Microwave Plasma Research Papers - Academia.edu (original) (raw)

2025

In this work, we present the results of a new approach of atmospheric microwave plasma torch (MPT), measuring the excitation temperature of the plasma. The new system consists of a cylindrical resonant cavity and a microwave source, a magnetron operating at a frequency of 2.45 GHz and power of 880 W, which is used to generate plasma inside a quartz tube, mounted coaxially along the cavity, with a diameter of 7 mm. The cylindrical cavity excites a dominant electric transverse mode TE 111 , in which surface waves transporting energy reach up to levels of 100 W/m 3 sr. The magnetron generator converts the input energy into plasma, in which the absorbed power is the result of the balance between the incident power and reflected power, but it depends on source losses in the cavity, the connection of the cavity, and the existence of other microwave harmonics. We use the optical emission spectroscopy to measure the excitation temperature, determined by Boltzmann plot method, based on the detection of several plasma emission lines, resulting in an excitation temperature of (3400 ±500)K. The development of the microwave plasma torch-MPT plasma technique has been allowed the built of devices for application to industrial, medical, and scientific fields .

2025, Solid-State Electronics

The purpose of this article is to report on the recent developments on the gate dielectric formation on strained-Si/ SiGe heterolayers. In the first part, growth of a high quality strained-Si layer on a relaxed, linear or step-graded SiGe buffer layer and SiGe-free strained-Si on Silicon-on-Insulator (SSOI) is briefly reviewed. Characterization results of strained-Si films using atomic force microscopy (AFM), transmission electron microscopy (TEM) and Raman spectroscopy are then presented. In the second part, the processing issues of gate dielectric formation on strained-Si films are critically examined and the thermal oxidation of strained-Si layers are discussed. Low thermal budget processing, such as rapid thermal oxidation (RTO) and low temperature microwave plasma oxidation and nitridation of strained-Si layers are discussed in the third part. Microwave plasma deposition of various high-k gate dielectrics, such as ZrO 2 , Ta 2 O 5 , and TiO 2 on strained-Si, their electrical properties and the current conduction mechanisms are also discussed.

2024

Abatement of NO using microwave micro-plasma is presented in this paper. The micro-plasma is generated using granular activated carbon (GAC) particles of size (size 2-3mm) in loosely fluidised bed in microwave filed operated at 2.45GHz. A single mode microwave cavity reactor (SMMCR) was constructed and microwave was injected through another slotted waveguide in a sandwiched manner. COMSOL Multiphysics software was used to investigate the microwave electric field and the power density within the SMMCR. Gas mixture of air and 500 ppm NO (in N2) at the flow rate of 2 l/min was passed through a quartz tube centered within SMMCR while the supplied microwave power was very low 10-80 W and NO reduction was greater than 98%. The mass of GAC used for generating the plasma was 5g. When air is mixed with NO (in N2), the efficiency of NOx reduction achieved vary greatly with respect to the supplied microwave energy and behavior has become complex and is not predictable. The gas analyzer (testo 350) was used to measure the gas (NO, NO 2 , CO and O2) concentration and temperature.

2024, Materials Today: Proceedings

The synthesis of carbon nanomaterials and the technique of encapsulated metals into a nanoshell by the electric arc method in a liquid medium will allow imparting synthesis products to various mechanical, electrical, magnetic and other physicochemical properties, thereby making them a ''New Generation Material", which increases their ability for various purposes. This topic is very interesting in that, for example, ferromagnetic carbon nanocomposite structures and their derivatives have unique electrically conductive, magnetic, optical, catalytic and biological properties. Based on them, it is possible to create new superconductors, sensors, electrode materials, catalysts, drugs, etc. As for the uniqueness of magnetic nanomaterials themselves, one of them is that controlling nanoparticles in liquids creates a unique opportunity to remotely control their parameters: pressure, density, electrical conductivity, thermal conductivity, and optical permeability. The creation of nanocomposites based on ferromagnetic nanoparticles and carbon nanostructures will make it possible to take a step towards the creation of new materials, such as various coatings sensitive to electromagnetic radiation of various wavelengths. And this creation of new equipment and protective structures will protect against various types of radiation. That is why the focus is on the study of a new synthesis strategy for ferromagnetic nanoparticles immobilized in a carbon matrix and the study of their structure and magnetic properties.

2024, European Polymer Journal

The paper describes a method for preparation of polymer support suitable for covalent invertase immobilization. Modification of poly(phenylene oxide) films by plasma polymerization of allylamine has been applied to introduce amine functionality on the polymer surface. It has been observed that the polymer surface became covered in plasma by a loosely fixed, moderately hydrophilic layer that should be removed before the immobilization process. The chemical character of the stable sub-layer has been related to several modification parameters: geometry of reactor, mode of plasma action and composition of gaseous mixture. Methods for determination of surface concentration of amine groups have also been presented and discussed from the immobilization point of view.

