Search

As a fundamental physical process in the ionosphere, photoionization and the associated photoelectrons play vital roles in determining the ionospheric electron density and temperature for Earth and other planets with atmospheres such as Mars and Venus. The production and transport of ionospheric photoelectrons have been widely examined on Earth, but relatively less studied for other terrestrial planets, such as Mars and Venus. In this study, a two‐stream photoelectron transport model for Mars and Venus is constructed, in which the photoelectron fluxes, photoelectron heating rates, primary and secondary ionization rates are calculated. The simulated photoelectron fluxes agree with Mars Atmosphere and Volatile Evolution (MAVEN) observations at various altitudes, with the input of solar spectrum irradiance, electron density and temperature, neutral density and temperature observed by MAVEN. Moreover, by parametrically fitting the simulation results for various solar zenith angles and solar activities, we obtain empirical parameterized formulas for ionization and heating efficiencies which can potentially be adapted to planetary ionospheric models for the community. Key Points: A two‐stream model for Venus and Mars provides photoelectron flux, secondary ionization and photoelectron heating ratesThe photoelectron fluxes simulated by the two‐stream model agree with the Mars Atmosphere and Volatile Evolution observationsParameterized models of ionization and heating efficiencies are available for the community [ABSTRACT FROM AUTHOR]

SO2 (Sulfur dioxide) is the major precursor to the production of sulfuric acid (H2SO4), contributing to acid rain and atmospheric aerosols. Sulfuric acid formed from SO2 generates light-reflecting sulfate aerosol particles in the atmosphere. This property has prompted recent geoengineering proposals to inject sulfuric acid or its precursors into the Earth’s atmosphere to increase the planetary albedo to counteract global warming. SO2 oxidation in the atmosphere by the hydroxyl radical HO to form HOSO2 is a key rate-limiting step in the mechanism for forming acid rain. However, the dynamics of the HO + SO2 → HOSO2 reaction and its slow rate in the atmosphere are poorly understood to date. Herein, we use photoelectron spectroscopy of cryogenically cooled HOSO2-anion to access the neutral HOSO2 radical near the transition state of the HO+SO2 reaction. Spectroscopic and dynamic calculations are conducted on the first ab initio-based full-dimensional potential energy surface to interpret the photoelectron spectra of HOSO2-and to probe the dynamics of the HO + SO2 reaction. In addition to the finding of a unique pre-reaction complex (HO⋯SO2) directly connected to the transition state, dynamic calculations reveal that the accessible phase space for the HO + SO2 → HOSO2 reaction is extremely narrow, forming a key reaction bottleneck and slowing the reaction rate in the atmosphere, despite the low reaction barrier. This study underlines the importance of understanding the full multidimensional potential energy surface to elucidate the dynamics of complex bimolecular reactions involving polyatomic reactants. [ABSTRACT FROM AUTHOR]

In situ produced photoelectrons and precipitating solar wind electrons are two distinct hot electron populations in the dayside Martian upper atmosphere. While each population has been known for decades, its relative contribution to the measured hot electron flux has not been adequately characterized up to now. In this study, we implement a two‐stream kinetic model to compute the hot electron flux for a open magnetic field configuration. By comparing model results to realistic data acquired by the Mars Atmosphere and Volatile Evolution mission, we show that the electron fluxes predicted by the pure photoelectron model are enormously underestimated, especially in the direction toward Mars, but the measurements can be adequately reproduced once solar wind electron precipitation is taken into account. Such a precipitation plays a crucial role above 180 km, not only for hot electrons at all energies that move toward Mars but also for electrons above 1,000 eV that move away from Mars due to the backscattering of precipitating electrons. In contrast, the hot electron population is predicted to be mostly composed of photoelectrons below 180 km. The significance of precipitating solar wind electrons is also evaluated, revealing an appreciable impact on the structure of the dayside Martian upper atmosphere at high altitudes, where electron impact ionization is enhanced by a factor of 7 and cold electron heating enhanced by a factor of 4. Plain Language Summary: This study examines two hot electron populations in the dayside Martian upper atmosphere: locally produced photoelectrons and precipitating solar wind electrons. We intend to figure out how much each population contributes to the total hot electron flux. For this purpose, we construct a kinetic model and compare the model results to the realistic data collected by the Mars Atmosphere and Volatile Evolution mission. We find that the measurements are seriously underestimated by the model with pure photoelectrons, but adequately reproduced when both electron populations are included. In particular, solar wind electrons account for all hot electrons moving toward Mars and part of them moving away. Meanwhile, solar wind electrons likely exert an appreciable impact on the structure of the dayside Martian upper atmosphere, enhancing both ionization and cold electron heating. Key Points: A two‐stream kinetic model is employed to provide a preliminary distinction between photoelectrons and solar wind electrons at MarsPhotoelectrons are found to dominate the hot electron population in all directions below 180 km in the dayside Martian ionospherePrecipitating solar wind electrons are vital above 180 km, for all hot electrons moving toward Mars and part of them moving away from Mars [ABSTRACT FROM AUTHOR]

The chemical co-precipitation method, an effective approach in the synthesis of nanomaterials, was used to synthesize CuO nanoparticles (NPs). Structural and morphological modification of undoped and nitrogen (N) doped CuO nanoparticles were studied thoroughly using X-ray diffraction (XRD), FT-IR and field emission scanning electron microscope (FE SEM). Doping effect on defects was investigated using X-ray photoelectron spectroscopy (XPS), Raman spectroscopy and photoluminescence (PL) spectroscopy. Thus, the effect of doping on crystallinity, crystallite size, strain induced in lattice, defects and electron-hole recombination rate were investigated. Optical band gap was calculated using Kubelka-Munk function from the diffuse reflectance spectra (DRS) obtained using ultraviolet visible (UV–Vis) spectroscopy. Finally, photocatalytic performance was studied from rhodamine B (Rh B) degradation and reaction kinetics were analyzed. Maximum degradation efficiency was obtained for 1.0 mol% N doped CuO NPs which also exhibited minimum band gap and lowest electron-hole recombination rate. For the optimum doping concentration, nitrogen was found to create oxygen vacancies while substituting oxygen in the lattice, and thus reduce electron-hole recombination rate and increase photocatalytic degradation rate effectively.

