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Angewandte Chemie / International edition e202218850 (2023). doi:10.1002/anie.202218850 special issue: "Hot Topic: Water Splitting", Published by Wiley-VCH, Weinheim

The main topic of this article is uninterruptible power supply (UPS) in railway applications, focusing on the power factor correction (PFC) stage of UPS and its interaction with overvoltages and energy strikes. The PFC topology used in this article is a two-phase interleaved DC/DC boost converter with diode bridge rectifier connected to the 25 kV, 50 Hz contact line via 25 kV/0.23 kV transformer. Since overvoltages and energy strikes can occur in the contact line due to thyristor locomotive commutation or self- induction, these interferences can disturb the normal operation of the PFC module and in some cases even destroy the module. A simulation model of the PFC is created, tested with simulated overvoltages, and three modifications/improvements to the existing topology are proposed.

A mass spectrometer with a custom sampling system comprising one fixed and one variable orifice is presented. The custom sampling system allows the determination of the gas composition in the pressure range from 5 mbar to 1000 mbar, with low gas-demixing (1.5%). A case study of mass spectrometer optimization and calibration for the measurement of relative concentration of CO

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

The most striking difference between HiPIMS and other magnetron sputtering discharges, in terms of the plasma process itself, lies in the high-power discharge pulses applied and the large discharge currents generated. We therefore start this chapter on the physics of HiPIMS by exploring the current composition at the target surface and the physical and chemical mechanisms operating at different stages of the discharge pulse and afterglow, which give rise to large discharge currents. Of particular interest is how internal process features such as gas rarefaction, ionization of the sputtered species, self-sputter recycling, and working gas recycling can be influenced by (as well as influence) the choice of pulse length, repetition frequency, applied power density, magnetic field strength and topology, target material, working gas, and so on. Using our understanding of the physics behind the discharge pulse, we then turn to discussing several key aspects in non-reactive and reactive HiPIMS, which includes dealing with the much debated issues of deposition rate as well as loss and transport of charged particles. The latter topic will, by necessity, also address plasma instabilities in HiPIMS.

We report the in situ measurement of the ultraviolet/vacuum-ultraviolet (UV/VUV) emission from a plasma produced by high power impulse magnetron sputtering with aluminum target, using argon as background gas. The UV/VUV detection system is based upon the quantification of the re-emitted fluorescence from a sodium salicylate layer that is placed in a housing inside the vacuum chamber, at 11 cm from the center of the cathode. The detector is equipped with filters that allow for differentiating various spectral regions, and with a front collimating tube that provides a spatial resolution ≈ 0.5 cm. Using various views of the plasma, the measured absolutely calibrated photon rates enable to calculate emissivities and irradiances based on a model of the ionization region. We present results that demonstrate that Al++ ions are responsible for most of the VUV irradiance. We also discuss the photoelectric emission due to irradiances on the target ~ 2×1018 s-1 cm-2 produced by high energy photons from resonance lines of Ar+.

A mass spectrometer with a custom sampling system comprising one fixed and one variable orifice is presented. The custom sampling system allows the determination of the gas composition in the pressure range from 5 mbar to 1000 mbar, with low gas-demixing (2, CO, O2, and N2 gases is presented, together with an example of the CO2 conversion at a microwave plasma torch. The absolute error of the measured conversion of CO2 in CO is found to be less than 1.6% in the complete pressure range. The conversion determination routine presented here allows us to determine relative molar flows of CO2, CO, O2, and N2 and to distinguish between CO and N2 gases, which is important for the determination of the CO2 conversion in the case of air impurities or in the case of CO2/N2 mixtures.

The energy and the composition of the film forming species strongly influence the properties of the films being deposited. In HiPIMS, the film forming material consists of neutral atoms sputtered off the target and its ions. In the case of reactive sputtering, atoms, molecules and ions of the reactive gas also contribute to the film. In this chapter we give an extended overview of the measured fundamental plasma parameters related to ions and neutrals along with a description of suitable techniques for characterizing these species. One of the key differences between dcMS and HiPIMS is the ionization fraction of the sputtered material. Here we also discuss the methods applied to determine the ionization fraction of the sputtered material and the different ways it is quantified, and then survey the ionized flux fraction determined for the HiPIMS discharge. Furthermore, the method of laser-induced fluorescence is utilized to explore the spatio-temporal behavior of the ions and neutrals, and the observations are discussed. We also discuss and compare the ion energy distribution from dcMS and HiPIMS discharges.

