MHz Radio Frequency Plasma Research Articles

Development of RF plasma generator based on Class E Power Amplifier

Abstract The plasma produced at 2 MHz radio frequency has substantial energy release stability and can be used to modify a material’s surface. The objective of this research is to create a plasma generator operating at a radio frequency of 2 MHz and examine how voltage affects the plasma spectrum that is generated. An AD9833 frequency generator, a class E amplifier, and impedance matching are used in the design of a 2 MHz radio frequency plasma generator as power amplifiers to create plasma. Variations in voltage, gas, and gas flow have been used. The input voltage variations used were 10V and 15V from the power supply. Two different media, free air (atmospheric gas) and argon gas flow, are used for plasma generation. In free air, the plasma formed is Nitrogen plasma with a wavelength of 300 to 380 nm. Argon gas flow is given a variation of Argon gas rate of 2 LPM, and 3 LPM. The plasma formed is Argon plasma with a wavelength of 700 to 850 nm.

Comparison of sintering condition and radio frequency plasma discharge on the conversion of coal/biomass fly ash into high-temperature thermal energy storage material

Abstract The management of solid waste has become increasingly challenging with the accelerated growth in residency in Singapore. Alternative utilization, such as high temperature thermal energy storage material, valorizes the waste to the status of a new resource, thereby reducing the need of virgin material and ensuring sustainability. In Singapore, coal is co-fired with biomass and the coal/biomass fly ash is partially reused and the rest is landfilled. This research evaluated two different fabrication routes: conventional sintering and plasma processing. The novelty of this study is that unlike most studies whereby plasma arc is used to melt the ash at high temperature, in this study, a 13.56 MHz radio frequency plasma is used to control discharge parameters through in-situ diagnostics of active species density and temperatures. This allows for high throughput and uniform processing. An optimized plasma process could potentially reduce the total number of processing phases, with a lower energy budget for processing, while increasing the controllability of the processes to achieve the desired material properties. The chemical composition, and the thermal properties such as specific heat capacity, energy density and thermal conductivity of the ceramics made from coal/biomass fly ash were evaluated. Experimental evaluation shows that the radio frequency plasma processed coal/biomass fly ash samples were found to improve the thermal properties of coal/biomass fly ash in general. It is hypothesized that the mechanism of improvement from radio frequency plasma was due to the incorporation of hydrogen into the material and the conversion of mineralogical composition (i.e. quartz) which gave rise to the better performance. In conclusion, this study has shown the potential of using coal/biomass fly ash as thermal energy storage material through innovative process such as radio frequency plasma discharge.

Effects of RF plasma modification on the thermal and mechanical properties of electrospun chitosan/poly(vinyl alcohol) nanofiber mats

On the design and fabrication of biomedical devices, the mechanical integrity and the thermal stability of the materials used are of paramount consideration. In this study, the effects of 13.56 MHz radio frequency plasma modification using argon (Ar) and oxygen (O2) discharges on the morphology, thermal properties, and tensile properties of the nonwoven electrospun chitosan/poly(vinyl alcohol) nanofiber mats were investigated. The scanning electron microscope images showed a significant change in the morphology of the nanofiber mats due to the Ar and O2 plasma treatment. The thermogravimetric-differential thermogravimetry data revealed two major degradation steps for both the pristine samples and the Ar plasma-treated samples due to the molecular backbone degradation and decomposition of polyene and carbonyl residues. However, a third peak was observed for O2 plasma-treated samples which may be due to the oxygen functionalities imparted by the discharge as seen from the Fourier-transform infrared spectroscopy data. Differential scanning calorimetry (DSC) results have shown the glass transition temperature at 65–68 °C and a melting temperature at around 200–220 °C. Also, a decrease in the crystallinity of the plasma-treated samples were noted from the DSC thermograms. A significant (p < 0.05) decrease in the tensile strength, yield strength, Young's modulus, and elongation at break were noted for the plasma-treated samples due to the etching and ablation effects induced by energetic particle interactions. However, the mechanical properties are still comparable with the tensile properties of human tissues such as the skin. These nonwoven mats with tunable properties have potential use in biomedical engineering, particularly as tissue scaffolds, wound dressings, sutures, and antibacterial gauzes.

