Effect of DC steam plasma on gasifying carbonized waste

A feasibility study has been conducted to determine whether steam plasma can be used for the treatment of carbonized wastes, such as the carbide of the hazardous waste. The gasification which was often called “water gas reaction” was studied to reduce the volume and weight of wastes and to produce the combustible gas like hydrogen from them by using steam plasma. In this study, the thermal plasma generated by DC plasma was used as a heat source, where steam was added to react with carbon. Graphite was used as a test piece instead of carbonized wastes. The weight of the test piece was measured before and after treatment to decide the weight reduction during the experiment. The gas produced in the reaction was analyzed. The result indicated that it is possible to reduce the weight of graphite and to produce the combustible gas from graphite by using the DC steam plasma.     

Levels of polychlorinated biphenyls (PCBs) in transformer oils from Korea

Using Korean waste official method, polychlorinated biphenyls (PCBs) were analyzed from 33 transformer oils collected under National Institute of Environmental Research (NIER) in Republic of Korea (ROK) and their emission rate in Korea was estimated. Practical quantification limits analyzed by this method were in the ranges of 0.02 and 0.05 mg L(-1), and recovery of samples was in the ranges of 77-97%. The analytical results showed that PCBs in the transformer oils were identified as Aroclor 1242, 1254 or 1260. Twenty-nine samples were determined to contain PCBs of >0.05 mg L(-1) and among these samples, nine samples contained to have >2 mg kg(-1) which is limit of Waste Control Act (WCA) with regard to PCBs in transformer oil from Korea. The concentrations of PCBs in transformer oils were between N.D. (not detected) and 48.33 mg kg(-1). PCBs concentrations did not exceed 50 mg kg(-1) which is generally accepted limit for the definition of waste in POPs Guideline of Basel Convention.     

A spectroscopic study into the decomposition process of titanium isopropoxide in the nitrogen-hydrogen 100 kHz low-pressure plasma

Optical emission spectroscopy was employed for the study of the nitrogen-hydrogen and nitrogen-hydrogen-titanium (IV) isopropoxide mixtures in the 100 kHz low pressure capacitively coupled discharge. High-energy species were identified in the plasma phase. The behavior of the excited species versus the gas composition has also been investigated. The optical actinometry technique was applied in order to evaluate the N₂, CH, CO, CN, N, C and the H relative concentrations versus the hydrogen concentration in reactive mixtures. The effect of the hydrogen concentration in the nitrogen-hydrogen mixture on the decomposition processes of titanium isopropoxide was investigated. The plasma temperature (the H excitation temperature, the CN, N₂ and N₂⁺ vibrational temperatures and the N₂⁺ rotational temperature) as well as the electron number density were determined here. The temperature magnitudes (T_exc≈5700-7400 K, T_vib(CN)≈4700-8100 K, T_vib(N₂)≈2700-3050 K, T_vib(N₂⁺)≈1500-1600 K and T_rot(N₂⁺)≈660-890 K) indicated a very significant deviation from the LTE state.     

Formation of silicon dioxide layers at low temperatures (150-400 °C) by atmospheric pressure plasma oxidation of silicon

The formation of silicon dioxide (SiO₂) layers at low temperatures (150-400 °C) by atmospheric pressure plasma oxidation of Si(0 0 1) wafers have been studied using a gas mixture containing He and O₂. A 150 MHz very high frequency (VHF) power supply was used to generate high-density atomic oxygen in the atmospheric pressure plasma. Oxidation rate, structure, and thickness and refractive index profiles of the oxidized layers were investigated by ellipsometry and infrared absorption spectroscopy. Atomic force microscopy was also employed to observe atomic-scale morphologies of the layer surface and wafer Si surface, after chemical removal of the oxidized layers. It was found that stoichiometric SiO₂ layers were obtained at higher oxidation rates than conventional dry O₂ thermal oxidation and radical oxidation processes, even at a very low substrate temperature of 150 °C. Although thickness variations were observed in the plasma region, the refractive index was independent of both substrate temperature and VHF power. In addition, the SiO₂ surface and SiO₂/Si interface roughnesses were comparable to those obtained in conventional dry oxidation at high temperatures.     