Minerals are ubiquitous in the natural environment and have close contact with microorganisms. In various scenarios, microorganisms that harbor extracellular electron transfer (EET) capabilities have evolved a series of beneficial strategies through the mutual exchange of electrons with extracellular minerals to enhance survival and metabolism. These electron exchange interactions are highly relevant to the cycling of elements in the epigeosphere and have a profound significance in bioelectrochemical engineering applications. In this review, we summarize recent advances related to the effects of different minerals that facilitate the EET process and discuss the underlying mechanisms and outlooks for future applications. The promotional effects of minerals arise from their redox-active ability, electrical conductivity and photocatalytic capability. In mineral-promoted EET processes, various responses have concurrently arisen in microorganisms, such as stretching of electrically conductive pili (e-pili), upregulated expression of outer-membrane cytochromes (Cyts) and production of specific enzymes, and secretion of extracellular polymeric substances (EPSs). This review synthesizes the understanding of electron exchange mechanisms between microorganisms and minerals and highlights potential applications in development of renewable energy production and pollutant remediation, which are topics of particular significance to future exploitation of biotechnology.

Minerals are ubiquitous in the natural environment and have close contact with microorganisms. In various scenarios, microorganisms that harbor extracellular electron transfer (EET) capabilities have evolved a series of beneficial strategies through the mutual exchange of electrons with extracellular minerals to enhance survival and metabolism. These electron exchange interactions are highly relevant to the cycling of elements in the epigeosphere and have a profound significance in bioelectrochemical engineering applications. In this review, we summarize recent advances related to the effects of different minerals that facilitate the EET process and discuss the underlying mechanisms and outlooks for future applications. The promotional effects of minerals arise from their redox-active ability, electrical conductivity and photocatalytic capability. In mineral-promoted EET processes, various responses have concurrently arisen in microorganisms, such as stretching of electrically conductive pili (e-pili), upregulated expression of outer-membrane cytochromes (Cyts) and production of specific enzymes, and secretion of extracellular polymeric substances (EPSs). This review synthesizes the understanding of electron exchange mechanisms between microorganisms and minerals and highlights potential applications in development of renewable energy production and pollutant remediation, which are topics of particular significance to future exploitation of biotechnology.

Dolomite exhibits a wide distribution in geological strata. The metabolic activities of microorganisms in marine sediments play a crucial role in the formation of dolomite. Semiconducting minerals, such as hematite, goethite, and rutile, generate photoelectrons when exposed to sunlight, which can impact the community structure and metabolic activities of microorganisms. In this study, a simulated photoelectron system was conducted to investigate the response of the microbial community, as well as the regulation of sulfate reduction, to photoelectrons using high-throughput sequencing of the 16S rRNA gene. The regulatory effect of semiconducting mineral photoelectrons on the induction of carbonate precipitation by sulfate-reducing bacteria was explored. X-ray diffraction and Raman spectroscopy were used to characterize carbonate precipitation. During cultivation, the pH values of the system increased from 8.0 to approximately 8.5 and the rate of sulfate reduction was significantly enhanced under the influence of simulated photoelectrons. The alpha diversity of the microbial community decreased, and the semiconducting mineral photoelectronic system had a promoting effect on the enrichment of sulfate-reducing bacteria, mainly Desulfovibrio. Under the regulation of photoelectrons, sulfate-reducing bacteria can effectively oxidize organic matter and reduce sulfate in the environment, and proto-dolomite can be formed at a low Mg/Ca ratio. This process has important implications for carbon and sulfur element cycling in estuarine and oceanic photic zones, and provides a new explanation for the formation of large amounts of dolomite in geological history. [ABSTRACT FROM AUTHOR]

Based on ZnO and melamine, the ZnO/g-C3N4 for photocatalytic U(Ⅵ) reduction was pre-pared by thermal polymerization methods. The surface morphology, lattice structure, element composition and photocatalytic efficiency were analyzed by SEM, XRD, XPS, PL and UV-Vis methods.The results show that the doping of ZnO reduces the recombination rate of photogenerated electrons and holes, expands the response range of the material to visible light, makes ZnO/g-C3N4 have higher photocatalytic activity. When pH=5 and dosage is 0.5 g/L, the highest U(Ⅵ) removal rate can reach 97% after dark reaction for 30 min and light reaction for 30 min. The U(Ⅵ) on the surface of the photocatalyst can be reduced to U(Ⅳ). The photoelectron e- is the main factor for reducing U(Ⅵ) to U(Ⅳ).

