2D Electronic Structure Research Articles

Large-Gap Quantum Spin Hall Insulators in Two-Dimensional Hafnium Halides: Unraveling the Impact of Strain and Substrate.

Two-dimensional (2D) topological insulators (TIs) or quantum spin Hall (QSH) insulators, characterized by insulating 2D electronic band structures and metallic helical edge states protected by time-reversal symmetry, offer a platform for realizing the quantum spin Hall effect, making them promising candidates for future spintronic devices and quantum computing. However, observing a high-temperature quantum spin Hall effect requires large-gap 2D TIs, and only a few 2D systems have been experimentally confirmed to possess this property. In this study, we employ first-principles calculations, combined with a structural search based on an evolutionary algorithm, to predict a class of 2D QSH insulators in hafnium halides, namely, HfF, HfCl, and HfBr with sizable band gaps of 0.12, 0.19, and 0.38 eV. Their topological nontrivial nature is confirmed by a Z2 invariant which equals to 1 and the presence of gapless edge states. Furthermore, the QSH effect in these materials remains robust under biaxial tensile strain of up to 10%, and the use of h-BN as a substrate effectively preserves the QSH states in these materials. Our findings pave the way for future theoretical and experimental investigations of 2D hafnium halides and their potential for realizing the QSH effect.

Ideal two-dimensional electronic structure in bulk lead titanate for superior thermoelectrics

An ideal two-dimensional (2D) electronic structure is revealed in n-type tetragonal perovskite PbTiO3 through first-principle calculations. This opens exciting prospects for its applications in thermal-to-electrical energy conversion. The electronic structure is regarded as ideally 2D when it is highly dispersive only along two axes, while along the remaining axis, it is nearly non-dispersive with a bandwidth smaller than 1 meV – insignificant when compared to thermal energy above room temperature (i.e., kBT ≥ 25.9 meV). As a basis for comparison, the electronic structure of the cubic perovskite SrTiO3 is calculated. It is nonideal 2D with the bandwidth along the less dispersive axis larger than the thermal energy. The ideal 2D electronic structure in PbTiO3 leads to a 2D-like density of states, resembling a step function around the conduction minimum while for SrTiO3, the density of states remains 3D-like with a square-root energy dependence. Consequently, n-type PbTiO3 exhibits superior effective band degeneracy within the Fermi window compared to SrTiO3, even though PbTiO3 is nondegenerate at the conduction band minimum, while cubic SrTiO3 is three-fold degenerate. This demonstrates the important role of the ideality in the 2D electronic structure. The ab-initio results demonstrate the potential of PbTiO3 as a promising thermoelectric material.

Key Roles of Initial Calcination Temperature in Accelerating the Performance in Proton Ceramic Fuel Cells via Regulating 3D Microstructure and Electronic Structure

Key Roles of Initial Calcination Temperature in Accelerating the Performance in Proton Ceramic Fuel Cells via Regulating 3D Microstructure and Electronic Structure

Carrier Transport Switching of Ferroelectric BTBT Derivative.

Alkylamide-substituted [1]benzothieno[3,2-b][1]benzothiophene (BTBT) derivative of BTBT-NHCOC14H29 (1), which has ferroelectric N-H···O= hydrogen-bonding network of alkylamide group and two-dimensional (2D) electric structure of BTBT π-cores, was prepared to design the external electric field-responsive organic semiconductors. The short-chain derivative of BTBT-NHCOC3H7 (1') revealed the coexistence of a 2D electronic band structure based on the herringbone BTBT arrangement and the one-dimensional (1D) hydrogen-bonding chain. 1 formed a smectic E (SmE) liquid crystal phase above 412 K and showed ferroelectric hysteresis in the electric field-polarization (P-E) curves at 403-433 K. The remanent polarization (Pr) and coercive electric field (Ec) of 1 at 408 K, 0.1 Hz were 24.0 μC cm-2 and 5.54 V μm-1, respectively. By thermal annealing of thin-film 1 at 443 K, the molecular assembly structure of 1 changed from a monolayer to a bilayer structure with high crystallinity, resulting in conducting layers of BTBT parallel to the substrate surface. The organic field-effect transistor (OFET) device with thermally annealed thin-film 1 showed p-type semiconducting behavior with the hole mobility of 1.0 × 10-3 cm2 V-1 s-1. Furthermore, device 1 showed switching behavior of semiconducting properties by electric field poling and thermal annealing cycle. The electric field response of ferroelectrics modulated the molecular orientation and conduction properties of organic semiconductors, resulting in external electric field control of carrier transport properties.

