Frequency Plasma Research Articles

Plasma etching for carbon materials by inward RF plasma apparatus

ABSTRACT Diamond has high wear resistance and shape stability, and poly-crystalline chemical vapour deposition (CVD) diamond is difficult to mechanically process because of cleavage and wear anisotropy. On the other hand, diamond can be removed under an oxidising atmosphere with O2 as the etching gas by reactive ion etching which is processing using plasma. In this study, the fabrication of an inward radio frequency (RF) plasma apparatus and the possibility of a removal process for carbon materials such as CVD diamond film and graphite plate by using it were investigated. OES, confocal laser scanning microscope and Raman spectroscopy were used for the evaluation of the etching. It was confirmed that the inward RF plasma apparatus fabricated could be applied to plasma etching for carbon materials. In addition, it was suggested that carbon materials were etched as CO with O2 in the atmosphere, and amorphous structures were etched preferentially over crystalline ones.

Eco-friendly approach to improve traits of winter wheat by combining cold plasma treatments and carbonization of subtropical biomass waste

This study aims to improve the quality and quantity of winter wheat by using the potential of combining the use of cold plasma and waste biorefinery products for improving wheat yield. Plasma was applied by a radio frequency (RF) plasma reactor operated with air for 180 s and 50 W. The waste biorefinery products, including pyroligneous acid, biochar, and azolla compost, were used as plant nutrition. The effects of cold plasma treatment and waste biorefinery products were determined by measuring plant photosynthesis, grain yield, and content of chlorophyll, carotenoids, anthocyanin, protein, and starch. The experiment was conducted during the cropping seasons 2016−18 in a randomized complete block design with four replications. The combination of cold plasma and pyroligneous acid increased the grain yield up to 40.0%. The photosynthesis rate was improved up to 39.3%, and total chlorophyll content up to 48.3% in both years. Seed plasma treatment combined with biochar application increased the starch content by 36.8%. Adding azolla compost increased the protein content by 35.4%. Using seed plasma treatment with biochar increased the microbial biomass carbon by 16.0%. The application of plasma and azolla compost increased the microbial biomass nitrogen by 29.0%.

Measurement of the electron energy distribution functions in low density RF plasmas through a tunable external RF filter

Abstract The electron energy distribution function (EEDF) measurement in radio frequency (RF) plasmas is of fundamental interests, especially in low-density RF capacitively coupled plasma. For this purpose, a new external filter with very high impedances is developed. The impedance of the filter at the fundamental and its harmonic frequencies (13.56, 27.12 and 40.68 MHz) through careful circuit design is maximized. Experimental verifications are performed by measuring the EEDFs in RF discharges. The result shows that the RF distortion in the EEDF measurement is significantly reduced by tuning the filter under various discharge conditions in an inductively coupled plasma. Accurate plasma densities can be obtained and the electron heating mode transition is observed through high-quality EEDF measurement in an capacitively coupled plasma, where RF plasma potential fluctuates severely.

Deposition of Very-Low-Hydrogen-Containing Silicon at a Low Temperature Using Very-High-Frequency (162 MHz) SiH4 Plasma.

Low-hydrogen-containing amorphous silicon (a-Si) was deposited at a low temperature of 80 °C using a very high frequency (VHF at 162 MHz) plasma system with multi-split electrodes. Using the 162 MHz VHF plasma system, a high deposition rate of a-Si with a relatively high deposition uniformity of 6.7% could be obtained due to the formation of high-ion-density (>1011 cm−3) plasma with SiH4 and a lack of standing waves by using small multi-split electrodes. The increase in the radio frequency (RF) power decreased the hydrogen content in the deposited silicon film and, at a high RF power of 2000 W, a-Si with a low hydrogen content of 3.78% could be deposited without the need for a dehydrogenation process. The crystallization of the a-Si by ultraviolet (UV) irradiation showed that the a-Si can be crystallized with a crystallinity of 0.8 and a UV energy of 80 J without dehydrogenation. High-resolution transmission electron microscopy showed that the a-Si deposited by the VHF plasma was a very small nanocrystalline-like a-Si and the crystalline size significantly grew with the UV irradiation. We believe that the VHF (162 MHz) multi-split plasma system can be used for a low-cost low-temperature polysilicon (LTPS) process.

