Magnetron Sputtering Plasma Research Articles

Fast charge exchange ions in high power impulse magnetron sputtering of titanium as probes for the electrical potential

High power impulse magnetron sputtering (HiPIMS) plasmas exhibit a high ionization fraction of the sputtered material and ions with high kinetic energies, which produce thin films with superior quality. These ion energy distribution functions (IEDF) contain energetic peaks, which are believed to be linked to a distinct electrical potential hump inside rotating localized ionization zones, so called spokes, at target power densities above 1 kW cm−2. Any direct measurement of this electrical potential structure is, however, very difficult due to the dynamic nature of the spokes and the very high local power density, which hampers the use of conventional emissive probes. Instead, we use a careful analysis of the IEDFs for singly and doubly charged titanium ions from a HiPIMS plasma at varying target power density. The energy peaks in the IEDFs measured at the substrate depend on the point of ionization and any charge exchange collisions on the path between ionization and impact at the substrate. Thereby, the IEDFs contain a convoluted information about the electrical potential structure inside the plasma. The analysis of these IEDFs reveal that higher ionization states originate at high target power densities from the central part of the plasma spoke, whereas singly charged ions originate from the perimeter of the plasma spoke. Consequently, we observe different absolute ion energies with the energy of Ti2+ being slightly higher than two times the energy of Ti+. Additional peaks are observed in the IEDFs of Ti+ originating from charge exchange reactions from Ti2+ and Ti3+ with titanium neutrals. Based on this analysis of the IEDFs, the structure of the electrical potential inside a spoke is inferred yielding = 25 V above the plasma potential, irrespective of target power density.

Thermal annealing effect on nitrogen-doped TiO2 thin films grown by high power impulse magnetron sputtering plasma power source

The work reports plasma assisted growth of nitrogen-doped titanium dioxide (N-TiO2) thin films using high power impulse magnetron sputtering (HiPIMS) power source and effect of post-deposition thermal annealing. The films were deposited at low pressure. The binding energies of elements of interest, the energy gap, crystallinity and morphology of the films were analyzed before and after annealing. The results showed an increase in binding energies, a fact attributed to enhanced oxidation, after the annealing process. Only nitrogen doped samples grown by HiPIMS exhibited the presence of substitutional nitrogen. The energy gap of the films was found to decrease after doping and annealing. Improvement in crystallinity with a small shift in the crystalline peaks indicating decrease in lattice parameter, which could be seen by surface smoothing, was observed after thermal annealing. As a result of the growth of films by HiPIMS, nitrogen doping and post-deposition thermal annealing, improvements in the properties of the films which have relevance for photocatalytic and energy applications were observed.

Functionalization of the Polymeric Surface with Bioceramic Nanoparticles via a Novel, Nonthermal Dip Coating Method.

The only nonthermal method of depositing a bioceramic-based coating on polymeric substrates is by incubation in liquid, e.g., simulated body fluid to form an apatite-like layer. The drawbacks of this method include the long processing time, the production of low scratch resistant coating, and an end product that does not resemble the intended bioceramic composition. Techniques, such as plasma spraying and magnetron sputtering, involving high processing temperature are unsuitable for polymers, e.g., PMMA. Here, we introduce a nonthermal coating method to immobilize hydroxyapatite (HAp) and TiO2 nanoparticles on PMMA via a simple and fast dip coating method. Cavities that formed on the PMMA, induced by chloroform, appeared to trap the nanoparticles which accumulated to form layers of bioceramic coating only after 60 s. The resulting coating was hydrophilic and highly resistant to delamination. In the context of our research and to address the current clinical need, we demonstrate that the HAp-coated PMMA, which is intended to be used as a visual optic of a corneal prosthetic device, improves its bonding and biointegration with collagen, the main component of a corneal stroma. The HAp-coated PMMA resulted in better adhesion with the collagen than untreated PMMA in artificial tear fluid over 28 days. Human corneal stromal fibroblasts showed better attachment, viability, and proliferation rate on the HAp-coated PMMA than on untreated PMMA. This coating method is an innovative solution to immobilize various bioceramic nanoparticles on polymers and may be used in other biomedical implants.

