Low-powered Plasma Research Articles

Conversion of CO2 in a low-powered atmospheric microwave plasma: In-depth study on the trade-off between CO2 conversion and energy efficiency

The influence of microwave input power (P) and gas flow rate (F) was compared by analyzing the change of CO2 conversion and energy efficiency with the specific energy input. It was found that the influence of input power and flow rate on CO2 conversion (P > F) is opposite to that on energy efficiency (P < F). When the input power and flow rate were increased in the same proportion from (60 W, 600 mL/min) to (150 W, 1500 mL/min), CO2 conversion and energy efficiency could be both improved by a factor of 1.43. The emission spectroscopy diagnostic suggested that this improvement could be attributed to more electron-impact vibrational excitation, which was proved by the increase in vibrational temperature and electron density associated with the decrease in electron temperature.

Plasma Spraying of Solution Precursor in Pulsed Mode: In-Flight Phenomena and Coating Deposition

In the field of plasma spray technologies, new processes were developed in order to obtain coatings with nanostructured architectures. Among them, solution precursor plasma spraying is a promising technique. However, to be industrially viable, efforts must be made to understand and control the steps of the process. In alternative to instabilities attenuations, the time-modulation of current–voltage characteristics of a low-powered arc plasma jet was proposed, resulting in time-modulation of plasma properties. This modulation was synchronized with a drop-on-demand printhead for injection to improve the control of plasma/material interaction. An aluminum nitrate ink was formulated to be compatible with a drop-on-demand printhead dispenser. Plasma composition was calculated by the Gibbs free energy minimization method. Moreover, in-flight diagnostics coupled with coating characterization were carried out. Results showed that the controlled injection system leads to the formation of vapors of aluminum oxide that leaded to the deposition of nanostructured cauliflowers-like structures. Amorphous alumina coatings with inclusions of γ-alumina micro-sized particles were obtained and a description of main in-flight mechanisms was proposed.

Long-term stability of superhydrophilic oxygen plasma-modified single-walled carbon nanotube network surfaces and the influence on ammonia gas detection

Single-walled carbon nanotube (SWCNT) networks are subjected to a low-powered oxygen plasma for the surface modification. Changes in the surface chemical composition and the stability of the plasma-treated SWCNT (p-SWCNT) with aging in air for up to five weeks are studied using X-ray photoelectron spectroscopy (XPS) and contact angle analysis. The contact angle decreases from 120° of the untreated hydrophobic SWCNT to 0° for the superhydrophilic p-SWCNT. Similarly, the ratio of oxygen to carbon (O:C) based on the XPS spectra increases from 0.25 to 1.19, indicating an increase in surface energy of the p-SWCNT. The enhanced surface energy is gradually dissipated and the p-SWCNT network loses the superhydrophilic surface property. However, it never revert to the original hydrophobic surface state but to a metastable hydrophilic state. The aging effect on sensitivity of the p-SWCNT network-based ammonia sensor is investigated to show the importance of the aging process for the stabilization of the p-SWCNT. The best sensitivity for monitoring NH3 gas is observed with the as-prepared p-SWCNT, and the sensitivity decreases as similar as the p-SWCNT loses its hydrophilicity with time goes by. After a large performance degradation during the aging time for about two weeks, the response characteristics including sensitivity and response time of the p-SWCNT to ammonia gas are stabilized and eventually saturated.

Low temperature Si-Si, SiO2-SiO2 covalent bonding structures with thin siloxane layer

We present new Si to Si, SiO2 to SiO2 bonding technologies for low temperature applications (&amp;lt;200°C). Direct bonding process between Si (or SiO2) substrates makes high bonding strength without contamination problems. However, high temperature over 1000°C is needed for the reliable Si to Si and SiO2 to SiO2 direct bonding processes. To reduce the bonding temperature, thin siloxane layer and low-powered oxygen plasma treatment was used in this study. We used dimethyl siloxane layer having siloxane chains (-Si-O-)n and methyl ends. Siloxane layer is able to be bonded strongly with Si-based substrates at low temperature (&amp;lt;200°C) when oxygen plasma is treated on it. Polymerized siloxane layer such as PDMS has much higher coefficient of thermal expansion (CTE) of 300ppm/K than Si of 2.6ppm/K. When the bonded structure is cooled or heated, the interfaces is possibly distorted and cracked by the high residual stress between siloxane layer and Si substrate. To solve these problems, we developed new fabrications of reducing the siloxane layer thickness to 3∼4nm, that is the monomer layer levels. Extremely thin thickness of siloxane layer prevented the problems of the CTE differences. The Si to Si bonding structure with siloxane layer showed strong adhesion properties in this study. The bonded body kept reliable bonding force when it was heated to high temperature (∼900°C). The feasible wafer-level bonding process was demonstrated. We investigated the siloxane layer thickness by TEM images. The bonding strength was confirmed by dicing test by 1mm and measured over 20MPa. We also expended this new development to SiO2 to SiO2 bonding structures. Low temperature bonding between non-Si substrates such as GaN was possible with thin siloxane layer when amorphous Si thin film was deposited on these substrates.

