Emission Density Research Articles

The centimeter emission from planet-forming disks in Taurus

The last decade has witnessed remarkable advances in the characterization of the (sub-)millimeter emission from planet-forming disks. Conversely, the study of (sub-)centimeter emission has made more limited progress, to the point that only a few exceptional disk-bearing objects have been characterized in the centimeter regime. This work takes a broad view of the centimeter emission from a large sample with Karl G. Jansky Very Large Array (VLA) observations that is selected from previous Atacama Large (sub-)Millimeter Array (ALMA) surveys of more representative disks in brightness and extent . We report on the detection and characterization of flux at centimeter wavelengths from 21 sources in the Taurus star-forming region. Complemented by literature and archival data, the entire photometry from 0.85 mm to 6 cm is fit by a two-component model that determines the ubiquitous presence of free-free emission entangled with the dust emission. The flux density of the free-free emission is found to scale with the accretion rate but is independent of the outer-disk morphology depicted by ALMA. The dust emission at 2 cm is still appreciable and offers the possibility to extract an unprecedented large set of dust spectral indices in the centimeter regime. A pronounced change between the median millimeter indices (2.3) and centimeter indices (2.8) suggests that a large portion of the disk emission is optically thick up to 3 mm. The comparison of both indices and fluxes with the ALMA disk extent indicates that this portion can be as large as 40 au and suggests that the grain population within this disk region that emits the observed centimeter emission is similar in disks with different sizes and morphologies. All these results await confirmation and dedicated dust modeling once facilities such as next generation VLA (ngVLA) or Square Kilometre Array (SKA)-mid are able to resolve the centimeter emission from planet-forming disks and disentangle the various components.

Carbon Emission Status and Regional Differences of China: High-Resolution Estimation of Spatially Explicit Carbon Emissions at the Prefecture Level

There are disagreements regarding the accuracy of estimation and spatial distribution of carbon emissions in China. It is of great significance to estimate a more detailed carbon emission inventory for China and analyze the carbon emission characteristics of different regions. This study comprehensively estimated carbon dioxide and methane emissions (and their spatial distributions) across eight carbon-emitting sectors in 360 prefecture-level cities in China in 2020. The results indicated that total carbon emissions in China amounted to 146.00 × 108 t, with carbon dioxide and methane accounting for 95.87% and 4.13%, respectively. The industrial sector was the main source of carbon emissions, accounting for 75.42% of the total. The North China Plain, the Northeast Plain, and the Sichuan Basin were identified as the carbon emission hotspot areas with the most intensive carbon emission densities. Among the clustered four carbon emission zones based on carbon emission density and economic carbon intensity, the High Carbon Emission Density and High Economic Carbon Intensity zones accounted for 41.73% of total carbon emissions. To achieve carbon neutrality, it is essential to devise emission reduction strategies for specific areas by thoroughly considering spatially explicit variation at the prefecture level, with a focus on primary carbon-emitting cities and sectors.

Predictions of Dust Continuum Emission from a Potential Circumplanetary Disk: A Case Study of the Planet Candidate AB Aurigae b

Abstract Gas-accreting planets embedded in protoplanetary disks are expected to show dust thermal emission from their circumplanetary disks (CPDs). However, a recently reported gas-accreting planet candidate, AB Aurigae b, has not been detected in (sub)millimeter continuum observations. We calculate the evolution of dust in the potential CPD of AB Aurigae b and predict its thermal emission at 1.3 mm wavelength as a case study, where the obtained features may also be applied to other gas-accreting planets. We find that the expected flux density from the CPD is lower than the 3σ level of the previous continuum observation by the Atacama Large Millimeter/submillimeter Array with broad ranges of parameters, consistent with a nondetection. However, the expected planet mass and gas accretion rate are higher if the reduction of the observed near-infrared continuum and Hα line emission due to the extinction by small grains is considered, resulting in higher flux density of the dust emission from the CPD at (sub)millimeter wavelengths. We find that the corrected predictions of the dust emission are stronger than the 3σ level of the previous observation with the typical dust-to-gas mass ratio of the inflow to the CPD. This result suggests that the dust supply to the vicinity of AB Aurigae b is small if the planet candidate is not the scattered light of the star but is a planet and has a CPD. Future continuum observations at shorter wavelengths are required to obtain more robust clues to the question of whether the candidate is a planet or not.