Numerical Investigation on Ion Inertia Force in Low-Temperature Plasma Using Fluid Model Considering Ion Momentum Equation

In this paper, we would like to numerically investigate the effect of ion inertia force in a typical argon gas discharge using fluid model considering the ion momentum equation, which becomes important under various operating conditions. The proposed self-consistent fluid model consists of the electron continuity equation with the drift-diffusion approximation, the ion continuity equation, the electron energy density equation, the ion momentum equation, and the Poisson equation for electric potential. We studied the plasma properties affected by the inertia force by comparing between the use of momentum equation and drift-diffusion approximation for ion momentum. The results show that the ion inertia force is significant under the low-pressure conditions (<100 mtorr) as expected, e.g., for plasma etching and radio frequency magnetron sputtering plasma. In addition, we also found when the pressure is higher than 100 mtorr, the inertia force becomes important (e.g., more than 15%) in the sheath region when the driving frequency is high enough (e.g., 60 MHz), e.g., for high-frequency plasma-enhanced chemical vapor deposition. Thus, inclusion of inertia force in the modeling of momentum equation becomes necessary under these operating conditions.

The improvement of all-solid-state electrochromic devices fabricated with the reactive sputter and cathodic arc technology

The all-solid-state electrochromic device (ECD) with the one substrate structure fabricated by the reactive dc magnetron sputtering (DCMS) and cathodic vacuum arc plasma (CVAP) technology has been developed for smart electrochromic (EC) glass application. The EC layer and ion conductor layer were deposited by reactive DCMS and CVAP technology, respectively. The ion conductor layer Ta2O5 deposited by the CVAP technology has provided the better porous material structure for ion transportation and showed 1.76 times ion conductivity than devices with all sputtering process. At the same time, the EC layer WO3 and NiO deposited by the reactive DCMS have also provided the high quality and uniform characteristic to overcome the surface roughness effect of the CVAP ion conductor layer in multilayer device structure. The all-solid-state ECD with the CVAP ion conductor layer has demonstrated a maximum transmittance variation (ΔT) of 55% at 550nm and a faster-switching speed. Furthermore, the lower equipment cost and higher deposition rate could be achieved by the application of CVAP technology.

Characterization of electromagnetic fluctuations in a HiPIMS plasma

A high power impulse magnetron sputtering (HiPIMS) plasma has been characterized by means of Langmuir probes measuring floating potential, electron temperature and density. Moreover, magnetic sensors have been employed in the analysis of the magnetic fluctuations. A low frequency electro-magnetic structure has been detected to propogate in the HiPIMS plasma at a velocity of about 5 km s−1 in the direction of the drift. It has been characterized in terms of time and space periodicities for different plasma conditions. It exhibits common features with the so-called rotating spokes, observed in various HiPIMS plasmas. The increasing relevance of the electromagnetic nature of the fluctuating structure at high power levels is highlighted.

Microstructure formation and evolution mechanism of Cu-Ti coating during dual-magnetron sputtering and thermo plasma nitriding

Dual magnetron sputtering and thermo plasma nitriding were performed to fabricate Cu-Ti-N coating on the surface of Cu substrate, and the microstructure formation and evolution mechanism were investigated. The results showed that the composition of the Cu-Ti coating could be tuned to be around Cu:Ti = 1:1.2 by the appropriate choice of sputtering power for the dual targets, and only amorphous Cu-Ti phases formed. During the thermo plasma nitriding process, crystalline CuTi and Cu3Ti occurred. Moreover, a nitride layer of about 0.3 μm containing nanocrystalline TiN formed on the surface, and the multi-phase coating developed to be about 4 μm, which could provide better support for the nitrided layer.

