Low-pressure Argon Plasma Research Articles

Alter the sheet resistance of carbon nanotube-coated cellulose fabric with argon plasma pretreatment

Cellulose fabrics were coated with single-walled carbon nanotubes (SWCNTs) by a dip-drying process. Scanning electron microscopy (SEM) and Raman spectroscopy analyses indicate the attachment of SWCNTs. The sheet resistance of SWCNT-coated fabrics can be altered by modifying the raw cellulose fabrics with low-pressure argon plasma. An initial plasma ablation of up to 3 min results in the decrease of sheet resistance, which can be ascribed to the increase of fibre surface roughness, evidenced by SEM analyses. A further increase in the extent of plasma ablation brings about the increase in sheet resistance, which is associated with the incorporation of oxygen functionalities, supported by the data obtained on colour strength measurements.

Inkjet Printing for Applications in Microfluidic Lab-on-Chip Systems

Inkjet printing is a digital printing technique that is capable of depositing various functional materials onto different substrates in an additive way. In this contribution, applications of inkjet printed structures for smart microfluidic lab-on-chip systems are discussed. Such systems can be used e.g. for different chemical or biochemical analysis tasks and are often fabricated from polymers. Inkjet-printed electrodes and electroactive polymer (EAP) actuators for use in microfluidic lab-on-chip systems are shown. Silver and gold electrodes are presented that are fabricated by printing metal nanoparticle inks onto polymer substrates. After printing the structures are sintered using low-pressure argon plasma sintering, a low-temperature sintering process that is compatible with polymer substrates with a low glass transition temperature TG. The structures consist of several electrodes and contact pads and feature minimum structure sizes of approximately 70 μm. These structures are in principle suitable for requirements in lab-on-chip systems. The use of all inkjet-printed EAP actuators in a polymer-based micropump is discussed. Cantilever-type bending actuators generate deflections of more than 190 μm when a voltage of 600 V is applied. Based on these results, performance characteristics of a micropump with printed actuators are estimated.

Excitation of electrostatic plasma waves using a dielectric covered metallic electrode

Plasma response to high positive and negative voltage pulses is studied using pulsed capacitive excitation in a uniform and unmagnetized plasma. The positive or negative voltage pulse is applied to a metallic electrode, covered by a dielectric (Kapton) film, immersed in a low pressure argon plasma. The pulse magnitude is much greater than the electron temperature (U0 ≫ kTe/e). Experiments are carried out for different plasma parameters, to find how the plasma perturbations propagate for various applied pulse widths in comparison to ion plasma period ( fi-1). Plasma perturbations are studied by varying the thickness of the dielectric. For positive pulse bias, depending on the dielectric thickness, excitation of solitary electron holes, or solitary ion holes are observed. For negative pulse bias, varying the dielectric thicknesses, only ion rarefaction waves are excited.

Development of compact high voltage switched mode power supply for microwave plasma sources supply for low pressure plasma

Although microwave induced plasmas are well known as high efficiency plasma sources, their uses in laboratories are limited since the microwave power systems are complicated and expensive. The output power of commercially available low-cost microwave ovens is fixed and discontinuous resulting from the high voltage doubler topology of the magnetron tube power supply. In this paper, a high voltage switched mode power supply of forward topology has been developed for continuous microwave power radiation. The forward converter can generate a no-load high voltage output maximum of 7 kV. When driving the magnetron tube, the microwave output power could be varied from 0 to 35 W while the high voltage output level was constantly regulated at -3.4 kV. A microwave induced plasma system was setup to investigate the plasma produced. A low pressure argon plasma was produced with only 2 W over a wide range of pressures.

