O2 Ratio Research Articles

Degradation of Micropollutants in Water by O Atoms Produced by an Atmospheric Pressure He/O2 Plasma Jet

ABSTRACTAn atmospheric pressure He/O2 COST reference microplasma jet was used to study interactions of O atoms with four different organic micropollutants used as target compounds treated by plasma in water (atrazine, carbamazepine, 1,7‐α‐ethinylestradiol, and bisphenol A). Various ratios of O2 to He were used to achieve different exposures of reactive oxygen species to the plasma‐treated micropollutants, and their degradation efficiencies were determined. The degradation of all four micropollutants was merely associated with the variable exposure to the O atom, whereas the role of O3 was minimal. A comprehensive investigation was conducted on the degradation pathways and toxicity reduction assessment of atrazine after the treatment by plasma.

Migration and Transformation of Heavy Metals During the CO2-Assistant Thermal Treatment of Oily Sludge

Thermal treatment has significant advantages in resource recovery for oily sludge (OS). However, the instability of heavy metals (HMs) within the residue poses a considerable risk of secondary pollution. This study explored the migration and transformation of HMs from OS under varying conditions (i.e., temperature, constant-temperature duration time, and different ratios of O2 and CO2). The elevation of the pyrolysis temperature augmented the decomposition of organic matter and total petroleum hydrocarbons (TPHs). However, the increased temperature also diminished the stabilization of HMs, and facilitating the HM’s transfer to oil and gas, particularly for HMs (i.e., As and Pb) with low boiling points. The constant-temperature duration time exhibited a weak impact on HM transformation, but the internal heating mechanism of microwave pyrolysis promoted the stabilization of HMs through vitrification. The existing O2 with oxidizing properties facilitated the oxidation of organic matter and TPHs to CO2 and H2O, which also promoted the transformation of HMs into oxidized states for stabilization. Comparatively, CO2 promoted the thermal cracking and disrupted the stability of HMs to a certain extent. Above all, this work revealed the migration and transformation of HMs in OS varied with the thermochemical methods and possessed an important significance for the immobilization and stabilization of HMs.

Key Sputtering Parameters for Precursor In2O3 Films to Achieve High Carrier Mobility.

Owing to their extremely high carrier mobility (μ) of >100 cm2/(V s) and suitable low carrier concentrations, transparent conducting films of solid-phase crystallized H-doped In2O3 (spc-IO:H) exhibit high conductivity with high optical transparency over a broad frequency range. These properties can be attributed to solid-phase crystallization of the amorphous precursor film. Therefore, the development of high-quality spc-IO:H films requires the deposition conditions of the precursor films to be optimized. This study systematically investigates the effects of three key sputtering parameters, namely, water vapor partial pressure (PH2O), radio frequency magnetron sputtering power (PRF), and flow ratio of O2 to total sputter gas (fO2) on the crystallographic texture evolution of spc-IO:H films during solid-phase crystallization. In addition, the carrier transport in the resulting films is examined. PH2O, PRF, and fO2 are found to be indispensable for producing high-mobility (>100 cm2/(V s)) spc-IO:H films. Furthermore, it is found that introducing a small amount of PH2O during deposition, a lower PRF, and a suitable fO2 facilitates the formation of precursor films having a lower crystallite density. Moreover, after annealing at a temperature of 200 °C, the IO:H precursor films with a lower crystallite density are found to have larger crystal grains. However, the μ values of the postannealed IO:H films are mainly correlated with the stoichiometric deviation.

