear regression analysis to determine the effects of gas scattering. The results revealed that neon and argon promote similar scattering of the titanium vapour and this may point to a lower likelihood of gas-phase metal cluster formation in neon. The coating microstructure was found to change from a tapered grain structure, obtained under vacuum conditions, to a faceted one at low gas pressure (0.33 Pa), becoming more porous as gas pressure increased. For a given gas pressure, no significant differences could be observed in coating microstructure between the use of argon or neon. These findings may be significant when considering the use of neon as an alternative gas to argon, for improving reactive gas ionisation (through Penning mechanisms) in Plasma-Assisted Physical Vapour Deposition.

Degradation of a solid state electrochromic device

A full monolithic inorganic electrochromic device was deposited by means of plasma assisted physical vapor deposition. The layer stack was evaporated under different conditions that optimized the performance of each individual layer. Optical and electrochemical characterizations were carried out on the EC-device in order to establish its performance. Electro-optical data were registered over more than 6000 cycles of mixed chronoamperometric and voltammetric cycles. Degradation of the electro-optical characteristics of the device was observed during the test, probably due to atmospheric interaction.

Investigation of interactions between inert gases and nitrogen in direct current triode discharges

Neon–nitrogen and argon–nitrogen thermionically supported dc triode discharges (typical of those used in plasma-assisted physical vapor deposition processes) have been investigated using optical emission spectroscopy. All discharges were operated with the cathode current density and voltage maintained at 0.06 mA/cm2 and −100 V. A range of nitrogen partial pressures was examined in each inert gas discharge at total pressures of 1.3 and 4.7 Pa. Spectral line intensity ratios were used to obtain information on the species within the plasma region of the discharge, from which the following effects were noted at both total pressures: (i) The N2+/N20 ratio was observed to increase significantly at low nitrogen partial pressures in the neon-based discharges; this is attributed to Penning ionization by neon metastables. (ii) The maximum in the N2+/N20 ratio and minimum in the Ne+/Ne0 ratio occurred at ∼10% nitrogen partial pressure, indicating optimum conditions for Penning ionization. (iii) For nitrogen partial pressures of less than 10%, an increase in atomic nitrogen species was observed for both inert gas discharges; this effect is attributed to the dissociation of nitrogen molecular species (both ionized and neutral) by inert gas metastables.

Transparent thermoplastic polymers in plasma-assisted coating processes

The performance of polymethylacrylate, polycarbonate, Zeonex ® and Topas ® as substrate materials in plasma-assisted physical vapour deposition processes has been studied. Different effects of UV radiation, plasma and ion bombardment on the polymers’ optical features, surface energy and adhesion properties for oxide layers are shown. As a consequence, conditions for the deposition of optical coatings on these substrates are discussed.

Optical and mechanical characteristics of nanocrystalline boron carbonitride films synthesized by plasma-assisted physical vapor deposition

Nanocrystalline boron carbonitride thin films were prepared using the electron-cyclotron- wave-resonance plasma-assisted deposition, whereby the energy for precursor ions was adjusted between 70 and 180 eV. Fourier-transform infrared spectroscopy confirmed the presence of ternary sp3-bonded structure and high-resolution transmission electron microscopy revealed a punctured lattice. The deposits unfold grains of about 200 nm in dimension under atomic force microscope, yet they exhibit extremely flat surfaces with a root-mean-square roughness less than 3 nm. For a 1.2 μm thick film, the transmittance in the visible light range is as high as 80%. The Vicker’s hardness measures over 28 GPa. Therefore, this ternary material is competitive to nanocrystalline diamond in application as protective coatings for optical components. Remarkably, also very strong photoluminescence peaked at 430 nm was detected in the as-deposited films at room temperature.

Electronic characterization of n-ScN/p+ Si heterojunctions

We report the electronic characterization of n-ScN in heterojunctions, including deep level transient spectroscopy of electrically active deep levels. ScN material has been grown by plasma assisted physical vapor deposition on commercial p+ Si substrates. Current–voltage and capacitance–voltage measurements indicate that the built-in voltages for the heterojunctions used in this study are approximately 1.74 and 0.40 eV, as seen by electrons and holes. Deep level transient spectroscopy results show the presence of an electronic trap with activation energy EC−ET=0.51 eV. The trap has a higher concentration (1.2–1.6×1013 cm−3) closer to the ScN/Si interface.