The optical emission spectra of high pressure CO2 microwave plasmas are usually dominated by the C2 Swan bands. In this paper, the use of the C2 Swan bands for estimating the gas temperature in CO2 microwave plasmas is assessed. State by state fitting is employed to check the correctness of assuming a Boltzmann distribution for the rotational and vibrational distribution functions and, within statistical and systematic uncertainties, the C2 Swan band can be fitted accurately with a single temperature for rotational and vibrational levels. The processes leading to the production of the C2 molecule and particularly its d 3 Π g state are briefly reviewed as well as collisional relaxation times of the latter. It is concluded that its rotational temperature can be associated to the gas temperature of the CO2 microwave plasma and the results are moreover cross-checked by adding a small amount of N2 in the discharge and measuring the CN violet band system. The 2.45 GHz plasma source is analyzed in the pressure range 180–925 mbar, for input microwave powers ranging from 0.9 to 3 kW and with gas flow rates of 5–100 l min−1. An intense C2 Swan bands emission spectrum can be measured only when the plasma is operated in contracted regime. A unique temperature of about 6000 ± 500 K is obtained for all investigated conditions. A spectroscopic database is constructed using the recent compilation and calculations by Brooke et al (2013 J. Quant. Spectrosc. Radiat. Transfer 124 11–20) of the line strengths and molecular constants for the C2 (d 3 Π g −a 3 Π u ) Swan bands system and made available as supplementary material in a format compatible with the open source MassiveOES software.

Discharge current voltage (IV) curves are directly measured at the target of a high impulse power magnetron sputtering (HiPIMS) plasma for the target materials aluminium, chromium, titanium and copper. These discharge IV curves have been correlated with ICCD camera images of the plasma torus. A clear connection between the change in the discharge IV curve slopes at specific currents and the appearance of localized ionization zones, so-called spokes, in a HiPIMS plasma is identified. These spokes appear above typical target current densities of 2 A/cm2. The slope of the discharge IV curves, at current densities when spokes are formed, depends on the mass of the target atoms with a higher plasma conductivity for higher mass target materials. This is explained by the momentum transfer from the sputter wind to the argon background gas, which leads to higher plasma densities for heavier target materials. The change in the VI curve slope can be used to identify the spokes regime for HiPIMS plasmas, as being mandatory for deposition of good quality materials by HiPIMS. Consequently, the discharge IV curve slope monitoring can be regarded an essential control approach of any industrial HiPIMS process, where discharge IV curves are much easier accessible compared to more complex diagnostics such as time and space resolved ICCD camera measurements. (© 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Gepulste Hochleistungsplasmen (High Power Pulsed Magnetron Sputtering — HPPMS) eignen sich hervorragend zur Synthese von hochwertigen keramischen Schichten, da der Fluss der schichtbildenden Teilchen sehr energiereich ist. Diese besondere Form der Energieverteilung hat ihre Ursache in der Bildung von lokalisierten Ionisationszonen, wie man sie mit schnellen Kameramessungen beobachten kann. In der Praxis sind allerdings nur kostengunstigere Methoden wie Strom-Spannungsmessungen am Target verfugbar. Durch Interpretation der Strom-Spannungskennlinien ist es trotzdem moglich, den richtigen Betriebsmodus eines HPPMS-Plasmas zu finden. Diese Strom-Spannungskennlinien sind je nach Targetmaterial sehr unterschiedlich, zeigen aber eindeutig die Bildung von lokalisierten Ionisationszonen an und damit den optimalen Betriebsmodus eines HPPMS-Plasmas. Control of High Power Pulsed Magnetron Plasmas (HPPMS) by Monitoring Current-Voltage Characteristics High Power Pulsed Magnetron Sputtering (HPPMS) plasmas are perfectly suited for the synthesis of ceramic coatings with superior properties. This excellent performance is induced by the very peculiar energetic particle flux reaching the substrate to be coated. The ion energy distribution originates from the formation of localized ionization zones which can be imaged by fast cameras. In commercial HPPMS reactors, however, only much simpler methods such as current voltage characteristics (VI curves) are accessible. By a proper interpretation of those VI curves, it is possible to identify the favorable operation mode of an HPPMS plasma. The VI curves vary with target material, but they are sensitive to the occurrence of localized ionization zones, which represent the optimum for the operation parameter window of HPPMS plasmas.

