Pulsed Plasma Mode Research Articles

Acceleration analysis of repetitive multi-MeV ion beams from pulsed plasmas

Multi−MeV ion spectra reproduced with absolute spectral index agrees with the experimental data and meet the needs to critically analyze the repetitive pulsed plasma mode of applications. The ion acceleration parameter, (Ip.rp), predicts mean ion energy and that is related to the electric discharge components based upon the precision measurements. Proper selection of repetition rate offers a relatively stable proton beam to acquire the survival curves of irradiated targets. DSB rate for plasma focus operated at 1Hz, is 10DSB/s with corresponding surviving probability of the order of 10−5. The surviving fraction is likely to be more affected by higher dose frequencies.

Structure of plasma‐deposited copolymer films prepared from acrylic acid and styrene: Part III sulfonation and electrochemical properties

AbstractAcrylic acid‐styrene copolymer films were deposited plasma‐chemically more gently using the pulsed plasma mode instead of the continuous mode, with linear and some slightly branched chains and marginal crosslinking. Then, the styrene unit of copolymers was wet‐chemically sulfonated by chlorosulfuric acid. On exposure to air, the formed 4‐chlorosulfonic acid groups hydrolyze to sulfonic acid groups (–SO3H). Fourier transform infrared spectroscopy, X‐ray photoelectron spectroscopy, and broadband dielectric spectroscopy were employed to characterize the composition, structure, functional groups, and electrochemical performance of the copolymers. A high concentration of sulfonic acid‐containing groups was obtained in the sulfonated polystyrene sample. The values of the DC conductivity σDC for the sulfonated sample of the acrylic acid and styrene copolymer are ca. five orders of magnitude higher than that of the not‐sulfonated copolymer materials.

Improvement of wetting properties of expanded perlite particles by an organic conformal coating

Expanded perlite particles were surface functionalized using poly(hydroxyethyl methacrylate) (PHEMA) thin film under radio frequency (RF) plasma conditions in a rotating-bed plasma enhanced chemical vapor deposition (PECVD) system. Using a rotating-bed system allowed effective agitation and mixing of the particles during depositions, which ensure uniform surface coating of highly porous and particulate materials. The effects of plasma power and plasma operation mode, namely pulsed and continuous modes on the deposition rates, structure, wettability and water holding capacities of expanded perlite particles were investigated. Chemical and morphological properties of uncoated and coated expanded perlites were determined by SEM, FTIR, contact angle, and BET analyses. Observed deposition rates changed between 10 and 35 nm/min., which were dependent on the deposition conditions. It was found that pulsing the discharge helped to minimize undesirable monomer fragmentation while providing better film structure. The most hydrophilic PHEMA thin films were fabricated at 50 W plasma power and under pulsed-plasma mode. When the expanded perlite was modified with PHEMA under suitable experimental conditions, the water holding capacity of untreated particles is increased by more than twenty percent.

Gas phase grown silicon germanium nanocrystals

We report on the gas phase synthesis of highly crystalline and homogeneously alloyed Si1−xGex nanocrystals in continuous and pulsed plasmas. Agglomerated nanocrystals have been produced with remarkable control over their composition by altering the precursor GeH4 gas flow in a continuous plasma. We specially highlight that in the pulsed plasma mode, we obtain quantum-sized free standing alloy nanocrystals with a mean size of 7.3nm. The presence of Si1−xGex alloy particles is confirmed with multiple techniques, i.e. Raman spectroscopy, XRD (Xray diffraction) and HRTEM (high resolution transmission electron microscopy) studies, with each of these methods consistently yielding the same composition. The nanocrystals synthesized here have potential applications in band-gap engineering for multijunction solar cells.