Soy Consumption, but Not Dairy Consumption, Is Inversely Associated with Fatty Acid Desaturase Activity in Young Adults.

Past research using hepatic rat microsomes showed that soy protein suppressed delta-6 desaturase activity (D6D) compared to casein (a dairy protein). The effects of soy and dairy on desaturase pathway activity in humans remain poorly investigated. The objective of this analysis was to investigate the association between soy and dairy consumption with plasma fatty acids and estimate the desaturase pathway activity in a multiethnic Canadian population of young adults. We analyzed data from men (n = 319) and women (n = 764) previously collected for the Toronto Nutrigenomics and Health Study. Food frequency questionnaires and plasma fatty acids were assessed. Relationships between soy and dairy beverages and food consumption with estimated desaturase activities were assessed by regression models and by grouping participants according to beverage and food intake data. Weak inverse associations (p ≤ 0.05) were found between soy consumption and the overall desaturation pathway activity, specifically D6D activity. When participants were grouped based on soy and dairy consumption habits, omega-6 LC-PUFAs, as well as various estimates of the desaturase pathway activity, were significantly lower in individuals consuming soy (with or without dairy) compared to individuals consuming only fluid milk and dairy products. In conclusion, soy consumption, not dairy consumption, appears to suppress desaturase pathway activity.

Abstract P061: Dairy Consumption, Dairy Fat Biomarkers And Type 2 Diabetes Risk After Myocardial Infarction

Introduction: Dairy consumption, especially yogurt, and circulating biomarkers of dairy fat (odd chain fatty acids, OCFAs), have been associated with a lower risk of type 2 diabetes (T2D) in population-based studies. Whether these associations are also present in post-myocardial infarction (MI) patients is unknown. Hypothesis: We hypothesized that dairy consumption and circulating OCFAs (pentadecanoic [15:0] plus heptadecanoic acid [17:0]) may be inversely associated with incident T2D after MI. Methods: We included 3347 Dutch post-MI patients from the Alpha Omega Cohort, who were initially free of T2D. At baseline (2002-2006), dairy consumption was estimated with a 203-item food frequency questionnaire and plasma OCFAs were measured in cholesteryl esters using gas chromatography. Incident T2D was ascertained through self-reported physician diagnosis and medication use. Multivariable Cox models were used to obtain hazard ratios (HRs) and 95% confidence intervals (CI) for incident T2D and dairy types and OCFAs (per 1 standard deviation (SD) increment). Results: At baseline, patients were on average 68.9 years old (± 5.5 SD), 80% were men and 87% used statins (2684 and 2908 of 3347 patients respectively). During a median follow-up time of 40 months (10,550 person-years), 181 patients developed T2D. Almost all patients consumed dairy (3300 of 3347), with a median intake of 273 g/d for total dairy. After multivariable adjustment, dairy and its subtypes consumption was not associated with T2D incidence, with HRs ranging from 1.01 to 1.07 per 1-SD increment (all p> 0.05). When analysed in categories (highest vs lowest intake), HRs (95% CI) were 1.05 (0.73-1.52) for milk and 1.08 (0.77-1.51) for yoghurt intake. In line with these findings, no significant association was found for circulating OCFAs 0.97 (0.83-1.12)( Figure 1 ). Conclusion: Dairy consumption, based on self-report and plasma biomarkers, was neutrally associated with T2D incidence in a population of Dutch post-MI patients with a relatively high habitual dairy intake.

