Increasing Plasma Power Research Articles

High power impulse sputtering of chromium: correlation between the energy distribution of chromium ions and spoke formation

High power magnetron sputtering (HiPIMS) discharges generate ions with high kinetic energies in comparison to conventional dc magnetron sputtering. The peculiar shape of the ion energy distribution function (IEDF) is correlated to the formation of localized ionization zones (IZ) in the racetrack of a HiPIMS discharge, so called spokes. This is explained by a local maximum of the electrical potential inside these localized IZ. By using ion energy mass spectrometry, probe experiments and plasma spectroscopy the connection between IZ and IEDFs is evaluated with high temporal resolution. The data of a floating probe next to the target is used to directly monitor the movement of the spokes in the direction. Chromium is used as target material, because the plasma undergoes a sequence from stochastic spoke formation, to regular spoke pattern rotating in the direction to a homogeneous plasma torus with increasing plasma power. In particular, the analysis of the transition from the regular spoke pattern to the homogeneous plasma torus at very high plasma powers shows that the high energy part of the IEDF is not affected and only the low energy part is modified. Consequently, one could consider the homogenous plasma torus at very high plasma powers as a a single ionization zone localized over the complete torus, which is formed by merging individual spokes with increasing power. Details and consequences of that model are discussed.

Microstructural, mechanical and tribological properties of nanostructured YSZ coatings produced with different APS process parameters

Plasma sprayed ceramic coatings can be used in turbine engines as thermal barrier or abradable coatings, in order to improve the durability of the components as well as the efficiency. The presence of nanostructures, deriving from partial melting of agglomerated nanostructured particles, represents an interesting technological solution in order to improve their functional characteristics. In this work nanostructured yttria stabilized zirconia (YSZ) coatings were deposited by air plasma spraying (APS). The influence of the main process parameters on their microstructural, mechanical and tribological properties was investigated by scanning electron microscopy (SEM), indentation techniques at micro- and nano-scale and wear tests, respectively. Their porous microstructure was composed of well melted overlapped splats and partially melted nanostructured areas. This bimodal microstructure led to a bimodal distribution of the mechanical properties. An increase of plasma power and spraying distance was able to produce denser coatings, with lower content of embedded nanostructures, which exhibited higher elastic modulus and hardness as well as lower wear rate.

A comparative study on GaN luminescence under/after inductively coupled plasma exposure

GaN luminescence, induced by ultraviolet light under/after inductively coupled plasma exposure, has been measured in situ and ex situ. After the plasma exposure, both near-band edge (NBE) and yellow luminescence (YL) intensities decrease. The decay times of NBE and YL in the in situ measurement are shorter than those of the ex situ measurement on account of the temperature rise induced by the plasma. On the other hand, with increasing plasma power, the decay times decrease. It is considered that this decrease is strongly related to non-radiative defects introduced by the Ar plasma. The results suggest that in situ photoluminescence monitoring can be used to reveal plasma-induced damage at GaN surfaces.

Matrix effects of carbon and bromine in inductively coupled plasma optical emission spectrometry

In inductively coupled plasma based techniques the signal enhancing effect of carbon on high ionization potential elements is not only caused by changes in the nebulization efficiency and charge exchange reactions, but also by increased plasma power density and the state of matter of the introduced carbon species.

Properties of Titanium Oxynitride Prepared by RF Plasma

Titanium oxynitrides combine the properties of metallic oxides and nitrides. In this presentation, titanium was oxynitrided using inductively coupled RF plasma in a gas mixture containing 80% N2 and 20% O2. The effect of plasma-processing power from 350 up to 550 W on microstructure, mechanical, tribological, wettability and electrochemical properties of the oxynitrided titanium was examined using different characterizations and testing techniques. The results demonstrated the formation of TiO, TiO2 rutile phase, TiNxOy and Ti2N as a result of plasma oxynitriding. The micro-hardness of the oxynitrided layers increases up to 766 HV0.1 as the plasma-processing power increases up to 550 W. The wear and corrosion resistance are improved for oxynitrided titanium in comparison with untreated samples. Moreover, the friction coefficient decreases from nearly 0.75 for the pure titanium to nearly 0.3 for oxynitrided titanium. The obtained data show an increase of surface energy and wettability of titanium oxynitride as the plasma power increases. The formation of hard oxide and oxynitride phases and the transformation of TiO2 from anatase to rutile structure at relatively high temperature are the main reasons for the good physical and electrochemical properties of titanium oxynitride.

