In–Ga–Zn–O thin film transistor with HfO2 gate insulator prepared using various O2/(Ar + O2) gas ratios

We have investigated the effect of the deposition of an HfO₂ thin film as a gate insulator with different O₂/(Ar + O₂) gas ratios using RF magnetron sputtering. The HfO₂ thin film affected the device performance of amorphous indium–gallium–zinc oxide transistors. The performance of the fabricated transistors improved monotonously with increasing O₂/(Ar + O₂) gas ratio: at a ratio of 0.35, the field effect mobility of the amorphous InGaZnO thin film transistors was improved to 7.54 cm²/(V s). Compared to those prepared with an O₂/(Ar + O₂) gas ratio of 0.05, the field effect mobility of the amorphous InGaZnO thin film transistors was increased to 1.64 cm²/(V s) at a ratio of 0.35. This enhancement in the field effect mobility was attributed to the reduction of the root mean square roughness of the gate insulator layer, which might result from the trap states and surface scattering of the gate insulator layer at the lower O₂/(Ar + O₂) gas ratio.     

Effect of N2 / Ar gas flow ratio on the deposition of TiN/Ti coatings on NiTi shape memory alloy by PIIID

TiN coating with a thin Ti intermediate layer was deposited on the NiTi shape memory alloy substrate using plasma immersion ion implantation and deposition technique. The effect of nitrogen to argon gas flow ratio on the surface characteristics, chemical composition and mechanical properties of the as-deposited samples were investigated. Atomic force microscopy analysis indicates that all the coatings exhibited island morphology and the average root mean square (RMS) values were determined to be 2.912, 4.152 and 4.227 nm for N₂ / Ar ratios of 1 / 3, 1 / 2 and 2 / 3, respectively. The results of XPS and X-ray diffraction show that the chemical composition, phase composition and preferred orientation of the TiN coating varied significantly with the N₂ / Ar gas ratio. Nanoindentation, scratch and wear tests results demonstrated that coatings deposited with N₂ / Ar = 1 / 2 exhibited the highest hardness and elastic modulus, good adhesion strength and excellent wear resistance.     

Studies of carbon behavior in tungsten under carbon and hydrogen mixed irradiation

The erosion of W coatings with the different content of C was investigated in Ar and Ar + H₂ plasmas. The enhanced erosion was registered in Ar + H₂ plasma for coatings containing 40 at.% of C and more, which might be owing to chemical erosion of carbon. The erosion kinetics was analyzed together with the studies of coatings microstructure, phase composition and Vicker hardness properties.The C distribution profiles in W were investigated in dependence on the redeposition rate of sputtered C and simultaneous 0.3 keV Ar⁺ ion irradiation. It is shown that C penetration depth depends on the coverage of W by C during ion irradiation. Deep C penetration was registered when W was partially covered by redeposited carbon.The computer simulation was used to extrapolate obtained results to experimental investigations performed by Ueda Y, Fukumoto M, Sawamura I, Sakizono D, Shimada T, Nishikawa M. [Fusion Eng Des 2006;81:233–9]. It is revealed that the ballistic relocation of implanted C atoms is the dominant process which explains the deep penetration of C and formation of WC compound in the near-surface region of W.     

Effect of different annealing atmospheres on crystallization and corrosion resistance of Al86Ni9La5 amorphous alloy

The effect of different annealing atmospheres (H₂, air, Ar and N₂) on precipitated phases, corrosion resistance and hardness of Al₈₆Ni₉La₅ amorphous alloy was investigated using X-ray diffraction (XRD), transmission electron microscopy (TEM), differential scanning calorimetry (DSC), thermogravimetry (TG), electrochemistry experiment and microhardness tester. During annealing at 523 K, the primary crystallized fcc-Al is independent on the annealing atmospheres. During annealing at 584 K, the final crystalline phases, i.e. fcc-Al + Al₁₁La₃ + Al₃Ni, are also independent on the different annealing atmospheres. However, during annealing at 523 K, H₂ and air can promote the eutectic crystallization process, and induce the formation of metastable Al₃Ni₂ phase. The promoting effect of different annealing atmospheres is in the order of H₂ > air > Ar > N₂. The microhardness and corrosion resistance in the 3.5 wt.% NaCl solution are improved by annealing in H₂ and air atmospheres. The property promotion caused by annealing process can be ascribed to the formation of nanocrystalline phases, which is possibly helpful to develop the alloy's application in the seawater environment.     

