Surface Electronic States Research Articles

Tunable Catalytic Vertex Wall Chemistry in Metal-free Covalent Organic Frameworks for Enhanced Oxygen Reduction.

Metal-free covalent organic frameworks (COFs) have emerged as promising catalysts for the oxygen reduction reaction (ORR) because of their unique structural properties and notable stability. To enhance both catalytic activity and selectivity, a variety of linkers and linkages have been investigated in efforts to precisely engineer COFs. However, the impact of vertex structures within COFs on ORR catalysis remains largely underexplored. Here, to modulate COF catalytic performance, we introduce tunable catalytic vertex wall chemistry by introducing diverse triazine and thiophene units. The catalytic vertex wall approach allows the fine-tuning of electronic surface states, leading to improved intermediate adsorption characteristics and accelerated ORR activity. Remarkably, the engineered COF achieved a half-wave potential of 0.76 V, surpassing COFs modified by linker or linkage strategies. Theoretical calculations suggest that this enhanced activity arises from the strong binding affinity of OOH* intermediates to carbon atoms adjacent to the thiophene vertex, facilitating OOH* reduction to a O2 molecule, which is the rate-limiting step of the ORR. These findings reveal the pivotal role of vertex wall engineering in conjugated COF frameworks, and offer critical insights to advance COFs design toward superior ORR performance.

Tunable Catalytic Vertex Wall Chemistry in Metal‐free Covalent Organic Frameworks for Enhanced Oxygen Reduction

Metal‐free covalent organic frameworks (COFs) have emerged as promising catalysts for the oxygen reduction reaction (ORR) because of their unique structural properties and notable stability. To enhance both catalytic activity and selectivity, a variety of linkers and linkages have been investigated in efforts to precisely engineer COFs. However, the impact of vertex structures within COFs on ORR catalysis remains largely underexplored. Here, to modulate COF catalytic performance, we introduce tunable catalytic vertex wall chemistry by introducing diverse triazine and thiophene units. The catalytic vertex wall approach allows the fine‐tuning of electronic surface states, leading to improved intermediate adsorption characteristics and accelerated ORR activity. Remarkably, the engineered COF achieved a half‐wave potential of 0.76 V, surpassing COFs modified by linker or linkage strategies. Theoretical calculations suggest that this enhanced activity arises from the strong binding affinity of OOH* intermediates to carbon atoms adjacent to the thiophene vertex, facilitating OOH* reduction to a O2 molecule, which is the rate‐limiting step of the ORR. These findings reveal the pivotal role of vertex wall engineering in conjugated COF frameworks, and offer critical insights to advance COFs design toward superior ORR performance.

The NaBH4 Reduction and pH Effects on the Optical Property of Bismuth Vanadate

In this study, oxygen vacancies were created on the surface of BiVO4 nanoparticles using the NaBH4 reduction technique, resulting in BiVO4−x samples that are oxygen-deficient. Optical absorption data using a UV-visible diffuse reflectance spectrophotometer showed that the reduction process increases the maximum absorption edge to 575 nm and reduces the band gap energy to 2.78 eV at high pH. Furthermore, modulating pH during synthesis allowed tuning of the electronic structure and surface states of BiVO₄, which significantly impacts the photocatalytic efficiency. Higher pH levels during reduction led to narrower band gaps and enhanced visible-light responsiveness. These vacancies should serve as charge traps and adsorption sites, improving the charge transport within the BiVO₄ matrix by limiting electron-hole recombination. This improves photogenerated electron availability, enabling better pollutant photodegradation and water oxidation potential in environmental applications. The study highlights the role of NaBH₄ as a reduction, effectively creating oxygen vacancies and optimizing photocatalytic performance. This research underscores the potential of engineered BiVO₄ nanoparticles with tailored oxygen vacancies for advanced photocatalytic applications, especially in environmental remediation.