Gas flow characteristics of a time modulated APPJ: the effect of gas heating on flow dynamics

This work investigates the flow dynamics of a radio-frequency (RF) non-equilibrium argon atmospheric pressure plasma jet. The RF power is at a frequency of 50 Hz or 20 kHz. Combined flow pattern visualizations (obtained by shadowgraphy) and gas temperature distributions (obtained by Rayleigh scattering) are used to study the formation of transient vortex structures in initial flow field shortly after the plasma is switched on and off in the case of 50 Hz modulation. The transient vortex structures correlate well with observed temperature differences. Experimental results of the fast modulated (20 kHz) plasma jet that does not induce changes of the gas temperature are also presented. The latter result suggests that momentum transfer by ions does not have dominant effect on the flow pattern close to the tube. It is argued that the increased gas temperature and corresponding gas velocity increase at the tube exit due to the plasma heating increases the admixing of surrounding air and reduces the effective potential core length. With increasing plasma power a reduction of the effective potential core length is observed with a minimum length for 5.6 W after which the length extends again. Possible mechanisms related to viscosity effects and ionic momentum transfer are discussed.

Characterization of low temperature graphene synthesis in inductively coupled plasma chemical vapor deposition process with optical emission spectroscopy.

Low-temperature graphene was synthesized at 400 degrees C with inductively coupled plasma chemical vapor deposition (PECVD) process. The effects of plasma power and flow rate of various carbon containing precursors and hydrogen on graphene properties were investigated with optical emission spectroscopy (OES). Various radicals monitored by OES were correlated with graphene film properties such as sheet resistance, I(D)/I(G) ratio of Raman spectra and transparency. C2H2 was used as a main precursor and the increase of plasma power enhanced intensity of carbon (C2) radical OES intensity in plasma, reduced sheet resistance and increased transparency of graphene films. The reduced flow rate of C2H2 decreased sheet resistance and increased transparency of graphene films in the range of this study. H2 addition was found to increase sheet resistance, transparency and attributed to reduction of graphene grain and etching graphene layers. OES analysis showed that C2 radicals contribute to graphite networking and sheet resistance reduction. TEM and AFM were applied to provide credible information that graphene had been successfully grown at low temperature.

Ar/O2 and H2O plasma surface modification of SnO2 nanomaterials to increase surface oxidation

Tin oxide operates widely as a gas sensor for a variety of molecules via a mechanism that relies on interactions with adsorbed oxygen. To enhance these interactions by increasing surface oxygen vacancies, commercial SnO2 nanoparticles and CVD-grown SnO2 nanowires were plasma modified by Ar/O2 and H2O plasmas. Scanning electron microscopy revealed changes in nanomaterial morphology between pre- and post-plasma treatment of H2O treated materials but not Ar/O2 treated materials. Powder X-ray diffraction patterns of the bulk SnO2 showed the Sn4+ is reduced by H2O and not Ar/O2 plasma treatments. X-ray photoelectron spectroscopy indicated Ar/O2 treatment results in increasing oxygen adsorption with increasing plasma power and treatment time, without changing Sn oxidation. With the lowest plasma powers and treatment times, however, H2O plasma treatment results in nearly complete bulk Sn reduction. Although both plasma systems increased oxygen adsorption over the untreated materials, there were clear differences in the tin and oxygen as well as morphological variations upon plasma treatment.

Effects of plasma power on material and optical quality of GaN nanorods grown by plasma-assisted molecular beam epitaxy

The growth of wurtzite GaN(0001) nanorods on Si(111) substrates in the nitrogen-rich regime was studied in comparison with nitrogen species generated from a remote inductively coupled plasma source. A reduction in incorporation rate and a substantial deterioration in the quality of GaN nanorods were found to be correlated with an increase in plasma power. On the basis of the observation of defect formation in the initial growth stage and its propagation during the growth, the degradation of material perfection by the increased energy delivered by active nitrogen species at high power was discussed.

Fabrication of Uniform Sized Metal Spheres by Plasma Induced Dewetting

Sn and InSn metal spheres were fabricated by plasma induced dewetting with various conditions. Dewetting was effective under a hydrogen plasma environment despite the absence of an external heat source. FE-SEM images revealed that hydrogen plasma dewetting of Sn and InSn films proceeded through heterogeneous hole nucleation on the film surface and films changed to spherical with no large aggregation while there were large aggregations under thermal dewetting. Droplet size was controllable by selecting the plasma treatment conditions and initial film thickness. The longer films were plasma-treated, sphere size was decreased and larger spheres were divided to smaller ones. In addition, increasing plasma power yielded increasing sphere size regularity. It was suggested that plasma induced the digestive ripening of the metal spheres which interpreted by charge effect in colloid system.

