Surface States Research Articles

Enhanced electrical parameters of the Au/n-Si Schottky barrier diodes with graphite/graphane oxide doped PVC interlayer

In this work, Schottky Barrier diodes (SBDs) formed on n-Si substrates were created using polyvinyl-chloride (PVC) and graphite/graphene-oxide (Gt/GO) nanoparticles (NPs) doped PVC interlayers and the conduction mechanisms of the structures were compared to the reference Au/n-Si (MS) diode. The characterization methods, including x-Ray Diffraction (XRD), Field Emission Scanning Electron Microscope (FE-SEM), and Energy Dispersive x-Ray (EDX), were used to analyze Gt/GO NPs and examine their structural, morphological, and analytical properties. In addition to the standard I-V method, modified Norde and Cheung methods were applied to analyze the forward bias I-V characteristics to determine the impact of pure-PVC and (PVC: Gt-GO) interlayers’ main electronic parameters on the SBDs. The surface state density (N ss ) depending on energy was also determined from the forward bias current–voltage by considering the voltage-dependent ideality coefficient, n(V), and barrier height (BH), ΦB(V). The outcomes showed that, as compared to MS structures, both the pure-PVC and (PVC: Gt-GO) interlayer leads to a decrease of n, leakage-current, N ss , an increase of rectification ratio (RR), shunt-resistance (R sh ) and zero-bias barrier-height (Φ B0 ). The differences in the electronic parameters observed between the I-V, Norde, and Cheung functions indicate that these parameters are highly reliant on the voltage and the computation method utilized. The barrier inhomogeneities at the metal/semiconductor surface also affect the current-transport or conduction mechanisms.

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Copper‐based catalysts are frequently employed for carbon dioxide reduction reactions (CO2RR), yet the regulation of pore structure and surface state of electrocatalysts remains a prominent challenge in previous research endeavors. In this study, we introduce a novel technique to produce mesoporous Cu2O nanocrystals, with finely tuned pore size and surface amine functionality leveraging the incorporation of various amine compounds during the oxidative process of copper nanocrystals. The synergistic effect of pore structure confinement and surface amine functionalization culminates in an impressive Faradaic efficiency (FE) of 51.9% for the selective production of C2H4. More details are discussed in the article by Huang et al. on page 1846—1852.image

Electric and dielectric responses of Au/n-Si structure by Mn doped PVC interfacial layers

This paper has investigated and compared the impact of polyvinyl chloride (PVC) without/with manganese (Mn) metallic nanoparticles interfacial layer on the electric and impedance characteristics of Schottky diode (SD) with a structure of Au/n-Si (MS). The structures of these two metal-polymer-semiconductor (MPS) SDs are Au/PVC/n-Si and Au/PVC:Mn/n-Si. A detailed description of the SDs manufacturing process is given. The x-ray diffraction (XRD) analysis, Scanning Electron Microscope (FE-SEM) images, and Electron Dispersive x-ray (EDX) spectroscopy are three methods that have been utilized to examine mean size of crystallite, morphology of surface, purity specification. The fundamental electronic variables of these devices are ascertained and contrasted with one another using the I-V characteristic measurement at ±6 V. Ohm’s law, Thermionic Emission (TE) theory, modified Norde, and Cheung functions are used to calculate the SDs’ leakage current (I0), ideality coefficient (n), potential barrier height (BH), shunt (Rsh), and series (Rs) resistances. Investigations are conducted on the energy dependence of surface states density (Nss) and the current conduction mechanisms (CCMs) for both reverse and forward biases. These interfacial layers are known to decrease the n, Rs, and Nss. The PVC polymer interlayer leads to improve the efficiency of the MS-type SD, but it does not when doped by Mn nanoparticles. Additionally, by measuring impedance at a bias of 1.5 V and 100 Hz-1 MHz frequency range, the frequency dependence of dielectric properties of the prepared SDs is studied. The dielectric permittivity, dielectric loss tangent, electronic modulus, and ac electronic conductivity of these SDs are all studied.

