O2 Environment Research Articles

Influence of O2 on the erosion-corrosion performance of 3Cr steels in CO2 containing environment.

With the introduction of O2 during oil and gas production, the erosion-corrosion rate of tubing steels increases; the objective of this report is to explore the reason for this. Erosion–corrosion experiments were performed in environments of CO2 and CO2–O2, respectively. Macrographs, microstructures, and the compositions of erosion-corrosion scales were investigated using a digital camera, scanning electron microscope (SEM), Kevex-SuperDry energy spectrometer (EDS) and X-ray diffraction (XRD). The results show that the erosion-corrosion products are composed of large FeCO3 particles and some amorphous product in the CO2 environment, while they are made up of FeCO3, Fe2O3, Fe3O4, and bits of amorphous product in the CO2–O2 environment. The interface between erosion-corrosion scales and the substrate of 3Cr steel is smooth, and Cr enrichment obviously exists in the erosion-corrosion products in the CO2 condition. However, the erosion-corrosion scale is loose and porous with little Cr enrichment in the CO2–O2 environment, which makes the protectiveness of the erosion–corrosion scale weak, and pitting corrosion occurs. The addition of O2 may destroy the protective FeCO3 scale and Cr enrichment in the erosion-corrosion scale, which may be the main reason for the decline in the level of protectiveness of the erosion-corrosion scale, making it weak in terms of preventing the corrosive medium from diffusing to the substrate.

Atomistic insight into the microexplosion-accelerated oxidation process of molten aluminum nanoparticles

Aluminum particle is a metal fuel applied the most frequently in energetic formulations; thus, it is fundamental to clarify its oxidation or combustion mechanism to make them work more effectively. By means of reactive molecular dynamics simulations, this work focuses upon the atomic details of the direct oxidation of molten Al nanoparticles (ANPs) with O2, which governs the energy release of Al fuels added in energetic materials, and clarifies the origin of the microexplosion-accelerated oxidation mechanism (MEAOM) mentioned experimentally only. The MEAOM occurs in a hot and dense O2 environment, and stems from the fast evaporation self-sustained by huge oxidation heat release, and the fast formation of hot spots and voids. High temperature, dense O2 and small particle size favor MEAOM. And the MEAOM features fast particle dispersion, fast consumption of reactants, fast heat release and pressure increase, much complex reactions and intermediates involved, and rapid formation of hot spots, voids and amorphous products. Our simulation results are in good agreement with the available experiment and simulation reports. Meanwhile, the MEAOM is complementary to the recently proposed chain-like oxide nucleation and growth mechanism at mild oxidation conditions; thereby, it is expected to establish a complete mechanism for describing the oxidation of ANPs with O2, and guide the better use of ANPs, as well as of other metal fuels.

Disentangling oxygen and water vapor effects on optoelectronic properties of monolayer tungsten disulfide.

By understanding how the environmental composition impacts the optoelectronic properties of transition metal dichalcogenide monolayers, we demonstrate that simple photoluminescence (PL) measurements of tungsten disulfide (WS2) monolayers can differentiate relative humidity environments. In this paper, we examine the PL and photoconductivity of chemical vapor deposition grown WS2 monolayers under three carefully controlled environments: inert gas (N2), dry air (O2 in N2), and humid nitrogen (H2O vapor in N2). The WS2 PL is measured as a function of 532 nm laser power and exposure time and can be decomposed into the exciton, trion, and lower energy state(s) contributions. Under continuous illumination in either O2 or H2O vapor environment, we find dramatic (and reversible) increases in PL intensity relative to the PL in an inert environment. The PL bathochromically shifts in an O2 environment and is dominated by increased trion emission and diminished exciton emission. In contrast, the WS2 PL increase in a H2O environment results from an overall increase in emission from all spectral components where the exciton contribution dominates. The drastic increases in PL are anticorrelated with corresponding decreases in photoconductivity, as measured by time-resolved microwave conductivity. The results suggest that both O2 and H2O react photochemically with the WS2 monolayer surface, modifying the optoelectronic properties, but do so via distinct pathways. Thus, we use these optoelectronic differences to differentiate the amount of humidity in the air, which we show with 0%, 40%, and 80% relative humidity environments. This deeper understanding of how ambient conditions impact WS2 monolayers enables novel humidity sensors as well as a better understanding of the correlation between TMDC surface chemistry, light emission, and photoconductivity. Moreover, these WS2 measurements highlight the importance of considering the impact of the local environment on reported results.

