Dual Plasma Process Research Articles

Low temperature deposition of a-SiC:H thin films applying a dual plasma source process

The utilization of silicon carbide (SiC) thin films is of great interest whenever a high robustness is requested for MEMS/NEMS-based devices, which are operated in harsh environments beyond the applicability of standard silicon technology. Hydrogenated amorphous SiC (a-SiC:H) is especially attractive for these scenarios, as it can be deposited at temperatures lower than 400°C while still being beneficial for enhanced device performance. Furthermore, the thin film properties can be tailored to a great extent during synthesis or via post-deposition annealing. This study reports on the deposition of a-SiC:H thin films at a substrate temperature of 250°C applying a dual plasma process by superimposing a radio frequency (RF) plasma which excites the substrate table to an inductively-coupled RF plasma. This auxiliary plasma source has a huge impact on the resulting thin film properties due to the interaction of various opposing processes during film growth. To understand these processes, the layer composition was determined using time-of-flight elastic recoil detection analyses, Fourier transform infrared spectroscopy and by mass effusion measurements up to 1000°C, thus revealing changes in chemical composition, but also the power dependent incorporation of gaseous species from the plasma. This, for example, allows modification of the residual stress ranging from nearly stress free to highly compressively stressed layers of more than −2GPa, Young's modulus values ranging from about 168GPa down to 48GPa, but also greatly affects the surface topography which can be adjusted to a very low root mean squared roughness of less than 0.1nm.

Iron–Polypyrrole Catalysts for the Oxygen Reduction in Proton Exchange Membrane Fuel Cells Produced with a Dual Plasma Process Using Varying Magnetron Powers and Process Gases

Recently, a new dual plasma-process to produce non noble metal catalysts for the oxygen reduction in proton exchange membrane fuel cells has been developed and catalytically active cobalt–polypyrrole-films have been produced. This paper shows a modification to this process, so that iron–polypyrrole is formed. The magnetron power as well as the process gases were varied. The structure of the compounds was then analyzed by energy-dispersive X-ray spectroscopy, X-ray diffraction, near edge X-ray absorption fine structure and extended X-ray absorption fine structure. It is shown that the oxidation of the compounds is suppressed when hydrogen or nitrogen is added to the process. Furthermore, cyclic voltammetry and rotating ring-disk electrode measurements were done to determine the electrochemical properties of the films. Only films produced in hydrogen or nitrogen containing gases show catalytic activity and it can be seen that the four-electron reduction mechanism is dominant.

Tuning the Process Gas in a Dual Plasma Process to Enhance the Performance of Cobalt-Polypyrrole Catalyts for the Oxygen Reduction Reaction in Fuel Cells

In this contribution, the dual plasma process to produce catalytically active cobalt-polypyrrole-compounds is enhanced. This is done by adding nitrogen, hydrogen and oxygen to argon during the plasma process. The so-obtained compounds were analysed by EDX,XRD and NEXAFS to get information on the structural composition. Furthermore, CVmeasurements were done to determine the electrochemical properties of the films. It is shown that the catalytic activity increases slightly while the stability of the films can be greatly improved.

Tuning the Process Gas in a Dual Plasma Process to Enhance the Performance of Cobalt–Polypyrrole Catalysts for the Oxygen Reduction Reaction in Fuel Cells

In this contribution, an improvement to the dual plasma process for producing catalytically active cobalt–polypyrrole-compounds is reported. This is achieved by adding nitrogen, hydrogen and oxygen to the plasma process. The so-obtained compounds were analyzed by Edx, Xrd, Nexafs and Exafs to get information on the structural composition. The structure of the films changes drastically when nitrogen is added to the process gas – the polymeric matrix is more strongly cross-linked and more catalytically active Co–N–C-structures are produced. When hydrogen is added, the structure only changes slightly and using oxygen as a process gas leads to the formation of catalytically inactive cobalt oxides. Furthermore, Cv and Rrde measurements were done to determine the electrochemical properties of the films. It is shown that the catalytic activity increases slightly while the stability of the films can be greatly improved by adding nitrogen to the process.

Using a Dual Plasma Process to Produce Cobalt-Polypyrrole Catalysts for the Oxygen Reduction Reaction in Fuel Cells

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Using a Dual Plasma Process to Produce Cobalt-Polypyrrole Catalysts for the Oxygen Reduction Reaction in Fuel Cells: II. Analysing the Chemical Structure of the Films

The chemical structure of cobalt–polypyrrole – produced by a dual plasma process – is analyzed by means of X-ray photoelectron spectroscopy (XPS), near edge X-ray absorption spectroscopy (NEXAFS), X-ray diffraction (XRD), energy-dispersive X-Ray spectroscopy (EDX) and extended X-ray absorption spectroscopy (EXAFS). It is shown that only nanoparticles of a size of 3 nm with the low temperature crystal structure of cobalt are present within the compound. Besides that, cobalt–nitrogen and carbon–oxygen structures are observed. Furthermore, more and more cobalt–nitrogen structures are produced when increasing the magnetron power. Linking the information on the chemical structure to the results about the catalytic activity of the films – which are presented in part I of this contribution – it is concluded that the cobalt–nitrogen structures are the probable catalytically active sites. The cobalt–nitrogen bond length is calculated as 2.09 Å and the carbon–nitrogen bond length as 1.38 Å.