Microwave plasmas are a promising technology for energy-efficient CO2 valorization via conversion of CO2 into CO and O2 using renewable energies. A 2.45 GHz microwave plasma torch with swirling CO2 gas flow is studied in a large pressure (20–1000 mbar) and flow (1–100 L min−1) range. Two different modes of the plasma torch, depending on the operating pressure and microwave input power, are described: at pressures below 120 mbar the plasma fills most of the plasma torch volume whereas at pressures of about 120 mbar an abrupt contraction of the plasma in the center of the resonator is observed along with an increase of the gas temperature from 3000 K to 6000 K. The CO outflow is generally found to be proportional to the plasma effective power and exhibits no significant dependence on the actual CO2 flow injected into the reactor but only on the input power at certain pressure. Thermal dissociation calculations show that, even at the lowest pressures of this study, the observed conversion and energy efficiency are compatible with a thermal dissociation mechanism.

Neutral species and positive ions are measured by means of mass spectrometry in the effluent of the non-equilibrium atmospheric plasma jet operated in He/0%–1%CO2 gas mixture. The capacitively coupled plasma source is the predecessor of the known COST reference jet with identical performance and it is operated in a diffuse mode with gas temperature close to the room temperature. Threshold ionisation molecular beam mass spectrometry is used to measure absolute densities of CO, O2, O and O3 species. The CO molecules are generated with densities up to 2 × 1015 cm−3 at 1 W absorbed power. The O2 density is ∼6 times lower than the CO density and even lower than the O density at level of 4.5 × 1014 cm−3. The O3 density is negligibly small at 4 × 1012 cm−3. The measured O2, O3 and O absolute densities add up to ∼57% of the expected oxygen amount. The high O density could indicate that the vibrational excitation of CO2 is ineffective in this plasma and gas mixture, because O would otherwise react quickly with vibrationally excited CO2(v) to form CO and O2, the low energy efficiency is in agreement with the possibly low vibrational excitation. The highest energy efficiency is just 5% with 1% conversion efficiency. Ion mass spectrometry have been used to measure positive and negative ions, where only positive ions have been detected. The ion with highest signal is the O 2 + ion, probably due to its low ionisation energy. CO 2 + , O 3 + , ( CO ) 2 + , but no CO+, and protonated clusters or clusters containing water molecules have been detected as well. Neutrals and positive ions have been measured as a function of CO2 admixture, applied power and distance to the jet nozzle. The observed trends can be used for validation of plasma-chemistry models.

The velocity distribution function of titanium neutrals in the target region of a high power impulse magnetron sputtering discharge was investigated by optical emission spectroscopy. A high-resolution plane grating spectrograph combined with a fast, gated, intensified CCD camera was used to study the shape of selected optical emission lines. Doppler broadening and shift were analyzed to gain information about the velocity distribution of sputtered titanium neutrals. The velocity distribution function was found to depend on the discharge power for target power densities up to 0.6 kW cmlsupg-2l/supg. Above that value, the velocity distribution was constant. The collision processes of sputtered neutrals close to the target could be described using a modified version of the Krook collisional operator. Using this interpretation, evidence for strong scattering of the titanium neutrals in the target region was found. This scattering can be explained by resonant charge exchange with previously scattered titanium ions.

In our previously published paper, the life span of metal ions in high-power impulse magnetron sputtering (HIPIMS) discharges was measured up to 5 ms from the start of the pulse. To investigate the influence of the ion mass, ionization energy, and sputter yield on the time evolution and life span of singly and doubly charged metal and gas ions in the HIPIMS plasma discharge, the most frequently used materials for thin-film deposition carbon, aluminium, titanium, chromium, copper, and niobium have been used. The ion energy distribution function of each material was measured using energy resolved mass spectrometry in time-resolved mode. The setup of the mass spectrometer was the same for all materials. To investigate the influence of working gas pressure on the time evolution of ion fluxes, measurements have been performed at two pressures, 0.3 Pa and 3 Pa.