Accessing Basic Sites on Modified CoFe2O4 Nanoparticles: Addressing the Selective e 4 Oxidation of Benzyl Alcohol and Unraveling the Au:Pd Ratio Effects by XPS

AuPd nanoparticles have gained substantial attention due to their application in selective oxidation of alcohols. However, due to the radical nature of the oxidation of benzyl alcohol, under specific conditions, even without a catalyst, the reaction occurs and affects the selectivity of the system. Therefore, we aimed to develop a catalyst that enables the control of the oxidation leading to higher reaction selectivity. To accomplish this, we have prepared a catalytic support comprised of CoFe2O4 nanoparticles impregnated with Sr(OH)2 that presented a significant control of the reaction selectivity without any metal or external base addition. After the impregnation of AuPd nanoparticles in a specific ratio, the reaction reached a selectivity of > 99% for benzaldehyde, in 3.5 h, with a recycle regime of five runs without loss of activity and selectivity. Our results show that the judicious choice of the ratio of the metals prevents the necessity of manipulating the reaction conditions to improve the performance of the system. Additionally, studies under N2 and O2 environments, with or without water, confirmed the role of the O2 in the system. Holding all this information, we propose a possible mechanism for the prepared system.

Long non-coding RNA DANCR alleviates hypoxia-caused H9c2 cells damage through up regulation of HIF-1α

Hypoxia is an important cause of myocardial cell loss, further inducing various heart illnesses, including acute myocardial infraction (AMI). Long non-coding RNA (LncRNA) discrimination antagonising non-protein coding RNA (DANCR) was firstly identified as epidermal cell differentiation suppressor. Here, we aimed to explore the effects and mechanism of DNACR in hypoxia-induced H9c2 cells. Hypoxic cells were made through 94% N2, 5% CO2, and 1% O2 environment for 24 h. Cell viability and apoptosis were detected via methyl thiazolyl tetrazolium (MTT) method and flow cytometry analysis, respectively. The expression of DANCR and HIF-1α was examined via qRT-PCR. The expression of proteins related to cell apoptosis and PI3K/AKT/mTOR and ERK1/2 signal pathways was examined through western blot analysis. We found that hypoxia induced obvious cell activity inhibition and apoptosis increasing in H9c2 cells. DANCR was negatively regulated under hypoxia condition. Overexpression of DANCR rescued activity and attenuated apoptosis. Moreover, the overexpression of DANCR elevated the activation of PI3K/AKT/mTOR and ERK1/2 pathways. Further study indicated that DANCR could up-regulate the expression of HIF-1α. Si-HIF-1α transfection could remove the beneficial effects of DANCR overexpression in hypoxia-caused H9c2 cells damage. In conclusion, DANCR alleviated hypoxia-caused H9c2 cells damage through positive regulation of HIF-1α.

Protective Fabrics: Metal-Organic Framework Textiles for Rapid Photocatalytic Sulfur Mustard Simulant Detoxification

Summary Metal-organic frameworks (MOFs) can catalyze toxic chemical decontamination, but new MOF materials and synthesis strategies are needed to improve performance, particularly in field-usable MOF-textile formats. This article reports for the first time the exceptional photocatalytic reactivity of Al-PMOF (Al-porphyrin-based MOF), composed of an earth-abundant metal-containing Al(OH)O4 cluster bridged by H2TCPP (5,10,15,20-tetrakis(4-carboxyphenyl)porphyrin) chromophores, against the toxic sulfur mustard simulant 2-chloroethyl ethyl sulfide (CEES) under visible-light irradiation. Furthermore, Al-PMOF is strongly immobilized into polymeric fibers via well-controlled Al2O3 solid film conversion using dimethylformamide/water cosolvent. The approach enables a secure integration of conformal Al-PMOF films onto polymer fibers at a relatively low synthesis temperature (120°C). In addition, on a per-unit mass of MOF basis, the surface-bound Al-PMOF films enable extremely rapid CEES detoxification turnover frequency, up to 170 mol CEES mol chromophore − 1 min − 1 , more than 10-fold faster than the best MOF powders and 2-fold better than MOF films reported to date.

