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4f electron-based topological Kondo insulators have long been researched for their potential to conduct electric current via protected surface states, while simultaneously exhibiting unusually robust insulating behavior in their interiors. To this end, we have investigated the electrical transport of the 3d-based correlated insulators FeSi and FeSb2, which have exhibited enough similarities to their f electron cousins to warrant investigation. By using a double-sided Corbino disk transport geometry, we show unambiguous evidence of surface conductance in both of these Fe-based materials. In addition, by using a four-terminal Corbino inverted resistance technique, we extract the bulk resistivity as a function of temperature. Similar to topological Kondo insulator SmB6, the bulk resistivity of FeSi and FeSb2 is confirmed to exponentially increase by up to 9 orders of magnitude from room temperature to the lowest accessible temperature. This demonstrates that these materials are excellent bulk insulators, providing an ideal platform for studying correlated 2D physics. [ABSTRACT FROM AUTHOR]

Phonon-based Weyl points (WPs) are usually considered to appear in pairs with opposite chirality. Here, we report the phonon dispersion in a realistic material monosodium phosphoramidate, NaHPO3NH2, which has two types of unpaired WP phonon systems: (i) two hourglass charge-3 (C-3) WPs and six C-1 conventional WPs forming a topological Weyl complex; (ii) one C-2 WP, with a topologically charged Weyl nodal surface, forming a topologically charged Weyl point-surface system. Remarkably, the simultaneous presence of the C-1, C-2, and hourglass C-3 WPs in NaHPO3NH2 results in the formation of clean and long phononic double and sextuple-helicoid surface states on the (10 1 ¯ 0) and (001) surfaces, respectively. The phononic double and sextuple-helicoid surface states span the entire first surface Brillouin zones of the (10 1 ¯ 0) and (001) surfaces, which will facilitate their detection in future experimental studies. [ABSTRACT FROM AUTHOR]

In this paper, we describe the development and state of archaeological surface survey in the Mediterranean. We focus especially on surface survey as a means of documenting long-term settlement patterns at various scales, as an approach to the archaeology of regions, and as a pathway to the interpretation of past landscapes. Over the last decades, the literature on Mediterranean survey has increasingly emphasized a distinct set of practices, viewed both favorably and critically by regional archaeologists in the Mediterranean and elsewhere. We show that Mediterranean survey in fact comprises several discrete regional traditions. In general, these traditions have much to offer to wider dialogs in world archaeology, particularly concerning sampling and research design, the interpretation of surface assemblages, and the integration of complex, multidisciplinary datasets. More specifically, survey investigations of Mediterranean landscapes provide comparative data and potential research strategies of relevance to many issues of global significance, including human ecology, demography, urban–rural dynamics, and various types of polity formation, colonialism, and imperialism. [ABSTRACT FROM AUTHOR]

Dirac cones (DCs) are an important band structure in topological insulators (TIs) for realizing topological phase transition, and they provide unique ways to artificially regulate wave transport. Herein, we proposed a simple method to achieve Dirac hierarchy in three-dimensional (3D) acoustic TIs with rich and controllable topological phase transitions. The split of multifold DCs in each bulk Dirac hierarchy induced boundary Dirac hierarchy, including topological surface states and topological hinge states. We successfully realized 3D higher-order topological insulators (HOTIs) that exhibited two-fold boundary Dirac hierarchy with hinge states and achieved energy transport along three independent directions based on hinge-to-hinge channels. The proposed method is not limited to single hinges, and it provides a new design idea for multidimensional sound transport, serving as the basis for controllable acoustic functional devices. [ABSTRACT FROM AUTHOR]

The high‐cycle fatigue (HCF) and very‐high‐cycle fatigue (VHCF) behavior of Ti‐6Al‐4V manufactured by laser powder bed fusion (L‐PBF) was investigated to reveal the effects of surface roughness and stress ratio on fatigue performance. Fatigue tests were performed by an ultrasonic vibration machine with a frequency of 20 kHz. The fatigue strength of surface‐polished specimens is generally higher than that of as‐built specimens in HCF and VHCF regimes. Fatigue cracks initiated from the subsurface of as‐built and surface‐polished L‐PBF Ti‐6Al‐4V. The values of size and depth for the defects that acted as fatigue crack origins present large scattering for L‐PBF Ti‐6Al‐4V due to the interaction between surface roughness and subsurface defects. For surface‐polished L‐PBF Ti‐6Al‐4V, fatigue cracks have almost the same resistance to propagation at both stress ratios of R = −1 and 0.7. Highlights: Fatigue strength of surface‐polished specimens higher than as‐built L‐PBF Ti‐6Al‐4VFatigue crack initiation from lack‐of‐fusion defects in subsurface defect‐enriched layerDefect & surface roughness with greater effect on crack initiation than stress ratioCrack propagation much easier in as‐built than surface‐polished L‐PBF Ti‐6Al‐4V [ABSTRACT FROM AUTHOR]

Changes in the total quantity of electric charge with time for different ratios of corrosion inhibitors in a steel–organic surfactant–electrolyte system are shown. Approximation equations are derived for each system of the inhibitors to calculate the slow adsorption surface electronic states of the interface. The adsorption surface electronic states are calculated by the Kots equation. The synergic effect of the inhibitors is shown. [ABSTRACT FROM AUTHOR]

Even the most efficient inverted p–i–n architecture perovskite solar cells (PSCs) are still inferior to those with regular n–i–p architecture, which is mainly limited by interfacial loss. Herein, both wet and dry metal–halide perovskite films are regulated through organic molecules–assisted sequential interfacial engineering for high‐performance inverted PSCs. In specific, organic acetic acid treatment on the wet film potently regulates the nucleation and crystallization of perovskite films. Then, further loading 4‐(dimethylamino)benzoic acid on the dry perovskite film creates a passivating agent layer to suppress defect formation, leading to more phase‐pure and conductive perovskite films. Combined experimental and theoretical results illustrate that such sequential treatment is beneficial for decreasing surface trap states, non‐radiative recombination, and carrier transport loss. As a result, the target inverted PSC exhibits an unprecedented high fill factor (FF) of 85.31% together with a champion efficiency of 21.37%, which is greatly improved relative to the reference (FF of 79.60%, and efficiency of 19.40%). It should be noted that such a high FF is among the highest report and corresponding to 94.38% of the Shockley–Queisser limited FF (90.39%) of PSCs with a bandgap of 1.576 eV. In addition, the storage stability against moisture of target inverted PSCs is remarkably enhanced. [ABSTRACT FROM AUTHOR]