Influence of water addition on the structure of plasma-deposited allyl alcohol polymer films

One hundred and fifty nanometre thick polymer films made of allyl alcohol and H2O addition were deposited onto aluminium substrates using the radio-frequency (rf) pulsed plasma mode. The structure–property relationships of polymer films were studied in dependence on the precursor ratio allyl alcohol-water. Both the regularity of structure and composition of such thin films in comparison to chemically polymerized allyl alcohol were investigated using by bulk-sensitive Fourier transform infrared spectroscopy (FTIR) in the spectral range of 4000–500 cm−1 as well as surface-sensitive X-ray photoelectron spectroscopy (XPS). The intention of this work was to increase the yield in OH groups by addition of water to the allyl alcohol precursor. For an unambiguous identification of the functionality of the deposited films, the OH groups were labelled with trifluoroacetic anhydride and subsequently measured by XPS as well as quantitatively by FTIR. As expected, the O/C ratio grew with increasing water admixture by oxidation of both the plasma polymerized allyl alcohol layer to preferably aldehyde and/or carboxylic acid groups. In contrary, the concentration of OH groups in the deposited polymer film decreases dramatically with increasing admixture of water to the allyl alcohol plasma. It has been shown that the additional water has produced preferably higher oxidized C-Ox species with two or three C–O bonds. This fits also very well with the observation that almost no deuterium is introduced into the surface of plasma polymer if D2O was added instead of H2O.

Effect of source frequency and pulsing on the SiO2 etching characteristics of dual-frequency capacitive coupled plasma

A SiO2 layer masked with an amorphous carbon layer (ACL) has been etched in an Ar/C4F8 gas mixture with dual frequency capacitively coupled plasmas under variable frequency (13.56–60 MHz)/pulsed rf source power and 2 MHz continuous wave (CW) rf bias power, the effects of the frequency and pulsing of the source rf power on the SiO2 etch characteristics were investigated. By pulsing the rf power, an increased SiO2 etch selectivity was observed with decreasing SiO2 etch rate. However, when the rf power frequency was increased, not only a higher SiO2 etch rate but also higher SiO2 etch selectivity was observed for both CW and pulse modes. A higher CF2/F ratio and lower electron temperature were observed for both a higher source frequency mode and a pulsed plasma mode. Therefore, when the C 1s binding states of the etched SiO2 surfaces were investigated using X-ray photoelectron spectroscopy (XPS), the increase of C–Fx bonding on the SiO2 surface was observed for a higher source frequency operation similar to a pulsed plasma condition indicating the increase of SiO2 etch selectivity over the ACL. The increase of the SiO2 etch rate with increasing etch selectivity for the higher source frequency operation appears to be related to the increase of the total plasma density with increasing CF2/F ratio in the plasma. The SiO2 etch profile was also improved not only by using the pulsed plasma but also by increasing the source frequency.

MgH2 thin films deposited by one-step reactive plasma sputtering

The morphology, crystal structure, hydrogen content, and sorption properties of magnesium hydride thin films prepared by reactive plasma-assisted sputter deposition were investigated. Few micrometers-thick films were deposited on Si and SiO2/Si substrates, at low pressure (0.4 Pa) and close to room temperature using (Ar + H2) plasma with H2 fraction in the range 15–70%. The microstructure and hydrogen content of the films are closely related to the surface temperature and hydrogen partial pressure during the deposition process. Operating in pulsed-plasma mode allows the hydrogenation rate of the MgH2 thin film to top up to 98%, thereby producing a nearly fully hydrogenated film in a single-step process. The positive effect of the pulsed process is explained by the significant decrease in the whole energy flux incident on the surface and the favourable impact of the transient process for the rearrangement/relaxation of the materials. As for the hydrogen storage properties, desorption experiments and cycling of the films show the destabilizing effect of Mg2Si formation at the interface between the film and the Si substrate resulting in a drastically increased desorption kinetics compared to less reactive SiO2 substrate. However, the reaction is regrettably not reversible upon hydrogenation and the hydrogen storage capacity is consequently reduced upon cycling. Nevertheless, the deposition process carried out on inert substrates would offer true potential for reversible storage. Finally, our experimental results, which show the possibility to preferentially grow the metastable medium pressure γ-MgH2 phase, open possibilities for the synthesis of more complex metastable phases such as magnesium-based ternary compounds.