2024, The Journal of Physical Chemistry B

2024, The European Physical Journal Applied Physics

Methods to induce non-thermal atmospheric pressure plasma filaments are presented with related properties for micro, streamer and prevented spark discharges, respectively induced in planar Dielectric Barrier Discharges with one electrode covered by dielectric material (mono-DBD) or point-to-plane Corona. Two mechanisms of nano-particles formation are depicted from aerosol size distributions and TEM analysis. 0.1 to 10 mJ prevented spark discharges produce 10-100nm droplets ejected from melted craters as well as nucleated primary particles and subsequent 10-100nm agglomerates, by nucleation and coagulation in expanding vapors jets. With smaller energy per filament, 0.1-10µJ micro-discharges and 0.1-100µJ streamers, the initial local vapor fluxes emitted from spots of interaction between plasma filaments and electrodes are reduced. Subsequent smaller primary particle density limits the local coagulation in the vapor plume since 2-10nm non-agglomerated crystalline metal nano-particles are produced in mono-DBD with Au, Ag and Cu electrode. Besides, the evolution of the aerosol size from primary nano-particles to agglomerates with transit time, suggests slow coagulation of these primary metal particles in mono-DBD. Aerosol properties depend on the energy per filament and on the electrode. The final size is controlled by plasma parameters and transit time in and after the plasma. The aim is to underline emerging applications of atmospheric pressure plasmas for the production of tailored particles with tunable size, composition and structure with nonthermal plasma filaments to control the resulting properties of nano-powders and materials. Production rates and related energetic yields are compared.

2024, Vacuum

Microwave plasma annealing of sol-gel deposited tantalum oxide and zinc oxide films

2024, Acta Physica Polonica A

A few micrometers thick nanocrystalline α-Fe layer with the mean crystallite size dXRD = 14 nm was deposited in low-pressure microwave plasma, using Fe(CO)5 vapour. Its nanocrystalline character was proved on its surface under SEM (surface was formed of deposited nanoparticles) and in its volume using TEM (deposited nanoparticles were stacked up, creating columns). No signicant iron oxide phases were observed in the transmission 57 Fe Mössbauer spectrum measured at 5 K nor in the surface-sensitive 57 Fe conversion electron Mössbauer spectrum measured at 293 K.

2024, Materials Letters

The article reports on ε-Fe 2 O 3 nanoparticles synthesized in a single step by atmospheric-pressure microwave torch discharge using gaseous precursors only. Morphology and composition of the assynthesized nanopowder were studied by HR-TEM, XRD, and Mössbauer spectroscopy. In the studied nanopowder, ε-Fe 2 O 3 phase (d XRD ¼25 nm, 32 wt%) together with α-Fe 2 O 3 and γ-Fe 2 O 3 phases was found. The characteristic ε-Fe 2 O 3 and α/γ-Fe 2 O 3 sextets in the Mössbauer spectra measured at 293 and 5 K confirmed the phase composition of the powder. Compared with the methods currently used for the synthesis of ε-Fe 2 O 3 nanoparticles, atmospheric-pressure microwave torch discharge appears as a new synthesis route for obtaining ε-Fe 2 O 3 nanoparticles.

2024, nanocon.cz

Microwave torch discharge ignited in Ar at atmospheric pressure has been used for the synthesis of maghemite-Fe 2 O 3 nanoparticles. A double-walled nozzle electrode enabled to introduce gases separately: Ar flowed in the central channel, whereas the mixture of H 2 /O 2 /Fe(CO) 5 was added into the Ar torch discharge through the outer channel. The composition and properties of the synthesized nanopowder were studied by TEM, XRD, Raman and Mössbauer spectroscopies. For magnetic measurements in the range 293-1073 K a vibrating sample magnetometer was used. The measurements of ZFC/FC curves and heat capacity in the range 4-293 K were done on a PPMS Quantum Design device. Only-Fe 2 O 3 phase with the mean crystallite size of 20 nm was identified by XRD in the representative sample. The measured Raman spectrum matched well those reported for-Fe 2 O 3 powders in the literature. In the Mössbauer transmission spectrum measured at 5 K the two sextets characteristic for-Fe 2 O 3 were clearly identified. Structural changes and phase transformations of the nanopowder up to 1073 K are described.

2024, Materials Today: Proceedings

2024, Spectrochimica Acta Part B: Atomic Spectroscopy

2023, Springer eBooks

A series of Al 3+-substituted ε-Fe 2 O 3 nanomagnets, ε-Al x Fe 2−x O 3 (x = 0, 0.21, 0.40), with large coercive field values was studied by 57 Fe Mössbauer spectroscopy. The hyperfine field and absorption coefficient in the Mössbauer spectra changed with x. These behaviors can be explained by the selective replacement of Fe 3+ ions with Al 3+ ions. This is the first report on the Mössbauer spectra of metalsubstituted ε-Fe 2 O 3 .