Interface and plasma damage analysis of PEALD TaCN deposited on HfO2 for advanced CMOS studied by angle resolved XPS and C–V

Plasma enhanced atomic layer deposition (PEALD) TaCN deposited on HfO2 was studied by X-ray photoelectron spectroscopy (XPS) to understand the reactions taking place at the interface and connect them with C–V electrical characteristics of MOS devices. Moreover, angular resolved XPS (AR-XPS) was used for composition depth profiling of TaCN/HfO2/SiO2/Si stacks. Clear oxidation of the metal electrode through TaO bonding formation and migration of N in the dielectric with HfN are shown. These modifications of chemical bonding give an insight on the electrical results. Low equivalent oxide thicknesses (EOT), as low as 0.89nm and current leakage improvement by more than 5 decades, are observed for deposition with low plasma power and can be related to HfN content in HfO2 layer. The increase of plasma power used for TaCN deposition results in densification of the layer and promotes the creation of TaC in TaCN material. However H2 plasma has an impact on HfO2 with a reduction and scattering of the measured current leak gain. TaCN/HfO2 interface is also impacted with further creation of TaOx, leading to an increase of EOT when plasma power is increased. Based on these findings, reaction mechanisms with the corresponding Gibbs free energy are proposed.

Synthesis of N-doped Ethylcyclohexane Plasma Polymer Thin Films with Controlled Ammonia Flow Rate by PECVD Method

In this study, we investigated the basic properties of N-doped ethylcyclohexene plasma polymer thin films that deposited by radio frequency (13.56 MHz) plasma-enhanced chemical vapor deposition (PECVD) method with controlled ammonia flow rate. Ethylcyclohexene was used as organic precursor with hydrogen gas as the precursor bubbler gas. Additionally, ammonia (NH₃) gas was used as nitrogen dopant. The as-grown polymerized thin films were analyzed using ellipsometry, Fourier-transform infrared [FT-IR] spectroscopy, UV-Visible spectroscopy, and water contact angle measurement. We found that with increasing plasma power, film thickness is gradually increased while optical transmittance is drastically decreased. However, under the same plasma condition, water contact angle is decreased with increasing NH₃ flow rate. The FT-IR spectra showed that the N-doped ethylcyclohexene plasma polymer films were completely fragmented and polymerized from ethylcyclohexane.

Conductive Transparent TiNx/TiO2 Hybrid Films Deposited on Plastics in Air Using Atmospheric Plasma Processing

The successful deposition of conductive transparent TiNx/TiO2 hybrid films on both polycarbonate and silicon substrates from a titanium ethoxide precursor is demonstrated in air using atmospheric plasma processing equipped with a high‐temperature precursor delivery system. The hybrid film chemical composition, deposition rates, optical and electrical properties along with the adhesion energy to the polycarbonate substrate are investigated as a function of plasma power and plasma gas composition. The film is a hybrid of amorphous and crystalline rutile titanium oxide phases and amorphous titanium nitride that depend on the processing conditions. The visible transmittance increases from 71% to 83% with decreasing plasma power and increasing nitrogen content of the plasma gas. The film resistivity is in the range of ∼8.5 × 101 to 2.4 × 105 ohm cm. The adhesion energy to the polycarbonate substrate varies from ∼1.2 to 8.5 J/m2 with increasing plasma power and decreasing plasma gas nitrogen content. Finally, annealing the film or introducing hydrogen to the primary plasma gas significantly affects the composition and decreases thin‐film resistivity.

Atmospheric plasma deposition of transparent semiconducting ZnO films on plastics in ambient air

Transparent zinc oxide (ZnO) thin films have been successfully synthesized on poly (methyl methacrylate) (PMMA), polycarbonate (PC), and polyethylene terephthalate (PET) substrates by atmospheric plasma deposition in ambient air at room temperature. The structural, optical and electrical properties of the ZnO films as well as their adhesion to the polymer substrates were investigated for various deposition conditions. The film surface exhibited a dome-shaped topography comprised of nanometer-sized grains. The size of both the domes and the grains became larger as the plasma power increased. The visible transmittance increased above 95% with decreasing plasma power. The resistivity exhibited a wide variation in the range of 102–108ohmcm. The adhesion energies to PMMA varied from 0.2 to 1.5J/m2 with increasing plasma power. While a finer grain structure achieved with lower plasma power was preferable for higher transmittance, it resulted in lower adhesion to the plastic substrates. The study demonstrated the feasibility of depositing semiconducting transparent ZnO films on polymer substrates at low temperature in ambient air using atmospheric plasma deposition.