Structure, mechanical, and tribological properties of Ag2CrO4 high-temperature oxide coatings

In this research, a series of Ag2CrO4 high-temperature self-lubricating oxide coatings were prepared by reactive radio frequency magnetron sputtering under different argon-oxygen flow ratio (Ar:O2 ratio) conditions. Effects of the gas flow ratio on phase composition, coating morphology, high temperature treatment in air atmosphere, mechanical and tribological properties are studied. A low Ar:O2 flow ratio is beneficial for the formation of Ag2CrO4 phase. At high temperature treatment, formation of surface Ag particle and volatility and decomposition of the Ag2CrO4 phase are observed, and the volatility and decomposition of the coating are slight at temperatures below 500 °C. When the Ar:O2 ratio is 1:1, the coating shows exceptional comprehensive performance, it is dense with a smooth surface, excellent toughness and bond strength, and the lowest wear rate and coefficient of friction, which is 0.14 mm3/10−3N∙m and 0.35 respectively. The coating can function as a lubricant in temperature environments of 500 ℃ and below, demonstrating practical application value.

Comparison of plasma-activated saline prepared with plasma gases with different N2/O2 ratios activated by gliding arc discharge

Methicillin-resistant Staphylococcus aureus (MRSA) presents a significant threat due to the multiple resistance to antibiotics, leading to severe and challenging-to-treat infections. Plasma-activated saline (PAS) prepared by plasma gases, could efficiently inactivate various pathogenic bacteria including both sensitive and antibiotic-resistant bacteria. In this study, the PAS was prepared by plasma gases with different ratios of N2 and O2 activated by gliding arc discharge. First, the gaseous reactive species in the plasma gases were compared, revealing that the highest levels of NO x including NO2 and N2O5 were generated in the gases with the N2/O2 ratios of 4:6, 5:5, and 6:4. Subsequently, the PAS prepared by the two plasma-activated gases at the N2/O2 ratios of 5:5 and 6:4 exhibited the strongest inactivation effects on both planktic MRSA and biofilms. Furthermore, the aqueous reactive species in the PAS exhibited varied change trends with the increasing N2/O2 ratios. Additionally, ultraviolet spectroscopy combined with the probe of N, N-diethyl-p-phenylenediamine was applied for the detection of O2NOO− in the PAS, and the levels of O2NOO− in the PAS were positively correlated with the inactivation effects. Moreover, the PAS induced varying levels of nitration modification on the soluble proteins in MRSA cells, which were related to the intensities of O2NOO− in the PAS. This study regulated the reactive species in the PAS through gas composition and explored the inactivation mechanism of the PAS, providing a new strategy to promote the preparation efficiency of plasma-activated solutions for biomedical applications.

Experimental study on thermal conversion characteristics of char in a pressurized O2/CO2/H2O atmosphere

Pressurized oxy-fuel combustion represents an advanced coal-fired power generation technology advantageous for CO2 capture and system efficiency enhancement. This study employed a pressurized tube furnace experimental system to investigate the thermal conversion characteristics of char in a pressurized O2/CO2/H2O atmosphere. The carbon conversion under varying pressures (0.1–1.3 MPa), atmospheres, and residence times were analyzed. The physical and chemical structural evolutions of char, which are directly related to its reactivity, were elucidated using nitrogen adsorption, XPS, Raman, and FTIR analysis. The findings indicate that both pressurization and increasing O2/CO2 enhanced char conversion. Transitioning from kinetic to diffusion control in the O2/CO2/H2O atmosphere necessitated high pressure. The influence of CO2 on the physical and chemical structure of char under pressurized conditions was found to be less significant compared to that of O2 and H2O. Furthermore, pressurization and elevated O2 ratios were observed to reduce the microporous structure's contribution to the specific surface area of the char. Pressurization also increased the degree of graphitization of the char. Elevated O2/CO2 concentrations facilitated the breakdown of C–C structures, the melting of large aromatic rings, and the reduction in the degree of graphitization, particularly under higher pressures. In the O2/CO2/H2O pressurized atmosphere, more oxygen-containing functional groups were formed within the char structure, with the C–OH structure forming initially, followed by the O–CO structure.

Corrosion Behavior of Al-Containing CoNiV Medium Entropy Alloy Coating Fabricated by Laser Cladding.

