Capacitively Coupled Radio Frequency Plasma Research Articles

Initiation mechanism of arcing generated in RF capacitively coupled plasma

In our previous study, we established an arcing generation and measurement system and we observed prior light emission before arcing current development. However, we briefly analyzed those light emissions with strong assumptions without detailed experiment evaluations and thus, the investigation of the formation mechanism in the initiation phase with detailed experiment evaluations has yet to be conducted. In this work, we investigated the initiation mechanism of arcing generated on an arcing inducing probe (AIP) in a radio frequency capacitively coupled plasma (CCP) environment. Here, the AIP is an aluminum rod covered by anodized film and its tip edge is partially stripped to localize arcing on this edge. We measured emission light, voltage, and current waveforms induced by arcing. The spatiotemporal image of the emission light revealed that the tip glow is the brightest intensity and has longest lifetime during arcing, meaning that it is the primary process in whole arcing process. The current waveform induced by arcing corresponds to the time evolution of the tip glow and estimations revealed that the electron emission is the predominant component of the current formation. Furthermore, snapshot images with AIPs having enlarged stripping area exhibited that arcing occurs at the boundary between the alnuminum and anodized film (dielectric), where charging of ions from the CCP on the film surface can induce high-electric field. In addition, we found that the energy relaxation length of emitted electrons for collisions with Ar atoms, which are the background gas, is much larger than the tip glow diameter, meaning that the electon-Ar collision cannot maintain tip glow. This result supports additional source of atoms to sustain the tip glow such as the surface evaporation from arcing spot, of which evidence was speculated our previous study. We estimated minimum aluminum vapor density and surface temperature, which is sufficiently high enough to induce surface vaporization. Combining those experiment results and estimations, that are electron emission, high surface temperature, and surface evaporation, we can speculate that the initiation mechanism of arcing near dielectric surface in radio-frequency CCP environment is the thermionic emission and surface evaporation from arcing spot.

The electrical asymmetry effect in electronegative CF4 capacitive RF plasmas operated in the striation mode

The Electrical Asymmetry Effect (EAE) provides control of the mean ion energy at the electrodes of multi-frequency capacitively coupled radio frequency plasmas (CCP) by tuning the DC self-bias via adjusting the relative phase(s) between the consecutive driving harmonics. Depending on the electron power absorption mode, this phase control affects the ion flux in different ways. While it provides separate control of the mean ion energy and flux in the α-mode, limitations were found in the γ- and Drift-Ambipolar modes. In this work, based on experiments as well as kinetic simulations, the EAE is investigated in the striation-mode, which is present in electronegative CCPs driven by low frequencies. The discharge is operated in CF4 and is driven by two consecutive harmonics (4/8 MHz). The simulation results are validated against measurements of the DC self-bias and the spatio-temporally resolved dynamics of energetic electrons. To include heavy particle induced secondary electron emission realistically, a new computationally assisted diagnostic is developed to determine the corresponding secondary electron emission coefficient from a comparison of the DC self-bias obtained experimentally and from the simulations. Based on the validated simulation results, the EAE is found to provide separate control of the mean ion energy and flux in the striation mode, while the axial charged particle density profiles and the number of striations change as a function of the relative phase. This is understood based on an analysis of the ionization dynamics.

Roll-to-Roll Deposition of Thin Graphitic Films and Dependence on Discharge Modes in Radio Frequency Capacitively Coupled Plasma

We report the deposition of nanocrystalline graph- itic films on Cu foil in a roll-to-roll (R2R) plasma-enhanced chemical vapor deposition (PECVD) system. The influence of discharge modes on the graphitic film synthesis is studied in radio frequency (RF) capacitively coupled Ar/H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> /CH <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> plasma. First, electrical and spectroscopic characterizations supported with modeling are carried out to study the properties of hybrid and gamma modes in Ar plasma at an excitation frequency of 80 kHz. A hybrid mode, which exhibits both alpha and gamma characteristics, exists at 950 Pa for Ar plasma at powers up to 1100 W. However, Ar plasma transitions at 1380 Pa from hybrid to gamma mode when the power is greater than 750 W. Second, the quality of the nanocrystalline graphitic films, which is assessed with Raman spectroscopy, is correlated with the characteristics of hybrid and gamma modes in Ar/H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> /CH <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> plasma. The hybrid mode in Ar/H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> /CH <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> plasma has relatively less ion bombardment. However, the gamma mode in Ar/H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> /CH <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> plasma provides abundant intermediate carbon species and heats the Cu substrate directly to around 1193 K. Hence, thin films of nanocrystalline graphite with different qualities can be produced at a web feed rate of 30 mm/min without supplemental heating by adjusting the discharge modes.