Electron beam techniques are indispensable tools for the analysis of surfaces in fundamental as well as applied fields of science and technology. Significant improvements have been made in the past decades in the quantitative understanding of electron spectra, particularly with respect to the near-surface transport of signal electrons. The concept of partial intensities is a simple approach providing physical insight into transport of electrons in solids, a numerically convenient means for spectrum modelling and an essential ingredient for spectrum interpretation. The energy-dissipation process of energetic electrons in solids is discussed from the perspective of the partial intensities, offering a unified model for any type of electron beam technique, be it in the quasi-elastic (QE) or the continuous slowing down (CSD) regime. Examples are given for modelling and analysis of electron spectra such as X-ray photoelectron spectra (XPS), Elastic peak electron spectra (EPES) and electron energy-loss spectra (EELS). The physical model as well as the quantities for electron beam interaction with solids are reviewed, and methods for spectrum modelling and analysis are presented. The examples considered demonstrate the high level of accuracy nowadays attainable for characterisation of surfaces and nanostructures employing techniques using medium energy electrons (>100 eV). This is in contrast to the low energy regime, where a number of problems prevent a similar level of understanding. The topic of low energy electrons (LEEs) is rapidly gaining importance since in this energy range the involved electrons not only act as signal carriers, but also actively participate in electrochemical processes of importance in fields ranging from nanotechnology to life sciences. Issues of future importance in the field of LEEs are discussed and recent developments such as the 2-dimensional electron cascade in the scanning field electron microscope are highlighted.

A cryogenic octopole accumulation trap (COAT) has been coupled to a photoelectron-photofragment coincidence (PPC) spectrometer allowing for improved control over anion vibrational excitation. The anions are heated and cooled via collisions with buffer gas

Oxyanions-nitrate, bromate, and perchlorate in water bodies can do harms of different levels to human health. Photocatalytic reduction is one of the most promising and effective means to convert them into harmless ions. In this article, we discuss the photocatalytic mechanisms of TiO2 catalyst in nitrogen removal process. The factors determining the catalytic activity and the selectivity of nitrogen are elaborated. An overview of the pathway of photocatalysis toward bromate and perchlorate reduction is presented, and the reduction performance of different photocatalysts is evaluated. It is of vital importance to the development of low-cost photocatalytic materials and the use of their activities.

Copyright of Journal of Materials Engineering / Cailiao Gongcheng is the property of Journal of Materials Engineering Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Dolomite exhibits a wide distribution in geological strata. The metabolic activities of microorganisms in marine sediments play a crucial role in the formation of dolomite. Semiconducting minerals, such as hematite, goethite, and rutile, generate photoelectrons when exposed to sunlight, which can impact the community structure and metabolic activities of microorganisms. In this study, a simulated photoelectron system was conducted to investigate the response of the microbial community, as well as the regulation of sulfate reduction, to photoelectrons using high-throughput sequencing of the 16S rRNA gene. The regulatory effect of semiconducting mineral photoelectrons on the induction of carbonate precipitation by sulfate-reducing bacteria was explored. X-ray diffraction and Raman spectroscopy were used to characterize carbonate precipitation. During cultivation, the pH values of the system increased from 8.0 to approximately 8.5 and the rate of sulfate reduction was significantly enhanced under the influence of simulated photoelectrons. The alpha diversity of the microbial community decreased, and the semiconducting mineral photoelectronic system had a promoting effect on the enrichment of sulfate-reducing bacteria, mainly Desulfovibrio. Under the regulation of photoelectrons, sulfate-reducing bacteria can effectively oxidize organic matter and reduce sulfate in the environment, and proto-dolomite can be formed at a low Mg/Ca ratio. This process has important implications for carbon and sulfur element cycling in estuarine and oceanic photic zones, and provides a new explanation for the formation of large amounts of dolomite in geological history.

• Synergistic system eliminated NO 3 − and degraded 91.2% of OTC in artificial wastewater. • Photoelectron transportation promoted microbial metabolism. • Synergistic system enhanced microbial degradation in aquaculture wastewater. The low carbon-to-nitrogen (C/N) ratio in aquaculture wastewater presents challenges for biological treatments, particularly regarding combined pollution, such as nitrate and oxytetracycline. Herein, this study introduces a synergistic system that integrates photocatalysts (N-doped carbon dots/g-C 3 N 4) with a domesticated microbial community. In artificial wastewater at a C/N ratio of 2, the synergistic system removed completely nitrate and degraded 91.2 % of oxytetracycline simultaneously at 24 h. Moreover, within this system, the accumulation of nitrite was effectively eliminated and the nitrogen production ratio was increased to 82.6 %. Noticeably, oxytetracycline was transformed efficiently into low molecular weight products. In the synergistic treatment process, photocatalysis serves a role in enhancing biodegradation. The generated photoelectrons are efficiently transported through the biofilms, boosting microbial metabolic activity. This increase in microbial activity leads to improved removal of both nitrate and oxytetracycline. The synergistic system was also operated in actual aquaculture wastewater environment to evaluate its practical application potential. The Synergistic system exhibited removal efficiencies for nitrate and oxytetracycline that were 2.1 and 1.8 times higher, respectively, compared to biodegradation treatments. The proposed synergistic system offers a promising strategy to simultaneously tackle nitrate-oxytetracycline pollution, particularly in wastewater characterized by a low C/N ratio, without limiting its applicability to aquaculture wastewater. [ABSTRACT FROM AUTHOR]

Oxyanions-nitrate, bromate, and perchlorate in water bodies can do harms of different levels to human health. Photocatalytic reduction is one of the most promising and effective means to convert them into harmless ions. In this article, we discuss the photocatalytic mechanisms of TiO2 catalyst in nitrogen removal process. The factors determining the catalytic activity and the selectivity of nitrogen are elaborated. An overview of the pathway of photocatalysis toward bromate and perchlorate reduction is presented, and the reduction performance of different photocatalysts is evaluated. It is of vital importance to the development of low-cost photocatalytic materials and the use of their activities. [ABSTRACT FROM AUTHOR]

