Heterostructure Interface Research Articles

Tuneable Vertical Hysteresis Loop Shift in Exchange Coupled La0.67Sr0.33MnO3‐SrRuO3 Bilayer

AbstractHarnessing extra degrees of freedom at the heterostructure interface is of crucial importance to bring additional functionalities in modern spintronic devices. Here, a vertical hysteresis loop shift (vertical bias) is demonstrated in an exchange biased system of ferromagnetic thin film heterostructure of La0.67Sr0.33MnO3 (10 nm)‐SrRuO3 (SRO) (20 nm), after field cooling with ±1 T below 100 K close to the Curie temperature (TC) ≈125 K of SRO and loop sweeping under ±1 T field. Besides, a positive exchange bias (HEB) is also observed below TC ≈125 K showing a maximum ≈11 mT at 2 K. The vertical shift is modeled closely using micromagnetic simulations and the layers’ thickness dependency is demonstrated. The reason for the shift is attributed to the simultaneous role of the interfacial antiferromagnetic interaction and the hard anisotropy of SRO against the Zeeman energy. Finally, from the experimental and simulation results, a generalized model of controllable and tunable vertical shift is proposed applicable for other material systems possessing glassy phases, uncompensated/canted spins, absent interfacial exchange coupling, etc., and hence can be informative for the use of vertical shift in future spintronic devices.

Probing the multi-disordered nanoscale alloy at the interface of lateral heterostructure of MoS2–WS2

Abstract Transition metal dichalcogenide (TMDs) heterostructure, particularly the lateral heterostructure of two different TMDs, is gaining attention as ultrathin photonic devices based on the charge transfer (CT) excitons generated at the junction. However, the characteristics of the interface of the lateral heterostructure, determining the electronic band structure and alignment at the heterojunction region, have rarely been studied due to the limited spatial resolution of nondestructive analysis systems. In this study, we investigated the confined phonons resulting from the phonon-disorder scattering process involving multiple disorders at the lateral heterostructure interface of MoS2–WS2 to prove the consequences of disorder-mediated deformation in the band structure. Moreover, we directly observed variations in the metal composition of the multi-disordered nanoscale alloy Mo1−x W x S2, consisting of atomic vacancies, crystal edges, and distinct nanocrystallites. Our findings through tip-enhanced Raman spectroscopy (TERS) imply that a tens of nanometer area of continuous TMDs alloy forms the multi-disordered interface of the lateral heterostructure. The results of this study could present the way for the evaluation of the TMDs lateral heterostructure for excitonic applications.

Ce-doped multi-phase NiMo-based phosphorus/sulfide heterostructure for efficient photo-enhanced overall water splitting at high current densities

NiMo-based electrocatalysts are widely regarded as promising electrocatalysts for overall water splitting (OWS). However, to solve the problem of slow reaction kinetics and serious deactivation at high current density, the reasonable design of NiMo-based electrocatalysts is still a great challenge. In this work, NiMo-based phosphorus/sulfide heterostructure electrocatalysts with different Ce doping ratios (5%/10%/15%Ce-NiMo-PS@NF) have been designed using the combination of cation doping and heterostructure engineering. The doping of Ce not only changes the electronic environment of the heterostructure, accelerates the electron transport at the heterostructure interface, but also enhances the light absorption capacity of the heterostructure. The experimental results show that 10%Ce-NiMo-PS@NF has the best photo-enhanced electrocatalytic activity (hydrogen evolution reaction (HER): η1000 = 250 mV, oxygen evolution reaction (OER): η1000 = 242 mV, and OWS: E1000 = 1.864 V). In addition, its solar-to-hydrogen (STH) efficiency in a photoelectric coupled water splitting system is as high as 18.68%. This study not only provides a new method for the synthesis of new heterostructure electrocatalysts, but also provides a reference for the rational use of light energy to enhance electrocatalytic activity.

Heterostructured Co/CeO2-Decorating N-Doped Porous Carbon Nanocubes as Efficient Sulfur Hosts with Enhanced Rate Capability and Cycling Durability toward Room-Temperature Na-S Batteries.