Application of AFM for identification of fibre surface changes after plasma treatments

<title/>The application of low pressure argon and oxygen plasma treatment as an eco-friendly process of Lyocell textile modification was investigated. Using atomic force microscopy, the changes in nanomorphology induced by plasma treatments were recorded. The chemical groups of the outer fibre layer treated with plasmas and silver compounds (AgNO3 and AgCl) were analysed using Fourier transform infrared-attenuated total reflectance spectroscopy. The viscosimetric method was used to determine possible changes of the cellulose polymer molecular weight after plasma treatments. The experimental results provided data useful for better understanding the art of plasma action on the fibre surface, depending on the nature of gases. They also indicate different mechanisms of silver nanoparticle binding and their distribution on the surface of the treated Lyocell fabric, depending on the parameters of the applied plasma process.

Dynamic sheath expansion in a non-uniform plasma with ion drift

Dynamic sheath expansion in front of a target biased with a negative, high-voltage pulse is investigated in a non-uniform plasma, taking into account the influence of ion drift, which is inevitable in diffusive plasmas with a non-uniform density profile. Temporal evolutions of a sheath edge and a rarefaction wave measured in a low-pressure argon plasma diffusing towards the target agree well with numerical predictions of their transient behaviors as obtained using a dynamic sheath model for non-uniform plasmas with ion drift. It is found that the thickness of the expanding sheath edge is reduced considerably by the ion drift velocity when compared with the thickness without ion drift. Moreover, because the ion drift prevents the propagation of the rarefaction wave significantly, the phase velocity of the wave is observed to be much less than the Bohm speed. The propagating characteristics of the rarefaction wave confirm that the ion drift velocity plays an important role in the dynamic sheath expansion in non-uniform plasmas with ion drift. The results are expected to be useful in analyzing the dose and energy of implanted ions as well as understanding the sheath dynamics in a real plasma source ion implantation system in which the plasma sheath commonly evolves in a non-uniform plasma with ion drift.

Pattern Formation in a Complex Plasma in High Magnetic Fields

Low-pressure room-temperature neon, argon, krypton, and air plasmas were studied in magnetic fields up to flux densities of 2.3 T. Filaments appeared parallel to the magnetic field lines, and patterns such as spirals and concentric circles formed in the perpendicular direction. We link these effects to the magnetization of the ions. We also used a layer of embedded microparticles as probes in the plasma. Their motion changed dramatically from a collective rotation of the whole ensemble in moderate magnetic fields to a rotation in several small vortices centered at the filaments.

Excitation of ion rarefaction waves in a low pressure plasma by applying a short high negative voltage pulse

The ion rarefaction response to a high negative voltage pulse (U0 >> kTe/e) applied to a metal plate immersed in a low pressure argon plasma, for time duration lower than ion plasma period, is experimentally examined. In the present experiment the pulse duration is kept intermediate between the ion and electron plasma response times. Such a pulse duration is chosen so that ions are collectively undisturbed and, according to general understanding, no force is given to ions. Hence no ion rarefaction wave should be excited. But contrary to the general understanding, excitation of a rarefaction wave is observed. The results indicate that the speed of the rarefaction waves for various conditions (like plasma density, applied pulse magnitude, and pulse duration) is supersonic. After a distance from the exciter (biased plate), typically three-fourth of the exciter diameter, the rarefaction waves are turned into ion acoustic waves. The experimental results indicate that even though the bias durations are shorter than the ion plasma period, if the bias magnitude is large enough, some collective plasma behavior can still be excited.

Metallurgical Consideration on the Calibration Curve for Binary Alloy Samples in Low-pressure Argon Laser-induced Plasma Spectrometry

The composition dependence of the emission intensities was investigated in Cu-Ni as well as Ni-Zn binary alloy samples when a low-pressure argon laser-induced plasma was employed as the excitation source. The calibration curve in the Cu-Ni alloy system gave a linear relationship, implying that the selective evaporation of Cu or Ni atoms was caused less in those alloys having several chemical compositions. The Cu-Ni binary alloy has a solid solution phase all over the chemical compositions (all-proportional solid solution): Cu and Ni atoms form no intermetallic compounds but can occupy any positions of a face-centered cubic lattice without any particular interaction. This metallurgical structure would enable Cu and Ni atoms to be released from the sample surface individually, which means that the amount of ablation corresponds to the chemical composition of the alloy sample. For a comparison, a Ni-Zn binary alloy system was also investigated to find calibration curves yielding a nonlinear relationship, differing from those of the Cu-Ni alloy. The reason for this is that the Ni-Zn binary alloy has several metallurgical phases comprising different intermetallic compounds which would each vary the evaporation behavior of Zn. It should be paid attention in LIPS that the ablated composition after laser irradiation is sometimes different from the chemical composition, depending on the kinds of samples and their metallurgical structures.