Spatio-Temporal Change in Urban Carbon Metabolism Based on Ecological Network Analysis: A Case Study in the Beijing–Tianjin–Hebei Urban Agglomeration, China

Urban carbon emissions significantly contribute to climate change, exacerbating environmental issues such as global warming. Understanding carbon metabolism is vital for identifying key emission sources and implementing targeted mitigation strategies. This study presents an innovative carbon metabolism analysis framework that integrates an ecological network analysis (ENA) with land use dynamics, enriching the theoretical system and providing policy recommendations for sustainable urban development. We investigated carbon metabolism in the Beijing–Tianjin–Hebei Urban Agglomeration (BTHUA) from 2000 to 2020 using land use and statistical data. The ENA method quantified the ecological relationships between land use compartments. Our findings revealed that industrial and transportation land exhibited the highest carbon emission density, while forest land demonstrated the highest carbon sequestration density. Notably, the negative net horizontal carbon flow indicated that land use changes exacerbated the disorder of carbon metabolism. The increasing mutualism index suggested a reduction in the negative impacts of land use changes on carbon metabolism. This study highlights the importance of spatial planning in transforming ecological relationships and provides a comprehensive understanding of carbon metabolism dynamics influenced by land use changes. The insights gained can inform effective mitigation strategies in the BTHUA and similar urban agglomerations, ultimately contributing to sustainable urban development.

Interaction between the supernova remnant W44 and the infrared dark cloud G034.77-00.55: Shock induced star formation

We have studied the dense gas morphology and kinematics towards the infrared dark cloud (IRDC) G034.77-00.55, shock-interacting with the SNR W44, to identify evidence of early-stage star formation induced by the shock. We used high angular resolution N$_2$H$^+$(1-0) images across G034.77-00.55, obtained with the Atacama Large Millimeter/sub-Millimeter Array. N$_2$H$^+$ is a well-known tracer of dense and cold material, optimal for identifying gas that has the highest potential to harbour star formation. The N$_2$H$^+$ emission is distributed in two elongated structures, one towards the dense ridge at the edge of the source and one towards the inner cloud. Both elongations are spatially associated with well-defined mass-surface density features. The velocities of the gas in the two structures (i.e. 38-41 km s$^ $ and 41-43 km s$^ $) are consistent with the lowest velocities of the J- and C-type parts, respectively, of the SNR-driven shock. A third velocity component is present at 43-45.5 km s$^ $. The dense gas shows a fragmented morphology with core-like fragments at scales consistent with the Jeans lengths, masses of sim 1-20 M$_ odot $, densities of (n(H$_2$)geq 10$^5$ cm$^ $) sufficient to host star formation in free-fall timescales (a few 10$^4$ yr), and with virial parameters that suggest a possible collapse. The W44 driven shock may have swept up the encountered material, which is now seen as a dense ridge, almost detached from the main cloud, and an elongation within the inner cloud, well constrained in both N$_2$H$^+$ emission and mass surface density. This shock compressed material may have then fragmented into cores that are either in a starless or pre-stellar stage. Additional observations are needed to confirm this scenario and the nature of the cores.

Heavy metal emissions from on-road vehicles in Xia-Zhang-Quan metropolitan area in southeastern China from 2015 to 2060: impact of vehicle electrification.