2023, Surface and Coatings Technology

The photoactivity of both un-doped and carbon-doped titanium dioxide (TiO 2) coatings has been widely reported. In this paper, the use of a microwave plasma as a novel oxidation treatment for the fabrication of these coatings is evaluated. The photoactivity performance of the microwave plasma-formed coatings is benchmarked against those fabricated through air furnace oxidation as well as those deposited using reactive magnetron sputtering. The un-doped and carbon-doped TiO 2 coatings were prepared respectively by microwave plasma-oxidizing titanium metal sheets and sputter deposited titanium carbide thin films. The resulting oxides were characterized using XPS, XRD, FEG-SEM, and optical profilometry. The oxide layer thicknesses achieved over the 15 to 45 minute oxidation times were in the range of 0.15 to 3.44 µm. These coatings were considerably thicker than those obtained by air furnace oxidation. The microwave plasma-formed oxides also exhibited significantly higher surface roughness values compared with the magnetron-sputtered coatings. The photoactivity performance of both un-doped and carbon-doped coatings was assessed using photocurrent density measurements. Comparing the un-doped TiO 2 coatings, it was observed that those obtained using the microwave plasma oxidation route yielded photocurrent density measurements that were 4.3 times higher than the TiO 2 coatings of the same thickness that were deposited by sputtering. The microwave plasmaoxidized titanium carbide coatings did not perform as well as the un-doped TiO 2 probably due to the presence of un-oxidized carbide in the coatings, which reduced their photoactivity.

2023, Science & Technique

Design of non-transferred DC electric arc plasma torches (EAPTs) operated with plasma gases containing alkane hydrocarbons, as a promising type of heaters for a number of technologies (thermal spraying, surface hardening, testing of thermal protection systems, etc.), requires taking into account the evaporation rate of surface cathode material (as one of the channels of its ablative degradation). For this procedure, as the first stage, thermodynamic methods can be used to simulate the composition and properties of reactive C–H–O–N–Ar–Me-systems with variable set of such input parameters as the ratio of components of plasma-forming mixture, its pressure and temperature. We theoretically estimated the evaporative degradation of the material for three variants of EAPT cathode with alkane-containing plasmas (“hot” thermochemical zirconium and thermionic tungsten, and “cold” copper) in equilibrium and quasi-equilibrium modes of “plasma gas + surface cathode material”-mixture, with use of...

2023, Journal of Nanoparticle Research

Plasma methods using the direct evaporation of a transition metal are well suited for the costefficient production of ceramic nanoparticles. In this paper, we report on the development of a simple setup for the production of titanium-ceramics by reactive anodic arc evaporation and the characterization of the aerosol as well as the nanopowder. It is the first report on TiC X N 1-X synthesis in a simple anodic arc plasma. By means of extensive variations of the gas composition, it is shown that the composition of the particles can be tuned from titanium nitride over a titanium carbonitride phase (TiC X N 1-X) to titanium carbide as proven by XRD data. The composition of the plasma gas especially a very low concentration of hydrocarbons around 0.2 % of the total plasma gas is crucial to tune the composition and to avoid the formation of free carbon. Examination of the particles by HR-TEM shows that the material consists mostly of cubic single crystalline particles with mean sizes between 8 and 27 nm.

2023, Journal of Physics D: Applied Physics

A unique large-scale synthesis method for Al-doped TiO 2 nanopowder was developed using 20-kW Ar-O 2 pulse-modulated induction thermal plasmas (PMITP) with time-controlled feedstock feeding (TCFF). This PMITP-TCFF method is characterized by intermittent feedstock powder feeding synchronized with modulated power of the PMITP. The method enables heavy-load feeding of raw material powder to the thermal plasmas for complete evaporation. Synthesized nanopowder was analyzed using different methods including FE-SEM, XRD, BF-TEM, TEM/EDX mapping, XPS, and spectrophotometry. Results showed that Al-doped TiO 2 nanopowder can be synthesized with mean diameters of 50-60 nm. The Al doping in TiO 2 was confirmed from the constituent structure in XRD spectra, the uniform presence of Al on the nanopowder in TEM/EDX mapping, the chemical shift in XPS spectra, and the absorption edge shift in the optical property. The production rate of Al-doped TiO 2 nanopowder was estimated as 400 g h −1 .

2023, International Journal of Modern Physics: Conference Series

Plasma torch is device that efficiently converts electrical energy in to thermal energy for various high temperature applications. The conventional plasma torch comprises of consumable electrodes namely anode and cathode electrodes. The replacement of these electrodes is a complex process owing to its cooling and process shut down requirements. However, microwave plasma arc is electrode-less plasma arc system that is an alternative method to conventional arc technology for generating plasma arc. In this technique, microwave power is efficiently coupled to generate plasma arc by using the property of polar molecule to absorb microwave power. The absorption of microwave power is in form of losses due to intermolecular friction and high collisions between the molecules. This is an efficient method because all microwave power can be absorbed by plasma arc. The main feature of microwave plasma arc is its large uniform high temperature column which is not possible with conventional arc di...