A one-dimensional TiO2 nanorod-based thin film transistor (TFT) for butanone sensing is presented here. A low-cost hydrothermal process was used to deposit TiO2 nanorods on a Si/SiO2 substrate. X-ray diffraction, field-emission scanning electron microscopy (FESEM), photoluminescence spectroscopy, and Raman spectroscopy were used to examine the structural, morphological, and optical features of the nanostructure. Formation of aligned nanorods as the carrier transport channels in FET structure were confirmed through FESEM. Electrical characterization revealed the threshold voltage (VT), mobility (µ), transconductance (gm), Ion/Ioff ratio, and sub-threshold swing (SS) as 0.77 V, 12.2 cm2/V-s, 5.37 mS, 0.6 × 104, and 64.63 mV/dec, respectively. Sensor study exhibited an increase in the drain current (Id) and shifts in the threshold voltage (VT) upon exposure to different concentrations of butanone with respect to those in air. These two effects were correlated with the de-trapping of charge carriers at surface sites in association with resistance variation in the sensing layer. However, the room- temperature response towards butanone (82%) at Vgs of 3 V were found to be 16 times greater than the response under a no biasing (5%) condition. The repeatability of the as-fabricated and aged TFT indicates the potentiality of the device over conventional device structures even in harsh environments. [ABSTRACT FROM AUTHOR]

Angle-resolved photoemission spectroscopy (ARPES) and torque magnetometry (TM) measurements have been carried out to study the electronic structures of a correlated topological insulator (TI) candidate YbB6. We observed clear surface states on the [001] surface centered at the Γ and M points of the surface Brillouin zone. Interestingly, the fermiology revealed by the quantum oscillation of TM measurements agrees excellently with ARPES measurements. Moreover, the band structures we observed suggest that the band inversion in YbB6 happens between the Yb5d and B2p bands, instead of the Yb5d and Yb4f bands as suggested by previous theoretical investigation, which will help settle the heavy debate regarding the topological nature of samarium/ytterbium hexaborides.

The electrical transport in bismuth nanowires is strongly influenced by both sample geometry and crystallinity. Compared to bulk bismuth, the electrical transport in nanowires is dominated by size effects and influenced by surface states, which gain increasing relevance with increasing surface-to-volume ratios, i.e. with decreasing wire diameter. Bismuth nanowires with tailored diameter and crystallinity constitute, therefore, excellent model systems, allowing to study the interplay of the different transport phenomena. Here, we present temperature-dependent Seebeck coefficient and relative electrical resistance measurements of parallel bismuth nanowire arrays with diameters between 40 and 400 nm synthesized by pulsed electroplating in polymer templates. Both electrical resistance and Seebeck coefficient exhibit a non-monotonic temperature dependence, with the sign of the Seebeck coefficient changing from negative to positive with decreasing temperature. The observed behavior is size-dependent and is attributed to limitations of the mean free path of the charge carriers within the nanowires. The observed size-dependent Seebeck coefficient and in particular the size-dependent sign change opens a promising avenue for single-material thermocouples with p- and n-legs made from nanowires with different diameters. [ABSTRACT FROM AUTHOR]

The century-long development of surface sciences has witnessed the discoveries of a variety of quantum states. In the recently proposed "obstructed atomic insulators", symmetric charges are pinned at virtual sites where no real atoms reside. The cleavage through these sites could lead to a set of obstructed surface states with partial electronic occupation. Here, utilizing scanning tunneling microscopy, angle-resolved photoemission spectroscopy and first-principles calculations, we observe spectroscopic signature of obstructed surface states in SrIn2P2. We find that a pair of surface states that are originated from the pristine obstructed surface states split in energy by a unique surface reconstruction. The upper branch is marked with a striking differential conductance peak followed by negative differential conductance, signaling its localized nature, while the lower branch is found to be highly dispersive. This pair of surface states is in consistency with our calculational results. Our finding not only demonstrates a surface quantum state induced by a new type of bulk-boundary correspondence, but also provides a platform for exploring efficient catalysts and related surface engineering. The authors observe spectroscopic signature of obstructed surface states on the (0001) plane of SrIn2P2. Due to structural reconstruction, the surface state undergoes an adiabatic evolution and split into two branches, the upper of which being spatially localized with unusual negative differential conductance. [ABSTRACT FROM AUTHOR]

Based on the widely used wet metal-assisted electroless etching, we develop in this work a novel vapor-phase silver-assisted chemical etching (VP-Ag-ACE) suitable for the elaboration of highly doped p-silicon (Si) nanostructures with strong, visible, and multi-peak photoluminescence (PL) emissions. The lateral and vertical etching rates (LER and VER) were discussed based on the etching mechanism of the VP-Ag-ACE. The antireflective suitability of the vapor-etched layer has been evaluated by a reflectivity measurement and exhibits reflectivity values lower than 3%. The PL emission at both room and low temperatures emissions were deeply discussed and correlated with the structural properties of the Si morphologies and their surface states based on the FTIR results. [ABSTRACT FROM AUTHOR]

Tungstate-based scheelite structures have attracted much attention for the photocatalytic, adsorption and luminescence. To improve their performance, several ways have been considered, such as morphology control, thermal treatment and nanostructuring materials. In this work, three uniform and homogeneous morphologies, such as spindles, spheres and flowers, of self-assembled three-dimensional Na 0.5 Ce 0.5 WO 4 were used as photocatalysts for methylene blue dye photodegradation under solar irradiation. Depending on morphology, they required different temperatures to reach crystallization. Thermal treatments at 500 °C and 800 °C resulted in changes in crystallite size, porosity, surface state, but also in bandgap and emission properties. Thus, the crystallite sizes are about 50 nm for samples (spindles and flowers) treated at 500°Cand 87–167 nm for those treated at 800 °C. Their respective bandgap values measured by diffuse reflectance were 2.85 eV beyond 3.15 eV. The samples treated at 500 °C showed a lower emission and a longer charge carrier lifetime. A strong trend to adsorption was revealed, especially at low pH value and for the samples treated at 500 °C, reaching 100% at a pH value of 2.5. With decreasing pH, the photocatalysis activity increases (up to 50%), being also more efficient with catalysts treated at low temperature. It follows that the degradation efficiency of spindles treated at 500 °C is clearly higher compared to other morphologies treated at different temperature, and suitable for solar photocatalysis. [ABSTRACT FROM AUTHOR]