Room-temperature sodium-sulfur (RT Na-S) batteries have gained significant interest thanks to their satisfactory energy density and abundant earth resources. Nevertheless, practical implementations of RT Na-S batteries are still impeded by serious shuttle effects of sodium polysulfide (NaPS) intermediates, sluggish redox kinetics of cathodes, and poor electronic conductivity from S-species. To solve these problems, heterostructured Co/CeO2-decorating N-doped porous carbon nanocubes (Co/CeO2-NPC) are constructed as a S support, which integrates the strong adsorption and fast conversion of NaPSs, together with superior electronic conductivity. Consequently, the as-synthesized S@Co/CeO2-NPC cathode for RT Na-S batteries exhibits improved rate performance (1275, 561.1, and 485 mAh g-1 at 0.1, 5, and 10 C, respectively) and superior cyclic durability (capacity degeneration of 0.027% per cycle after 1000 cycles at 5 C). Such a S cathode combining a heterostructure interface, hierarchical porous carbon nanocubes, and polar compositions can considerably increase electronic conductivity and promote NaPS adsorption and conversion, achieving superior performance toward RT Na-S batteries.

Microstructure regulation and microwave absorption properties of ZnO/RGO composites.

Electromagnetic waves can cause different degrees of damage to the human body. People are developing unique nanomaterials with excellent reflection loss (RL), thin thickness, wide frequency band and light weight to improve the absorption efficiency of electromagnetic waves. Using a hydrothermal method, ZnO nanocrystals are combined with graphene oxide (GO). After heat treatment, evenly dispersed ZnO nanocrystals are attached to the GO surface or inserted into the lamellae, and the amount of Zn(CH3COO)2·2H2O and GO is selected to obtain ZnO/RGO nanocomposites with different mass ratios (1 : 1, 1 : 2, 1 : 3). The ZnO/RGO nanocomposites were mixed with paraffin wax with different mass ratios (15, 20, 25, 30 wt%) to explore their electromagnetic parameters and wave absorption properties. It is found that at 25 wt%, ZnO : GO = 3 : 1 and thickness of 3 mm, the sample exhibits excellent wave absorption performance (-36.6 dB) and wide effective absorption bandwidth (6.6 GHz). The microwave absorption performance is enhanced because ZnO nanocrystals inhibit RGO agglomeration and improve impedance matching between the heterostructure interface and RGO.

Phase-field crystal modeling of graphene/hexagonal boron nitride interfaces.

Two-dimensional (2D) materials such as graphene and hexagonal boron nitride (h-BN) are an essential class of materials with enhanced structural and electronic properties compared to their bulk counterparts. The phase-field crystal (PFC) model can reach diffusive time scales to study nucleation, growth of crystallites, and relaxation of strain-driven 2D monolayers that are much larger in comparison to molecular dynamics (MD) and quantum mechanical density functional theory (QMDFT) methods while retaining atomic resolution. The model also naturally incorporates an atomic length scale and elastic and plastic deformations. We simulate the morphological transition of the crystal growth of various equilibrium crystal shapes. In this work, we generalize the one-mode PFC model to study the graphene/h-BN heterostructure interface by using conserved dynamics to describe the dynamics of the model. The model was used to find the equilibrium shape of the crystal of the h-BN crystal embedded in a graphene monolayer.

Magnetic phase transition regulated by an interface coupling effect in CrBr3/electride Ca2N van der Waals heterostructures.