Effects of discharge-forming gases on the antibacterial sensitivity of plasma-reduced silver impregnated in natural zeolites

The influence of plasma-forming gases such as argon and oxygen in the reduction of silver ions ($${\text {Ag}}^+$$) infused into a natural zeolite framework has been investigated for antibacterial applications. Impregnation by soaking and ion exchange were combined with 13.56 MHz radio-frequency plasma to reduce $${\text {Ag}}^+$$ to their metallic state for a greener and energy-efficient process. The plasma treatment of the silver zeolite (AgZ) composites did not alter the crystalline structure of the zeolite, while successfully reducing $${\text {Ag}}^+$$ to its metallic form as a nanoparticle encapsulated by the zeolite. The antibacterial index of the AgZ composites against Staphylococcus aureus and Escherichia coli confirmed the fervent antibacterial activity of plasma-reduced Ag NP embedded in the zeolite matrix against the two bacterial strains. The highest activity belongs to the samples treated with oxygen plasma. This result is related to increased active area of contact and the incorporation of reactive oxygen species in the zeolite matrix, which contributed to the antibacterial sensitivity of the plasma-treated AgZ.

Properties of spray-deposited liquid-phase exfoliated graphene films

In this study, we demonstrate the feasibility of spray-depositing exfoliated graphene on flexible polyimide (PI) and rigid (soda lime glass) substrates for optoelectronic applications. The water contact angles of the substrates increased by 13% (for PI) and 49% (for glass) when the surfaces are pretreated with hexamethyldisiloxane, which significantly improved the adhesion of the films. Raman spectral analyses confirmed a minimum of 15 and a maximum of 23 layers of exfoliated graphene deposited on the substrates. After deposition, the films were exposed to 13.56 MHz radio-frequency plasma containing an admixture of argon and nitrogen gases. Plasma treatment modified the electrical properties with a response analogous to that of a rectifier. A 39% increase in transmittance in the visible region was also observed especially for glass substrates after plasma treatment without a significant change in film electrical conductivity.

Characterisation of intrinsic silicon oxide absorber layers for use in silicon thin film solar cells

The use of a wide bandgap absorber layer in the top cell of a multi-junction silicon thin film solar cell is necessary to achieve a high-conversion efficiency. A higher bandgap of the absorber results in a higher open-circuit voltage (Voc) of the cell. In this work, intrinsic hydrogenated amorphous silicon oxide (i)a-SiO:H films have been prepared by using 13.56 MHz radio frequency plasma enhanced chemical vapour deposition (RF-PECVD) at a substrate temperature of 195 °C. The carbon dioxide (CO2) to silane (SiH4) ratio rc was varied and the influence of the ratio rc on the optoelectronic film properties was investigated. These thin films have been studied in detail in terms of their dark (σd) and photo (σph) conductivity and photoresponse PR (σph/σd). The defect density Nd and Urbach energy EU were determined by constant photocurrent method (CPM). The optical bandgap Eg,Tauc was derived from Tauc plots. Optical constants were determined by spectroscopic ellipsometry measurements in the range between 300 and 1000 nm. It was found that the increase in the CO2 to SiH4 ratio rc not only leads to a higher optical bandgap, but also higher defect density Nd and Urbach energy EU and on the other hand to a lower photoresponse PR. A suitable photoresponse PR = 8.64 × 105 at a high bandgap of Eg,Tauc = 1.91 eV and a defect density of Nd = 1.7 × 1016 cm−3 was achieved. The refraction index and extinction coefficient were lowered with increasing rc. The analysis of light-induced degradation in the (i)a-SiO:H layers showed a smaller increase of deep defects Nd and a higher increase of the Urbach energy EU in terms of the light soaking time with respect to the (i)a-Si:H reference layer.

Radio Frequency Titanium Plasma Modified Vanadium Oxide for Electrochromic Applications

Titanium tetrachloride plasma were used to enhance the electrochromic properties of vanadium oxide (V2O5) powder. The plasma treatments were performed in a rotating 13.56 MHz radio frequency plasma system with optimized parameters. Titanium tetrachloride plasma treated and untreated V2O5 powders were deposited by pyrolysis spraying methods on to indium tin oxide conductive electrodes and the electrochromic properties were investigated. The film characterizations were carried out by using cyclic voltammetry, optic spectroscopy, scanning electron microscope and energy dispersive X-ray spectrometer. The properties of electrochromic devices were investigated with optic transmission changes in visible spectral range.

