Atomic Electronic States Research Articles

Origin of Efficient and Tunable Dual‐Band Emission From Zinc Chalcogenide Quantum Dots for Sustainable Photonics

AbstractImpurity‐induced optical modulation in quantum‐confined colloidal nanocrystals has attracted intense interest thanks to the unique fundamental photo‐physics and application prospects. However, the present doping strategy is still facing limitations including spectral tunability and impurity controllability. Herein, a new route toward the tunable and efficient dual‐band emission in chlorine‐doped ZnSe (ZnSe:Cl) eco‐friendly quantum dots (QDs) is provided. Corroborated by the comprehensive spectroscopic characterization and first‐principles calculations, the emerging broadband sub‐gap emission is disclosed to originate from the self‐activating center constituted by a fusion of a Cl‐substituted Se point defect and a nearby Zn vacancy (ClSe‐VZn pair). First‐principles calculations confirm that the optically active center state stems from the distorted electron states of Se atoms surrounding the impurity rather than the Cl electron orbitals, which results in robust sub‐gap emission at ambient conditions. A dynamic model involving the transition between the charge and neutral states of the self‐activated center is established. By virtue of the controllable dual‐emission states, the transparent information encryption and the single‐component white light‐emitting diodes are realized, demonstrating the promising potential in sustainable photonic applications.

A Fundamental Correlative Spectroscopic Study on Li1‐xNiO2 and NaNiO2

AbstractThe intricate relationship between local atomic arrangements and electronic states significantly influences the electrochemical properties of Li‐ion battery cathode materials. Despite decades of investigation, a consensus regarding the local atomic and electronic structure of LiNiO2 remains elusive. This ambiguity stems from the potential distortion of Ni sites, either via Jahn‐Teller (JT) distortion or bond disproportionation (BD), complicating the understanding of the charge compensation mechanism involving Ni and O. This study compares the structures of LiNiO2 and NaNiO2, a JT system, using an innovative approach that integrates bulk spectroscopy techniques on standardized interoperable samples for enhanced reliability. While X‐r and theoretical calculations fail to differentiate between the proposed scenarios, Raman spectroscopy highlights local structural distinctions between monoclinic NaNiO2 and rhombohedral LiNiO2. HAXPES confirms various formal oxidation states for Ni, supported by RIXS data indicating 3d8 states, emphasizing negative charge transfer from Ni and some bond disproportionation in LiNiO2. Regarding charge compensation, XRS and RIXS suggest oxygen hole involvement in redox activity, whereas Raman spectroscopy does not detect molecular oxygen. This comprehensive spectroscopic analysis highlights the importance of correlative characterization workflows in elucidating complex structural‐electrochemical relationships.

Boron/nitrogen-trapping and regulative electronic states around Ru nanoparticles towards bifunctional hydrogen production

Developing a straightforward and general strategy to regulate the surface microenvironment of a carbon matrix enriched with N/B motifs for efficient atomic utilization and electronic state of metal sites in bifunctional hydrogen production via ammonia-borane hydrolysis (ABH) and water electrolysis is a persistent challenge. Herein, we present a simple, green, and universal approach to fabricate B/N co-doped porous carbons using ammonia-borane (AB) as a triple functional agent, eliminating the need for hazardous and explosive functional agents and complicated procedures. The pyrolysis of AB induces the regulation of the surface microenvironment of the carbon matrix, leading to the formation of abundant surface functional groups, defects, and pore structures. This regulation enhances the efficiency of atom utilization and the electronic state of the active component, resulting in improved bifunctional hydrogen evolution. Among the catalysts, B/N co-doped vulcan carbon (Ru/BNC) with 2.1 wt% Ru loading demonstrates the highest performance in catalytic hydrogen production from ABH, achieving an ultrahigh turnover frequency of 1854 min−1 (depending on the dispersion of Ru). Furthermore, this catalyst shows remarkable electrochemical activity for hydrogen evolution in alkaline water electrolysis with a low overpotential of 31 mV at 10 mA cm−2. The present study provides a simple, green, and universal method to regulate the surface microenvironment of various carbons with B/N modulators, thereby adjusting the atomic utilization and electronic state of active metals for enhanced bifunctional hydrogen evolution.

