Interfacial band structure modulation at electron coupled heterojunction balances sulfur redox kinetics in Li–S batteries

Surface, interface and valence band structures of ultra-thin silicon oxides

Quantum well (QW) states formed in a double-barrier magnetic tunnel junction (DMTJ) enable the coherent resonant tunneling of electrons. This phenomenon is significant for both the fundamental understanding of quantum transport and the development of advanced functionalities in spintronic devices. Careful engineering of the structural and chemical disorders at the QW/barrier interface is essential to maintain strong electron phase coherence, thereby ensuring reliable conductance oscillations in DMTJ. In this study, we systematically investigate the influence of interfacial disorders and band structure on QW-induced conductance oscillations in epitaxial Fe/MgAlOx/Fe (QW)/MgAlOx/Co/Fe DMTJs grown by molecular beam epitaxy. It is found that the amplitude of QW oscillations is reduced to one-third due to chemical disorders caused by the incorporation of 2–4 monolayers of Co at the Fe (QW)/MgAlOx interface. In contrast, structural disorder induced by the incorporation of a single Fe monolayer completely suppresses the oscillations. In addition, the QW oscillation depends on the available majority Δ1 states of the injecting electrons at the Fermi level (EF) with k// = 0 from the upper electrode. Replacing the Fe upper electrode with Fe4N, which lacks a majority of Δ1 states at EF, significantly reduces the oscillation amplitude. Instead, using the bcc Co upper electrode, which possesses majority Δ1 states, results in no change in QW oscillation. Our findings highlight the critical role of interfacial disorder and band structure in QW-induced conductance oscillations, advancing the development of spin-dependent quantum resonant tunneling applications.

Charged defects at the surface of the organic–inorganic perovskite active layer are detrimental to solar cells due to exacerbated charge carrier recombination. Here we show that charged surface defects can be benign after passivation and further exploited for reconfiguration of interfacial energy band structure. Based on the electrostatic interaction between oppositely charged ions, Lewis-acid-featured fullerene skeleton after iodide ionization (PCBB-3N-3I) not only efficiently passivates positively charged surface defects but also assembles on top of the perovskite active layer with preferred orientation. Consequently, PCBB-3N-3I with a strong molecular electric dipole forms a dipole interlayer to reconfigure interfacial energy band structure, leading to enhanced built-in potential and charge collection. As a result, inverted structure planar heterojunction perovskite solar cells exhibit the promising power conversion efficiency of 21.1% and robust ambient stability. This work opens up a new window to boost perovskite solar cells via rational exploitation of charged defects beyond passivation.

A better understanding of how interfacial structure affects charge carrier recombination would benefit the development of highly efficient organic photovoltaic (OPV) devices. In this paper, transient photovoltage (TPV) and charge extraction (CE) measurements are used in combination with synchrotron radiation photoemission spectroscopy (SRPES) to gain insight into the correlation between interfacial properties and device performance. OPV devices based on PCDTBT/PC71BM with a Ca interlayer were studied as a reference system to investigate the interfacial effects on device performance. Devices with a Ca interlayer exhibit a lower recombination than devices with only an Al cathode at a given charge carrier density (n). In addition, the interfacial band structures indicate that the strong dipole moment produced by the Ca interlayer can facilitate the extraction of electrons and drive holes away from the cathode/polymer interface, resulting in beneficial reduction in interfacial recombination losses. These results help explain the higher efficiencies of devices made with Ca interlayers compared to that without the Ca interlayer.

The first-principles all electron relativistic calculations within the general gradient approximation are performed to investigate the interface structure, the electronic and the optical absorption properties of quaternary InAs/GaSb superlattices with InSb or GaAs type of interface. Because of the complexity and low symmetry of the quaternary interfaces, the equilibrium structural parameters of relaxed interfaces are determined by the minimization of total electronic energy and strain in InAs/GaSb superlattices. The band structures and the optical absorption spectra of InAs/GaSb superlattices with special InSb or GaAs and normal (two types are alternate) interfaces are calculated, with the consideration of the superlattice interface atomic relaxation effects. The calculation of relativistic Hartree-Fock functional and local density approximation with the plane wave method is also implemented to demonstrate the calculated band structure results. The calculated band structures of InAs/GaSb superlattices with different types of interfaces are systematically compared. We find that the chemical bonding and ionicity of interfacial Sb atoms are essentially important in determining the interface structures, the band structures and the optical properties of InAs/GaSb superlattices.

Interfacial and electronic band structure optimization for the adsorption and visible-light photocatalytic activity of macroscopic ZnSnO3/graphene aerogel

Normally off AlGaN/GaN high electron mobility transistors with a p-type gate are promising for power switching applications, with advantages of low energy consumption and safe operation. In this work, p-NiO is employed as a gate stack, and the interfacial reconstruction and band structure modification at the p-NiO/AlGaN interface have been demonstrated to manipulate channel transport of AlGaN/GaN high electron mobility transistors by post-annealing. In addition to achieving a positive threshold voltage of 0.6 V and a large saturation output current of 520 mA/mm, we found that the gate leakage and On/Off drain current ratio can be improved significantly by more than 104 due to the p-NiO/AlGaN interfacial reconstruction. However, high annealing temperature also results in an increasing ON-resistance and a dramatically increased knee voltage (VK), which can be attributed to the formation of an ultra-thin γ-Al2O3 layer and the substitution of O on N site as a shallow donor at the p-NiO/AlGaN interface confirmed by experimental analyses. Theoretical calculations indicate that such interface reconstruction facilitates an additional potential well at the p-NiO/AlGaN interface to which electrons are spilled out from a two-dimensional electron gas channel under high forward gate voltage, resulting in the increased VK. Finally, an optimized annealing condition was confirmed that can eliminate this increased VK phenomenon and simultaneously remain these significantly improved device performances. These findings provide deep understanding of the performance manipulation of AlGaN high electron mobility transistors, which is very important for engineering the p-NiO/AlGaN interface toward high-performance and stable devices.