Electron pitch angle distributions similar to bidirectional electron conics (BECs) have been reported at Mars in previous studies based on analyses of Mars Global Surveyor measurements. BEC distribution, also termed “butterfly” distribution, presents a local minimum flux at 90° and a maximum flux before reaching the local loss cone. Previous studies have focused on 115 eV electrons that were produced mainly via solar wind electron impact ionization. Here using Solar Wind Electron Analyzer measurements made onboard the Mars Atmosphere and Volatile Evolution spacecraft, we identify 513 BEC events for 19–55 eV photoelectrons that were generated via photoionization only. Therefore, we are investigating electrons observed in regions well away from their source regions, to be distinguished from 115 eV electrons observed and produced in the same regions. We investigate the spatial distribution of the 19–55 eV BECs, revealing that they are more likely observed on the nightside as well as near strong crustal magnetic anomalies. We propose that the 19–55 eV photoelectron BECs are formed due to day-to-night transport and the magnetic mirror effect of photoelectrons moving along cross-terminator closed magnetic field lines.

An important population of the dayside Martian ionosphere are photoelectrons that are produced by solar Extreme Ultraviolet and X-ray ionization of atmospheric neutrals. A typical photoelectron energy spectrum is characterized by a distinctive peak near 27 eV related to the strong solar HeII emission line at 30.4 nm, and an additional peak near 500 eV related to O Auger ionization. In this study, the extensive measurements made by the Solar Wind Electron Analyzer on board the recent Mars Atmosphere and Volatile Evolution spacecraft are analyzed and found to verify the scenario that Martian ionosphere photoelectrons are driven by solar radiation. We report that the photoelectron intensities at the centers of both peaks increase steadily with increasing solar ionizing flux below 90 nm and that the observed solar cycle variation is substantially more prominent near the O Auger peak than near the HeII peak. The latter observation is clearly driven by a larger variability in solar irradiance at shorter wavelengths. When the solar ionizing flux increases from 1 mW·m-2 to 2.5 mW·m-2, the photoelectron intensity increases by a factor of 3.2 at the HeII peak and by a much larger factor of 10.5 at the O Auger peak, both within the optically thin regions of the Martian atmosphere.

The photoelectron peak at 22–27 eV, a distinctive feature of the energetic electron distribution in the dayside Martian ionosphere, is a useful diagnostic of solar extreme ultraviolet (EUV) and X-ray ionization as well as of large-scale transport along magnetic field lines. In this work, we analyze the pitch angle distribution (PAD) of energetic electrons at 22–27 eV measured during several representative Mars Atmosphere and Volatile Evolution (MAVEN) orbits, based on the electron spectra gathered by MAVEN’s Solar Wind Electron Analyzer (SWEA) instrument. On the dayside, most photoelectron spectra show an isotropic PAD as is expected from production via solar EUV/X-ray ionization. The photoelectron spectra occasionally observed on the nightside show instead a strongly anisotropic PAD, indicative of cross-terminator transport along ambient magnetic field lines. This would in turn predict the presence of dayside photoelectrons, also with a strongly anisotropic PAD, which was indeed revealed in SWEA data. Comparison with magnetic field measurements made by the MAVEN Magnetometer suggests that on average the photoelectrons with anisotropic PAD stream away from Mars on the dayside and towards Mars on the nightside, further supporting the scenario of day-to-night transport. On both sides, anisotropic photoelectrons tend to be observed above the photoelectron exobase at ~160 km where photoelectron transport dominates over local production and energy degradation.

Photoelectrons are an integral part of the sunlit lunar plasma environment. This paper formulates the characteristic velocity distribution of the emitted photoelectrons over the sunlit Moon. As an advancement, Fowler's photoemission theory has been coupled with observed solar spectra, photoelectric quantum yield, and latitude-dependent surface temperature in deriving the velocity distribution function (VDF) of the photoelectrons. It is noticed that the dominant contribution in the photoelectron VDF comes from extreme ultraviolet photons of the solar spectra and it significantly deviates from the Maxwellian nature. Moreover, within a photoelectron sheath which refers to finite surface potential, the velocity distributions significantly differ from that of the uncharged surface — VDF has been evaluated in terms of free and trapped photoelectron population densities. The derived VDF is found in close agreement with the measured photoelectron velocity distribution. • Photoelectron velocity distribution over sunlit Moon is formulated. • Fowler's theory is coupled with observed solar/lunar parameters to characterize photoelectrons. • Trapped and free photoelectron populations coexist with different mean energies. • Derived photoelectron distribution closely matches the measured distribution. [ABSTRACT FROM AUTHOR]

Photoelectrons are produced by solar Extreme Ultraviolet radiation and contribute significantly to the local ionization and heat balances in planetary upper atmospheres. When the effect of transport is negligible, the photoelectron energy distribution is controlled by a balance between local production and loss, a condition usually referred to as local energy degradation. In this study, we examine such a condition for photoelectrons near Mars, with the aid of a multi-instrument Mars Atmosphere and Volatile Evolution data set gathered over the inbound portions of a representative dayside MAVEN orbit. Various photoelectron production and loss processes considered here include primary and secondary ionization, inelastic collisions with atmospheric neutrals associated with both excitation and ionization, as well as Coulomb collisions with ionospheric thermal electrons. Our calculations indicate that photoelectron production occurs mainly via primary ionization and degradation from higher energy states during inelastic collisions; photoelectron loss appears to occur almost exclusively via degradation towards lower energy states via inelastic collisions above 10 eV, but the effect of Coulomb collisions becomes important at lower energies. Over the energy range of 30–55 eV (chosen to reduce the influence of the uncertainty in spacecraft charging), we find that the condition of local energy degradation is very well satisfied for dayside photoelectrons from 160 to 250 km. No evidence of photoelectron transport is present over this energy range.