Regulating the electronic state of MFI zeolite encapsulated Pt nanoparticles to boost the atom efficiency in reductive amination of biomass-derived furfural

Furfural is an abundant biomass-derived building block that can be converted into furan-based N-containing compounds through direct reductive amination by using dihydrogen (H2). Nonetheless, the synthesis of furan-based tertiary amines is highly limited via this route. Herein, we reported the straightforward synthesis of MFI zeolite encapsulated Pt nanoparticles and finely modulated the surface electronic state by facilely controlling the reduction process. The constructed catalyst Pt@Z5 effectively catalyzed the amination of furfural with diethylamine for the synthesis of N-ethyl-N-(furan-2-ylmethyl)ethanamine, affording the high yield (>95 %), large turnover number (TON) of 2058, turnover frequency (TOF) of 1029 h−1, and stable recyclability. Systematic investigations comprising in-situ Fourier transform infrared spectroscopy (FTIR) spectra and kinetic isotope effect (KIE) unraveled that the mild reduction condition allowed the catalyst with a superior affinity towards H atom and beneficial furfural adsorption behavior, accelerating the H2 activation in the rate-determining step for the conversion of furfural into furan-based amine.

First-principles study on thermodynamic stability and electronic structures of the ferroelectric binary HfO2 and ZrO2 (001) polar surfaces

Using the reliable first-principles thermodynamic method, the relative stability and electronic states of ferroelectric binary HfO2 and ZrO2 (001) polar surfaces with different stoichiometry are comprehensively investigated. The results predict that the thermodynamically preferred surface termination is the O4-(Hf or Zr)2- for both the HfO2/ZrO2 positively (Z+) and negatively (Z−) polar surfaces under most chemical environmental conditions, which is in same oxygen content as each other, providing convenient and feasible strategy for designing high-performance devices based on HfO2 (or ZrO2) ferroelectric dielectric. In addition, the surface morphology, atomic geometries, and electronic states of HfO2 and ZrO2 (001) polar surfaces show evident dependence on polarization direction. There exists significant difference in the polar surface atomic relaxations, electronic band structures, work functions, and compensating charges between the Z+ and Z− polar surfaces of ferroelectric HfO2/ZrO2. In other words, the surface properties of HfO2/ZrO2Z± polar surfaces are strongly revised by the partially occupied surface electronic states induced by the polar surface terminations. Our study is of great significance for the design and development of the next generation of high-performance and energy-efficient field-effect nanodevices based on HfO2 (or ZrO2) ferroelectric dielectric.

Topological material in the III–V family: Heteroepitaxial InBi on InAs

InBi(001) is formed epitaxially on InAs(111)-A by depositing Bi onto an In-rich surface. Angle-resolved photoemission measurements reveal topological electronic surface states, close to the M¯ high symmetry point. This demonstrates a heteroepitaxial system entirely in the III–V family with topological electronic properties. InBi shows coexistence of Bi and In surface terminations, in contradiction with other III–V materials. For the Bi termination, the study gives a consistent physical picture of the topological surface electronic structure of InBi(001) terminated by a Bi bilayer rather than a surface formed by splitting to a Bi monolayer termination. Theoretical calculations based on relativistic density functional theory and the one-step model of photoemission clarify the relationship between the InBi(001) surface termination and the topological surface states, supporting a predominant role of the Bi bilayer termination. Furthermore, a tight-binding model based on this Bi bilayer termination with only Bi–Bi hopping terms, and no Bi–In interaction, gives a deeper insight into the spin texture. Published by the American Physical Society 2024

Physical, optical properties and antibacterial activity of silver nanoparticles: Nanoclusters to nanoparticles formation on glass substrate by in-situ annealing

Silver nanoparticles (AgNPs) formed on in-situ annealed microscopic glass substrates from silver nanoclusters (AgNCs) generated by DC magnetron sputtering with inert gas condensation (IGC) technique. The substrate’s annealing temperature was below and above the glass transition temperature of 500 ºC and 600 ºC. The influence of annealing temperature on the surface morphology was studied using atomic force microscopy (AFM). X-ray photoelectron spectroscopy (XPS) and ultraviolet photoelectron spectroscopy (UPS) were employed to investigate the surface composition, chemical states, and electronic states of the AgNPs on the glass substrates. On the in-situ annealed glass substrate at 500 ºC, the produced AgNPs revealed accumulation and aggregation. For in-situ annealed at 600 ºC, a homogeneous distribution of AgNPs on the glass substrate was witnessed. The refractive index test revealed that AgNPs deposition at 600 ºC achieved higher sensitivity with 27 nm/RIU (Refractive index unit). The antibacterial activity of AgNPs was also investigated using Escherichia coli and Bacillus cereus. In contrast, better antibacterial activity was obtained with in-situ annealing at 500 ºC, where 4-fold reductions compared with the control sample. Pre-determined properties can be precisely executed to achieve the desired performance as the so-called application-oriented engineered surface in the UHV system is established. This research highlighted the differences between two different annealing temperatures' effect on the base substrate material, which subsequently impacts the structure of AgNPs and their applications. Furthermore, the outcome of this work could contribute to the multifunctional surface for detecting heavy metals, various organic pollutants, and disinfection of water and food-borne pathogenic diseases.

