Deep Transition Research Articles

Dopability of divalent tin containing phosphates for p -type transparent conductors

Tin(II) containing phosphates, ${\mathrm{Sn}}_{n}{\mathrm{P}}_{2}{\mathrm{O}}_{5+n}$ ($n$ is an integer), are promising candidates for $p$-type transparent conductors due to their good stability, suitable band gaps, and reasonable hole effective masses. Here we conduct first-principles calculations on ${\mathrm{Sn}}_{n}{\mathrm{P}}_{2}{\mathrm{O}}_{5+n}$ type compounds by exploring their defect properties along with the dopability to find better candidates for $p$-type transparent conducting oxides. We consider two compounds, ${\mathrm{Sn}}_{3}{\mathrm{P}}_{2}{\mathrm{O}}_{8}$ ($n=3$) and ${\mathrm{Sn}}_{5}{\mathrm{P}}_{2}{\mathrm{O}}_{10}$ ($n=5$), with their binary counterpart SnO for a thorough comparison. Various likely native defects, as well as possible hydrogen-related extrinsic impurities have been examined. In ${\mathrm{Sn}}_{n}{\mathrm{P}}_{2}{\mathrm{O}}_{5+n}$, Sn interstitial and Sn vacancy are the dominant donor and acceptor defects. In contrast to SnO, Sn vacancies have quite deep charge transition levels in ${\mathrm{Sn}}_{n}{\mathrm{P}}_{2}{\mathrm{O}}_{5+n}$. The results indicate that both the studied phosphates are not good $p$-type transparent conductors even at the optimal growth conditions. However, our findings suggest that ${\mathrm{Sn}}_{n}{\mathrm{P}}_{2}{\mathrm{O}}_{5+n}$ with a higher $n$ would allow for a relatively higher hole concentration and a shallow-level defect for Sn vacancy, thus calling future research in this direction.

Deep Phase Transition of MoS2 for Excellent Hydrogen Evolution Reaction by a Facile C-Doping Strategy.

Metallic 1T-phase MoS2 is considered to be the ideal electrocatalyst to carry out hydrogen evolution reaction (HER) because of favorable conductivity and sufficient active site compared with 2H-phase MoS2. Nevertheless, 1T-phase MoS2 is conventionally synthesized in a complicated process, with the production of an unstable product, which hinders their practical applications. Herein, we propose a facile approach through a carbon-doping-induced phase transition to obtain highly stable 1T-2H mixed MoS2 nanosheets. The phase transition process is characterized by Raman and X-ray photoelectron spectroscopy, as well as high-resolution transmission electron microscopy images and delivers a high phase purity of ∼60% for 1T-MoS2. According to density functional theory simulations and experimental results, C-doped 1T-2H mixed MoS2 has the advantages of abundant active sites, facilitated charge transfer rate, and high activity toward HER. The obtained C-doped MoS2 exhibits a superb HER electrocatalytic performance, with a current density of 10 mA cm-2 and the overpotential as low as 40 mV in 1 M KOH solution, and brilliant stability.

Global 3D Hydrodynamic Modeling of In-transit Lyα Absorption of GJ 436b

Abstract Using a global 3D, fully self-consistent, multifluid hydrodynamic model, we simulate the escaping upper atmosphere of the warm Neptune GJ 436b, driven by the stellar X-ray and ultraviolet (XUV) radiation impact and gravitational forces and interacting with the stellar wind. Under the typical parameters of XUV flux and stellar wind plasma expected for GJ 436, we calculate in-transit absorption in Lyα and find that it is produced mostly by energetic neutral atoms outside of the planetary Roche lobe, due to the resonant thermal line broadening. At the same time, the influence of radiation pressure has been shown to be insignificant. The modeled absorption is in good agreement with the observations and reveals such features as strong asymmetry between blue and red wings of the absorbed Lyα line profile, deep transit depth in the high-velocity blue part of the line reaching more than 70%, and the timing of early ingress. On the other hand, the model produces significantly deeper and longer egress than in observations, indicating that there might be other processes and factors, still not accounted for, that affect the interaction between the planetary escaping material and the stellar wind. At the same time, it is possible that the observational data, collected in different measurement campaigns, are affected by strong variations of the stellar wind parameters between the visits, and therefore they cannot be reproduced altogether with the single set of model parameters.