Corrosion resistance of multi-layered plasma-assisted physical vapour deposition TiN and CrN coatings

The corrosion resistance of mild steel coated with single layered and multi-layered TiN and CrN coatings has been studied. The base material was coated with TiN and CrN by an electron-beam plasma-assisted physical vapour deposition (PAPVD) technique. ‘Single’ layers of TiN or CrN, which normally include an interlayer (approx. 100–200 nm) of Ti or Cr under the main TiN or CrN film, were prepared; four layers of TiN (or CrN) were produced by four sequential repetitions of the single-layer process. The microstructural features and corrosion performance were then compared. It is shown that applying four layers of coating can enhance the corrosion performance of PVD TiN and CrN coated mild steel. The corrosion resistance improvement is not only attributed to the increase in thickness, but also to the internal microstructure and phase composition. CrN coatings produced in this work proved to be particularly promising in terms of corrosion resistance, owing to their dense non-columnar structure which contained a mixture of three phases: Cr (b.c.c.), Cr 2N (hexagonal) and CrN (f.c.c.). Mild corrosion reactions were observed in CrN coated steel during various electrochemical tests in aqueous salt solution, indicating that inter-phase corrosion had caused a redistribution of the current flow, so as to eliminate current concentration at small through-coating pinholes. This prevented rapid galvanic attack at the coating/substrate interface. More importantly however, in comparison with the columnar structure of TiN coatings, the dense structure with fine equiaxed crystallites made the CrN coatings less permeable to the corrosive medium.

Investigation of metal contacts on ScN

Metal contacts deposited on ScN films grown by plasma assisted physical vapor deposition (PAPVD) and rf-sputtering were examined. The metal contacts Ti, Ni, Pd were dc-sputtered while Al and Cu were evaporated. For PAPVD ScN it was found that the best ohmic contact was formed by depositing Pd, with specific contact resistance in the range of 9.0E+01Wcm2. In the case of rf-sputtered ScN films deposited at 300K, all metals tried to form ohmic contacts with specific contact resistance of the order of 106Wcm2. For the films sputtered at 1000K, it was found that Pd made the best ohmic contact with a value for the contact resistance similar to PAPVD samples, while for the Ti and Ni contacts, values of the order of 106Wcm2 were calculated. For all samples where Al and Cu metals form contacts, these were ohmic with very high contact resistance. Trends in the ohmic contact formation and properties are believed to be related to the crystalline structure of the ScN.

ScN/GaN heterojunctions: fabrication and characterization

We report the fabrication of ScN/GaN isotype (n–n) heterojunctions by plasma-assisted physical vapor deposition (PAPVD) of ScN onto metal-organic chemical vapor deposited (MOCVD) GaN. Two types, corresponding to different temperature growth conditions (900 and 1000K) for ScN were used. The samples grown at 900K, display rectifying current–voltage (I–V) behavior with turn on voltage between 1.26 and 1.56V and ideality factors of 4.61 and 5.90. From capacitance–voltage (C–V) measurements, the “built-in” potential values of approximately 0.06 and 1.00V on each side of the junction were obtained.

Electrically Active Deep Levels in ScN

AbstractWe report the electronic characterization of n-ScN in ScN-Si heterojunctions using Deep Level Transient Spectroscopy of electrically active deep levels. ScN material was grown by plasma assisted physical vapor deposition and by reactive sputtering on commercial p+ Si substrates. Deep level transient spectroscopy of the junction grown by plasma assisted physical vapor deposition shows the presence of an electronic trap with activation energy EC-ET= 0.51 eV. The trap has a higher concentration (1.2–1.6 1013cm−3) closer to the ScN/Si interface. Junctions grown by sputtering also have an electronic trap, situated at about EC-ET= 0.90 eV.

Application of Temperature Modulated Relative Dilatometry. Temperatures of adhesion degradation

Application of temperature modulated dilatometry (TM DIL) to investigation on degradation of the adhesion between ceramic films and the substrate is presented. Layers of titanium nitride deposited by plasma assisted physical vapour deposition (PA PVD) methods on the Armco iron substrates were tested. This paper shows that the TM DIL method is helpful in determining the usefulness of the titanium nitride covering of the cutting tools and machine parts.