Using a Dual Plasma Process to Produce Cobalt-Polypyrrole Catalysts for the Oxygen Reduction Reaction in Fuel Cells: I. Characterization of the Catalytic Activity and Surface Structure

A new dual plasma coating process to produce platinum-free catalysts for the oxygen reduction reaction in a fuel cell is introduced. The catalysts thus produced were analyzed with various methods. Electrochemical characterisation was carried out by cyclic voltammetry, rotating ring- and rotating ring-disk electrode. The surface porosity of the different catalysts thus obtained was characterized with the nitrogen gas adsorption technique and scanning electron microscopy was used to determine the growth mechanisms of the films. It is shown that catalytically active compounds can be produced with this dual plasma process. Furthermore, the catalytic activity can be varied significantly by changing the plasma process parameters. The amount of H2O2 produced was calculated and shows that a 2 electron mechanism is predominant. The plasma coating mechanism does not significantly change the surface BET area and pore size distribution of the carbon support used. Furthermore, scanning electron microscopy pictures of the produced films are presented and show the preference of columnar growth mechanisms. By using different carbons as the support it is shown that there is a strong dependence of the catalytic activity that is probably related to the chemical properties of the carbon.

Dual plasma synthesis and characterization of a stable copper–ethylene glycol nanofluid

This article addresses the issue of metallic nanoparticle suspension (nanofluid) stabilization without the use of traditional surface-stabilizing agents such as surfactants. A dual plasma process for the single-step synthesis of a copper–ethylene glycol nanofluid is presented. The process uses a combination of low-pressure pulsed cathodic arc erosion to generate metal nanoparticles and in-flight radio-frequency glow discharge plasma functionalization for surface stabilization. The surface-stabilized nanoparticles are collected in situ by a falling film of ethylene glycol, the vapours of which are used for plasma functionalization. Little to no agglomeration is observed in the suspension, although this process is shown to occur when the produced suspensions are heated to temperatures well beyond the range of effectiveness of typical surfactants. This thermally induced agglomeration is demonstrated to be fully reversible. The stability of the suspension is confirmed by UV–Vis absorption spectrometry and electron microscopy. The particles synthesized are also shown to be re-dispersible in aqueous media. Though no heat transfer enhancement was observed due to the low nanoparticle loading, this study demonstrates for the first time that high temperature-stable nanofluids containing metal nanoparticles can be synthesized in a single-step, without manipulation outside the controlled synthesis environment and without the post-addition of surfactants.

Novel method to produce cobalt–polypyrrole catalysts for oxygen reduction reaction by dual plasma process

Platinum-free electrocatalysts based on cobalt and polypyrrole were successfully produced with a dual plasma process and characterised for the oxygen reduction reaction by cyclic voltammetry (CV). The results show that composites with catalytic activity were obtained. Furthermore, by varying the plasma process parameters, the activity of the samples was changed. Structural properties were also investigated by means of energy dispersive X-Ray spectroscopy (EDX), to obtain the elemental contents, and Fourier transform infrared spectroscopy (FT-IR) to identify the chemical structure of the films. The results indicate that, with increasing magnetron power, more and more cobalt nitrogen bonds are formed. The formation of these complexes correlates with the increase in catalytic activity.

Structural Investigations of Composites Produced from Copper and Polypyrrole with a Dual PVD/PE‐CVD Process

AbstractCopper–polypyrrole composites were successfully produced with a dual plasma process. X‐ray photoelectron spectroscopy (XPS), X‐ray diffraction (XRD) and Fourier transform infrared spectroscopy (FT‐IR) were used to characterise the structural properties. Topological and electrochemical investigations were also performed using atomic force and scanning electron microscopy (AFM, SEM) as well as cyclic voltammetry (CV) respectively. The results show that different composites were produced. When a low power was used, copper atoms bound to aromatic polymer structures were formed. Indications for the formation of electroactive copper–polypyrrole complexes are presented. Using higher power values, copper(I)oxide (ca. 3 nm) and copper nanoparticles (5–40 nm) embedded in a polymeric matrix were produced. Pulsing of the magnetron resulted in a modification of the chemical bonds within the samples.magnified image

Improved Dual-Plasma Process for the Synthesis of Coated or Functionalized Metal Nanoparticles

An improved dual-plasma process for the synthesis of nonagglomerated, organic layer-coated metal nanoparticles is presented. Nanoparticle synthesis is achieved by means of pulsed arc erosion of a copper cathode. Particles are coated in-flight through RF plasma polymerization of ethane. The axially symmetric geometry takes advantage of the initial nanoparticle trajectories and charging effects within the RF plasma, thus enhancing particle collection efficiency.

Plasma-based ion process in the dual-plasma configuration

A novel plasma-based ion process characterized by the dual plasma configuration, which we call the dual-plasma immersion ion process and which has been developed for the surface treatment of electrically insulating materials, is reported. In this process, the plasma is divided into two parts by a negatively biased grid: the target plasma and the driver plasma. The workpiece to be treated is set in the target plasma. If a dc or pulsed positive bias is applied to the driver plasma against the target plasma at ground potential, an ion sheath develops on the grid and a potential difference happens across the ion sheath. When we see the dual-plasma process from the workpiece, it gets the impact of ions from the driver plasma while being immersed in the target plasma at ground potential. Thus, this new process enables treatment of insulating materials because the surface charge induced by the ion impact is completely reduced by the inflow of electrons from the target plasma. In the present paper, the basic idea of the dual-plasma immersion ion process and results of the proof-of-principle experiment are presented.

Synthesis of organic layer-coated copper nanoparticles in a dual-plasma process

Copper nanoparticles were synthesized in an inert (Ar) low-pressure pulsed arc system using a simple copper rod as the cathode and the source of metal vapors and subsequently coated in-flight with a thin organic layer in a capacitively coupled RF C2H6 plasma. The produced copper nanoparticles were characterized by field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), and Fourier-transform infrared spectroscopy (FT-IR). Typical nanoparticle size ranges from a few to 50 nm, while the thickness of the organic layer deposited onto the nanoparticles ranges from 3 to 10 nm. The copper nanoparticles are crystalline while the coatings show a polymer-like structure.