Low Pressure Plasma Deposition Research Articles

Catalytic activity of plasma-deposited Co3O4-based thin films for CO2 hydration – A new approach to carbon capture applications

Addressing the challenge of increasing the rate of CO2 capture by accelerating the hydration process, we proposed the use of a new class of heterogeneous inorganic catalysts for this purpose. The presented research focused on Co3O4-based nanocatalysts produced by low-pressure plasma deposition (PECVD) in the form of thin films that can be deposited on any structured packing. The kinetic studies of this process were performed by bubbling CO2 through pure water with catalytic or inert packing, measuring changes in pH value over time. The developed kinetic model described the experimental data very well and showed that the reaction at the interface between the CO2 bubble and the catalyst surface is responsible for the catalytic effect. Studies of the molecular structure of the catalyst surface, carried out by the XPS technique, showed that the chemisorbed H2O clusters on this surface are the active centers for the interaction with gaseous CO2.

Study on electronic properties of diamond/SiNx-coated AlGaN/GaN high electron mobility transistors operating up to 500 °C

We report on the research related to integration and characterization of AlGaN/GaN heterostructure-based circular high electron mobility transistors (c-HEMTs) with diamond thin films. Prior to diamond deposition the transistors were coated by thin SiNx layer in order to protect AlGaN/GaN heterostructure from deposition process impact. The diamond thin film was selectively grown on the top of SiNx-coated c-HEMTs using low-pressure low-temperature microwave plasma deposition equipment with substrate table 20 × 30 cm2 from C/O/H gas mixture. We demonstrate the functionality of the diamond/SiNx-coated and the SiNx-coated AlGaN/GaN-based c-HEMTs in the temperature range from room temperature to 500 °C. The electrical measurements revealed increase of c-HEMTs' leakage currents at reversed gate voltages after diamond deposition, although the transistors remained operable in the tested temperature range. The increase of gate leakage currents and thus more negative pinch-off voltages were attributed to hydrogen penetrated towards AlGaN/GaN interface during the 60 h deposition process despite the SiNx protection. The influence of temperature rise on electronic properties of the diamond/SiNx-coated and the SiNx-coated AlGaN/GaN-based c-HEMTs is discussed.

Atmospheric plasma etching of polymers: A palette of applications in cleaning/ashing, pattern formation, nanotexturing and superhydrophobic surface fabrication

Atmospheric Pressure Plasmas (APPs) are promising alternatives to their low-pressure counterparts for material surface treatment due to their potential for cost-effective continuous processing. Here we present for the first time to our knowledge a palette of applications of polymer etching showing the potential of APPs for cleaning/ashing, nanopattern formation, nanotexturing, and hierarchical superhydrophobic surface fabrication using the same plasma source configuration. First, we used a dielectric barrier discharge (DBD) plasma source to study etching/cleaning/ashing of different polymers such as PMMA films and AZ photoresist with lithographic patterns using He/O2 mixtures. We achieved high-rate, uniform etching, indicating the source potential for cleaning/ashing even in ambient air conditions. We have noticed that thick photoresist films are damaged after prolonged etching in air plasmas, a phenomenon resembling photoresist damage observed during low-pressure plasma etching. Second, we applied colloidal lithography with polystyrene (PS) nanoparticles followed by isotropic APP etching in order to form nanopatterns on both Silicon and Polymers. We observed that APP induces “cauliflower-like” nanotexturing of the PS spheres. This nanotexturing in combination with plasma etching of the underlying polymer and the spheres allow the fabrication of hierarchical surfaces. Optimization of plasma etching duration (i.e. hierarchical topography) followed by low-pressure plasma deposition of a low surface energy fluorocarbon (hydrophobic) coating led to the preparation of superhydrophobic surfaces with water contact angle 158° and hysteresis 9° (roll-off behavior).

Formation of lateral chemical gradients in plasma polymer films shielded by an inclined mask

Low pressure plasma deposition conditions are investigated yielding oxygen‐containing lateral gradient coatings (aC:H:O) by means of an inclined static mask partly shielding the substrate. Such lateral gradient coatings are formed by the diffusion of film‐forming species with different reactivities underneath the mask. Surface characterization revealed varying film growth conditions below the mask different from direct plasma exposure with increasing distance from the mask/plasma edge: i) exponentially decreasing film growth; ii) decreasing roughness following the thickness trend; iii) decreasing hydrophilicity; iv) variation in cross‐linking; and v) different chemical composition. Oxygen‐rich film‐forming species appeared to react closer to the mask/plasma edge, while oxygen‐poor film‐forming species can diffuse deeper, leading to a pronounced gradient in chemical composition and in cross‐linking in the masked area.