Influence of layer type and order on barrier properties of multilayer PECVD barrier coatings

Due to their macromolecular structure, plastics are limited in their scope of application whenever high barrier functionality against oxygen and water vapour permeation is required. One solution is the deposition of thin silicon oxide coatings in plasma-enhanced chemical vapour deposition (PECVD) processes. A way to improve performance of barrier coatings is the use of multilayer structures built from dyad layers, which combine an inorganic barrier layer and an organic intermediate layer. In order to investigate the influence of type and number of dyads on the barrier performance of coated 23 µm PET films, different dyad setups are chosen. The setups include SiOCH interlayers and SiOx-barrier layers deposited using the precursor hexamethyldisiloxane (HMDSO). A single reactor setup driven in pulsed microwave plasma (MW) mode as well as capacitively coupled plasma (CCP) mode is chosen. In this paper the effects of a variation in intermediate layer recipe and stacking order using dyad setups on the oxygen barrier properties of multilayer coatings are discussed with regard to the chemical structure, morphology and activation energy of the permeation process.Changes in surface nano-morphology of intermediate layers have a strong impact on the barrier properties of subsequent glass-like coatings. Even a complete failure of the barrier is observed. Therefore, when depositing multilayer barrier coatings, stacking order has to be considered.

Practical Amine Functionalization of Multi‐Walled Carbon Nanotubes for Effective Interfacial Bonding

AbstractImproved methods of functionalizing the surfaces of multi‐walled carbon nanotubes (MWCNTs) have been investigated. It is shown that a level of primary amines of 2.3%, higher than previously reported for any nitrogen‐containing gas plasma treatment, can be achieved using a mixture of N2 and H2, which is preferable to using NH3. Even higher levels (3.5%) of primary amines can be achieved by coating the MWCNTs with a thin layer of plasma polymerized heptylamine. In both cases, the highest levels were achieved using a combined continuous plus pulsed plasma mode which was superior to either continuous wave or pulsed wave alone. The integrity of the MWCNT structure is maintained by the plasma treatments, and the functionalized surface improves the dispersion of the MWCNTs and their interfacial bonding with epoxy, giving superior nanoindentation performance of the composites. magnified image

Polyethylene Oxide Films Polymerized by Radio Frequency Plasma-Enhanced Chemical Vapour Phase Deposition and Its Adsorption Behaviour of Platelet-Rich Plasma

We present polyethylene oxide (PEO) functional films polymerized by rf plasma-enhanced vapour chemical deposition (rf-PECVD) on p-Si (100) surface with precursor ethylene glycol dimethyl ether (EGDME) and diluted Ar in pulsed plasma mode. The influences of discharge parameters on the film properties and compounds are investigated. The film structure is analysed by Fourier transform infrared (FTIR) spectroscopy. The water contact angle measurement and atomic force microscope (AFM) are employed to examine the surface polarity and to detect surface morphology, respectively. It is concluded that the smaller duty cycle in pulsed plasma mode contributes to the rich C-O-C (EO) group on the surfaces. As an application, the adsorption behaviour of platelet-rich plasma on plasma polymerization films performed in-vitro is explored. The shapes of attached cells are studied in detail by an optic invert microscope, which clarifies that high-density C-O-C groups on surfaces are responsible for non-fouling adsorption behaviour of the PEO films.

Characterisation of plasma polymers by thermoluminescence

Thin plasma polymer films were deposited using the pulsed plasma mode. These plasma polymers should possess a more regular structure than those produced by the conventional continuous-wave (cw) mode, because of lower monomer fragmentation caused by the plasma pulses and the chemical chain propagation during the plasmaless (free!) periods. The thermoluminescence method was applied to functional groups carrying plasma polymer layers which are used in medical technology. Examples are formation of biocompatible, biosensoric and bioactive coatings or in metal polymer composites such as adhesion-promoting interlayers. In addition to the use of the conventional X-ray Photoelectron Spectroscopy for thin film characterization, the new method of thermoluminescence was applied to characterize undesired defects and structural specifics produced in the polymer films by pp or cw plasma mode. The main areas of focus were oxygen-containing groups produced by post-plasma oxygen introduction via auto-oxidation, oxidation of implemented unsaturations and trapped radical sites known as typical irregular structures in plasma polymers.