Vehicle electrification is an important means of reducing urban air pollution. However, vehicle electrification does not necessarily reduce particulate matter (PM2.5 and PM10) and heavy metals (HM) due to the increase in non-exhaust emissions. In this study, we established the emission inventories of PM2.5, PM10, and their associated heavy metals (PM2.5-HM and PM10-HM) from the on-road vehicles in the Xiamen-Zhangzhou-Quanzhou metropolitan area in southeastern China between 2015 and 2060. In the base year 2021, brake wear emissions account for 66.6% of PM2.5-HM and 76.9% of PM10-HM, much higher than the contributions of exhaust emissions to PM2.5-HM (12.4%) and PM10-HM (6.2%). Light-duty passenger vehicles, heavy-duty trucks, and light-duty trucks are the three main contributors to PM and HM. HM emissions have a high emission density in urban areas. In the business-as-usual (BAU) scenario, HM emissions continue to increase from 2021 to 2060 due to the combined effects of the stricter emission standards and the growth of vehicle population, while the health risk of HM shows an initial decrease and then an increasing trend. Compared with BAU, moderate and aggressive electrification scenarios show a significant reduction in PM2.5-HM emissions between 2030 and 2060, but not in PM10-HM emissions. Further increases in vehicle electrification will bring forward the peak of PM2.5-HM emissions, with the potential to reduce adverse health effects. In the process of vehicle electrification, the reduction of heavy metal emissions from the braking system should be prioritized in order to effectively reduce traffic pollution.

Alkaline Hydrogen Evolution Reaction Electrocatalysts for Anion Exchange Membrane Water Electrolyzers: Progress and Perspective.

For the aim of achieving the carbon-free energy scenario, green hydrogen (H2) with non-CO2 emission and high energy density is regarded as a potential alternative to traditional fossil fuels. Over the last decades, significant breakthroughs have been realized on the alkaline hydrogen evolution reaction (HER), which is a fundamental advancement and efficient process to generate high-purity H2 in the laboratory. Based on this, the development of the practical industry-oriented anion exchange membrane water electrolyzer (AEMWE) is on the rise, showing competitiveness with the incumbent megawatt-scale H2 production technologies. Still, great challenges lie in exploring the electrocatalysts with remarkable activity and stability for alkaline HER, as well as bridging the gap of performance difference between the three-electrode cell and AEMWE devices. In this perspective, we systematically discuss the in-depth mechanisms for activating alkaline HER electrocatalysts, including electronic modification, defect construction, morphology control, synergistic function, field effect, etc. In addition, the current status of AEMWE is reviewed, and the underlying bottlenecks that impede the application of HER electrocatalysts in AEMWE are summarized. Finally, we share our thoughts regarding the future development directions of electrocatalysts toward both alkaline HER and AEMWE, in the hope of advancing the commercialization of water electrolysis technology for green H2 production.

Spatiotemporal Evolution of Territorial Spaces and Its Effect on Carbon Emissions in Qingdao City, China

Land use change has always been a significant factor affecting global carbon emissions. Dissecting the characteristics of territorial space evolution and its impact on carbon emissions is crucial for developing low-carbon-oriented territorial space optimization and governance strategies. This paper calculates the carbon emissions associated with territorial spaces in Qingdao from 2000 to 2020, utilizing land use data alongside various statistical data. Based on the accounting results, the evolution characteristics of territorial spaces and their corresponding carbon emissions, as well as the carbon transition dynamics resulting from space transfer, are analyzed. A carbon transition decomposition formula is then proposed to quantify the differential and spatially heterogeneous impacts of changes in space types and socio-economic development on emissions. The results indicate that: (1) the evolution of territorial spaces in Qingdao during 2000–2020 is characterized by an expansion of living space and a contraction of production and ecological spaces; (2) net carbon emissions rose from 313.98 × 104 tons to 1068.58 × 104 tons, with urban production space contributing the most (69.96% in 2020) due to its significantly high emission density. The spatial distribution of carbon emissions exhibited a stable “northwest–southeast” pattern, with increased dispersion and weakened directionality; (3) the transformation of territorial spaces promoted carbon emissions in Qingdao, with the conversion of urban production space to other uses yielding the most favorable carbon transitions, while the expropriation of agricultural production spaces for urban production and residents’ living has resulted in the most detrimental carbon transitions; (4) socio-economic development shapes the overarching pattern of regional emission density changes, whereas space transfers account for local variations. This paper also identifies priorities for spatial optimization and key sectors for emission reduction. The findings contribute to a deeper understanding of the carbon emission consequences of territorial space transformation in Qingdao, thereby providing valuable insights for regional spatial planning and optimization aimed at promoting low-carbon development.