Surface modification by nitrogen plasma immersion ion implantation into new steel 460Li–21Cr in a capacitively coupled radio frequency discharge

Abstract A novel steel 460Li–21Cr belonging to a new generation of superferritic grade steel has been implanted with nitrogen in a low power 13.56 MHz radio frequency plasma by the plasma immersion ion implantation (PIII) technique in order to study its physical and chemical properties under different experimental conditions. We observed improved hardness and wear behavior of 460Li–21Cr steel with a layer thickness between 1.5 and 4.0 μm after 60 min implantation in the temperature range from 350 to 550 °C. The modified surface layer containing nitrogen does not show CrN in X-ray diffraction (XRD). Compared to untreated substrates, the hardness can be increased by a factor of 4, depending on the experimental conditions, and the wear behavior was also improved by two orders of magnitude. The results are very similar to those for austenitic stainless steel with a similar pronounced increase in wear resistance and plateau-like nitrogen depth profiles.

Hydrogen production by radio frequency plasma stimulation in methane hydrate at atmospheric pressure

Methane hydrate, formed by injecting methane into 100 g of shaved ice at a pressure of 7 MPa and reactor temperature of 0 °C, was decomposed by applying 27.12 MHz radio frequency plasma in order to produce hydrogen. The process involved the stimulation of plasma in the methane hydrate with a variable input power at atmospheric pressure. It was observed that production of CH4 is optimal at a slow rate of CH4 release from the methane hydrate, as analyzed by in light of the steam methane reforming (SMR) and the methane cracking reaction (MCR) processes in accordance with the content of gas production. In comparison with the steam methane reforming (SMR), it was found that methane-cracking reaction (MCR) was dominant in conversion of CH4 into hydrogen. An H2 content of 55% in gas production was obtained from conversion of 40% of CH4 at an input power of 150 W. The results clearly show that hydrogen can be directly produced from methane hydrate by the in-liquid plasma method.

FTIR Spectroscopy Characterization of Si-C bonding in SiC Thin Film prepared at Room Temperature by Conventional 13.56MHz RF PECVD

SiC thin film has been synthesized by using conventional 13.56MHz radio frequency plasma enhanced chemical vapour deposition (PECVD). The mixture of silane (SiH4) and methane (CH4) were used as precursor gases while hydrogen as carrier gas. The SiH4/CH4 ratio and the substrate temperature have been varied in order to examine the reaction of the active species which can produce the Si-C bonding in the deposited film. FTIR spectroscopy was used to analyse the type of bonding and particularly to confirm the existence of Si-C bonding by comparing the spectrums obtained from deposited thin film samples and standard reference sample of bulk SiC single crystal wafer. The existence of Si-C bonding was confirmed and it was slightly shifted from the bulk SiC wafer at around 722cm-1 and 817cm-1.

Crystallization of ITO and TiO2 by RF plasma treatment

The crystallization of amorphous thin films was achieved with using a novel technology in which 13.56 MHz RF (radio frequency) plasma is applied to the film samples for few minutes without heating. The key parameter of this plasma crystallization process is the plasma gas pressure. The best plasma gas pressure depends on the plasma gas species and applied RF power and is independent to film materials and substrate materials. Easiness of plasma crystallization of ITO (Indium Tin Oxide) and TiO2 films was found to depend on the film preparation conditions and to correlate with Hall mobility. The experimental results suggest that the excitation process in crystallization on plasma treatment should be different from that on heat treatment.

Fabrication of high open‐circuit voltage a‐Si1–xOx:H solar cells by using p‐a‐Si1–xOx:H as window layer

AbstractWe have deposited p‐type hydrogenated amorphous silicon oxide (p‐a‐Si1‐xOx:H) by 13.56 MHz radio frequency plasma enhanced chemical vapor deposition (RF‐PECVD) using a gas mixture of silane (SiH4), hydrogen (H2), carbon dioxide (CO2) and diborane (B2H6). Optical and electrical characterization showed that high quality wide optical band‐gap (Eopt) p‐a‐Si1‐xOx:H films could be achieved by using low doping concentration and high H2 dilution. We also fabricated a‐Si1‐xOx:H single‐junction p‐i‐n solar cells by using p‐a‐Si1‐xOx:H and intrinsic a‐Si1‐xOx:H as window and absorber layer, respectively. These solar cells exhibited open circuit voltages of over 1.05 V and good short‐circuit currents as well as fill factors (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Room-temperature crystallization of amorphous films by RF plasma treatment

The crystallization of amorphous thin films was achieved by 13.56 MHz RF (radio frequency) plasma treatment. This crystallization process has a strong advantage that the sample temperature is lower than 120 °C during the plasma treatment even without compulsory cooling and various amorphous films are crystallized after 2 min or so. This treatment works on amorphous films of various materials, independently of the film preparation method and substrate materials. Crystallization has been confirmed on amorphous thin films of sputtered ITO (tin doped indium oxide) deposited on soda-lime glass and PET (polyethylene terephthalate), of sputtered TiO 2 on soda-lime glass, of sol–gel derived TiO 2 on silicon wafer and of sputtered hydrogen-doped silicon on soda-lime glass. The plasma gas pressure was found to be the key parameter in the plasma crystallization process. The appropriate gas pressure depends on the plasma gas species and not on film or substrate materials. A Cu electrode, attached to the backside of the substrate and is electrically floated from the electric ground, was found to enhance the plasma crystallization performance.