Possible excitation of solitary electron holes in a laboratory plasma

Plasma response to a fast rising high positive voltage pulse is experimentally studied in a uniform and unmagnetized plasma. The pulse is applied to a metallic disk electrode immersed in a low pressure argon plasma (np∼109 cm−3 and Te∼0.5–2 eV) with the pulse magnitude U0⪢kTe/e, where Te is the electron temperature. Experiments have been carried out for various applied pulse widths τp ranging from less than 3fi−1 to greater than 3fi−1, where fi is the ion plasma frequency. For pulse widths less than 3fi−1, potential disturbances are observed to propagate in two opposite directions from a location different from the actual exciter (metal disk electrode), indicating the presence of a virtual source. For pulse widths equal or greater than 3fi−1, there is no indication of such virtual source. These disturbances propagate with two phase speeds, i.e., vp/ve=1.36±0.11 and 0.4±0.15, where ve is the electron thermal speed. It is also observed that by increasing plasma density, the speed of these disturbances increases, whereas the speed is independent of pulse magnitude. Analysis of these disturbances indicates the excitation of solitary electron holes.

Experimental investigation of a conical helicon double layer thruster arrangement

A conical pyrex plasma source with a conical helicon antenna surrounded by two cylindrically wound solenoids has been used in a helicon double layer thruster (HDLT) arrangement with the aim of investigating a new plasma cavity geometry and imposing a misalignment between the geometric and magnetic axis. An ion beam is measured with an energy analyser placed 6 cm downstream of the source exit for a low pressure argon plasma (∼0.4 mTorr) for various currents in the two solenoids. Operation with current in the exhaust solenoid only also shows the presence of the ion beam. For a given radiofrequency power and similar total solenoidal current, the ion beam current measured downstream of the conical HDLT is about seven times greater than that previously measured downstream of the cylindrical HDLT. This may result from a larger plasma density in the source and from a source peak density shift by about 10 cm towards the tube exit measured in the conical arrangement compared with previous observations in the cylindrical arrangement. When an angle between the geometric and magnetic axis of up to 9° is mechanically imposed, the ion beam is detected for angles less than 5°.

Further research of the collisional instability. An extensive study of growth and a notable influence of the boundaries

AbstractIn a cylindrical geometry, a low-pressure magnetized argon plasma is lit, using the rf upper hybrid resonance. As a radial dc electric field is formed, a perpendicular drift velocity is obtained on the charged particles and a collisional instability is raised. The description, study and identification of that wave were given in the last published work from NCSR ‘Demokritos’, both experimentally and theoretically. Since then, the research has been continued and significant results have been obtained concerning the fields of plasma parameters, wave further understanding, growth research and boundaries' strong influence. The aim of the present paper is to inform that the rising instability has many of the characteristics of drift instabilities that are caused by the density gradient, as well as the ability of it's frequency to overcome the ion gyro-frequency. In addition, it gives an answer to the well-known problem of the need to consider a small component of the wave vector in the parallel direction, in order the wave to rise through the electron-neutral collisions' proceedings; a strong influence of cavity length on wave amplitude has been observed and measured.