Correlation between the characteristics of a pulsed microwave plasma used for diamond growth and the properties of the produced films

Previous studies have pointed out the advantages of using a pulsed discharge for diamond growth by microwave plasma assisted chemical vapour deposition (MPACVD): increase of the growth rate and/or enhancement of the diamond quality. It has been shown that the duration of the pulse and that of the pause between two pulses have a particular influence on the deposition process. Optimal values can be determined that depends mainly on the geometry and size of the reactor and on the working conditions.In the present work, new results are obtained in a MPACVD reactor working in a pulsed plasma mode, H2/CH4 gas mixture and 6 kW peak power. These conditions are similar to those of industrial reactors. The most important species in such process are CHx, C2Hy and H, which are considered, respectively, as the key species for diamond deposition, graphite deposition and graphite etching. A particular interest was devoted to the atomic hydrogen evolution during the discharge phase and the afterglow. Quantitative measurements of H-atom ground state concentration are carried out by two-photon Laser Induced Fluorescence (LIF). The study of the kinetic processes which are responsible of atomic hydrogen creation and loss permits us to determine the production rate of H-atoms in pulsed mode as compared with the continuous one (CW), and leads to a better understanding of its influence on the diamond growth rate and its chemical quality as estimated by micro-Raman spectroscopy.The correlation established between the results of the diamond film analysis and the plasma characteristics points out the benefit of this study for the optimisation and the control of the diamond growth process by pulsed MPACVD.

A Cold Plasma Generator and its Applications to Combinatorial Copolymerization of Carbon Dioxide with Organic Molecules

AbstractSummary: As an energy minimum process for CO2 fixation, we propose the reaction of CO2 with a hydrocarbon excited by our originally designed plasma reactor. In this reactor, the CO2/hydrocarbon ratio and pulsed plasma mode can be changed combinatorially to produce plasma copolymers under sequentially controlled conditions. The presence of CO double bonds in the FT‐IR spectra of the insoluble films confirmed that CO2 has actually been incorporated into the plasma polymerized products.FT‐IR spectra of products copolymerized from a CO2/C2H4 system (a), and relative intensities of the carbonyl absorbance (b).magnified imageFT‐IR spectra of products copolymerized from a CO2/C2H4 system (a), and relative intensities of the carbonyl absorbance (b).

Plasma deposition of amorphous carbon films on copper

The plasma source ion implantation (PSII) technique was used in an attempt to promote diamond formation on a copper substrate via the so-called carbon-implantation-out-diffusion (CIOD) method. Carbon films were deposited on copper substrates in DC and pulsed plasma modes at temperatures and substrate bias voltages (BV) ranging from room temperature (RT) to 950°C and 0 to −30 kV, respectively. All carbon films deposited in the DC-plasma mode at 800–950°C with a BV up to 10 kV exhibited G-band and D-band Raman shifts typical of polycrystalline graphite. Very similar Raman spectra were also obtained from carbon films deposited in the pulsed plasma mode at 800–950°C and a BV up to −30 kV. The Raman spectral shape of the carbon film deposited at RT and −300 V in the pulsed plasma mode showed an asymmetric broad single peak typical of an amorphous diamond-like carbon film with G-band peak shifted toward the lower frequency end at 1520 cm −1 from the original graphite G-line position at 1580 cm −1. No trace of crystalline diamond, signatured by a distinct sharp peak at 1332 cm −1, was found under the experimental conditions examined. Results from XPS analyses were consistent with those of the Raman studies.

Plasma impulse chemical vapour deposition—a novel technique for the production of high power laser mirrors

Chemical vapour deposition (CVD) methods are known to be most advantageous for the production of very high quality optical materials ( i.e. performs for low loss fibres or high damage threshold, and reflection coatings on thin fibres). It is also well known that plasma-enhanced CVD methods show improved deposition efficiencies. Pulsed microwave plasmas (2.45 GHz) are used to realize interference filters with very high laser damage threshold as well as high reflection. The impact of the coating temperature on the layer quality is discussed. The high deposition rate together with the almost monolayer-by-monolayer growth control in the pulsed plasma mode is suitable for producing extreme small-band, high reflection coatings, which have no harmonics. By almost individual shaping of the refractive index distribution within one λ/4 layer a new degree of freedom in the design of these coatings has been accomplished. The theoretical background as well as experimental results are discussed.