In this paper, the novel technique of THz time domain spectroscopy has been applied to obtain time-resolved measurements of the plasma density in the active zone of a HiPIMS discharge with a titanium target. The obtained peak values are in the range of 1012–1013 cm−3 for discharge current densities of 1–4 A cm−2 at 0.5 and 2 Pa argon pressure. The measured densities show good correlation with the discharge current and voltage and the intensity of various atomic and ionic lines. The well known phases of the discharge have been identified and related to the variation of the electron density. The measurement results show that the plasma density remains nearly constant during the runaway/self-sputtering phase. Based on that, it is conjectured that singly charged titanium ions are the dominant ion species during this phase.

High power impulse magnetron sputtering (HiPIMS) is a versatile technology to deposit thin films with superior properties. During HiPIMS, the power is applied in short pulses of the order of 100 μs at power densities of kW to a magnetron target creating a torus shaped dynamic high density plasma. This plasma torus is not homogeneous, but individual ionization zones become visible, which rotate along the torus with velocities of 10 km . Up to now, however, any direct measurement of the electron density inside these rotating ionization zones is missing. Here, we probe the electron density by measuring the target current locally by using small inserts embedded in an aluminium target facing the plasma torus. By applying simple sheath theory, a plasma density of the order of at the sheath edge can be inferred. The plasma density increases with increasing target current. In addition, the dynamics of the local target current variation is consistent with the dynamics of the traveling ionization zone causing a modulation of the local current density by 25%.

In this work, a fundamental investigation of an industrial (Cr,Al)N reactive high power pulsed magnetron sputtering (HPPMS) process is presented. The results will be used to improve the coating development for the addressed application, which is the tool coating for plastics processing industry. Substrate-oriented plasma diagnostics and deposition of the (Cr,Al)N coatings were performed for a variation of the HPPMS pulse frequency with values from f = 300 Hz to f = 2000 Hz at constant average power P = 2.5 kW and pulse length ton = 40 μs. The plasma was investigated using an oscilloscope, an intensified charge coupled device camera, phase-resolved optical emission spectroscopy, and an energy-dispersive mass spectrometer. The coating properties were determined by means of scanning electron microscopy, glow discharge optical emission spectroscopy, cantilever stress sensors, nanoindentation, and synchrotron X-ray diffraction. Regarding the plasma properties, it was found that the average energy within the pl...

Correlatively employing density functional theory and experiments congregated around high power pulsed magnetron sputtering, a plasma-surface model for metastable Cr0.8Al0.2N (space group Fm 3 ¯m) is developed. This plasma-surface model relates plasma energetics with film composition, crystal structure, mass density, stress state, and elastic properties. It is predicted that N Frenkel pairs form during Cr0.8Al0.2N growth due to high-energy ion irradiation, yielding a mass density of 5.69 g cm−3 at room temperature and Young's modulus of 358–130 GPa in the temperature range of 50–700 K for the stress-free state and about 150 GPa larger values for the compressive stress of 4 GPa. Our measurements are consistent with the quantum mechanical predictions within 5% for the mass density and 3% for Young's modulus. The hypothesis of a stress-induced Young's modulus change may at least in part explain the spread in the reported elasticity data ranging from 250 to 420 GPa.

Spokes, localised ionisation zones, are commonly observed in magnetron sputtering plasmas, appearing either with a triangular shape or with a diffuse shape, exhibiting self-organisation patterns. In this paper, we investigate the spoke properties (shape and emission) in a high power impulse magnetron sputtering (HiPIMS) discharge when reactive gas (N2 or O2) is added to the Ar gas, for three target materials; Al, Cr, and Ti. Peak discharge current and total pressure were kept constant, and the discharge voltage and mass flow ratios of Ar and the reactive gas were adjusted. The variation of the discharge voltage is used as an indication of a change of the secondary electron yield. The optical emission spectroscopy data demonstrate that by addition of reactive gas, the HiPIMS plasma exhibits a transition from a metal dominated plasma to the plasma dominated by Ar ions and, at high reactive gas partial pressures, to the plasma dominated by reactive gas ions. For all investigated materials, the spoke shape ch...