Oxygen plasma treatment of SiOxCy(− H) films polymerized by atmospheric pressure dielectric barrier discharge using hexamethylcyclrotrisiloxane

The SiO₂-like layers were obtained by plasma-oxidation of the SiO_xC_y(− H) films deposited from hexamethylcyclotrisiloxane (HMCTSO) with helium and oxygen. The SiO₂-like layers were formed on as-deposited SiO_xC_y(− H) films within a second by oxidation using the He/O₂ atmospheric pressure dielectric barrier discharge (APDBD). The elemental ratio of oxygen to silicon in the layer was increased up to 1.95 which is closed to stoichiometry of SiO₂. The elemental composition and surface morphology were studied by means of x-ray photoelectron spectroscopy and atomic force microscopy. Wettability of the oxidized thin films was investigated by water droplet contact angle measurement. The contact angle of SiO_xC_y(− H) films are decreased from 63° to below 10° within a second by oxidation. Correlation between the elemental composition and the contact angle were discussed. The effects of oxidation duration and discharge generation voltage on the composition and surface morphology of the film were investigated.     

Growth process of CuO(1 1 1) and Cu2O(0 0 1) thin films on MgO(0 0 1) substrate under metal-mode condition by reactive dc-magnetron sputtering

The growth process of CuO and Cu₂O thin films on MgO(0 0 1) substrates by reactive dc-magnetron sputtering was studied by reflection high-energy electron diffraction (RHEED) and atomic-force microscopy (AFM). The RHEED pattern and AFM image showed that (1) three-dimensional Cu(0 0 1) islands grew on MgO under the nonreactive sputtering condition, (2) CuO(1 1 1) was deposited layer by layer on MgO at 400 °C under the reactive sputtering condition, and (3) the film deposited at 600 °C in the initial growth stage was composed of three-dimensional Cu islands because O₂ gas could not be incorporated into them due to the low sticking coefficient of O₂ on MgO under the reactive sputtering condition. The layer-by-layer CuO(1 1 1) thin-film growth process is discussed from the viewpoint that Cu and oxygen species are supplied in stoichiometry onto the MgO substrate to form CuO thin-film crystals while maintaining minimum interfacial energy between CuO and MgO.     

Effects of oxygen pressure on the growth of pulsed laser deposited ZnO films on Si(0 0 1)

ZnO thin films were prepared on Si(0 0 1) substrates using a pulsed laser deposition (PLD) technique and then their growth and properties were investigated particularly as a function of ambient O₂ pressure during film growth. It was found that the microstructure, crystallinity, orientation and optical properties of the films grown are strongly dependent on the O₂ pressures used. Completely c-axis oriented ZnO films are grown in a low O₂ pressure regime (5×10⁻⁴-5×10⁻² Torr), whereas a randomly oriented film with a much lower crystallinity and a rougher grained-surface is grown at an O₂ pressure of 5×10⁻¹ Torr. This deterioration in film quality may be associated with the kinetics of atomic arrangements during deposition. Our results suggest that ambient O₂ pressure is an important processing parameter and should be optimized in a narrow regime in order to grow a ZnO film of good properties in PLD process.     

Non-thermal plasma for oxidation of gaseous products originating from thermal treatment of wastes

A plasma reactor generating non-equilibrium plasma in a gliding discharge was applied as one of the modules of a new laboratory device for hazardous waste destruction. The degradation process of wastes containing an organic part was carried out in two stages. The first one consisted of thermal decomposition of wastes in an inert atmosphere (pyrolysis process in argon flow—the gaseous products are formed from the organic part of wastes). In the second stage products of pyrolysis were oxidized in a gliding discharge. This work was focused on study of the parameters influencing the oxidation process of gases originating from pyrolysis and flowing into the plasma reactor. Oxygen was introduced into the plasma reactor simultaneously with the gases. We investigated two factors significantly affecting the oxidation process: (a) the oxygen concentration in the initial mixture of argon and oxygen and (b) the total flow of argon and oxygen gases. The best oxidation efficiency of the processing gases in the plasma was reached when the oxygen content did not exceed 20% and when the total flow of argon and oxygen was low enough not to cause disturbances of functioning of the plasma reactor.     

Oxygen treatment effects on properties of MgO thin films grown on single-crystalline diamond (1 0 0)

Oxygen post-treatment effects on the electronic structure and electrical properties of MgO films grown on homoepitaxial single-crystalline (1 0 0) diamond have been studied. MgO films examined were deposited at room temperature (RT) using an electron beam evaporator and were subsequently either annealed at 573-773 K for 12 h in oxygen ambient or treated by O₂ plasma for 10-40 min. RT resistivities remarkably increased after the O₂ annealing and plasma treatment, indicating that the post treatments play an essential part on the formation and positioning of bandgap states. Cathodoluminescence (CL) spectra had a broad band feature in a wavelength region from 360 to 530 nm, which were decomposed to several peaks originating mainly from the oxygen-vacancy-related F and F⁺ centers and the interstitial vacancies of MgO film. A prominent rectifying behavior of I-V property was observed for a Au/MgO/p-diamond layered structure. Based on temperature dependences of the electrical properties in a temperature region from RT to 600 K, the electrical conduction mechanism in the MgO films is discussed in relation to polaron-related conduction as well as the ionic conduction.     