Tribological properties of atmospheric plasma sprayed Cr3C2–NiCr/20% nickel-coated graphite self-lubricating coatings

Using atmospheric plasma spraying technology, Cr3C2–NiCr (CN)and Cr3C2–NiCr/20 % Nickel-coated graphite (CG) composite coatings were successfully deposited on 304 stainless steel substrates, with three different spraying distance parameters designed to optimize the experiment. The study investigated the influence of nickel-coated graphite on the structure, hardness, porosity, and friction-wear performance of the composite coatings. Wear mechanisms were investigated based on analyses of morphologies and chemical states of the worn surfaces of the CG composite coatings. Our results demonstrate that the CG coating exhibits lower friction coefficients, ranging from 0.24 to 0.28, than that of the CN coating. The incorporation of nickel-coated graphite leads to formation of a solid-lubricating film at friction interface, lowering friction and wear. What's more, presence of nickel-coated graphite mitigates brittleness of the CN coating, as is deemed important for improving abrasion resistance of the coatings.

Assessments of Arctic Cloud Vertical Structure From AIRS Using Radar‐Lidar Observations

AbstractThe Atmospheric InfraRed Sounder (AIRS) aboard Aqua provides essential long‐term data on vertical cloud fraction, particularly valuable in the Arctic region. This study offers a comprehensive assessment of Arctic vertical cloud fraction derived from AIRS through a comparison with independent ground‐ and space‐based radar and lidar observations. In comparison to the measurements at the North Slope Alaska site, results reveal a significant underestimation of low‐level cloud cover by AIRS, especially for near‐surface clouds, while mid‐ and high‐level cloud fractions show better consistency. In comparison to the satellite‐based product from 3S‐GEOPROF‐COMB, the accuracy varies across different underlying surfaces (land vs. sea) and seasons. AIRS shows significant positive biases in mid‐level cloud fraction over sea surfaces with sea ice concentration below 15%, indicating potential limitations in the cloud retrieval algorithm in regions with large sea ice variations. The issue of low‐level clouds identification is primarily caused by the limited penetrating capability of infrared hyperspectral sensing and the accuracy of preceding surface and atmospheric state products, which diminish the accuracy of AIRS low‐level cloud fraction.

On the role of surface stress in environment-assisted fracture

Abstract Environment effects in plasticity and fracture of metals, well studied for several decades, still pose many unanswered questions. A micro-mechanics explanation of how dislocation activity is influenced by the material surface state, that can answer these questions, has been elusive. We build on a recently discovered effect in metal cutting – organic monolayer embrittlement (OME) – wherein metal surfaces are rendered brittle by long-chain organic adsorbates, to explore how material state variables influence surface plasticity and fracture. In particular, cutting experiments with Al containing Self Assembled Monolayers (SAMs), show that the OME is controlled by surface stress (f) induced by the adsorbates. This is contrary to many instances of environment-assisted fracture which are usually attributed to surface energy changes, and wherein f is largely ignored. Other contributions include (a) a cantilever technique to measure surface stress, (b) demonstration of strong effect of SAM molecule chain length on f, (c) characterization of how dislocation activity at crack-tips is affected by adsorbate-induced f, and (d) large improvements in machining processes enabled by controlled environment-assisted fracture. We make the case that surface stress, due to adsorbates, likely influences all environmentally assisted cracking (EAC) phenomena, warranting a revisit of extant models of EAC.

Secondary electron emission yield in thick dielectric materials: a comparison between Kelvin probe and capacitive methods

The recent high demand of secondary electron emission yield (SEY) measurements in dielectric materials from space industry has driven SEY laboratories to improve their facilities and measurement techniques. SEY determination by the common capacitive method, also known as pulsed method, is well accepted and has given satisfactory results in most cases. Nevertheless, the samples under study must be prepared according to the experimental limitations of the technique, i.e. they should be manufactured separated from the devices representing faithfully the surface state of the own device and be as thin as possible. A method based on the Kelvin probe (KP) is proposed here to obtain the SEY characteristics of electrically floating Platinum, Kapton and Teflon placed over dielectric spacers with thicknesses ranging from 1.6 to 12.1 mm. The results are compared with those of the capacitive method and indicate that KP SEY curves are less sensitive to spacer thickness. An explanation based on the literature is also given. In all, we have established that KP is better suited for the analysis of dielectric samples thicker than 3 mm.