Firetube formation through sheath-plasma instability in expanding RF plasma

Formations of complex structures observed during the instability instigated expanding capacitive mode of RF discharge in a linear vacuum vessel, in the absence of an externally applied magnetic field or any other additional constraint applied. Systematic measurements of the plasma parameters, using multiple probe diagnostics, carried out to investigate the parametric dependence of sheath development reveal visible cylindrical tube like multiple double-layer formations around a mesh-type cylindrical plasma source. Such firetube formations provide many interesting and vital information on expanding radio frequency (RF) plasma sheath, charge particle trapping and the associated sheath instability with the RF discharge. The sheath structures, glowing spot formations, space charge formations, complex structure and firetube formations in the expanding plasma are some of the features discussed here in relation to such an expanding RF discharge. Low-frequency sheath instabilities are also observed in connection to the firetube formations using a coaxial mesh-type cylindrical plasma source powered at an operating frequency of 13.56 MHz. The ion acoustic frequency-dominated instability is identified as a sheath-plasma instability associated with the RF plasma.

Study of Si and Ge Atoms Termination Using H-Dilution in SiGe:H Alloys Deposited by Radio Frequency (13.56 MHz) Plasma Discharge at Low Temperature.

In this work, we present the study of the atomic composition in amorphous SiXGeY:HZ films deposited by radio frequency (RF—13.56 MHz) plasma discharge at low deposition temperature. A study and control of Si and Ge atoms termination using H-dilution in SiGe:H alloys deposited by RF plasma discharge was conducted and we made a comparison with low-frequency plasma discharge studies. Solid contents of the main elements and contaminants were determined by SIMS technique. It was found that for low dilution rates from RH = 9 to 30, the germanium content in the solid phase strongly depends on the hydrogen dilution and varies from Y = 0.49 to 0.68. On the other hand, with a higher presence of hydrogen in the mixture, the germanium content does not change and remains close to the value of Y = 0.69. The coefficient of Ge preferential incorporation depended on RH and varied from PGe = 0.8 to 4.3. Also, the termination of Si and Ge atoms with hydrogen was studied using FTIR spectroscopy. Preferential termination of Si atoms was observed in the films deposited with low RH < 20, while preferential termination of Ge atoms was found in the films deposited with high RH > 40. In the range of 20 < RH < 40, hydrogen created chemical bonds with both Si and Ge atoms without preference.

A Multitorch RF Plasma System as a Way to Improve Temperature Uniformity for High-Power Applications

This article presents a new approach and preliminary modeling results of the temperature field nonuniformity reduction by using a multitorch radio frequency (RF) plasma system. This is also a way to achieve technical and economic feasibility for plasma systems with plume power over 200 kW, significantly reducing the development and production cycle. The mixing of plasma jets was numerically simulated by solving a system of equations, describing high-temperature turbulent plasma flows. The data obtained could be used for engineering of high-power plasma systems, including the ones for testing high-temperature thermal protection materials, waste to power, syntheses of new materials, and so on.

4T Analog MOS Control-High Voltage High Frequency (HVHF) Plasma Switching Power Supply for Water Purification in Industrial Applications

High-power plasma power supply is very useful for many industrial and medical applications. Plasma is generated artificially in the laboratory or industry by applying the electric or magnetic field. In this manuscript, we presented the simple 4T analog MOS control high voltage high frequency inverter circuit as a plasma power supply using modulation index technique. The presented plasma power supply operated at 25 kHz frequency and 10 kV peak to peak voltage. It generates a 0 V to 10 kV controllable electric field. The generated electric field is applied and produces plasma, which can be used for many industrial applications. A 10 kV to 5 kW plasma power supply has been practically developed based on the proposed topology and experimentally tested and, additionally, excellent output power conversion efficiency is achieved. From these results, the 4T analog MOS control high voltage high frequency (HVHF) plasma switching power supply is verified.

