The involvement of plasmas in deposition processes opens the possibility for non-equilibrium processes including atomic scale heating by ions and electrons. This can be very beneficial from several points of view, including, but not limited to, a reduction of the requirements for conventional substrate heating, the possibility to deposit films on temperature-sensitive substrates, the formation of metastable or otherwise unattainable phases, and the combination of deposition and etching effects. Non-equilibrium heating implies transient (sub-picosecond to picoseconds) and highly localized (nanometer-squared) events associated with the arrival of energetic particles from the plasma. These particles carry kinetic and potential energies to the substrate or film surface. While conventional heating drives the system always toward equilibrium, non-equilibrium heating events involve competing effects of defect generation (affected by momentum transfer) and annealing (by localized heating). The most often used approach to control the kinetic energy of ions is tuning the difference between plasma and surface potentials, i.e., using suitable substrate or plasma bias. When the kinetic ion energy exceeds the displacement energy, film growth can occur under the surface (very shallow ion implantation or "subplantation"), which is utilized, for example, in the deposition of diamond-like carbon and of metastable cubic phases of ternary nitrides. Besides kinetic energy, potential energy is brought to the growing film, especially if the arriving ion flux contains multiply charged ions, which is common in cathodic arc deposition. The extremely fast and localized heating events accumulate and thereby lead to an increase of the global film surface temperature. The relation of equilibrium and non-equilibrium heating is captured by generalized temperature and energy axes in structure zone diagrams. This review focuses on non-equilibrium heating processes by ions and electrons.

A unipolar arc is a form of an arc discharge that ignites and burns between the surface of a conducting, but floating, plasma-facing component and the plasma. Phenomenological similarities between unipolar arcs and vacuum arcs suggest that the spots are cathode spots, which, in the case of unipolar arcs, require a ring-like area around the spot that acts as an anode. All models of unipolar arcs seek to explain how a sufficiently high electron return current can be achieved. Building on elements of various existing models, it is shown that the combination of high density of expanding spot plasma and high electron temperature in the spot vicinity enables high return current. Taking the traveling double layer of an expanding plasma into account, it follows that the electron return current may be even larger than the net arc current in the case of the vacuum arc, while the ion current to the surface plays only a minor role. The similarity between vacuum arcs and unipolar arcs suggests that the vacuum arc has effectively two anodes, the one connected to the power supply, and the ring-like area around each cathode spot. The arguments, underpinned by analytical formulas and experimental data from the literature, could serve as a blueprint for future simulations and targeted experiments.

The evaporation of droplets in an arc plasma flow under the action of an electron beam injected into the arc plasma and the condition of direct heating of microdroplets by beam electrons are considered. Analytical modeling shows that droplets ≤1 μm in size can be completely evaporated over time scales typical for cathodic arc deposition systems. It is shown that small microdroplets evaporate more intensively. The lower limit working points in terms of plasma electron density, and the electron energy and density of the injected energetic electrons required for droplet evaporation are found.

The burning voltage of cathodic arcs is a key indicator of plasma-cathode interactions, yet its dependence on material, gas environment, and transient surface processes remains is not fully understood and well described. In this work, we investigated the burning voltage dynamics of cathodic arcs on titanium, aluminum, copper, and graphite cathodes in vacuum, argon, oxygen, and nitrogen atmospheres. We addressed how the burning voltage dynamics can be analyzed through the dynamics in the burning voltage amplitude and the power spectrum. We proposed the use of the Poisson point process to interpret burning voltage power spectrum dynamics. Argon reduces burning voltage through gas-enhanced ion bombardment nearby the operating spot, while reactive gases promote dielectric-covered surfaces that increase the prevalence short-lived type 1 spots. The presence of short-lived type 1 spots is reflected in the increasing decay rate gamma max of the Poisson point process model. In aluminum-oxygen discharges, a disappearing anode effect drives voltage drift to higher values, whereas graphite shows distinct spectral behavior due to its thermal and emission properties. The use of the Poisson point process model provides a framework linking burning voltage amplitude and spectra to the established cathodic arcs physics.