Compared with ferromagnetic (FM) materials, antiferromagnetic (AFM) materials have the advantages of not generating stray fields, resisting magnetic field disturbances, and displaying ultrafast dynamics and are thus considered as ideal candidate materials for next-generation high-speed and high-density magnetic storage. In this study, a new AFM device was constructed based on density functional theory calculations through the formation of a CrBr3/Ca2N van der Waals heterostructure. The FM ground state in CrBr3 undergoes an AFM transition when combining with the electride Ca2N. In such a system, since the metal Ca atoms form the exposed layer in the electride, the heterostructure interface has a high binding energy and a large amount of charge transfer. However, for individual electron doping, the FM ground state in the CrBr3 monolayer is robust. Therefore, the main factor in magnetic phase transition is the interface orbital coupling caused by the strong binding energy. Furthermore, the interface coupling effect was revealed to be a competition between direct exchange and superexchange interactions. Additionally, different pathways of orbital hybridization cause a transition of the magnetic anisotropy from out-of-plane to in-plane. This work not only provides a feasible strategy for changing the ground state of magnetic materials on electride substrates but also brings about more possibilities for the construction and advancement of new AFM devices.

A stable N-doped NiMoO4/NiO2 electrocatalyst for efficient oxygen evolution reaction.

Recently, there has been a significant interest in the study of highly active and stable transition metal-based electrocatalysts for the oxygen evolution reaction (OER). Non-noble metal nanocatalysts with excellent inherent activity, many exposed active centers, rapid electron transfer, and excellent structural stability are especially promising for the displacement of precious-metal catalysts for the production of sustainable and "clean" hydrogen gas through water-splitting. Herein, efficient electrocatalyst N-doped nickel molybdate nanorods were synthesized on Ni foam by a hydrothermal process and effortless chemical vapor deposition. The heterostructure interface of N-NiMoO4/NiO2 led to strong electronic interactions, which were beneficial for enhancing the OER activity of the catalyst. Excellent OER catalytic activity in 1.0 M KOH was shown, which offered a small overpotential of 185.6 mV to acquire a current density of 10 mA cm-2 (superior to the commercial benchmark material RuO2 under the same condition). This excellent electrocatalyst was stable for 90 h at a constant current density of 10 mA cm-2. We created an extremely reliable and effective OER electrocatalyst without the use of noble metals by doping a nonmetal element with nanostructured heterojunctions of various active components.

Zr-doped heterostructure interface to tune the electronic structure of bi-functional electrocatalysts for water splitting

Electrocatalysts for water splitting with earth-abundant materials are proposed to obtain high activity and durability simultaneously by a Zr-doping interface based on physical chemistry and materials science for engineering applications.

PPy-Coated Mo3S4/CoMo2S4 Nanotube-like Heterostructure for High-Performance Lithium Storage.

Heterostructured materials show great potential to enhance the specific capacity, rate performance and cycling lifespan of lithium-ion batteries owing to their unique interfaces, robust architectures, and synergistic effects. Herein, a polypyrrole (PPy)-coated nanotube-like Mo3S4/CoMo2S4 heterostructure is prepared by the hydrothermal and subsequent in situ polymerization methods. The well-designed nanotube-like structure is beneficial to relieve the serious volume changes and facilitate the infiltration of electrolytes during the charge/discharge process. The Mo3S4/CoMo2S4 heterostructure could effectively enhance the electrical conductivity and Li+ transport kinetics owing to the refined energy band structure and the internal electric field at the heterostructure interface. Moreover, the conductive PPy-coated layer could inhibit the obvious volume expansion like a firm armor and further avoid the pulverization of the active material and aggregation of generated products. Benefiting from the synergistic effects of the well-designed heterostructure and PPy-coated nanotube-like architecture, the prepared Mo3S4/CoMo2S4 heterostructure delivers high reversible capacity (1251.3 mAh g-1 at 300 mA g-1), superior rate performance (340.3 mAh g-1 at 5.0 A g-1) and excellent cycling lifespan (744.1 mAh g-1 after 600 cycles at a current density of 2.0 A g-1). Such a design concept provides a promising strategy towards heterostructure materials to enhance their lithium storage performances and boost their practical applications.

