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In this paper the overview of the most important approximate methods for the optical characterization of inhomogeneous thin films is presented. The following approximate methods are introduced: Wentzel–Kramers–Brillouin–Jeffreys approximation, method based on substituting inhomogeneous thin films by multilayer systems, method based on modifying recursive approach and method utilizing multiple-beam interference model. Principles and mathematical formulations of these methods are described. A comparison of these methods is carried out from the practical point of view, ie advantages and disadvantages of individual methods are discussed. Examples of the optical characterization of three inhomogeneous thin films consisting of non-stoichiometric silicon nitride are introduced in order to illustrate efficiency and practical meaning of the presented approximate methods.

Low ductility and brittle deformation behaviors are major drawbacks of currently used commercial hard ceramic-based protective coatings. Recent ab-initio calculations revealed that the coexistence of metallic, boride and carbide bonds in a nanolaminate structure of crystalline W2BC system provides a combination of high hardness together with moderate ductility. The present paper deals with coatings containing W, B and C with different compositions and investigates the effect of the boron to tungsten ratio (B/W) on the structural and mechanical properties of W-B-C coatings prepared by pulsed-DC magnetron sputtering at a moderate temperature. Coatings with low B/W were deposited in a nanocomposite structure, whereas coatings with high B/W ratios were near-amorphous. The structure of the coatings was not a decisive factor in determining their mechanical properties. These were, however, directly correlated with the chemical bonds present. All the coatings exhibited high fracture resistance. These properties together with good adhesion to cemented tungsten carbides make W-B-C coatings promising candidates for the future protective coatings of tools which undergo large deformation in their working cycle.

Ta&ndash, B&ndash, C coatings were non-reactively sputter-deposited in an industrial batch coater from a single segmented rotating cylindrical cathode employing a combinatorial approach. The chemical composition, morphology, microstructure, mechanical properties, and fracture resistance of the coatings were investigated. Their mechanical properties were linked to their microstructure and phase composition. Coatings placed stationary in front of the racetrack of the target and those performing a 1-axis rotation around the substrate carousel are compared. Utilization of the substrate rotation has no significant effect on the chemical composition of the coatings deposited at the same position compared to the cathode. Whereas the morphology of coatings with corresponding chemical composition is similar for stationary as well as rotating samples, the rotating coatings exhibit a distinct multilayered structure with a repetition period in the range of nanometers despite utilizing a non-reactive process and a single sputter source. All the coatings are either amorphous, nanocomposite or nanocrystalline depending on their chemical composition. The presence of TaC, TaB, and/or TaB2 phases is identified. The crystallite size is typically less than 5 nm. The highest hardness of the coatings is associated with the presence of larger grains in a nanocomposite structure or formation of polycrystalline coatings. The number, density, and length of cracks observed after high-load indentation is on par with current optimized commercially available protective coatings.

This research was devoted to studying the influence of the taper angle on the micro-compression of micro-pillars fabricated from near-amorphous and nanocrystalline Mo-B-C coatings. A series of micro-pillars with a taper angle between 4–14° was fabricated by focused ion beam technique. The deformation mechanism was found to be dependent on the taper and, also, on the crystallinity of the coating. In order to obtain correct values of yield strength and Young’s modulus, three empirical models of stress correction were experimentally tested, and the results were compared with nanoindentation measurements. It was shown that the average stress correction model provided comparable results with nanoindentation for the yield strength for taper angles up to ~10°. On the other hand, the average radius or area model gave the most precise results for Young’s modulus if the taper angle was

Publisher's version (útgefin grein), The self-organised plasma patterns, known as spokes or ionisation zones in magnetron sputtering discharges, were observed in a wide range of power densities, from low power direct current magnetron sputtering (dcMS) discharge to high power impulse magnetron sputtering (HiPIMS) discharge. For some target materials and non-reactive gases, it was observed that at very high power densities (>3 kW cm-2) the plasma exhibits a transition from a regime where spokes are observed to a homogeneous plasma regime. In this contribution, we present a comparison of plasma properties: plasma emission (optical emission spectroscopy) and flux of argon and chromium ions (mass spectrometry), measured both in the spoke regime and in the homogeneous plasma regime, aimed to expand the understanding of the plasma transition between the two modes. A simple biased flat probe was used to distinguish between the spoke regime and the homogeneous plasma regime. It was found that the flux of multiply charged ions (Ar2+, Cr2+, Cr3+, Cr4+) increases abruptly at the transition between the spoke regime and the homogeneous plasma regime. Similarly, the emission from Cr+ ions exhibits a strong increase of about 50% when the plasma torus becomes homogeneous. These observations are interpreted as an increase in electron temperature and a change in the electron heating mode, from a combination of secondary electron heating and Ohmic heating towards pure Ohmic heating. The transition to the homogeneous plasma regime and pure Ohmic heating is only observed in non-reactive HiPIMS discharges for target atoms with the second ionisation potential higher than the first ionisation potential of Ar (15.76 eV), and a self-sputter yield larger than 1., This research has been supported by project LM2018097 funded by the Ministry of Education, Youth and Sports of the Czech Republic and project GA19-00579S funded by the Czech Science Foundation. This work has been supported by the German Science Foundation (DFG) within the frame of the collaborative research centre SFB-TR 87