CoNiV medium entropy alloys (MEAs) have been widely recognized for their superior corrosion resistance. Nonetheless, their extensive application has been hindered by high production costs and complex fabrication processes. In this study, CoNiVAlx MEA coatings were synthesized on AISI 304 stainless steel substrates via laser cladding technology. The microstructure, phase composition, corrosion resistance, and corrosion mechanisms of the coatings were systematically investigated by using advanced characterization techniques, including optical microscopy, scanning electron microscopy, transmission electron microscopy, X-ray diffractometry, and electrochemical workstation analysis. The ratio of O2-/OH- in the passivation film of the coated surface exhibited a gradual increase with the addition of Al. The formation of the Al-containing precipitated phase L21 was observed at x = 0.3 and 0.4. The results demonstrated that moderate Al doping (x ≤ 0.2) enhanced corrosion resistance by improving the stability of the passivation film and reducing the thermodynamic tendency toward corrosion. In contrast, excessive Al doping (x > 0.2) led to the formation of the L21 phase, which increased the susceptibility to localized corrosion, thus compromising the overall corrosion resistance.

Discharge mode and particle transport in radio frequency capacitively coupled Ar/O2 plasma discharges

Abstract Simulations are conducted on capacitively coupled Ar/O2 mixed gas discharges employing a one-dimensional fluid coupled with an electron Monte Carlo (MC) model. The research explores the impact of different O2 ratio and pressures on the discharge characteristics of Ar/O2 plasma. At a fixed Ar/O2 gas ratio, with the increasing pressure, higher ion densities, as well as a slight increase in electron density in the bulk region can be observed. The discharge remains dominated by the drift–ambipolar (DA) mode, and the flux of O(3P) at the electrode increases with the increasing pressure due to higher background gas density, while the fluxes of O(1D) and Ar* decrease due to the pronounced loss rate. With the increasing proportion of O2, a change in the dominant discharge mode from α mode to DA mode can be detected, and the O2-associated charged particle densities are significantly increased. However, Ar+ density shows a trend of increasing and then decreasing, while for neutral fluxes at the electrode, Ar* flux decreases, and O(3P) flux increases with the reduced Ar gas proportion, while trends in O(1D) flux show slight differences. The evolution of the densities of the charged particle and the neutral fluxes under different discharge parameters are discussed in detail using the ionization characteristics as well as the transport properties. Hopefully, more comprehensive understanding of Ar/O2 discharge characteristics in this work will provide a valuable reference for the industry.

Investigation of the effect of oxygen flow modulation on ITO film properties to improve the performance of SHJ solar cells

Photovoltaics offer a sustainable solution for the growing energy needs of the world, while reducing environmental impact. Transparent Conductive Oxides (TCOs), which are essential in photovoltaic technology, offer high light transmittance and effective charge carrier extraction. This research focuses on the impact of oxygen (O2) flow rates in the deposition of indium tin oxide (ITO) films on n-type crystalline silicon (c-Si) substrates by DC magnetron sputtering. The structural, optical, and electrical properties were analyzed. Based on the results, the optimal O2 ratio was determined and used in the fabrication of SHJ solar cells, achieving an efficiency of 18.6%.

Forward and reverse uncertainty analyses for RRKM/master equation based kinetic predictions: A case study of ethyl with oxygen

