Ar Gas Atmosphere Research Articles

Influence of Aging, Poisoning and Residual Charges on the Gasochromic Behavior of WO3 Thin Films

Thin films of WO3 were deposited in a mixed atmosphere of O2 and Ar gas from a high purity target of 99.99 % tungsten using reactive DC-sputtering technique. Pt catalyst was sputtered on top of the WO3 films from a high purity target of 99.99 % platinum in Ar atmosphere. Coloration takes place in hydrogen gas and bleaching in oxygen gas. During the Coloration/bleaching process several optical and electrical parameters were determined. The influence of the aging time and poisoning in air was investigated, and the residual charges resulting from the coloring/bleaching processes were discussed. It was found that gasochromic coloration velocity decreases with increasing aging time.

Influence of Aging, Poisoning and Residual Charges on the Gasochromic Behavior of WO3 Thin Films

Thin films of WO3 were deposited in a mixed atmosphere of O2 and Ar gas from a high purity target of 99.99 % tungsten using reactive DC-sputtering technique. Pt catalyst was sputtered on top of the WO3 films from a high purity target of 99.99 % platinum in Ar atmosphere. Coloration takes place in hydrogen gas and bleaching in oxygen gas. During the Coloration/bleaching process several optical and electrical parameters were determined. The influence of the aging time and poisoning in air was investigated, and the residual charges resulting from the coloring/bleaching processes were discussed. It was found that gasochromic coloration velocity decreases with increasing aging time.

Dependence of the Structural and Electrical Properties of Co-Sputtered Zn-Doped ITO Thin Films on the Composition and Oxygen Partial Pressure

Zn-In-Sn-O films were prepared at room temperature by combinatorial RF-magnetron co-sputtering system. The cationic contents of the films were varied using a compositionally combinatorial technique. The effects of the oxygen partial pressure and film compositionon the structural and electrical properties were investigated. The Zn-In-Sn-O films deposited at Ar gas atmosphere showed an amorphous phaseirrespective of the film composition. However, the amorphous Zn-In-Sn-O films with a Zn content below 30.0 at% were converted into a bixbyite type-ITO polycrystalline phase with an increase in the oxygen partial pressure. The resistivity, carrier concentration, and Hall mobility were strongly affected by the oxygen partial pressure and chemical composition of the film. At sufficiently high carrier densities above 5 × 10 18 cm ?3 , the conduction behavior of amorphous Zn-In-Sn-O film changes from thermally activated to degenerate band conduction accompanied with high mobility.

Shadowed off-axis production of Ge nanoparticles in Ar gas atmosphere by pulsed laser deposition: Morphological, structural and charge trapping properties

In this work, a novel customized shadowed off-axis deposition set-up is used to perform an original study of Ge nanoparticles (NPs) formation in an inert Ar gas atmosphere by pulsed laser deposition at room temperature varying systematically the background Ar gas pressure (Pbase(Ar)), target–substrate distance (d) and laser repetition rate (f). The influence of these parameters on the final NPs size distributions is investigated and a fairly uniform droplets-free and non-agglomerated NPs distribution with average height 〈h〉=2.8±0.6nm is obtained for optimized experimental conditions (Pbase(Ar)=1mbar; d=3cm; f=10Hz) with a fine control in the NPs density (from 3.2×109cm−2 to 1.1×1011cm−2). The crystalline quality of as-deposited NPs investigations demonstrate a strong dependence with the Ar gas pressure and a crystalline to amorphous phase volume fraction χc>50% is found for Pbase(Ar)=2mbar. The NPs functionality for charge trapping applications has been successfully demonstrated by capacitance–voltage (C–V) electrical measurements.