Surfactant-induced layered growth in homoepitaxy of Fe on Fe(100)-c(2 × 2)O reconstruction surface

In this study, the effects of several surfactants (Pb, Bi, and Ag) on the homoepitaxial growth of Fe(100) were studied and compared. The reflection high-energy electron diffraction measurements clearly reveal that these surfactants enhance the layer-by-layer growth of Fe on an Fe(100)-c(2 × 2)O reconstruction surface. The dependence of growth on the surfactant layer thickness suggests that there exists a suitable amount of surfactant layer that induces a smoother layer-by-layer growth. Comparisons between the atomic force microscopy images reveal that the root-mean-square surface roughness of Fe films mediated by Pb and Bi surfactants are considerably smaller than those of the films mediated by Ag surfactant. The Auger electron spectra show that Pb and Bi segregate at the top of the surface. It has been concluded that Pb and Bi are effective surfactants for enhancing layer-by-layer growth in Fe homoepitaxy. Ag has the same effect, but it is less efficient due to the weak surface segregation of Ag.     

Preparation and characterization of La-doped Ba(1 − x)SrxTiO3 powders and thin films

Ba_(1 − x)Sr_xTiO₃ powders with different Ba/Sr ratios (x = 0.10, 0.25, 0.40, 0.55, 0.70) and La-doped Ba_0.9Sr_0.1TiO₃·yLa powders (y = 0.002, 0.004, 0.006, 0.008, 0.010) have been prepared by sol-gel technology using dehydrated barium-acetate, strontium-carbonate, lanthanum-nitrate, and titanium-isopropoxide as raw materials. The experimental results show that the dielectric properties of Ba_(1 − x)Sr_xTiO₃ powders depend on the Ba/Sr ratios. When the Sr fraction is 0.10, the dielectric constant is relatively higher and the dielectric loss is relatively lower, which are more than 2000 and less than 2.0 × 10^− 2 at 1000 Hz, respectively, the most important is that this kind of powder has better frequency stability. La-doping can increase the dielectric constant distinctly, but the dielectric loss can also be increased. Their dielectric properties at 1.0 × 10³ Hz are better than those at 1.0 × 10⁵ Hz. At 1.0 × 10³ Hz the dielectric constant is much higher, while the dielectric loss is much lower. The dielectric constant of different La-doping contents is nearly 3.5 × 10⁴ and the dielectric loss is less than 0.20 when La fraction is 0.008. The La-doped BST sample also has better frequency stability, especially at high frequency. La-doped BST thin films are successfully deposited on mild steel substrates by using plasma spray system with suspension precursors of Ba_0.90Sr_0.10TiO₃·0.8La powders. The XRD patterns of Ba_0.90Sr_0.10TiO₃ and Ba_0.90Sr_0.10TiO₃·0.8La powders are almost the same. No new peaks appear after La-doping, but the peaks move slightly to a larger degree, which indicates that the element La has entered the lattice of the Ba_0.90Sr_0.10TiO₃ and has made the constant of the crystal cell reduce. The XRD pattern of the thin films is just like that of the Ba_0.90Sr_0.10TiO₃·0.8La powders except a peak corresponding to Fe substrate. The SEM results show that the thin films have a uniform and smooth surface. The morphology of cross-section shows a columnar grain structure indicating smooth surface and uniform thickness of the film. The thickness of the film is about 15 um. The thin films obtained are expected to be prospective material for applications in tunable microwave devices.     

Double electrodeposition and heat treatment process for the fabrication of superconducting oxides on the intensified {1 1 3} <1 2 1> Ag substrate

The Tl-1223 coated conductor (Tl_0.8Pb_0.2Bi_0.2Sr_1.8Ba_0.2Ca_2.2Cu₃O_δ) was synthesized by using electrodeposition on the intensified {1 1 3} <1 2 1> Ag substrate applying the new method of the repeating electrodeposition/heat treatment. The films were fabricated conducting the first electrodeposition and then heat treatment, after that the second electrodeposition on the first electrodeposition/heat treatment coated conductors. The second electrodeposition on the first electrodeposition/heat treatment/the first electrodeposition/heat treatment coated conductor showed the better quality of the Tl-1223 phases than that of the first electrodeposition/heat treatment coated conductor, showing more compact and dense grains on the films. The thin Tl-1223 films caused by the thinning process were discussed by considering the properties of Tl and the epitaxial growth aspects. The purer Tl-1223 grains obtained at the double electrodeposition/heat treatment are due to the growth from Tl-1223 grains already synthesized during the first electrodeposition/heat treatment, facilitating the epitaxial growth easier than that of the Ag substrate. The second electrodeposition process was successfully performed, obtaining 1.9 × 10⁵ A/cm² of J_c at 0 T at 10 K.     