Protein ion yield enhancement in matrix-assisted laser desorption/ionization mass spectrometry after sample and matrix low-pressure glow discharge plasma irradiation.

Plasma-assisted ionization is widely used in mass spectrometry; in this study, a low-pressure glow discharge is introduced as a new method to improve the detection of large proteins, and bovine serum albumin (BSA) is used as a protein model. The treatment of analyte, matrix, and the matrix/analyte mixture is evaluated under optimal conditions. Low-pressure radio-frequency capacitively coupled plasma (RF-CCP) treatment is utilized in the sample preparation step of matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) to enhance the protein MALDI ion signal. Plasma treatment can be an effective tool for enhancing the non-covalent binding of the analyte with the matrix, incorporation of the analyte into the matrix, production of matrix/analyte crystals, and analyte protonation through plasma activation, resulting in an improved MALDI ion signal. Fourier-transform infrared (FTIR) spectroscopy allows us to distinguish between the functional groups of plasma-treated and control samples. In addition, optical emission spectroscopy (OES) determines the plasma species, and zeta potential analysis characterizes the potential difference between plasma-treated and control samples before MALDI-TOF MS analysis. Plasma-treated BSA can provide a five-times enhancement of ion intensity. The combination of the plasma-treated analyte with the plasma-treated matrix leads to an increase in the ion intensity by a factor of 14. Low-pressure glow discharge plasma treatment greatly enhances MALDI ion signals, with a noticeable increase in incorporation, co-crystallization, protonation, and the concentration of the sample functional groups.

N2–H2 capacitively coupled radio-frequency discharges at low pressure. Part I. Experimental results: effect of the H2 amount on electrons, positive ions and ammonia formation

The mixing of N2 with H2 leads to very different plasmas from pure N2 and H2 plasma discharges. Numerous issues are therefore raised involving the processes leading to ammonia (NH3) formation. The aim of this work is to better characterize capacitively-coupled radiofrequency plasma discharges in N2 with few percents of H2 (up to 5%), at low pressure (0.3–1 mbar) and low coupled power (3–13 W). Both experimental measurements and numerical simulations are performed. For clarity, we separated the results in two complementary parts. The actual one (first part), presents the details on the experimental measurements, while the second focuses on the simulation, a hybrid model combining a 2D fluid module and a 0D kinetic module. Electron density is measured by a resonant cavity method. It varies from 0.4 to 5 × 109 cm−3, corresponding to ionization degrees from 2 × 10−8 to 4 × 10−7. Ammonia density is quantified by combining IR absorption and mass spectrometry. It increases linearly with the amount of H2 (up to 3 × 1013 cm−3 at 5% H2). On the contrary, it is constant with pressure, which suggests the dominance of surface processes on the formation of ammonia. Positive ions are measured by mass spectrometry. Nitrogen-bearing ions are hydrogenated by the injection of H2, N2H+ being the major ion as soon as the amount of H2 is >1%. The increase of pressure leads to an increase of secondary ions formed by ion/radical–neutral collisions (ex: N2H+, NH4+, H3+), while an increase of the coupled power favours ions formed by direct ionization (ex: N2+, NH3+, H2+).

Generation of carbon nanowhiskers, nanotips, and nanodots by controlling plasma environment: Ion energy and radical effects

Carbon nanotips and nanowhiskers were produced through etching of an amorphous carbon layer (ACL) by controlling the plasma environment. Discharge types and different gases induced significant changes in the carbon nanostructure owing to the independent or combined effect of ions and radicals. The carbon nanowhiskers were obtained by both ion bombardment and oxygen radicals in a radiofrequency (RF) capacitively coupled plasma (CCP) under the O2 gas environment. In contrast, RF CCP in an Ar gas environment or inductively coupled plasma (ICP) in an O2 gas environment formed carbon nanotips or nanodots, respectively, through the rearrangement of carbon atoms due to ion bombardment or chemical etching by radicals. The carbon nanowhiskers and nanotips were vertically grown in these plasma conditions due to the effect of an electric field, and its effect on the vertical growth was confirmed when using ICPs with RF bias where the electric field of the plasma sheath is controlled. Raman spectroscopy and high-resolution transmission electron microscopy measurements indicate that the crystalline area in carbon nanostructures increased during the rearrangement of the ACL induced by ion bombardment and radical reaction.