A ternary–3D analysis of the optical properties of amorphous hydrogenated silicon–rich carbide

Abstract We introduce a novel method for the analysis of the dependence of the optical parameters of Hydrogenated Silicon–rich Carbide (SRC:H) on the alloy composition by using a ternary–3D diagram. The SRC:H samples were fabricated using the very high frequency (VHF) plasma enhanced chemical vapour deposition technique. The composition is given as Si%+C%+H% = 100, with the carbon fraction Cf = C%/(C%+Si%) varying between 0.18 and 0.72. The actual composition was determined by Rutherford Back Scattering analysis. The optical constants are determined by means of Reflectance and Transmittance UV–visible spectroscopy, and are modelled by means of the Jellison–Tauc–Lorentz–with Gaussian Band Tail model. The unique properties of the ternary–3D diagram give unexpected insight on the origin of the dependence of optical properties on composition. It is shown that the wavelength position of the Lorentz oscillator is governed by Cf with virtually no influence of H%. Conversely, the refractive index is strongly affected by H%, besides Cf. We show that using the ternary–3D diagram approach it is possible to separate the contributions of the different components, and derive the analytical dependence between optical parameters and composition. In the second part of the paper such findings are used for a reversed analysis, that is, we employ the obtained analytical formulations in order to retrieve the SRC:H composition within better than ±4% absolute error for all components.

Trinal Nature of the Excitation of Bulk Plasmons by a Fast Charged Particle at Grazing Incidence on the Interface between Vacuum and a Metal with Strong Spatial Dispersion

The excitation and propagation of bulk and surface (surface waves of transition radiation of plasmons at frequencies above the plasma frequency) plasma waves by incident electrons moving both in vacuum toward the surface of a metal and inside the metal whose boundary elastically and spectacularly reflects internal nonequilibrium electrons have been analyzed. In contrast to work [B. N. Libenson, J. Exp. Theor. Phys. 113, 553 (2011)], attention in this work is focused on the influence of surface effects on bulk-plasmon excitation by incident electrons. The probabilities and spectra of single characteristic energy loss of an intermediate- energy electron (50–500 eV) moving at an angle to the surface of the medium in three regions: in vacuum, in the medium, and again in vacuum after the electron leaves the medium are calculated. The kinetic approximation is used for the dielectric function, where the entire range of the plasmon spectrum is taken into account correctly for the problem under consideration. In the indicated energy range of incident electrons, surface effects, on the one hand, significantly reduces the probability of excitation of bulk plasma waves in the medium with strong spatial dispersion, in particular, as compared to the results obtained in [B.N. Libenson, J. Exp. Theor. Phys. 113, 553 (2011)], where surface effects were disregarded and the probability of bulkplasmon excitation by a 200-eV electron incident and emitted perpendicularly to the boundary is about one third of that in the unbounded medium. On the other hand, at grazing incidence from vacuum, the probability of transition radiation of bulk plasmons increases significantly and can lead to a change in the character of the angular dependence of the intensity of bulk plasma energy loss. Thus, the main result of this work is that a decrease in the glancing angle of the fast electron with respect to the vacuum–metal interface is accompanied both by an increase in the contribution from the transition mechanism to the probability of bulk-plasmon excitation in the vacuum region and by a decrease in the contribution from Cherenkov and bremsstrahlung mechanisms of excitation in the medium. The probability of bulk-plasmon excitation in the vacuum region exceeds the probability of excitation at the further motion of the electron in metallic aluminum at angles of incidence larger than 65°, 70°, and 75° at the energies E = 200, 350, and 500 eV, respectively.

Radio frequency magnetron sputter deposited ZnO films doped with Al, Ga and Ti

Zinc oxide (ZnO) is a key material in the field of transparent large-area electronics. Some of the ZnO applications in large-area electronics include sensors, transistors and solar cells. In this work, ZnO films doped with aluminium (Al), gallium (Ga) and titanium (Ti) with different doping concentrations were deposited on glass substrates via the radio frequency (R.F.) plasma magnetron sputtering technique. The correlations of different doping concentration with the structural, optical and electrical properties were investigated by Atomic Force Microscopy, Ultraviolet–Visible Spectrometer and Hall Electronic Transport Measurement System, respectively.

