Effects Of Plasma Gas Composition Research Articles

The Effect of Plasma Gas Composition on the Nanostructures and Optical Properties of TiO2 Films Prepared by Helicon-PECVD

TiO2 films were deposited from oxygen/titanium tetraisopropoxide (TTIP) plasmas at low temperature by Helicon-PECVD at floating potential ([Formula: see text] or substrate self-bias of [Formula: see text]50[Formula: see text]V. The influence of titanium precursor partial pressure on the morphology, nanostructure and optical properties was investigated. Low titanium partial pressure ([TTIP] [Formula: see text] 0.013[Formula: see text]Pa) was applied by controlling the TTIP flow rate which is introduced by its own vapor pressure, whereas higher titanium partial pressure was formed through increasing the flow rate by using a carrier gas (CG). Then the precursor partial pressures [TTIP[Formula: see text]CG] [Formula: see text][Formula: see text]Pa and 0.093[Formula: see text]Pa were obtained. At [Formula: see text], all the films exhibit a columnar structure, but the degree of inhomogeneity is decreased with the precursor partial pressure. Phase transformation from anatase ([TTIP] [Formula: see text] 0.013[Formula: see text]Pa) to amorphous ([TTIP[Formula: see text]CG] [Formula: see text][Formula: see text]Pa) has been evidenced since the O[Formula: see text] ion to neutral flux ratio in the plasma was decreased and more carbon contained in the film. However, in the case of [Formula: see text]50[Formula: see text]V, the related growth rate for different precursor partial pressures is slightly ([Formula: see text] 15%) decreased. The columnar morphology at [TTIP] [Formula: see text] 0.013[Formula: see text]Pa has been changed into a granular structure, but still homogeneous columns are observed for [TTIP[Formula: see text]CG] [Formula: see text][Formula: see text]Pa and 0.093[Formula: see text]Pa. Rutile phase has been generated at [TTIP] [Formula: see text][Formula: see text]Pa. Ellipsometry measurements were performed on the films deposited at [Formula: see text]50[Formula: see text]V; results show that the precursor addition from low to high levels leads to a decrease in refractive index.

Influence of N2/H2 and N2 plasma on binary III-nitride films prepared by hollow-cathode plasma-assisted atomic layer deposition

The authors reported the hollow-cathode plasma-assisted atomic layer deposition of AlN, GaN, and InN films using N2-only and N2/H2 plasma. In this study, the authors analyzed the effect of plasma gas composition on the properties of deposited binary III-nitride thin films. Toward this goal, AlN, GaN, and InN films were deposited on Si (100) substrates using N2-only (50 sccm), as well as N2/H2 (50 + 50, 50 + 25 sccm) plasma to investigate the impact of H2 flow. Grazing-incidence x-ray diffraction (GIXRD) patterns of AlN and GaN thin films deposited with N2/H2 plasma remained almost unchanged when H2 flow decreased from 50 to 25 sccm. On the other hand, the use of N2 plasma without any H2 resulted in amorphous GaN thin films with significant carbon impurity within the bulk film. In the case of AlN, similar behavior was observed as the crystal structure is significantly altered to amorphouslike material. Thicknesses of AlN and GaN thin films increased tremendously when N2-only was used as the plasma gas. Furthermore, refractive index values of both AlN and GaN films decreased upon the use of N2-only plasma, which confirm the deterioration of the film quality. Structural weaknesses of GaN and AlN films deposited with N2-only plasma are due to presences of carbon impurities that are trapped inside the growing film. Interestingly, the authors did not observe similar results in InN films grown with N2/H2 plasma. For InN, GIXRD and spectroscopic ellipsometry results show that the phases of deposited films change from InN to In+InN as H2 content in the plasma gas is increased. On the other hand, InN films grown with N2-only plasma show improved structural properties. However, significantly higher N2 plasma exposure times are needed to minimize the residual carbon content in deposited InN layers.

Effects of Processing Parameters on the Deposition of Yttria Partially Stabilized Zirconia Coating During Suspension Plasma Spray

The process–microstructure relationship in suspension plasma spray (SPS) of yttria partially stabilized zirconia (YSZ) has been studied experimentally. An ethanol‐based suspension with a powder loading of 25 wt% was plasma sprayed with radial injection under four different plasma conditions, to examine the effects of plasma gas composition (Ar/He ratio), secondary gas (Ar/He and Ar/H2), and the nozzle diameter of the plasma gun. The suspension feeding rate was optimized firstly and coatings were prepared for microstructural observation. Capturing of in‐flight particles into water as well as collection of splats formed on heated flat metal substrates were utilized in order to better understand the more complicated intermediate process steps in SPS. It was found that a plasma jet with higher momentum allowed a higher suspension flow rate and both columnar and deep vertically cracked structure could be created depending on the plasma parameters as well as the substrate surface roughness.