Stability of plasma-treated silicone rubber and its influence on the interfacial aspects of blood compatibility

Medical-grade polydimethylsiloxane elastomer was subjected to low-powered plasma treatment in the presence of four different gases: O 2, Ar, N 2 and NH 3. Changes to the surface chemistry immediately after processing and the stability of the treatments following ageing in phosphate buffered saline or air for up to 1 month were investigated using X-ray photoelectron spectroscopy and dynamic contact angle analysis. Changes in surface morphology were assessed using optical microscopy and atomic force microscopy. All treatments resulted in an increase in wettability, attributed to major changes in chemistry combined with modest etching. Furthermore, the primary site of attack of the plasma species appeared to be dependent upon the feed gas implemented. The two main chemical changes observed after ageing were due to reactions with the storage media and relaxation processes resulting in further changes in wettability. The influence of the surface modifications on the blood compatibility of the materials was investigated by assessing contact phase activation using a partial thromboplastin time assay. It was demonstrated that the O 2 and Ar plasma treatments reduced the performance of the silicone but the N 2 and NH 3 treatments had a significantly beneficial effect on the activation of the coagulation cascade.

Surface modification of a segmented polyetherurethane using a low-powered gas plasma and its influence on the activation of the coagulation system

A medical grade segmented polyetherurethane (PEU) was treated with a low-powered gas plasma using O 2, Ar, N 2 and NH 3 as the treatment gases. Changes in the surface functional group chemistry were studied using X-ray photoelectron spectroscopy. The wettability of the surfaces was examined using dynamic contact angle measurements and the surface morphology was evaluated using atomic force microscopy. The influence of the surface modification to the polyurethane on the blood response to the polyetherurethane was investigated by measuring changes in the activation of the contact phase activation of the intrinsic coagulation cascade. The data demonstrate that the plasma treatment process caused surface modifications to the PEU that in all cases increased the polar nature of the surfaces. O 2 and Ar plasmas resulted in the incorporation of oxygen-containing groups that remained present following storage in an aqueous environment. N 2 and NH 3 plasmas resulted in the incorporation of nitrogen-containing groups but these were replaced with oxygen-containing groups following storage in the aqueous environment. In all plasma treatments there was a lowering of contact phase activation compared to the untreated surface, the N 2 and NH 3 treatments dramatically so.

Evactron™ Cleaning of SEM Specimens using an In-Situ RF Plasma on the SEM Chamber

The EVACTRON is a new device (US Patent 6,105,589) designed to remove hydrocarbons from SEM specimens and SEM chambers to prevent contamination artifacts. The device uses a lowpowered RF plasma to make oxygen radicals from air. These radicals oxidize hydrocarbons to make CO, H2O, and CO2 that can be removed by the vacuum pump. The use of air as an oxygen source is convenient to the SEM operator but limits the cleaning effectiveness of the system to easily oxidized carbon species. The system does remove high percentages of the usual contamination problems of vacuum pump oil and skin oil hydrocarbons from surfaces in a relatively short time.The EVACTRON SEM-CLEAN™ system provides a safe method for plasma cleaning inside the SEM. Air as a diluted oxygen gas mixture is chosen as the plasma reactant gas. Air is passed through a low-power RF glow-discharge to create oxygen radicals inside a generator mounted on a specimen chamber port. The generator chamber is subject to the same vacuum as the specimen chamber, and the vacuum pressure and gas flow are controlled by the EVACTRON SEM-CLEAN controller. The radicals are carried out of the plasma into the whole of the specimen chamber by convection. in the chamber they react with all exposed surfaces including the specimen if present. The plasma itself is confined to the generator chamber, which prevents ion and electron bombardment damage to the instrument or specimen.

Experimental study for the optimization of plasma torch operations

In this paper the electric and efficiency attributes of a low-powered dc plasma torch has been investigated. Torch operations require reproducibility, reliability and economicity to be attained. The characterisation allowed to scope operative ranges on the basis of minimum voltage fluctuations and maximum thermal efficiency levels for different gas flow rates, anode dimensions, arc current and two process gases \(\).