Exploring the interplay between topological phases and photons opens new avenues for investigating novel quantum states. Here we show that superconducting resonators can serve as sensitive probes for properties of topological insulator nanowires (TINWs) embedded within them. By combining a static, controllable magnetic flux threading the TINW with an additional oscillating electromagnetic field applied perpendicularly, we show that orbital resonances can be generated and are reflected in periodic changes of the Q-factor of the resonator as a function of the flux. This response probes the confinement of the two-dimensional Dirac orbitals on the surface of the TINW, revealing their density of states and specific transition rules, as well as their dependence on the applied flux. Our approach represents a promising cross-disciplinary strategy for probing topological solid state materials using state-of-the-art photonic cavities, which would avoid the need for attaching contacts, thereby enabling access to electronic properties closer to the pristine topological states. Coupling topological states to photons could lead to new testing grounds for topology and to the generation of novel quantum states. Here, the authors theoretically consider a topological insulator nanowire embedded in a superconducting resonator with high Q-factor and explore its use as a detector for the resulting dissipative response under an applied oscillating electromagnetic field. [ABSTRACT FROM AUTHOR]

Biological systems convert chemical energy into mechanical work by using protein catalysts that assume kinetically controlled conformational states. Synthetic chemomechanical systems using chemical catalysis have been reported, but they are slow, require high temperatures to operate, or indirectly perform work by harnessing reaction products in liquids (e.g., heat or protons). Here, we introduce a bioinspired chemical strategy for gas-phase chemomechanical transduction that sequences the elementary steps of catalytic reactions on ultrathin (<10 nm) platinum sheets to generate surface stresses that directly drive microactuation (bending radii of 700 nm) at ambient conditions (T = 20 °C; Ptotal = 1 atm). When fueled by hydrogen gas and either oxygen or ozone gas, we show how kinetically controlled surface states of the catalyst can be exploited to achieve fast actuation (600 ms/cycle) at 20 °C. We also show that the approach can integrate photochemically controlled reactions and can be used to drive the reconfiguration of microhinges and complex origami- and kirigami-based microstructures. [ABSTRACT FROM AUTHOR]

The interplay between quantum interference, electron-electron interaction (EEI), and disorder is one of the central themes of condensed matter physics. Such interplay can cause high-order magnetoconductance (MC) corrections in semiconductors with weak spin-orbit coupling (SOC). However, it remains unexplored how the magnetotransport properties are modified by the high-order quantum corrections in the electron systems of symplectic symmetry class, which include topological insulators (TIs), Weyl semimetals, graphene with negligible intervalley scattering, and semiconductors with strong SOC. Here, we extend the theory of quantum conductance corrections to two-dimensional (2D) electron systems with the symplectic symmetry, and study experimentally such physics with dual-gated TI devices in which the transport is dominated by highly tunable surface states. We find that the MC can be enhanced significantly by the second-order interference and the EEI effects, in contrast to the suppression of MC for the systems with orthogonal symmetry. Our work reveals that detailed MC analysis can provide deep insights into the complex electronic processes in TIs, such as the screening and dephasing effects of localized charge puddles, as well as the related particle-hole asymmetry. The authors extend the theory of quantum conductance corrections to 2D electron systems with the symplectic symmetry, such as topological-insulator surface states. They find that magnetoconductance can be enhanced significantly by second-order interference and electron-electron interaction effects. [ABSTRACT FROM AUTHOR]

[Display omitted] • HER thermodynamics and kinetics is evaluated on V 2 C (0001) MXene by density functional theory. • While –OH surface termination is less relevant for HER, the reaction is facile on -H termination. • The reaction switches from Volmer-Heyrovsky to Volmer-Tafel depending when increasing the overpotential. • V2C MXene features HER reaction similarities to Pt-based electrocatalysts. Both experimentally and theoretically, the MXene family has shown promising hydrogen evolution reaction (HER) capabilities. However, so far, the theoretical approach has been relying on the well-known thermodynamic descriptor, Δ G H , whereas experimental studies report Tafel plots, containing kinetic rather than thermodynamic information. Aiming to link theory to experiments, the present study explores five different HER pathways over the exemplary V 2 C (0001) MXene by density functional theory calculations. While the surface coverage under HER conditions (with either H* or OH* adsorbates) is extracted from a Pourbaix diagram, we determine the energetics of the reaction intermediates and transition states for both surface species as active sites. This enables the construction of free-energy diagrams for the Volmer-Heyrovsky and Volmer-Tafel mechanisms and allows for the simulation of Tafel plots by a rigorous microkinetic framework. While the active-site motif V 2 C-OH seems to be less relevant for the HER under typical reaction conditions, we demonstrate that the HER is kinetically facile on the V 2 C-H surface. For this surface termination, we report a potential-depending switching of the preferred mechanism from the Volmer-Heyrovsky to the Volmer-Tafel description with increasing overpotential while encountering similarities to the HER over Pt. [ABSTRACT FROM AUTHOR]

Peculiarities of the effects of TiB2 and BN coatings on the deformation and stress state of the surface layer of Sn3N4–TiC ceramics under the influence of force loading were studied. The BN coating was found to have a more favorable effect on the stress-strain state of the ceramic structural elements than the TiB2 coating. The effects of the TiB2 and BN coatings on the stress state of the interface between the coating and ceramic was not so unambiguous. Three coefficients were in favor of each coating. [ABSTRACT FROM AUTHOR]

In the present work, a diamond-like carbon film (DLC) was electrodeposited on a p-Si substrate and was used to fabricate an Al/DLC/p-Si/Au metal/interlayer/semiconductor (MIS) Schottky diodes (SDs). The structural analysis of the DLC interfacial layer produced by the electrochemical method were done using scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS) methods. The SEM images showed that the silicon surface was completely coated with DLC film and spherical particles and islets appeared on the film surface. The XPS spectrum showed that the film mainly consists of C and O elements. The frequency/voltage-dependent capacitance and conductance measurements of the fabricated electronic device were made between 1 to 1 MHz and − 1 V to 4 V, respectively. The slope and intercept of the linear part of the C−2 plot are used to extract the main electrical parameters of the structure, e.g., diffusion potential (V D) , doping concentration of acceptor atoms (N A) , Fermi energy (E F) , maximum electric field (E m) , depletion layer width (W D) , and barrier height (Φ B) . Furthermore, the density of surface states N ss and the lifetime of the charges in the states τ are calculated from the parallel conduction method and these values vary from 3.8 × 10 11 to 7.2 × 10 11 eV - 1 cm - 2 and 140 to 4.7 μ s , respectively. The lower magnitude of the N ss arises from the passivation effect of the DLC interlayer. As a result, the DLC film showed outstanding characteristics as an interlayer and, therefore, has potential usage instead of oxide or other insulator layers for the purpose of decreasing the N ss and other dislocations in SDs. [ABSTRACT FROM AUTHOR]