Effect of Silicon Content on Wear Behavior of Heat Treated Powder Metallurgy Steels

AbstractThree different steel compositions with 1, 3 and 5 mass% Si were prepared using atomized iron (ASC.100.29) and 0.35 mass% natural graphite powders. The mixed powders were cold pressed at 700 MPa and sintered at 1200 °C for 30 min under pure Ar gas atmosphere. Some of the sintered specimens was quenched from 850 °C and then tempered at 100 °C for 1 h. The other sintered specimens were annealed at intercritical heat treatment temperature of 750 °C for 10 min and rapidly water-quenched. The experimental results showed that in as-sintered specimens inhomogeneously dispersed typical pearlitic structure in the ferrite matrix formed and its amount decreased with increasing Si content. In intercritically annealed specimens, the microstructure obtained was a mixture of partially transformed martensite and ferrite + pearlite. In quenched plus tempered specimens, beside tempered martensite, ferritic structure formed and its amount increased with increasing Si content. The wear tests were carried out under dry sliding conditions using a pin-on-disk type machine at constant load, speed and sliding distance. It was seen that, in all specimens, the friction coefficient and the wear rate both increased with increasing Si content. The increase of these values was less in the heat treated specimen than the as-sintered specimen.

Controllable synthesis of single-, double- and triple-walled carbon nanotubes from asphalt

Single-, double- and triple-walled carbon nanotubes (SWNTs, DWNTs and TWNTs) have been controllably synthesized by an arc discharge method using asphalt as carbon source. The morphology and structure of three kinds of products synthesized with Fe as catalyst were characterized by scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), Raman spectroscopy and energy dispersive X-ray spectroscopy (EDX). It was found that different buffer gases strongly affect the number layers in the synthesized nanotubes. In the He gas atmosphere only SWNTs were found to be synthesized by arc discharge in contrast to the case in Ar gas atmosphere in which only TWNTs were formed. In N2 atmosphere both SWNTs and DWNTs were synthesized. Our findings indicate that asphalt is a suitable industrial carbon source for the growth of different type nanotubes.

Mixture formation of ErxYb2-xSi2O7 and ErxYb2-xO3 on Si for broadening the C-band in an optical amplifier

Thin films composed of polycrystalline ErxYb2-xO3 grains and crystalline ErxYb2-xSi2O7 layers were formed on a Si(111) substrate by RF - sputtering and subsequent thermal annealing in Ar gas ambient up to 1100 °C. The films were characterized by synchrotron radiation grazing incidence X-ray diffraction, cross-sectional transmission microscopy, energy dispersive X-ray spectrometry and micro photoluminescence measurements. In the annealed film of 950 °C it is observed that the I15/2 - I13/2 Er3+photoluminescent transition exhibits simultaneously maximum intensity and peak width at room temperature. This effect satisfies the requirements for broadening the C-band of an optical amplifier on Si.

Investigation of sintering behavior of octanethiol-coated copper nano ink under various atmospheres

In this study, octanethiol-coated, nonoxidized 10wt.% copper (Cu) nano ink was examined under different gas atmospheres during sintering. The Cu nanoparticles, 100±10nm in size, were coated with 1-octanethiol using a vapor self-assembled multilayer coating technique, under ultra-high vacuum and variable atmospheric conditions. 10μL of the octanethiol-coated (surface-modified) nano ink was dropped onto a glass substrate to form a Cu pattern. The Cu pattern was sintered at 350°C in a tube furnace under various gas atmospheres: hydrogen gas (H2), ammonia (NH3), an Ar/H2 gas mixture (Ar 95% : H2 5%), and Ar gas. The effect of sintering in different gas atmospheres on the octanethiol-coated Cu thin-film patterns was investigated by high-resolution transmission electron microscopy, scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), and resistivity analysis. The resistivity of the fabricated thin films after sintering was 5.8×10−6, 3.82×10−5, 1.15×10−3, and 8.64×10−3Ωcm for the H2, NH3, Ar/H2 gas mixture, and Ar gas atmospheres, respectively. The H2 atmosphere exhibited the lowest resistivity, which was close to that observed for bulk Cu. XPS analysis confirmed that the H2 and NH3 atmospheres completely removed the octanethiol coating from the Cu surface, due to their high reactivity. Additionally, the grain growth observed in the SEM images under H2 conditions was significantly better than that observed for the other gases. The technique used in this study to produce octanethiol-coated Cu nano ink provides an effective, environmentally friendly fabrication method for the electronic printing of materials.