Deposition using filtered pulsed cathodic arc plasma is known to produce dense and adherent thin films due to energetic ions which carry significant ion kinetic and potential energies. The role of potential energy coming from multiply charged metal ions in film formation remains under-explored, since the enhancement of charge states in cathodic arcs is coupled with an increased flux and kinetic energies of ions. In this work, the influence of ion potential energy on structural properties of thin films is investigated, while keeping the mean ion kinetic energies unchanged. Two material systems are considered: metallic V-Al and compound V-Al-N in non-reactive and reactive deposition, respectively. For V-Al plasma and thin films, the impact of metal ion potential energy is demonstrated. In the V-Al-N case, in addition to metal ions, activated (namely, ionized, dissociated, and excited) nitrogen species are found to be a significant factor for crystalline growth of the metastable cubic phase.

Intermetallic phases are preferred to reduce the amount of platinum used for catalytic applications as compared to solid solution alloys, due to their stability at elevated temperatures while preserving or even enhancing the catalytic properties. Here, we show a two-step process to form an intermetallic NiPt L10 phase. In this work, NiPt solid solution thin films were fabricated by direct current and high-power impulse magnetron sputtering processes, which allow for precise thickness and chemical composition control. Following deposition, an additional annealing step is used to form the desired intermetallic phase. We show that the required annealing time for intermetallic phase formation is considerably reduced for NiPt thin films with a thickness of 240 nm, as compared to its bulk counterpart.

This work provides a quantitative analysis of what it would take to fully evaporate copper macroparticles embedded in a cathodic arc plasma flow. This analysis is important for the justification of efforts to develop an evaporation scheme based on adding an electron beam. We want to explore if this approach could be an alternative to conventional plasma filtering to obtain macroparticle-free plasma from a cathodic arc plasma source. If successful, cathodic arc plasma deposition could be extended from a popular technology for hard and decorative coatings to much more demanding coatings applications, for example in microelectronics. Here, we study the feasibility and economical implication of evaporating micrometer-sized macroparticles on length and time scales typical for cathodic arc deposition systems. We show by analytical modeling that macroparticles with a radius ⩽1 µ m can be completely evaporated in a plasma of density 10 16 m −3 when using an electron beam of at least 3 keV and a beam electron density of at least 10 14 m −3 . While the theoretical opportunity is shown, we acknowledge the significant practical and economic challenges in the practical implementation of the approach.

Spokes are regions of enhanced ionization in magnetron sputtering discharges that are interesting because of their role for magnetron operation and their potential effect on deposition processes. Here, we show that spokes can intentionally be generated by introducing a strong-to-weak magnetic field strength transition along the racetrack. Spokes are triggered at the transition point from an accelerating electron drift when weakening the magnetic field strength. The spokes are then propagating against the electron drift into the strong magnetic field strength section of the racetrack. At the weak-to-strong magnetic field transition, we observe the inverse effect. The electron drift is decelerated at this point, creating a region of enhanced optical emission. From rectangular racetracks this is known as the cross-corner effect. Here, we show that a corner is not necessary for observing that effect. Pronounced spokes at low working gas pressure of 0.2 Pa exhibit a substructure that could be caused by the diocotron instability previously predicted by computer simulations.

Ever since they have been studied, gas discharges have been classified by their visual appearance as well as by their current and voltage levels. Glow and arc discharges are the most prominent and well-known modes of discharges involving electrodes. In a first approximation, they are distinguished by their current and voltage levels, and current–voltage characteristics are a common way to display their relations. In this review, glow discharges are defined by their individual electron emission mechanism such as secondary electron emission by photons and primary ions, and arcs by their respective collective mechanism such as thermionic or explosive electron emission. Emitted electrons are accelerated in the cathode sheath and play an important role in sustaining the discharge plasma. In some cases, however, electron emission is not important for sustaining the plasma, and consequently we have neither a glow nor an arc discharge but a third type of discharge, the ohmic discharge. In part 1 of this review, these relationships are explained for quasi-stationary discharges, culminating with updated graphical presentations of I–V characteristics (Figs. 15 and 16). In part 2, further examples are reviewed to include time-dependent discharges, discharges with electron trapping (hollow cathode, E×B discharges) and active anode effects.