A new approach to calculation of optical quantities of inhomogeneous layers is presented. In this approach, the Richardson extrapolation is used to improve the accuracy of the method, in which the inhomogeneous layer is approximated by a stack of thin homogeneous layers. The results presented in this paper are based on the assumption that the media are isotropic and the inhomogeneity is along the axis normal to the boundary. The results obtained by the new method are compared with those obtained without the Richardson extrapolation. The Richardson extrapolation brings significant improvement in accuracy, especially if the number of approximating layers is large. Moreover, the method using the Richardson extrapolation proceeds in steps with an error estimate available in each step; thus, the calculation can be stopped when the desired accuracy is reached. The use of the method is illustrated by means of the optical characterization of strongly inhomogeneous film of non-stoichiometric silicon nitride.

Preparation of coatings simultaneously exhibiting high hardness and enhanced fracture resistance is a hot topic, as nowadays used ceramic protective coatings show difficulties to cope with increased demands due to their inherent brittleness. Material exhibiting seemingly contradictory combination of mechanical properties like high hardness and moderate ductility enhancing the fracture resistance - was recently predicted by ab initio calculations in the crystalline X2BC system. The presented study is focused on the study of the influence of the C/W ratio on the microstructure, the content of different chemical bonds and the mechanical properties of WBC coatings prepared by magnetron sputtering at moderate temperature.

State-of-the-art protective coatings often suffer from brittleness. Therefore, the coatings are intensively sought which would simultaneously exhibit high hardness and stiffness with moderate ductility and fracture resistance. In this paper, we report on the nanostructure designing of coatings containing metal, boron, and carbon enabling the simultaneous presence of stiff boridic and carbidic bonds together with weaker metallic bonds to provide coatings with these desirable properties. Three designs are presented with different relative amounts of nanocrystalline and amorphous phases, ranging from near-amorphous to prevalently crystalline microstructure. All presented coatings exhibit an unusual combination of high fracture resistance and high hardness that cannot be achieved with state-of-the-art protective coatings. Indentation tests at high loads revealed that no cracks are present at the surface of the investigated coatings while state-of-the-art ceramic protective coatings already exhibit significant cracking. Cracks in the bulk of the presented coating are detected only when the deformation is so severe that the substrate itself fails.

The deposition rate, as well as the structure of a coating for a given magnetron sputtered material are determined by the plasma properties which are significantly dependent on the type of plasma generation. Single-pulse high power impulse magnetron sputtering (s-HiPIMS), multipulse HiPIMS (m-HiPIMS) with the same energy per pulse sequence and conventional direct current magnetron sputtering (DC-MS) were employed to deposit metallic Ti coatings. Varying the number of pulses in one pulse sequence in multipulse HiPIMS operation enables us to influence the ion fluxes on the substrate and the ionisation of the sputtered titanium. The grain size for the HiPIMS-deposited coatings was in the range of 5 to 25 nm depending on the number of pulses in the pulse sequence, whereas it was 15 nm for the coating prepared by the DC-MS. By the use of multipulse HiPIMS, it was also possible to achieve coatings with a smoother surface morphology and lower roughness as well rougher coatings with larger asperities and higher roughness compared to DC-MS. The texture and the deposition rate were significantly affected by the number of pulses, too.