Photoelectron images have been measured following the ionisation of aligned distributions of gas phase naphthalene and aniline molecules. Alignment in the adiabatic regime was achieved by interaction with a 100 ps infrared laser pulse, with ionisation achieved in a two-photon resonant scheme using a low intensity UV pulse of ∼6 ps duration. The resulting images are found to exhibit anisotropy that increases when the alignment pulse is present, with the aniline PADs peaking along the polarisation vector of the ionising light and the naphthalene PADs developing a characteristic four-lobed structure. Photoelectron angular distributions (PADs) that result from the ionisation of unaligned and fully aligned distributions of molecules are calculated using the ePolyScat ab initio suite and converted into two-dimensional photoelectron images. In the case of naphthalene excellent agreement is observed between experiment and the simulation for the fully aligned distribution, showing that the alignment step allows us to probe the molecular frame, but in the case of aniline it is clear that additional processes occur following the one-photon resonant step. [ABSTRACT FROM AUTHOR]

The chemical co-precipitation method, an effective approach in the synthesis of nanomaterials, was used to synthesize CuO nanoparticles (NPs). Structural and morphological modification of undoped and nitrogen (N) doped CuO nanoparticles were studied thoroughly using X-ray diffraction (XRD), FT-IR and field emission scanning electron microscope (FE SEM). Doping effect on defects was investigated using X-ray photoelectron spectroscopy (XPS), Raman spectroscopy and photoluminescence (PL) spectroscopy. Thus, the effect of doping on crystallinity, crystallite size, strain induced in lattice, defects and electron-hole recombination rate were investigated. Optical band gap was calculated using Kubelka-Munk function from the diffuse reflectance spectra (DRS) obtained using ultraviolet visible (UV-Vis) spectroscopy. Finally, photocatalytic performance was studied from rhodamine B (Rh B) degradation and reaction kinetics were analyzed. Maximum degradation efficiency was obtained for 1.0 mol% N doped CuO NPs which also exhibited minimum band gap and lowest electron-hole recombination rate. For the optimum doping concentration, nitrogen was found to create oxygen vacancies while substituting oxygen in the lattice, and thus reduce electron-hole recombination rate and increase photocatalytic degradation rate effectively., Competing Interests: The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (© 2024 The Authors. Published by Elsevier Ltd.)

This article reports on an advanced level physical chemistry laboratory experiment designed for college-level undergraduate education and for scholars who need specialized training on using and interpreting X-ray photoelectron spectroscopy. A presentation and discussion of the use of X-ray photoelectron spectroscopy in the surface characterization of six common samples are emphasized. The six samples were copper foil, copper nanoplatelets, amorphous carbon, graphite rod, uncoated and coated glass (respectively labeled as glass side A and glass side B). Survey spectra obtained for each sample were compared to known literature spectra allowing for the identification of the element types present in each sample. Furthermore, quantitative information regarding the mass percentages of each element type was also obtained and is presented herein. On an educational standpoint, this article will allow any reader, in particular, undergraduate and graduate students, to gain a better understanding of the theory and practice of X-ray photoelectron spectroscopy. [ABSTRACT FROM AUTHOR]

The photoelectrochemical characteristic of semiconducting minerals plays an imperative role in supporting the growth of many electroactive microorganisms. In order to study the effects of photoelectrons triggered from semiconducting mineral by solar energy on the marine microbial growth, metabolism, and community structure, a dual-chamber electrochemical system was established by incubating seawater microbial community with varying simulated electrochemical conditions. The absolute quantifications of 16S rRNA and 18S rRNA genes suggested that photoelectrons could support the growth and reproduction of bacteria with an increase of two magnitudes from 1.34 ± 0.76 × 1012 to 1.41 ± 0.93 × 1014, and archaea with a slight increase from 0.50–8.74 × 1011 to 2.37–14.80 × 1011, whereas not for the growth of eukaryote in consideration of the complicated regulating mechanism of eukaryotic cells. The bacterial and archaeal communities were shaped by the supplement of photoelectron, also not for the eukaryotic community. Proteobacteria, Bacteroidetes, Firmicutes, and Actinobacteria accounted for over 80% of the total bacterial community. Photoelectrons with appropriate energy could stimulate the diversity and maintain the community structure of bacteria and archaea while lower or higher electric potential caused lower diversity and more divergent microbial assemblages. The abundance of genes related to the electron transport chain was significantly higher in photoelectron regulated setups than that in open circuit ones, indicating that the extracellular photoelectrons experienced the transmembrane transition and entered the bacterial electron transport chain coupling cell anabolism and catabolism. This study proposed the potential impact of photoelectrons produced by semiconducting minerals on marine microorganisms and the putative electron flow under sunlight in the natural environments. [ABSTRACT FROM AUTHOR]