AbstractIn the realm of combustion kinetic modeling, the norm involves employing thousands of reactions to delineate the chemical conversion of hundreds of species. Notably, theoretically predicted rate coefficients and branching ratios, derived through the RRKM/master equation (ME) model, play an increasing role in kinetic modeling. Thus minimizing the uncertainty of theoretical prediction across wide working conditions is crucial to refine a kinetic model. The present study takes ethyl (C2H5) + oxygen (O2) reaction system to show that combined forward and reverse uncertainty analysis can be used to further constrain calculated rate coefficients and branching ratios, which were already calculated by high‐level quantum chemistry methods. Forward global uncertainty analysis with the artificial neural network‐high dimensional model representation (ANN‐HDMR) method is employed to select key parameters affecting total rate coefficients of C2H5 + O2 and branching ratios of C2H5 + O2 = C2H4 + HO2 (C1). Reverse uncertainty analysis with Bayesian method was then applied to refine the key input parameters based on experimental data at working conditions selected by sensitivity entropy. Although the target RRKM/ME model system was built on high level theoretical calculations, the combined forward and reverse uncertainty analyses are still able to reduce uncertainties of predicted total rate coefficients of C2H5 + O2 and branching ratios for C1 across a wide range of working conditions. Specifically, the uncertainties of total rate coefficient and C1 branching ratio have been reduced from 1.46 and 1.52 to 1.30 and 1.36 at 298 K and 1 Torr. The analysis process proposed in the present work effectively extrapolates the constraint ability of accurate measured data at one condition to wide working conditions based on the RRKM/ME model.

Fast, Efficient Tailoring Growth of Nanocrystalline Diamond Films by Fine-Tuning of Gas-Phase Composition Using Microwave Plasma Chemical Vapor Deposition.

Nanocrystalline diamond (NCD) films are attractive for many applications due to their smooth surfaces while holding the properties of diamond. However, their growth rate is generally low using common Ar/CH4 with or without H2 chemistry and strongly dependent on the overall growth conditions using microwave plasma chemical vapor deposition (MPCVD). In this work, incorporating a small amount of N2 and O2 additives into CH4/H2 chemistry offered a much higher growth rate of NCD films, which is promising for some applications. Several novel series of experiments were designed and conducted to tailor the growth features of NCD films by fine-tuning of the gas-phase compositions with different amounts of nitrogen and oxygen addition into CH4/H2 gas mixtures. The influence of growth parameters, such as the absolute amount and their relative ratios of O2 and N2 additives; substrate temperature, which was adjusted by two ways and inferred by simulation; and microwave power on NCD formation, was investigated. Short and long deposition runs were carried out to study surface structural evolution with time under identical growth conditions. The morphology, crystalline and optical quality, orientation, and texture of the NCD samples were characterized and analyzed. A variety of NCD films of high average growth rates ranging from 2.1 μm/h up to 6.7 μm/h were successfully achieved by slightly adjusting the O2/CH4 amounts from 6.25% to 18.75%, while that of N2 was kept constant. The results clearly show that the beneficial use of fine-tuning of gas-phase compositions offers a simple and effective way to tailor the growth characteristics and physical properties of NCD films for optimizing the growth conditions to envisage some specific applications.

Achieving Visible Light Triggered Overall Water Splitting over Plasmonic Au/SrTiO3:Al Photocatalyst

AbstractThe surface plasmon resonance (SPR) effect has garnered extensive attention in semiconductor photocatalysis for solar energy conversion, thanks to its remarkable optical properties. However, the majority SPR‐induced photocatalytic systems have been limited to achieving hydrogen evolution or oxygen evolution half reactions, and attaining overall water splitting on a SPR‐induced photocatalyst under visible light remains a formidable challenging. In this study, we employed a plasmonic photocatalyst Au/SrTiO3, and further enhanced its performance by doping aluminum (Al) into the SrTiO3 lattice (denoted as Au/SrTiO3:Al). By constructing reduction cocatalyst (RhCrOx) and oxidation cocatalyst (CoOOH), the Au/SrTiO3:Al photocatalyst successfully realizes photocatalytic overall water splitting with a stoichiometric ratio of H2 and O2 under visible light (λ≥440 nm). We revealed that the introduction of Al species effectively modified the electronic structure of SrTiO3, thereby enhancing the hydrogen evolution reaction in Au/SrTiO3:Al. Simultaneously, the RhCrOx and CoOOH cocatalysts synergistically capitalized on the short‐lived hot electrons and holes generated by the plasmonic Au/SrTiO3:Al photocatalyst, enabling to realize photocatalytic overall water splitting. This work offers a promising avenue for the rational design of plasmon‐induced overall water splitting photocatalysts through the integration of suitable cocatalysts and surface/interface engineering strategies.