Sorption and diffusion of compressed carbon dioxide in polycaprolactone for the development of porous scaffolds

In this work different phenomena related to sorption of carbon dioxide in polycaprolactone (PCL) have been investigated systematically. The use of compressed carbon dioxide is discussed for obtaining porous scaffolds from this biocompatible polymer. In order to determine the plasticization effect of carbon dioxide on the degree of foaming it is necessary to discuss sorption data with respect to morphological features of the polymer at conditions nearby the melting point. The amount of carbon dioxide dissolved and the kinetics of the sorption process are found to depend strongly on temperature and pressure. The solubility takes values of up to 25 wt.% being favoured by a melting and glass transition temperature depression which can be observed along with an enhanced mass transfer rate. In general, CO₂ sorption in PCL increases linearly with pressure. When decompressing, microfoaming occurs which enhances the rate of gas release. Changes in morphology and crystallinity occur as a consequence of the pressure treatment. Compared to the melting temperature at atmospheric pressure there is a dramatic reduction observed under pressure where melting occurs already at a temperature below 40 °C. Even after pressure-treatment, there is a remaining change in melting temperature and crystallinity observed. Optimum conditions for obtaining adequate porous scaffolds of PCL are a relatively slow decompression after treatment at 17 MPa and 35 °C.     

Effect of the hydrogen and argon ion-beam treatments on the structural and electrical properties of Cz Si wafers: Comparative study

Standard commercial 0.5–40 Ω cm both n- and p-type Cz Si wafers were subjected to hydrogen or argon ion-beam treatments at 298–623 K. The ion energy was equal to 300 eV, the current density 0.15 mA/cm², the treatment duration 30 min. As follows from the experiments, the hydrogen and argon ion-beam treatments had similar influence on the electrical properties of Cz Si wafers. In the case the p-type wafers, in particular, growth of the sheet resistance and change of the thermo-EMF sign on the ion-treated surface as well as appearance of a photovoltage signal over a wide spectral range were observed, pointing to the occurrence of the surface band bending. As found from our experiments, both hydrogen and argon ion beam treatments lead to the formation of a thin (several nanometers) oxygen-containing insulating layer on the treated surface. However, the thickness of this layer and the oxygen in-depth distribution strongly depend on the regime of ion-beam treatment and type of the ions; namely in the case of H⁺ ion-beam treatment, the oxygen-containing layer is much thicker compared to that with the use of Ar⁺.     

A ZnO/PET assembly study: Optimization and investigation of the interface region

Zinc oxide thin films are deposited on polyethylene terephthalate (PET) by r.f. magnetron sputtering process from a ceramic target in oxygen–argon plasmas. Structural studies show that the thin films are highly oriented along the (0 0 2) direction of the würtzite phase when the oxygen partial pressure is lower than 0.2 Pa. The crystallinity is accentuated when the oxygen partial pressure of the sputtering gas is increased from 0 to 0.02 Pa. The composition of the films determined by Rutherford backscattering spectrometry (RBS) varies in a wide range and it is necessary to add a few amount of oxygen in the plasma composition to establish the stoichiometry. The oxygen partial pressure is found to influence also the microstructure and consequently the density of the coatings.Various cold plasmas are used to treat the polymer surface before the deposition of zinc oxide films. Wettability measurements show an increase in the polar component of the PET surface free energy whatever the nature of the plasma used for the treatment. This increase is more obvious with the carbon dioxide plasma. XPS examinations of the CO₂ plasma treated PET surface in optimized conditions show a functionalisation of the polymer surface. The carbon dioxide plasma treatments of PET surface are found to enhance the peeling energy. The adhesion level depends also on the sputtering parameters, mainly the oxygen partial pressure and the r.f. power which influence the coating properties. The zinc oxide/PET interface is studied by XPS at the different stages of deposition and at various take-off angles. AFM observations show a regular growth of zinc oxide layers with smooth topographies on PET films. The different findings obtained from C1s, O1s, Zn2p3/2, Zn3p peaks and Auger Zn L₃M_4.5M_4.5 peak are corroborated and discussed. New chemical bonds between the polymer and the further coming zinc oxide thin layer are evidenced.     