Exploration of the Photoluminescence Behavior and Emission Mechanism of Thioester Polyacrylamide Tablets During the Gradual Increase of Molecular Weight.

To enhance the photoluminescence (PL) of unconventional luminescent compounds, particularly their persistent room temperature phosphorescence (p-RTP) performance, compressing the powder into tablets has been demonstrated as a viable approach. Nevertheless, the alterations in the emission capability of PL in compacted tablets have not been comprehensively investigated. In this study, four polyacrylamide (PAM) with controllable molecular weight (MW) are fabricated from powder to tablets, and their PL emission properties are thoroughly examined and compared with corresponding powders to elucidate the emission mechanism. As MW increases, both PL and p-RTP emissions of the tablets gradually intensify, exhibiting significant enhancement compared to the corresponding powder while retaining the characteristic blue shift. Through small angle X-ray scattering (SAXS), construction of molecular models for tablets, detailed analysis of molecular interactions, and theoretical calculations are conducted to reasonably explain these emission phenomena using clustering-triggered emission (CTE) and average packing density promoted emission (PDE) mechanisms. These findings not only advance the understanding of nonconventional luminogens' emission mechanisms but also offer new insights for preparing nonconventional luminescent polymers with controllable p-RTP emission performance.

Investigating plasma activated water as a sustainable treatment for improving growth and nutrient uptake in maize and pea plant

In this study, an atmospheric pressure air plasma jet (APAPJ) was employed to generate plasma-activated water (PAW), which was applied to treat maize (monocot) and pea (dicot) seeds for evaluating its influence. This research explored APAPJ diagnostics by varying the air feed rate as 1, 2, and 3 liter per minute (Lpm) through current-voltage characterization, optical emission spectroscopy, electron temperature and density, nitrogen metastable state density, and rotational and vibrational temperature of the plasma. Additionally, various reactive oxygen and nitrogen species (RONS) formed and physicochemical properties of PAW were analyzed by varying plasma treatment time from 0 to 8 min. Furthermore, the water uptake of maize (Zea mays) and pea (Pisum sativum) seeds were examined by the measurement of the contact angle. Results indicated that APAPJ has the capacity of fostering germination, growth, chlorophyll, phosphorus, nitrite, nitrate, ammonium ion and leaf area in plants significantly with an optimized 6 min treated PAW for maize and 2 min treated PAW for peas. Among various categories, seeds soaked in PAW and irrigated with PAW exhibited the most outstanding result in germination and plant growth. Non-thermal plasma showed promising green methods for enhancing plant growth and boosting nutrient content.

Molten Salt-Assisted Synthesis of Ferric Oxide/M-N-C Nanosheet Electrocatalysts for Efficient Oxygen Reduction Reaction.