Compaction of Ti–6Al–4V powder using high velocity compaction technique

High velocity compaction technique was applied to the compaction of pre-alloyed, hydride–dehydride Ti–6Al–4V powder. The powder was pressed in single stroke with a compaction speed of 7.10–8.70ms−1. When the speed was 8.70ms−1, the relative density of the compacts reaches up to 85.89% with a green density of 3.831gcm−3. The green samples were sintered at 1300°C in Ar-gas atmosphere. Scanning electron microscope (SEM) was used to examine the surface of the sintered samples. Density and mechanical properties such as Vickers micro hardness and bending strength of the powder samples were investigated. Experimental results indicated that with the increase in impact force, the density and mechanical properties of the compacts increased. The sintered compacts exhibited a maximum relative density of 99.88% with a sintered density of 4.415gcm−3, hardness of 364–483 HV and the bending strength in the range of 103–126.78MPa. The springback of the compacts decreased with increasing impact force.

Growth of preferentially c-axis oriented hydroxyapatite thin films on Si(1 0 0) substrate by electron-cyclotron-resonance plasma sputtering

We deposited hydroxyapatite (HAp) thin films on Si(100) substrates by means of electron cyclotron resonance (ECR) plasma sputtering from a HAp target and characterized their structural properties by X-ray diffraction (XRD) and Fourier transform infrared absorption spectroscopy. Deposition in the presence of an H2O vapor at room temperature incorporated H2O and OH species in the deposited films. Post-annealing in an O2 ambient self-organized OH− and PO43− functional groups in HAp crystals. The XRD patterns revealed randomly orientation when the annealing temperature ranged between 700 and 900°C. In contrast, preferentially c-axis-oriented HAp crystals nucleated after prolonged annealing at 550–600°C. The possible scenario for the preferred orientation is that C-plane terminated HAp crystallites were initially created in the near-surface region, and the following crystallization proceeded exclusively on the seed surface. After post annealing in a vacuum or in an Ar gas ambient at 900°C, films were reduced into tricalcium phosphate, increasing photoabsorption in the infrared range.

Formation of graphene nano-particle by means of pulsed discharge to ethanol

Nano-graphene particles (NGPs) were deposited by a pulsed discharge (PD) to ethanol in Ar gas atmosphere of about 600 Torr. The frequency (f) of the PD was changed from 1 to 5 kHz at constant duty ratio of 20%. Evaluations of the NGPs were performed with scanning electron microscope, high resolution transmission electron microscope, and Raman spectra. When f was changed from 1 to 5 kHz, domain size of the NGPs was decreased from 34 to 19 nm. The number of the graphene layers (GLs) was decreased from about 20 to 4, though the number of GLs was scattered from 24 to 2. These results show that the domain size and the number of the GLs can be controlled with f of the PD.

Effect of gas ambient and varying RF sputtering power for bandgap narrowing of mixed (ZnO:GaN) thin films for solar driven hydrogen production

The ZnO and mixed (ZnO:GaN) thin films are synthesized by (RF) magnetron sputtering in Ar and mixed O2 and N2 gas ambient at 100 °C, followed by post-annealing at 500 °C in ammonia for 4 h. The mixed (ZnO:GaN) thin films deposited under Ar gas ambient failed to reduce the bandgap, whereas (ZnO:GaN) thin films grown under mixed O2 and N2 gas ambient showed bandgap reduction. The (ZnO:GaN) films deposited under mixed O2 and N2 gas exhibited enhanced crystallinity, with shifting the optical absorption into the visible light regions. The bandgap reduction in mixed (ZnO:GaN) thin films is realized by varying the RF power. As a result, mixed (ZnO:GaN) films grown under mixed O2 and N2 showed higher photocurrents than the mixed (ZnO:GaN) thin films deposited under Ar gas ambient. Our results indicate that reduced bandgap with enhanced PEC response can be attained using the appropriate gas ambient and by varying the RF power using mixed (ZnO:GaN) films.