Effects of ionic surfactants on methane hydrate formation kinetics in a static system

This paper reports an experimental study of the kinetics of methane hydrate formation in the presence of ionic surfactants with equal carbon chain length, such as sodium dodecyl sulfate (SDS), dodecylamine hydrochloride (DAH), dodecyltrimethylammonium chloride (DTAC) and N-dodecylpropane-1,3-diamine hydrochloride (DN₂Cl). Methane hydrates were formed at 274 K with incipient gas pressure of 15 MPa in an unstirred isochoric/isothermal reactor containing aqueous solutions at different initial surfactant loadings. It was found that addition of DTAC had little effect on methane hydrate formation whereas SDS, DAH, and DN₂Cl had pronounced promoting effects. This result coincides with the fact that the Krafft point of DTAC is below 273 K and those of SDS, DAH, and DN₂Cl are near room temperature. At a given initial surfactant loading, the effectiveness of the surfactants for reducing the induction time of methane hydrate formation followed the order of SDS > DAH > DN₂Cl. SDS also gave higher hydrate growth rates than DAH and DN₂Cl. At 1000 and 2000 ppm, however, DN₂Cl gave slightly higher final methane uptake than SDS. It was also found that during the nucleation or induction period, addition of SDS, DAH and DN₂Cl instead of DTAC, considerably reduced methane mole fraction in the liquid phase. Possible promotion mechanisms of surfactants during the hydrate nucleation period were discussed.     

Lightweight carbon-bonded carbon fiber composites with quasi-layered and network structure

Lightweight carbon-bonded carbon fiber (CBCF) composites were fabricated with chopped carbon fibers and dilute phenolic resin solution by pressure filtration, followed by carbonization at 1000 °C in argon. The as-prepared CBCF composites had a homogenous fiber network distribution in xy direction and quasi-layered structure in z direction. The pyrolytic carbon derived from phenolic resin was mainly accumulated at the intersections and surfaces of chopped carbon fibers. The composites possessed compressive strengths ranged from 0.93–6.63 MPa in xy direction to 0.30–2.01 MPa in z direction with a density of 0.162–0.381 g cm^− 3. The thermal conductivity increased from 0.314–0.505 to 0.139–0.368 Wm^− 1 K^− 1 in xy and z directions, respectively. The experimental results indicate that the CBCF composites prepared by this technique can significantly contribute to improve the thermal insulation and mechanical properties at high temperature.     

Ultralow density carbon aerogels with low thermal conductivity up to 2000 °C

Ultralow density (0.052 g cm^?3) carbon aerogels (CAs) were prepared for ultrahigh temperature thermal insulation, and their thermal conductivities were determined by laser flash method. The CAs have a total thermal conductivity as low as 0.601 W m^?1 K^?1, which is only one third of the value for closed-pore carbon foam (CF) with a density of 0.054 g cm^?3, at 2000 °C under 0.15 MPa argon. The solid, gaseous, and radiative conductivities of the CA are all much lower than those of the CF, because of the special nanoporous and pearl-necklace nanoparticle structures of the CA. The ultralow density CA clearly demonstrates its great potentials as thermal insulations for extreme applications.     