Heteroatom surface engineering with distinct doping ways and valence state regulation: Boosting electrocatalysis performance of Ni-doped MoS2/rGO host for excellent lithium sulfur batteries

Sulfur host materials are crucial to the electrochemical performances of lithium sulfur batteries (LSBs). Two-dimensional (2D) nanomaterials with close atomic thickness and large specific surface area are considered as excellent sulfur hosts in lithium sulfur batteries due to their extraordinary physical properties and special structures, which play a key role in improving the redox reaction kinetics of sulfur/Li2S. The heteroatom doping, which is usually applied in surface engineering, can not only adjust surface coordination environment but also form surface functional groups. Herein, the surface structures and properties of 2D Ni-doped MoS2/rGO composite are regulated via two surface engineering strategies. One is that nickel atoms are doped into 2D MoS2 nanosheets by two distinct hydrothermal techniques, which would result in notable differences of surface heteroatom content, and another is that the valence state of surface heteroatom nickel is changed by the thermal reduction technology. The content and valence state of surface heteroatom nickel can significantly influence the electrocatalysis activities of host materials during the redox reaction processes of sulfur/Li2S, which would substantially alter the electrochemical performances of LSBs. When the S@3%Ni-MoS2/rGO-IIRe is used as sulfur host, the lithium‑sulfur cell has an initial discharge capacity of 936.4 mA h g−1 and a low capacity attenuation of only 0.027 % each cycle with the high capacity of 819.7 mA h g−1 after 450 cycles at 1C, exhibiting an excellent coulombic efficiency and outstanding cycle stability. This study would provide some inspiration for improving the electrochemical performance of advanced lithium‑sulfur batteries through the rational regulation of surface atomic structures and electronic states of sulfur hosts.

2D Atomic Layers for CO2 Photoreduction.

Artificial photosynthesis can convert carbon dioxide into high value-added chemicals. However, due to the poor charge separation efficiency and CO2 activation ability, the conversion efficiency of photocatalytic CO2 reduction is greatly restricted. Ultrathin 2D photocatalyst emerges as an alternative to realize the higher CO2 reduction performance. In this review, the basic principle of CO2 photoreduction is introduced, and the types, advantages, and advances of 2D photocatalysts are reviewed in detail including metal oxides, metal chalcogenides, bismuth-based materials, MXene, metal-organic framework, and metal-free materials. Subsequently, the tactics for improving the performance of 2D photocatalysts are introduced in detail via the surface atomic configuration and electronic state tuning such as component tuning, crystal facet control, defect engineering, element doping, cocatalyst modification, polarization, and strain engineering. Finally, the concluding remarks and future development of 2D photocatalysts in CO2 reduction are prospected.

Vacancy‐Ordered Superstructure‐Induced Delocalized States Enable Superior Sodium Ion Storage

AbstractTransition metal sulfides (TMSs) are perceived as competitive candidate anodes for sodium‐ion batteries (SIBs) on account of their high capacity and admirable reversibility. However, a majority of TMSs suffer from huge volume expansion and poor kinetics so they cannot achieve durable and fast Na+ storage. Herein, a cation vacancy‐ordered Cr2/3S is fabricated by extracting quantitative Cr atoms from nickel arsenide type CrS via sulfur “atomic pump,” that is, sulfur and particular sit Cr atoms are bonded to extend a new structure. The ordered vacancies not only construct a loosely‐packed crystal structure but also induce delocalized electron states of Cr atoms, hence effectively accelerating Na+ diffusion and releasing volume strain to enable high‐rate and longevous SIBs. The new Cr2/3S anode presents a high reversible capacity of 544 mAh g−1 after 100 cycles at 1 A g−1 and excellent high‐rate performance of ≈100% capacity retention after 7000 cycles at 20 A g−1. Subsequent in situ and ex situ characterizations reveal the Na+ storage mechanism of Cr2/3S. The proposed cation exaction strategy through an innovative sulfur “atomic pump” can be an efficient way to achieve loosely‐packed structure material for large‐capacity and fast‐kinetics anodes.

Intermediate states in Andreev bound state fusion

Hybridization is one of the most fundamental quantum mechanical phenomena, with the text book example of binding two hydrogen atoms in a hydrogen molecule. Here we report tunnel spectroscopy experiments illustrating the hybridization of another type of discrete quantum states, namely of superconducting subgap states that form in segments of a semiconducting nanowire in contact with superconducting reservoirs. We discuss a collection of intermediate states with unique (tunnel) spectroscopic fingerprints in the process of merging well-known individual bound states, hybridized by a central quantum dot and eventually coherently linking the reservoirs, carrying a Josephson current. These coupled and fused Andreev bound states can be seen as superconducting analogues to atomic and molecular single electron states in nature, and explain a variety of recent bound state spectra, with specific fingerprints that will have to be winnowed in future Majorana fusion experiments.