Anisotropic Local Structure of SrFe2-xNixAs2 (x = 0.00, 0.16, and 0.23) Superconductor Probed by Polarized X-ray Absorption Fine Structure Measurements.

We have investigated the effect of the Ni substitution on the local structure and the valence electronic states of the SrFe2-xNixAs2 (x = 0.00, 0.16, and 0.23) superconductor with a multi-edge extended X-ray absorption fine structure (EXAFS) and X-ray absorption near edge structure (XANES) spectroscopy. The As K-edge and Fe K-edge EXAFS measurements in the two polarizations (E‖ab and E‖c) show a clear change in the local structure with Ni concentration. The near-neighbor bondlengths and the related mean-square relative displacements (MSRDs) decrease as the Ni content increases. The polarized XANES spectra at the As, Fe and Ni K edges reveal a systematic change in the anisotropy of the valence electronic structure. The results suggest that the quasi 2D electronic structure of this system tends to become more isotropic as the Ni content increases. The local structure and the valence electronic states are discussed in the frame of the evolving electronic transport of the SrFe2-xNixAs2 system.

Key Roles of Initial Calcination Temperature in Accelerating the Performance in Proton Ceramic Fuel Cells via Regulating 3D Microstructure and Electronic Structure

Developing cathode materials with high performance in oxygen reduction reaction (ORR) is desirable for proton ceramic fuel cells (PCFCs) for energy conversion technology. BaCo0.4Fe0.4Zr0.1Y0.1O3–δ (BCFZY) is widely investigated as a cathode. Herein, BCFZY cathode is used as a paradigmatic example to study the impact of calcination temperature on microstructure, electronic structure, and ORR performance. Ion beam‐scanning electron microscopy indicates BCFZY prepared at 800 °C (BCFZY800) exhibits the largest specific surface area and cathode/electrolyte contact area. BCFZY800 exhibits a peak power density of 1.32 W cm−2 at 650 °C, which is 37% and 193% higher than that of BCFZY prepared at 700 °C (BCFZY700) and 1100 °C (BCFZY1100), respectively. Furthermore, BCFZY800 demonstrates high long‐term stability over 500 h. Soft X‐Ray absorption spectra indicate that the oxidation state of BCFZY800 is reduced, suggesting more catalytically active sites than those of BCFZY700 and BCFZY1100 after the ORR. This work provides a new understanding for enhanced PCFCs performance by proper porosity structure via fine‐tuning the calcination temperature.

3D Printed Electronic Skin for Strain, Pressure and Temperature Sensing

AbstractElectronic skin (E‐skin) that can mimic the flexibility and stretchability of human skin with sensing capabilities, holds transformative potential in robotics, wearable technology, and healthcare. However, developing E‐skin poses significant challenges such as creating durable materials with skin‐like flexibility, integrating biosensing abilities, and using advanced fabrication techniques for wearable or implantable applications. To overcome these hurdles, a 3D‐printed electronic skin utilizing a novel class of nanoengineered hydrogels with tunable electronic and thermal biosensing capabilities is fabricated. This methodology takes advantage of the shear–thinning behavior in hydrogel precursors, allowing to construct intricate 2D and 3D electronic structures. The elasticity of skin using triple crosslinking in a robust fungal exopolysaccharide, and pullulan is simulated, while defect‐rich 2D molybdenum disulfide (MoS2) nanoassemblies ensure high electrical conductivity. The addition of polydopamine nanoparticles enhances adhesion to wet tissue. The hydrogel exhibits outstanding flexibility, stretchability, adhesion, moldability, and electrical conductivity. A distinctive feature of this technology is the precise detection of dynamic changes in strain, pressure, and temperature. As a human motion tracker, phonatory‐recognition platform, flexible touchpad, and thermometer, this technology represents a breakthrough in flexible wearable skins and holds transformative potential for the future of robotics and human‐machine interfaces.

Mixed-ligand, radical, gold bis(dithiolene) complexes: from single-component conductors to controllable NIR-II absorbers.