In the present work, the effects of ion implantation on structural, surface, optical, and photoluminescence behavior of MgTiO3 thin films have been investigated. Cobalt ions were implanted into crystalline films by varying the fluence from 3 × 1014 to 1 × 1016 ions/cm2. An intensity reduction and shift of the peak position upon implantation are attributed to amorphization and generation of strain, respectively. The root-mean-square roughness is reduced from 8.2 (pristine) to 6.4 nm upon implantation at 3 × 1014 ions/cm2 fluence and increases to 7.9 nm with a further upsurge in fluence. A non-monotonous variation in transmittance with implantation fluence is observed. The bandgap of pristine sample is ~ 4.22 eV, and the implanted samples exhibit a bandgap in the range of 4.03–3.88 eV. The surface chemical states of pristine and implanted films were analyzed using X-ray photoelectron spectroscopy. An enhancement in defects upon implantation of Co ions results in the variation of luminescence properties. A broad photoluminescence (PL) emission band extending from near UV to visible region is observed for the pristine film. The PL emission intensity is quenched upon implantation. Average decay lifetime of pristine film is observed to be 17.9 ns, which is slightly increased to 19.1 ns at 3 × 1014 ions/cm2 implantation fluence. Afterward, with a subsequent rise in implantation fluence from 1 × 1015 to 1 × 1016 ions/cm2, the average decay lifetime varied within the range of 17.2–18.9 ns. Factors responsible for different luminescent centers, structure, and morphology evolution as a consequence of Co ion implantation are reported. [ABSTRACT FROM AUTHOR]

[Display omitted] Platinum-based (Pt) catalysts are the most common commercial catalysts for oxygen reduction reactions (ORR). Unfortunately, their high price, scarcity and poor durability hinder their further development. Therefore, the development of effective and economical ORR electrocatalysts has received increasing attention. Here, carbon dots (CDs) enriched in amino functional groups were successfully loaded onto carbon nanotubes (CNTs) with a large surface area and helical structure through a surface state engineering strategy. The resulting composites (CD/CNTs) are 0D/1D nano heterojunction structures. The CD/CNTs showed superior ORR activity compared with CNTs and CDs (E oneset = 0.95 V, E 1/2 = 0.81 V and limiting current density = 4.74 mA cm−2). In addition, the stability of CD/CNTs in an alkaline medium was up to 30000 s. The excellent ORR performance of CD/CNTs can be attributed to the dominant role of amino-N, the synergistic effect of heterojunctions formed by CDs and CNTs, and the high Lewis basicity. The composite electrocatalyst synthesized by the CD-regulated CNT strategy is expected to be a reliable cathode candidate for future energy conversion devices. [ABSTRACT FROM AUTHOR]

Experimental investigations of antiferromagnetic topological insulator MnBi2Te4 have shown that the energy gap in samples may vary in a wide range. Since the energy gap is a key parameter of this system when used in developing new functional electronic devices, the reason for variation of the MnBi2Te4 energy gap at the Dirac point and its possible interrelation with magnetic interactions are matters of great importance and call for thorough analysis. To elucidate factors influencing the energy gap, we analyzed the variation of the electronic structure of the given topological insulator with surface van der Waals gap. Calculation data have shown that the energy gap at such structure modifications may vary in a wide range from 80–88 meV to 4–5 meV because of an intense spatial redistribution of topological surface states between septuple-layer MnBi2Te4 blocks with oppositely directed Mn magnetic moments. Our results suggest that the spatial localization of topological surface states is a primary factor governing the value of the energy gap, this localization being strongly dependent on structure modifications on the crystal surface. [ABSTRACT FROM AUTHOR]

Plasmons supported in the massless electron surface states of topological insulators (TIs), known as Dirac plasmons, have great potential in next generation optoelectronics. However, their inherent confinement to the surface makes the investigation of Dirac plasmons challenging. Near-field techniques provide the ideal platform to directly probe Dirac plasmons due to the sensitivity to evanescent fields at the surface. Here, we demonstrate the use of aperture near-field spectroscopy for the investigation of localized terahertz (THz) Dirac plasmon resonances in Bi2Se3 ribbon arrays with widths ranging from 10 to 40 µm. Unlike scattering THz near-field techniques, the aperture method is most sensitive to plasmons with the relevant lower-momenta corresponding to plasmon wavelengths on the scale of ∼20 µm. The combination of THz time-domain spectroscopy and aperture near-field microscopy enables sampling of localized Dirac plasmons in the near-field zone in the 0.5–2.5 THz range. We map the plasmon dispersion, which reveals a coupled plasmon–phonon polariton interaction. The near-field spectra show a higher contrast of the upper polariton branch in comparison with far-field observations. The information revealed by aperture near-field spectroscopy could deepen our understanding of the behavior of Dirac plasmons, leading to the potential development of real-world TI devices. [ABSTRACT FROM AUTHOR]

Constructing 2D/2D face-to-face heterojunctions is believed to be an effective strategy to enhance photocatalytic performance due to the enlarged contact interface and increased surface active sites. Herein, 2D porous NiCo oxyphosphide (NiCoOP) was synthesized for the first time and coupled with graphitic carbon nitride (g-C3N4) nanosheets to form 2D/2D heterojunctions via an in-situ phosphating method. The optimal 4 wt.% 2D/2D NiCoOP/g-C3N4 (OPCN) photocatalyst achieves a hydrogen evolution rate of 1.4 mmol·h−1·g−1, which is 33 times higher than that of pure g-C3N4. The greatly improved photocatalytic performance of the composite photocatalysts could be attributed to the formation of interfacial surface bonding states and sufficient charge transfer channels for accelerating carrier separation and transfer and the porous structure of NiCoOP nanosheets with abundant surface active sites for promoting surface reactions. Amazingly, the 2D/2D OPCN composite photocatalysts also exhibit superior stability during photocatalytic reactions. This study not only designs new noble-metal-free NiCoOP/g-C3N4 composite photocatalysts but also provides a new sight in fabricating face-to-face 2D/2D heterojunctions for their application in energy conversion areas. [ABSTRACT FROM AUTHOR]