2023, Plasma Sources Science and Technology

In this paper, a stripline split-ring resonator microwave-induced plasma source, aimed for integration in complex systems, is presented and compared with a traditional microstrip design. Devices based on the two designs are evaluated using a plasma breakdown test setup for measuring the power required to ignite plasmas at different pressures. Moreover, the radiation efficiency of the devices is investigated with a Wheeler cap, and their electromagnetic compatibility is investigated in a variable electrical environment emulating an application. Finally, the basic properties of the plasma in the two designs are investigated in terms of electron temperature, plasma potential, and ion density. The study shows that, with a minor increase in plasma ignition power, the stripline design provides a more isolated and easy-to-integrate alternative to the conventional microstrip design. Moreover, the stripline devices showed a decreased antenna efficiency as compared to their microstrip counterparts, which is beneficial for plasma sources. Furthermore, the investigated stripline devices exhibited virtually no frequency shift in a varying electromagnetic environment, whereas the resonance frequency of their microstrip counterparts shifted up to 17.5%. With regards to the plasma parameters, the different designs showed only minor differences in electron temperature, whereas the ion density was higher with the stripline design.

2023, International Journal of Hydrogen Energy

Liquid ethanol introduced as microdroplets into the tip of microwave nitrogen plasma, operating at 2.45 GHz under atmospheric pressure, has been investigated. Injection of ethanol outside the region of plasma generation eliminated a problem of soot formation at that region, which was responsible for short reactor lifetime. Using liquid ethanol allows to save energy needed for vaporization. Hydrogen, carbon monoxide and solid carbon were the main outlet products. Other products detected with gas chromatography were CH 4 , C 2 H 4 and C 2 H 2. The best results concerning hydrogen production were as follows: concentration in the outlet gas up to 28%, production rate up to 1043 L/h, energy yield up to 209 L per kWh of microwave power, and were obtained for liquid C 2 H 5 OH flow rate of 3.7 L/ h. A numerical 0D model was used to determine contributions of chemical reactions in formation of measured gaseous products. Simplified model involving only radical reactions without any ions and electrons predicts final concentrations of main compounds quite well for microwave power up to 4 kW.

2023, Plasma Chemistry and Plasma Processing

In this paper, results of the pyrolysis of Freon HFC-134a (tetrafluoroethane C 2 H 2 F 4) in an atmospheric pressure microwave plasma are presented. A waveguide-based nozzleless cylinder-type microwave plasma source (MPS) was used to produce plasma for the destruction of Freon HFC-134a. The processed gaseous Freon HFC-134a at a flow rate of 50-212 l min-1 was introduced to the plasma by four gas ducts which formed a swirl flow in the plasma reactor (a quartz cylinder). The absorbed microwave power was 0.6-3 kW. The experimental results showed that the Freon was converted into carbon black, hydrogen and fluorine. The total conversion degree of HFC-134a was up to 84% with selectivity of 100% towards H 2 , F 2 and C 2 , which means that there was no conversion of HFC-134a into other hydrocarbons. The Freon destruction mass rate and corresponding energetic mass yield were up to 34.5 kg h-1 and 34.4 kg per kWh of microwave energy absorbed by the plasma, respectively.

2023, Journal of Power Sources

In this paper, results of hydrogen production via methane reforming in the atmospheric pressure microwave plasma are presented. A waveguidebased nozzleless cylinder-type microwave plasma source (MPS) was used to convert methane into hydrogen. Important advantages of the presented waveguide-based nozzleless cylinder-type MPS are: stable operation in various gases (including air) at high flow rates, no need for a cooling system, and impedance matching. The plasma generation was stabilized by an additional swirled nitrogen flow (50 or 100 l min −1). The methane flow rate was up to 175 l min −1. The absorbed microwave power could be changed from 3000 to 5000 W. The hydrogen production rate and the corresponding energy efficiency in the presented methane reforming by the waveguide-based nozzleless cylinder-type MPS were up to 255 g[H 2 ] h −1 and 85 g[H 2 ] kWh −1 , respectively. These parameters are better than those typical of the conventional methods of hydrogen production (steam reforming of methane and water electrolysis).

2023, Plasma Sources Science and Technology

In the present paper, a detailed investigation of the spatio-temporal dynamics of the recently developed time reversal microwave plasma source is presented. This novel source allows to ignite a plasma at a desired location in a reverberant cavity by focusing the electromagnetic energy in time and space. An important feature is the possibility to control the plasma position only by changing the input microwave waveform. The source is operated in a repetitive pulsed mode with very low duty cycle (typically 5 × 10−2%). Nanosecond pulses have rise time lower than 1 ns. The generated plasmas have typical sizes in the millimeter range and are observed using imaging for dozens of nanoseconds. The plasma behavior is investigated for different pressures and repetition frequencies. A strong dependence is observed between each discharge pulse suggesting the existence of an important memory effect. The latter is probably due to argon metastable atoms and/or residual charges remaining in the pos...