Investigation of the Bending Behavior in Silicon Nanowires: A Nanomechanical Modeling Perspective

Nanowires (NWs) play a crucial role across a wide range of disciplines such as nanoelectromechanical systems, nanoelectronics and energy applications. As NWs continue to reduce in dimensions, their mechanical properties are increasingly affected by surface attributes. This study conducts a comprehensive examination of nanomechanical models utilized for interpreting large deformations in the bending response of silicon NWs. Specifically, the Heidelberg, Hudson, Zhan, SimpZP and ExtZP nanomechanical models are explored regarding their capability to predict the elastic properties of silicon NWs with varying critical dimensions and crystal orientations. Molecular dynamics simulations are employed to model silicon NWs with unreconstructed surface states. The calculation of intrinsic stresses and the methodology for quantifying surface properties, including surface stresses and surface elasticity constants, are carried out using atomistic modeling. The findings reveal significant disparities of up to 100 GPa among nanomechanical models in interpreting a singular force-deflection response obtained for a silicon NW. Inadequate consideration of surface and intrinsic effects in nanomechanical modeling of NWs leads to substantial variability in their mechanical properties. This investigation yields valuable insights into the surface characteristics of silicon NWs, thereby enhancing our understanding of the essential role played by nanomechanical models in the intricate interpretation of mechanical properties at the nanoscale.

Influence of Surface State on the Corrosion Behavior of Si-Reinforced F/M Steels under Solid-Phase Oxygen-Controlled Static Liquid LBE Environment

Influence of Surface State on the Corrosion Behavior of Si-Reinforced F/M Steels under Solid-Phase Oxygen-Controlled Static Liquid LBE Environment

Fluorescent carbon dots for sensing applications: a review.

Luminescent carbon dots (CDs) are important class of nanomaterials with fantastic photoluminescence (PL) properties, great biocompatibility, extraordinary solubility in water, minimal expense, and so on. There are many methods for their preparation and they are mainly classed into two groups, top-down and bottom-up approaches. In order to understand the origin of fluorescence in quantum CDs, three mechanisms have been proposed namely molecular state, surface state, and quantum confinement phenomenon. Fluorescent CDs have significant application in the fields of biochemical sensing, photocatalysis, bioimaging, delivery of drugs, and other related fields. In this review article the application of quantum dots as detecting component, for the sensing of different targets, has been summed up. In fact, the detection of several analytes including, anions, cations, small molecules, polymers, cells, and microscopic organisms has been discoursed. Moreover, the future aspects of CDs as detecting resources have been explored.

Structure Engineering of Ni/SiO2 Vegetable Oil Hydrogenation Catalyst via CeO2.

Inspired by our finding that metallic Ni particles could be uniformly distributed on a reduced CeO2 surface and stabilized on Ce3+ sites, we suppose a possible improvement in the activity and selectivity of the MgNi/SiO2 vegetable oil hydrogenation catalyst by increasing the surface metal Ni availability via modification by ceria. The proposed approach involved the addition of a CeO2 modifier to the SiO2 carrier and as a catalyst component. Evaluation of the structure, reducibility, and surface and electronic states of the CeO2-doped MgNi/SiO2 catalyst was performed by means of the Powder X-ray diffraction (PXRD), Scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS), and X-ray photoelectron spectroscopy (XPS) combined with High-resolution transmission electron microscopy (HRTEM), Temperature-programmed reduction with hydrogen (H2-TPR), and H2-chemisortion techniques. So far, no studies related to this approach of designing Ni/SiO2 catalysts for the partial hydrogenation of vegetable oil have been reported. The added ceria impact was elucidated by comparing fatty acid compositions obtained by the catalysts at an iodine value of 80. In summary, tuning the hydrogenation performance of Ni-based catalysts can be achieved by structural reconstruction using 1 wt.% CeO2. The introduction mode changed the selectivity towards C18:1-cis and C18:0 fatty acids by applying ceria as a carrier modifier, while hydrogenation activity was improved upon ceria operation as the catalyst dopant.