Photoelectrons are an extensively studied component of planetary ionospheres which have been frequently used as a diagnostic of ambient magnetic fields. We show in this study that they also provide information on atmospheric composition via the altitude variation of photoelectron intensity at specific energies. Such an idea is applied to Mars for which a large observational sample of photoelectrons is available from the Solar Wind Electron Analyzer measurements made by the Mars Atmosphere and Volatile Evolution (MAVEN). Our analysis reveals a strong decline in photoelectron intensity from 160 to 200 km, but this trend is restricted to a narrow energy range of 10–15 eV. By employing analytical yield spectrum calculations, we derive the model variations based on different choices of the background atmosphere. We find that the presence of CO is crucial for reproducing the observed variations. This allows atmospheric CO densities to be estimated from photoelectron measurements, which are a factor of 3–7 lower than the published densities based on the MAVEN Neutral Gas and Ion Mass Spectrometer measurements and in better agreement with existing model results. In general, the usefulness of photoelectron intensity at a specific energy as a tracer of atmospheric composition relies critically on the species‐dependent inelastic electron impact cross section at this energy. Plain Language Summary: On each solar system body with a substantial atmosphere, the ionization of atmospheric neutrals by solar photons produces photoelectrons at a typical energy of several eV to several hundred eV. These electrons have caught extensive research interests for decades because their spatial distribution has been recognized as a good tracer of ambient magnetic fields. In this study, we propose that photoelectrons could also be used as a tracer of atmospheric composition. Such an idea is applied to Mars, showing that the change of photoelectron flux with altitude at 10–15 eV relies critically on the distribution of atmospheric CO. When applied to other planets, the combination of the atmospheric species and photoelectron energy involved may vary, depending on the detailed characteristics of inelastic collisions between electrons and neutrals. Our idea provides a potentially useful constraint on the abundance of key atmospheric species when it cannot be measured accurately by a mass spectrometer, a situation often encountered in modern planetary missions. Key Points: The altitude variation of photoelectronintensity at specific energies is a potential tracer of atmospheric compositionThe altitude variation of photoelectronintensity is controlled by the species‐dependent inelastic electron impact cross sectionFor Mars, a strong altitude variation of photoelectron intensity occurs at 10–15 eV and is sensitive to the CO abundance [ABSTRACT FROM AUTHOR]

[Display omitted] • Three kinds of absorbed stages are explored in structural evolutions. • Simulated photoelectron spectra agree with experiments. • Infrared and Raman spectra have deformation and breathing mode. • Neutral TiSn 16 cluster is the most stability motif. • TiSn 16 cluster has optoelectronic property from UV–Vis adsorption. The structural evolution, chemical stability, electronic and vibrational properties, as well as charge transfer and bonding character of TiSn n 0/−/2− (n = 4–17) clusters have been performed with density functional theory calculations using ABCluster search technique. Structurally, it is found that the growth patterns prefer three kinds of absorbed stages from polygonal bipyramidal configuration for n = 4–6, to absorbing additional Sn on the adjacent surfaces of pentagonal bipyramid unit from n = 7–12, and finally to the TiSn 13 0/−/2− cluster as the first foundational architectures, of which the encapsulated cage structure is formed when n = 11. The simulated PES spectra agree with available experiments. More interestingly, the neutral TiSn 16 cluster not only possesses the high thermodynamic and relative stability but also preferable photochemical reactivity, that can be further explained by superatom features and delocalized multi-center bonds (AdNDP), while the strong p-d hybridization between Ti atom and Sn unit plays an important role in the stabilities of clusters, making it as the most suitable building units. In addition, the UV–Vis absorption spectra of TiSn 16 are discussed, and the main transitions of crucial excited states are analyzed in detail. The Infrared and Raman vibrational characteristic peaks of all these neutral and charged species are properly assigned, of which the TiSn n 0/−/2− (n = 10–17) clusters possess degenerating deformation mode of Ti atom wagging in Sn cage framework (Infrared active) and breathing mode of Sn cage framework (Raman active). All these findings will provide a further understanding for the nanoalloy cluster as the most suitable building block with further development as a potential optoelectronic material. [ABSTRACT FROM AUTHOR]

In this paper, we report X-ray absorption and core-level electron spectra of the nucleobase derivative 2-thiouracil at the sulfur L1- and L2,3-edges. We used soft X-rays from the free-electron laser FLASH2 for the excitation of isolated molecules and dispersed the outgoing electrons with a magnetic bottle spectrometer. We identified photoelectrons from the 2p core orbital, accompanied by an electron correlation satellite, as well as resonant and non-resonant Coster–Kronig and Auger–Meitner emission at the L1- and L2,3-edges, respectively. We used the electron yield to construct X-ray absorption spectra at the two edges. The experimental data obtained are put in the context of the literature currently available on sulfur core-level and 2-thiouracil spectroscopy.

We have investigated magneto-optic properties of ultrathin Fe films grown on Pt(111) surfaces by using the in situ surface magneto-optic Kerr effect (SMOKE) and X-ray photoelectron spectroscopy (XPS). SMOKE measurements show that the Fe layers are not ferromagnetic when the film is thinner than approximately 4.5 MLs (monolayers), but the in-plane magnetization is present for a 4.1 ML Fe film on Pt(111) annealed at 550 K. Upon post-annealing at 770 K, a 9.2 ML Fe film does not show any Kerr signal, while a 6.3 ML Fe film has the in-plane Kerr signal with increased coercivity. The oxidation and reduction of ultrathin Fe films have also been studied by using XPS. Upon an oxygen exposure of 300 Langmuir at a film temperature of 873 K, the Fe layers were mostly oxidized as Fe3O4. When the Fe films were exposed to the same amount of oxygen at room temperature, a partial oxidation as Fe3O4 was observed for a 3 ML Fe film, while there was no oxidation for a 2 ML Fe film. On heating the 873 K oxidized films, Fe3O4O was reduced to FeO, and even the decomposition was observed. Underlying reasons for these chemical changes of Fe and iron-oxide films are discussed.