Efficient, stable, and low-cost oxygen reduction catalysts are the key to the large-scale application of metal-air batteries. Herein, high-dispersive Fe2O3 nanoparticles (NPs) with abundant oxygen vacancies uniformly are anchored on lignin-derived metal-nitrogen-carbon (M-N-C) hierarchical porous nanosheets as efficient oxygen reduction reaction (ORR) catalysts (Fe2O3/M-N-C, M═Cu, Mn, W, Mo) based on a general and economical KCl molten salt-assisted method. The combination of Fe with the highly electronegative O induces charge redistribution through the Fe-O-M structure, thereby reducing the adsorption energy of oxygen-containing substances. The coupling effect of Fe2O3 NPs with M-N-C expedites the catalytic activity toward ORR by promoting proton generation on Fe2O3 and transfer to M-N-C. Experimental and theoretical calculation further revealed the remarkable electronic structure evolution of the metal site during the ORR process, where the emission density and local magnetic moment of the metal atoms change continuously throughout their reaction. The unique layered porous structure and highly active M-N4 sites resulted in the excellent ORR activity of Fe2O3/Cu-N-C with the onset potential of 0.977V, which is superior to Pt/C. This study offers a feasible strategy for the preparation of non-noble metal catalysts and provides a new comprehension of the catalytic mechanism of M-N-C catalysts.

Differentiated strategies for synergistic mitigation of ammonia and methane emissions from agricultural cropping systems in China

Ammonia (NH3) and methane (CH4) emissions from agricultural cropping systems in China have substantially impacted environmental quality and climate change, which become the key sector for synergizing pollution control and carbon reduction. However, the experiences of synergistic NH3 and CH4 emission governance at fine scales in this sector are still lacking. Here, we estimated NH3 and CH4 emissions from agricultural cropping systems in China in 2019 and identified regional characteristics of these emissions using advanced spatial analysis techniques. Subsequently, we developed an innovative synergistic mitigation zoning identification method to establish targeted and spatially differentiated reduction measures, addressing a critical gap in mitigation strategies for agricultural cropping systems in China. The results showed that NH3 and CH4 emissions from the three most important crops were 3.04 Tg N yr-1 and 8.13 Tg C yr-1, respectively. NH3 and CH4 emissions exhibited the highest values in Eastern China, but the highest emission densities of NH3 (49.8 kg N ha-1 yr-1) and CH4 (394 kg C ha-1 yr-1) were observed in Northwest and South China, respectively. Further, bivariate local indicators of spatial association (LISA) maps revealed that the middle and lower reaches of the Yangtze River were hotspots for simultaneous high emissions of NH3 and CH4. Finally, based on the identified eight categories of zones, region-specific mitigation measures were proposed, including improved fertilization practices, irrigation methods, and straw management. These targeted, spatially differentiated mitigation strategies provide a reference framework and feasible approach for synergistic pollution control and carbon reduction in China's agricultural sector.

Carbon emission measurement and regional decomposition analysis of China’s beef cattle farming industry

IntroductionWarming caused by greenhouse gas (GHG) emissions has become a global environmental issue of widespread concern, and China, as a responsible power, has the pressing task of reducing carbon emissions. China is one of the world’s major beef producers and consumers, and at the same time, beef cattle, as a large livestock, is the largest source of GHG emissions in the livestock industry.MethodsThis study considered the panel data of 31 provinces in China from 2008 to 2022. The kernel density estimation and Dagum Gini coefficient were used to analyze the spatiotemporal dynamic evolution patterns and influencing factors of carbon emissions from China’s beef cattle farming industry.Results(1) The carbon emission trajectory of beef cattle production follows a distinctive “ascend-descend-ascend” three-phase pattern. By 2022, the sector’s cumulative carbon emissions had burgeoned by 37.62% relative to 2008, reflecting an average annual escalation of 2.31%. Despite the overall upward trend in carbon emissions, significant regional differences were observed. The Central Plains region has witnessed a consistent decline, in stark contrast to the Southwest and Northeast regions, which have emerged as hotspots for heightened carbon emissions and intensified emission densities within China’s beef cattle production landscape, underscoring the intensifying significance of carbon mitigation measures. (2) The kernel density curve shows an overall rightward shift with a specific gradient effect on carbon emissions. In addition, the range of the right drag of the curve in 2022 was significantly reduced, which laterally reflects the narrowing of the difference between the provinces with the highest and lowest carbon emissions from beef cattle farming. The principal source of variance in the overall carbon emissions from beef cattle production is the disparities between regions, which accounts for an average annual contribution rate of 52.52%. Conversely, the within-region contribution rates have remained relatively stable, while those for the intensity of transvariation have witnessed a substantial rise, with annual averages of 18.31 and 28.96%, respectively. (3) Regarding the factors influencing carbon emissions reduction, environmental regulations and production efficiency significantly drive carbon emissions reduction in beef cattle farming.DiscussionRelevant government departments should actively guide farmers toward green production, establish perfect policies and regulations for low-carbon beef cattle farming, and promote low-carbon beef cattle farming models based on local conditions.