An approach to a non-LTE Saha equation based on the Druyvesteyn energy distribution function: a comparison between the electron temperature obtained from OES and the Langmuir probe analysis

Plasma diagnostics using the optical emission spectroscopy (OES) technique is often based on the assumption of Maxwellian distribution functions. Whenever the equilibrium condition is not fulfilled, the electron energy distribution function (EEDF) is no longer Maxwellian and there appear discrepancies between the electron temperature obtained via the spectral line ratio (e.g. Saha equation) and the effective temperature obtained from the EEDF, measured by a Langmuir probe. In this work we derive a modified version of the Saha equation by assuming a Druyvesteyn energy distribution function for the electrons. We apply the modified Saha equation to a low pressure argon plasma produced in an inductive RF discharge to obtain the electron temperature. We show that the modified version introduces substantial corrections in the measured values of the electron temperature given by OES, which approach those given by the second derivative method of Langmuir probe analysis.

Observation of Cathode-Spot Phenomena at the Surface of a Dielectric Powder-Covered Electrode in the Presence of a Background Plasma and Applied Magnetic Field

An electrode containing a layer of micrometer-sized ceramic powder was exposed to a low-pressure background argon plasma. Negative biasing of the electrode resulted in the formation of localized arcs which manifested attributes similar to that observed in vacuum cathode-spot discharges. The arcing action on the electrode in the presence of an applied magnetic field ejected particles and metal vapor, eventually etching repeatable tracks into the electrode surface. The regular tracks left by the action of the cathode spots on the electrode surface suggest J times B effects. The cathode-spot waveforms and erosion tracks with and without an applied magnetic field were documented using a fast frame rate camera and oscilloscope.

Control of ion energy distribution in low-pressure and triple-frequency capacitive discharge

One-dimensional particle-in-cell Monte Carlo collision (PIC-MCC) simulations of low-pressure (10 mTorr) argon plasmas sustained by a triple-frequency (1, 30 and 120 MHz) source in symmetrical current-driven and voltage-driven capacitively coupled plasma reactors are carried out. We concluded that the effective current, the effective voltage and the effective frequency are helpful in explaining the physics of triple-frequency capacitively coupled plasma sources (CCPs) alike single-frequency CCPs. The rf discharge parameters such as the ion energy distribution function (IEDF), the sheath length, the plasma potential and the powers dissipated by electrons and ions can be expressed as the effective frequency and the effective current density (or effective voltage). The analytical model of the IEDF for triple-frequency CCPs in the high-frequency regime is developed. The analytical calculations of the IEDF in the high-frequency regime through the effective frequency visualized in this paper are compared with the simulation results of the IEDF calculated from the 1D PIC-MCC model. The ion energy width and the average ion energy of the IEDF are controlled by the effective frequency, which is expressed as a function of the current density (or voltage) and frequency ratios of the triple-frequency source. The evolution of the effective frequency with the current density or voltage ratio of three frequency sources is different depending on the mode of operating source, which is either voltage or current. The effective frequency in voltage-driven CCPs is 2–10 times higher than that of current-driven CCPs at the same ratio of current density and voltage. As a result, the current-driven CCPs is more desirable than the voltage-driven CCPs from the aspect of independent control of ion flux and ion bombardment energy because the ion energy width increases with decreasing effective frequency.

Hydrophilization of Amorphous Perfluoropolymer using Low-pressure Argon Plasma

The amorphous perfluoropolymer CytopTM (Asahi Glass Co., Ltd.) is an attractive material for use in microdevices for biological and chemical analysis because of its high optical transparency, excellent chemical stability, and low refractive index of 1.34, which is almost the same as that of water. In this study, to increase the applicability of this polymer for such microdevices, the modification of its surface properties was investigated using low-pressure argon plasma. Hydrophilicity control with a water contact angle in the range from 30° to 110° and, moreover, the long-term stability of the hydrophilized surface were achieved for the first time. Although oxygen plasma treatment caused etching instead of hydrophilization, exposure to argon plasma led to bond breaking, the formation of free radicals, and finally the incorporation of hydrophilic groups as a result of the reaction with the oxygen or water from the atmosphere after the polymer was removed from the plasma reactor. Furthermore, to evaluate the suitability of this material for applications involving cell cultivation, the cell adhesion and proliferation properties of the plasma-treated surface were also investigated.