The average ion energy per deposited atom (Ed) is defined as the product of the ion energy (Ei) and ion-deposition flux ratio (Ji/Jd) in magnetron sputtering deposition. Ed captures both the geometrical, and plasma characteristics of the deposition system and hence is regarded as a fundamental parameter for describing the energy dependency of coating structure and properties. Nevertheless, Ed is not a universal parameter since an independent variation of its components, i.e., Ei and Ji/Jd, may result in the same Ed but different coating structures and properties. While the controlling of Ji/Jd is not possible in most conventional magnetron sputtering systems, this study employed an industrially developed SCIL® (sputter coatings induced by lateral glow discharge) technology to independently control the ion flux (Ji) and investigate the dependence of structure, mechanical properties, and cutting performance of the AlCrN coatings on the Ed and its components. The results revealed that the structure of the AlCrN coatings was mainly dependent on the Ji/Jd component of Ed, where a transition from a cubic structure into a hexagonal structure took place beyond a critical level of Ji/Jd. The elastic modulus showed no Ed dependency and was only affected by coating structure. However, the hardness was strongly dependent on the Ed. Whether in Ei or Ji/Jd, an increase led to a hardness enhancement through the synergic effect of the residual stress hardening, coating densification, and grain refining mechanisms. The cutting performance of deposited tools under real working conditions was also found to be dependent on the Ed and, in particular, on Ji/Jd. Increasing Ed from ~860 to ~1170 eV/atom led to a ~55% increase in tool lifetime, reaching 90% performance of the benchmark arc-deposited coating.

Titanium carbide/carbon coatings were deposited by hybrid PVD-PECVD process of titanium sputtering in an atmosphere containing acetylene. Samples were placed above the titanium target centre and above the target racetrack in the same vertical distance to the target to examine the effect of the relative substrate to target position on the properties of the deposited coatings. The different positions of the samples led to significantly different levels of the energy influx onto the growing coating. These differing conditions at the substrate led to altering of the coating's chemical as well as phase composition. Also, the grain size, lattice parameter and the mean grain separation were affected by the energy flux change. Coatings deposited above the racetrack with carbon content ≲ 60% exhibited smaller grains, higher amount of the a-C phase and higher mean grain separation. This microstructure refinement yielded 20–30% higher hardness of the coatings deposited above the target racetrack than corresponding coatings deposited above the target centre. Thus, the sample positioning in the chamber proved to be an important parameter for resulting properties of the deposited coatings.

In the present work, nanocomposite Mo-B-C coatings were deposited on high speed steel and hard metal substrates by magnetron sputtering of three targets. These coatings were subjected to annealing to final temperatures in the range from 500 °C to 1000 °C. It was found that the as deposited Mo-B-C coatings exhibited hardness of ∼20 GPa, nanocomposite microstructure with very fine grains (∼2 nm) and low degree of crystallinity. The X-ray diffraction and transmission electron microscopy together with selective area electron diffraction were used to study the temperature induced changes of the microstructure of the coating and its crystallinity. The annealing process significantly improved the hardness (from ∼20 GPa to ∼30 GPa) and effective elastic modulus (from initial 330 GPa–500 GPa) of coatings while their resistance to fracture was kept sufficiently high.

Nanocomposite coatings consisting of titanium carbide crystallites embedded in amorphous carbon matrix were deposited utilizing direct current magnetron sputtering (DCMS) and high power impulse magnetron sputtering (HiPIMS) of titanium target in argon/acetylene atmosphere. DC driven depositions of coatings with high amount of carbon were accompanied by significant arcing during the deposition. HiPIMS utilization made reliable arc-free deposition of coatings with high carbon content possible. Analyses of the coating structure revealed that utilization of HiPIMS favours carbon incorporation into the TiCx grains rather than to the matrix. HiPIMS deposited coatings exhibited stoichiometry of the TiCx grains closer to unity with grains exhibiting lower lattice parameter and a lower fraction of the a-C matrix. This led to a smaller mean TiCx grain separation by the a-C:H matrix. Also the surface structure of the HiPIMS deposited coatings was much finer. The structure refinement resulted in overall higher hardness of HiPIMS deposited coatings with the hardest coatings reaching the superhard region of > 40 GPa and in 40% increase of H/E ratio and nearly threefold increase of H3/E2 ratio.

Nanocomposite nc-TiC/a-C:H thin films exhibit unique combination of mechanical properties, high hardness, low friction, and wear. Selective doping by weak-carbide forming element can be used in order to specifically design the physical and chemical properties of nc-TiC/a-C:H coatings. In this paper we report on an effect of nickel addition on structure and hardness of the nc-TiC/a-C:H coatings. The effect of Ni alloying on the coating structure under conditions of DCMS and HiPIMS depositions was studied. The coating structure was correlated with the coating hardness. The grain size, the grain carbon vacancy concentration, and the mean grain separation were found to be the key parameters determining the coating hardness. Ni doping proved to have a significant effect on the coating microstructure which resulted in changes of the hardness of the deposited coatings.