Impact of ocean in-situ observations on ECMWF sub-seasonal forecasts

We assess for the first time the impact of in-situ ocean observations on European Centre for Medium-Range Weather Forecasts (ECMWF) sub-seasonal forecasts of both ocean and atmospheric conditions. A series of coupled reforecasts have been conducted for the period 1993-2015, in which different sets of ocean observations were withdrawn in the production of the ocean initial conditions. Removal of all ocean in-situ observations in the initial conditions leads to significant degradation in the forecasts of ocean surface and subsurface mean state at lead times from week 1 to week 4. The negative impact is predominantly caused by the removal of the Argo observing system in recent decades. Changes in the mean state of atmospheric variables are comparatively small but significant in the forecasts of lower and upper atmospheric circulation over large regions. Our results highlight the value of continuous, real-time in-situ observations of the surface and subsurface ocean for coupled forecasts in the sub-seasonal range.

A dual mode immunosensing platform constructed on CdIn2S4 near-infrared electrochemiluminescence emitter and AuNPs@g-C3N4 for zearalenone sensing

In this study, a near-infrared (NIR) electrochemiluminescence (ECL) emitter CdIn2S4 was synthesized by a convenient hydrothermal strategy. The ECL properties of the obtained CdIn2S4 were examined in the presence of potassium persulfate coreactant at an excitation potential of − 1.25 V. The low trigger voltage of CdIn2S4 may be ascribed to its lower bandgap. This lower excitation potential could effectively reduce the side-effects induced by high voltages, while maintaining the biological activity of antibodides and antigens. The ECL features of CdIn2S4 were also investigated, demonstrating that CdIn2S4 exhibited excellent NIR characteristics, and surface state transitions led to the ECL emission. Importantly, CdIn2S4 was introduced into ECL and electrochemical impedance spectroscopy (EIS) to establish a dual-mode immunosensing interface. Meanwhile, AuNPs@g-C3N4 with excellent properties were used to promote electron transmission and increase the immobilization amount of zearalenone (ZEA) antibodies in the dual-mode sensing system. The developed immunosensing strategy displayed superior sensing performance in ZEA analysis. The detection limits of ZEA were 30 fg mL−1 (ECL model) and 10 fg mL−1 (EIS model), respectively. The desirable recovery results of ZEA in corn samples prove the application potential of the NIR emitter CdIn2S4 in developing a dual-mode immunosensing system for early real-time use.

Search for an antiferromagnetic Weyl semimetal in (MnTe) m (Sb2Te3) n and (MnTe) m (Bi2Te3) n superlattices

The interaction between topology and magnetism can lead to novel topological materials including Chern insulators, axion insulators, and Dirac and Weyl semimetals. In this work, a family of van der Waals layered materials using MnTe and Sb2Te3 or Bi2Te3 superlattices as building blocks are systematically examined in a search for antiferromagnetic Weyl semimetals, preferably with a simple node structure. The approach is based on controlling the strength of the exchange interaction as a function of layer composition to induce the phase transition between the topological and the normal insulators. Our calculations, utilizing a combination of first-principles density functional theory and tight-binding analyses based on maximally localized Wannier functions, clearly indicate a promising candidate for a type-I magnetic Weyl semimetal. This centrosymmetric material, Mn10Sb8Te22 (or (MnTe) m (Sb2Te3) n with m = 10 and n = 4), shows ferromagnetic intralayer and antiferromagnetic interlayer interactions in the antiferromagnetic ground state. The obtained electronic bandstructure also exhibits a single pair of Weyl points in the spin-split bands consistent with a Weyl semimetal. The presence of Weyl nodes is further verified with Berry curvature, Wannier charge center, and surface state (i.e. Fermi arc) calculations. Other combinations of the MnSbTe-family materials are found to be antiferromagnetic topological or normal insulators on either side of the Mn:Sb ratio, respectively, illustrating the topological phase transition as anticipated. A similar investigation in the homologous (MnTe) m (Bi2Te3) n system produces mostly nontrivial antiferromagnetic insulators due to the strong spin–orbit coupling. When realized, the antiferromagnetic Weyl semimetals in the simplest form (i.e. a single pair of Weyl nodes) are expected to provide a promising candidate for low-power spintronic applications.