The Green Light or The Green Line? Challenges Facing the Energy Choices for Switzerland.

For most of its history, even though Switzerland has relied on imported fossil fuels to meet its energy needs, low-carbon energy sources such as hydropower and nuclear power have been at the forefront of the electricity generation sector for the last 50 years. However, after the Fukushima nuclear accident in 2011, Switzerland decided to phase out nuclear energy by 2034 through the “Energy Strategy 2050”, a national plan adopted in 2017 that represents a structural break in its energy pattern. Compared to Germany, Switzerland has chosen a less environmentally harmful but more risky strategy, which consists of limiting the substitution of nuclear energy with fossil fuel energy sources, while filling the gap created by the progressive nuclear phase-out through the massive development of alternative and renewable energy sources in the long term. Facing this “green challenge”, Switzerland would need to import electricity from European foreign suppliers. However, one missing element of this global reform appears in the transport sector, which still produces significant CO2 emissions. Such historical constraint would undoubtedly affect Switzerland’s energy security and independence patterns. However, the real challenge created by this nuclear phase-out may not be about becoming energy-independent, because such a deep transition necessitates important electricity imports, but rather about answering the growing electricity demand in the future and securing its energy supply, with the share of renewable energy sources becoming increasingly important. Indeed, Switzerland will have to deal with the trilemma of energy security, independence and sovereignty.

The Effect of Hydrogen on the Device Stability of Amorphous InGaZnO Thin‐Film Transistors under Positive Bias with Various Temperature Stresses

The effects of hydrogen incorporation in the active layer of amorphous InGaZnO (a‐IGZO) thin‐film transistors (TFTs) on device characteristics and instability under positive bias stress (PBS) and positive bias temperature stress (PBTS) are studied. To control the amount of incorporated hydrogen, rapid thermal annealing (RTA) treatment is conducted on the gate insulator layer before active layer deposition. It is confirmed that the amount of residual hydrogen in the gate insulator layer decreases with increasing RTA treatment time. Device stability is examined with RTA treatment times of 1 and 3 min under PBS. The device fabricated with a shorter RTA treatment time shows relatively better stability. This result is attributed to defect passivation by hydrogen that diffuses to the active layer from the gate insulator during the post‐annealing process. Additionally, TFT shows the negative shift of Vth under a high‐temperature PBTS condition. This result is due to the additional diffusion of residual hydrogen from the gate insulator into the active layer and hydrogen‐related deep state transition in the active layer by external thermal energy and a PBS condition.

DTMT: A Novel Deep Transition Architecture for Neural Machine Translation

Past years have witnessed rapid developments in Neural Machine Translation (NMT). Most recently, with advanced modeling and training techniques, the RNN-based NMT (RNMT) has shown its potential strength, even compared with the well-known Transformer (self-attentional) model. Although the RNMT model can possess very deep architectures through stacking layers, the transition depth between consecutive hidden states along the sequential axis is still shallow. In this paper, we further enhance the RNN-based NMT through increasing the transition depth between consecutive hidden states and build a novel Deep Transition RNN-based Architecture for Neural Machine Translation, named DTMT. This model enhances the hidden-to-hidden transition with multiple non-linear transformations, as well as maintains a linear transformation path throughout this deep transition by the well-designed linear transformation mechanism to alleviate the gradient vanishing problem. Experiments show that with the specially designed deep transition modules, our DTMT can achieve remarkable improvements on translation quality. Experimental results on Chinese⇒English translation task show that DTMT can outperform the Transformer model by +2.09 BLEU points and achieve the best results ever reported in the same dataset. On WMT14 English⇒German and English⇒French translation tasks, DTMT shows superior quality to the state-of-the-art NMT systems, including the Transformer and the RNMT+.