A cryogenic octopole accumulation trap (COAT) has been coupled to a photoelectron-photofragment coincidence (PPC) spectrometer allowing for improved control over anion vibrational excitation. The anions are heated and cooled via collisions with buffer gas

SO 2 (Sulfur dioxide) is the major precursor to the production of sulfuric acid (H 2 SO 4 ), contributing to acid rain and atmospheric aerosols. Sulfuric acid formed from SO 2 generates light-reflecting sulfate aerosol particles in the atmosphere. This property has prompted recent geoengineering proposals to inject sulfuric acid or its precursors into the Earth's atmosphere to increase the planetary albedo to counteract global warming. SO 2 oxidation in the atmosphere by the hydroxyl radical HO to form HOSO 2 is a key rate-limiting step in the mechanism for forming acid rain. However, the dynamics of the HO + SO 2 → HOSO 2 reaction and its slow rate in the atmosphere are poorly understood to date. Herein, we use photoelectron spectroscopy of cryogenically cooled HOSO 2 - anion to access the neutral HOSO 2 reaction. Spectroscopic and dynamic calculations are conducted on the first ab initio-based full-dimensional potential energy surface to interpret the photoelectron spectra of HOSO 2 reaction. Spectroscopic and dynamic calculations are conducted on the first ab initio-based full-dimensional potential energy surface to interpret the photoelectron spectra of HOSO 2 - and to probe the dynamics of the HO + SO 2 reaction. In addition to the finding of a unique pre-reaction complex (HO⋯SO 2 ) directly connected to the transition state, dynamic calculations reveal that the accessible phase space for the HO + SO 2 → HOSO 2 reaction is extremely narrow, forming a key reaction bottleneck and slowing the reaction rate in the atmosphere, despite the low reaction barrier. This study underlines the importance of understanding the full multidimensional potential energy surface to elucidate the dynamics of complex bimolecular reactions involving polyatomic reactants., Competing Interests: Competing interests statement:The authors declare no competing interest.

Multiple studies have reported either isotropic or trapped pitch angle distributions of high‐energy (>100 eV) electrons on closed crustal field lines on the dayside of Mars. These pitch angle distributions are not to be expected from collisional scattering and conservation of adiabatic invariants alone. We use 2 years of data from the Mars Atmosphere and Volatile EvolutioN mission to analyze the pitch angle distributions of superthermal electrons on dayside‐closed crustal magnetic fields and compare to results from an electron transport model. Low‐energy electrons (10–60 eV) have pitch angle distributions in agreement with modeling results, while high‐energy electrons (100–500 eV) do not. High‐energy electrons have a flux peak at perpendicular pitch angles which suggests there is a ubiquitous energization process occurring on crustal fields. Wave‐particle interactions seem to be the most likely candidate. Trapping of high‐energy electrons may impact the nightside ionosphere dynamics. Plain Language Summary: Superthermal electrons are electrons with energies between 1 and 1,000 eV and can be produced from ionizing a neutral atmospheric molecule (photoelectron). These electrons are efficient at shifting energy around in space environments due to their high speeds and their ability to interact with the more ubiquitous lower energy (thermal) plasma. Past studies have investigated the distribution of photoelectrons on the crustal magnetic fields of Mars, and they do not always agree with past modeling results and a basic understanding of electron transport. In this study, we use data from the Mars Atmosphere and Volatile EvolutioN mission in order to understand the distribution of these electrons throughout the Mars space environment, previously impossible due to spacecraft orbits. We find that the lower energy electrons (10–60 eV) behave as expected but the higher‐energy electrons (100–500 eV) do not. We find that the type of distribution statistically seen by Mars Atmosphere and Volatile EvolutioN for these high‐energy electrons suggests that a ubiquitous energization process is occurring on the dayside crustal magnetic fields of Mars. We consider multiple physical processes capable of producing such observed distributions and conclude that wave‐particle interactions are the most likely candidate. Key Points: Low‐energy photoelectrons on the Martian dayside have pitch angle distributions consistent with conservation of adiabatic invariantsHigh‐energy electrons on the Martian dayside have a flux peak at perpendicular pitch angles, indicating a ubiquitous energization processWave‐particle interactions are the most likely candidate to produce such distributions for high‐energy electrons [ABSTRACT FROM AUTHOR]

Photoelectrons are an important population of the dayside Martian upper atmosphere that contributes substantially to the local ionization and heat balances. This study is focused on the broad shape of the photoelectron energy spectrum at 10–50 eV. Assuming a power law distribution, we derive the hardness of each photoelectron energy spectrum measured on the dayside of Mars by the Solar Wind Electron Analyzer on board the Mars Atmosphere and Volatile Evolution spacecraft. Our analysis reveals two distinctive features: (1) The hardness tends to increase with decreasing altitude down to 140 km and then decrease toward lower altitudes; (2) the hardness tends to decrease with increasing solar zenith angle. These variations are restricted to regions below 250 km whereas the hardness appears to be fairly constant at higher altitudes. In practice, the hardness is modulated by the ionization of atmospheric neutrals by solar Extreme Ultraviolet and X‐ray photons, inelastic collisions with atmospheric neutrals, Coulomb collisions with ionospheric thermal electrons, and photoelectron transport. While inelastic collisions tend to harden the photoelectron energy spectrum, both primary production and Coulomb collisions tend to soften it instead. We argue that the observed variations of the hardness can be understood in terms of the relative contributions of different processes. Our analysis also suggests the presence of appreciable temporal variability in hardness with a typical timescale of 10 min. Key Points: We investigate the broad shape of the photoelectron energy spectrum at 10–50 eV on the dayside of MarsThe photoelectron spectral shape presents interesting variations with both altitude and solar zenith angleAppreciable temporal variability in the photoelectron spectral shape is present on a typical timescale of 10 min [ABSTRACT FROM AUTHOR]