GaN high-electron-mobility transistors (HEMTs) have attracted widespread attention for high-power microwave applications, owing to their superior properties. However, the charge trapping effect has limitations to its performance. To study the trapping effect on the device large-signal behavior, AlGaN/GaN HEMTs and metal-insulator-semiconductor HEMTs (MIS-HEMTs) were characterized through X-parameter measurements under ultraviolet (UV) illumination. For HEMTs without passivation, the magnitude of the large-signal output wave ( X 21 FB ) and small-signal forward gain ( X 2111 S ) at fundamental frequency increased, whereas the large-signal second harmonic output wave ( X 22 FB ) decreased when the device was exposed to UV light, resulting from the photoconductive effect and suppression of buffer-related trapping. For MIS-HEMTs with SiN passivation, much higher X 21 FB and X 2111 S have been obtained compared with HEMTs. It suggests that better RF power performance can be achieved by removing the surface state. Moreover, the X-parameters of the MIS-HEMT are less dependent on UV light, since the light-induced performance enhancement is offset by excess traps in the SiN layer excited by UV light. The radio frequency (RF) power parameters and signal waveforms were further obtained based on the X-parameter model. The variation of RF current gain and distortion with light was consistent with the measurement results of X-parameters. Therefore, the trap number in the AlGaN surface, GaN buffer, and SiN layer must be minimized for a good large-signal performance of AlGaN/GaN transistors. [ABSTRACT FROM AUTHOR]

A spin-topological electronic valve was discovered in a Ni/hBN–graphene–hBN/Ni magnetic junction to control the in-plane conductance of graphene. By manipulating the mass-gapped Dirac cone (MGDC) of graphene's topology using the magnetic proximity effect, the spin-topological electronic valve was made possible. The first-principles investigation was conducted to show how the mechanism of graphene's MGDC is controlled. Twelve stacking configurations for the anti-parallel configuration (APC) and parallel configuration (PC) of the magnetic alignment of Ni slabs were calculated using spin-polarized density functional theory. Three groups can be made based on the relative total energy of the 12 stacking configurations, which corresponds to a van der Waals interaction between hBN and graphene. Each group exhibits distinctive features of graphene's MGDC. The configuration of the Ni(111) surface state's interaction with graphene as an evanescent wave significantly impacts how the MGDC behaves. By utilizing the special properties of graphene's MGDC, which depend on the stacking configuration, a controllable MGDC using mechanical motion was proposed by suggesting a device that can translate the top and bottom Ni(111)/hBN slabs. By changing the stacking configuration from Group I to II and II to III, three different in-plane conductances of graphene were observed, corresponding to three non-volatile memory states. This device provides insight into MJs having three or more non-volatile memory states that cannot be found in conventional MJs. [ABSTRACT FROM AUTHOR]

Volatile organoamines are important industrial raw materials and chemicals. Long-term exposure to amines could be harmful to human health and even cause serious pollution. In this study, SnO2 decorated g-C3N4 material was fabricated and used as a sensor material for the detection of ethanolamine (EA). The structures, morphology, surface chemical states, and band structure were characterized, and gas sensing was studied. The results showed that SnO2 nanoparticles were dispersed on g-C3N4, and band structure was dependent on g-C3N4 doping. Notably, the interface heterojunction was conducive to electron transferring and O2 molecule adsorption; the formed reactive oxygen species enhanced the reaction between oxygen and EA, thus leading to high sensitivity to EA. This composite exhibited a high response that was 2.6 times higher than that of pure SnO2, and the detection limit reached 294 ppb. A g-C3N4/SnO2-based sensor displayed a high selectivity to EA with a fast response time (1 s) and recovery time (20 s) at low operating temperatures. In particular, this sensor exhibited a linear relationship between the response and concentration, which is required for quantitative analysis. [ABSTRACT FROM AUTHOR]

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Experimental investigations of antiferromagnetic topological insulator MnBi2Te4 have shown that the energy gap in samples may vary in a wide range. Since the energy gap is a key parameter of this system when used in developing new functional electronic devices, the reason for variation of the MnBi2Te4 energy gap at the Dirac point and its possible interrelation with magnetic interactions are matters of great importance and call for thorough analysis. To elucidate factors influencing the energy gap, we analyzed the variation of the electronic structure of the given topological insulator with surface van der Waals gap. Calculation data have shown that the energy gap at such structure modifications may vary in a wide range from 80–88 meV to 4–5 meV because of an intense spatial redistribution of topological surface states between septuple-layer MnBi2Te4 blocks with oppositely directed Mn magnetic moments. Our results suggest that the spatial localization of topological surface states is a primary factor governing the value of the energy gap, this localization being strongly dependent on structure modifications on the crystal surface. [ABSTRACT FROM AUTHOR]

With the development of the high-end equipment manufacturing industry, the requirements for the surface performance of critical components are likewise increasing. To control the heat and mass transfer in the laser surface treatment process more efficiently and flexibly, the multiangle double laser surface treatment technology shows unique advantages. This study is focused on the experimental study of the laser surface treatment process for Ti6Al4V material. By changing the laser power and the incidence angle of the laser beam, the effects of single-laser beam surface treatment (SLST) and dual-laser beam surface treatment (DLST) on the surface morphology of the alloy were studied. The effects of laser treatment on the surface morphology, element distribution, roughness, surface chemical state, and surface structure of the alloy were emphatically analyzed. The mechanism of SLST and DLST at different incident angles of heat source and the effect of DLST on the formation of an oxide layer on the surface of the alloy were compared and analyzed. The results show that when the average power of the high-power nanosecond pulse width laser in DLST is 100 W and the incident angle is 135°, the surface oxygen content reaches the lowest, as low as 8.31%. The secondary effect of the laser makes the alloy surface remelt again, and then the best roughness after laser processing is obtained, with a roughness value of 2.801 μm. Finally, we obtain the optimal process for laser surface treatment and conclude that DLST can significantly optimize the surface state after a high-energy laser beam action. [ABSTRACT FROM AUTHOR]