Transmission electron microscopy study of carbon nanophases produced by ion beam implantation

The formation of carbon nanocrystals, produced by ion implantation of carbon ions into fused SiO₂ substrates, followed by 1 h thermal annealing at 1000 °C, in an Ar + 5% H atmosphere has been studied. Combined high-resolution transmission electron microscopy (HRTEM) and selected area electron diffraction (SAED) have been employed for structural characterization of carbon nanophases embedded in the quartz substrate. The dependence of grain size and sample morphology of the carbon nanophases on implantation dose was studied. The carbon nanocrystals formed by the implantation for a dose of 1 × 10¹⁶ C/cm² at 320 keV have been identified as a mixture of c-diamond nanophase and a modified diamond nanophase known as n-diamond. For a higher implantation dose, 5 × 10¹⁶ C/cm², besides n-diamond, another solid carbon nanophase was observed, with a structure known as i-carbon. Following the highest implantation dose 1 × 10¹⁷ C/cm² the sample contained the i-carbon nanophase only. A least-square refinement of SAED patterns was employed for the calculation of unit-cell parameters of identified carbon nanophases.     

Highly active copper chromite catalyst produced by thermal decomposition of ammoniac copper oxalate chromate

Calcinations of a complex precursor, ammoniac copper oxalate chromate in air or argon flow produces final products of different compositions and phases, having different morphologies and textural properties following different mechanisms of decomposition depending on the ambient atmospheres. In air, oxidative decomposition of the precursor occurs in four steps and the overall process is highly exothermic, whereas the process completes in two steps only in argon, preventing oxidation of the products and so resulting negligible heat of decomposition. The elemental analysis and thermo-gravimetric measurements suggest the stoichiometric formula of the precursor closely approximating CuNH₃C₂O₄NH₄CrO₄. Bi-dispersed particles of CuO · CuCr₂O_4, known as Adkins' copper chromite catalyst, are obtained in air while mono-dispersed particles of Cu · CuCr₂O₄ (novel Adkins' catalyst) result in argon environment. The extraordinary performance of the novel catalyst in dehydrogenation of ethanol to acetaldehyde is associated with its unusual morphology.     

Development of CO2 Selective Poly(Ethylene Oxide)-Based Membranes: From Laboratory to Pilot Plant Scale

Membrane gas separation is one of the most promising technologies for the separation of carbon dioxide (CO₂) from various gas streams. One application of this technology is the treatment of flue gases from combustion processes for the purpose of carbon capture and storage. For this application, poly(ethylene oxide)-containing block copolymers such as Pebax^® or PolyActive™ polymer are well suited. The thin-film composite membrane that is considered in this overview employs PolyActive™ polymer as a selective layer material. The membrane shows excellent CO₂ permeances of up to 4 m³(STP)·(m²·h·bar)⁻¹ (1 bar = 10⁵ Pa) at a carbon dioxide/nitrogen (CO₂/N₂) selectivity exceeding 55 at ambient temperature. The membrane can be manufactured reproducibly on a pilot scale and mounted into flat-sheet membrane modules of different designs. The operating performance of these modules can be accurately predicted by specifically developed simulation tools, which employ single-gas permeation data as the only experimental input. The performance of membranes and modules was investigated in different pilot plant studies, in which flue gas and biogas were used as the feed gas streams. The investigated processes showed a stable separation performance, indicating the applicability of PolyActive™ polymer as a membrane material for industrial-scale gas processing.     

Effects of heat treatment on the microstructure of amorphous boron carbide coating deposited on graphite substrates by chemical vapor deposition

A two-layer boron carbide coating is deposited on a graphite substrate by chemical vapor deposition from a CH₄/BCl₃/H₂ precursor mixture at a low temperature of 950 °C and a reduced pressure of 10 KPa. Coated substrates are annealed at 1600 °C, 1700 °C, 1800 °C, 1900 °C and 2000 °C in high purity argon for 2 h, respectively. Structural evolution of the coatings is explored by electron microscopy and spectroscopy. Results demonstrate that the as-deposited coating is composed of pyrolytic carbon and amorphous boron carbide. A composition gradient of B and C is induced in each deposition. After annealing, B₄C crystallites precipitate out of the amorphous boron carbide and grow to several hundreds nanometers by receiving B and C from boron-doped pyrolytic carbon. Energy-dispersive spectroscopy proves that the crystallization is controlled by element diffusion activated by high temperature annealing, after that a larger concentration gradient of B and C is induced in the coating. Quantified Raman spectrum identifies a graphitization enhancement of pyrolytic carbon. Transmission electron microscopy exhibits an epitaxial growth of B₄C at layer/layer interface of the annealed coatings. Mechanism concerning the structural evolution on the basis of the experimental results is proposed.     