• First measurement of the full energy spectrum of electrons emitted from Ag. • Contribution from Auger-unrelated events was subtracted from the Auger spectrum of Ag. • Compared with a Monte-Carlo model to obtain an estimate of multi-electron processes. • Results indicate that 20%–60% of the core holes decay via CVVV like multi-electron process. We report the first measurement of the full energy spectrum (down to 0 eV) of electrons emitted from the surface of Ag(100) as a result of the N 3 VV Auger transition. A comparison with a Monte-Carlo model was used to obtain an estimate of the contribution of multi-electron Auger processes to the low energy part of the Auger spectrum. The experimental Auger spectrum was obtained in time coincidence with photo-emitted 4p 3/2 core electrons from Ag using Auger-Photoelectron coincidence spectroscopy (APECS). The coincidence condition in APECS can remove most, but not all, spectral contributions from events unrelated to the Auger transition. The remaining contributions to the APECS spectrum from Auger-unrelated events, which are significant, were determined from a series of coincidence measurements of inelastically scattered valence band photoelectrons. The contribution from Auger-unrelated events was subtracted from the APECS Auger spectrum of Ag(100) to obtain the full Auger spectrum down to 0 eV. The resulting spectrum includes, in addition to Auger electrons emitted without energy loss, inelastically scattered Auger electrons. We observe that the spectral weight of the low energy tail (LET) in the APECS spectrum is reduced by more than a factor of two after subtracting the Auger-unrelated contributions. However, the intensity of the LET after this subtraction is still two times the integrated intensity in the Auger peak. A Monte Carlo model that includes the inelastic transport of the N 3 VV Auger electrons through the surface showed that LET produced by the inelastic scattering of the Auger electrons has the same intensity as the integrated intensity in the Auger peak. The excess intensity in the experimental LET provides strong evidence that the Auger related spectrum also includes contribution from multiple electron emissions that are intrinsic to the creation and/or the Auger decay of the core hole. Our estimate shows that as low as 20% to as high as 60% of the core hole decay events result in the emission of more than one Auger electron from Ag (100). This result demonstrates the need for a better understanding of the contribution of valence-electron correlations to the entire CVV Auger spectrum down to 0 eV. [ABSTRACT FROM AUTHOR]

Lead pollution is rapidly becoming a serious concern, and remediation of lead contamination is a major challenge. Biological remediation is both environmentally friendly and sustainable process. In this study, we investigated the application of Aspergillus niger (Bpb1) for removing lead ion from a liquid medium by using photoelectron generated from a light-semiconductor mineral-microbial system. Synthetic anatase electrodes were systematically characterized and used as a photoelectron provider. Under light irradiation, the adsorption rates of Pb(II) by A. niger in the experimental groups increased by 204% (the maximum) on the fourth day, while the total adsorption rates remained the same. Further study of lead products revealed that lead ion combines with organic acids to form extracellular lead-containing products, which wrap around the fungal hyphae and combine with the cell wall. The anatase photoelectron enhanced the adsorption rate of Pb(II) by A. niger by forming larger lead-containing products, and by accelerating the transportation of Pb(II) into the inner cell. This novel approach provides newer insights into the application of biological degradation for environmental remediation. [ABSTRACT FROM AUTHOR]

The dynamics of the photoelectric effect in solid-state systems can be investigated via attosecond-time-resolved photoelectron spectroscopy. This article provides a comparison of delay information accessible by the two most important techniques, attosecond streaking spectroscopy and reconstruction of attosecond beating by interference of two-photon transitions (RABBITT) at solid surfaces, respectively. The analysis is based on simulated time-resolved photoemission spectra obtained by solving the time-dependent Schrödinger equation in a single-active-electron approximation. We show a continuous transition from the few-cycle RABBITT regime to the streaking regime as two special cases of laser-assisted photoemission. The absolute delay times obtained by both methods agree with each other, within the uncertainty limits for kinetic energies >10 eV. Moreover, for kinetic energies >10 eV, both streaking delay time and RABBITT delay time coincide with the classical time of flight for an electron propagating from the emitter atom to the bulk-vacuum interface, with only small deviations of less than 4 as due to quantum mechanical interference effects. [ABSTRACT FROM AUTHOR]

The solar light response and photoelectrons produced by widespread semiconducting mineral play important roles in biogeochemical cycles on Earth’s surface. To explore the potential influence of photoelectrons generated by semiconducting mineral particles on nitrate-reducing microorganisms in the photic zone, a marine heterotrophic denitrifier Halomonas sp. strain 3727 was isolated from seawater in the photic zone of the Yellow Sea, China. This strain was classified as a Halomonadaceae. Whole-genome analysis indicated that this strain possessed genes encoding the nitrogen metabolism, i.e., narG, nasA, nirBD, norZ, nosB, and nxr, which sustained dissimilatory nitrate reduction, assimilatory nitrate reduction, and nitrite oxidation. This strain also possessed genes related to carbon, sulfur, and other metabolisms, hinting at its substantial metabolic flexibility. A series of microcosm experiments in a simulative photoelectron system was conducted, and the results suggested that this bacterial strain could use simulated photoelectrons with different energy for nitrate reduction. Nitrite, as an intermediate product, was accumulated during the nitrate reduction with limited ammonia residue. The nitrite and ammonia productions differed with or without different energy electron supplies. Nitrite was the main product accounting for 30.03% to 68.40% of the total nitrogen in photoelectron supplement systems, and ammonia accounted for 3.77% to 8.52%. However, in open-circuit systems, nitrite and ammonia proportions were 26.77% and 11.17%, respectively, and nitrogen loss in the liquid was not observed. This study reveals that photoelectrons can serve as electron donors for nitrogen transformation mediated by Halomonas sp. strain 3727, which reveals an underlying impact on the nitrogen biogeochemical cycle in the marine photic zone.