Functionalization of Ti-40Nb implant material with strontium by reactive sputtering

BackgroundSurface functionalization of orthopedic implants with pharmaceutically active agents is a modern approach to enhance osseointegration in systemically altered bone. A local release of strontium, a verified bone building therapeutic agent, at the fracture site would diminish side effects, which could occur otherwise by oral administration. Strontium surface functionalization of specially designed titanium-niobium (Ti-40Nb) implant alloy would provide an advanced implant system that is mechanically adapted to altered bone with the ability to stimulate bone formation.MethodsStrontium-containing coatings were prepared by reactive sputtering of strontium chloride (SrCl2) in a self-constructed capacitively coupled radio frequency (RF) plasma reactor. Film morphology, structure and composition were investigated by scanning electron microscopy (SEM), time of flight secondary ion mass spectrometry (ToF-SIMS) and X-ray photoelectron spectroscopy (XPS). High-resolution transmission electron microscopy (HR-TEM) was used for the investigation of thickness and growth direction of the product layer. TEM lamellae were prepared using the focused ion beam (FIB) technique. Bioactivity of the surface coatings was tested by cultivation of primary human osteoblasts and subsequent analysis of cell morphology, viability, proliferation and differentiation. The results are correlated with the amount of strontium that is released from the coating in biomedical buffer solution, quantified by inductively coupled plasma mass spectrometry (ICP-MS).ResultsDense coatings, consisting of SrOxCly, of more than 100 nm thickness and columnar structure, were prepared. TEM images of cross sections clearly show an incoherent but well-structured interface between coating and substrate without any cracks. Sr2+ is released from the SrOxCly coating into physiological solution as proven by ICP-MS analysis. Cell culture studies showed excellent biocompatibility of the functionalized alloy.ConclusionsTi-40Nb alloy, a potential orthopedic implant material for osteoporosis patients, could be successfully plasma coated with a dense SrOxCly film. The material performed well in in vitro tests. Nevertheless, the Sr2+ release must be optimized in future work to meet the requirements of an effective drug delivery system.

Metamaterials based on wedge-shaped electrodynamic structures

The paper studies a possibility of simulation of artificial composite media with negative values of the real part of the equivalent dielectric (magnetic) permittivity, by the use of segments of hollow composite waveguides with cylindrical guided waves in evanescent mode. Reactive evanescent fields of wedge-shaped waveguide eigenmodes are formed in the evanescent region before the critical section of the waveguide which separates the quasistatic field region from the distributing field of the evanescent waveguide mode. The possibility of simulation is determined by the equivalence of dispersion equation of the eigenmode propagation constant and the dispersion equation for the electric (magnetic) permittivity of plasma-like medium if cut-off frequency and electric (magnetic) plasma frequency of the medium are equal.

Morphological characteristics and optical properties of hydrogenated amorphous silicon thin films

Hydrogenated amorphous silicon (a-Si:H) thin films were prepared by radio frequency (RF) plasma enhanced chemical vapor deposition (RF-PECVD) technique with silane (SiH[Formula: see text] as reactive gas. The influence of process parameters on the morphological characteristics and optical properties of a-Si:H thin films were systematically investigated. When the RF power density was taken as the only variable, it firstly improves the smoothness of the surface with increasing the RF power density below the value of 0.17 W/cm2, and then exhibits an obvious degradation at further power density. The refractive index, extinction coefficient, optical energy gap initially increase and reach a maximum at 0.17 W/cm2, followed by a significant decrease with further RF power density. When the RF power density was taken as the only variable, the surface of a-Si:H thin films become smoother by increasing the reaction pressure in the investigated range (from 50 Pa to 140 Pa), and the refractive index, extinction coefficient, optical energy gap increase with increasing of reaction pressure. The effect of RF power density and the reaction pressure on the morphological characteristics and optical properties of a-Si:H thin films was obtained, contributing to the further studies of the performance and applications of a-Si:H thin films.