Autoregressive Planet Search: Feasibility Study for Irregular Time Series

Abstract Sensitive signal processing methods are needed to detect transiting planets from ground-based photometric surveys. Caceres et al. show that the autoregressive planet search (ARPS) method—a combination of autoregressive integrated moving average (ARIMA) parametric modeling, a new transit comb filter (TCF) periodogram, and machine learning classification—is effective when applied to evenly spaced light curves from space-based missions. We investigate here whether ARIMA and TCF will be effective for ground-based survey light curves that are often sparsely sampled with high noise levels from atmospheric and instrumental conditions. The ARPS procedure is applied to selected light curves with strong planetary signals from the Kepler mission that have been altered to simulate the conditions of ground-based exoplanet surveys. Typical irregular cadence patterns are used from the Hungarian-made Automated Telescope Network-South (HATSouth) survey. We also evaluate recovery of known planets from HATSouth. Simulations test transit signal recovery as a function of cadence pattern and duration, stellar magnitude, planet orbital period, and transit depth. Detection rates improve for shorter periods and deeper transits. The study predicts that the ARPS methodology will detect planets with ≳0.1% transit depth and periods ≲40 days in HATSouth stars brighter than ∼15 mag. ARPS methodology is therefore promising for planet discovery from ground-based exoplanet surveys with sufficiently dense cadence patterns.

Educational Services for Intellectual Capital Growth or Transmission of Culture for Transfer of Knowledge—Consumer Satisfaction at St. Petersburg Universities

Higher education has complex roles in society, the economy, and politics; it helps to transmit culture, transfer knowledge, and develop the personality of citizens. This diversity of roles is confronted with the limited resources that are related to the sources of financing, that is, students and their families, the national government, and local authorities, among others. The discussions related to the role of universities concern the economy of knowledge and the digital tools influencing education. The specific case of St. Petersburg universities simultaneously represents the impact of the deep socio-political transition from Soviet society to the liberal principles of a market economy, including the perception of higher education institutions as service sector companies. The services allowed by universities include research and training; however, from the consumer point of view, universities should create specific value: the increase of the intellectual components of human capital. These complex functions are interconnected. During 2017–2018, a survey in St. Petersburg was organised to ascertain the opinion of students, professors, and employers on the quality of education. The results of the survey demonstrate the impact of the exaggerated implementation of the liberal principles on education, both positive and negative. The positive effect is the renewing of content and innovative training techniques due to competition among universities. The negative impacts include the preference for popular disciplines and the opportunistic behavior of students that lose their passion for acquiring knowledge and choose instead the passive attitude of consumers of a competitive service. They are less interested in the sphere of their studies, in searching for a job, in the interaction with other social and economic actors, and even in the research and education options presented by the universities.

Effects of indium surfactant and MgN intermediate layers on surface morphology and crystalline quality of nonpolar a-plane AlGaN epi-layers

High quality non-polar a-plane AlGaN epi-layers with dual MgN interlayers were successfully grown on semi-polar r-plane sapphire substrates with the indium-surfactant-assisted metal organic chemical vapor disposition (MOCVD) technology, and characterized with atomic force microscopy, cathode luminescence (CL), and high-resolution X-ray diffraction rocking curve. It was found that both surface morphology and crystalline quality of the non-polar AlGaN films were strongly dependent on the mass flow of indium surfactant in the MOCVD growth process. In fact, the great suppression of the deep energy level impurity-related transitions in the CL spectra indicates a significant enhancement in crystalline quality for the non-polar AlGaN films. Moreover, with the optimization of the indium surfactant mass flow, a root mean square value as small as 10.9 nm was achieved, demonstrating a remarkable improvement in surface morphology for the a-plane AlGaN epi-layer.

Nitrifier abundance and diversity peak at deep redox transition zones

More than half of the global ocean floor is draped by nutrient-starved sediments characterized by deep oxygen penetration and a prevalence of oxidized nitrogen. Despite low energy availability, this habitat hosts a vast microbial population, and geochemical characteristics suggest that nitrogen compounds are an energy source critical to sustaining this biomass. However, metabolic rates of nitrogen transformation and their link to microbial survival in this global-scale ecosystem remain virtually unknown. Here we provide quantitative constraints on microbial nitrogen cycling in open ocean oligotrophic sediments from seafloor to basement, spanning approximately 8 million years. We find active microbial nitrogen transformation throughout the sediment column but at very low rates. Local peaks in diversity and abundance of nitrifiers and denitrifiers occur at redox transition zones deep within the sediments, strongly indicating that these microbes are revived from their maintenance state and start growing again after millions of years of attrition.