Optical Emission Spectroscopy in Cooking Exhaust from a Wet Scrubber/Atmospheric Plasma Reactor

This study introduced a self-developed wet scrubber/plasma reactor (WSB/PR) system to treat cooking fumes, and measured the changes in the optical emissions spectra (OES), before and after treatment using OES, in order to understand the changes of OES in a gaseous phase from waste gas. In terms of operational parameters of the experiment, the scrubbing solution used in WSB was tap water and an enzyme scrubbing solution, and atmospheric pressure plasma was applied inside PR. Furthermore, five different output powers (0.112 kJ/m^3, 0.129 kJ/m^3, 0.138 kJ/m^3, 0.146 kJ/m^3, and 0.156 kJ/m^3) were utilized to conduct experiments. The experimental results showed that, through the operations of five different plasma output powers, active species C, C_2, CH, N, H_γ, N_2, N_2^+, NO, C^+, NH, O_2^+, H_2, and O can be tested under the following three situations: (i) start PR (plasma background value) without importing cooking fumes; (ii) cooking fumes pass through WSB/PR; and (iii) cooking fumes pass through ESB/PR. When cooking fumes are treated with WSB/PR, light emission intensity intensifies with increased plasma power, from 0.112 kJ/m^3 to 0.146 kJ/m^3. The same tendency occurs in the situation of cooking fumes treated with ESB/PR, which increases plasma power from 0.112 kJ/m^3 to 0.138 kJ/m^3. In addition, the number of active species is reduced when plasma power is increased. This indicates that, electron energy is reduced due to the H_2O decomposition function in the plasma reaction, which results in a decrease in the number of active species.

Radio frequency plasma power dependence of the moisture permeation barrier characteristics of Al2O3 films deposited by remote plasma atomic layer deposition

In the present study, we investigated the gas and moisture permeation barrier properties of Al2O3 films deposited on polyethersulfone films (PES) by capacitively coupled plasma (CCP) type Remote Plasma Atomic Layer Deposition (RPALD) at Radio Frequency (RF) plasma powers ranging from 100 W to 400 W in 100 W increments using Trimethylaluminum [TMA, Al(CH3)3] as the Al source and O2 plasma as the reactant. To study the gas and moisture permeation barrier properties of 100-nm-thick Al2O3 at various plasma powers, the Water Vapor Transmission Rate (WVTR) was measured using an electrical Ca degradation test. WVTR decreased as plasma power increased with WVTR values for 400 W and 100 W of 2.6 × 10−4 gm−2day−1 and 1.2 × 10−3 gm−2day−1, respectively. The trends for life time, Al-O and O-H bond, density, and stoichiometry were similar to that of WVTR with improvement associated with increasing plasma power. Further, among plasma power ranging from 100 W to 400 W, the highest power of 400 W resulted in the best moisture permeation barrier properties. This result was attributed to differences in volume and amount of ion and radical fluxes, to join the ALD process, generated by O2 plasma as the plasma power changed during ALD process, which was determined using a plasma diagnosis technique called the Floating Harmonic Method (FHM). Plasma diagnosis by FHM revealed an increase in ion flux with increasing plasma power. With respect to the ALD process, our results indicated that higher plasma power generated increased ion and radical flux compared with lower plasma power. Thus, a higher plasma power provides the best gas and moisture permeation barrier properties.