Charge redistribution of a spatially differentiated ferroelectric Bi4Ti3O12 single crystal for photocatalytic overall water splitting

Artificial photosynthesis is a promising approach to produce clean fuels via renewable solar energy. However, it is practically constrained by two issues of slow photogenerated carrier migration and rapid electron/hole recombination. It is also a challenge to achieve a 2:1 ratio of H2 and O2 for overall water splitting. Here we report a rational design of spatially differentiated two-dimensional Bi4Ti3O12 nanosheets to enhance overall water splitting. Such a spatially differentiated structure overcomes the limitation of charge transfer across different crystal planes in a single crystal semiconductor. The experimental results show a redistribution of charge within a crystal plane. The resulting photocatalyst produces 40.3 μmol h–1 of hydrogen and 20.1 μmol h–1 of oxygen at a near stoichiometric ratio of 2:1 and a solar-to-hydrogen efficiency of 0.1% under simulated solar light.

Effect of nitrogen/oxygen ratios on surface charge distributions generated by repetitive surface dielectric barrier discharges

Studies on the dielectric surface parameters and dielectric barrier discharges (DBD) characteristics considering the influence of gases in DBD on the surface charge distribution are scarce. Thus, to overcome this research gap, this study measured the potential distributions of AC-driven surface DBD in oxygen (O2), synthetic air and nitrogen (N2) as background gases using the Pockels effect. The results showed that the patterns of the filamentary discharges generated during the positive voltage polarity phase differed depending on the O2 ratio. In addition, the electrostatic repulsion forces between the residual charge and the newly created filament were analysed from the measured potential distribution and the greatest effect was observed in air, rather than in N2 and O2. The potential distribution was transformed into a charge density distribution and compared with the discharge luminescence in air and N2. The results showed that the shape of the filament tip differed between the charge density and discharge luminescence only in the case of air, which was attributed to the effect of attachment reactions on the formation of residual charge. The measurements showed that in a surface discharge, similar to the case in a volume discharge, the photoionisation and ionisation coefficients significantly affected the geometrical properties of the discharges.

Effects of methane to oxygen ratio on cell growth and polyhydroxybutyrate synthesis in high cell density cultivation of Methylocystis sp. MJC1.

Polyhydroxybutyrate (PHB) production through CH4 conversion by methanotrophs offers a solution for greenhouse gas emissions and plastic waste concerns. In this study, we aimed to achieve high cell density cultivation of Methylocystis sp. MJC1 for efficient PHB production. Cultivating MJC1 using CH4 and air (3:7, v/v) yielded a final cell density of 52.9 g/L with a 53.7% (28.4 g/L) PHB content after 210 h, showcasing PHB mass production potential. However, long-term cultivation led to a low volumetric productivity of 0.200g/L/h. To address this, we conducted cultivation at various O2/CH4 ratios using O2 instead of air, which significantly improved the PHB productivity. Under high O2 conditions (O2/CH4 ratio of 1.5), biomass productivity increased 1.51-fold compared to that under low O2 conditions in the same time frame; however, PHB accumulation was delayed. Using an equal ratio of CH4 and O2 induced active cell growth and selective PHB production, achieving the highest PHB productivity (0.365 g/L/h) with a final cell density of 55.9 g/L and PHB content of 61.7% (34.5 g/L) in 162 h. This study highlighted the significance of the O2/CH4 ratio in CH4 conversion and PHB production by M. sp. MJC1.