Aerosol-assisted low pressure plasma deposition of antimicrobial hybrid organic-inorganic Cu-composite thin films for food packaging applications

Abstract An innovative low pressure plasma process for deposition of copper-containing hybrid organic-inorganic thin films was developed. The discharge was fed with an aerosol of an aqueous solution of a copper complex, i.e. bis(ethylenediamine)copper(II) hydroxide and argon. Polymeric films, incorporating inorganic Cu(I) and Cu(II) compounds, were obtained. Morphological and chemical characterizations of the coatings were carried out. Antimicrobial properties were assessed on two species of Pseudomonas spp. In vitro tests were carried out by contact of the optimized films, deposited on square polycarbonate samples (~ 4 cm 2 ), with cell suspensions of 1 × 10 4 CFU/mL for 18 h at 25 °C. It was demonstrated that, the hybrid organic-inorganic thin coatings have potential utilization as active packaging material, showing an antimicrobial effect of up to three orders of magnitude (final microbial concentration 10 5 CFU/mL), compared to control polycarbonate (final microbial concentration 10 8 CFU/mL). Industrial relevance An innovative low pressure plasma process for deposition of copper-based, hybrid organic-inorganic thin films was developed. The optimized thin coatings have potential industrial utilization as active packaging material, being very effective against pseudomonads. Viability of Pseudomonas was reduced by three orders of magnitude (from 10 8 CFU/mL to 10 5 CFU/mL) in the presence of developed films, thus suggesting further investigation of the technique under food packaging conditions.

Atmospheric-pressure plasma enhanced chemical deposition: role of the reactor flow dynamics

An atmospheric- instead of low-pressure plasma deposition reactor for the inline production and processing of thin films is investigated. Process optimization and scale-up require a fundamental understanding of the reactor behaviour. The influence of the reactor design and the operating conditions on the reactor hydrodynamics and the film deposition rate are studied experimentally and by means of detailed computational fluid dynamics simulations. The influence of the process gas and its flow rate to the inlet channels, the precursor injection velocity and different geometric reactor design parameters is focused on.

Micro‐/Nanoscale Structuring of Cell‐Culture Substrates with Fluorocarbon Plasmas

AbstractWe describe the tailoring of polymer surfaces with CFx composition and roughness/density of different micro‐/nanometric relieves (ribbons, petals, domes, dots) tuned independently in low pressure plasma deposition and etching processes. Similarity of outer chemical composition grants the comparison of cell culture results to analyze the impact of topographical features on cellular behavior. Such surfaces are of interest for biomedical substrates since tuning their surface composition and morphology can drive the behavior of cells in contact with them.magnified image

Surface technology for automotive engineering

The presented paper describes the role of surface technologies in the automotive industry. Various hard coatings like nitrides, diamond and cBN are used on tools for the manufacturing process. Due to their high hardness and low coefficient of friction, diamond-like carbon films will be indispensable for engine and power train components. The improvement of automotive glazings by optimization of optical and thermal properties of the glass is an ongoing development task. Coatings with switchable transmission, thin film solar cells as self-cleaning and self-healing surfaces will be features in the car of the future. Various atmospheric pressure and low pressure deposition processes are available. In this paper low pressure plasma and electrochemical deposition are in focus.

Electron dynamics of low-pressure deposition plasma

Abstract When the electric field in the dark gas phase reaches the threshold value, an electron avalanche (breakdown) occurs, which causes dissociation of organic molecules, excitation of chemically reactive molecular gas, and/or ionization of atomic gas, depending on the type of gas involved. The principles that govern these electron-impact reactions are collectively described by the term "electron dynamics". The electron-impact dissociation of organic molecules is the key factor for the deposition plasma. The implications of the interfacial avalanche of the primary electrons on the deposition plasma and also other plasma processes are discussed. The system dependency of low-pressure plasma deposition processes is an extremely important factor that should be reckoned, because the electron dynamic reactions are highly dependent on every aspect of the reaction system. The secondary electron emission from the cathode is a misinterpretation of the interfacial electron avalanche of the primary electrons described in this paper.