28 Short equilibration improves vitrification of invitro-produced bovine embryos using VitTrans device

For the successful application of vitrification technology to field conditions, the procedures for the warming and transfer of the cryopreserved bovine embryos should be as simple as possible. The device VitTrans, designed by our group, enables warming/dilution of embryos and their transfer directly to recipient females in field conditions (Morato and Mogas 2014 Cryobiology 68, 288). VitTrans vitrification protocol consists of an incubation in equilibration solution during 12min followed by an exposure of 40s to vitrification solution. However, there are other reports using similar vitrification devices where equilibration length is shorter than ours. This study aimed to improve VitTrans methodology by comparing two vitrification protocols: short equilibration (SE) and long equilibration (LE). A total of 63 invitro-produced Day 7 blastocysts (IETS stage code 7) were randomly placed in an equilibration solution with 7.5% ethylene glycol + 7.5% dimethyl sulfoxide in holding medium (tissue culture medium-199 HEPES + 20% fetal calf serum) for either 3min (SE) or 12min (LE). Then, blastocysts were transferred to vitrification solution (15% ethylene glycol + 15% dimethyl sulfoxide + 0.5M sucrose in holding medium) for 40s, loaded onto the VitTrans device, plunged into liquid nitrogen, and covered with a 0.5mL straw. Fresh nonvitrified blastocysts (n=30) were set as control. For warming, the VitTrans was quickly submerged into a water bath at 45°C, while a syringe containing 0.3mL of diluting solution (0.5M sucrose in holding medium) at 45°C was injected through the hollow of the device. Blastocysts were then transferred to synthetic oviductal fluid medium and cultured for 24h at 38.5% in a 5% CO2 and 5% O2 environment in a humidified atmosphere. Re-expansion rates were recorded 3 and 24h after warming. Blastocysts were fixed and stained with SOX2 (Invitrogen) for inner cell mass (ICM) count, TUNEL (Roche) for apoptosis index assessment, and DAPI (Vector Laboratories) for total cell count (TCC). Images were captured using a Leica TCS SP5 confocal microscope (Leica Microsystems) and examined with Imaris 9.2 software (Oxford Instruments). Blastocyst survival rates were compared between groups using chi-squared test. Blastocyst TCC, ICM count, and apoptosis indices were analysed using analysis of variance. Significance was set at P ≤ 0.05. No differences were observed in re-expansion rate at 3h postwarming (61.3 and 59.4% for SE and LE, respectively). However, significantly higher re-expansion rates were found after 24h of culture for the blastocysts of the SE group (74.2%) when compared with the blastocysts of the LE group (65.7%). Blastocysts vitrified using the LE protocol produced the lowest TCC (115±5.9; P ≤ 0.05), whereas TCC of the SE (152±9.7) and fresh control (138±8.6) treatments were similar. No differences were found in ICM count among groups. Nevertheless, apoptosis index was higher (P ≤ 0.05) in both vitrification groups when compared with fresh control. These results indicate that short equilibration vitrification not only improves VitTrans outcomes but adds efficiency by taking less time to perform. Supported by MCIU, Spain (Project AGL2016-79802-P and Grant BES-2017-081962).

Sputtering yield measurements of laser ablated Mg-alloy correlated with surface, structural and mechanical modifications

Sputtering yield of laser ablated Mg-alloy has been measured by Quartz Crystal Microbalance at various fluences ranging from 11.6–44.2 J/cm2, under two different environments of Ar and O2· The sputtering yield initially increases from 14.58 × 1014 to 23.49 × 1014 and from 4.5 × 1014 to 22.60 × 1014 (atoms/pulse) by increasing fluence and then decreases upto a value of 19.78 × 1014 and 19.94 × 1014 (atoms/pulse) at the maximum fluence, under Ar and O2 environment respectively. Scanning Electron Microscope analysis reveals the formation of cones, cavities, droplets, ripples and island like structures on the irradiated Mg surface. Surface profilometry analysis reveals that the crater depth of laser irradiated Mg-alloy ranges from 188 to 209 μm. It initially increases by increasing laser fluence and afterwards, decreases at the maximum fluence. Energy Dispersive X-ray spectroscopy (EDX), X-Ray Diffraction analysis (XRD) and Ultraviolet-Visible (UV–vis) spectroscopy confirm the oxide formation for the laser treated target of Mg in O2. The Vickers Micro-hardness testing reveals that hardness of laser irradiated Mg-alloy is increased by increasing fluence. The surface structures, crater depth and hardness of laser irradiated Mg-alloy are strongly dependent upon laser fluence and are correlated with sputtering yield measurements.