2023, IEEE Access

The demonstration of enhanced spatial control of nanosecond microwave plasmas generated by the time reversal plasma source is presented in this paper. This new microwave plasma source relies on the spatio-temporal control of the electric field inside an all-metal plasma reactor by modifying the waveform of a high power microwave signal. More specifically, it originally used the spatio-temporal focusing capabilities of the time reversal method to focus a high electric field in a small location. However, a parasitic microwave breakdown can still occur at sharp corners or wedges inside the cavity due to the local enhancement of the residual electric field during time reversal focusing. Thus, it is proposed to use the linear combination of configuration field method to improve field control inside the reactor. Its transient electric field shaping capabilities turn out to be a good candidate for the development of a low pressure microwave ''plasma brush''. INDEX TERMS Microwave plasma sources, transient field shaping, inverse source problem, reverberation chamber, time reversal.

2023

Il est très important pour moi de rédiger ces quelques lignes pour remercier les nombreuses personnes qui ont permis ce travail. En effet, que ce soit mon entourage scientifique, familial ou mon cercle d'amis, tous ont influencés mon travail, directement ou plus subrepticement. Je tiens à remercier en premier lieu Christian Trassy, Directeur de Recherche et Yves Fautrelle, Professeur, directeurs successifs du laboratoire EPM, pour m'avoir accueilli dans leur laboratoire. Je remercie également Eric Beaugon, Maître de Conférence et directeur du CRETA, pour nous avoir hébergé dans son laboratoire la première année de ma thèse. Mes remerciements s'adressent aussi à Johann Collot, Professeur et directeur du LPSC, pour avoir accueilli notre équipe, le Centre de Recherche Plasma-Matériaux-Nanostructures (CRPMN), dans son laboratoire. Je dois beaucoup à la commission Européenne, qui grâce au projet MATECO (contrat STRP 505928), a apporté une grande partie des moyens consacrés à mes travaux de thèse, et je l'en remercie vivement. J'adresse mes remerciements aux membres du jury de ma thèse, tout d'abord à Caroline Boisse-Laporte, Chargée de Recherche, et Yvan Ségui, Directeur de Recherche, pour le dur travail de rapporteur qu'ils ont dû accomplir. Je remercie doublement Yves Pauleau, Professeur, d'avoir accepté d'être président du jury et de m'avoir formé lors de mon DEA. Merci aussi à Michel Touzeau, Directeur de Recherche, pour avoir accepté d'être membre du jury et pour le temps qu'il m'a consacré pour tenter de comprendre mes plasmas d'oxygène. Je remercie également Agnès Granier d'avoir accepté d'être membre de mon jury et pour les corrections judicieuses qu'elle a suggérées pour ma thèse. J'adresse des remerciements très particuliers à Ana Lacoste, Professeur et directeur de ma thèse, pour ses conseils, son soutien tout au long de ma thèse, la confiance qu'elle m'a accordée et ses idées lumineuses qui m'ont permis d'avancer lorsque tout espoir semblait perdu. J'exprime aussi toute ma gratitude envers Jacques Pelletier, Directeur de Recherche, directeur du CRPMN et co-directeur de ma thèse, pour ses conseils avisés, son optimisme qui permet toujours de faire avancer l'équipe, pour les orientations qu'il a pu me donner et pour m'avoir proposé cette thèse. Mes remerciements s'adressent aussi à Michel Moisan, Professeur et directeur du Groupe de Physique des Plasmas de l'Université de Montréal, pour m'avoir accueilli au sein de son équipe durant un mois pour modéliser mon plasma. Bien entendu, je remercie aussi Kremena Makasheva, Docteur, sans qui la modélisation n'aurait pas été possible et pour le temps qu'elle y a consacré, je la remercie également pour sa bonne humeur, son humour et pour m'avoir sorti au Canada sans quoi je me serais sévèrement ennuyé.