Intergrain scattering in polycrystals

Transport through grain boundaries in polycrystals is described from first principles using quantum scattering theory, explicitly including Feshbach resonances to account for intermittently trapped electronic surface states. An effectiveT-matrix is derived then used to calculate the electrical conductivity which exhibits breakdown, a sharp increase at a critical intergrain bias. Under typical conditions where the electron thermal energy,kBT, is much less than the intergrain barrier height,φb, the electrical conductivity has the formσ∼T-1/2e-φb/kBT. Temperature dependence of the conductivity is also considered for thermal energies much larger than the applied bias, as may be realized in tightly-compressed grains.

Bifunctional electrolyte additive enabling long cycle life of vanadium-based cathode aqueous zinc ion batteries

Aqueous zinc ion batteries have received extensive attention due to their many advantages, but they still face problems such as dendrite growth and interface reaction of Zn anode and collapse of vanadium-based cathode structure. Here, a bifunctional electrolyte additive Methionine (MET) is proposed, which exhibits a unique role in inducing uniform deposition of zinc anode and inhibiting the failure of vanadium-based cathode materials. MET affects the solvated structure of the electrolyte to inhibit water activity and reduce HER and other related parasitic reactions. At the same time, it regulates the flux of Zn2+, improves the deposition kinetics of Zn2+ on the zinc anode side, and induces the preferential growth of the Zn (1 0 1) crystal plane to promote ordered Zn deposition. In particular, MET can in-situ generate a CEI containing such as ZnF2 on the surface of the vanadium-based cathode to inhibit the failure of the vanadium-based cathode, while adjusting the surface electronic state and Zn2+ diffusion behavior, and reducing the structural damage of the vanadium-based cathode caused by the Zn2+ intercalation process by inducing a strengthened surface pseudocapacitive reaction. Compared with the bare electrolyte, the capacity retention rate of the K2V8O21||Zn full-cell with OTF-M50 electrolyte increased from 10.2 % to 99.8 % after 800 cycles at a low current density of 1 A/g. Therefore, MET exhibits considerable application prospects as a bifunctional additive that can improve the stability of vanadium-based cathode and promote the stable deposition of zinc anode.

Enhancing detection of thermal runaway gases: Exploiting doping and vacancy effects in GeS quantum dots

This study investigates chemical modifications on Germanium Sulfide (GeS) quantum dots (QDs) for selective detection of thermal runaway gases (TRGs). We examine how doping with oxygen, phosphorus, silicon, and introducing sulfur vacancies at edge and surface regions affect the structural, electronic, and optical properties of GeS-QDs and their derivatives. Our findings reveal significant changes in bond parameters, formation energy, electronic band gap, and light absorption behavior. Oxygen doping enhances stability, while other dopants and sulfur vacancies increase reactivity towards TRGs (H2, CO, CH4, C2H4). All materials show favorable adsorption for these gases, with C2H4 displaying the strongest binding affinity. Adsorption minimally affects core electronic structure (HOMO) but shifts surface electronic states (LUMO). Sulfur vacancies reduce the energy gap, enhancing conductivity and facilitating TRGs detection. These results suggest that GeS-QDs can be effectively tuned for selective TRG detection by manipulating their chemical composition and surface characteristics.