Relationship between nanostructure-magnetic property induced by temperature for iron oxide nanoparticles in vacuum, Ar and O2 environments

It is known that superparamagnetic magnetite (Fe3O4) nanoparticles (NPs) become ferromagnetic under Si2+ ion irradiation due to particle size growth and microstructure evolution; it has been proposed that this feature could be used for in situ high temperature (up to 500 °C) radiation monitoring in the core of nuclear reactors. Herein, magnetite NPs synthesized by a nanocluster deposition system are heated to 800 °C in three different environments (argon, oxygen and vacuum), and nanostructure-magnetic property correlations are investigated by vibrating sample magnetometry, scanning electron microscopy, and X-ray diffraction. Magnetization of the NPs is increased due to the sintering and overall size growth by the agglomeration of the particles, while the morphology remains nearly unchanged up to 800 °C, with the one anomaly that zerovalent Fe appeared due to the reduction of the Fe3O4 at 800 °C in vacuum. In argon and oxygen at high-temperature, antiferromagnetic hematite is created, which causes a reduction of the magnetization, and abrupt growth of particle size above 500 °C.

Supercritical water gasification of naphthalene over iron oxide catalyst: A ReaxFF molecular dynamics study

ReaxFF molecular dynamics simulation has been employed to investigate the iron oxide-catalyzed supercritical water gasification (SCWG) of naphthalene (NAP), a common component of refractory polycyclic aromatic hydrocarbons. Simulation results showed that synergistic effects between SCW and iron oxide catalyst enormously promoted the degradation of NAP and the production of H2 and CO. During the gasification process, SCW served not only as H source for H2 generation but also as O source for CO generation and lattice oxygen recompense, while the major roles of iron oxide catalyst were to provide lattice oxygen with high hydrogen-abstraction ability, catalyze SCW to produce more active species, and weaken the C–C bonds. The effects of different parameters were subsequently revealed: increasing the use of H2O molecules raised H2 and CO yields along with the lattice oxygen supplement but slowed the rate of CO generation, high hydrogen recovery was achieved at high NAP concentration accompanied by a low carbon gasification efficiency. Our simulated results further demonstrated that the deactivation of iron oxide catalyst was caused by carbon deposition, lattice oxygen exhaustion and iron loss. SCW media effectively inhibited the iron loss, while calcination in O2 environment could successfully regenerate the iron oxide catalyst by cleaning up the carbon deposition and replenishing the lattice oxygen.

Annealing environment dependent electrical and chemical state correlation of Li-doped NiO

The effects of annealing environments and dopants on the structural, chemical, optical, and electrical properties of NiO are investigated. Pristine NiO exhibits electrically insulating behavior regardless of the annealing environments (e.g., vacuum and O2 environments). On the other hand, Li-doped NiO exhibits electrical resistivities of ∼350 Ω cm and ∼9 Ω cm for the ceramics annealed under vacuum and O2, respectively with reduced optical band-gap. The structural analysis revealed that all the samples exhibit a cubic structure (Fm-3m, SG 225) without any measurable secondary phases. However, Li-doped NiO samples showed a reduction in the unit cell volume as compared to the undoped NiO samples. X-ray photoelectron spectroscopy revealed different residual Li content depending on the annealing environments, and the presence of induced Ni3+ state in the Li-doped NiO. These induced Ni3+ states and doped Li are responsible for the observed change in the structural and electrical properties of the Li-doped NiO samples.

I-V characteristics of magnetron with hot titanium target sputtered in argon-oxygen mixture

The discharge current-voltage characteristics of a dc magnetron with a single hot titanium target in Ar + O2 environment are studied. It was found that the I-V characteristics measured in the range of current densities of 10-200 mA/cm2 have three inflection points and a maximum. The competition of several processes can cause the discovered features. In the oxide target operating mode, these processes include the chemical reaction for the formation of oxide on the surface of the target and its sputtering by argon ions. In the metal mode, gas rarefaction near the target and thermionic emission compete.