A study of a hybrid PVD-PECVD process of sputtering a titanium target in an argon/acetylene gas mixture was performed. This process was used for the deposition of nanocomposite coatings consisting of titanium carbide grains embedded in an amorphous hydrogenated carbon matrix (nc-TiC/a-C:H). The study was performed under industrial conditions employing a large-scale deposition device with a cylindrical sputtering cathode. When the acetylene supply was gradually increased, a discharge voltage drop and total pressure saturation simultaneously occurred at a certain acetylene supply. The hardest coatings were found always to be deposited at the acetylene supply corresponding to these deposition conditions. However, the acetylene supply to detect the voltage drop and pressure saturation was determined to be dependent on the cathode thickness. A fully automatic procedure suitable for the preparation of hard nc-TiC/a-C:H coatings by the hybrid PVD-PECVD process was proposed in this paper. This approach ensured that the optimal deposition setting was consistently found for the deposition process independent of the cathode thickness. The procedure was thoroughly tested, and it was demonstrated to be reliable and robust. Furthermore, the algorithm ensured the deposition of coatings with the same composition and the same high hardness throughout the cathode lifetime.

A detailed experimental study of high power impulse magnetron sputtering discharges is performed using time-resolved ground state density mapping of the sputtered neutrals and ions. This Paper deals with the effects related to the plasma-on phase and can be considered as an extension of Paper I being published simultaneously. The influence of plasma pulse duration, pulse energy, gas pressure as well as molecular oxygen admixture on the spatial and temporal particle density evolution is examined. Special attention is given to the temporal evolution of the ionization fraction distribution of the sputtered atoms. In addition, the 2D vector maps reflecting particle propagation, sputtering, and ionization in the discharge volume are also presented and discussed, similarly to the first part of this study [J. Appl. Phys. 128, 043303 (2020)].

A detailed experimental study of high power impulse magnetron sputtering processes is performed by time-resolved imaging of the ground state sputtered particles. New details related to the behavior of both neutral and singly ionized atoms are shown, as a result of separate treatment of the plasma-on and plasma-off time phases. In Paper I, the ion/neutral density redistribution in the ionization zone during sputtering is analyzed; the role of main discharge parameters, such as pulse repetition rate, pulse energy, etc., is discussed systematically. The time-resolved evolution of the ground state levels population for both sputtered neutrals and ions is also considered. In addition, propagation of the sputtered particles is analyzed using 2D density gradient diagrams calculated based on the measured particle density distributions. The results of this work are compared, when possible, to the data obtained previously [Britun et al., J. Appl. Phys. 117, 163302 (2015)].

In this paper, the hysteresis behaviour of a reactive magnetron sputtering process with oxygen admixture is studied by both experiment and model. The ground state number densities of titanium atoms and ions, and the deposition rates in high power impulse magnetron sputtering discharge were determined for a constant average applied power and pulse duration, while the repetition frequency and reactive gas supply were varied. The hysteresis curve reduced in width and shifted towards the lower oxygen supply with a decrease in the repetition frequency. These experimentally observed trends were well reproduced by a modified Berg model. The presented model utilised measured ionisation fraction of sputtered species and considered the back-attraction of the ionised sputtered species to the target. Significance of the back-attraction process was observed as large fraction of ionised sputtered particles was found to be lost back to the target. This drastically decreased the number of particles deposited onto the substrate, which reduced not only the deposition rate, but also the gettering of the reactive gas. Consequently, the simulated hysteresis curve was shifted and reduced in width as it was observed experimentally.

To gain more information on the temporal and spatial behaviour of self-organized spoke structures in HiPIMS plasmas, a correlation between the broadband optical image of an individual spoke (taken over 200 ns) and the current it delivers to the target has been made for a range of magnetron operating conditions. As a spoke passes over a set of embedded probes in the niobium cathode target, a distinct modulation in the local current density is observed, (typically up to twice the average value), matching very well the radially integrated optical emission intensities (obtained remotely with an ICCD camera). The dual diagnostic system allows the merging and splitting of a set of spokes to be studied as they rotate. It is observed that in the merger of two spokes, the trailing spoke maintains its velocity while the leading spoke either decreases its velocity or increases its azimuthal length. In the spoke splitting process, the total charge collected by an embedded probe is conserved. A simple phenomenological model is developed that relates the spoke mode number m to the spoke dimensions, spoke velocity and gas atom velocity. The results are discussed in the context of the observations of spoke dynamics made by Hecimovic et al (2015 Plasma Sources Sci. Technol. 24 045005).