Inductive coupled radio frequency plasma bridge neutralizer

A 13.56 MHz radio frequency plasma bridge neutralizer (rf-PBN) for ion thruster applications as well as ion beam surface processing of insulating materials is presented. The energy for the plasma excitation is inductively coupled into the plasma chamber. Because no components are located inside the plasma, the lifetime of the rf-PBN is expected to be very long. A compact tuning system adapts the input power to the plasma impedance. The electron current may be controlled over a wide range by the rf input power. An electron current of up to 1.6 A has been extracted.

The effect of chlorine on dopant activation in hydrogenated amorphous silicon

The dark conductivity of hydrogenated amorphous silicon (a-Si:H) films deposited from dichlorosilane (SiCl2H2) and silane (SiH4), and doped with diborane (B2H6), increases by as much as a factor of 100 over the usual a-Si:H,B films deposited without SiCl2H2. The effect is observed at gas phase concentrations of diborane ranging from 0.006 to 0.5 vol %, and for both direct current (dc) and 13.56 MHz radio frequency plasma depositions, although it is more noticeable for the dc discharge. An increase in dark conductivity is also observed in boron doped hydrogenated amorphous silicon carbon alloys (a-SiC:H) deposited with dichlorosilane, albeit coupled with a change in the Tauc gap. Chlorine reduces the conductivity of undoped and phosphorus doped a-Si:H films. A B–Cl cluster acceptor that is not passivated by H is proposed as a possible mechanism for chlorine enhanced conductivity. This increase in p-layer conductivity translates into an increase of solar cell efficiency, but surprisingly by an increase in photocurrent rather than open circuit voltage.

A 13.56MHz multicusp ion source for gaseous ion-beam production

Abstract A 10 cm×9 cm cylindrical radio-frequency (RF) driven multicusp ion source has been developed for producing high-current ion beams from gases. An inductively coupled 13.56 MHz RF plasma is produced in the presence of 20 rows of Sm–Co 5 magnets which form a longitudinal line-cusp field configuration. The field design was generated using the computer program magnus . By using a 0.35 Tesla magnet, the 100 eV electrons were confined in the source chamber. The RF antenna coil, coated with a thin layer of hard flexible glass to prevent electrical leakage and contamination, has power inlets into the source chamber. A 10:1 turns-ratio matching transformer was used in order to match the 50 Ω output impedance of the RF generator to the impedance of the plasma load. A test run has been performed with 0–500 W of RF power. The source parameters were measured with a Langmuir probe, a mass analyzer and a Faraday cup. For oxygen at 3 mtorr and power set at 500 W, the ion-current density is 36 mA cm −2 , representing an ion density of 1.5×10 11 cm −2 . The value for nitrogen operating at the same pressure is 34 mA cm −2 and, for argon and helium at 10 mtorr source pressure, it is 29 and 27 mA cm −2 , respectively.

Advanced Helium Glow-Discharge Emission Source by Conducting d.c. Self-Bias Current in the 13.56 MHz Radio Frequency Plasma.

Advanced Helium Glow-Discharge Emission Source by Conducting d.c. Self-Bias Current in the 13.56 MHz Radio Frequency Plasma.

Diamond synthesis in capacitively coupled 13.56 MHz radio frequency plasma using parallel plate electrodes with the addition of direct current power

Capacitively coupled radio frequency plasmas offer some advantages over other techniques such as microwave induced plasmas with regard to the large area homogeneous deposition of thin films. Diamond films were synthesized from methane and hydrogen gas mixtures in a capacitively coupled radio frequency plasma using a standard 13.56 MHz source in a popular parallel plate electrode geometry with the addition of dc power. The rf+dc plasma is stable and homogeneous and suitable for prolonged operation. The diamond films deposited by this method were characterized by x-ray diffraction, scanning electron microscopy and Raman spectra measurements. Preliminary experiments with electrodes having a diameter of 60 mm were done to investigate the possibility of scaling up of this technology for large-area diamond deposition.