2023, NATO Science Series

This work deals with the modelling of Ar/H 2 /CH 4 discharges ignited in microwave cavity systems and used for nanocrystalline diamond film deposition. These microwave discharges are characterized by a strong thermal and chemical non-equilibrium and the gas mixture is typically composed of an argon amount greater than 90% and a CH 4 concentration of around 1 %. Plasma models were developed and used in order to describe the considered discharges under quasi-homogeneous plasma assumption. They allowed the determination of the plasma composition, gas temperature and electron energy in the bulk of the discharge. As far as chemistry is concerned, the discharges used for nanocrystalline diamond growth are characterized by H/C ratio ranging between 8 and 18. For these H/C values, heavy hydrocarbons and soot particles may form for some discharge conditions, depending on pressure and input power values. Thus, in order to describe the plasma chemistry various thermochemical models were developed. The description of the kinetics of the discharges was first focused on conditions where the formation of heavy hydrocarbons and soot particles is limited and may be neglected. In these situations the gas temperature is higher than 2000 K, which corresponds to the conditions met in the plasma bulk. Consequently, only species containing up to 2 carbon-atoms were considered in a first numerical model (2C model) that permitted to understand the main energetic characteristics of the investigated plasma and to evaluate the population of active species in growth conditions. In particular, the gas temperature inside the discharge was estimated to be higher than 4000 K. The validity of the numerical and kinetic schemes was partially checked by experimental spectroscopic measurements. In order to probe the soot particle sources, the numerical model was extended to take into account Poly-Aromatic Hydrocarbons (PAHs) growth, following several mechanisms. The first one took into account large neutral PAHs up to 4 aromatic rings (A4 model) from which the particle nucleation was assumed to take place. This study was performed in such a way to investigate the whole temperature domain that characterize both the plasma bulk, the plasma-substrate boundary layer and the regions outside the discharge (plasma edges and post-discharge regions). This was achieved by exploring a large domain of input microwave power which includes conditions that do not correspond to those used for NCD deposition. The soot formation is obtained for gas temperature values below 1500 K with a nucleation rate as high as 10 8 part./cm 3 /h. At high gas temperature, the 2C and A4 models predicted the same species evolutions, and we concluded that the 2C model is accurate enough to describe such a discharge under deposition conditions. Thus, taking into account the formation of PAHs and soot nucleation is necessary only for temperature values less than 1500 K, which correspond to the boundary layer between the plasma and the substrate surface or reactor walls. In the second mechanism, we studied the kinetic that leads to the formation of PAHs up to 9 aromatic rings (A9 model). The purpose was to investigate how the assumption on the size of the PAHs that lead to soot nucleation affects the nucleation rate. Results showed that the values found for this rate by the A4 and A9 models are quite similar. It was therefore concluded that the A4 model is adequate for studying PAHs formation and soot nucleation in Ar/H 2 /CH 4 microwave discharges. Then the chemistry of the model was extended in order to take into account the formation of ionic PAHs. Ions with up to four aromatic rings were considered (A4+ model). We showed that the growth of PAHs and nucleation of soot through this ionic mechanism is significant especially at high temperatures (>1500K). This means that soot particles may also nucleate in the bulk of the discharge where temperature is quite high (~4000K). The last part of this work dealt with the investigation of the particle population dynamic. This was performed using the method of moment where we took into account the nucleation from PAHs molecules, growth by PAHs and small hydrocarbon condensation, coagulation and transport through diffusion, thermophoresis and drag forces, as well.

2023, Surface and Coatings Technology

Crystalline titanium dioxide (TiO 2) coatings have been widely used in photoelectrochemical solar cell applications. In this study, TiO 2 and carbon-doped TiO 2 coatings were deposited onto unheated titanium and silicon wafer substrates using a DC closed-field magnetron 2 sputtering system. The resultant coatings had an amorphous structure and a post-deposition heat treatment is required to convert this amorphous structure into the photoactive crystalline phase(s) of TiO 2. This study investigates the use of a microwave plasma heat treatment as a means of achieving this crystalline conversion. The treatment involved placing the sputtered coatings into a 2.45 GHz microwave-induced nitrogen plasma where they were heated to approximately 550°C. It was observed that for treatment times as short as 1 minute, the 0.25-µm thick coatings were converted into the anatase crystalline phase of TiO 2. The coatings were further transformed into the rutile crystalline phase after treatments at higher temperatures. The doping of TiO 2 with carbon was found to result in a reduction in this phase transformation temperature, with higher level of doping (up to 5.8% in this study) leading to lower anatase-to-rutile transition temperature. The photoactivity performance of both doped and un-doped coatings heat-treated using both furnace and microwave plasma was compared. The carbon-doped TiO 2 exhibited a 29% increase in photocurrent density compared to that observed for the un-doped coating. Comparing carbon-doped coatings heat-treated using the furnace and microwave plasma, it was observed that the latter yielded a 19% increase in photocurrent density. This enhanced performance may be correlated to the differences in the coatings' surface morphology and band gap energy, both of which influence the coatings' photoabsorption efficiency.

2023, Modern Research in Catalysis

Thermal treatment either in the presence of oxygen (calcination) or of a reducing agent (reduction) result is all the time a key issue within the preparation of a catalyst. In this work, a microwave plasma treatment was chosen as an alternative to typical calcinations, because it is a more energy efficient process. Thus, a Microwave Fluidized Bed Plasma reactor (MFBP) was employed in catalyst synthesis process under different gas compositions, such as argon and argon/oxygen mixtures over -alumina supported silver catalysts, which are generally used for selective reduction of NO x by ethanol. After the first catalytic tests performed in the presence of plasma treated catalyst, it can be concluded that plasma treatment process represents an interesting alternative to conventional calcination during catalyst synthesis, resulting in a more sustainable process, moreover in view of its industrial application. In order to understand the particular effect of plasma treatment, the catalysts submitted to this treatment were carefully characterized by means of thermo gravimetric analysis (TGA), differential thermal analysis (DTA) and UV-VIS-NIR.

2023, Nanotechnology in Construction 3

Alumina nanopowders were prepared by a sol-gel process from the mixture of boehmite gel and carbon black followed by microwave heating (2.45 GHz and 900 W) at different times. The average size of boehmite particles in sol was 25 nm. After heating, the products were characterized by powder x-ray diffraction. The results show that the main phase is γ-Al 2 O 3 at low heating times (4 and 6 min, 610° and 790°C, respectively), while after 8 min heat-treatment (960°C), besides the strong peaks of γ-Al 2 O 3 , the weak peaks of α-Al 2 O 3 were also appeared. α-Al 2 O 3 was the only crystalline phase after 10 min heating (1050°C). Synthesized particles were observed by TEM and the average size of particles was measured to be 35 nm. The surface area of powder heated for 10 min was 51 m 2 /g.