Temperature dependent physicochemical properties of poly(N-isopropylacrylamide-co-N-(1-phenylethyl) acrylamide) thin films

The physicochemical properties of thermo-responsive polymer films are dynamically altered upon changes in environmental conditions. We report on the design and detailed characterization of a novel thermo-responsive polymer film with a temperature transition tuned to fit applications related to the control of marine biofouling. A copolymer consisting of poly(N-isopropylacrylamide) (PNIPAAm) and N-(1-phenylethyl) acrylamide (PEAAm) was synthesized and immobilized as a thin film onto Teflon AF surfaces using a low pressure argon plasma treatment. The temperature dependent physicochemical properties of the thermo-responsive film were thoroughly characterized and the impact of sea water on the film properties was investigated. The immobilized thermo-responsive film exhibits a reversible swelling/deswelling with temperature. Atomic force microscopy showed no morphological changes with varying temperature. Streaming current measurements performed above and below the transition temperature of the thermo-responsive hydrogel indicated that the charging of the polymer/aqueous solution interface is mainly determined by the preferential water ion adsorption at the Teflon AF surface. Inverse contact angles measured using captive air bubbles and analysed by axisymmetric drop shape analysis (ADSA) supported the intrinsic properties of the thermo-responsive film, as surface hydrophilicity decreased with increasing temperature. The advancing water contact angle decreased with increasing temperature, which may be explained by the different molecular mobility at different temperatures, allowing or hampering the re-orientation of hydrophobic segments at the solid–liquid and solid–fluid interfaces. These new films will allow investigations on the interaction of microorganisms with environmentally sensitive surfaces.

Argon plasma sintering of inkjet printed silver tracks on polymer substrates

An alternative and selective sintering method for the fabrication of conductive silver tracks on common polymer substrates is presented, by exposure to low-pressure argon plasma. Inkjet printing has been used to pattern a silver nanoparticle ink. This resulted in conductive features with a resistivity less than one order of magnitude higher than the bulk value of silver without affecting the polymer substrate. This process may be employed in the production of conductive features with low material usage on common polymer substrates in, for example, printed electronics.

Application of Low-Pressure Plasma Pretreatment in Silk Fabric Degumming Process

A novel and effective method was developed for raw silk fabric degumming with the application of low-pressure argon plasma in pretreatment combining a subsequent one-step mild wet-chemical process. The plasma parameters, such as argon pressure, discharge power and exposure time, were optimized according to degumming loss and the properties of fabric such as capillary rise, tensile strength, bending rigidity, etc. An optimized plasma pretreatment for raw silk fabric degumming was at 80 Pa of argon gas and 60 W glow discharge power for 5–10 min. The raw silk fabric and fibers pretreated by argon plasma were characterized by scanning electronic microscopy and X-ray powder diffraction. In comparison with a conventional degumming process, the proposed method achieved comparable degumming efficiency and properties of silk fabric, and it was more environmentally friendly by shortening the conventional wet-chemical treatment process, saving the dosage of degumming agents, water and energy.

Double layer in an expanding plasma: Simultaneous upstream and downstream measurements

Ion energy measurements were taken simultaneously using one retarding field energy analyzer placed at the open end of the plasma source, and one in the plasma diffusion region of an expanding low pressure argon plasma. An electric double layer was found, which is well separated from the region of high magnetic field and which is downstream of the maximum in the magnetic field gradient. An axially movable analyzer was used to determine the position of the double layer. It appears to be more closely connected to the rapid change in diameter from the source to the diffusion chamber, but still has a radial dimension close to that of the source diameter. These results suggest that the double layer forms, not as much as a result of a magnetic nozzle, but rather as a reaction to a dramatic change in boundary conditions. Still, a magnetic field of at least a few tens of Gauss in the double layer region is necessary for its spontaneous formation.