Deposition of epitaxial oxide semiconductor films using physical vapor deposition methods requires a detailed understanding of the role of energetic particles to control and optimize the film properties. In the present study, Ga2O3 thin films are heteroepitaxially grown on Al2O3(0001) substrates using oxygen ion beam sputter deposition. The influence of the following relevant process parameters on the properties of the thin films is investigated: substrate temperature, oxygen background pressure, energy of primary ions, ion beam current, and sputtering geometry. The kinetic energy distributions of ions in the film-forming flux are measured using an energy-selective mass spectrometer, and the resulting films are characterized regarding crystalline structure, microstructure, surface roughness, mass density, and growth rate. The energetic impact of film-forming particles on the thin film structure is analyzed, and a noticeable decrease in crystalline quality is observed above the average energy of film-forming Ga+ ions around 40 eV for the films grown at a substrate temperature of 725 °C.

Focusing of femtosecond laser pulses in gases can produce different gas breakdown phenomena depending on the focusing conditions: from simple optical breakdown like laser “sparks” to a nonlinear optical breakdown like filamentation. The dynamics of such plasmas after the pulse exposure is dependent on the energy deposited by the laser in the breakdown volume. Using a time- and position-dependent breakdown model, we estimate the breakdown volume and show that the energy deposited by the laser in this breakdown volume determines the characteristics of laser-induced plasma in the post-pulse exposure regime. Experimentally we find that for different focal lengths there exists a threshold value of the energy density beyond which a transition from an ellipsoidal shape to a spherical shape can be observed, followed by a toroidal expansion of the produced plasma. When electron density and electron temperature are expressed as a function of the energy density, deviations from the parabolic dependence on irradiance are observed. They imply additional ionization by multiphoton ionization in the plasma volume that occurs when the peak power of the laser pulse is above the critical power for self-focusing in air. The relevance of this experimental and theoretical study is to prevent undesired self-focusing conditions during material processing, a step toward well-controlled laser-plasma etching without laser ablation.

Ultrashort-pulse laser processing of copper is performed in air to reduce the secondary electron yield (SEY). By UV (355 nm), green (532 nm), and IR (1064 nm) laser-light induced surface modification, this study investigates the influence of the most relevant experimental parameters, such as laser power, scanning speed, and scanning line distance (represented as accumulated fluence) on the ablation depth, surface oxidation, topography, and ultimately on the SEY. Increasing the accumulated laser fluence results in a gradual change from a Cu2O to a CuO-dominated surface with deeper micrometer trenches, higher density of redeposited surface particles from the plasma phase, and a reduced SEY. While the surface modifications are less pronounced for IR radiation at low accumulated fluence (<1000 J/cm2), analogous results are obtained for all wavelengths when reaching the nonlinear absorption regime, for which the SEY maximum converges to 0.7. Furthermore, independent of the extent of the structural transformations, an electron-induced surface conditioning at 250 eV allows a reduction of the SEY maximum below unity at doses of 5×10-4 C/mm2. Consequently, optimization of processing parameters for application in particle accelerators can be obtained for a sufficiently low SEY at controlled ablation depth and surface particle density, which are factors that limit the surface impedance and the applicability of the material processing for ultrahigh vacuum systems. The relations between processing parameters and surface features will provide guidance in treating the surface of vacuum components, especially beam screens of selected magnets of the Large Hadron Collider or of future colliders.