Spatial Correlation of Land Use Carbon Budget Based on Social Network Analysis： A Case Study of Chongqing Metropolitan Area

Clarifying the temporal and spatial changes in the carbon budget in the Chongqing metropolitan area and exploring the spatial correlation of land use carbon budget are of great significance for realizing the regional "double carbon" goal. Using 21 districts and counties in Chongqing metropolitan area as the research scale, the IPCC inventory method, carbon emission coefficient method, Gini coefficient, gravity model, and social network analysis were used to estimate the net carbon emissions from land use in Chongqing metropolitan area from 2000 to 2020, and the spatial correlation of the carbon budget was obtained. The results revealed that： ① In the past 20 years, the carbon budget of the Chongqing metropolitan area showed an overall upward trend, with an average annual growth rate of 2.83%, and the spatial distribution was "higher in the north and south, higher in the east and west, and lower in the middle." ② During the past 20 years, the spatial difference of net carbon emissions in the Chongqing metropolitan area became highly average, and the overall Gini coefficient decreased by 11.42%, whereas the intra-group difference was the largest in key development zones. ③ In the past 20 years, the overall structure of the spatial correlation network of land use carbon budget in the Chongqing metropolitan area has become stable and complex, and the network density and network correlation number have increased by 0.43 and 180, respectively, the network correlation degree has increased to 1, and the network health degree has improved. ④ In the individual network structure of land use carbon budget in the Chongqing metropolitan area, the degree centrality of each district and county has increased, and the increase in the central urban area was the most significant, with an increase of 81, whereas the decline in intermediate centrality and proximity centrality has promoted the regional coordinated development and integration process in the metropolitan area. ⑤ In the past 20 years, the density of net carbon emissions in the Chongqing metropolitan area has increased as a whole, with the density of the core area increasing by 0.35 and the density of the core-edge area increasing by 0.34. By exploring the change and spatial correlation of land use carbon budget in the Chongqing metropolitan area, this study clarified the spatial distribution difference of carbon budget and provided support for regional green development.

Boosting hydrogen production via alkaline water splitting: Impact of Ag doping in Gd2O3 nanosheet arrays

Hydrogen is a preferable renewable energy carrier in decarbonization efforts to develop sustainable and carbon-free economies due to its high energy density and absence of pollutant emissions during combustion. Among others, electrochemical water splitting (EWS) is a sustainable and eco-friendly technology for producing green hydrogen, representing an essential initial step towards achieving carbon neutrality. In this study, we synthesized a bifunctional electrocatalyst by vertically anchoring Ag-doped Gd2O3 nanosheet arrays onto a three-dimensional nickel foam (NF) substrate. The developed materials were thoroughly investigated using various analytical techniques. Furthermore, the electrocatalyst effectively performed oxygen evolution reactions (OER) and hydrogen evolution reactions (HER). The Ag4%-Gd2O3/NF exhibited boosted HER activity, achieving higher current densities ranging from 10 to 400 mA cm−2 at an overpotential between 14 and 122 mV. This study also highlights the considerable impact of metal sites in both Ag4%-Gd2O3/NF and Gd2O3/NF on the HER catalytic process. Similarly, the Ag4%-Gd2O3 electrocatalyst exhibited superior OER activity, with an overpotential of 209 mV at 10 mA cm−2. The optimized composition also shows Tafel slope of 25 and 20 mVdec−1. Furthermore, Ag4%-Gd2O3 demonstrated the ability to generate oxygen gas bubbles in approximately 20 h for OER, making it an attractive material for energy conversion and storage devices.