Titanium–carbon hard coatings were deposited by sputtering using a rotating cylindrical titanium target in an argon/acetylene gas mixture on cemented tungsten-carbide substrates which were placed on a DC-biasable holder to perform a complex rotation around the central rotating cylindrical Ti cathode. While the optimal deposition process parameters to grow the coating of the highest possible hardness and low friction coefficient were sought, the plasma parameters were monitored and correlated with the properties of the deposited coatings. The Ti/Ar line intensity and the cathode voltage exhibited a sudden drop at the conditions for which the maximal hardness was reached. EDX analyses also showed a sudden drop in the atomic concentration of titanium and a sudden increase in that of carbon at the same moment. The maximal hardness of the coating was always achieved at the conditions that preceded these sudden changes, so this phenomenon was used to set the optimal deposition parameters to produce hard, well-adherent and sufficiently thick titanium–carbon coatings using the industrially attractive concept of a rotating cylindrical magnetron.

This work is aimed at the study of thermal stability of nc-TiC/a-C:H coatings deposited on steel substrates by unbalanced reactive magnetron sputtering of titanium in an acetylene containing atmosphere. The as-deposited coatings show high hardness and elastic modulus together with low wear and low friction coefficients. The coating properties were investigated as a function of annealing temperature using thermal desorption spectroscopy under UHV conditions. The hardness and elastic modulus did not change substantially up to 700 °C compared to the properties of the as-deposited coatings. The most significant changes were observed in case of their fracture toughness, which decreased due to the hydrogen loss from amorphous carbon matrix.

The aim of the present work is to study the nanoindentation induced defects in as-deposited and annealed nanocomposite n-TiC/a-C:H coatings. Furthermore, the resistance of the coatings against indentation induced defect creation was studied using TEM analysis of lamellas prepared using a focused ion beam for both as-deposited and annealed samples.

Several amorphous Mo–B–C coatings with wide range of compositions were subjected to thermal annealing to a final temperature of 1000 °C in UHV conditions. The nature of the induced recrystallization depended mostly on the Mo content in the coating. A higher Mo content resulted in a nanocrystalline Mo2C phase, a lower Mo content in a nanocrystalline Mo2BC phase and Mo content in-between resulted only in a near-amorphous microstructure. In all cases, the hardness and effective elastic modulus increased significantly after annealing up to values of ∼29 GPa and 500 GPa, respectively. The cobalt diffusion from the WC-Co substrates affected the lower parts of coatings forming a MoCoB interface.

This paper presents the results of the optical characterization of inhomogeneous thin films of polymer-like SiO x C y H z and non-stoichiometric silicon nitride SiN x. An efficient method combining variable angle spectroscopic ellipsometry and spectroscopic reflectometry applied at the near-normal incidence based on the multiple-beam interference model is utilized for this optical characterization. The multiple-beam interference model allows us to quickly evaluate the values of ellipsometric parameters and reflectance of the inhomogeneous thin films, which exhibit general profiles of their optical constants. The spectral dependencies of the optical constants of the inhomogeneous SiO x C y H z and SiN x thin films are determined using the Campi–Coriasso dispersion model. The profiles of the optical constants of these films can also be determined. Furthermore, the transition layers at the lower boundaries of the characterized films are also taken into account. Spectral dependencies of the optical constants of these transition layers are also determined using the Campi–Coriasso dispersion model.This paper presents the results of the optical characterization of inhomogeneous thin films of polymer-like SiO x C y H z and non-stoichiometric silicon nitride SiN x. An efficient method combining variable angle spectroscopic ellipsometry and spectroscopic reflectometry applied at the near-normal incidence based on the multiple-beam interference model is utilized for this optical characterization. The multiple-beam interference model allows us to quickly evaluate the values of ellipsometric parameters and reflectance of the inhomogeneous thin films, which exhibit general profiles of their optical constants. The spectral dependencies of the optical constants of the inhomogeneous SiO x C y H z and SiN x thin films are determined using the Campi–Coriasso dispersion model. The profiles of the optical constants of these films can also be determined. Furthermore, the transition layers at the lower boundaries of the characterized films are also taken into account. Spectral dependencies o...

Reactive high power impulse magnetron sputtering offers a great opportunity for high quality coating production, thus understanding the processes accompanying deposition is of great importance. In this paper, the evolution of numerous discharge parameters such as total pressure, discharge current and sputtered species number densities are studied in argon with oxygen, nitrogen or acetylene admixture. The experiments are compared to the reactive direct current magnetron sputtering where the deposition process usually exhibits hysteresis behaviour and the ionization fraction of sputtered species is significantly lower. The decrease in the titanium atom and ion number densities with the increasing degree of target poisoning is detected for all the studied admixtures. However, while the sputtered species number densities decrease the sputtered species ionization fraction increases. Depending on the reactive gas admixture, the ionization fraction of the sputtered species increases from 75% achieved in pure argon discharge up to 90% attained in the poisoned mode of the reactive sputtering. This increase was the most pronounced for oxygen and nitrogen admixtures. Mutual comparison of the reactive sputtering with nitrogen, oxygen and acetylene indicated multiple causes for the observed increase.