Reactive high power impulse magnetron sputtering (HiPIMS) of metals is of paramount importance for the deposition of various oxides, nitrides and carbides. The addition of a reactive gas such as nitrogen to an argon HiPIMS plasma with a metal target allows the formation of the corresponding metal nitride on the substrate. The addition of a reactive gas introduces new dynamics into the plasma process, such as hysteresis, target poisoning and the rarefaction of two different plasma gases. We investigate the dynamics for the deposition of chromium nitride by a reactive HiPIMS plasma using energy- and time-resolved ion mass spectrometry, fast camera measurements and temporal and spatially resolved optical emission spectroscopy. It is shown that the addition of nitrogen to the argon plasma gas significantly changes the appearance of the localized ionization zones, the so-called spokes, in HiPIMS plasmas. In addition, a very strong modulation of the metal ion flux within each HiPIMS pulse is observed, with the metal ion flux being strongly suppressed and the nitrogen molecular ion flux being strongly enhanced in the high current phase of the pulse. This behavior is explained by a stronger return effect of the sputtered metal ions in the dense plasma above the racetrack. This is best observed in a pure nitrogen plasma, because the ionization zones are mostly confined, implying a very high local plasma density and consequently also an efficient scattering process.

Correlation between the plasma self-organization areas (also known as ionization zones or spokes) and the ground state/metastable atoms behavior during magnetron sputtering glow discharge is investigated. High-power impulse magnetron sputtering case is considered. For this purpose, the imaging of the ground states atomic Ti(3d24s2 a3F2), Ti+(3d2(3F)4s a4F3/2) and metastable Ar(3s23p54s (3P2)) is performed using laser-induced fluorescence. Results indicate a correlation between the studied Ti+ atomic density and the spoke dynamics. A qualitative model for the spoke-assisted magnetron sputtering is proposed, taking into account spoke formation, strong electron excitation in plasma, and other inherent phenomena of the sputtering discharge.

Localized light emission patterns observed during on time of a high power impulse magnetron sputtering (HiPIMS) discharge on a planar magnetron, known as spokes or ionization zones, have been identified as a potential source of anomalous cross-B field diffusion. In this paper experimental evidence is presented that anomalous diffusion is triggered by the appearance of spokes. The Hall parameter , product of the electron cyclotron frequency and the classical collision time, reduces from Bohm diffusion values ( and higher) down to the value of 3 as spokes appear, indicating anomalous cross-B field transport. A combination of intensified charge coupled device imaging and electric probe measurements reveals that the ions from the spokes are instantaneously diffusing away from the target. The ion diffusion coefficients calculated from a sideways image of the spoke are six times higher than Bohm diffusion coefficients, which is consistent with the reduction of the Hall parameter.

Summary form only given. High Power Pulsed Magnetron Sputtering (HPPMS) is a recently developed Ionized Physical Vapor Deposition (IPVD) technique. A bias voltage is applied to the target for a few hundred microseconds with a frequency of a few hundreds of Hertz, delivering several kW cm−2 of power to the target. This results in the production of an ultra dense plasma with a high ionization degree, showing some peculiar behaviors.

A time-resolved analysis of the emission of power impulse magnetron sputtering plasmas reveals inhomogeneities in the form of rotating spokes. The shape of these spokes depends on the target material in a characteristic manner; the peculiar shape of the emission profiles is explained by the localization of the sputtering process as being governed by Ar gas rarefaction and the local dynamics of secondary electrons generation. This general picture is able to explain the observed emission patterns for different target materials as presented.

High power magnetron sputtering (HiPIMS) discharges generate ions with high kinetic energies in comparison to conventional dc magnetron sputtering. The peculiar shape of the ion energy distribution function (IEDF) is correlated to the formation of localized ionization zones (IZ) in the racetrack of a HiPIMS discharge, so called spokes. This is explained by a local maximum of the electrical potential inside these localized IZ. By using ion energy mass spectrometry, probe experiments and plasma spectroscopy the connection between IZ and IEDFs is evaluated with high temporal resolution. The data of a floating probe next to the target is used to directly monitor the movement of the spokes in the E×B ?> direction. Chromium is used as target material, because the plasma undergoes a sequence from stochastic spoke formation, to regular spoke pattern rotating in the E×B ?> direction to a homogeneous plasma torus with increasing plasma power. In particular, the analysis of the transition from the regular spoke pattern to the homogeneous plasma torus at very high plasma powers shows that the high energy part of the IEDF is not affected and only the low energy part is modified. Consequently, one could consider the homogenous plasma torus at very high plasma powers as a a single ionization zone localized over the complete torus, which is formed by merging individual spokes with increasing power. Details and consequences of that model are discussed.