Plasma cleaning of steam ingressed ITER first mirrors

Abstract In ITER, the first mirrors (FMs) are vulnerable to an in-vessel coolant leak which could severely diminish their optical properties. To understand the scope of this potential impact, several FM samples were exposed to a steam and humidity test simulating the event in ITER. Both rhodium and molybdenum mirrors, observed a loss in specular reflectivity as a result (the loss being greater for the Mo mirror). Their surfaces were tarnished with the development a thin Rh oxide and a thick Mo oxide (120–170 nm). This study focusses on capacitively coupled radio frequency (CCRF) plasma cleaning of steam ingressed (SI) FM samples and follow their optical recovery. Plasma cleaning experiments were performed with 13.56 MHz CCRF plasma using argon and/or hydrogen as process gas (with 230 eV ion energy). Initial and final reflectivity measurements, chemical surface analysis using in vaccuo X-ray photoelectron spectroscopy, scanning electron microscopy, focused ion beam and roughness measurements, were carried out for each sample to evaluate the cleaning efficiency. Using the plasma cleaning technique, it was possible to remove the SI induced contamination from the mirror surfaces and recover their optical properties to the pristine levels. Several ‘voids/inclusions’ were seen to arise along the grain boundaries as a result of the SI procedure. The concentration of these ‘voids/inclusions’ was observed to increase till a certain point followed by a decrease with increasing cleaning time.

Effect of frequency on the uniformity of symmetrical RF CCP discharges

A 2D Cartesian electrostatic particle-in-cell/Monte Carlo collision (PIC/MCC) model presented previously (Liu et al 2018 Plasma Sources Sci. Technol. 27 025006) is used to investigate the effect of the driving frequency (over the range of 15–45 MHz) on the plasma uniformity in radio frequency (RF) capacitively coupled plasma (CCP) discharges in a geometrically symmetric reactor with a dielectric side wall in argon gas. The reactor size (12 cm electrode length, 2.5 cm gap) and driving frequency are sufficiently small that electromagnetic effects can be ignored. Previously, we showed (Liu et al 2018 Plasma Sources Sci. Technol. 27 025006) that for 15 MHz excitation, Ohmic heating of electrons by the electric field perpendicular to the electrodes is enhanced in a region in front of the dielectric side wall, leading to a maximum in electron density there. In this work we show that increasing the excitation frequency (at constant applied voltage amplitude) not only increases the overall electron heating and density but also causes a stronger, narrower peak in electron heating closer to the dielectric wall, improving the plasma uniformity along the electrodes. This heating peak comes both from enhanced perpendicular electron heating and from the appearance at high frequency of significant parallel heating. The latter is caused by the presence of a significant parallel-direction RF oscillating electric field in the corners. Whereas at the reactor center the sheaths oscillate perpendicularly to the electrodes, near the dielectric edge they move in and out of the corners and must be treated in two dimensions.

Tunable wettability and pH‐responsiveness of plasma copolymers of acrylic acid and octafluorocyclobutane

Novel and intelligent plasma copolymers based on hydrophilic/hydrophobic monomers with tunable wettability and pH‐responsiveness are demonstrated. A series of plasma copolymer coatings with various carboxylic acid and fluorocarbon group ratio are prepared on the low‐density polyethylene (LDPE) surfaces via capacitively coupled radio frequency plasma (CCP). The static water contact angles (SWCA) of C4F8‐co‐AA plasma polymer coatings on nanotextured LDPE surfaces tuned from 163 to 4°. These C4F8‐co‐AA plasma polymer coatings showed different pH‐responsiveness by the combined effect of the carboxylic acid to fluorocarbon group ratios and surface nanotexture. The increase of carboxylic acid groups of C4F8‐co‐AA plasma polymers shifted the reversibly switchable wettability of pH‐responsiveness towards low SWCA range. The magnifying effect of surface nanotexture on pH‐responsiveness was also observed.

Experimental Observation and Computational Analysis of Striations in Electronegative Capacitively Coupled Radio-Frequency Plasmas.

Self-organized spatial structures in the light emission from the ion-ion capacitive rf plasma of a strongly electronegative gas (CF_{4}) are observed experimentally for the first time. Their formation is analyzed and understood based on particle-based kinetic simulations. These "striations" are found to be generated by the resonance between the driving radio frequency and the eigenfrequency of the ion-ion plasma (derived from an analytical model) that establishes a modulation of the electric field, the ion densities, as well as the energy gain and loss processes of electrons in the plasma. The growth of the instability is followed by the numerical simulations.