Preparation of Cobalt Nanofibres by Means of Mild Thermal Precipitation and Thermal Decomposition Process

Abstract Through a mild thermal precipitation and aging process, hydrated cobalt oxalate nanorods were synthesized using CoSO3 and (NH4)2C2O4·H2O as raw materials at the reaction and aging temperature of 65 °C. Afterwards, the metal cobalt nanofibres were prepared by decomposition of cobalt oxalate nanorods precursor in Ar gas atmosphere. The composition and morphology of products were characterized by means of atomic absorption spectrometer (AAS), organic elemental analyzer (OEA), Fourier transform infrared spectroscopy (FT-IR), thermogravimetry analysis and derivative thermogravimetry (TGA-DTG), the X-ray diffraction (XRD), and scanning electron microscope (SEM). The results demonstrate that the product is hydrated cobalt oxalate, and the chemical formula CoC2O4·3H2O is confirmed. The sizes of the cobalt oxalate nanorods as-prepared are about 0.2-0.4 μm in diameter, and 1.0-5.0 μm in length; the metal nanofibres prepared via decomposition process of hydrated cobalt oxalate nanorods are about 0.2 μm in diameter, and 1.0-5.0 μm in length.

A shadowed off-axis production of Ge nanoparticles in Ar gas atmosphere by pulsed laser deposition

In this work, we report on the production of Ge nanoparticles (NPs) in an inert Ar gas atmosphere by pulsed laser deposition (PLD) at room temperature (RT). The direct deposition of energetic particles/droplets resulting from the ablation process of the target material has been avoided by using an original and customized off-axis shadow mask (shadowed off-axis) deposition set-up where the NPs deposition on the substrate takes place by means of scattering between the NPs formed in the vapor phase and the background Ar atoms. It is found that the Ar gas pressure parameter has a relevant role in the crystallization process, with better crystallinity obtained as the background Ar pressure is raised for the given experimental conditions.

Fabrication and Structural and Optical Characterizations of GaN Nano and Micro Structures Grown by Thermal Evaporation Method

Abstract. Gallium Nitride (GaN) nano and micro structures were grown on different substrates, such as ceramic boat and alumina plate using thermal evaporation method with commercial GaN powder under the flow of Argon (Ar) gas atmosphere. Micro structural studies by scanning electron microscopy (SEM) revealed the role of different substrates in the nucleation of the GaN nano and micro wires and ribbons. Additional structural and optical characterizations were performed using energy-dispersive X-ray spectroscopy (EDX) and photoluminescence (PL) spectroscopy. Results indicated that the nanowires and nanoribbons are of single-crystal hexagonal GaN and are more and less orderly in their growth with different substrates. The quality of growth of the GaN nanowires and nanoribbons for different substrates is highly dependent on the lattice mismatch between the nanowires and their substrates and it also depends on the conditions of the growth.

Optimization of fabrication conditions of MgB2/Fe superconducting tapes using response surface methodology

We have optimized fabrication conditions of MgB2/Fe superconducting monofilament tapes fabricated using ex-situ powder-in-tube method without any intermediate annealing. Influences of three effective parameters (annealing temperature, annealing time and argon (Ar) gas atmosphere pressure during the heat treatments) on the transport critical current densities (Jc) were investigated. The samples were characterized using X-ray diffraction, scanning electron microscope, energy dispersive X-ray spectrometer, optical microscope, critical transition temperature and Jc measurements. Response surface methodology was used to optimize the conditions for the maximum Jc of the samples and to understand the significance and interaction of the factors affecting Jc. 3-level-3-factor central composite design was employed to evaluate the effects of the fabrication conditions parameters such as annealing temperatures (850–950 °C), annealing times (30–120 min.) and Ar pressures (1–5 bars) on Jc of the samples. Based on the analysis of ridge max, the optimum fabrication conditions were as follows: annealing temperature 948 °C, annealing time 58 min. and Ar pressure 3 bars.