Control of High Power Pulsed Magnetron Discharge by Monitoring the Current Voltage Characteristics

AbstractDischarge 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 &amp; Co. KGaA, Weinheim)

Absolute densities of Cu, Zn, Sn, and S atoms in magnetron sputtering plasmas employing a Cu2ZnSnS4 target

Absolute densities of Cu, Zn, Sn, and S atoms in magnetron sputtering plasmas were measured by ultraviolet absorption spectroscopy and vacuum ultraviolet absorption spectroscopy. A stoichiometric Cu2ZnSnS4 (CZTS) target was used in this work. It was found that, at various Ar pressures, the S density ranged between (2–8) × 1010 cm−3, the Cu and Sn densities ranged between (0.6–3) × 1010 cm−3, and the Zn density ranged between (2–3) × 109 cm−3. The effective depositing flux, which was evaluated from the absolute densities and the sticking probabilities, was comparable with that evaluated from the deposition rate of the CZTS film. However, the composition ratio of Cu, Zn, Sn, and S in the gas phase deviated from the ideal stoichiometry of CZTS. We discussed the possible mechanisms for the difference among the element compositions of the target, the deposited film, and the gas-phase densities.

RP and RQA Analysis for Floating Potential Fluctuations in a DC Magnetron Sputtering Plasma

The nonlinear dynamics of a direct current magnetron sputtering plasma is visualized using recurrence plot (RP) technique. RP comprises the recurrence quantification analysis (RQA) which is an efficient method to observe critical regime transitions in dynamics. Further, RQA provides insight information about the system’s behavior. We observed the floating potential fluctuations of the plasma as a function of discharge voltage by using Langmuir probe. The system exhibits quasi-periodic–chaotic–quasi-periodic–chaotic transitions. These transitions are quantified from determinism, Lmax, and entropy of RQA. Statistical investigations like kurtosis and skewness also studied for these transitions which are in well agreement with RQA results.

Doped and Decorated Carbon Nanomaterials

This work shows the preliminary results concerning to the synthesis or modification of carbon-based nanomaterials by plasma discharge, magnetron sputtering, and chemical vapor deposition methodologies. As a first approach to show the potential of these techniques, scanning electron microscopy analysis was performed in order to verify morphological changes and to proof that it is possible to design the morphology of doped and decorated carbon nanomaterials. In spite of none further characterization was performed, from the discussion of results in literature, it can be suggest that these methods would permit to design novel carbon-based nanomaterials&lt;br /&gt;for the energy production and storage, catalytic and photocatalytic processes related with environment and green chemistry applications.

Spoke rotation reversal in magnetron discharges of aluminium, chromium and titanium

The rotation of localised ionisation zones, i.e. spokes, in magnetron discharge are frequently observed. The spokes are investigated by measuring floating potential oscillations with 12 flat probes placed azimuthally around a planar circular magnetron. The 12-probe setup provides sufficient temporal and spatial resolution to observe the properties of various spokes, such as rotation direction, mode number and angular velocity. The spokes are investigated as a function of discharge current, ranging from 10 mA (current density 0.5 mA cm−2) to 140 A (7 A cm−2). In the range from 10 mA to 600 mA the plasma was sustained in DC mode, and in the range from 1 A to 140 A the plasma was pulsed in high-power impulse magnetron sputtering mode. The presence of spokes throughout the complete discharge current range indicates that the spokes are an intrinsic property of a magnetron sputtering plasma discharge. The spokes may disappear at discharge currents above 80 A for Cr, as the plasma becomes homogeneously distributed over the racetrack. Up to discharge currents of several amperes (the exact value depends on the target material), the spokes rotate in a retrograde direction with angular velocity in the range of 0.2–4 km s−1. Beyond a discharge current of several amperes, the spokes rotate in a direction with angular velocity in the range of 5–15 km s−1. The spoke rotation reversal is explained by a transition from Ar-dominated to metal-dominated sputtering that shifts the plasma emission zone closer to the target. The spoke itself corresponds to a region of high electron density and therefore to a hump in the electrical potential. The electric field around the spoke dominates the spoke rotation direction. At low power, the plasma is further away from the target and it is dominated by the electric field to the anode, thus retrograde rotation. At high power, the plasma is closer to the target and it is dominated by the electric field pointing to the target, thus rotation.