Topological boundary states in engineered quantum-dot molecules on the InAs(111)A surface: Odd numbers of quantum dots

Atom manipulation by scanning tunneling microscopy was used to construct quantum dots on the InAs(111)A surface. Each dot comprised six ionized indium adatoms. The positively charged adatoms create a confining potential acting on surface-state electrons, leading to the emergence of a bound state associated with the dot. By lining up the dots into N-dot chains with alternating tunnel coupling between them, quantum-dot molecules were constructed that revealed electronic boundary states as predicted by the Su-Schrieffer-Heeger (SSH) model of one-dimensional topological phases. Dot chains with odd N were constructed such that they host a single end or domain-wall state, allowing one to probe the localization of the boundary state on a given sublattice by scanning tunneling spectroscopy. We found probability density also on the forbidden sublattice together with an asymmetric energy spectrum of the chain-confined states. This deviation from the SSH model arises because the dots are charged and create a variation in on-site potential along the chain—which does not remove the boundary states but shifts their energy away from the midgap position. Our results demonstrate that topological boundary states can be created in quantum-dot arrays engineered with atomic-scale precision. Published by the American Physical Society 2024

Photoionization of aziridine: Nonadiabatic dynamics of the first six low-lying electronic states of the aziridine radical cation.

In this article, the theoretical photoionization spectroscopy of the aziridine (C2H5N) molecule is investigated. To start with, we have optimized the geometry of this molecule at the neutral electronic ground state at the density functional theory/augmented correlation-consistent polarized valence triple zeta level of theory using the G09 program. The electronic structure calculations were restricted to the first six low-lying electronic states in order to account for the experimental photoelectron spectrum of the C2H5N molecule. The first six low-lying electronic states (X̃2A', Ã2A', B̃2A″, C̃2A″, D̃2A', and Ẽ2A') of the potential energy surfaces (PESs) are calculated by both equation of motion-ionization potential-coupled cluster singles and doubles and multi-configuration quasi-degenerate perturbation theory abinitio quantum chemistry methods along the dimensionless normal displacement coordinates in which multiple conical intersections were established among the considered electronic states. A (6 × 6) model vibronic Hamiltonian is constructed on a diabatic electronic basis, using the symmetry selection rules and Taylor series expansion. The Cs symmetry point group of the aziridine molecule leads to electronic states symmetry of either A' or A″, and these states are close in energy, due to which the same symmetry electronic states avoid each other. To get a smooth diabatic PES, a fourfold diabatization scheme is used, which is implemented in the General Atomic and Molecular Electronic Structure Systems suite of programs. All the parameters used in the diabatic vibronic coupling model Hamiltonian are calculated in terms of the normal modes of vibrational coordinates. Finally, the vibronic model Hamiltonian constructed for the coupled six electronic states is used to solve both time-independent and time-dependent Schrödinger equations using the multi-configuration time-dependent Hartree program module to obtain the dynamical observables. The theoretical vibronic band structure is found to be in good accord with the available experimental results.

Tailoring surface terminals of Ti3C2Tx MXene microgels via interlayer domain-confined polyphosphate ammonium for flexible supercapacitor applications

The MXene material shows potential for flexible energy storage devices due to its high pseudocapacitance and mechanical flexibility. However, MXene nanosheet self-stacking and –F terminal functional groups can hinder active site and ion dynamics, thus affecting the energy storage performance. Herein, we present an interlayer domain-confined strategy that involves the introduction and crosslinking of ammonium polyphosphate (APP) confined to the interlayer of Ti3C2Tx MXene sheets, which induces gelation of the MXene to form a 3D network structure and enlarge their interlayer spacing. And then the cross-linked APP is converted into nitrogen and phosphorus terminals on Ti3C2Tx MXene via thermal treatment. The nitrogen terminals in the form of the pyrrole nitrogen and pyridine nitrogen, and phosphorus terminals of P–O bonds enhance the activity of the redox reaction and the dynamics of the ions, resulting in the boosted energy storage capacity of MXene. The density functional theory (DFT) calculations reveal that nitrogen-phosphorus co-doping modulates the surface electronic states of MXene and contributes to the increase of the electrical conductivity of Ti3C2Tx MXene. As a supercapacitor electrode, Ti3C2Tx MXene with N/P terminals exhibits a higher specific capacitance of 597.8 F/g (1777F cm−3) than the raw Ti3C2Tx MXene (384 F/g). In addition, the quasi-solid state flexible symmetric supercapacitor assembled by Ti3C2Tx MXene with N/P terminals can achieve an energy density of 12.5 Wh kg−1 at a power density of 250 W kg−1. Therefore, this work provides a new strategy for terminal modification of MXene and high-performance MXene supercapacitors.