Nanocomposites like nc-TiC/a-C:H show promising combinations of properties such as high hardness and Young's modulus combined with low friction and wear. These properties can be furthermore tailored to suit particular industrial needs. In this paper, we report on the preparation and analyses of several μm thick and well adherent nc-TiC/a-C:H coatings with different stoichiometry. These coatings were deposited in a relatively low ion bombardment environment using magnetron sputtering of titanium target operated in well-balanced magnetic field configuration on high speed steel and hardmetal substrates. Gaseous hydrocarbon (acetylene) was added to the deposition chamber as source of carbon. Hardness and Young's modulus of 46 GPa and 415 GPa respectively were reached.

The ambient air plasma cleaning and activation effects on aluminum surface using the Diffuse Coplanar Surface Barrier Discharge in ambient air are presented. Atomic Force Microscopy, Attenuated Total Reflectance FTIR and Laser Desorption/Ionization Time-of-Flight Mass Spectroscopy techniques were used to characterize the changes on the surface before and after plasma treatments. The plasma cleaning effect on aluminum, i.e. decrease of hydrocarbon contamination, was proven. Also the air plasma treatment resulted in a significant increase of amount of OH groups on the surface and in a decrease of the surface roughness.

Hybrid PVD–PECVD process of target sputtering in hydrocarbon containing atmosphere combines aspects of both conventional reactive magnetron sputtering (PVD) and plasma enhanced chemical vapour deposition (PECVD). Such process is being typically used for deposition of metal carbides embedded in hydrogenated carbon matrix. Compared to the conventional co-sputtering of metal and carbon targets, in the hybrid deposition process the source of the carbon is dissociated hydrocarbon vapour in plasma. The aim of this paper is to study the extent of similarities or differences between this hybrid process and the conventional reactive magnetron sputtering. We have chosen the sputtering of titanium target in acetylene containing atmosphere as a representative of the hybrid processes. We focused on experimental measurements of the hybrid PVD–PECVD process behaviour, the time necessary for the process to achieve steady-state conditions and basic modelling of the process.

Nanocrystalline titanium carbide embedded in an hydrogenated amorphous carbon matrix (nc-TiC/a-C:H) shows high hardness and Young's modulus together with low wear and low friction coefficient. In this paper, we report on the preparation of well adherent nc-TiC/a-C:H coatings ~ 5 μm thick on stainless steel substrates using a well balanced magnetic field configuration and only very low power RF bias on the substrate. Hardness and Young's modulus of these coatings are 43 GPa and 380 GPa, respectively. The mechanical properties – hardness and Young's modulus – measured from the coating's top reach the values obtained at optimized experiments where the unbalanced magnetic field configuration was used. A simple method of depth profiling suitable for evaluation of mechanical properties of several micrometers thick coatings is developed and employed. The paper reports on the depth profile analyses of the coating hardness, Young's modulus, composition and morphology.

The objective of this paper is to study the effect of magnetic field strength on spoke behaviour in a high power impulse magnetron sputtering discharge. In three magnetic field configurations, a broad range of experimental conditions was investigated by high-speed camera imaging. The dual image feature of the employed camera enabled us to determine the shape and spoke mode number, as well as the velocity of the spokes. Five distinct spoke shapes were detected. For each magnetic field, a map was created relating the occurrence of the spoke shape with the discharge conditions. Similarly, the spoke mode number, as well as the spoke velocity, was found to be strongly dependent on the discharge conditions. Based on the optical emission results, it was proposed that the trailing edge of the triangular spoke is related to the production of secondary electrons created by argon ions on the spoke edges, while in the case of a round spoke shape, the secondary electrons are mainly created by multiple charged titanium ions in the centre of the spoke.

This paper is focused on experimental studies of a high power pulsed magnetron discharge stabilized by low current pre-ionization. Time resolved studies were performed for a Cu target by optical emission spectroscopy and electrical measurements for different pressures of Ar buffer gas. Due to the elimination of the statistical delay time and a fast discharge current rise the quasi-stationary state was reached in 6 µs. The quasi-stationary state is characterized by an extremely high and pressure independent discharge current density of ~10 A cm−2 and stable Cu+ and Cu++ emissions. Such fast discharge dynamics permits the magnetron cathode current to be driven with a pulse of duration of the order of a few µs, significantly shorter than in other devices. During this short time, the plasma does not have time to undergo the transition from the glow to the arc discharge even at the extremely high cathode loads met in our case. Different stages of the fast discharge development are identified and the composition of the magnetized plasma as a function of the pressure is discussed in detail.