Thermally driven sign switch of static dielectric constant of VO2 thin film

Smart multifunctional materials exhibiting phase transition and tunable optical and/electrical properties provide a new direction towards engineering switchable devices. Specifically, the reversible, tunable and sign switch dielectric constants via external temperature stimuli observed in vanadium dioxide (VO₂) make it a candidate of choice for tunable and switchable technologies devices. Here we report new aspect of the metal-insulator transition (MIT) through the sign switch of the static dielectric constant ε_S of pure VO₂. As it is shown, the static dielectric constant showed an abrupt change from positive at T < 70 °C to negative at T > 70 °C. ε_S > 0 confirms the insulating phase where charges are localized while ε_S < 0 confirms the metallic phase of VO₂ where charges are delocalized. We report for the first time the tunability of the dielectric constant from a negative sign for the static dielectric constant of VO₂ thin film rarely found in real physical systems. We also demonstrate the tunability and switchability of the real and imaginary part of the dielectric constant (ε) via external temperature stimuli. More specifically, the real (ε) and Imaginary (ε) showed an abrupt thermal hysteresis which clearly confirms the phase transition.     

Heat treatment effects on the characteristics and sonocatalytic performance of TiO2 in the degradation of organic dyes in aqueous solution

The ambient sonocatalytic degradation of congo red, methyl orange, and methylene blue by titanium dioxide (TiO₂) catalyst at initial concentrations between 10 and 50 mg/L, catalyst loadings between 1.0 and 3.0 mg/L and hydrogen peroxide (H₂O₂) concentrations up to 600 mg/L is reported. A 20 kHz ultrasonic processor at 50 W was used to accelerate the reaction. The catalysts were exposed to heat treatments between 400 and 1000 °C for up to 4 h to induce phase change. Sonocatalysts with small amount of rutile phase showed better sonocatalytic activity but excessive rutile phase should be avoided. TiO₂ heated to 800 °C for 2 h showed the highest sonocatalytic activity and the degradation of dyes was influenced by their chemical structures, chemical phases and characteristics of the catalysts. Congo red exhibited the highest degradation rate, attributed to multiple labile azo bonds to cause highest reactivity with the free radicals generated. An initial concentration of 10 mg/L, 1.5 g/L of catalyst loading and 450 ppm of H₂O₂ gave the best congo red removal efficiency of above 80% in 180 min. Rate coefficients for the sonocatalytic process was successfully established and the reused catalyst showed an activity drop by merely 10%.     

Electronic structure and photoelectrical properties of Ag2In2SiSe6 and Ag2In2GeSe6

High-quality Ag₂In₂SiSe₆ and Ag₂In₂GeSe₆ single crystals have been successfully grown by the vertical Bridgman–Stockbarger method and the horizontal gradient freeze technique, respectively. For pristine and Ar⁺ ion-irradiated surfaces of the single crystals under study, X-ray photoelectron core-level and valence-band spectra have been measured. Results of these studies allow for concluding that the Ag₂In₂SiSe₆ and Ag₂In₂GeSe₆ single crystal surfaces are sensitive with respect to Ar⁺ ion-irradiation. In particular, Ar⁺ ion-bombardment with energy of 3.0 keV during 5 min at an ion current density of 14 μA/cm² has induced some modification in top surface layers leading to an increase of content of In atoms in the layers. Comparison on a common energy scale of the X-ray emission Se Kβ₂ bands representing energy distribution of the Se 4p states and the X-ray photoelectron valence-band spectra reveal that the main contribution of the valence Se p states occur in the upper portion of the valence band, with also their significant contributions in other valence band regions of the Ag₂In₂SiSe₆ and Ag₂In₂GeSe₆ single crystals. In addition, for the single crystals under consideration, temperature dependences of specific dark conductivity and spectral distributions of photoconductivity have been explored. It has been established that the Ag₂In₂SiSe₆ and Ag₂In₂GeSe₆ single crystals are high-resistance semiconductors with value of the specific electrical conductivity σ ≈ 1.67 × 10^–9 Ω^–1 сm^–1 (at Т = 300 K). The both compounds are materials with p-type conductivity.     