Enhanced UV Photoresponse Performances of TiO2/Bi2Se3 Heterostructure‐Based Photoelectrochemical Photodetector

Bi2Se3 has a unique surface state and excellent electron transport performance, but because of its narrow band gap, Bi2Se3‐based photodetectors are difficult to achieve high response to ultraviolet (UV) light. In this paper, the TiO2/Bi2Se3 heterostructure was constructed by spin‐coating TiO2 on Bi2Se3 film, and TiO2/Bi2Se3 heterostructure‐based photoelectrochemical (PEC) photodetector was constructed, and a series of measurements were carried out. The measure results showed that the photoresponse performance of TiO2/Bi2Se3 heterostructure‐based photodetector was improved in the visible region, and the performance in the UV was further improved. This is because the type ii band alignment between TiO2 and Bi2Se3 is beneficial for the effective separation and transfer of photogenerated electron‐hole pairs, reducing recombination losses and enhancing the overall photoresponse. In addition, under the action of the built‐in electric field formed by the heterostructure, the photogenerated electrons and holes are easier to separate, which reduces the recombination probability of the photogenerated electron‐hole pair and improves the photoelectric conversion efficiency. In the UV, TiO2/Bi2Se3 heterostructure can make more efficient use of the light absorption characteristics of TiO2 and absorb more photons, resulting in a larger photocurrent. These results indicate that TiO2/Bi2Se3 heterostructure‐based photodetector has great application potential in the UV.

Artificial Graphene Nanoribbons with Tailored Topological States

Low-dimensional materials functioning at the nanoscale are a critical component for a variety of current and future technologies. From the optimization of light harvesting solar technologies to novel electronic and magnetic device architectures, key physical phenomena are occurring at the nanometer and atomic length-scales and predominately at interfaces. In this presentation, I will discuss low-dimensional material research occurring in the Quantum and Energy Materials (QEM) group at the Center for Nanoscale Materials. Specifically, the synthesis of artificial graphene nanoribbons by positioning carbon monoxide molecules on a copper surface to confine its surface state electrons into artificial atoms positioned to emulate the low-energy electronic structure of graphene derivatives. We demonstrate that the dimensionality of artificial graphene can be reduced to one dimension with proper “edge” passivation, with the emergence of an effectively-gapped one-dimensional nanoribbon structure. Remarkably, these one-dimensional structures show evidence of topological effects analogous to graphene nanoribbons. Guided by first-principles calculations, we spatially explore robust, zero-dimensional topological states by altering the topological invariants of quasi-one-dimensional artificial graphene nanostructures. The robustness and flexibility of our platform allows us to toggle the topological invariants between trivial and non-trivial on the same nanostructure. Our atomic synthesis gives access to nanoribbon geometries beyond the current reach of synthetic chemistry, and thus provides an ideal platform for the design and study of novel topological and quantum states of matter. Figure 1

Atomic Layer Engineering of Pd Nanosheets for an Enhanced Hydrogen Evolution Reaction.

Thickness control of two-dimensional (2D) metal nanosheets (metallenes) has scientific significance for energy and catalyst applications, yet is unexplored owing to the lack of an efficient approach for the tailored synthesis of metallenes with controlled atomic layers. Here we report a 2D template-directed synthesis of ultrathin Pd nanosheets with well-controlled thicknesses. Molecularly thin single-crystalline Pd nanosheets with well-defined hexagonal morphologies were synthesized via a one-pot method with 2,4,6-trichlorophenyl formate. Such Pd nanosheets were used as hard templates for the tailored synthesis of the Pd nanosheets with controlled thicknesses (9, 11, 13, and 15 atomic layers). Hard X-ray photoelectron spectroscopy and density functional theory calculations revealed unique electronic states in thickness-controlled Pd nanosheets; these states included reduced surface charges to bulk, increased work functions, and decreased d-band centers. Thus, atomic layer engineering of Pd nanosheets enabled the fine-tuning of the surface electronic states to improve the hydrogen evolution reaction.