The recognition and optimization study on the dominant agricultural space in Cangzhou based on the suitability evaluation of agricultural production

Agricultural spatial division and suggestions for the optimization of the partition space were obtained by constructing a recognition system of the dominant agricultural space. The prerequisite was to master natural economic development in agriculture. It was vital to maintain national food security and promote healthy and sustainable agriculture. The suitability evaluation of agricultural production and the dominance evaluation of agricultural development were incorporated to recognize the dominant agricultural space in Cangzhou, Hebei, China in 2020. Besides, priority scenarios were set, e.g., economic development, low-carbon protection, and coordinated development of a low-carbon economy. The NSGA-II genetic algorithm model was used to optimize the quantitative structure of cultivated lands in the agricultural space of Cangzhou in three scenarios in 2030. The research results are as follows: (1) Cangzhou had the largest number of general suitable areas for agricultural production in 2020, accounting for 27.04%; suitable areas were the least, accounting for 10.99%. The proportion of current cultivated lands in unsuitable agricultural production areas still stood at 11.26%; (2) The dominance of agricultural development in 2020 in Cangzhou was mainly at Tier III, accounting for 33.60% with the general dominance of agricultural development; (3) The total area of the dominant agricultural space in Cangzhou was 238208.75 hm2, accounting for 16.72% of the national territorial area of Cangzhou. It included 35 villages and towns beyond ecological red lines, mainly distributed in the western part of Cangzhou; (4) The agricultural space of Cangzhou in 2030, optimized by the multi-objective NSGA-II genetic algorithm model, exhibited decreased cultivated lands across three scenarios. The total amount of cultivated lands was the largest under the priority scenario of economic development, and that was the smallest under the priority scenario of coordinated development of a low-carbon economy. Meanwhile, agricultural economic benefits and carbon emission density were reduced under three scenarios. The benefits and density were moderate under the coordinated development of low carbon and economy. The work provides a reference for further formulating and improving the policies of the agricultural space in various regions.

Enhancing Field Emission in Air via Ultrascaled Nanorod Electrodes.

Enhancing field emission in ultrascaled electronics improves the device performance and energy efficiency. Conventional lithography defines electrodes with a few-nanometer spacing on the cost of strengthened electron scattering and the reduced field enhancement factor, thus presenting challenges to enhance field emission at a small bias. Here, we used self-assembled nanorods with sub-5 nm spacing as electrodes to overcome these challenges. Intrinsic ballistic transport through high-crystallinity solution-synthesized nanorods minimized charge scattering; meanwhile ultrascaled anisotropic morphologies concentrated local electric fields and thereby lowered the barrier height. Enabled by these structural features, we demonstrated field emission density up to 4.1 × 104 A cm-2 at 1 V in air, more than 10-fold higher than typical molecular and vacuum electronics at similar conditions, and constructed an air-operating electron source with an on/off ratio of 105 at the collector electrode. Energy-efficient high-conductance electron emission suggested the potential of using solution-synthesized nanomaterials in ultrascaled electronics.