In this work, we proposed an oxygen vacancy engineering strategy to boost the chemiluminescence (CL) efficiency in europia clusters/black phosphorus quantum dots (Eu2O3/BPQDs), which could dramatically amplify the ClO− CL emission through electron transfer. Accordingly, a sensitive and direct CL sensing platform for hypochlorite and titanium ions was constructed. This work provides a neoteric methodology by modulating the surface state of nanoparticles to boost the CL sensitivity. [ABSTRACT FROM AUTHOR]

The existence of the two-dimensional electron gas (2DEG) and two-dimensional hole gas (2DHG) in the same III-nitride heterostructure is advantageous for the development of complementary nitride electronics. However, it is still unclear whether the buried-2DHG and the top 2DEG can coexist in the same III-nitride heterostructure. This study has addressed this long-standing question. Using charge distribution model, a systematic analysis is done and proposed surface acceptor states as the origin of the two-dimensional hole gas (2DHG). Using this centralized analysis, factors affecting the formation of both surface and buried-2DHG in the nitride heterostructures are presented. Furthermore, it is proved that the buried-2DHG is absent in III-nitride heterostructures, particularly under the 2DEG. In the absence of buried-2DHG at the GaN/AlXGa1-XN interface, a hole trap is observed, which not only balances the charge distribution but also reduces the electric field in the GaN channel layer. [ABSTRACT FROM AUTHOR]

Many complex magnetic structures in a high-symmetry lattice can arise from a superposition of well-defined magnetic wave vectors. These "multi-q" structures have garnered much attention because of interesting real-space spin textures such as skyrmions. However, the role multi-q structures play in the topology of electronic bands in momentum space has remained rather elusive. Here we show that the type-I anti-ferromagnetic 1q, 2q and 3q structures in an face-centered cubic sublattice with band inversion, such as NdBi, can induce unconventional surface state pairs inside the band-folding hybridization bulk gap. Our density functional theory calculations match well with the recent experimental observation of unconventional surface states with hole Fermi arc-like features and electron pockets below the Neel temperature. We further show that these multi-q structures have Dirac and Weyl nodes. Our work reveals the special role that band-folding from anti-ferromagnetism and multi-q structures can play in developing new types of surface states. Complex magnetic formations, termed 'multi-q' structures, can give rise to magnetic spin textures, such as skyrmions, but how they influence band structure and topology is less clear. Here, the authors use a combination of calculated and experimental data to reveal the origin of the unconventional surface state pairs that emerge for NdBi for different type-I AFM multi-q structures. [ABSTRACT FROM AUTHOR]

Exploring new topological phenomena and functionalities induced by strong electron correlation has been a central issue in modern condensed-matter physics. One example is a topological insulator (TI) state and its functionality driven by the Coulomb repulsion rather than a spin-orbit coupling. Here, we report a 'correlation-driven' TI state realized in an organic zero-gap system α-(BETS)2I3. The topological surface state and chiral anomaly are observed in temperature and field dependences of resistance, indicating a three-dimensional TI state at low temperatures. Moreover, we observe a topological phase switching between the TI state and non-equilibrium Dirac semimetal state by a dc current, which is a unique functionality of a correlation-driven TI state. Our findings demonstrate that correlation-driven TIs are promising candidates not only for practical electronic devices but also as a field for discovering new topological phenomena and phases. Topological properties can theoretically be generated by electron correlation rather than spin-orbit coupling. Here, the authors report a correlation-driven topological insulator state in the organic material α-(BETS)2I3, and its current-driven switching to a Dirac semimetal state. [ABSTRACT FROM AUTHOR]

We synthesized a type of sulfur and nitrogen co-doped carbon dot, which can achieve tunable fluorescence both in solutions and solid matrices, that is dominated by the surface state. Moreover, it can be used to detect trace water in a variety of organic solvents, especially in acetone with a limit of detection as low as 0.042%. [ABSTRACT FROM AUTHOR]

Electrocatalysts play key roles in improving the performance of lithium sulfur (Li‐S) batteries. Here, the electrocatalytic activity of different CoSe2 surfaces for the polysulfide redox reactions in Li‐S batteries, by means of first‐principle calculations is considered. The authors demonstrate that there are obvious differences in surface energy (0.7–2.34 J m−2), adsorption energy for lithium polysulfides (LiPSs) (1.2–3.5 eV), Gibbs free energy of sulfur reduction reaction (SRR) (0.37–1.16 eV), and Li2S decomposition barrier (0.15–0.94 eV) among different CoSe2 surfaces, and thus lead to the different electrocatalytic activity for different CoSe2 surface. The stoichiometric CoSe2 surface with high surface energy, such as the (001) surface, tends to have stronger adsorption energy and larger SRR Gibbs free energy for LiPSs. The surface electron states are mainly dominated by p–d hybridization orbitals and the p‐band center is vital for the surface electrocatalytic properties. Such surface‐dependent mechanism may shed light on the design of sulfur host materials for high‐performance Li‐S batteries. [ABSTRACT FROM AUTHOR]

We study ultrafast population dynamics in the topological surface state of Sb 2 Te 3 in two-dimensional momentum space with time- and angle-resolved two-photon photoemission spectroscopy. Linearly polarized mid-infrared pump pulses are used to permit a direct optical excitation across the Dirac point. We show that this resonant excitation is strongly enhanced within the Dirac cone along three of the six Γ ¯ – M ¯ directions and results in a macroscopic photocurrent when the plane of incidence is aligned along a Γ ¯ – K ¯ direction. Our experimental approach makes it possible to disentangle the decay of transiently excited population and photocurent by elastic and inelastic electron scattering within the full Dirac cone in unprecedented detail. This is utilized to show that doping of Sb 2 Te 3 by vanadium atoms strongly enhances inelastic electron scattering to lower energies, but only scarcely affects elastic scattering around the Dirac cone. [ABSTRACT FROM AUTHOR]