Development of Plasma Polymerised SiOx Barriers on Polymer Films for Food Packaging Applications

Expensive polymer food packaging consisting of multilayer systems of different polymers will be increasingly replaced by cheap homopolymeric materials. Low-pressure plasma deposition of SiOx layers provides a promising alternative to achieve barrier properties on homopolymeric materials directly comparable to those of multilayer polymer packaging. Oxygen and HMDSO were applied for depositing SiOx layers on poly(propylene) (PP) and polyethyleneterephthalate (PET) foil samples by using two different low-pressure microwave plasma sources. Significant improvements of the barrier properties were achieved in the first experiments, e.g. the oxygen permeability could be reduced by a factor of 65.

Characterization of C-based materials: The evaluation of sp 2 and sp 3 hybrids

Low temperature, low pressure plasma deposition of carbon is widely used to obtain coatings having peculiar properties. These properties may range from those of graphite to those of diamond which are dependent on the number and the organization of the sp 2 and sp 3 hybrids in the film network. The prevalence of the first or of the second electronic configuration determines the physical, the electrical and the structural properties of the material. So the quantification of the sp 2 and sp 3 hybrids is one of the most important parameter to characterize the C-based materials. Unfortunately this kind of analysis is not straightforward. A common problem is related to the lack of proper references to obtain meaningful estimations of the abundance of the sp 2 and sp 3 hybrids. In this work we demonstrate that Ar + irradiated graphite may be used as a standard. Different doses of Ar + ions were delivered to Highly Oriented Pyrolytic Graphite in order to transform its crystalline structure in disorder. Among the methods commonly used to determine the sp 2 and sp 3 abundance, we evaluated the reliability of those based on X-ray photoemitted Auger KVV, C1s and valence band spectra. The modification of the spectral features under Ar + irradiation affects the various methods to a different extent. This work points out that caution has to be used when C-hybrids are quantified using XPS spectra. In fact all the spectral features are sensitive not only to the atoms' hybridization but also to the kind of bonds formed (dangling or saturated) and to the sample structure (crystalline or amorphous).

PLASMA-ASSISTED DEPOSITION OF NANOSTRUCTURED FILMS AND COATINGS

Recent work is reviewed on plasma-assisted deposition of nanostractured films and coatings. Several methods are being developed. These include conventional plasma spray in which nanostructure is induced in the coarse feed powder by mechanical milling before spraying; thermal plasma spray pyrolysis; plasma flash evaporation of fine powders injected into an RF torch; hypersonic plasma particle deposition; and low-pressure plasma synthesis and deposition of nanoparticles to produce thin films.

減圧熱プラズマ成膜法によるチタン酸鉛PbTiO<SUB>3</SUB>薄膜の合成に及ぼす成膜圧力の影響

PbTiO3 thin films were prepared by low-pressure thermal plasma deposition method on (100)MgO substrates. The mists of the mixed solution of each metal alkoxides and 2-methoxyethanol were introduced into a plasma flame and deposited onto substrates. The constituent phases, the crystal texture and the surface morphology were drastically changed by the chamber pressure. Over 13332 Pa, single phase PbTiO3 films were obtained. They were grown epitaxially and their surface morphology was composed of rectangular shaped grains. The remnant polarization and coercive field of the film from the hysteresis loop were about 0.104 C·m−2 and 5.12 MV·m−1, respectively.

Reactive synthesis and characterization of [formula omitted] using low-pressure plasma deposition and 100% methane

Reactive synthesis and characterization of [formula omitted] using low-pressure plasma deposition and 100% methane

In-Situ Processing and Characterization of Mosi2/Sic Formed by Reactive Low-Pressure Plasma Deposition

AbstractLow-pressure plasma deposition (LPPD) was used to synthesize an in-situ MoSi2/SiC composite using 100% methane (CH4) as a powder carrier gas. X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) identified MoSi2, Mo5Si3, Mo5Si3C, Si02, and SiC as the phases present in the composite. XRD and XPS revealed ∼6 vol% SiC in the as-sprayed material. Annealing of the as-sprayed composite increased the SiC content to ∼8 vol% while reducing the Si02 volume fraction. Transmission electron microscopy studies revealed a fine homogeneous distribution of SiC and/or carbide particles at prior splat boundaries in the MoSi2 matrix. Wavelength dispersive spectroscopy (WDS) confirmed the increased presence of carbon in the in-situ materials. Fracture toughness measurements yielded values on the order of 10 MPa m½ for annealed composites. The creep behavior of the LPPD reactive spray composite dramatically improved compared to unreinforced LPPD MoSi2. Additionally, the creep behavior was shown to be equal to or better than that of powder metallurgy MoSi2/SiC composites containing higher percentages of SiC.