A computationally assisted spectroscopic technique to measure secondary electron emission coefficients in radio frequency plasmas

A computationally assisted spectroscopic technique to measure secondary electron emission coefficients (γ-CAST) in capacitively-coupled radio-frequency plasmas is proposed. This non-intrusive, sensitive diagnostic is based on a combination of phase resolved optical emission spectroscopy and particle-based kinetic simulations. In such plasmas (under most conditions in electropositive gases) the spatio-temporally resolved electron-impact excitation/ionization rate features two distinct maxima adjacent to each electrode at different times within each RF period. While one maximum is the consequence of the energy gain of electrons due to sheath expansion, the second maximum is produced by secondary electrons accelerated towards the plasma bulk by the sheath electric field at the time of maximum voltage drop across the adjacent sheath. Due to these different excitation/ionization mechanisms, the ratio of the intensities of these maxima is very sensitive to the secondary electron emission coefficient γ. This sensitvity, in turn, allows γ to be determined by comparing experimental excitation profiles and simulation data obtained with various γ-coefficients. The diagnostic, tested here in a geometrically symmetric argon discharge, yields an effective secondary electron emission coefficient of for stainless steel electrodes.

Studies on the effect of finite geometrical asymmetry in dual capacitively coupled radio frequency plasma

In recent years, dual capacitively coupled radio frequency (CCRF) glow discharge plasma has been widely studied in the laboratory because of its simpler design and high efficiency for different material processing applications such as thin-film deposition, plasma etching, sputtering of insulating materials etc. The main objective of studies on dual frequency CCRF plasma has been the independent control of ion energy and ion flux using an electrical asymmetry effect (EAE). Most studies have been reported in electrode configurations that are either geometrically symmetric (both electrodes are equal) or completely asymmetric (one electrode is infinitely bigger than the other). However, it seems that most of the laboratory CCRF plasmas have finite electrode geometry. In addition, plasma series resonance (PSR) and electron bounce resonance (EBR) heating also come into play as a result of geometrical asymmetry as well as EAE. In this study, a dual frequency CCRF plasma has been studied in which the dual frequency CCRF has been coupled to the lumped circuit model of the plasma and the time-independent fluid model of the plasma sheath, in order to study the effect of finite geometrical asymmetry on the generation of dc-self bias and plasma heating. The dc self-bias is found to strongly depend on the ratio of the area between the electrodes. The dc self-bias is found to depend on the phase angle between the two applied voltage waveforms. The EAE and geometrical asymmetry are found to work differently in controlling the dc self-bias. It can be concluded that the phase angle between the two voltage waveforms in dual CCRF plasmas has an important role in determining the dc self-bias and may be used for controlling the plasma properties in the dual frequency CCRF plasma.

Electron heating via self-excited plasma series resonance in geometrically symmetric multi-frequency capacitive plasmas

The self-excitation of plasma series resonance (PSR) oscillations plays an important role in the electron heating dynamics in capacitively coupled radio-frequency (CCRF) plasmas. In a combined approach of PIC/MCC simulations and a theoretical model based on an equivalent circuit, we investigate the self-excitation of PSR oscillations and their effect on the electron heating in geometrically symmetric CCRF plasmas driven by multiple consecutive harmonics. The discharge symmetry is controlled via the electrical asymmetry effect (EAE), i.e. by varying the total number of harmonics and tuning the phase shifts between them. It is demonstrated that PSR oscillations will be self-excited under both symmetric and asymmetric conditions, if (i) the charge–voltage relation of the plasma sheaths deviates from a simple quadratic behavior and (ii) the inductance of the plasma bulk exhibits a temporal modulation. These two effects have been neglected up to now, but we show that they must be included in the model in order to properly describe the nonlinear series resonance circuit and reproduce the self-excitation of PSR oscillations, which are observed in the electron current density resulting from simulations of geometrically symmetric CCRF plasmas. Furthermore, the effect of PSR self-excitation on the discharge current and the plasma properties, such as the potential profile, is illustrated by applying Fourier analysis. High-frequency oscillations in the entire spectrum between the applied frequencies and the local electron plasma frequency are observed. As a consequence, the electron heating is strongly enhanced by the presence of PSR oscillations. A complex electron heating dynamics is found during the expansion phase of the sheath, which is fully collapsed, when the PSR is initially self-excited. The nonlinear electron resonance heating (NERH) associated with the PSR oscillations causes a spatial asymmetry in the electron heating. By discussing the resulting ionization profile in the nonlocal regime of low-pressure CCRF plasmas, we examine why the ion flux at both electrodes remains approximately constant, independently of the phase shifts.