Atomic and electronic structures of an Ag-containing 4A zeolite

Atomic structure of an Ag-containing 4A zeolite with the Ag/Al atomic ratio of about 10% was investigated by a pair distribution function (pdf) analysis. Valence- and conduction-band O 2p partial electronic structures of this insulating material were respectively measured by soft X-ray emission and absorption spectroscopies using an O 1s-2p resonance technique. Moreover, a density functional theory (DFT) hybridized by 25% of Hartree–Fock exchange was applied to determine the atomic structures and electronic states. Although the box size of the DFT calculation was small due to the limited computational power, the present DFT results excellently reproduce the pdf data as well as O 2p partial electron density of states (DOS). The electronic charge distributions in this zeolite with an antibacterial function obtained by the present DFT calculation revealed half-filled charges on the Ag atoms, which may act as a formation of deactivating the bacteria.

Electron States of Atoms in Monolayers Adsorbed on Silicon Carbide

Electron States of Atoms in Monolayers Adsorbed on Silicon Carbide

Achieving Tunable Selectivity and Activity of CO2 Electroreduction to CO via Bimetallic Silver-Copper Electronic Engineering.

Limited comprehension of the reaction mechanism has hindered the development of catalysts for CO2 reduction reactions (CO2 RR). Here, the bimetallic AgCu nanocatalyst platform is employed to understand the effect of the electronic structure of catalysts on the selectivity and activity for CO2 electroreduction to CO. The atomic arrangement and electronic state structure vary with the atomic ratio of Ag and Cu, enabling tunable d-band centers to optimize the binding strength of key intermediates. Density functional theory calculations confirm that the variation of Cu content greatly affects the free energy of *COOH, *CO (intermediate of CO), and *H (intermediates of H2 ), which leads to the change of the rate-determining step. Specifically, Ag96 Cu4 reduces the free energy of the formation of *COOH while maintaining a relatively high theoretical overpotential for hydrogen evolution reaction(HER), thus achieving the best CO selectivity. While Ag70 Cu30 shows relatively low formation energy of both *COOH and *H, the compromised thermodynamic barrier and product selectivity allows Ag70 Cu30 the best CO partial current density. This study realizes the regulation of the selectivity and activity of electrocatalytic CO2 to CO, which provides a promising way to improve the intrinsic performance of CO2 RR on bimetallic AgCu.

Uncommon 2D diamond-like carbon nanodots derived from nanotubes: atomic structure, electronic states, and photonic properties.

In this article, we report the results of a relatively facile fabrication of carbon nanodots from single-walled and multi-walled carbon nanotubes (SWCNTs and MWCNTs). The results of X-ray photoelectron spectroscopy (XPS) and Raman measurements show that the obtained carbon nanodots are quasi-two-dimensional objects with a diamond-like structure. Based on the characterization results, a theoretical model of the synthesized carbon nanodots was developed. The measured absorption spectra demonstrate the similarity in the local atomic structure of carbon nanodots synthesized from single-walled and multi-walled carbon nanotubes. However, the photoluminescence (PL) spectra of nanodots synthesized from both sources turned out to be completely different. Carbon dots fabricated from MWCNTs exhibit PL spectra similar to those of nanoscale carbon systems with sp3 hybridization and a valuable edge contribution. At the same time nanodots synthesized from SWCNTs exhibit PL spectra which are typical for quantum dots with an estimated size of ∼0.6-1.3 nm.