Self-supporting trimetallic NiCoFe layered-double-hydroxide/amorphous sulfide heterostructure on nickel foam for efficient water splitting

For efficient overall water splitting, a ternary layered double hydroxide (LDH) and sulfide (NiCoFeLDH/NiCoFeS) composite on nickel foam (NF) has been developed as a bifunctional catalytic electrode. The growth of NiCoFeLDH/NiCoFeS–NF catalysts take place employing a three-step process that involves hydrothermal-sulfurization-hydrothermal reaction. Ultrafine nano-needle NiCo(OH)2 is deposited on the NF using a hydrothermal process, followed by immersion in Na2S solution, which ensures its mild conversion to NiCo sulfide. The Fe ions incorporated during the secondary hydrothermal process participate in the dissolution-recrystallization process of the lattice and modify the electronic structure, thereby significantly enhancing endogenous activity. The hetero-structured interface between NiCoFeLDH and NiCoFeS provides additional catalytic reaction sites, improves electronic interactions, and facilitates water dissociation kinetics. NiCoFeLDH/NiCoFeS–NF demonstates improved performance in both oxygen evolution reaction (OER) and hydrogen evolution reaction (HER). The HER and OER overpotentials are measured to be only 191 and 241 mV at a current density of 100 mA cm−2 in 1 M KOH solution, respectively. Therefore, when NiCoFeLDH/NiCoFeS–NF has been employed as bifunctional electrodes for water splitting, 50 mA cm−2 is reached at only 1.63 V.

MXene heterostructures based on Cr2C and Cr2N: evidence of strong interfacial interactions that induce an antiferromagnetic alignment

In the present work, Cr2C and Cr2N MXenes are stacked to conform 2D heterostructures. The structural, electronic, and magnetic properties were further investigated. Two stackings were treated; the first, Cr2C on top of Cr2N, and the second, Cr2N is on Cr2C. The most favorable configuration is Cr2C/Cr2N, with a vertical distance of 2.35 Å. The antiferromagnetic alignment evidences a possible bias exchange effect. Cr2C MXene preserves its ferromagnetic behavior and changes the top Cr layer polarization of Cr2N form the antiferromagnetic alignment with Cr2C. The bottom Cr layer of Cr2N conserves the intrinsic polarization as antiparallel. Electronic properties evidence a metallic behavior. Although the vertical distance in the MXene heterostructure is comparable with a van der Waals interaction, the 2D charge density maps and electron local function indicate a metallic interaction at the interface, meanwhile the charge density difference exhibits a charge transfer in the interface heterostructure. The new 2D heterostructure and the properties that emerge from it could be interesting to the spintronics community due to their applications in information storage devices.

Thermal transport in composition graded silicene/germanene heterostructures

Through equilibrium and non-equilibrium molecular dynamics simulations, we have demonstrated the inhibitory effect of composition graded interface on thermal transport behavior in lateral heterostructures. Specifically, we investigated the influence of composition gradient length and heterogeneous particles at the silicene/germanene (SIL/GER) heterostructure interface on heat conduction. Our results indicate that composition graded interface at the interface diminishes the thermal conductivity of the heterostructure, with a further reduction observed as the length increases, while the effect of the heterogeneous particles can be considered negligible. To unveil the influence of composition graded interface on thermal transport, we conducted phonon analysis and identified the presence of phonon localization within the interface composition graded region. Through these analyses, we have determined that the decrease in thermal conductivity is correlated with phonon localization within the heterostructure, where a stronger degree of phonon localization signifies poorer thermal conductivity in the material. Our research findings not only contribute to understanding the impact of interface gradient-induced phonon localization on thermal transport but also offer insights into the modulation of thermal conductivity in heterostructures.