Treatment of refractory powders by a novel, high enthalpy dc plasma

Thermophysical properties of CO2–CH4 mixtures at high temperatures are very attractive for materials processing. In comparison with argon, at the same temperature, such a mixture possesses much higher enthalpy and higher thermal conductivity. At high temperatures, CO2–CH4 mixture has a complex composition with strong presence of CO which, in the case of powder treatment, could reduce oxidation. In this work, a dc plasma torch with graphite cathode was used to study the effect of plasma gas composition on spheroidization of tungsten carbide and alumina powders. Two different gas compositions were used to generate the plasma while the torch current was kept at 300 A. Various techniques were employed to assess the average concentration of carbides and oxides and the final shape of the treated powders. Process parameters such as input power and plasma gas composition allow controlling the degree of powder oxidation and spheroidization of high melting point ceramic powders.

Air plasma sprayed Cu–Co–GDC anode coatings with various Co loadings

In this work, Cu–Co–gadolinia doped ceria (GDC) anode coatings were fabricated by atmospheric plasma spraying (APS) of agglomerated CuO, Co3O4, and GDC feedstock powders. Screening tests were conducted to identify the effect of plasma gas composition on the coating phases, microstructure, and absolute deposition efficiency of each material. Based on screening tests, optimized plasma energy conditions were identified. Using the absolute deposition efficiency, feedstock powder mixing ratios were determined to produce anode coatings with Cu–Co weight ratios of Cu(100)–Co(0), Cu(90)–Co(10), Cu(70)–Co(30), and Cu(50)–Co(50), with 40 vol% of metal phases in the coating and 60 vol% of GDC. After reduction of the coatings, porosity and gas permeability were determined. Finally, carbon deposition behavior was examined by measuring the weight gain of the coatings after exposure to CH4 at 700 °C for 3 h. The coatings demonstrated good resistance to carbon deposition.

Modeling of Induction Plasma Process for Fullerene Synthesis: Effect of Plasma Gas Composition and Operating Pressure

A mathematical model has been developed on the continuous synthesis of fullerenes by direct evaporation of carbon-containing materials using induction thermal plasma technology. The main purpose of this study is to numerically investigate the effect of plasma gas composition and operating pressure on the fullerene formation. The simulation results confirmed that Ar–He mixture plasma is more efficient than argon plasma in terms of the particle evaporation, generation of fullerene precursors, fullerene growth and their annealing, and that low pressure operation would decrease the overall yield rate of fullerenes by enhancing the radial diffusion of carbon vapors towards the reactor walls. Thus an operating condition of relatively high helium content in the plasma gas and elevated gas pressure seems much more desirable for achieving a high yield rate of fullerenes. This conclusion is in line with the experimental evidences reported previously.

Effects of plasma gas composition on bond strength of hydroxyapatite/titanium composite coatings prepared by rf-plasma spraying

The effects of plasma gas composition on the bond-strength of HA/Ti composite coatings were investigated. HA/Ti composite coatings were deposited on titanium substrates by a radio-frequency (rf) thermal plasma spraying method with input powers of 10–30 kW. The ratio of the HA and Ti powders supplied into the plasma was precisely controlled by two microfeeders so as to change the coating's composition from Ti-rich at the bottom to HA-rich at its upper layer. The bond (tensile) strength of the obtained HA/Ti composite coatings was 40–65 MPa when sprayed with plasma gas containing N 2 (i.e., Ar–N 2). On the other hand, HA/Ti composite coatings prepared with plasma gas containing O 2 (i.e., Ar–O 2) had significantly lower bond strength (under 30 MPa). XRD patterns of Ti coatings without HA showed that titanium nitride and titanium dioxide formed, respectively, on titanium deposits sprayed with Ar–N 2 and Ar–O 2 plasma. Scanning electron microscopic (SEM) observation showed an acicular texture on the Ti deposits prepared with Ar–N 2 plasma. SEM observations implied that, when sprayed with Ar–O 2 plasma, a thin TiO 2 layer formed at the interfaces between the Ti splats in the deposits.