Creep behavior of plasma-sprayed SiC-reinforced MoSi2

In a previous paper, the authors presented some preliminary results on the synthesis, room temperature fracture toughness and creep resistance of a SiC ([approximately]9 vol.%) - reinforced MoSi[sub 2] composite processed by a low pressure plasma deposition technique. The results of the constant stress tests as a function of temperature suggested a change in the rate-controlling creep mechanism at 1300[degree]C from one with a high activation energy at temperatures lower than 1300[degree]C to one with a low activation energy at temperatures higher than 1300[degree]C. The creep mechanism in the low activation energy region was attributed to be grain boundary sliding, which is assisted by the presence of an amorphous silica grain boundary phase which melts or softens at a temperature of approximately 1300[degree]C. It is the purpose of this paper to confirm the suggestion that a change in the rate-controlling creep mechanism as a function of temperature occurs in the plasma-sprayed SiC-reinforced MoSi[sub 2]. The stress exponent(n), activation energy (Q) for creep, and microstructure as a function of temperature were investigated. In addition, the effect of orientation on the creep behavior (with respect to the spray direction).

Low-pressure plasma deposition of SiC-reinforced MoSi 2

Low-pressure plasma deposition of SiC-reinforced MoSi 2

Synthesis and Properties of MoSi2/SiC Processed by Low Pressure Plasma Co-Injection and Deposition

AbstractLow-pressure plasma deposition (LPPD) and co-injection has been used to fabricate a MoSi2 composite reinforced with 15 µm SiC particles. The microstructure and creep behavior of the LPPD processed composite are reported and discussed. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) showed the structure of the composite to be lamellar and energy dispersive X-ray analysis (EDAX) identified the phases present in the material as: MoSi2, Mo5Si3, SiO2, and SiC. Density characterization revealed a porosity of less than 1.0 vol. %, indicating a nearly fully dense material. A high concentration of SiO2 (∼8.0 vol. %) present in the MoSi2/SiC composite may be attributed to possible contamination of the starting powders before or during LPPD. Sublimation of SiC during co-injection led to a low volume fraction (< 2.0 vol. %) of reinforcement in the composite. The creep rate of the LPPD MoSi2/SiC was higher relative to that of MoSi2/SiC composites fabricated by powder metallurgy (PM) techniques. On the basis of the results of this study it has become evident that alternative processing methods such as LPPD insitu processing may be better suited for the fabrication of elevated volume fraction MoSi2/SiC composites.

Low-pressure microwave plasma nucleation and deposition of diamond films

Low-pressure microwave plasma nucleation and deposition of diamond films were investigated in the pressure range 10-mtorr to 10 torr, at substrate temperatures 400-750 C and with CH4 and O2 concentrations in H2 plasma of 2-15 percent and 2-10 percent, respectively. The experiments were performed in a microwave plasma system consisting of a microwave plasma chamber, a downstream deposition chamber, and an RF induction heated sample stage. Scanning electron microscopy of diamond films deposited at 600 C with 5 percent CH4 and 5 percent O2 in H2 plasmas showed high-quality well faceted crystallites of 1/2 micron size. Cathodoluminescence measurements of these films showed very few nitrogen impurities and no detectable silicon impurities.

Toughness of dense MoSi2 and composites produced by low pressure plasma deposition

The thrust to develop new high temperature materials for advanced aircraft turbine engines has focused on composite systems based on metal-matrix, ceramic-matrix, intermetallic matrix and carbon-carbon composites. For the case of intermetallic matrix composites, candidate materials such as aluminides and silicides have been identified as potential materials due to their excellent oxidation resistance at high temperatures. More specific to the class of silicides, is molybdenum disilicide (NoSi{sub 2}), which has been used as a high melting intermetallic (2030 {degrees} C) for more than eighty years. One of the properties which has discouraged the application of MoSi{sub 2}, as well as other intermetallic compounds, is the inherent lack of ductility at low to intermediate temperatures. Plasma spraying as a means of fabricating composite structures of metals has been addressed recently by a number of researchers. In this paper the use of low pressure plasma deposition (LPPD) for producing spray deposits of MoSi{sub 2} and MoSi{sub 2} with a 20 volume fraction of tantalum is investigated. Initial results focusing on the as-deposited densities and fracture toughness of the spray deposited material are compared to those properties measured on conventionally hot pressed MoSi{sub 2}. Effects of post consolidation on fracture toughness of themore » spray deposits are also addressed.« less