Yaratıcı Yıkımdan Kopuş: Neo-Klasik İktisadın İmhası

Sanayilesme surecinin Ingiltere’de baslayan hikâyesi, uretim iliskilerinde ciddi bir degisimi beraberinde getirmis, ortaya cikan yeni nesnel kosullar kurumsal ve dusunsel yapiyi da degistirerek, iktisat biliminin buyuk bir degisim surecine girmesine sebep olmustur. Ozgurluk ve tam rekabet gibi iyimser kavramlarla baslayip, zamanla “kasvetli bilime” evrilen klasik iktisadin yerini ise marjinal devrim olarak adlandirilan bir donusum ve gelen elestirilerle birlikte, matematigin buyulu dunyasina kapilmis neo-klasik iktisat akimi almistir. Bilimsellik amaciyla pratikten hizla uzaklasan ve neredeyse tamamen teorik bir kuram olan neo-klasik iktisat, insani fizik yasalari ile ele alarak, rasyonellik ilkesini on plana cikarmis ve ekonomiyi bir makine gibi gormeye yonelmistir. Buna karsilik, neo-klasik iktisadin zaman zaman dramatik olcude basarisizliklara konu olmasi, kuramin yetersizligine ve pratigi aciklamadaki zayifligina baglanmaktadir. Ozellikle kuramin gunumuz dunyasini aciklamadaki yetersizligi, niceligi on plana cikararak iktisadi soyut matematige indirgemesi ve iktisadin doga bilimleri kadar keskin bir neden-sonuc icinde aciklanabilecegi yanilgisi ile birleserek, iktisat biliminin disiplinler arasi bir dusunce baglaminda ele alinmayarak, kendi icinde hapsolmasina yol acmistir. Bu calismada, Neo-klasik iktisadin ortaya cikisinda etkili olan yapi ve kosullar tarihsel bir perspektifte ele alinarak elestirel olarak degerlendirilmistir.

Disappeared deep charge-states transition levels in the p-type intrinsic CsSnCl3 perovskite

Lead-free inorganic perovskites are promising for optoelectronic applications. Understanding their phase diagram and defect properties is beneficial to predict the stable phase and applications. Here, taking CsSnCl3 as an example, the stability and defect properties are investigated systemically. The results show that the stoichiometric CsSnCl3 can only be grown in a narrow area determined by Sn and Cs chemical potentials. No matter what the Sn condition is, both acceptor defects (Cs- and Sn-vacancies with low charge states) are formed spontaneously with negative formation energies, and the donor defects are difficult to be formed with high formation energies. Interestingly, these charge-state transition levels induced by such stable defects are in the valence band. Meanwhile, no deep acceptor and donor states are formed in the bandgap. In addition, although the Fermi levels can vary in a wide range, the Fermi levels are pinned in the valence band, irrespective of the atmospheric conditions, leading to p-type CsSnCl3 with high hole density and low electron density. Such electronic characters are elucidated in detail by the atomic orbitals and structural deformations. Our studies provide an insight view of the defect properties of CsSnCl3 and provide a valuable guideline for CsSnCl3 fabrication and further modulation.

Enhanced Valley Splitting of Transition-Metal Dichalcogenide by Vacancies in Robust Ferromagnetic Insulating Chromium Trihalides.

Recently, single-layer CrI3, a member of the chromium trihalides CrX3 (where X = Cl, Br, or I), has been exfoliated and experimentally demonstrated as an atomically thin material suitable for two-dimensional spintronics. Valley splitting due to the magnetic proximity effect has been demonstrated in a WSe2/CrI3 van der Waals heterojunction. However, the understanding of the mechanisms behind the favorable performance of CrI3 is still limited. Here, we systematically study the carrier mobility and the intrinsic point defects in CrX3 and assess their influence on valley splitting in WSe2/CrI3 by first-principles calculations. The flat-band nature induces extremely large carrier mass and ultralow carrier mobility. In addition, intrinsic point defects-localized states in the middle of the band gap-show deep transition energy levels and act as carrier recombination centers, further lowering the carrier mobility. Moreover, vacancies in CrI3 can enhance ferromagnetism and valley splitting in a WSe2/CrI3 heterojunction, proving that chromium trihalides are excellent ferromagnetic insulators for spintronic and valleytronic applications.