Besides chiral edge states, the hallmark of quantum Hall insulators, antichiral edge states can exhibit unidirectional transport behavior but in topological semimetals. Although such edge states provide more flexibility for molding the flow of light, their realization usually suffers from time-reversal breaking. In this study, we propose the realization of antichiral surface states in a time-reversal-invariant manner and demonstrate our idea with a three-dimensional (3D) photonic metacrystal. Our system is a photonic semimetal possessing two asymmetrically dispersed Dirac nodal lines. Via dimension reduction, the nodal lines are rendered a pair of offset Dirac points. By introducing synthetic gauge flux, each two-dimensional (2D) subsystem with nonzero kz is analogous to a modified Haldane model, yielding a kz-dependent antichiral surface transport. Through microwave experiments, the bulk dispersion with asymmetric nodal lines and associated twisted ribbon surface states are demonstrated in our 3D time-reversal-invariant system. Although our idea is demonstrated in a photonic system, we propose a general approach to realize antichiral edge states in time-reversal-invariant systems. This approach can be easily extended to systems beyond photonics and may pave the way for further applications of antichiral transport. Here the authors proposed an approach to realize the antichiral surface states in a time-reversal invariant photonic system. They harnessed a synthetic gauge flux and observed a kz-dependent antichiral surface transport in their 3D metacrystal. [ABSTRACT FROM AUTHOR]

Chiral edge states that propagate oppositely at two parallel strip edges are a hallmark feature of Chern insulators which were first proposed in the celebrated two-dimensional (2D) Haldane model. Subsequently, counterintuitive antichiral edge states that propagate in the same direction at two parallel strip edges were discovered in a 2D modified Haldane model. Recently, chiral surface states, the 2D extension of one-dimensional (1D) chiral edge states, have also been observed in a photonic analogue of a 3D Haldane model. However, despite many recent advances in antichiral edge states and chiral surface states, antichiral surface states, the 2D extension of 1D antichiral edge states, have never been realized in any physical system. Here, we report the experimental observation of antichiral surface states by constructing a 3D modified Haldane model in a magnetic Weyl photonic crystal with two pairs of frequency-shifted Weyl points (WPs). The 3D magnetic Weyl photonic crystal consists of gyromagnetic cylinders with opposite magnetization in different triangular sublattices of a 3D honeycomb lattice. Using microwave field-mapping measurements, unique properties of antichiral surface states have been observed directly, including the antichiral robust propagation, tilted surface dispersion, a single open Fermi arc connecting two projected WPs and a single Fermi loop winding around the surface Brillouin zone (BZ). These results extend the scope of antichiral topological states and enrich the family of magnetic Weyl semimetals. Here the authors report the first experimental observation of topological antichiral surface states by constructing a three-dimensional modified Haldane model in a magnetic Weyl photonic crystal. [ABSTRACT FROM AUTHOR]

This study proposes a new constitutive model to describe the smooth transition from an elastic to a plastic response in sands under monotonic shearing. The model modifies the conventional Mohr–Coulomb model by considering the concept of a bounding surface and critical state soil mechanics. The friction angle consists of the critical state friction angle and a portion of the dilatancy angle, which is determined from the distance to the critical state line. Incorporating the bounding surface and the dilatancy angle into constitutive relationships for Toyoura sand produces numerical simulation results that have good agreement with the experimental results. [ABSTRACT FROM AUTHOR]

Using DFT-based first-principles calculations, we demonstrate the tuning of the electronic structure of Weyl semimetal SrSi2 via external uniaxial strain. The uniaxial strain facilitates the opening of bandgap along Γ-X direction and subsequent band inversion between Si 𝑝 and Sr 𝑑 orbitals. Z2 invariants and surface states reveal conclusively that SrSi2 under uniaxial strain is a strong topological insulator. Hence, uniaxial strain drives the semimetallic SrSi2 into fully gapped topological insulating state depicting a semimetal to topological insulator phase transition. Our results highlight the suitability of uniaxial strain to gain control over the topological phase transitions and topological states in SrSi2. [ABSTRACT FROM AUTHOR]

The possibility of using the eddy current method to assess the depth of cracks in the rolling surface of rails in operation during the planning and acceptance of work of a rail grinding train is investigated. Experimental studies of the influence of the excitation frequency and the angle of inclination of the eddy current transducer, the surface state, and the depth and angle of inclination of the surface crack on the amplitude and phase of the eddy current signal are carried out. The possibilities of the amplitude-phase method of detuning from interfering factors associated with the inclination of the transducer and the curvature of the tested surface are determined. The resolution of the flaw detector was investigated when evaluating the characteristics of two or more closely spaced cracks—a defect of the crack "network" type. The depth of surface cracks in the range from 0.1 to 1.4 mm was determined by metallographic examination after eddy current testing. Optimal testing parameters have been experimentally substantiated and a correlation between the crack depth and the projection of the signal amplitude in the direction perpendicular to the direction of change of the interfering factor, i.e., the angle of transducer inclination, has been established. [ABSTRACT FROM AUTHOR]

Cities have a significant impact on the environment, forming microclimatic features such as urban heat island, an increase in the intensity of convective weather events, etc. Numerical models of the atmosphere with an integrated block that describes the interaction between the urbanized surface and the atmosphere—urban parameterization—are good at reproducing the meteorological features of the urban environment. Reviews of urban parameterizations are mostly outdated, and recent ones do not fully cover aspects of the methods used in the models to describe physical processes. This paper is dedicated to updating information on urban parameterizations, comparing the approaches used in them to describe physical processes, and forming proposals for their improvement. Based on the most common urban parameterizations of various levels of complexity, the main groups of physical processes describing "urban surface-atmosphere" interaction are identified. They are the surface energy balance, radiation heat transfer, surface moisture balance, turbulent heat and moisture exchange in the urban canopy, anthropogenic influence on heat and moisture fluxes, radiation, and turbulent interaction with urban vegetation. The main approaches to the parameterization of physical processes are defined within each block. Modern trends in the development of urban parameterizations are highlighted: (1) over the past 10 years, parameterizations have become more complicated due to the addition of the building energy model, a three-dimensional structure of urban vegetation, and vertical resolution when calculating turbulent fluxes; (2) at the same time, not much attention is paid to revising the original empirical formulas, often obtained on the basis of single field or laboratory experiments. Ways to improve urban parameterizations are proposed by clarifying the basic dependencies used mainly in the calculation of turbulent fluxes, particularly using the results of highly detailed large-eddy simulation modeling, which, with growing computational power, is increasingly used to simulate explicit heat transfer between the atmosphere and individual elements of the urban environment. [ABSTRACT FROM AUTHOR]