Atmospheric oxygen as a tracer for fossil fuel carbon dioxide: a sensitivity study in the UK

Abstract. We investigate the use of atmospheric oxygen (O2) and carbon dioxide (CO2) measurements for the estimation of the fossil fuel component of atmospheric CO2 in the UK. Atmospheric potential oxygen (APO) – a tracer that combines O2 and CO2, minimizing the influence of terrestrial biosphere fluxes – is simulated at three sites in the UK, two of which make APO measurements. We present a set of model experiments that estimate the sensitivity of APO simulations to key inputs: fluxes from the ocean, fossil fuel flux magnitude and distribution, the APO baseline, and the exchange ratio of O2 to CO2 fluxes from fossil fuel combustion and the terrestrial biosphere. To estimate the influence of uncertainties in ocean fluxes, we compare three ocean O2 flux estimates from the NEMO–ERSEM, the ECCO–Darwin ocean model, and the Jena CarboScope (JC) APO inversion. The sensitivity of APO to fossil fuel emission magnitudes and to terrestrial biosphere and fossil fuel exchange ratios is investigated through Monte Carlo sampling within literature uncertainty ranges and by comparing different inventory estimates. We focus our model–data analysis on the year 2015 as ocean fluxes are not available for later years. As APO measurements are only available for one UK site at this time, our analysis focuses on the Weybourne station. Model–data comparisons for two additional UK sites (Heathfield and Ridge Hill) in 2021, using ocean flux climatologies, are presented in the Supplement. Of the factors that could potentially compromise simulated APO-derived fossil fuel CO2 (ffCO2) estimates, we find that the ocean O2 flux estimate has the largest overall influence at the three sites in the UK. At times, this influence is comparable in magnitude to the contribution of simulated fossil fuel CO2 to simulated APO. We find that simulations using different ocean fluxes differ from each other substantially. No single model estimate, or a model estimate that assumed zero ocean flux, provided a significantly closer fit than any other. Furthermore, the uncertainty in the ocean contribution to APO could lead to uncertainty in defining an appropriate regional background from the data. Our findings suggest that the contribution of non-terrestrial sources needs to be better accounted for in model simulations of APO in the UK to reduce the potential influence on inferred fossil fuel CO2 using APO.

The fundamental role of pH in CH4 bioconversion into polyhydroxybutyrate in mixed methanotrophic cultures

Climate change and plastic pollution are likely the most relevant challenges for the environment in the 21st century. Developing cost-effective technologies for the bioconversion of methane (CH4) into polyhydroxyalkanoates (PHAs) could simultaneously mitigate CH4 emissions and boost the commercialization of biodegradable polymers. Despite the fact that the role of temperature, nitrogen deprivation, CH4:O2 ratio or micronutrients availability on the PHA accumulation capacity of methanotrophs has been carefully explored, there is still a need for optimization of the CH4-to-PHA bioconversion process prior to becoming a feasible platform in future biorefineries. In this study, the influence of different cultivation broth pH values (5.5, 7, 8.5 and 10) on bacterial biomass growth, CH4 bioconversion rate, PHA accumulation capacity and bacterial community structure was investigated in a stirred tank bioreactor under nitrogen deprivation conditions. Higher CH4 elimination rates were obtained at increasing pH, with a maximum value of 50.4 ± 2.7 g CH4·m−3·h−1 observed at pH 8.5. This was likely mediated by an increased ionic strength in the mineral medium, which enhanced the gas-liquid mass transfer. Interestingly, higher PHB accumulations were observed at decreasing pH, with the highest PHB contents recorded at a pH 5.5 (43.7 ± 3.4 %w·w−1). The strong selective pressure of low pH towards the growth of Type II methanotrophic bacteria could explain this finding. The genus Methylocystis increased its abundance from 34 % up to 85 and 90 % at pH 5.5 and 7, respectively. On the contrary, Methylocystis was less abundant in the community enriched at pH 8.5 (14 %). The accumulation of intracellular PHB as energy and carbon storage material allowed the maintenance of high CH4 biodegradation rates during 48 h after complete nitrogen deprivation. The results here obtained demonstrated for the first time a crucial and multifactorial role of pH on the bioconversion performance of CH4 into PHA.