Desempenho físico-químico de filmes hidrofóbicos de AlN e de Ti nanoestruturado crescidos por plasma frio sobre superfícies de isoladores cerâmicos de porcelana tipo pino

Resumo A resistência mecânica e a propriedade dielétrica de isoladores cerâmicos são características fundamentais para o suporte das redes de distribuição de energia elétrica. Porém, tanto a umidade quanto o teor de poluentes na atmosfera podem vir a ser prejudiciais e causar falhas na entrega de energia por elevação da sua corrente elétrica de fuga. O vidrado do isolador tem grande afinidade com a água resultante da interação da superfície do vidro com a atmosfera. No presente trabalho, foi realizada a deposição de filmes de nitreto de alumínio sobre o vidrado de amostras de isoladores elétricos cerâmicos, via plasma "magnetron sputtering" pulsado, de corrente contínua, e com uma mistura dos gases argônio e nitrogênio e de Ti sobre isoladores tipo pino para classes de tensão de 15 kV. A morfologia dos filmes e o desempenho dos isoladores foram medidos por MEV-FEG/EDS, AFM, máxima corrente de fuga RMS e grau de hidrofobicidade. O comportamento dos filmes depositados medido pelo grau de hidrofobicidade reduziu nas amostras de CM6 para CM4, com AlN, e de CM7 para CM3 quando foi depositado o Ti. A máxima corrente de fuga RMS medida nos isoladores sem e com filme nanométrico à base de Ti foi superior nos dispositivos sem a proteção, alcançando valores medidos de 5 mA e com desligamento do sistema computadorizado de medida (após 3 dias em Sauípe e 3 meses em Pituba) em consequência desta ter superado o intervalo de segurança de curto circuito estabelecido nos dispositivos eletrônicos de proteção (surtos superiores a 300 mA). Com a deposição dos filmes em 7 isoladores, foram verificadas alterações de comportamento em dois destes, com picos de máxima corrente de fuga atingindo 2,4 mA no campo. A maioria dos isoladores analisados teve como variações de correntes de fuga RMS, no período de medida, entre 0,2 e 2 mA, em condições adversas de clima (com chuva e diferentes velocidades de vento).

Influence of ionisation zone motion in high power impulse magnetron sputtering on angular ion flux and NbOx film growth

The ion energies and fluxes in the high power impulse magnetron sputtering plasma from a Nb target were analysed angularly resolved along the tangential direction of the racetrack. A reactive oxygen-containing atmosphere was used as such discharge conditions are typically employed for the synthesis of thin films. Asymmetries in the flux distribution of the recorded ions as well as their energies and charge states were noticed when varying the angle between mass-energy analyser and target surface. More positively charged ions with higher count rates in the medium energy range of their distributions were detected in than in direction, thus confirming the notion that ionisation zones (also known as spokes or plasma bunches) are associated with moving potential humps. The motion of the recorded negatively charged high-energy oxygen ions was unaffected. Nb thin films at different angles and positions were synthesised and analysed as to their structure and properties in order to correlate the observed plasma properties to the film growth conditions. The chemical composition and the film thickness varied with changing deposition angle, where the latter, similar to the ion fluxes, was higher in than in direction.

Evidence for breathing modes in direct current, pulsed, and high power impulse magnetron sputtering plasmas

We present evidence for breathing modes in magnetron sputtering plasmas: periodic axial variations of plasma parameters with characteristic frequencies between 10 and 100 kHz. A set of azimuthally distributed probes shows synchronous oscillations of the floating potential. They appear most clearly when considering the intermediate current regime in which the direction of azimuthal spoke motion changes. Breathing oscillations were found to be superimposed on azimuthal spoke motion. Depending on pressure and current, one can also find a regime of chaotic fluctuations and one of stable discharges, the latter at high current. A pressure-current phase diagram for the different situations is proposed.