Thermal stability and transport studies of (100 − 2x)TeO2-xAg2O-xWO3 (7.5 ≤ x ≤ 30) glass system

Differential scanning calorimetry (DSC), infrared (IR) and direct current (DC) conductivity studies have been carried out on (100 − 2x)TeO₂-xAg₂O-xWO₃ (7.5 ≤ x ≤ 30) glass system. The IR studies show that the structure of glass network consists of [TeO₄], [TeO₃]/[TeO₃₊₁], [WO₄] units. Thermal properties such as the glass transition (T_g), onset crystallization (T_o), thermal stability (ΔT), glass transition width (ΔT_g), heat capacities in the glassy and liquid state (C_pg and C_pl), heat capacity change (ΔC_p) and ratios C_pl/C_pg of the glass systems were calculated. The highest thermal stability (237 °C) obtained in 55TeO₂-22.5Ag₂O-22.5WO₃ glass suggests that this new glass may be a potentially useful candidate material host for rare earth doped optical fibers. The DC conductivity of glasses was measured in temperature region 27-260 °C, the activation energy (E_act) values varied from 1.393 to 0.272 eV and for the temperature interval 170-260 °C, the values of conductivity (σ) of glasses varied from 8.79 × 10⁻⁹ to 1.47 × 10⁻⁶ S cm⁻¹.     

Viscoplastic behavior of a FeCrAl alloy for high temperature steam electrolysis (HTSE) sealing applications between 700 °C and 900 °C

High temperature steam electrolysis (HTSE) is one of the most promising technologies for the industrial production of hydrogen. However one of the remaining problems lies in sealing at high temperature. The reference solution is based on glass seals which presents several drawbacks. That explains why metallic seals are under development. The expected seal will be submitted to creep under low stresses between 700 °C and 900 °C, possibly involving complex loading and thermal history. The candidate material investigated in this work is a FeCrAl (OC404, Sandvik) supplied as a 0.3 mm thick sheet. The ability of this material to develop a protective layer of alumina was studied first, as well as grain size growth during thermal ageing. Creep and tensile tests were performed between 700 °C and 900 °C to determine its mechanical properties. This database was used to propose and identify an elasto-viscoplastic behavior for the material. Creep was described by the Sellars-Tegart law. This law was then used to simulate and predict creep indentation tests performed in the same range of temperatures.     

Low temperature (< 100 °C) deposited P-type cuprous oxide thin films: Importance of controlled oxygen and deposition energy

With the emergence of transparent electronics, there has been considerable advancement in n-type transparent semiconducting oxide (TSO) materials, such as ZnO, InGaZnO, and InSnO. Comparatively, the availability of p-type TSO materials is more scarce and the available materials are less mature. The development of p-type semiconductors is one of the key technologies needed to push transparent electronics and systems to the next frontier, particularly for implementing p-n junctions for solar cells and p-type transistors for complementary logic/circuits applications. Cuprous oxide (Cu₂O) is one of the most promising candidates for p-type TSO materials. This paper reports the deposition of Cu₂O thin films without substrate heating using a high deposition rate reactive sputtering technique, called high target utilisation sputtering (HiTUS). This technique allows independent control of the remote plasma density and the ion energy, thus providing finer control of the film properties and microstructure as well as reducing film stress. The effect of deposition parameters, including oxygen flow rate, plasma power and target power, on the properties of Cu₂O films are reported. It is known from previously published work that the formation of pure Cu₂O film is often difficult, due to the more ready formation or co-formation of cupric oxide (CuO). From our investigation, we established two key concurrent criteria needed for attaining Cu₂O thin films (as opposed to CuO or mixed phase CuO/Cu₂O films). First, the oxygen flow rate must be kept low to avoid over-oxidation of Cu₂O to CuO and to ensure a non-oxidised/non-poisoned metallic copper target in the reactive sputtering environment. Secondly, the energy of the sputtered copper species must be kept low as higher reaction energy tends to favour the formation of CuO. The unique design of the HiTUS system enables the provision of a high density of low energy sputtered copper radicals/ions, and when combined with a controlled amount of oxygen, can produce good quality p-type transparent Cu₂O films with electrical resistivity ranging from 10² to 10⁴ Ω-cm, hole mobility of 1-10 cm²/V-s, and optical band-gap of 2.0-2.6 eV. These material properties make this low temperature deposited HiTUS Cu₂O film suitable for fabrication of p-type metal oxide thin film transistors. Furthermore, the capability to deposit Cu₂O films with low film stress at low temperatures on plastic substrates renders this approach favourable for fabrication of flexible p-n junction solar cells.     