A high-power pulsed-magnetron discharge (several kW/cm2) is described. It operates at pulse duration of the order of few μs, significantly shorter than in usual similar devices. The breakdown delay was reduced by using a low-current DC preionization. The study was performed for Cu target in Ar and He buffer gases by optical emission spectroscopy and electrical measurements. Saturation magnetron current is reached in a few μs which permits to shorten the pulse duration avoiding arc formation. Unusual high current density up to 10 A/cm2 induces very fast transition toward the stable self-sputtering regime. High plasma density favours high ion flux to the substrate. Preliminary result on Cu deposit in trenches is reported.

In the paper we study, be means of microwave interferometry, the evolution of electron density in afterglow of pulsed driven nitrogen discharge. Recombination coeffients are derived, too.

In this paper, comparison of standard and multi-pulse high power impulse magnetron sputtering is performed. The effective branching fraction method is used for titanium atom and ion number density determination, showing that the residual titanium atoms and ions from the preceding pulse are crucial for the subsequent pulse initiation and development. It is shown that the discharge current rises faster in the subsequent pulse, but does not reach the same maximum as in the preceding pulse. The time evolution of the titanium atom density shows different behaviour, initial increase is followed by decrease in the preceding pulse and a rather constant evolution during the subsequent pulse. As for the titanium ion number density, it reaches typically lower values in the subsequent pulse, approaching the maximum values from the preceding pulse only at long delays of 1.5 ms. The most significant increase of the total ion flux to the substrate, namely 43% increase with respect to standard high power impulse magnetron sputtering, is observed in the multi-pulse high power impulse magnetron sputtering with the shortest studied delay of 200 us. The residual titanium atoms produced by the preceding pulse are already thermalized at the beginning of the subsequent pulse, thus being available for ionization during the subsequent pulse. The reservoir of these thermalized atoms gets depleted as the delay increases. However, even for the longest studied delay of 1.5 ms the influence of the preceding pulse on the subsequent pulse is still distinct, including the enhancement of the total ion flux to the substrate by 23%.

Microstructure and mechanical properties of Ta-B-C nanocrystalline layers prepared by magnetron sputtering were studied. DC magnetron sputtering was used to prepare thin layers on rotated substrates. Various deposition parameters were tested. Microstructure of layers was studied by means of scanning and transmission electron microscopy on thin lamellar cross sections prepared using a focussed ion beam. Both undisturbed layers and the volume under relatively large indentation prints (load of 1 N) were observed. The microstructure observations were correlated with mechanical properties characterized by means of nanoindentation experiments in both the static and the dynamic loading regime. Elastic modulus, indentation hardness and fracture resistance of prepared nanostructured coatings were evaluated and discussed.

Hybrid PVD–PECVD process of titanium sputtering in argon and acetylene atmosphere combines aspects of both conventional techniques: sputtering of titanium target (PVD) and acetylene as a source of carbon (PECVD). This process can be used for preparation of metal carbon nanocomposites (MeC/C(:H)) or DLC layers doped with metal (DLC:Me). The aim of this paper is to describe and understand elementary processes influencing the hybrid PVD–PECVD process. A non-monotonous dependence of cathode voltage and current, total pressure and spectral line intensities on acetylene supply flow is reported. Explanation of non-monotonous evolutions through the analysis of the target state correlating the process characteristics with properties of coatings prepared by this process is proposed.

Mo 2 BC thin films show a favourable combination of high stiffness, hardness and elastic modulus together with moderate ductility. In this study we focused on the comparison of mechanical properties of Mo-B-C thin films with different structures (nanocrystalline or amorphous). The thin films were deposited on steel, hard metal and silicon substrates using DC magnetron sputtering. The mechanical properties of Mo-B-C films were studied using indentation techniques under both quasistatic and dynamic conditions using a wide range of loads from 50 μ N up to 1 N. The results showed that even amorphous Mo-B-C thin films had high hardness of 19.5 ± 0.5 GPa and elastic modulus of 276 ± 5 GPa. Their hardness is comparable with the common amorphous diamond-like carbon coatings. Moreover, their fracture toughness is significantly higher. The results of mechanical tests were correlated with microstructure observations carried out using scanning and transmission electron microscopy. The images of the deformed area under the residual indentation imprints showed no cracking even after high loads or after indentation with sharp cube corner indenter.