2023, 2008 GSW Proceedings

A method to modify ceramics using a low power microwave plasma torch is described. The size, shape, surface area, and phase of alumina particles were dramatically modified by passage through an atmospheric pressure argon plasma, operated at 1 kW or less power. Specifically, irregularly shaped particles of gamma-alumina with an average diameter of 11 mu m were converted to smaller (ca. 4 mu m) spherical particles primarily consisting of delta-and alpha-(corundum) phases. Also notable was the finding that modifications of the particles, such as changes in surface area, correlate to applied plasma energy. The plasma torch was operated with an argon flow rate of 5 slpm, power of between 400 and 1000 W, and average particle residence time in the plasma of 0.1 s.

2023, Journal of Physics D: Applied Physics

Self-standing graphene sheets were synthesized using microwave plasmas driven by surface waves at 2.45 GHz stimulating frequency and atmospheric pressure. The method is based on injecting ethanol molecules through a microwave argon plasma environment, where decomposition of ethanol molecules takes place. The evolution of the ethanol decomposition was studied in situ by plasma emission spectroscopy. Free gas-phase carbon atoms created in the plasma diffuse into colder zones, both in radial and axial directions, and aggregate into solid carbon nuclei. The main part of the solid carbon is gradually withdrawn from the hot region of the plasma in the outlet plasma stream where nanostructures assemble and grow. Externally forced heating in the assembly zone of the plasma reactor has been applied to engineer the structural qualities of the assembled nanostructures. The synthesized graphene sheets have been analysed by Raman spectroscopy, scanning electron microscopy, high-resolution transmission electron microscopy and x-ray photoelectron spectroscopy. The presence of sp 3 carbons is reduced by increasing the gas temperature in the assembly zone of the plasma reactor. As a general trend, the number of mono-layers decreases when the wall temperature increases from 60 to 100 • C. The synthesized graphene sheets are stable and highly ordered.

2023, physica status solidi c

2023, Plasma and Fusion Research

Structural bifurcation of microwave-sustained jet discharge at atmospheric gas pressure was found to produce a stable helium plasma jet, which may open the possibility of a new type of high-flux test plasma beam for plasmawall interactions in fusion devices. The fundamental discharge properties are presented including hysteresis characteristics, imaging of discharge emissive structure, and stable ignition parameter area.

2023, Journal of Nanoparticle Research

Si and its oxide are nonpoisonous materials, and thus, it can be taken for medical effects. We have developed a method of generation of hydrogen by use of reactions of Si nanopowder with water in the neutral pH region. Si nanopowder is fabricated by the simple bead milling method. Si nanopowder reacts with water to generate hydrogen even in cases where pH is set at the neutral region between 7.0 and 8.6. The hydrogen generation rate strongly depends on pH and in the case of pH 8.0, ∼55 ml/g hydrogen which corresponds to that contained in approximately 3 L saturated hydrogenrich water is generated in 1 h. The reaction rate for hydrogen generation greatly increases with pH, indicating that the reacting species is hydroxide ions. The change of pH after the hydrogen generation reaction is negligibly low compared with that estimated assuming that hydroxide ions are consumed by the reaction. From these results, we conclude the following reaction mechanism: Si nanopowder reacts with hydroxide ions in the rate-determining reaction to form hydrogen molecules, SiO 2 , and electrons in the conduction band. Then, generated electrons are accepted by water molecules, resulting in production of hydrogen molecules and hydroxide ions. The hydrogen generation rate strongly depends on the crystallite size of Si nanopowder, but not on the size of aggregates of Si nanopowder. The present study shows a possibility to use Si nanopowder for hydrogen generation in the body in order to eliminate hydroxyl radicals which cause various diseases. Keywords Hydrogen-rich water. SiO 2. Hydroxide ion. Hydroxyl radical. Medical applications

2023

In view of the need to find alternative sources to produce energy that could be considered to be profitable and that do not emit polluting gases, this study presents a procedure to obtain hydrogen. For this purpose, alcohols (methanol and ethanol) have been introduced into an argon surface wave sustained discharge (SWD) at atmospheric pressure. In this way, particles within the plasma, break the bonds of the alcoholic molecules, liberating the hydrogen contained in them. The SWDs have some characteristics that offer many advantages for this purpose; the microwave energy is coupled to the discharge using an excitation device placed outside the plasma tube, and in this way long plasma columns are obtained. In addition, very low microwave power is required for SWD generation, obtaining values of the electron density and temperature similar to those provided by other types of discharges.