Design of Hierarchical Nickel-Cobalt Phosphide/Nickel Oxide with Tunable Electronic Structure and Strong Chemical Interface for Advanced Supercapacitors

The design of a reasonable heterostructure electrode to achieve enhanced areal performance for supercapacitors remains a great challenge. Here, we constructed hierarchical porous NiCoP/NiO nanocomposites anchored on Ni foam with tunable electronic and structural properties, as well as robust interfacial interaction. In NiCoP/NiO, the interconnected NiO nanosheets serve as a carrier with enriched anchoring sites to confine the NiCoP and improve its stability. Meanwhile, the ultrathin NiCoP nanosheets with bimetallic centers are connected with porous NiO nanosheets to form a reliable heterojunction, enhancing the electrochemical reaction kinetics. Taking advantage of the synergistic contribution of bimetallic centers, phosphides and unique structure, the NiCoP/NiO delivers a high areal specific capacitance (1860 mF cm−2 at 5 mA cm−2), good rate performance of 78.5% at six times the increased current density, and remarkable durability (11.0% decrease after 10,000 cycles). Furthermore, the assembled hybrid supercapacitor NiCoP/NiO//porous-activated carbon (PAC) delivers a high areal energy density of 173.7 μWh cm−2 (116.4 μWh cm−2) at 1.6 mW cm−2 (32 mW cm−2). The results indicate that the design of the heterostructure interface with strong chemical interface and tunable electronic structure is an effective and promising approach to boost the electrochemical performance for advanced supercapacitors.

The comprehensive investigation of barrier layers on power loss mechanisms in AlGaN/GaN HEMT structures

The electron relaxation mechanism of the electrons in the pseudo triangle quantum well located in the Al0.3Ga0.7N/GaN heterostructure interface grown by the Molecular Beam Epitaxy (MBE) is studied by Shubnikov de-Haas (SdH) oscillations. Four different sample types were used in the experiments; the carrier density in the quantum well is the same for all samples, whereas the top layer structures are different. The effects of a spacer layer placed between the barrier layer and the quantum well layer, a doped barrier layer placed behind the undoped barrier layer, and a passivation layer placed as a top layer on the energy relaxation processes of the carriers in the quantum well were investigated. The SdH oscillation measurements were carried out under a magnetic field of up to 11 T at a temperature range of 1.8–20 K. The electron temperatures and energy relaxation mechanisms are obtained by comparing the change in the relative amplitude of SdH oscillations in different applied electric fields and lattice temperatures. It is deduced that the samples with a passivation layer and doped barrier layer have higher electron temperatures at lower applied electric fields. The hot electrons relax with acoustic phonon scattering for these samples, including deformation and piezoelectric interactions in the low-temperature region determined theoretically. However, the hot electrons relax with acoustic phonon scattering for samples with spacer layer and spacer/passivation layers in the high-temperature region determined theoretically. Furthermore, it was observed that the spacer and passivation layers lead to faster relaxation of hot electrons.

CVD Grown Nanodimensional Semiconductor Heterostructure: Structural and Optical Properties

The CdSe/CdS heterostructure nanolayer thin films grown by chemical vapour deposition (CVD) technique are discussed. The morphological characterization of heterostructure is examined using scanning electron microscopy (SEM) micrographs which demonstrate the polycrystalline structure is well-developed. The structural characterization of the heterostructure using X-ray diffraction (XRD) studies reveals that the sample’s structure is hexagonal. The optical characterization has been performed using a UV-Visible spectrophotometer that might illustrate the formation of the CdSe/CdS heterostructure interface. These studies could help to design new optoelectronic devices with a high level of efficiency.

Time-Resolved Structural Measurement of Thermal Resistance across a Buried Semiconductor Heterostructure Interface

The precise control and understanding of heat flow in heterostructures is pivotal for advancements in thermoelectric energy conversion, thermal barrier coatings, and efficient heat management in electronic and optoelectronic devices. In this study, we employ high-angular-resolution time-resolved X-ray diffraction to structurally measure thermal resistance in a laser-excited AlGaAs/GaAs semiconductor heterostructure. Our methodology offers femtometer-scale spatial sensitivity and nanosecond time resolution, enabling us to directly observe heat transport across a buried interface. We corroborate established Thermal Boundary Resistance (TBR) values for AlGaAs/GaAs heterostructures and demonstrate that TBR arises from material property discrepancies on either side of a nearly flawless atomic interface. This work not only sheds light on the fundamental mechanisms governing heat flow across buried interfaces but also presents a robust experimental framework that can be extended to other heterostructure systems, paving the way for optimized thermal management in next-generation devices.