Neutral radical bis(dithiolene) gold complexes [Au(dt)2]˙ are known to exhibit a strong absorption in the 1400-2000 nm NIR absorption range. Here, we demonstrate that the NIR signature of mixed-ligand bis(dithiolene) gold complexes [Au(dtA)(dtD)]˙ associating two different dithiolene, dtA and dtD, is found at higher energy, out of the range of the homoleptic analogs [Au(dtA)2]˙ and [Au(dtD)2]˙, in the looked-after NIR-II 1000-1400 nm absorption range. An efficient synthetic approach towards precursor mixed-ligand monoanionic gold bis(dithiolene) complexes [Au(dtA)(dtD)]-1 is reported. Using this strategy, no symmetrical complexes are formed and, upon electrocrystallization, no scrambling was observed in solution, allowing for the isolation of radical gold bis(dithiolene) complex such as [Au(bdt)(Et-thiazdt)]˙ (bdt: benzene-1,2-dithiolate; Et-thiazdt: N-ethyl-thiazoline-2-thione-3,4-dithiolate), which behaves as a single-component conductor. It is shown from theoretical calculations that the spin polarization induced by electron repulsions leads to a strong localization of the spin-orbitals, and provides a sound basis to understand, (i) the different ligand-based oxidation potentials, (ii) the NIR optical absorption at notably higher energies and (iii) the larger potential difference of the two redox processes than in the parent symmetric complexes. The solid-state properties of the radical complex [Au(bdt)(Et-thiazdt)]˙ are the consequence of a strongly 1D electronic structure with weakly dimerized chains and electronic localization favoring a semiconducting behavior, stable under pressures up to 18.2 GPa. Altogether, the versatility of the preparation method of [Au(dtA)(dtD)]-1 salts opens the route for a wide library of different mixed-ligand radical complexes [Au(dtA)(dtD)]˙ with simultaneously an adaptable absorption in the NIR-II range and the rich structural chemistry of single-component conductors.

Quasi 3D electronic structures of Dion–Jacobson layered perovskites with exceptional short interlayer distances

A new I-based (I(org)) dication affords DJ layered perovskites exhibiting very short I(ap)⋯I(ap) interlayer distances (<3.90 Å) and strong dispersion bands in the direction perpendicular to layers revealing a quasi 3D electronic structure.

Unraveling the role of Co(II)-phosphate complex in trace Co(II) activated peroxymonosulfate process for water decontamination with phosphate surrounding

The evolution and role of Co(II)-phosphate complex in pH-dependent peroxymonosulfate (PMS) activation by trace Co(II) for phosphate-contained water decontamination was experimentally and theoretically investigated. The HPO42− species play the most positive effect through forming Co-HPO4 coordination for enhancing radical generation and pharmaceutical degradation (3.59 times) in neutral condition. The reduction of Co(III) to Co(II) was identified as a proton-coupled electron transfer process. In Co(II)/PMS system without phosphate, the protons from the neighboring H2O coordination will bind with the generated SO4•−, inducing proton poisoning effect and in situ radical quenching. While the HPO42− coordination not only modulates the Co 3d electronic structure to optimize the PMS interaction and charge transfer, but also alters the proton affinity to alleviate the proton poisoning effect, securing the radical generation. This study provides insights into the impacts of background factors on advanced oxidation processes and develops strategies for efficient remediation in real (waste)water matrix.

Printed Electronic Devices and Systems for Interfacing with Single Cells up to Organoids

AbstractThe field of bioelectronics with the aim to contact cells, cell clusters, biological tissues and organoids has become a vast enterprise. Currently, it is mainly relying on classical micro‐ and nanofabrication methods to build devices and systems. Very recently the field is highly pushed by the development of novel printable organic, inorganic and biomaterials as well as advanced digital printing technologies such as laser and inkjet printing employed in this endeavor. Recent advantages in alternative additive manufacturing and 3D printing methods enable interesting new routes, in particular for applications requiring the incorporation of delicate biomaterials or creation of 3D scaffold structures that show a high potential for bioelectronics and building of hybrid bio‐/inorganic devices. Here the current state of printed 2D and 3D electronic structures and related lithography techniques for the interfacing of electronic devices with biological systems are reviewed. The focus lies on in vitro applications for interfacing single cell, cell clusters, and organoids. Challenges and future prospects are discussed for all‐printed hybrid bio/electronic systems targeting biomedical research, diagnostics, and health monitoring.

Ferroelectric Organic Semiconductor: [1]Benzothieno[3,2-b][1]benzothiophene-Bearing Hydrogen-Bonding -CONHC14H29 Chain.