Topological insulators (TIs) are under rapid and intensive study in the fields of condensed matter physics, due to exotic electronic properties. Recent studies of photocurrent generation in topological surface states (TSS) properties have insufficient evidence to rule out that of bulk states, hindering the application in optoelectronics. Herein, the chemical vapor transport (CVT) synthesis of GeBi4Te7 crystal by the way of Ge intercalation is realized, enabling isolated Dirac points‐associated high‐mobility Dirac carriers and larger Seebeck coefficients. Then, the antenna‐coupled photodetector in GeBi4Te7 based on planar metal–TI–metal structure is reported, successfully realizing sensitive terahertz response without bias. According to the results, the GeBi4Te7‐based terahertz photodetector has a short response time and a high photoresponsivity (0.42 A W−1 at 0.107 THz and 0.6 A W−1 at 0.28 THz, respectively). The GeBi4Te7–graphene heterostructure can further improve the responsivity by more than two orders of magnitude, reaching 12 A W−1 at 0.107 THz. These findings bring up doable avenues for GeBi4Te7 materials' low‐energy optoelectronic applications. [ABSTRACT FROM AUTHOR]

One of the greatest triumph of condensed matter physics in the past ten years is the classification of materials by the principle of topology. The existence of topological protected dissipationless surface state makes topological insulators great potential for applications and hotly studied. However, compared with the prosperity of strong topological insulators, theoretical predicted candidate materials and experimental confirmation of weak topological insulators (WTIs) are both extremely rare. By combining systematic first-principles calculation and angle-resolved photoemission spectroscopy measurements, we have studied the electronic structure of the dark surface of the WTI candidate Zintl Ba3Cd2Sb4 and another related material Ba3Cd2As4. The existence of two Dirac surface states on specific side surfaces predicted by theoretical calculations and the observed two band inversions in the Brillouin zone give strong evidence to prove that the Ba3Cd2Sb4 is a WTI. The spectroscopic characterization of this Zintl Ba3Cd2N4 (N = As and Sb) family materials will facilitate applications of their novel topological properties. [ABSTRACT FROM AUTHOR]

We study the scattering properties of Schrödinger operators with bounded potentials concentrated near a subspace of \mathbb {R}^d. For such operators, we show the existence of scattering states and characterize their orthogonal complement as a set of surface states, which consists of states that are confined to the subspace (such as pure point states) and states that escape it at a sublinear rate, in a suitable sense. We provide examples of surface states for different systems including those that propagate along the subspace and those that escape the subspace arbitrarily slowly. Our proof uses a novel interpretation of the Enss method [Comm. Math. Phys. 61 (1978), pp. 285–291] in order to obtain a dynamical characterization of the orthogonal complement of the scattering states. [ABSTRACT FROM AUTHOR]

Nonradiative recombination at perovskite/charge transport layer interfaces is caused by surface defects and instability, and it is known to limit the long-term development of perovskite solar cells (PSCs). To overcome this issue, the three-dimensional/two-dimensional (3D/2D) perovskite heterojunction has emerged as a possible solution to improve the stabilities and efficiency of PSCs. Herein, we employ a simple one-step method to prepare n-i-p-structured PSCs using a 3D/2D perovskite heterojunction as the absorption layer. For this purpose, the large and non-centrosymmetric 4,4-difluorocyclohexylammonium (DFCHA+) cation, which has been confirmed to be a valid organic spacer in 2D Ruddlesden–Popper (RP) phase perovskites, is employed as an organic ligand for post-treatment of the surfaces of MAPbI3 films. The presence of an ultrathin 2D RP phase perovskite was confirmed on the surface, and the 3D/2D perovskite heterojunction was successfully constructed. Benefitting from surface post-treatment, the density of the surface trap states was reduced with effective passivation. In addition, nonradiative recombination was suppressed, and the interface bands were aligned. As a result, the optimal device achieved a power conversion efficiency of 21.93% with a remarkable open-circuit voltage (VOC) of 1.14 V, a current density (JSC) of 23.71 mA cm−2, and a fill factor of 0.82. Furthermore, owing to the hydrophobicity of the DFCHA+ cation, the unencapsulated device was able to maintain an initial efficiency of 82.3% after storage for 500 h at a relative humidity of ∼45%. We believe that this post-treatment strategy has wide application potential in the field of photovoltaic devices. [ABSTRACT FROM AUTHOR]

One of the greatest triumph of condensed matter physics in the past ten years is the classification of materials by the principle of topology. The existence of topological protected dissipationless surface state makes topological insulators great potential for applications and hotly studied. However, compared with the prosperity of strong topological insulators, theoretical predicted candidate materials and experimental confirmation of weak topological insulators (WTIs) are both extremely rare. By combining systematic first-principles calculation and angle-resolved photoemission spectroscopy measurements, we have studied the electronic structure of the dark surface of the WTI candidate Zintl Ba3Cd2Sb4 and another related material Ba3Cd2As4. The existence of two Dirac surface states on specific side surfaces predicted by theoretical calculations and the observed two band inversions in the Brillouin zone give strong evidence to prove that the Ba3Cd2Sb4 is a WTI. The spectroscopic characterization of this Zintl Ba3Cd2N4 (N = As and Sb) family materials will facilitate applications of their novel topological properties. [ABSTRACT FROM AUTHOR]

Topological insulators (TIs) are under rapid and intensive study in the fields of condensed matter physics, due to exotic electronic properties. Recent studies of photocurrent generation in topological surface states (TSS) properties have insufficient evidence to rule out that of bulk states, hindering the application in optoelectronics. Herein, the chemical vapor transport (CVT) synthesis of GeBi4Te7 crystal by the way of Ge intercalation is realized, enabling isolated Dirac points‐associated high‐mobility Dirac carriers and larger Seebeck coefficients. Then, the antenna‐coupled photodetector in GeBi4Te7 based on planar metal–TI–metal structure is reported, successfully realizing sensitive terahertz response without bias. According to the results, the GeBi4Te7‐based terahertz photodetector has a short response time and a high photoresponsivity (0.42 A W−1 at 0.107 THz and 0.6 A W−1 at 0.28 THz, respectively). The GeBi4Te7–graphene heterostructure can further improve the responsivity by more than two orders of magnitude, reaching 12 A W−1 at 0.107 THz. These findings bring up doable avenues for GeBi4Te7 materials' low‐energy optoelectronic applications. [ABSTRACT FROM AUTHOR]