Quantum computation with electrons trapped on liquid Helium by using the centimeter-wave manipulating techniques

Surface-state electrons floating on liquid Helium have been served as one of the great potential experimental platforms to implement quantum computation, wherein the qubits are usually encoded by either the lowest two levels of the vertical vibrations (i.e., Hydrogen-like atoms) or the electronic spins. Given the relevant operations require additional techniques, such as the corresponding millimeter-wave or magnetic field manipulations, here we investigate how to implement the scalable quantum computation with a trapped electron array by alternatively using the usual centimeter-wave manipulating techniques. This is because the eigenfrequency of the present qubit, encoded by the two lowest levels of the lateral vibration of the trapped electron, is limited in the centimeter-wave band. We show that, by biasing the electrodes properly and driving the coplanar waveguide transmission line resonator, the electrons can be individually trapped in a series of anharmonic potentials on liquid Helium. Therefore, the well-developed circuit quantum electrodynamics technique for the implementation of superconducting quantum computation can be conveniently utilized here in the present quantum computing platform (proposed firstly in Phys Rev Lett 105:040503, 2010, to implement the fundamental logic gates, typically such as the single-qubit rotations of the individually addressable trapped electrons, the switchable two-qubit manipulations between the electrons trapped in the distant traps, and also the high-fidelity readouts of the target qubits. The feasibility of the proposal is also discussed by numerical simulations.

High-Entropy Engineering Reinforced Surface Electronic States and Structural Defects of Hierarchical Metal Oxides@Graphene Fibers toward High-Performance Wearable Supercapacitors.

Construction advanced fibers with high Faradic activity and conductivity are effective to realize high energy density with sufficient redox reactions for fiber-based electrochemical supercapacitors (FESCs), yet it is generally at the sacrifice of kinetics and structural stability. Here, a high-entropy doping strategy is proposed to develop high-energy-density FESCs based on high-entropy doped metal oxide@graphene fiber composite (HE-MO@GF). Due to the synergistic participation of multi-metal elements via high-entropy doping, the HE-MO@GF features abundant oxygen vacancies from introducing various low-valence metal ions, lattice distortions, and optimized electronic structure. Consequently, the HE-MO@GF maintains sufficient active sites, a low diffusion barrier, fast adsorption kinetics, improved electronic conductivity, enhanced structural stability, and Faradaic reversibility. Thereinto, HE-MO@GF presents ultra-large areal capacitance (3673.74mFcm-2) and excellent rate performance (1446.78mFcm-2 at 30mAcm-2) in 6M KOH electrolyte. The HE-MO@GF-based solid-state FESCs also deliver high energy density (132.85µWhcm-2), good cycle performance (81.05% of capacity retention after 10,000 cycles), and robust tolerance to sweat erosion and multiple washing, which is woven into the textile to power various wearable devices (e.g., watch, badge and luminous glasses). This high-entropy strategy provides significant guidance for designing innovative fiber materials and highlights the development of next-generation wearable energy devices.

High‐Entropy Engineering Reinforced Surface Electronic States and Structural Defects of Hierarchical Metal Oxides@Graphene Fibers toward High‐Performance Wearable Supercapacitors (Adv. Mater. 35/2024)

High‐Entropy Engineering Reinforced Surface Electronic States and Structural Defects of Hierarchical Metal Oxides@Graphene Fibers toward High‐Performance Wearable Supercapacitors (Adv. Mater. 35/2024)

Enhancing interfacial electron transfer through PANI electron bridge for tailoring dynamic reconstruction and achieving high-performance water oxidation

Tailoring the dynamic reconstruction of transition metal compounds into highly active oxyhydroxides through surface electron state modification is crucial for advancing water oxidation, yet remains a formidable challenge. In this study, a unique polyaniline (PANI) electron bridge was integrated into the metal–organic frameworks (MOFs)/layer double hydroxides (LDHs) heterojunction to expedite electron transfer from MOFs to LDHs, facilitating electron accumulation at the metal sites within MOF and electron-deficient LDHs. This configuration promotes the surface dynamic reconstruction of LDHs into highly active oxyhydroxides while safeguarding the MOF from corrosion in harsh environments over extended periods. The optimized electronic structure modification of both MOFs and LDHs enhances reaction kinetics. The superior MIL-88B(Fe)@PANI@NiCo LDH catalyst achieved 10 mA∙cm−2 at an overpotential of 202 mV and demonstrated stable operation for 120 h at this current density. This research introduces an innovative approach for guiding electron transfer and dynamic catalyst reconstruction by constructing a PANI electron bridge, potentially paving the way for more efficient catalytic systems.