An alkylamide-substituted [1]benzothieno[3,2-b][1]benzothiophene (BTBT) derivative of BTBT-CONHC14H29 (1) and C8H17-BTBT-CONHC14H29 (2) were prepared to design the multifunctional organic materials, which can show both ferroelectric and semiconducting properties. Single-crystal X-ray structural analyses of short-chain (-CONHC3H7) derivatives revealed the coexistence of two-dimensional (2D) electronic band structures brought from a herringbone arrangement of the BTBT π core and the one-dimensional (1D) hydrogen-bonding chains of -CONHC3H7 chains. The thin films of 1 and 2 fabricated on the Si/SiO2 substrate surface have monolayer and bilayer structures, respectively, resulting in conducting layers parallel to the substrate surface, which is suitable for a channel layer of organic field-effect transistors (OFETs). The thin film of 1 indicated a hole mobility μFET = 2.4 × 10-5 cm2 V-1 s-1 and threshold voltage VTh = - 29 V, whereas that of 2 showed a μFET = 2.1 × 10-2 cm2 V-1 s-1 and threshold voltage VTh = -9.7 V. Both 1 and 2 formed the smectic E (SmE) phase above 410 and 369 K, respectively, where the existence of a hole transport pathway was confirmed in the SmE phase. The ferroelectric hysteresis behavior was observed in bulk 1 and 2 in the polarization-electric field (P-E) curves at the SmE phase. 1 showed the remanent polarization Pr = 2.3 μC cm-2 and coercive electric field Ec = 5.2 V μm-1, whereas the Pr and Ec of 2 were 3.4 μC cm-2 and 7.0 V μm-1 at the conditions of 453 K and 1 Hz. Introduction of alkylamide units into the BTBT π core has the potential to develop the external stimulus-responsive organic semiconductors brought from both ferroelectricity and semiconducting properties.

Hierarchical electronic coupling engineering of bimetallic sulfide driven by CoFe bimetal MOFs anchored on MXene promotes efficient overall water splitting

Rational design cost-effective water-splitting catalysts are essential for current energy storage and conversion. Here, we ingeniously design alloy-phase bimetallic sulfides anchored on the conductive substrate MXene, obtained by a facile topological hydrothermal sulfide method of self-template sacrifice using bimetallic MOFs. Density functional theory calculations (DFT) and related material characterization demonstrate that electron rearrangement at the atomic/orbital level and hierarchical electronic coupling between Schottky heterostructures of MXene boosts charge transfer efficiency, the asymmetric 3d electronic structure of the Co-Fe atoms optimizes the d-band center value εd of the Co8FeS8 MXene/NF. Thus, the efficient composite electrocatalyst of Co8FeS8 MXene/NF with multi-metal active sites exhibits extraordinary electrocatalytic performance with remarkably low overpotentials of 171 mV (OER) and 108 mV (HER) at 10 mA cm−2, respectively. Notably, when used in 1 M KOH electrolytic cell, Co8FeS8 MXene/NF also accelerate overall water splitting at an ultra-low cell voltage of only 1.51 V at 10 mA cm−2, far exceeding that of standard Pt-C/NF//RuO2/NF electrodes (1.59 V). This work gives an effective strategy to construct MOF-derived alloy-phase bimetallic sulfides and improve the intrinsic activity of alloy-phase bimetallic sulfides electrochemical catalysts.

Experiment and Theory in Concert To Unravel the Remarkable Electronic Properties of Na-Doped Eu11Zn4Sn2As12: A Layered Zintl Phase.

Low-dimensional materials have unique optical, electronic, mechanical, and chemical properties that make them desirable for a wide range of applications. Nano-scaling materials to confine transport in at least one direction is a common method of designing materials with low-dimensional electronic structures. However, bulk materials give rise to low-dimensional electronic structures when bonding is highly anisotropic. Layered Zintl phases are excellent candidates for investigation due to their directional bonding, structural variety, and tunability. However, the complexity of the structure and composition of many layered Zintl phases poses a challenge for producing phase-pure bulk samples to characterize. Eu11Zn4Sn2As12 is a layered Zintl phase of significant complexity that is of interest for its magnetic, electronic, and thermoelectric properties. To prepare phase-pure Eu11-xNaxZn4Sn2As12, a binary EuAs phase was employed as a precursor, along with NaH. Experimental measurements reveal low thermal conductivity and a high Seebeck coefficient, while theoretical electronic structure calculations reveal a transition from a 3D to 2D electronic structure with increasing carrier concentration. Simulated thermoelectric properties also indicate anisotropic transport, and thermoelectric property measurements confirm the nonparabolicity of the relevant bands near the Fermi energy. Thermoelectric efficiency is known to improve as the dimensionality of the electronic structure is decreased, making this a promising material for further optimization and opening the door to further exploitation of layered Zintl phases with low-dimensional electronic structures for thermoelectric applications.