Global Warming and the Future Generation

Global Warming has become one of the burning problems of the day. Every year, the average temperature of the Earth is being increased. Such problem is called Global Warming. This problem has started long ago. In the last 50 years, the situation has become worst. There are many causes of Global Warming. Firstly, the trees are being destroyed in good number. As a result, there is no perfect balance in the ratio of CO2 and O2. Secondly, the excessive fuel consumption is another direct cause of Global Warming. Thirdly, the excessive use of CFC has made the situation alarming. The direct impact of Global Warming is that the condensed ice of the pole regions has begun to be melted. Gradually, the sea level rises. Shortly, the coastal countries of the world will be washed away. Besides, owing to Global Warming, the holes have been created in the O3 layer. As a result, the harmful rays of the sun enter the surface of the Earth. Some measures may be taken to solve the problem of Global Warming. Firstly, trees should be planted in good number. Secondly, the excessive use of CFC should be banned. Above all, public awareness should be created among the masses against the terrible consequence of the Global Warming.

Evaluating Atmospheric and Surface Drivers for O2 Variations at Gale Crater as Observed by MSL SAM

We explore and evaluate various processes that could drive the variations in the volume mixing ratio (VMR) of atmospheric O2 observed by the quadrupole mass spectrometer (QMS) of the Sample Analysis at Mars (SAM) instrument suite on the Mars Science Laboratory (MSL) Curiosity rover. First reported by Trainer et al. (), these ∼20% variations in the O2 VMR on a seasonal timescale over Mars Years 31–34, in excess of circulation and transport effects driven by the seasonal condensation and sublimation of CO2 at the poles, are significantly shorter than the modeled O2 photochemical lifetime. While there remains significant uncertainty about the various processes we investigated (atmospheric photochemistry, surface oxychlorines and H2O2, dissolution from brines, and airborne dust), the most plausible driver is surface oxychlorines, exchanging O2 with the atmosphere through decomposition by solar ultraviolet and regeneration via O3. A decrease in O3 from increased atmospheric H2O would reduce the removal rate of O2 from the atmosphere to form oxychlorines at the surface. This is consistent with the tentative observation that increases in O2 are associated with increases in water vapor. A lack of correlation with the local surface geology along Curiosity’s traverse within Gale crater, the nonuniqueness of the relevant processes to Gale crater, and the short mixing timescales of the atmosphere all suggest that the O2 variations are a regional, or even global, phenomenon. Nonetheless, further laboratory experiments and modeling are required to accurately scale the laboratory-measured rates to Martian conditions and to fully elucidate the driving mechanisms.

Band alignment engineering at ultra-wide bandgap GeO2/SiO2 heterointerfaces

Owing to the tremendous contribution for the carrier transport across the interface, the band alignment engineering in oxide semiconductor heterojunctions (OSHs) is of vital importance for developing oxide semiconductor optoelectronic devices. Here, we have deposited a series of ultra-wide bandgap GeO2 thin films on quartz substrates by the direct-current reactive magnetron sputtering method to construct the OSHs and described the effect of the flow rate ratios of O2 and Ar (O2:Ar) and substrate temperatures on the bandgap energies of GeO2 films and band alignments at the interface of OSHs. Based on the energy loss spectra of O 1 s peaks, the tunable bandgap energies ranging from 4.37 to 5.37 eV have been achieved for GeO2 films. An obvious variation of band alignments has been found in the OSHs, suggesting the dramatically influence of deposition conditions. The valence band offsets are determined to be ranging from 1.85 to 1.96 eV (from 1.88 to 1.95 eV) and the conduction band offsets are calculated to be ranging from 1.88 to 2.78 eV (from 1.74 to 2.19 eV) for the GeO2 films grown at different O2:Ar (substrate temperatures), respectively, due to the nonlocalization of the oxygen vacancies in valence band and the formation of single hexagonal phase in the GeO2 film. Our findings on the band alignment engineering in the GeO2/SiO2 heterointerfaces will open the way for developing GeO2-based optoelectronic devices.