Acceleration of bulk and surface charger transfer dynamics via FePi cocatalyst-coated Ti/(Sb)-Fe2O3:Sb/(Ti)-Fe2O3 type-II homojunction photoanode for photoelectrochemical performance

Hematite (α-Fe2O3) possesses notable benefits in the field of photoelectrochemical (PEC) water splitting. However, the overall low efficiency of the separation and transfer of photogenerated charge carriers significantly hinders its further utilization. Although the occurrence of an internal electric field has the potential to significantly augment the efficiency of charge separation and transfer, there is a crucial need to broaden the scope of its successful application. This study explores a strategy for modifying the coupling between homojunction formation with gradient doping and cocatalyst modification on hematite to boost PEC performance. The developed type II Ti-doped/(Sb-codoped) Fe2O3:Sb-doped/(Ti-codoped) Fe2O3 (Ti/(Sb)-HT:Sb/(Ti)-HT) homojunction with a staggered band alignment accelerated the bulk charge separation via an intrinsic built-in electric field, while the bulk conductivity was improved using a gradient co-doping approach. Furthermore, the deposition of a FePi cocatalyst expedited the transfer of holes from the photoanode to the electrolyte by increasing the surface states, thereby hastening the water oxidation kinetics. The resulting Ti/(Sb)-HT:Sb/(Ti)-HT@FePi photoanode exhibited a 78.7% increase in photocurrent density compared to the bare Ti-Fe2O3 photoanode (0.94–1.68 mA/cm2 at 1.23 VRHE), accompanied by a charge transfer efficiency of 72.5%. Comprehensive photoelectrochemical investigations revealed that the homojunction and cocatalyst play a vital role in improving the dynamics of both the bulk and surface of the hematite photoanode, thereby facilitating efficient water oxidation. These findings offer a deeper insight into the function of homojunction photoanodes adorned with cocatalysts in the solar water-splitting process.

Exchange bias in heterostructures combining magnetic topological insulator MnBi2Te4 and metallic ferromagnet Fe3GeTe2

Introducing magnetism into topological insulators enables exotic phenomena such as quantum anomalous Hall effect. By fabricating van der Waals (vdW) heterostructures using layered magnetic materials, we can not only induce a gap in the non-magnetic topological surface states through magnetic proximity but also further manipulate the magnetic properties of magnetic topological insulators. However, the scarcity of 2D ferromagnetic insulator materials limits the fabrication of such heterostructures. Here, we demonstrate the vdW heterostructure devices comprising metal ferromagnetic Fe3GeTe2 nanoflakes and few-layer antiferromagnetic topological insulator MnBi2Te4 separated by an insulating hexagonal-boron nitride spacer. These devices exhibit significant exchange bias with the exchange bias field of over 100 mT under certain conditions. Our results prove that besides magnetic insulators, metallic magnets can also effectively adjust the magnetic properties of topological insulators, thereby inspiring diverse configurations of the heterostructures between topological insulators and magnetic materials.

A Facile One-Step Self-Assembly Strategy for Novel Carbon Dots Supramolecular Crystals with Ultralong Phosphorescence Controlled by NH4.

A new methodological design is proposed for carbon dots (CDs)-based crystallization-induced phosphorescence (CIP) materials via one-step self-assembled packaging controlled by NH4 +. O-phenylenediamine (o-PD) as a nitrogen/carbon source and the ammonium salts as oxidants are used to obtain CDs supramolecular crystals with a well-defined staircase-like morphology, pink fluorescence and ultralong green room-temperature phosphorescence (RTP) (733.56ms) that is the first highest value for CDs-based CIP materials using pure nitrogen/carbon source by one-step packaging. Wherein, NH4 + and o-PD-derived oxidative polymers are prerequisites for self-assembled crystallization so as to receive the ultralong RTP. Density functional theory calculation indicates that NH4 + tends to anchor to the dimer on the surface state of CDs and guides CDs to cross-arrange in an X-type stacking mode, leading to the spatially separated frontier orbitals and the through-space charge transfer (TSCT) excited state in turn. Such a self-assembled mode contributes to both the small singlet-triplet energy gap (ΔEST) and the fast inter-system crossing (ISC) process that is directly related to ultralong RTP. This work not only proposes a new strategy to prepare CDs-based CIP materials in one step but also reveals the potential for the self-assembled behavior controlled by NH4 +.