PIT Processed ${\rm MgB}_{2}$ Thin Wires Sheathed With Stainless Steel

MgB <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> superconducting thin wires sheathed with stainless steel (SS) have been prepared by in-situ powder-in-tube (PIT) process. Using Magnesium hydride MgB <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> and amorphous B powders, SS sheathed MgB <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> thin wires have been fabricated through drawing to form the round wires of 0.20 mm ~ 0.10 mm in diameter. The SS sheath of 0.1 mm in diameter was hardened to be a Vickers hardness of around 600 HV through cold-working at room temperature without annealing. The heat treatment was performed at 630°C for 5 h in Ar gas atmosphere. The SS sheath recovered the hardness of 400 HV after heat treatment. The MgB <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> wires show the critical temperature (T <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> ) of around 35 K in onset and sharp transition of 2 K. The transport critical current (I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> ) at 4.2 K and self-field are 40 A and 8 A for the MgB <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> thin wires of 0.2 mm and 0.1 mm in diameter, respectively. The I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> values correspond to the critical current density (J <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> ) of around 4,000-5,000 A/mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> . The present MgB <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> thin wires with low thermal conductivity are promising as level sensors for liquid hydrogen and current leads with small heat leakage.

Control of Void Formation in 4H-SiC Solution Growth

Void formation in 4H-SiC crystals grown from solution has been investigated by secondary ion mass spectrometry and Raman scattering. It becomes clear that ambient Ar gas is filled in voids and the solvent (Si) partially remains. The result indicates that Ar dissolved in the solvent vaporizes and forms bubbles. The trapped bubbles at the crystal growth front are considered to be incorporated in the growing crystal as voids. We also have developed following methods for suppression of the void formation; (1) dipping seed crystals so that the growth front faces upward, (2) growth under He atmosphere, and (3) the high temperature treatment of the solvent before crystal growth.

Enhancement of Jc–B properties for binary and carbon-doped MgB2 tapes by hot pressing

The effect of the hot pressing method on in situ powder-in-tube-processed MgB2/Fe tapes was studied. The tapes doped with and without nanosized C are hot-pressed at 100 MPa and 650–800 °C for 1–5 h in a flowing Ar gas atmosphere. Compared to the non-hot-pressed tapes, the Jc–B property (at 4.2 K and 10 T) of pure and C-doped samples hot-pressed at 650 °C for 5 h was enhanced by a factor of 2.5 and 1.4, respectively. For hot-pressed tapes, the optimized sintering temperature is below 700 °C at 100 MPa. The enhancement of Jc performance for hot-pressed MgB2 samples is mainly attributed to the improved grain connectivity.

Gan Nanowire Growth by Thermal Evaporation Method

In this research we introduce an inexpensive method to produce highly crystalline GaN Nanowires (NWs) grown on porous zinc oxide (PZnO) using commercial GaN powder, either in argon gas or combination of nitrogen and Ar gas atmosphere, by thermal evaporation. Morphological structural studies using transmission electron microscope (TEM) and scanning electron microscopy (SEM) measurements showed the role of porosity and different gas flowing, in the alignment and nucleation of these NWs. The NWs grown under flow of mix gases have very different diameters of between 50 and 200 nm, but those which were grown in Ar gas atmosphere, have rather uniform diameter of around 50 nm. The length of the GaN NWs was uniform, (around 10 µm). Optical and structural characterizations were performed by energy-dispersive X-ray spectroscopy (EDX) and high resolution X-ray diffraction (HR-XRD). Results revealed that these NWs are of single-crystal hexagonal GaN with [oooı] and [ıoīı] growth directions for the NWs grown under Ar and mixed gas flow.