Strong ionization asymmetry in a geometrically symmetric radio frequency capacitively coupled plasma induced by sawtooth voltage waveforms.

The ionization dynamics in geometrically symmetric parallel plate capacitively coupled plasmas driven by radio frequency tailored voltage waveforms is investigated using phase resolved optical emission spectroscopy (PROES) and particle-in-cell (PIC) simulations. Temporally asymmetric waveforms induce spatial asymmetries and offer control of the spatiotemporal dynamics of electron heating and associated ionization structures. Sawtooth waveforms with different rise and fall rates are employed using truncated Fourier series approximations of an ideal sawtooth. Experimental PROES results obtained in argon plasmas are compared with PIC simulations, showing excellent agreement. With waveforms comprising a fast voltage drop followed by a slower rise, the faster sheath expansion in front of the powered electrode causes strongly enhanced ionization in this region. The complementary waveform causes an analogous effect in front of the grounded electrode.

Influences of electrode configurations in dual capacitively coupled radio frequency glow discharge plasma

Capacitively coupled radio frequency (CCRF) glow discharge plasma is widely studied in the laboratory because of its simpler design and high efficiency for different material processing applications such as thin-film deposition, plasma etching, sputtering of insulating materials etc. A negative dc potential develops between the bulk plasma and the powered electrodes, which is termed as ‘self-bias’ in RF plasma. This self-bias is generated as a consequences of the geometrical asymmetry of the electrodes, which can be achieved by appropriately design the area of the powered and the grounded electrodes. However, independent control of the dc self-bias in single frequency CCRF plasma is not possible, since the changing in any operating parameters including geometrical asymmetry will also change the plasma parameters. A study on the dual frequency CCRF plasma could be useful in understanding the separate control of the dc self-bias and plasma density, which respectively determine the ion energy and ion flux. In this work, a dual frequency CCRF plasma have been studied on the basis on nonlinear global model to understand the influences of electrode sizes and proper optimization of the CCRF plasma for specific applications.

Nanotexturing and Wettability Ageing of Polypropylene Surfaces Modified by Oxygen Capacitively Coupled Radio Frequency Plasma

Polypropylene (PP) was treated by an oxygen capacitively coupled radio frequency plasma (CCP) under a radio frequency (RF) power of 200 W for exposure time of 1, 5, and 10 min. The ageing process of the plasma-treated PP was studied at an ageing temperature of 90 °C during an ageing time up to 25 h. The formation of the nanotextures with different geometry and aspect ratio and the grafting of large number of oxygen-containing groups were achieved on as-treated PP surfaces under the oxygen CCP treatment for the increased exposure time. The hydrophilicity on the as-treated PP surfaces with the stable nanotextures was rapidly depressed during the ageing process at 90 °C due to the restructuring of chemical composition. The surface restructuring rate was dependent on the aspect ratio and the oxygen-containing groups on the nanotextured PP with increasing exposure time. The hydrophobic over-recovery to high hydrophobicity and superhydrophobicity were observed on the post-aged surfaces with the stable nanofibrils from as-treated hydrophilic surfaces. The superhydrophobicity with the low water adhesion was achieved on the post-aged surfaces preserving the nanofibrils with high aspect ratio and large distance due to the decrease of the oxygen-containing groups after the surface restructuring.

Influence of finite geometrical asymmetry of the electrodes in capacitively coupled radio frequency plasma

Capacitively coupled radio frequency (CCRF) plasmas are widely studied in last decades due to the versatile applicability of energetic ions, chemically active species, radicals, and also energetic neutral species in many material processing fields including microelectronics, aerospace, and biology. A dc self-bias is known to generate naturally in geometrically asymmetric CCRF plasma because of the difference in electrode sizes known as geometrical asymmetry of the electrodes in order to compensate electron and ion flux to each electrode within one rf period. The plasma series resonance effect is also come into play due to the geometrical asymmetry and excited several harmonics of the fundamental in low pressure CCRF plasma. In this work, a 13.56 MHz CCRF plasma is studied on the based on the nonlinear global model of asymmetric CCRF discharge to understand the influences of finite geometrical asymmetry of the electrodes in terms of generation of dc self-bias and plasma heating. The nonlinear global model on asymmetric discharge has been modified by considering the sheath at the grounded electrode to taking account the finite geometrical asymmetry of the electrodes. The ion density inside both the sheaths has been taken into account by incorporating the steady-state fluid equations for ions considering that the applied rf frequency is higher than the typical ion plasma frequency. Details results on the influences of geometrical asymmetry on the generation of dc self-bias and plasma heating are discussed.