Pulsed filtered cathodic arc deposition involves formation of energetic multiply charged metal ions, which help to form dense, adherent, and macroparticle-free thin films. Ions possess not only significant kinetic energy, but also potential energy primarily due to their charge, which for cathodic arc plasmas is usually greater than one. While the effects of kinetic ion energy on the growing film are well investigated, the effects of the ions’ potential energy are less known. In the present work, we make a step toward decoupling the contributions of kinetic and potential energies of ions on thin film formation. The potential energy is changed by enhancing the ion charge states via using an external magnetic field at the plasma source. The kinetic energy is adjusted by biasing the arc source (“plasma bias”), which allows us to approximately compensate the differences in kinetic energy, while the substrate and ion energy detector remain at ground. However, application of an external magnetic field also leads to an enhancement of the ion flux and hence the desired complete decoupling of the potential and kinetic energy effects will require further steps. Charge-state-resolved energy distribution functions of ions are measured at the substrate position for different arc source configurations, and thin films are deposited using exactly those configurations. Detailed characterization of the deposited thin films is performed to reveal the correlations of changes in structure with kinetic and potential energies of multiply charged ions. It is observed that the cathode composition (Al:V ratio) strongly affects the formation of the thermodynamically stable wurtzite or the metastable cubic phase. The external magnetic field applied at the arc source is found to greatly alter the plasma and, therefore, to be the primary, easily accessible “tuning knob” to enhance film crystallinity. The effect of “atomic scale heating” provided by the ions’ kinetic and potential energies on the film crystallinity is investigated, and the possibility to deposit crystalline (V,Al)N films without substrate heating is demonstrated. This study shows an approach toward distinguishing the contributions stemming from kinetic and potential energies of ions on the film growth, however, further research is needed to assess and distinguish the additional effect of ion flux intensity (current).

We study the conversion of two polymeric silicon precursor compound layers (perhydropolysilazane and polydimethylsiloxane) on a silicon wafer and polyethylene terephthalate substrates to silicon oxide thin films using a pulsed atmospheric pressure plasma jet. Varying the scan velocity and the number of treatments results in various film compositions, as determined by X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy. The mechanism suggested for the conversion process includes the decomposition of the precursor triggered by plasma-produced species, the oxidation of the surface, and finally, the diffusion of oxygen into the film, while gases produced during the precursor decomposition diffuse out of the film. The latter process is possibly facilitated by local plasma heating of the surface. The precursor conversion appears to depend sensitively on the balance between the different contributions to the conversion mechanism.

Ion-irradiation-induced changes in structure, elastic properties, and thermal stability of metastable c-(Ti,Al)N thin films synthesized by high-power pulsed magnetron sputtering (HPPMS) and cathodic arc deposition (CAD) are systematically investigated by experiments and density functional theory (DFT) simulations. While films deposited by HPPMS show a random orientation at ion kinetic energies (Ek)>105 eV, an evolution towards (111) orientation is observed in CAD films for Ek>144 eV. The measured ion energy flux at the growing film surface is 3.3 times larger for CAD compared to HPPMS. Hence, it is inferred that formation of the strong (111) texture in CAD films is caused by the ion flux-and ion energy-induced strain energy minimization in defective c-(Ti,Al)N. The ion energy-dependent elastic modulus can be rationalized by considering the ion energy-and orientation -dependent formation of point defects from DFT predictions: The balancing effects of bombardment-induced Frenkel defects formation and the concurrent evolution of compressive intrinsic stress result in the apparent independence of the elastic modulus from Ek for HPPMS films without preferential orientation. However, an ion energy-dependent elastic modulus reduction of similar to 18% for the CAD films can be understood by considering the 34% higher Frenkel pair concentration formed at Ek=182 eV upon irradiation of the experimentally observed (111)-oriented (Ti,Al)N in comparison to the (200)-configuration at similar Ek. Moreover, the effect of Frenkel pair concentration on the thermal stability of metastable c-(Ti,Al)N is investigated by differential scanning calorimetry: Ion-irradiation-induced increase in Frenkel pairs concentration retards the wurtzite formation temperature by up to 206 degrees C.