Breaking covalent bonds in the context of the many-body expansion (MBE). I. The purported “first row anomaly” in XHn (X = C, Si, Ge, Sn; n = 1–4)

We present a new, novel implementation of the Many-Body Expansion (MBE) to account for the breaking of covalent bonds, thus extending the range of applications from its previous popular usage in the breaking of hydrogen bonds in clusters to molecules. A central concept of the new implementation is the in situ atomic electronic state of an atom in a molecule that casts the one-body term as the energy required to promote it to that state from its ground state. The rest of the terms correspond to the individual diatomic, triatomic, etc., fragments. Its application to the atomization energies of the XHn series, X = C, Si, Ge, Sn and n = 1–4, suggests that the (negative, stabilizing) 2-B is by far the largest term in the MBE with the higher order terms oscillating between positive and negative values and decreasing dramatically in size with increasing rank of the expansion. The analysis offers an alternative explanation for the purported “first row anomaly” in the incremental Hn−1X–H bond energies seen when these energies are evaluated with respect to the lowest energy among the states of the XHn molecules. Due to the “flipping” of the ground/first excited state between CH2 (3B1 ground state, 1A1 first excited state) and XH2, X = Si, Ge, Sn (1A1 ground state, 3B1 first excited state), the overall picture does not exhibit a “first row anomaly” when the incremental bond energies are evaluated with respect to the molecular states having the same in situ atomic states.

Electronic state tuning over Mo-doped W18O49 ultrathin nanowires with enhanced molecular oxygen activation for desulfurization

Developing catalyst with abundant surface active sites is the core issue to achieve efficient catalytic oxidative desulfurization performance. In this work, Mo doped W18O49 ultrathin nanowires is fabricated through solvothermal method to provide plentiful low coordinated metal atoms around oxygen vacancies to trigger oxidative desulfurization reaction. As a non-stoichiometric oxide, the discorded lattice microstructure in W18O49 endows the formation of O vacancies neighboring low-valence W atoms, while the ultrathin structure ensure the fully exposure of surface atoms. Moreover, the doped Mo atoms will tune the surface atomic structure and electronic state of W18O49 nanowires, leading to the higher oxygen vacancy concentration and strengthened interaction with target sulfide molecules. Benefiting from these features, the higher molecular oxygen activation capacity can be realized over Mo-W18O49 nanowires to yield more superoxide radicals, making it with greatly improved oxidative desulfurization performance. The optimized 2 %Mo-W18O49 catalyst shows nearly 100% removal of dibenzothiophene within 5 h and maintain the good cycle stability. This work supply new insights for the design of catalytic sites towards selective catalytic oxidative desulfurization.

Electron states of atoms in monolayers adsorbed on silicon carbide

Estimates of charge transfer between adsorbate monolayer and SiC substrate based on account of the dipole-dipole repulsion and exchange interactions are presented. It is demonstrated that all the interaction channels lead to adlayer depolarization. Role of the band and local adatoms states are analyzed. Methods of experimental verification of the obtained results are proposed. Keywords: dipole-dipole interaction, direct and indirect exchange couplings.

Direct-ARPES and STM Investigation of FeSe Thin Film Growth by Nd:YAG Laser

Research on ultrathin quantum materials requires full control of the growth and surface quality of the specimens in order to perform experiments on their atomic structure and electron states leading to ultimate analysis of their intrinsic properties. We report results on epitaxial FeSe thin films grown by pulsed laser deposition (PLD) on CaF2 (001) substrates as obtained by exploiting the advantages of an all-in-situ ultra-high vacuum (UHV) laboratory allowing for direct high-resolution surface analysis by scanning tunnelling microscopy (STM), synchrotron radiation X-ray photoelectron spectroscopy (XPS) and angle-resolved photoemission spectroscopy (ARPES) on fresh surfaces. FeSe PLD growth protocols were fine-tuned by optimizing target-to-substrate distance d and ablation frequency, atomically flat terraces with unit-cell step heights are obtained, overcoming the spiral morphology often observed by others. In-situ ARPES with linearly polarized horizontal and vertical radiation shows hole-like and electron-like pockets at the Γ and M points of the Fermi surface, consistent with previous observations on cleaved single crystal surfaces. The control achieved in growing quantum materials with volatile elements such as Se by in-situ PLD makes it possible to address the fine analysis of the surfaces by in-situ ARPES and XPS. The study opens wide avenues for the PLD based heterostructures as work-bench for the understanding of proximity-driven effects and for the development of prospective devices based on combinations of quantum materials.

Single Pt Atoms on N-Doped Graphene: Atomic Structure and Local Electronic States

Single-atom catalysts are attracting attention due to their superior catalytic activity and cost. Nitrogen (N) enhances the stability of single platinum (Pt) atoms on graphene because Pt atoms disp...