2023, Journal of Chemical Technology & Biotechnology

Microwave plasma (MWP) technology is currently being used in application fields such as semiconductor and material processing, diamond film deposition and waste remediation. Specific advantages of the technology include the enablement of a high energy density source and a highly reactive medium, the operational flexibility, the fast response time to inlet variations and the low maintenance costs. These aspects make MWP a promising alternative technology to conventional thermal chemical reactors provided that certain technical and operational challenges related to scalability are overcome. Herein, an overview of state-ofthe-art applications of MWP in chemical processing is presented (e.g. stripping of photo resist, UV-disinfection, waste gas treatment, plasma reforming, methane coupling to olefins, coal/biomass/waste pyrolysis/gasification and CO 2 conversion). In addition, two potential approaches to tackle scalability limitations are described, namely the development of a single unit microwave generator with high output power (> 100 kW), and the coupling of multiple microwave generators with a single reactor chamber. Finally, the fundamental and engineering challenges to enable profitable implementation of the MWP technology at large scale are discussed.

2023, Journal of Crystal Growth

In order to elucidate the stability of a silicon oxide layer on ZnO, the dynamic behavior of SiO-and SiO 2-layer-coated ZnO ultrafine particle surfaces were directly observed by heating in a transmission electron microscope up to 700 C. In the case of SiO-coated ZnO ultrafine particles, ZnO nanocrystallites with the size of 2 nm grew in the SiO layer at 500 C. In the case of SiO 2-coated ZnO ultrafine particles, b-cristobalite with the size of 10 nm order was grown at 600 C. Zn 2 SiO 4 particles were grown by coalescence between b-cristobalite and ZnO at 700 C. By comparing the SiO and SiO 2 layers on ZnO ultrafine particles, it was found that the behaviors of the two silicon oxide layers are clearly different.

2023, Chemical Engineering Science

In this contribution the identification of new reaction conditions for the production of nearly monodisperse silicon nanoparticles via the pyrolysis of monosilane in a hot wall reactor is considered. For this purpose a full finite volume model has been combined with a state-of-the-art trust-region optimisation algorithm for process control. Verified against experimental data, specific process conditions are determined accomplishing a versatile range of prescribed product properties. The main achievement of the optimisation is the possibility to control the different mechanisms in the particle formation process by mainly adjusting the temperature profile. Due to a successful separation of the nucleation and growth process, significantly narrower particle size distributions are obtained. Moreover, the presented optimisation framework establishes rate constants based on measured data.

2023, Progress in Energy and Combustion Science

As the world races toward its urban future, the quantity of wastes, one of the vital by-products of an enhancement in the standards of living, is exponentially rising. The treatment of wastes employing plasma is an upcoming area of research and is globally used for the simultaneous processing of diverse wastes coupled with the recovery of energy and materials. Groundbreaking and cost-effective thermal plasma technologies with high efficiencies are a prerequisite for the growth of this technology. This paper delivers an evaluation of the fundamentals such as the generation and characteristics of the thermal plasma along with the various types of wastes treatable by thermal plasma and the related issues. Furthermore, the authors discuss different types of advanced technologies as well as the material and energy recovery techniques and their present status worldwide, at lab-scale and industrial scale. The application of different thermal plasma technologies is discussed as a means to promote this technology into alternative applications, which require higher flexibility and greater efficiency. Mathematical modeling studies are also assessed with an objective to derive ideal conditions and permissible limits for the reactors and to test a variety of waste materials. A strategy to improve the feasibility and sustainability of waste utilization is via technological advancement and the minimization of environmental effects and process economics. This paper sheds light on diverse areas of waste utilization via thermal plasma as a potentially sustainable and environmentally friendly technology.

2023, Surface and Coatings Technology

2023, Applied Surface Science

2023

A short review of recent work on the development of a transferred arc reactor concept applied to the vapour phase synthesis of nanoparticles is presented. Examples are given of experimental and modelling work carried out on the... more

2023, physica status solidi (a)

Silicon nanopowder that can be applied as a selective emitter in solar cells was prepared from the decomposition of silane (SiH 4) gas by a radio-frequency (RF) thermal plasma. The RF thermal plasma offers a high-temperature and contamination-free environment to produce pure silicon material from SiH 4. A steep temperature gradient in the thermal plasma enables the rapid quenching of decomposed material to synthesize nanosized particles. In this experiment, the input power of RF thermal plasma was controlled from 8 to 12 kW. The raw material of SiH 4 gas was injected into an argon thermal plasma plume with argon carrier gas. Argon was also used as quenching gas to suppress the growth of silicon nanoparticles. In addition to the input power, the flow rates of carrier and quenching gases were employed as operating variables. The flow rates of carrier and quenching gases were controlled from 15 to 45 L min À1 and from 50 to 250 L min À1 , respectively. Polycrystalline spherical silicon nanoparticles that were less than 100 nm in diameter were observed by transmission electron microscopy, Brunauer-Emmett-Teller (BET) surface area measurement, X-ray diffractometry, and Raman spectrometry. Among the operating variables, the flow rate of carrier gas showed the most significant effect on the size of the nanopowder. The smallest mean particle size of 36 nm was obtained from the highest carrier gas flow rate of 45 L min À1 , because the growth of nanopowder was limited by the enhanced axial velocity and quenching rate of in-flight silicon nanopowder.

2023, Surface and Coatings Technology