Plasma-induced adhesion improvement of cotton/polypropylene-laminated fabrics

In this study, improvement in the adhesion strength of plasma-pretreated and laminated cotton/polypropylene (PP) fabrics using acrylic-based adhesive was investigated. Low-temperature, low-pressure oxygen plasma was utilized for surface modification of cotton/PP-laminated fabrics. Water absorption time was measured on plasma-treated cotton fabrics at different plasma power and treatment time conditions. The plasma conditions providing the fastest liquid absorption on the surface were selected and applied during plasma pretreatments. Surface wettability increased with increasing plasma power and plasma exposure time. Plasma-induced surface morphology changes were observed via Scanning Electron Microscope (SEM) images. X-ray Photoelectron Spectroscopy (XPS) analysis showed that oxygen content on the surface increased with plasma treatment, which contributed to the surface polarity and hydrophilicity. Peel bond strength results of untreated and plasma-treated samples were analyzed to determine the effect of plasma pretreatment process. Adhesion strength values of laminated samples, before washing and after 40 wash cycles, were determined by peel bond strength tests. Before washing, adhesion strength of plasma pre-treated, laminated samples was 28–60% higher than that of untreated laminated fabrics. After 40 wash cycles, adhesion strength of plasma pre-treated and laminated samples was about 40–69% higher than the untreated laminated fabrics. Peel bond strength values decreased with the increased number of wash cycles. Plasma pretreatment enhanced both the adhesion strength and washing resistance of laminated samples.

Synthesis of Few Layer Graphene by Non-Transferred Arc Plasma System

Graphene has recently been the focus of a great deal of attention owing to its outstanding properties, which include high mobility, high thermal conductivity and high structural stability. In this study, a few layer graphene was successfully synthesized from methane gas using a non-transferred direct current arc plasma system. Non-transferred thermal plasma offers high temperature, steep temperature gradient and high enthalpy to enhance the reaction kinetics of graphene synthesis. In order to prepare high quality few layer graphene, graphene products synthesized under several conditions was analyzed comparatively. Effects of gap distance between the plasma torch and graphite substrate, the flow rate of additional reactant gas, and different types of plasma forming gas on the synthesis of few layer graphene were investigated. Methane gas was injected into the plasma jet as a carbon source for the synthesis of graphene and a thermal plasma jet was generated by pure argon or a mixture of argon-hydrogen. The results revealed that hydrogen gas improved the quality of few layer graphene by inducing surface etching and increasing plasma power.

NO production in an RF plasma jet at atmospheric pressure

A time modulated RF atmospheric pressure plasma jet, operated in ambient air with a flow of argon with a few per cent of air, N2 or O2, was characterized by measuring the gas temperature with Rayleigh scattering, the absolute NO density with laser-induced fluorescence, and the emission of NO A and N2 C with time resolved optical emission spectroscopy. The gas temperature, NO density and the emission measurements are carried out both time and spatially resolved. The atmospheric pressure plasma jet has the advantage that the plasma dissipated power can be measured, and it was found that the gas temperature depends on the power, rather than the gas mixture. The NO density increases with increasing plasma power, and was found to have a maximum around 1.5 × 1021 m−3 at an air admixture of 2%. The N2 C emission is modulated by the 13.9 MHz RF frequency, while the NO A emission front increases with much slower velocity during the 20 kHz duty cycle, which gives an insight into the excitation mechanisms in the plasma. Through the addition of either N2 or O2 to the plasma it was experimentally confirmed that the production of atomic N radicals are of key importance for the NO production in this atmospheric pressure plasma jet.

Surface modification of poly(dimethylsiloxane) by atmospheric pressure high temperature plasma torch to prepare high-performance gas separation membranes

In this study, an atmospheric pressure high temperature plasma torch (APHTPT) was used to modify poly(dimethylsiloxane) (PDMS) membranes in order to form a thin SiOx layer on the membrane surface. The chemical properties of the PDMS and APHTPT-treated membranes, as well as the conversion of polysiloxane, were determined by X-ray photoelectron spectroscopy (XPS) and energy-dispersive X-ray (EDX) microanalysis. The microstructure of the membranes as a function of depth was obtained with a variable monoenergy slow positron beam (VMSPB) spectroscopy. Results of XPS and EDX indicated that the conversion of polysiloxane to silica was favored with increasing plasma power. VMSPB data demonstrated that the treated membrane exhibited an asymmetric organic–inorganic hybrid structure. Based on the analysis of the treated membrane, the free-volume size increased with the depth and showed a bi-modal distribution. The gas permeation properties of O2, N2, and CO2 were tested. The change in the applied plasma power was found to have a great effect on the membrane gas separation performance. The membrane selectivity for O2/N2 and CO2/N2 increased from 2.11 to 4.93 and from 9.54 to 17.19, respectively, after treatment at 10kW. The APHTPT-treated PDMS membrane was found to have the advantages of both organic and inorganic membranes, leading to outstanding gas separation performance.