Symmetry-Engineering-Induced In-Plane Polarization Enhancement in Ta2NiS5/CrOCl van der Waals Heterostructure

Van der Waals (vdW) interfaces can be formed via layer stacking regardless of the lattice constant or symmetry of the individual building blocks. Herein, we constructed a vdW interface of layered Ta2NiS5 and CrOCl, which exhibited remarkably enhanced in-plane anisotropy via polarized Raman spectroscopy and electrical transport measurements. Compared with pristine Ta2NiS5, the anisotropy ratio of the Raman intensities for the B2g, 2Ag, and 3Ag modes increased in the heterostructure. More importantly, the anisotropy ratios of conductivity and mobility in the heterostructure increased by one order of magnitude. Specifically speaking, the conductivity ratio changed from ~2.1 (Ta2NiS5) to ~15 (Ta2NiS5/CrOCl), while the mobility ratio changed from ~2.7 (Ta2NiS5) to ~32 (Ta2NiS5/CrOCl). Such prominent enhancement may be attributed to the symmetry reduction caused by lattice mismatch at the heterostructure interface and the introduction of strain into the Ta2NiS5. Our research provides a new perspective for enhancing artificial anisotropy physics and offers feasible guidance for future functionalized electronic devices.

Spindle Nanorods of CeO2 and NiS Heterointerface Coated by the NC Layer: A High-Performance Bifunctional Electrocatalyst for Water Splitting.

Currently, nickel sulfides are widely employed in the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER), thanks to the narrow electronegativity difference of only 0.67 eV between nickel and sulfur. Among them, NiS stands out in terms of the OER performance; however, its HER performance and stability remain somewhat inadequate. The construction of heterogeneous interfaces can efficiently improve the HER performance and regulate the electronic structure of the NiS catalyst. CeO2 has been discovered to possess exceptional electronic modulation capabilities, which may lead to the effective enhancement of both HER and OER of the NiS catalyst. As a result, a nitrogen-doped carbon-coated CeO2-NiS heterogeneous interface catalyst (NC/NiS-CeO2) is designed as a bifunctional electrocatalyst for HER and OER with high performance. The NC/NiS-CeO2 catalyst demonstrates excellent HER (47 mV at 10 mA cm-2) and OER (92 mV at 10 mA cm-2) performances in a 1 M KOH alkaline solution. Characterization analysis reveals that the coupling of the heterostructure interface, which consists of CeO2 and NiS, significantly enhances electron conduction, the synergistic effect, and the electrocatalytic activity of the electrode. This study demonstrates that the HER and OER activity can be effectively improved by constructing a rational heterogeneous interface.

Carbon nanotubes at the Graphene/hBN interface abnormally enhance its fracture toughness

Different from Van der Waals heterojunction, defects often appear at the interface of the planar heterostructures due to the low-dimensional structure characteristics. These defects lead to complex mechanical problems, and seriously affect application of planar heterostructures in flexible electronics devices. The most commonly used method to improve the toughness is to reduce/eliminate the interfacial structural defects. Using a defective Graphene/hBN interface, we show surprisingly that Carbon Nanotubes (CNTs) are able to enhance the toughness at the interface. It is found that interlayer stress transfer, bonding strain energies and energy release rate of the defective Graphene/hBN interface with CNTs are higher than those of free-defect Graphene/hBN interface, which is in strong contrast to the general view that interfacial defects reduce toughness. By combining the analysis of atomic mechanics and fracture mechanics theory, we find that the abnormal enhancement in interfacial toughness comes from the stress field localization arising from sp2 + sp3 hybrid state and out-of-plane deformation at the interface. In addition, the stress field at the distal end of the simulated models gradually decays with the CNTs height, resulting in the stress fields to be controlled at the interface. This abnormal mechanism provides a new dimension for enhancing toughness in two-dimensional heterostructures.