Does culture of embryos in an ultra-low (2%) oxygen environment yield better blastocyst development than 6% oxygen using time-lapse morphokinetics?

Objective To evaluate if culture of mouse embryos in an ultra-low oxygen environment could enhance blastocyst development in terms of time-lapse morphokinetics. Design Prospective study Materials and methods A total of 214 commercially obtained frozen mouse embryos (B6D2F1 & B6C3F1 hybrid) were thawed and cultured in One-Step medium with 10%SPS using an EmbryoScope time lapse incubator at 37°C, 5.5% CO2, and either (1) 6.0% O2 (n=106) or (2) 2.0% O2 (n=108) Embryo images were recorded every 10 minutes for 6 days of culture. Time lapse videos were annotated for the following time points: 2cell (t2), 3cell (t3), 4cell (t4), 5cell (t5), 6cell (t6), 7cell (t7), 8cell (t8), start of compaction (tSC), morula (tsM), start of blastulation (tSB), blastocyst (tB), expanded blastocyst (tEB) and hatching blastocyst (tHB). The 2-cell stage was considered as time zero since the exact time of insemination was unknown. Time points were statistically compared between the two groups. Blastocyst development rates for both culture environments were also compared. Results There were no statistically significant differences between the two groups in any of the time points measured up to the 8-cell stage. However, after the 8-cell stage, the 2% O2 group showed significantly slower embryo development for each time point up to the hatching blastocyst stage. There was no difference in the blastocyst development rate between the 6% O2 and 2% O2 environments (99.1% vs 95.4%). Conclusions Our data did not show any benefit of culturing embryos in a 2% oxygen environment. Although there was no difference in the blastocyst development rate between culturing in 2% and 6% oxygen, the 2% oxygen group took significantly longer to reach the blastocyst stage than the 6% oxygen group. Disclosures Nothing to disclose Funding None

I-V characteristics of magnetron with hot target sputtered in three-component gas mixture

The discharge current-voltage characteristics of a dc magnetron with a single cold titanium target and a single hot titanium target in Ar + N2 + O2 environment were studied. Two series of experiments, in which the flow rates of nitrogen QN2 and oxygen Qo2 played different roles, were performed. In the first series, O2 was introduced into a mixture of Ar + N2 (QN2 = const and Qo2 = var). In the second one, N2 was introduced into a mixture of Ar + O2 (QN2 = const and Qo2 = var). It was found that the I-V characteristics of the studied sputtering instruments measured in the current density range of 10–200 mA/cm2 differ significantly. The I-V characteristics of a magnetron with a cold target can have one maximum or jump. The I-V characteristics of a magnetron with a hot target have two maxima and one minimum in one case, and in the other case, there is only one maximum.

Adaptation to life on land at high O2 via transition from ferredoxin-to NADH-dependent redox balance.

Pyruvate : ferredoxin oxidoreductase (PFO) and iron only hydrogenase ([Fe]-HYD) are common enzymes among eukaryotic microbes that inhabit anaerobic niches. Their function is to maintain redox balance by donating electrons from food oxidation via ferredoxin (Fd) to protons, generating H2 as a waste product. Operating in series, they constitute a soluble electron transport chain of one-electron transfers between FeS clusters. They fulfil the same function—redox balance—served by two electron-transfers in the NADH- and O2-dependent respiratory chains of mitochondria. Although they possess O2-sensitive FeS clusters, PFO, Fd and [Fe]-HYD are also present among numerous algae that produce O2. The evolutionary persistence of these enzymes among eukaryotic aerobes is traditionally explained as adaptation to facultative anaerobic growth. Here, we show that algae express enzymes of anaerobic energy metabolism at ambient O2 levels (21% v/v), Chlamydomonas reinhardtii expresses them with diurnal regulation. High O2 environments arose on Earth only approximately 450 million years ago. Gene presence/absence and gene expression data indicate that during the transition to high O2 environments and terrestrialization, diverse algal lineages retained enzymes of Fd-dependent one-electron-based redox balance, while the land plant and land animal lineages underwent irreversible specialization to redox balance involving the O2-insensitive two-electron carrier NADH.