Environments favoring dolomite formation at cold seeps: A case study from the Gulf of Mexico

Dolomite rarely occurs in modern marine environments, while it is ubiquitous in the geological record. This apparent contradiction made the formation mechanism of dolomite a long-standing problem haunting sedimentologists. However, dolomite is a constituent of many modern seep carbonates, providing an opportunity to investigate the conditions favoring dolomite formation at low temperatures in the shallow subseafloor. This study reports the petrology, mineralogy, carbon and oxygen stable isotopic compositions, as well as sulfur isotopic compositions of both carbonate-associated sulfate (CAS) and chromium reducible sulfur (CRS) of a set of dolomite-bearing carbonates from two seep sites (GC140 and GB382) on the northern slope of the Gulf of Mexico. The δ13C values of carbonates vary from −50.0‰ to 3.2‰ (V-PDB), confirming that carbonate minerals mostly resulted from methane oxidation. The corresponding δ18O values range from 2.6‰ to 5.9‰ (V-PDB), reflecting formation close to equilibrium with seawater composition. All carbonate samples with dolomite show similar petrologies and lack skeletal remains of seep-dwelling metazoans. The homogenous texture of microcrystalline dolomite agrees with its formation in the shallow subseafloor. Dolomite-bearing samples reveal δ18OCAS/δ34SCAS slopes of 0.425 and 0.435 for the two study sites, respectively. Such high slopes are significantly different from the smaller slopes of seep carbonates consisting of calcite from Gulf of Mexico seeps, suggesting low overall sulfate reduction rates during dolomite formation. This explanation is also supported by relatively high δ34SCRS values ranging from −29.4‰ to 19.0‰ (V-CDT) and the positive correlation of these values with dolomite contents. Interestingly, an approximately stoichiometric dolomite sample yielded the most positive δ34SCRS value, indicating a formation environment typified by low replenishment of seawater sulfate at a supposedly relatively deep sulfate methane transition zone (SMTZ). Overall, these results confirm that dolomite formation is facilitated where the SMTZ is situated at relatively great depth, where sulfate reduction rates are slowed down due to the buildup of high contents of dissolved sulfide and low seawater sulfate replenishment.

Eco-innovation pathways to a circular economy: Envisioning priorities through a Delphi approach

The present research seeks insights on potential “transformative” eco-innovation pathways towards a “Circular Economy”. By taking a neo-Schumpeterian perspective on sustainability transition and adopting a bottom-up foresight methodology, namely a (3-stage) policy-learning Delphi approach drawing on a (29-strong) panel of experts belonging to a variety of institutional sectors (public, business, academic actors, as well as NGOs) from diverse geographical backgrounds (11 countries across 3 continents), the study explores Circular Economy's key characteristics and appraises the fundamental strategies and trade-offs that must be understood and managed for transition. The evidence gathered through the participatory exercise, contrasted with prior knowledge from systematic literature reviews, suggests that Circular Economy is both a holistic concept and an operational tool. Results strongly suggest systemic eco-innovation, powered by multidimensional policies, as the key to unlock deep transition. In particular, over the next 20 years Circular Economy development is more than technological and economic puzzle-solving; it will be contingent on the ability to creatively overcome real political trade-offs and broader societal challenges needing to include in their action more social and behavioural considerations.

First-Principles Study of Aziridinium Lead Iodide Perovskite for Photovoltaics.

The long-term stability remains one of the main challenges for the commercialization of the rapidly developing hybrid organic-inorganic perovskite solar cells. Herein, we investigate the electronic and optical properties of the recently reported hybrid halide perovskite (CH2 )2 NH2 PbI3 (AZPbI3 ), which exhibits a much better stability than the popular halide perovskites CH3 NH3 PbI3 and HC(NH2 )2 PbI3 , by using density functional theory (DFT). We find that AZPbI3 possesses a band gap of 1.31 eV, ideal for single-junction solar cells, and its optical absorption is comparable with those of the popular CH3 NH3 PbI3 and HC(NH2 )2 PbI3 materials in the whole visible-light region. In addition, the conductivity of AZPbI3 can be tuned from efficient p-type to n-type, depending on the growth conditions. Besides, the charge-carrier mobilities and lifetimes are unlikely hampered by deep transition energy levels, which have higher formation energies in AZPbI3 according to our calculations. Overall, we suggest that the perovskite AZPbI3 is an excellent candidate as a stable high-performance photovoltaic absorber material.