Investigation of Single and Dual RF Capacitively Coupled Nitrogen Plasma Discharges Using Optical Emission Spectroscopy

High-resolution optical emission spectroscopy and automated Langmuir probe are applied to examine the production of active species in the pure nitrogen plasma excited by single (40.68 MHz) and dual high-frequency (HF) radio frequency (RF) power sources (40.68/2.1 MHz). The emission intensities of the spectral bands correspond to the (0, 2) transition of the second positive system (SPS) of N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> (λ =380.50 nm) and (0, 0) transition of the first negative systems (FNSs) of N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> (λ =391.40 and 427.81 nm have been measured and compared with plasma parameters using the Langmuir probe to investigate the dependence of their radiative states on operating conditions for both single and dual HF RF capacitively coupled plasma (CCP) discharge. It was found that the high power of the low-frequency (LF) source and the gas pressures are the most effective parameters in dual RF CCP discharge system. Thus, both SPS intensity decreases and FNS intensity increases with the increasing LF power at constant pressure. Furthermore, the emission intensity of the first negative band heads increases at least four times in dual RF mode in comparing with the single RF CCP discharge. In contrast, the intensity of the second band heads decreases dramatically to its half values. Likewise, it was found that the transition pressures for the electron heating mode (with increasing the gas pressure) and the transition from α to γ mode (with increasing the RF power) is close to 0.3 torr in single RF mode, but these transitions are about 0.5 torr for dual RF CCP mode.

Observation of transient electric fields in particle-in-cell simulation of capacitively coupled discharges

The analytical prediction of the presence of transient electric field regions between the bulk plasma and sheath edge in radio frequency capacitively coupled plasma (RF-CCP) discharges has been reported by Kaganovich [Phys. Rev. Lett. 89, 265006 (2002)]. In this paper, we have used the semi-infinite particle-in-cell (PIC) simulation technique to verify the theoretical prediction for the existence of transient electric field in the linear regime; it is shown that the PIC simulation results are in good agreement with the results predicted by analytical model in this regime. It is also demonstrated that the linear theory overestimates the transient electric field as one moves from linear to weakly nonlinear regime. The effect of applied RF current density and electron temperature on evolution of transition field and phase mixing regime has been explored.

Adhesion enhancement of polyethylene modified by capacitively coupled radio frequency plasma polymerization of ethanol

The plasma polymerization of ethanol monomer was carried out under the capacitively coupled radio frequency plasma (CCP) of a radio frequency (RF) power of 100W at different power to flow rate (P/F) ratios of 0.7, 1.0 and 2.7W/sccm. The influence of the P/F ratios on deposition rate, chemical composition, surface morphology, and wettability were studied for the plasma polymer films of ethanol monomer on the pristine low density polyethylene (LDPE) surfaces and the surfaces under the oxygen CCP pretreatment of a RF power of 200W for an exposure time of 1 and 5min. The deposition rate of the plasma polymer films gradually increased with the P/F ratios. The retention of the hydroxyl groups decreased and the contents of the ketone, carboxylic acid, ester, ether, and epoxide groups increased in the plasma polymer films with the increased P/F ratios. The conformal deposition of the plasma polymer films to the LDPE surfaces was found on the pristine surfaces with the sub-micrometer asperities and the surfaces under oxygen CCP pretreatment with the nanotextures. The dynamic contact angle of the plasma polymer films increased with the P/F ratios on the LDPE surfaces with the sub-micrometer asperities. The plasma polymer films showed the decrease of the dynamic contact angle with the P/F ratios on the surfaces with the nanonodules and the nanopillar array. The significant improvement of the adhesion was achieved for LDPE samples with the nanonodules and the nanopillar array under the surface modification of the oxygen CCP pretreatment followed by the deposition of the plasma polymer films of ethanol monomer due to the cooperation adhesion mechanisms of the mechanical interlocking and the chemical bonding.