Triboluminescence of tris(2,2′-bipyridyl)ruthenium(II) dichloride hexahydrate

The triboluminescence of tris(2,2′-bipyridyl)ruthenium(II) dichloride hexahydrate complex is detected during the mechanical grinding. The intense lines of N2 in the UV region and a band at 619 nm appeared due to luminescence of [Ru(bpy)3]2+ ion and coincided with the photoluminescence spectrum of the crystals are observed in the emission spectrum in air. The luminescence of N2 is due to electrification of the crystals during the destruction and subsequent discharges in the gas phase. We showed that the luminescence of [Ru(bpy)3]2+ does not occur due to absorption of UV luminescence of N2, because there is only luminescence of the crystal in O2 environment, whereas the luminescence of N2 is completely suppressed. The intense lines coincided with those of Ne and Ar atoms in the electric discharge are observed in the triboluminescence spectra of ruthenium(II) complex in neon and argon environments. In this case, there is an increase in intensity of N2 lines and of a band of [Ru (bpy)3]2+ due to more intense discharges than during the tribodestruction without inert gases. *OH radical is also detected in the triboluminescence spectrum due to mechanochemical decomposition of water molecules in the [Ru(bpy)3]Cl2·6H2O crystalline hydrate.

Performance of All Solid Li-Air Battery

The Li–Air battery converts the electrochemical reactions of lithium and O2 into electrical energy and has been receiving attention as the next generation battery because of its high theoretical specific energy of 3400 Wh kg-1. The high specific energy of the Li–Air battery can be attributed to the reaction in the cathode where only Li and O2 are needed, and it is an order of magnitude higher than that of the future generation Li ion battery that is predicted to reach at most 400 Wh kg-1. In the cathode, the carbon particles are used to provide electron conductivity as well as the surface area for the reactions, and the electrolytes are necessary to transport Li+ ions between the anode and cathode [1]. The pore distribution of the cathode is reported to influence the capacity [2], and the lifetime of the battery is reported to be limited by the stability of electrolyte [3]. To ensure higher stability against the oxidative conditions, the ionic liquid-based electrolytes are often used [4]. However, even the ionic liquid is known to decompose at the oxidative environment of the Li-Air battery operation conditions. To increase the cycle lifetime of the Li-Air battery, more stable form of electrolyte in cathode is desired. By constructing an all solid Li-Air battery which consists of Li metal, solid electrolyte, and oxide cathode, the source of cathode degradation can be greatly reduced by eliminating the liquid electrolyte and carbon in the cathode. The oxide material which showed both electronic and ionic conductivity in the order of 10-4 S/cm was used as the cathode. The cathode material was ball milled to obtain sub-micron sized particles and the surface area in the order of 10 m2/g. The cathode was coated to obtain a 10 μm cathode layer, and the layer was sintered onto a LATP (Lithium aluminum titanium phosphate) electrolyte layer. The Li metal was then attached to the cathode/electrolyte to form an all solid Li-Air battery. To operate the Li-Air battery, the Li metal was isolated from the O2 environment to which the cathode was exposed. The performance of the battery was evaluated in a O2 filled chamber which had the relative humidity up to 100%. The discharge and charge curves were analyzed to evaluate the feasibility and the cycle lifetime of the all solid Li-Air battery. The composition of the discharge product and the possible reaction mechanism will be presented. The strategy to increase the specific energy and cycle lifetime of the battery will be also discussed. [1] D. Aurbach, B. D. McCloskey, L. F. Nazar and P. G. Bruce, Nat . Energy , 2016, 1, 1–11. [2] N. Ding, S. W. Chien, T. S. A. Hor, R. Lum, Y. Zong and Z. Liu, J. Mater. Chem. A , 2014, 2, 12433–12441. [3] S. A. Freunberger, Y. Chen, Z. Peng, J. M. Griffin, L. J. Hardwick, F. Barde, P. Novak and P. G. Bruce, J. Am. Chem. Soc., 2011, 133, 8040–8047. [4] N. Mozhzhukhina, A. Y. Tesio, L. P. Mendez De Leo and E. J. Calvo, J. Electrochem. Soc., 2017, 164, A518–523.