Spokes, localised light emission patterns appearing during the HiPIMS discharge, are investigated using optical emission diagnostic and electrical probes. Both, temporal and spatial aspects of the spoke phenomenon have been investigated. The evolution from stochastic to self-organised patterns consisting of a finite number of spokes along the racetrack (= spoke mode number), the transition between two spoke modes, and the stability of a spoke mode is presented. For a constant discharge current, spokes steadily rotate above the magnetron racetrack. The transition between two spoke modes is described by a model which links the spoke mode number decrease with increasing discharge current. It is based on the interaction between the current in the spoke, the Ar rarefaction and Ar replenishment times that prevail over electrostatic repulsion and charged particle diffusion. Two spokes merge by an acceleration of the trailing spoke with respect to the direction of rotation.

Krypton is sometimes used in physical vapor deposition processes due to its greater atomic mass and size compared to argon, which leads to a lower gas incorporation and may have beneficial effects on kinetics of the coating growth. In this paper, the authors investigate the plasma composition and properties of deposited high power pulse magnetron sputtering Cr-N coatings for discharges with various Ar/Kr ratios and for various pulse lengths of 40 μs, 80 μs, and 200 μs, keeping the average discharge power constant. The results show that an addition of Kr influences the discharge process by altering the ignition and peak values of the discharge current. This influences the metal ion generation and growth conditions on the substrate by reducing the nucleation site densities, leading to a predominantly columnar grow. However, the deposition rate is highest for an Ar/Kr ratio of 120/80. The integral of the metal ion and atom emission exhibits the same trend, having a maximum for Ar/Kr ratio of 120/80. By decreasing the pulse length, the deposition rate of coatings decreases, while the hardness increases.

A time resolved analysis of the emission of HiPIMS plasmas reveals inhomogeneities in the form of rotating spokes. The shape of these spokes is very characteristic depending on the target material. The localized enhanced light emission has been correlated with the ion production. Based on these data, the peculiar shape of the emission profiles can be explained by the localized generation of secondary electrons, resulting in an energetic electron pressure exceeding the magnetic pressure. This general picture is able to explain the observed emission profile for different target materials including gas rarefaction and second ionization potential of the sputtered elements.

Current–voltage characteristics within the temporal pulse were recorded in high-power pulsed magnetron sputtering discharges for different target materials. These curves allowed identifying at a first glance the existence of separated plasma regimes clearly differentiated by the plasma conductivity and by the spatial arrangement of the plasma emission. We could establish that regimes of high plasma conductivity are univocally associated to the self-organization of the plasma in well-defined ionization zones. As the applied power is gradually increased, the high conductivity regime is abruptly replaced by a regime of high current and low plasma conductivity, associated to homogeneous plasma emission.

We observed that high-power pulsed magnetron plasmas show instabilities in the form of rotating emission structures. Fast CCD camera measurements show motion into the E × B direction. Their characteristic frequencies are in the 100 kHz range. They are correlated with a modulation of the floating potential and changes in the ion saturation current of a Langmuir probe. Rotation velocities are of the order of 10 km s−1. The azimuthal mode number, i.e. the number of emission nodes depends on current. The fast Fourier transform (FFT) analysis of the frequency spectra indicates that the structures condense out of broad band fluctuations suggesting transition from stochastic to periodic behaviour. FFT of the Langmuir probe signals also identifies other types of instabilities at around 2.4 MHz, which is corresponding to the frequency of a modified two-stream instability.

The processes of argon retention by the target and redeposition of target material were investigated by x-ray photoelectron spectroscopy as a function of radial position for different plasma conditions in high-power impulse magnetron sputtering of aluminum targets. Significant differences in Ar radial concentration profiles were observed for different discharge conditions. Inside the racetrack area, Ar ion flux-dominated implantation is compensated by radiation-enhanced diffusion loss terms. Outside the racetrack, the role of ion implantation is diminished, and Ar retention by the target may stem from a balance between gettering by redeposited Al and ion-induced Ar desorption.