Optical Properties of Multilayers TiO2/SnO2:F Thin films

AbstractThin films of TiO2/SnO2:F multilayers were prepared by spray pyrolysis technique on glass substrate. The samples were prepared using titanium (IV) isopropoxide 98%, ammonium fluoride and tin(II) chloride dehydrate extra pure as precursor materials. Thus, a TiO2 thickness dependence optical study of TiO2/SnO2:F/glass system is presented. The optical property was characterized by UV-Visible transmittance spectroscopy. For all the samples, the average transmissions in the visible wavelength region (400-800 nm) were between 69 and 84%. The optical parameters, such as the real part dielectric function ε1 and the imaginary part dielectric function ε2, of TiO2 and SnO2:F in the TiO2/SnO2:F thin films structure, determined by fitting the measured optical transmittance spectra, are presented and analyzed. Among the various classical dispersion relations for the dielectric function, the Drude model combined with the Lorentzian oscillators was used to get a good fit of transmittance in the measured spectral range. Results on related parameters such as high frequency dielectric constant, plasma frequency, film thickness and band gap are presented.

Structural, morphological and optical properties of rf – Sputtered CdS thin films

Cadmium sulfide (CdS) nanocrystalline semiconductor thin films were deposited using the technique of magnetron sputtering in radio – frequency plasma. Structural, morphological and optical characterizations of the prepared CdS thin films were carried out. The films were polycrystalline and well textured, with (002) crystallographic planes oriented parallel to the surface (crystallite sizes were between 30.6nm up to 48.2nm). RMS surface roughness was in the nanometer range and decreases with increasing film thickness. Optical constants (refractive indices and extinction coefficients) as well as film thicknesses (between 56.4nm and 174.6nm) and surface rugosities were computed by spectroscopic ellipsometry. This optical method was combined with optical spectrophotometry (absorption coefficients, optical transmittances, etc.) in UV – VIS – NIR for a better verification of the results. The range for the obtained values of optical band gaps is between 2.3eV and 2.36eV.

Characterization of microcrystalline silicon thin film solar cells prepared by high working pressure plasma-enhanced chemical vapor deposition

Using the high working pressure plasma-enhanced chemical vapor deposition (HWP-PECVD) technique, the hydrogenated microcrystalline silicon (μc-Si:H) films for photovoltaic layers of thin film solar cells was investigated. The $\pmb{\mu \mathrm{c}-\mathrm{Si}:\mathrm{H}}$ films were deposited on surface textured fluorine-doped tin oxide (FTO) glass substrates at 100 Torr in a 100 MHz very high frequency (VHF) plasma of gas mixtures containing He, H2, and SiH4. It was found that an optimum ratio of the H2/SiH4 flowrate existed for growing a homogenous microcrystalline through the whole film without amorphous incubation layer. When an intrinsic $\pmb{\mu \mathrm{c}-\mathrm{Si}:\mathrm{H}}$ thin film was deposited at n-i-p single junction solar cell, the cell performances were dependent on with or without an amorphous incubation layer. With an amorphous incubation layer, the open circuit voltage $(\mathrm{V}_{\mathrm{oc}})$ of cell was 0.8V, which was typical cell property of hydrogenated amorphous silicon (a-Si:H). On the other hand, at the optimum ratio of the H2/SiH4 flow-rate, μc-Si:H single cell responding an infrared light showed the Voc of 0.49 V. Intrinsic hydrogenated microcrystalline silicon (μc-Si:H) thin film, exhibiting the photovoltaic performance (Eff: 7.2%, $\pmb{\mathrm{V}_{\mathrm{oc}}:0.49\mathrm{V}, \mathrm{J}_{\mathrm{sc}}:23\mathrm{mA}/\mathrm{cm}^{2}}$ , FF:64%) was able to be successfully fabricated.

Generation of Uniform Large-Area VHF Plasmas by Launching a Traveling Wave

An innovative technique, i.e., creating a traveling wave by launching two specific standing waves at the same time, is proposed to generate uniform large-area very high frequency (VHF) plasmas. The viability of this approach has been verified by numerical simulation in this study. The electric field distribution for each standing wave is controlled by the phase difference between the corresponding two feeding points (phi) placed on opposite sides of electrode and designated to produce a specific standing wave pattern. The simulated electric filed distributions obtained at various phi are consistent with numerous experimental works. By applying these two standing waves at the same time, a traveling wave can be lanuched as the conditions that these two standing waves must have the same amplitude and be spatially and temporally out of phase by 90 degrees are met.