The effects of aluminate compounds on the free Ba generation and electron emission performance of dispenser cathode

Free barium (Ba) is critical to the formation of the active layer on the surface of dispenser cathode, which is contributed to the electron emission properties of the cathode. The Ba in the active layer of the dispenser cathode is generated by the chemical reaction between aluminate compounds and tungsten (W) under vacuum and high temperature. Nowadays, the effect of aluminate compounds on the generation of free Ba is not clear. In this work, aluminate impregnants called 411, 532 and 612 impregnants were prepared by coprecipitation method. The structure of the dominate compounds in 411, 532 and 612 impregnants were determined with density functional theory (DFT) calculation and Rietveld structure refinement. It was found that the dominate compounds of 411, 532 and 612 impregnants are Ba3.5Ca0.5Al2O7, Ba5CaAl4O12 and Ba3CaAl2O7, respectively. Then, the temperature dependence of the thermodynamic properties, such as Debye temperature, entropy, heat capacity and enthalpy, of the aluminate compounds were calculated. Based on the thermodynamic properties, the potential chemical reaction between aluminate compounds and W are energetically determined by deviation Gibbs energy. The effects of different aluminate compounds on the free Ba generation were evaluated with the equilibrium Ba(g) amounts that generated by the chemical reactions between aluminate compounds and W. It is shown that the equilibrium Ba(g) amounts generated by Ba3.5Ca0.5Al2O7 is higher than that by Ba5CaAl4O12 and Ba3CaAl2O7, implying the superiority of electron emission performance of Ba3.5Ca0.5Al2O7. The electron emission densities of the dispenser cathodes that impregnated with the 411, 612 and 532 impregnants are 5.06, 4.31 and 4.05 A/cm2, respectively. It is revealed that the Ba3.5Ca0.5Al2O7 has superiority in generating free Ba, which agreed well with thermodynamic simulation results.

Simple and efficient synthesis of [Ca24Al28O64]4+(4e−) electronic compounds and preliminary exploration of its electron emission as a cathode emitter

[Ca24Al28O64]4+(4e−) electronic compound (C12A7:e−) is a ceramic with extremely low work function, and it exhibits outstanding potential in cathode electron emission. However, the existing preparation methods for this material are cumbersome, time-consuming, and have limited electron density. In this paper, C12A7:e− were prepared using high-pressure hydrothermal reaction and plasma activation sintering. The free O2− in the cages of the sample achieved accelerated diffusion and transition under the high temperature, strong electric field, high-energy pulse current, and plasma activation. Meanwhile, a high concentration of electrons (2 × 1021 cm−3) was rapidly injected into the sample. In addition, the C12A7:e− blocks have fewer defects, such as pores, cracks, and impurities, and their relative density reaches 99.6 %. The electron emission density and effective work function of the C12A7:e− are 1.49 A/cm2 and 2.25 eV, respectively, at 1100 °C. This article provides a reference for preparing C12A7:e− and their applications in electronic emission.

Comparison of models for the warm-hot circumgalactic medium around Milky Way-like galaxies

ABSTRACT A systematic comparison of the models of the circumgalactic medium (CGM) and their observables is crucial to understanding the predictive power of the models and constraining physical processes that affect the thermodynamics of CGM. This paper compares four analytic CGM models: precipitation, isentropic, cooling flow, and baryon pasting models for the hot, volume-filling CGM phase, all assuming hydrostatic or quasi-hydrostatic equilibrium. We show that for fiducial parameters of the CGM of a Milky Way (MW)-like galaxy ($M_{\rm vir} \sim 10^{12}~{\rm M}_{\odot }$ at $z\sim 0$), the thermodynamic profiles – entropy, density, temperature, and pressure – show most significant differences between different models at small ($r\lesssim 30$ kpc) and large scales ($r\gtrsim 100$ kpc) while converging at intermediate scales. The slope of the entropy profile, which is one of the most important differentiators between models, is $\approx 0.8$ for the precipitation and cooling flow models, while it is $\approx 0.6$ and 0 for the baryon pasting and isentropic models, respectively. We make predictions for various observational quantities for an MW mass halo for the different models, including the projected Sunyaev–Zeldovich effect, soft X-ray emission (0.5–2 keV), dispersion measure, and column densities of oxygen ions (O vi, O vii, and O viii) observable in absorption. We provide Python packages to compute the thermodynamic and observable quantities for the different CGM models.