Reactive plasmas are highly valued for their ability to produce large amounts of reactive radicals and of energetic ions bombarding surrounding surfaces. The non-equilibrium electron driven plasma chemistry is utilized in many applications such as anisotropic etching or deposition of thin films of high-quality materials with unique properties. However, the non-equilibrium character and the high power densities make plasmas very complex and hard to understand. Mass spectrometry (MS) is a very versatile diagnostic method, which has, therefore, a prominent role in the characterization of reactive plasmas. It can access almost all plasma generated species: stable gas-phase products, reactive radicals, positive and negative ions or even internally excited species such as metastables. It can provide absolute densities of neutral particles or energy distribution functions of energetic ions. In particular, plasmas with a rich chemistry, such as hydrocarbon plasmas, could not be understood without MS. This review focuses on quadrupole MS with an electron impact ionization ion source as the most common MS technique applied in plasma analysis. Necessary information for the understanding of this diagnostic and its application and for the proper design and calibration procedure of an MS diagnostic system for quantitative plasma analysis is provided. Important differences between measurements of neutral particles and energetic ions and between the analysis of low pressure and atmospheric pressure plasmas are described and discussed in detail. Moreover, MS-measured ion energy distribution functions in different discharges are discussed and the ability of MS to analyse these distribution functions with time resolution of several microseconds is presented.

We report for the first time on instabilities of High Power Impulse Magnetron Sputtering Plasmas (HIPIMS) which are likely to be of the generalised drift wave type. They are characterized by well defined regions of high and low plasma emissivity along the racetrack of the magnetron and causes periodic shifts in floating potential. The azimuthal mode number m depends on plasma current, plasma density, and gas pressure. The structures rotate in

High power impulse magnetron sputtering (HIPIMS) is a plasma vapour deposition technique used for deposition of dense coatings. In order to contribute to a better understanding of the dynamics of a HIPIMS plasma discharge, time- and wavelength-resolved measurements of the light emitted from the plasma were performed. Lateral images of the HIPIMS plasma were recorded using an ICCD camera with a gate width of 1??s. For each picture, Abel inversion was performed to compute the radial emissivity profile of the plasma. Band-pass interference filters were used to isolate the desired wavelength in order to observe lines of ions and neutrals of metal and argon (Ar) in HIPIMS plasma discharges with an aluminium (Al), titanium (Ti) or chromium (Cr) target in Ar atmosphere. The result is the temporal evolution of the radial emissivity profile of metal and gas neutrals and singly charged ions.

We report on instabilities in high power impulse magnetron sputtering plasmas which are likely to be of the generalized drift wave type. They are characterized by well defined regions of high and low plasma emissivity along the racetrack of the magnetron and cause periodic shifts in floating potential. The azimuthal mode number m depends on plasma current, plasma density, and gas pressure. The structures rotate in E→×B→ direction at velocities of ∼10 km s−1 and frequencies up to 200 kHz. Collisions with residual gas atoms slow down the rotating wave, whereas increasing ionization degree of the gas and plasma conductivity speeds it up.

High power impulse magnetron sputtering (HIPIMS) is a novel deposition technology successfully implemented on full scale industrial machines. HIPIMS utilizes short pulses of high power delivered to the target in order to generate high amount of metal ions. The life-span of ions between the pulses and their energy distribution could strongly influence the properties and characteristics of the deposited coating. In modern industrial coating machines the sample rotates on a substrate holder and changes its position and distance with regard to the magnetron. Time resolved measurements of the ion energy distribution function (IEDF) at different distances from the magnetron have been performed to investigate the temporal evolution of ions at various distances from target. The measurements were performed using two pressures, 1 and 3 Pa to investigate the influence of working gas pressure on IEDF. Plasma sampling energy-resolved mass spectroscopy was used to measure the IEDF of Ti1+, Ti 2+, Ar1+, and Ar2+ ions in HIPIMS plasma discharge with titanium (Ti) target in Ar atmosphere. The measurements were done over a full pulse period and the distance between the magnetron and the orifice of the mass spectrometer was changed from 25 to 215 mm. © 2010 American Institute of Physics.