Interplay between Topological States and Rashba States as Manifested on Surface Steps at Room Temperature.

The unique spin texture of quantum states in topological materials underpins many proposed spintronic applications. However, realizations of such great potential are stymied by perturbations, such as temperature and local fields imposed by impurities and defects, that can render a promising quantum state uncontrollable. Here, we report room-temperature scanning tunneling microscopy/spectroscopy observation of interaction between Rashba states and topological surface states, which manifests local electronic structure along step edges controllable by the layer thickness of thin films. The first-principles theoretical calculation elucidates the robust Rashba states coexisting with topological surface states along the surface steps with characteristic spin textures in momentum space. Furthermore, the Rashba edge states can be switched off by reducing the thickness of a topological insulator Bi2Se3 to bolster their interaction with the hybridized topological surface states. The study unveils a manipulating mechanism of the spin textures at room temperature, reinforcing the necessity of thin film technology in controlling the quantum states.

Effect of AZO seed layers on the ultraviolet photoresponse of Ag/ZnO NRs Schottky junctions

Al-doped ZnO (AZO) thin films with different layers were prepared by sol-gel method. The SEM, XRD and AFM for three layers thin films demonstrates high crystal quality and low roughness. ZnO nanorods arrays (NRs) with different AZO seed layers were fabricated using hydrothermal process, and the effect of AZO seed layers on the structural, optical, and electrical characteristics was investigated. When there are three AZO seed layers present, ZnO NRs exhibit fewer surface states, smaller interface charge transfer resistance (Rce = 6.1 × 103Ωand Rct = 6.6 × 106Ω), longer carrier lifetimes (τe = 4.0 ms), higher carrier concentration (ND = 4.73 × 1019 cm−3), and narrower depletion region width W = 3.1 nm. Under weak UV light 381 nm (5.68 mW/cm2) at a bias −0.5 V, Ag/ZnO NRs Schottky devices with three AZO seed layers display a comparatively strong responsivity 34.64 mA/W. Appropriate AZO seed layers are favorable for highly efficient ZnO NRs-based photoelectric conversion devices.

Interfacial Spintronic THz Emission

AbstractThe broken inversion symmetry at the ferromagnet (FM)/heavy‐metal (HM) interface leads to spin‐dependent degeneracy of the energy band, forming spin‐polarized surface states. As a result, the interface serves as an effective medium for converting spin accumulation into 2D charge current through the inverse Rashba–Edelstein effect. Exploring and assessing this spin‐to‐charge conversion (SCC) phenomenon at the FM/HM interface can offer a promising avenue to surpass the presumed limits of SCC in bulk HM layers. Spintronic heterostructures are utilized as a platform to measure the SCC experienced by photoexcited spin currents. Therefore, FM/HM heterostructures emitting terahertz electric field upon illumination by femtosecond laser pulses enable quantitative measure of the ultrafast SCC process. This results demonstrate a robust interfacial spin‐to‐charge conversion (iSCC) within a synthetic antiferromagnetic heterostructure, specifically for the NiFe/Ru/NiFe configuration, by isolating the SCC contribution originating from the interface and the bulk heavy‐metal (HM). Through the measurements of the emitted terahertz pulse, the iSCC at the NiFe/Ru interface is identified to be ≈27% of the strength as compared to SCC from the highest spin‐Hall conducting heavy‐metal, Pt. The results thus highlight the significance of interfacial engineering as a promising pathway for achieving efficient ultrafast spintronic devices.