Revealing the failure mechanism and designing protection approach for MoS2 in humid environment by first-principles investigation

Abstract The moist circumstance (e.g., O2 and H2O molecule) is one of the critical factors affecting the application of MoS2, which lead to MoS2 failure. Fortunately, metal-atoms doping MoS2 is commonly used to decrease damage of MoS2 by O2 or H2O molecule. To understand and explore the microscopic mechanism of MoS2 failure, the interaction of O2, H2O molecule with defect-free, defected MoS2 is calculated using first-principles method. It could be found that the failure of MoS2 results mainly from the defects, which make the exposed Mo atoms more active and easy to react with O2 or H2O molecule. Therein to, S-vacancy defect of MoS2 (MoS2-VS1 species) is the reaction outset point of O2 environment, and triple vacancy defect of MoS2 (MoS2-VS2+Mo species) is that of H2O environment. Based on this failure mechanism, the typical Ti or Pb elementals doped MoS2 are studied, the calculation results indicate that Ti or Pb doping elements can retard effectively the failure of MoS2 in humid environment through reacting preferentially with or repulsing to O2 or H2O molecules, and even restraining the diffusion of H atom dissociated from H2O molecule. All of these will be helpful for the design, synthesis, and application of related transition metal dichalcogenides.

Al2O3 formed by post plasma oxidation of Al as a Gate dielectric for AlGaN/GaN MIS-HEMTs

We demonstrate patterned Al2O3 formation by post-plasma oxidation of a thin layer of aluminium (Al) film deposited by electron beam evaporator in area selective regions. The oxide quality is observed to further improve by annealing in O2 and N2 environment. Schottky and metal-insulator-semiconductor diodes are also fabricated to characterize its electrical behaviour. The thickness and high quality of the oxide formed is confirmed from Transmission Electron Microscope (TEM) and X-Ray Photoelectron Spectroscopy (XPS) analysis. The O2 and N2 annealed samples show Oxygen to Aluminium atomic ratio of ~1.5 confirming near-ideal stoichiometry. The energy band-gap (Eg) of the Plasma-Oxide, O2-Annealed and N2-Annealed estimated from energy loss spectra of O1s are found to be 5.0, 5.5 and 6.8 eV, respectively. The valance band off-set for the corresponding oxides as estimated from low energy spectra analysis are found to be 0.8, 0.7 and 0.8 eV, respectively. The electrical characteristics also confirm improvement over the control device. The ION/IOFF ratios are observed to be 106, 1010 and 106 for the Plasma Oxide, O2 Annealed and N2 Annealed oxides, respectively, as compared to 103 for the Control sample. The dielectric constants (εox) for the corresponding oxides as determined from the CV characteristics are found to be 5.3, 8.5 and 8.7, respectively.

Laser sputtering of Zr under Ar and O2 environments explored by quartz crystal microbalance and SEM analysis

AbstractThe effect of laser fluence and nature of ambient environments on the sputtering yield, surface modifications, crater depth, UV-visible absorption spectra, chemical composition, and micro hardness of Zr has been investigated. Nd: YAG laser (532 nm, 10 Hz, 6 ns) at different fluences varying from 16 to 60.8 Jcm−2was employed as an irradiation source. All measurements are performed under two ambient environments of Ar and O2at a constant pressure of 10 Torr. Quartz crystal microbalance has been employed for the measurement of sputtering yield of laser irradiated Zr. It is revealed that sputtering yield increases monotonically with increasing fluence under both environments however, it is higher in Ar as compared to O2environment. Scanning electron microscope (SEM) has been used to explore the surface morphology. SEM analysis exhibits the formation of cones, ridges, and cracks at the central ablated areas whereas, laser-induced periodic surface structures, periodic ridges and sharp cones are observed at inner boundaries in both environments of Ar and O2. Sharp spikes are observed in both environments, however, their height and distinctness are more pronounced in Ar as compared to O2. Cones are characteristic features in Ar, whereas, cavities and channels are dominant features in O2environment at outer boundaries. The formation and growth of surface structures are dependent upon laser fluence and ambient gas nature. The depth profilometry has been used to measure the crater depth of irradiated Zr target by using an optical microscope. UV visible spectroscopy and energy-dispersive X-ray analyses reveal the oxide formation in the case of Zr irradiation in O2environment. The Vicker Micro-hardness tester has been employed to measure the hardness. The higher observed values of sputtering yield, crater depth and hardness of laser ablated Zr in Ar as compared to O2are well correlated with distinct surface structures.