Direct determination of cadmium in solids using a capacitively coupled microwave plasma atomic emission spectrometer

A capacitively coupled microwave plasma (CMP) operating at 800 W was examined for the direct determination of cadmium in solids. The laboratory-constructed system contained a tungsten cup electrode capable of holding microsample quantities. A low-powered plasma was used to heat the sample, while at higher powers the plasma was used for sample vaporization and excitation. This plasma enabled thermal vaporization (TV) sample introduction to be accomplished in situ as the plasma formed directly around the sample. Thus, the need for sample preparation, procedural steps and sample transport was eliminated. This technique was capable of the direct determination of trace elements in solid samples in less than 5 min. The effects of experimental parameters such as gas flow rate, atomization power and electrode position were investigated. Detection limits obtained for Cd by TV-CMP-AES were in the picogram range with a relative standard deviation of <20%. The accuracy and precision of the method were also evaluated by measuring Cd in several NIST Standard Reference Materials.

Study of analytical performance of a low-powered microwave plasma torch in atomic emission spectrometry

The analytical performance of a low-powered argon microwave plasma torch (MPT) in atomic emission spectrometry (AES) was evaluated experimentally. The results indicated that low-powered Ar MPT-AES is a promising technique for elemental analysis.

Study of a Low-Powered He Microwave-Induced Plasma for Determination of P, Cl, Br, and I by Atomic Emission Spectrometry

Aqueous sample solutions were nebulized by an ultrasonic nebulizer and the solvent was removed by a desolvation apparatus before introduction of the aerosol into the microwave-induced plasma (MIP). The desolvation system consists of a heating tube and a condenser associated with a concentrated H2SO4 desiccator. The water vapor was removed almost completely with the desolvation system. The detectability of microwave-induced plasma atomic emission spectrometry was therefore improved. The detection limits for P, Cl, Br, and I were 0.0045, 0.12, 0.23. and 0.06 μg/ml, respectively. Based on a study of the emission spectra of P, Cl, Br, and I in the range of 200 to 600 nm in He MIP, the optimum analytical lines for determination of corresponding elements were chosen.

Evaluation of a low-powered argon microwave plasma discharge as an atomizer for the determination of mercury by atomic fluorescence spectrometry

A low-powered argon microwave plasma torch discharge is introduced into atomic fluorescence spectrometry (AFS) for the first time. The configuration and the characteristics of the plasma for AFS are described in this paper. Some factors influencing the determination of mercury, such as the flow rates of the carrier gas and the plasma gas, are discussed in detail. The detection limit for mercury by this method is shown to be 3 ppb and the relative standard deviation for a solution concentration of 1 µg ml–1 is 2.5%(n= 11). The proposed method is relatively free from background interference and gives a large dynamic range.

Evaluation of Line and Continuum Sources for Atomic Fluorescence Spectrometry Using a Low-Powered Argon Microwave-Induced Plasma

An atomic fluorescence spectrometry system employing a low-powered, highly efficient MIP as the atom cell (MIP-AFS) has been developed and is evaluated with the use of direct aqueous nebulization. The MIP-AFS system employs hollow cathode lamp and Xe-arc lamp excitation sources. Detection limits of 14 elements were studied and compared to results for ICP-AFS. Linear working ranges of at least 5 orders of concentration magnitude were found. Interelement effects (i.e., vaporization, ionization, and scatter interferences) were also investigated.

Direct Introduction of Aqueous Samples into a Low-Powered Microwave-Induced Plasma for Atomic Emission Spectrometry

The direct introduction of aqueous samples into a low-power microwave plasma is achieved with the use of a highly efficient TM010 microwave plasma. A toroidal plasma is sustained in the cavity solely by the Ar gas output of the nebulizer. Samples from a concentric glass nebulizer/Scott type spray chamber are fed directly into the cavity with no desolvation apparatus. A toroidal plasma can be sustained from the output of the nebulizer while 1 mL/min water is being aspirated at power levels of 36 W. This plasma is characterized as an atom cell by the study of emission profiles, working curves, and limits of detection. Also, ionization and vaporization interferences that occur with the use of this plasma are discussed.

Application of hydride generation to the determination of trace concentrations of arsenic by inductively-coupled plasma atomic emission spectrometry

A method is described for the determination of traces of arsenic, based on sodium tetrahydroborate reduction of arsenic and introduction of the arsine formed to a relatively low-powered (1.6 kW) inductively-coupled plasma where the arsenic atomic emission is generated, Inter-element interference effects are described; many can be eliminated by addition of potassium iodide to the sample solutions, but the standard additions method is recommended for accurate arsenic determination. Potassium iodide is also used for prereducing arsenic(V) to arsenic(III). The method has a detection limit of 0.1 ng As ml -1 and the linear calibration range spans nearly four orders of magnitude. The proposed method is applied to the determination of ng ml -1 levels of arsenic in waste waters.