Effect of the Ti/Na molar ratio on the acidity and the structure of TiO2 nanostructures: Nanotubes,nanofibers and nanowires

TiO₂ nanotubes were prepared by the hydrothermal treatment of TiO₂ particles with different NaOH concentrations (5, 7, 10 and 12 N) at 140 °C; afterwards, HCl was added until reaching pH 1. Both the crystalline phase and coordination of the TiO₂ nanotubes, composed principally of H₂Ti₃O₇ and H₂Ti₄O₉·2H₂O, were significantly affected by the NaOH rinsing treatment. Likewise, the surface area, pore volume and pore size of the TiO₂ nanotubes changed with the NaOH rinsing treatment. Finally, the NaOH rinsing treatment exerted a notable effect on the generation of Brönsted sites, which is shown by the following sequence: NT7 > NT10 > NT12 > NT5; meanwhile Lewis sites were only present on the NT5 sample.     

Novel load responsive multilayer insulation with high in-atmosphere and on-orbit thermal performance

Aerospace cryogenic systems require lightweight, high performance thermal insulation to preserve cryopropellants both pre-launch and on-orbit. Current technologies have difficulty meeting all requirements, and advances in insulation would benefit cryogenic upper stage launch vehicles, LH₂ fueled aircraft and ground vehicles, and provide capabilities for sub-cooled cryogens for space-borne instruments and orbital fuel depots. This paper reports the further development of load responsive multilayer insulation (LRMLI) that has a lightweight integrated vacuum shell and provides high thermal performance both in-air and on-orbit.LRMLI is being developed by Quest Product Development and Ball Aerospace under NASA contract, with prototypes designed, built, installed and successfully tested. A 3-layer LRMLI blanket (0.63 cm thick, 77 K cold, 295 K hot) had a measured heat leak of 6.6 W/m² in vacuum and 40.6 W/m² in air at one atmosphere. In-air LRMLI has an 18× advantage over Spray On Foam Insulation (SOFI) in heat leak per thickness and a 16× advantage over aerogel. On-orbit LRMLI has a 78× lower heat leak than SOFI per thickness and 6× lower heat leak than aerogel.The Phase II development of LRMLI is reported with a modular, flexible, thin vacuum shell and improved on-orbit performance. Structural and thermal analysis and testing results are presented. LRMLI mass and thermal performance is compared to SOFI, aerogel and MLI over SOFI.     

Wear characteristics of mechanically milled TiO2 nanoparticles incorporated in electroless Ni–P coatings

Nanosized TiO₂ particles have been prepared by top down approach using mechanical milling with high energy planetary ball mill at 250 rpm for different extents of time (5, 10, 20, 30 and 40 h). Electroless (EL) Ni–P–TiO₂ nanocomposite coatings were developed using alkaline bath containing milled TiO₂ nanoparticles (4 g/l). The results show that, the morphology of TiO₂ particles milled for 40 h exhibit irregular shape with a particle diameter in the range of 33–45 nm. Wear studies of the coatings with 30 μm thickness were investigated using 1, 1.5 and 2 N loads with 0.1 and 0.2 m/s rotation speeds. The Ni–P–TiO₂ nanocomposite coatings exhibit the enhanced hardness and wear resistance as compared to that of Ni–P alloy coatings. Also the composite after heat treatment at 400 °C for 1 h in argon atmosphere showed improved hardness (1010 VHN) and wear resistance (1.5e-06 mm³/N m).