High-energy photoemission final states beyond the free-electron approximation

Three-dimensional (3D) electronic band structure is fundamental for understanding a vast diversity of physical phenomena in solid-state systems, including topological phases, interlayer interactions in van der Waals materials, dimensionality-driven phase transitions, etc. Interpretation of ARPES data in terms of 3D electron dispersions is commonly based on the free-electron approximation for the photoemission final states. Our soft-X-ray ARPES data on Ag metal reveals, however, that even at high excitation energies the final states can be a way more complex, incorporating several Bloch waves with different out-of-plane momenta. Such multiband final states manifest themselves as a complex structure and added broadening of the spectral peaks from 3D electron states. We analyse the origins of this phenomenon, and trace it to other materials such as Si and GaN. Our findings are essential for accurate determination of the 3D band structure over a wide range of materials and excitation energies in the ARPES experiment.

Charge-counterbalance modulated amorphous nickel oxide for efficient alkaline hydrogen and oxygen evolution

Nickel oxides have been extensively explored as electrocatalysts for hydrogen and oxygen evolution in water splitting, of which the 3d8 electron and the partly occupied 3d orbitals configuration are modulable, but the catalytic activity is still far from expected. Herein, we report a charge-counterbalance strategy to engineer the 3d electronic structure by constructing unique chemical environmental, in which alkaline-earth metal (Sr, 4p6), electron-deficiency nonmetal (B, 2p1) and early-transition metal (V, 3d3) were synergistically combined. We confirm both experimentally and theoretically that the charge-counterbalance effect is critical, by which nickel shows optimized adsorption strength for the key reaction intermediates and promote the charge transfer in the electrochemical reactions. Consequently, the as-obtained SrVB-NiO catalyst demonstrates impressive HER and OER activities, along with remarkable long-term stability in alkaline solution. This work shed light on a new approach for the further design of electrocatalysts.

Morphology‐Controllable Perovskite‐Like RbCu2Br3 Single Crystals with Strong Photoelectronic Anisotropy for UV Detection

AbstractThe carrier transport characteristics of grain boundary‐free, high‐purity metal halide single crystals make them ideal materials for photodetectors. However, the relationship between photoelectric properties and crystal morphology as well as electronic structure is not sufficiently explored. In this work, RbCu2Br3 single crystals with high quality and multiple morphologies are successfully prepared for the first time. Based on angle‐resolved polarized Raman spectroscopy and polarized photoluminescence, the anisotropy of the 1D atomic chain structure of these crystals is identified. Besides, according to the calculation of partial charge density (PCD), electron localization function (ELF), and carrier mobility related to deformation potential theory (DPT), it is found that RbCu2Br3 single crystals have formed a transport path located in [CuBr4] tetrahedral double chain from 1D electronic structure. It is also explored how the factors including electronic constraints, effective mass, mechanical properties, and deformation potential affect the mobility of crystal plane. Moreover, the device constructed on crystal {100} planes has shown great potential for UV detection. This work not only provides a theoretical basis for the performance regulation of RbCu2Br3 single crystals in experiments but also offers scientific guidance for the growth of single crystal materials with an asymmetric structure and for the application of anisotropy‐related optoelectronics.

In situ engineering 3D conductive core-shell nano-networks and electronic structure of bismuth alloy nanosheets for efficient electrocatalytic CO2 reduction

In situ engineering 3D conductive core-shell nano-networks and electronic structure of bismuth alloy nanosheets for efficient electrocatalytic CO2 reduction

Facet-dependent electrochemical performance and electronic structure of LiCoO2 polyhedral particles revealed by microscopic resonant X-ray photoelectron spectroscopy

The Co 3d electronic structure of each facet of a layered LiCoO2 cathode particle was selectively extracted by microscopic resonant photoelectron spectroscopy to elucidate the surface stability of each facet.

Tuning Fe-spin state of FeN4 structure by axial bonds as efficient catalyst in Li-S batteries

In lithium-sulfur (Li-S) batteries, the root-cause solution is to accelerate the polysulfide conversion to their end products by electrocatalysts. Herein, we put forward a molecular spin engineering to break the symmetry of Fe-N-C and achieve the spin modulation for triplet-to-singlet conversion by the ligand field theory. The Fe-N-C shows an 3d-electronic structure of (dxy)2(dxz)2(dyz)2 and dramatically speeds up the LPSs conversion kinetics. According to the density functional theory (DFT), there is an upshift of energy levels after the adsorption of LPSs on Fe center. As a result, the optimized catalyst delivers a capacity fading rate of 0.026% per cycle at 2 C. In addition, a high capacity of 1042 mA h g−1 is achieved with satisfied capacity retention with the sulfur loading of about 4 mg cm−2. This strategy provides a novel route for the regulation of Fe-spin state and the exploration of catalytic effect in Li-S batteries.