Theoretical insights into the origin of highly efficient photocatalyst NiO/NaTaO3 for overall water splitting

Adjusting the energy band of Cu2O by changing the deposition conditions and its effect on photoelectrochemistry performance of Cu2O/TiO2 heterojunction

HighlightsA carbon free self supported Mott-Schottky heterostructure was constructed as an efficient cathode catalyst for lithium oxygen batteries, achieving homogeneous contact between the two materials for strong interfacial interactions.The heterostructure triggered interfacial perturbations and band structure changes, which accelerated oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) kinetics, resulting in an extremely long cycle life of 800 cycles and an extremely low overpotential of 0.73 V.Combined with advanced characterization techniques and density functional theory calculations, the underlying mechanism behind the boosted ORR/OER activities and the electrocatalytic mechanism were revealed.

Mesoporous ZnO/TiO2 composites with the morphology of yolk-shell microspheres were synthesized via one-step solvothermal method. Modifying crystalline TiO2 microspheres with amorphous ZnO led to the enhancement of photocatalytic activity for both H2 evolution and degradation of organic dyes. Such improvement was mainly attributed to the heterostructure constructed between amorphous ZnO and crystalline TiO2. The mechanism of the growth for such heterostructural microspheres was discussed. The modulation of electronic structure and tuning of the atomic packing mode, along with its yolk-shell structure, would generate large quantities of unsaturated sites, leading to the much accessible adsorption of reactants and accelerating the surface reactions on the mixed phases. Besides, the efficient separation of photogenerated charges was facilitated by their appropriate interfacial band structures between ZnO and TiO2. Such synergetic effect resulted in the improvement of photocatalytic activities, and it provided new routes to better utilize amorphous materials in solar energy conversion. Favorable photocatalytic activity is achieved on ZnO/TiO2 composite microspheres by constructing amorphous/crystalline phase boundary with the optimal component percentage and porosity.

Lithium cobalt oxide (LCO) is widely used in Li-ion batteries due to its high volumetric energy density, which is generally charged to 4.3 V. Lifting the cut-off voltage of LCO from 4.3 V to 4.7 V will increase the specific capacity from 150 to 230 mAh g-1 with a significant improvement of 53%. However, LCO suffers serious problems of H1-3/O1 phase transformation, unstable interface between cathode and electrolyte, and irreversible oxygen redox reaction at 4.7 V. Herein, interface stabilization and band structure modification are proposed to strengthen the crystal structure of LCO for stable cycling of LCO at an ultrahigh voltage of 4.7 V. Gradient distribution of magnesium and uniform doping of nickel in Li layers inhibit the harmful phase transitions of LCO, while uniform LiMgx Ni1- x PO4 coating stabilizes the LCO-electrolyte interface during cycles. Moreover, the modified band structure improves the oxygen redox reaction reversibility and electrochemical performance of the modified LCO. As a result, the modified LCO has a high capacity retention of 78% after 200 cycles at 4.7 V in the half cell and 63% after 500 cycles at 4.6 V in the full cell. This work makes the capacity of LCO one step closer to its theoretical specific capacity.

The performances of heterojunction-based electronic devices are extremely sensitive to the interfacial electronic band structure. Here we report a largely enhanced performance of photoelectrochemical (PEC) photoanodes by ferroelectric polarization-endowed band engineering on the basis of TiO2/BaTiO3 core/shell nanowires (NWs). Through a one-step hydrothermal process, a uniform, epitaxial, and spontaneously poled barium titanate (BTO) layer was created on single crystalline TiO2 NWs. Compared to pristine TiO2 NWs, the 5 nm BTO-coated TiO2 NWs achieved 67% photocurrent density enhancement. By numerically calculating the potential distribution across the TiO2/BTO/electrolyte heterojunction and systematically investigating the light absorption, charge injection and separation properties of TiO2 and TiO2/BTO NWs, the PEC performance gain was proved to be a result of the increased charge separation efficiency induced by the ferroelectric polarization of the BTO shell. The ferroelectric polarization could be switched by external electric field poling and yielded PEC performance gain or loss based on the direction of the polarization. This study evidence that the piezotronic effect (ferroelectric or piezoelectric potential-induced band structure engineering) holds great promises in improving the performance of PEC photoelectrodes in addition to chemistry and structure optimization.

The design of epitaxial semiconductor–superconductor and semiconductor–metal quantum devices requires a detailed understanding of the interfacial electronic band structure. However, the band alignment of buried interfaces is difficult to predict theoretically and to measure experimentally. This work presents a procedure that allows to reliably determine critical parameters for engineering quantum devices; band offset, band bending profile, and number of occupied quantum well subbands of interfacial accumulation layers at semiconductor‐metal interfaces. Soft X‐ray angle‐resolved photoemission is used to directly measure the quantum well states as well as valence bands and core levels for the InAs(100)/Al interface, an important platform for Majorana‐zero‐mode based topological qubits, and demonstrate that the fabrication process strongly influences the band offset, which in turn controls the topological phase diagrams. Since the method is transferable to other narrow gap semiconductors, it can be used more generally for engineering semiconductor–metal and semiconductor–superconductor interfaces in gate‐tunable superconducting devices.

Novel BP/BiOBr S-scheme nano-heterojunction for enhanced visible-light photocatalytic tetracycline removal and oxygen evolution activity