Palladium (+ 2) reduction: A key step for the electroless Ni metallization of insulating substrates by a tin-free process

The tin-free electroless metallization process developed in our laboratory consists in attaching the Pd(+ 2)-based catalyst on surfaces which were previously grafted with nitrogen-bearing groups. The so-functionalized surfaces lead to the formation of true covalent bonds between palladium and nitrogen-based species. In this work, the different steps of the process are studied, namely: (i) the grafting of nitrogen-bearing groups on an insulating surface by various processes already used in our laboratory, (ii) the seeding of the surface with Pd(+ 2) species, (iii) the reduction of Pd(+ 2) to Pd(0) by different routes (this step is needed due to the use of industrial plating baths which contain strong stabilizers that prevent or delay plating), (iv) the Ni metallization using low- and high-phosphorus plating baths. Phosphorus which originates from the plating bath reducer is partly incorporated in the Ni films and creates some stresses. Adhesion of the resulting films is evaluated by the Scotch® tape test. The main parameters responsible for adhesion and governing the characteristics of the Ni film/substrate interface are: the nature of the substrate, the Pd(+ 2) reduction route and the phosphorus content of the Ni plating bath. All these parameters influence the amount of stresses generated both at the metal/substrate interface and within the film.     

Low temperature (~ 250 °C) layer exchange crystallization of Si1 − xGex (x = 1-0) on insulator for advanced flexible devices

Low-temperature (~ 250 °C) layer exchange crystallization of poly-Si_1 − xGe_x (x = 1-0) films on insulators has been investigated for realization of advanced flexible devices. We propose utilization of Au as catalyst to enhance the crystallization at low temperatures. By annealing (~ 250 °C, 20 h) of the a-Si_1 − xGe_x (x = 1-0)/Au stacked structures formed on insulating substrates, the SiGe and Au layers exchange their positions, and Au/poly-SiGe stacked structures are obtained. The Ge fractions of the obtained poly-SiGe layers are identical to that of the initial a-SiGe layers, and there is no Si or Ge segregation. This low temperature crystallization technique enables poly-SiGe films on plastic substrates, which are essential to realize advanced flexible devices.     

Preparation and magnetic properties of SrFeO3−x (x = 0.25 ∼ 0.5) using RF magnetron sputtering optimized through sputtering plasma analysis

We investigated the preparation and the magnetic properties of SrFeO_3−x using conventional RF magnetron sputtering. Photoluminescence spectrum analyses of the sputtering plasma revealed that the film composition was changed even using the stoichiometry target. After fixing the composition of the targets from an intensity ratio of the Sr and Fe plasma, the polycrystalline SrFeO_3−x films with different oxygen deficiencies were able to prepare using the various sputtering gas ratio. The magnetic properties of the samples were also changed with changing the sputtering gas ratio. This magnetic property change was likely due to the suppression of the oxygen deficiency in the film.     

Resistivity of sub-50 nm copper lines epitaxially grown on Si(100) substrate

We report the creation of 50 nm thick epitaxial Cu lines with line widths ranging from 20 nm to 120 nm on Si(100) substrate using a combination of electron beam lithography, oblique angle deposition, and lift-off techniques. The increase of measured resistivity as a function of decreasing line width is dominated by surface scattering that is completely diffuse. The measured resistivity of the 20 nm wide lines is ~ 4 μΩ-cm.     

DFT study of the coverage effects for Al adsorption on Si(1 1 1) surfaces

Density functional theory (DFT) calculations have been carried out to investigate the interactions between the Si(1 1 1) surface and the Al adatoms. Different adsorption sites and coverage effects have been considered. For low Al coverage, the threefold-filled adsorption site is the most energy favored site. With the increase of Al coverage, adatom-adatom interactions become increasingly important and Al atomic chains or clusters are formed. With the clean Si(1 1 1) surface of metallic feature, we found that 1/3 ML Al adsorption leads to a semiconducting surface. The results for the electronic behavior suggest the formation of the polarized covalent bonding between the Al adatom and the Si(1 1 1) surface.