Linked influences on slab stagnation: Interplay between lower mantle viscosity structure, phase transitions, and plate coupling

An endothermic phase transition in mantle material at 660-km depth constitutes a barrier that in most cases prevents the direct penetration of subducted slabs. Seismic tomography shows that subducted material is in many subduction zones trapped at the bottom of the transition zone, just above the 660-km phase boundary. Recent tomographic models however also report subducted material that penetrates to the shallow lower mantle, and there it is observed to flatten at about 1000-km depth. Models of slab dynamics that generally assume sharp rheological transition at 660-km depth, however, mostly predict slab stagnation at the bottom of the transition zone. Multiple lines of evidence, including recent experiments, indicate that viscosity may gradually increase in the uppermost ∼300 km of the lower mantle, rather than simply changing abruptly at the upper-lower mantle boundary. Here we present the results of a modeling study focused on the effects of rheological transition between upper and lower mantle material on slab deformation and stagnation. We test the effects of smoothing the viscosity increase over 300 km and shifting it to a depth of 1000 km or even deeper. We show that slab ability to penetrate to the lower mantle is mainly controlled by the trench migration rate, which in turn is affected by crustal viscosity. Coupling between the subducting and overriding plates thus plays a key role in controlling slab penetration to the lower mantle and stagnation in the deep transition zone or shallow lower mantle. Models with strong crust and consequently negligible rollback display penetration to the lower mantle without much hindrance and no stagnation above or below the 660-km interface, regardless of viscosity stratification in the shallow lower mantle. Models with weak crust are characterized by fast rollback, and penetration is very limited as slabs buckle horizontally and flatten above the 660-km boundary. Most interesting from the point of view of shallow lower mantle stagnation are models with intermediate crustal viscosity. Here rollback is efficient, though slower than in weak-crust cases. Horizontally lying slab segments are trapped in the transition zone if the sharp viscosity increase occurs at 660 km, but shifting the viscosity increase to 1000 km depth allows for efficient sinking of the flat-lying part and results in temporary stagnation below the upper-lower mantle boundary at about 1000 km depth.

Exoplanet transits with next-generation radio telescopes

Nearly everything we know about extrasolar planets to date comes from optical astronomy. While exoplanetary aurorae are predicted to be bright at low radio frequencies (< 1 GHz), we consider the effect of an exoplanet transit on radio emission from the host star. As radio emission from solar-like stars is concentrated in active regions, a planet occulting a starspot can cause a disproportionately deep transit which should be detectable with major radio arrays currently under development, such as the Square Kilometre Array (SKA). We calculate the radiometric sensitivity of the SKA stages and components, finding that SKA2-Mid can expect to detect transits around the very nearest solar-like stars and many cool dwarfs. The shape of this radiometric light curve will be affected by scintillation and lensing from the planet's magnetosphere and thereby encode magnetospheric parameters. Furthermore, these transits will also probe the distribution of stellar activity across a star's surface, and will help scrub out contamination from stellar activity on exoplanet transmission spectra and radial velocity spectra. This radio window on exoplanets and their host stars is therefore a valuable complement to existing optical tools.

First-principles study of intrinsic point defects in MgSiAs2.

MgSiAs2 is a potential infrared-nonlinear optical (IR-NLO) material, due to its fine second harmonic generation (SHG) performance and high laser damage threshold (LDT). In this study we systematically investigate its native point defects including vacancies, interstitials, and antisites using first-principles calculations with the Heyd-Scuseria-Ernzerhof hybrid functional. The defect formation energies and transition levels at the dilute limit are evaluated. Of the thirteen different point defects studied, nine kinds of defects show deep transition levels, which might contribute to the limiting of the transparency spectrum of MgSiAs2 compounds. The defects with the highest concentration at equilibrium are found to be cation antisites, MgSi and SiMg, serving as acceptors and donors respectively. Because of their significantly low formation energies, they lead to Fermi level pinning in the band gap and constrain the carrier concentration doping. Our calculations show that a change in growth conditions affects modestly the formation energy of defects or the concentration of charge carriers.

The complex defect chemistry of antimony selenide

Sb2Se3 is a highly promising solar absorber material, however a comprehensive study of its intrinsic defects finds multiple deep transition levels within the gap that could limit open circuit voltages of cells.