The high-speed sequence imaging of two different atmospheric pressure plasma jets illuminates the low-frequency dynamics of discharge filaments. Usually, atmospheric plasma jets consist of several contracted filaments occurring in the active zone of the plasma randomly in space and stochastically in time. However, particular plasma excitation schemes support collective regimes where the filaments are self-organized at large spatial and temporal scales, even at atmospheric pressure. Moreover, self-organized dynamics can act in a similar manner at different types of plasma. In this paper, evident similarities in filament patterning are pointed out for radio-frequency and microwave atmospheric pressure jets by publishing images of short exposure time (6 ms) from which the filament movement can be derived.

This study reports on a periodic instability in a microwave atmospheric pressure surface wave plasma. Time-resolved observation by means of a high-speed camera reveals that the discharge can operate in two different regimes. The discharge operates either in a static mode of a controlled number of filaments propagating alongside the wall of the fused silica tube or in a dynamic mode of one or more straight filaments together with one revolving filament. Microwave power and argon flow rate are interpreted as the scaling parameters that govern the self-organization in the discharge. The operating diagram is formed by alternating stripes of static and dynamic mode with well-defined borders.

Methods giving absolute concentrations of various species in the plasma are of utmost importance to plasma research. Besides currently prevalent laser methods, a method based on microwave absorption—electron paramagnetic resonance—can be successfully used for plasma diagnostics. It is able to detect many atoms, molecules and radicals in the ground or excited states. In this paper we give an overview of the method and several practical examples. (Some figures in this article are in colour only in the electronic version)

It is well known that the dissociation degree of nitrogen can be substantially increased if a small amount of oxygen is added into an active discharge. In this work it is experimentally shown that a very similar phenomenon occurs also when oxygen is added into the nitrogen late post-discharge. A detailed kinetic model, valid for the oxygen addition into the active discharge, fails to interpret these new experimental observations, and, consequently, its completeness has to be questioned.

In this paper, we report the influence of the various stages of the preionized high power pulsed magnetron discharge on the saturated ion substrate holder current. Our system allows superposition of a preionization low current dc discharge with high voltage pulses applied directly on the magnetron cathode. This system is characterized by a very fast and perfectly reproducible discharge current rise. For a 33?mm copper target, Ar pressure of ~1?Pa, voltage applied in a pulse of ~1?kV, the maximum cathode current of ~40?A is reached in 6??s. The dependence of the saturated ion substrate holder current was analyzed for varying time duration of the high power pulse from 2 up to 8??s by 0.5??s steps. It allows the discrimination of the contribution of elemental temporal intervals to the overall saturated ion substrate holder current. This analysis led to the conclusion that the transport of ballistic ions during the current pulse and in the afterglow is independent of time. We concluded that space charge effects are negligible for both discharge and post-discharge conditions and that electrons act as a neutralizing background. Finally, on the basis of a phenomenological kinetic model for the electron transport, physical explanations of these results are proposed which involve the transverse diffusion of low energy electrons out of the magnetized glow region through electron?ion Coulomb collisions.

A spatio-temporal theoretical model of pulsed microwave discharge was developed. This model is based on the macroscopic continuity equation for electrons and on the wave equation for an electromagnetic wave passing through the discharge plasma. These equations were solved together and in a self-consistent manner. For simplicity, the continuity equation was solved in one dimension only and the electromagnetic wave was assumed to be plane and transversal. Both equations were solved numerically and the spatio-temporal dependences of electron concentration and the amplitude of the microwave electric field were obtained. It was found that the discharge development depends, significantly, on the initial spatial distribution of electron concentration. Two different cases were studied: the discharge development during the first microwave pulse only and after several successive pulses. The calculations were performed particularly for the discharge in nitrogen. The results were compared with experimental data from our previous work.

This paper reports on the oscillations both on the cathode voltage and on the discharge current which emerged suddenly and simultaneously during a high-power impulse magnetron sputtering pulse. Detailed experiments identified the pressure and the discharge current ranges to detect these oscillations. The oscillations originated from the magnetized plasma and their frequency ranged from 225 kHz to 400 kHz depending on the experimental conditions. Simultaneous measurement of both oscillations and spokes was conducted to find mutual correlations. The oscillations always accompanied the spokes and no particular conditions to detect oscillations in the absence of spokes were found. The oscillations were not caused by the rotational motion of the spokes but emerged when a certain threshold amount of spokes was overreached.