Coated Stainless Steel Bipolar Plates for Proton Exchange Membrane Electrolyzers

Given its rapid response to fluctuating currents and wide operation range, proton exchange membrane (PEM) water electrolysis is utmost suitable for generation of hydrogen from renewable power. However, it is still hindered by the high cost of the stack components compared to those used in the alkaline technology. In particular, the titanium bipolar plates (BPP) are an issue and the replacement of this metal by stainless steel is a challenge, due to the highly corrosive environment inside PEM electrolyzer stack. Herein, we coat stainless steel BPPs with 50–60 μm Ti and 1.5 μm Pt coatings by vacuum plasma spraying (VPS) and magnetron sputtering physical vapor deposition (PVD), respectively. The BPPs are evaluated at constant 1 A cm−2 for more than 1000 h. The thermally sprayed Ti coatings fully protect the stainless steel substrate during this period of time, and the Pt surface modification allows achieving a cell performance comparable to the baseline.

Discharge current modes of high power impulse magnetron sputtering

Based on the production and disappearance of ions and electrons in the high power impulse magnetron sputtering plasma near the target, the expression of the discharge current is derived. Depending on the slope, six possible modes are deduced for the discharge current and the feasibility of each mode is discussed. The discharge parameters and target properties are simplified into the discharge voltage, sputtering yield, and ionization energy which mainly affect the discharge plasma. The relationship between these factors and the discharge current modes is also investigated.

Membrane patterned by pulsed laser micromachining for proton exchange membrane fuel cell with sputtered ultra-low catalyst loadings

Proton exchange membranes were nano- and micro-patterned on their cathode side by pressing them against stainless steel molds previously irradiated by a Ti:Sapphire femtosecond laser. The membranes were associated to ultra-low loaded thin catalytic layers (25 μgPt cm−2) prepared by plasma magnetron sputtering. The Pt catalyst was sputtered either on the membrane or on the porous electrode. The fuel cell performance in dry conditions were found to be highly dependent on the morphology of the membrane surface. When nanometric ripples covered by a Pt catalyst were introduced on the surface of the membrane, the fuel cell outperformed the conventional one with a flat membrane. By combining nano- and micro-patterns (nanometric ripples and 11–24 μm deep craters), the performance of the cells was clearly enhanced. The maximum power density achieved by the fuel cell was multiplied by a factor of 3.6 (at 50 °C and 3 bar): 438 mW cm−2 vs 122 mW cm−2. This improvement is due to high catalyst utilization with a high membrane conductivity. When Pt is sputtered on the porous electrode (and not on the membrane), the contribution of the patterned membrane to the fuel cell efficiency was less significant, except in the presence of nanometric ripples. This result suggests that the patterning of the membrane must be consistent with the way the catalyst is synthesized, on the membrane or on the porous electrode.

Experimental investigation of quasiperiodic-chaotic-quasiperiodic-chaotic transition in a direct current magnetron sputtering plasma

Floating potential fluctuations from a direct current magnetron sputtering plasma have been analysed using time series analysis techniques like phase space plots, power spectra, frequency bifurcation plot, etc. The system exhibits quasiperiodic-chaotic-quasiperiodic-chaotic transitions as the discharge voltage was increased. The transitions of the fluctuations, quantified using the largest Lyapunov exponent, have been corroborated by Hurst exponent and the Shannon entropy. The Shannon entropy is high for quasiperiodic and low for chaotic oscillations.

Nanostructured Titanium Film Deposited by Pulsed Plasma Magnetron Sputtering (Pdms) on a High Voltage Ceramic Insulator for Outdoor Use

In this study, the cold plasma technique was used to produce nanometric titanium films with hydrophobic and anti-fouling properties. The films where deposited on porcelain electrical insulators surfaces to minimize the effects of leakage current. The magnetron sputtering technique was used with a target of pure titanium sheet, and argon as the ionization gas. The deposited films present an average thickness of 58 to 350 nm. After coating the insulators, the assays performed indicated a greater degree of hydrophobicity and maintenance of leakage current after exposure to salt spray. Lower leakage current values were observed in both natural and saline environments compared with the uncoated device.