Iron oxide nanoparticles with a mean size of approximately 5 nm were synthesized by irradiating micro-emulsions containing iron salts with energetic electrons. The properties of the nanoparticles were investigated using scanning electron microscopy, high-resolution transmission electron microscopy, selective area diffraction and vibrating sample magnetometry. It was found that formation of superparamagnetic nanoparticles begins at a dose of 50 kGy, though these particles show low crystallinity, and a higher portion is amorphous. With increasing doses, an increasing crystallinity and yield could be observed, which is reflected in an increasing saturation magnetization. The blocking temperature and effective anisotropy constant were determined via zero-field cooling and field cooling measurements. The particles tend to form clusters with a size of 34 nm to 73 nm. Magnetite/maghemite nanoparticles could be identified via selective area electron diffraction patterns. Additionally, goethite nanowires could be observed.

Recently, plasma produced by focusing femtosecond laser in gases has been introduced as an etching tool in materials processing. Proper control of the plasma in this application necessitates the apt understanding of the different morphological features of the plasma. In this contribution we show that, the plasma produced in air goes through several stages of morphological development–from ellipsoidal to spherical to toroidal plasma, whereas in argon, axial compression of an ellipsoidal plasma is observed. To explain this dissimilarity, we have quantified the temperature by emission spectroscopy (Planck analysis with Wien’s approximation). The evolution of temperature shows a triple exponential dependence in time which can be correlated with different stages of morphological changes of the plasma. Open Source Field Operation and Manipulation simulations using experimentally determined temperature values show that—(i) the reverse pressure gradient propagates radially inwards and compresses the plasma in both air and argon and forms a localized high pressure zone at the center that generates a secondary pressure wave in air, but not in argon, and (ii) the baroclinic torque that is generated because of the Richtmyer–Meshkov instability, dominates the rate of vorticity in air, whereas effects of flow compressibility and velocity gradients dominate the vortices in argon. Knowledge of the initial state and the dynamics of the subsequent stages of the plasma formation can be utilized for control and optimization of laser-induced plasma applications.

A transparent conductive oxide (TCO) should have a combination of high electrical conductivity and optical transmission property to fulfill the challenging demands of industrial applications. So far, doped TCOs have been mostly considered to fulfill the technological challenges. In this study, we demonstrate that indium oxide (In2O3) thin films without intentional doping can be deposited with high crystallinity under specific film growth con-ditions leading to thin films with high mobility, high electrical conductivity, and high transmittance. In2O3 thin films have been deposited by reactive pulsed direct current magnetron sputtering (pulsed DCMS) from an indium target on substrates in a temperature range from room temperature (RT) to 600 & DEG;C. Detailed investigations on In2O3 thin films are performed and the film properties such as crystallinity, microstructure, chemical bonding states, electrical and optical properties are revealed. Enhanced plasma density and ionization degree provided by the employed reactive pulsed DCMS and the intentional substrate heating during the thin film deposition give possibility to deposit highly crystalline thin films which are preferentially oriented in (222) direction. The substrate heating enhances the crystallinity of the grown films up to a certain optimum temperature: 400 & DEG;C. When the substrate temperature is above 400 & DEG;C, the carrier concentration and mobility decrease due to the grain refinement effect caused by growth competition of grains in different orientations. The films grown at 400 & DEG;C indicate the presence of high oxygen vacancy concentrations, which can directly be associated with a high charge carrier concentration despite the lack of intentional doping. The undoped In2O3 films in this study grown at 400 & DEG;C show highly promising and competitive electrical properties such as low resistivity of 1.28 x 10(-4) omega.cm and the high carrier mobility of 69 cm(2)/Vs. The average transmittance of the In2O3 films with the highest conductivity is found to be greater than 80% in the visible to the near-infrared spectral region owing to an enhancement in the carrier mobility and an optical bandgap in the range from 3.61 eV to 3.77 eV.