Insights into the sandwich-like ultrathin Ni-doped MoS2/rGO hybrid as effective sulfur hosts with excellent adsorption and electrocatalysis effects for lithium-sulfur batteries

Dual redox mediator based on a novel ultrathin sandwich-type Ni-doped MoS 2 /rGO with rich MoS 2 -defect accelerate the electrochemical kinetics for high performance lithium-sulfur batteries. • The sandwich-type Ni-MoS 2 /rGO is developed as sulfur host via hydrothermal method. • The rich MoS 2 -defect plays key role in adsorption and redox kinetics of LiPSs. • Adsorption-electrocatalysis synergy enhances the electrochemical properties. • The S@Ni-MoS 2 /rGO cathode has high specific capacity and long cycle stability. The design of sulfur hosts with high conductivity, large specific surface area, strong adsorption and electrocatalytic ability is crucial to advance high performance lithium-sulfur batteries. Herein, a novel ultrathin sandwich-type Ni-doped MoS 2 /reduced graphene oxide (denote as Ni-doped MoS 2 /rGO) hybrid is developed as a sulfur host through a simple one-step hydrothermal route. The two-dimensional layered structure Ni-doped MoS 2 /rGO hybrid with heterostructure and heteroatom architecture defects not only plays a key role in adsorption of lithium polysulfide but also catalyzes on redox kinetics of sulfur and polysulfide species. Meanwhile, it can contribute to the large specific surface area for Li 2 S/S 8 deposition, fast Li-ion and electron transportation, thus enhancing the electrocatalytic properties, as confirmed firstly by cyclic voltammetry (CV) results. Due to the adsorption-catalytic synergistic effect, the Ni-doped MoS 2 /rGO cathode exhibits high specific capacity (1343.6 mA h g −1 at 0.2 C, 921.6 mA h g −1 at 1 C), high coulombic efficiency and an outstanding cycle stability (with the low attenuation rate of 0.077% per cycle over 140 cycles at 0.5 C and 0.11% per cycle over 400 cycles at 1 C, respectively). This work proposes some inspiration for exploring the construction of advanced lithium-sulfur batteries through the rational design defects of atomic structure and electronic states of MoS 2 as sulfur host.

STEM imaging artifacts with three-fold astigmatism in monolayer transition metal dichalcogenides

Aberration-corrected scanning transmission electron microscopy has been demonstrated as a versatile tool to probe the atomic defects and local electronic states in 2D materials. However, the residual aberration of the probe may give rise to considerable deviations from the perfect imaging, especially in polyphase transition metal dichalcogenides. Here, we clarify the misleading imaging artifact of opposite subdomains in monolayer MoS2 through both image simulations and experimental in-plane rotation series. This non-honeycomb imaging artifact turns out to be caused by both probe residual threefold astigmatism and local sample tilt or fluctuation. Our results suggest that the direct STEM imaging should be cautiously treated to achieve accurate phase assignment.

Electron structure and density of states’ calculations of Ag2S and Ag2Se crystals from first-principle

The results of calculations of the electron structure for Ag2S and Ag2Se crystals from first-principle in the framework of density functional theory (DFT) are presented in this work. The origin of the bands from [Formula: see text] and [Formula: see text] electron states of Ag, S and Se atoms are investigated. It was established that the orthorhombic Ag2Se crystal shows semiconductor properties in P2221and P212121space groups and semimetallic properties in Im-3m space groups with cubic crystal system. Monoclinic crystal type of Ag2S shows semiconductor properties in P21/c space group. However, semimetallic properties manifested itself in monoclinic Ag2S in P21and cubic Ag2S structure in Im-3m phases.

Atomic Structure and Local Electronic States of Single Pt Atoms Dispersed on Graphene

In single-atom catalysis, the atomic structure and local electronic states of single atoms on a supporting material remain a fundamental question. We experimentally and theoretically solved these problems for single Pt atoms dispersed on freestanding graphene using plasma sputtering. Electron microscopy revealed the atomic arrangements of Pt atoms binding to carbon atoms at the step edges of nanographene flakes. X-ray photoelectron spectroscopy revealed a large binding energy shift of the Pt 4f state of a single Pt atom. First-principles calculations elucidated that the Pt 5dxy-orbital in the step edge plays a crucial role in the formation of chemical bonds to C atoms and in the considerable charge transfer from Pt to C atoms, resulting in the large binding energy shift of the Pt 4f state.