High power impulse magnetron sputtering (HIPIMS) discharges produce metal ions with energies up to 100 eV and the degree of metal ionization can be up to 90%. The ion energy distribution function (IEDF) of ions in HIPIMS of a chromium target in an argon atmosphere was measured using plasma sampling energy resolved mass spectrometry. The time resolved measurements show that in the pulse-on phase the IEDF of Cr1+ comprises a single high energy group of ions, whereas at the end of the pulse, ions are thermalized due to collisions with Ar and the IEDF comprises both a low energy group of ions and a high energy group of ions. Finally, after 320 mu s from the start of the pulse only a main low energy peak is present. The IEDF of Ar1+ comprises an intense low energy peak and a high energy shoulder, the latter appearing simultaneously with the high energy Cr ions and probably created due to collisions with the hot metal ions. After the pulse only a low energy group of ions of Ar1+ IEDF was detected. The temporal evolution of the total ion density extracted from Langmuir probe measurements is linked with metal ion-to-gas ion ratios giving an insight into the time evolution of deposition fluxes in the plasma. The influence of the time evolution of IEDF and plasma composition on the thin film growth is discussed.

Plasma composition near the substrate was investigated in a high power impulse magnetron sputtering (HIPIMS) discharge using Langmuir probe analysis, mass spectroscopy, and atomic absorption spectroscopy. The HIPIMS discharge was operated in nonreactive Ar atmosphere at a pressure of 2.66 Pa and the magnetron cathode was furnished with Ti target. Plasma density, metal ion-to-neutral ratio, and gas ion-to-metal ion ratio were studied as a function of discharge current. At peak discharge current densities of ∼1 A cm−2, the results show that a dense plasma (ne∼1018 m−3) expanded from the target toward the substrate and lasted more than 330 μs after the supplied power was turned off. The shape of the time-averaged ion energy distribution function of sputtered material exhibited a transition from Thompson to Maxwellian distribution, indicating efficient energy transfer in the discharge. The metal content in the plasma monotonically increased with discharge current and the metal ion-to-neutral ratio reached app...

High-power impulse magnetron sputter deposition of metallic films was investigated. Time-averaged mass spectroscopy was performed to provide information on the energy distribution of individual ions and the composition of total ion fluxes over a wide range of deposition conditions. Chromium and niobium targets were used, the repetition frequency was 50 Hz and 60 Hz, respectively, and argon pressures were 0.29 Pa and 2.7 Pa. The strong effect of the working gas pressure on the ion energy distribution was shown. For low pressure (0.29 Pa) the metal ion energy distribution reveals a significant high energy tail (up to 20 eV). It was also shown that the increase in the average pulse current results in a higher fraction of metal ions in the total ion flux. Argon ions were dominant over niobium ions, while chromium ions became dominant in the total ion flux onto the substrate at high values of target power loading. At a high pressure (2.7 Pa), the high energy tail of metal ion energy distribution became negligible. Film deposition experiments showed that the efficiency of the sputtering process and particle transport to the substrate decreased with increasing target power loading.

The ion energy distribution function (IEDF) in high power impulse magnetron sputtering (HIPIMS) discharges was studied by plasma sampling energy-resolved mass spectroscopy. HIPIMS of chromium (Cr), titanium (Ti) and carbon ( C) targets in argon (Ar) atmosphere was analysed. Singly and doubly charged ions of both the target and the gas were detected. Time-averaged IEDFs were measured for all detected ions at the substrate position at a distance of 150mm from the target. The effects of target current and discharge pressure on the IEDF were investigated. Measurements were done at two pressures and for three peak discharge currents. The IEDF of both the target and the gas ions was found to comprise two Maxwellian distributions. Quantitative analysis of target IEDFs at a low pressure showed that the main peak had a lower average energy with an approximate value of E-AV = 1 eV which is attributed to collisions with thermalized gas atoms and ions. The higher energy distribution has a tail extending up to 70 eV, which is assumed to originate from a Thompson distribution of sputtered metal atoms which, due to collisions, are thermalized and appear as a Maxwell distribution. The proportion of high energy IEDFs for metal ions increases monotonically as a function of Id. The effective ion temperature k(B)T, extracted from the main low energy peak, showed a weak dependence on peak current. The effective ion temperature extracted from the high energy tail showed a strong correlation with the change in Id. The IEDF at high pressure shows that a proportion of high energy IEDFs was very low and dominated by a low energy main peak. The gas IEDF at high pressure was completely thermalized. The metal-ion-to-gas-ion ratio was found to increase with Id and with the sputtering yield of the target material.