Heterostructure Interface Research Articles

Giant spin-to-charge conversion at an all-epitaxial single-crystal-oxide Rashba interface with a strongly correlated metal interlayer.

The two-dimensional electron gas (2DEG) formed at interfaces between SrTiO3 (STO) and other oxide insulating layers is promising for use in efficient spin-charge conversion due to the large Rashba spin-orbit interaction (RSOI). However, these insulating layers on STO prevent the propagation of a spin current injected from an adjacent ferromagnetic layer. Moreover, the mechanism of the spin-current flow in these insulating layers is still unexplored. Here, using a strongly correlated polar-metal LaTiO3+δ (LTO) interlayer and the 2DEG formed at the LTO/STO interface in an all-epitaxial heterostructure, we demonstrate giant spin-to-charge current conversion efficiencies, up to ~190 nm, using spin-pumping ferromagnetic-resonance voltage measurements. This value is the highest among those reported for all materials, including spin Hall systems. Our results suggest that the strong on-site Coulomb repulsion in LTO and the giant RSOI of LTO/STO may be the key to efficient spin-charge conversion with suppressed spin-flip scattering. Our findings highlight the hidden inherent possibilities of oxide interfaces for spin-orbitronics applications.

The charge transfer pathway of g-C3N4 decorated Au/Ni3(VO4)2 composites for highly efficient photocatalytic hydrogen evolution

The photocharge carrier separation and migration within the heterostructure interface plays a pivotal role in the photoelectrocatalytic hydrogen production and the photocatalytic degradation activity. Herein, a series of the 2D/3D g-C3N4/Ni3(VO4)2 photocatalyst were successfully fabricated via a facile hydrothermal method. The prepared samples were characterized by scanning electron microscopy (SEM), scanning transmission electron microscopy (STEM), transmission electron microscopy (TEM), X‐ray diffraction (XRD), ultraviolet‐visible (UV‐vis), Brunauer‐Emmett‐Teller (BET) surface area, and photoluminescence spectroscopy (PL) emission spectroscopy. The highest photocatalytic hydrogen production rate of g-C3N4/Au/Ni3(VO4)2 was about 3345 μmol g−1 h−1, which largely beyond that obtained of g-C3N4/Ni3(VO4)2 (501 μmol g−1 h−1), and pristine g-C3N4 (14 μmol g−1 h−1). The optimal apparent quantum efficiency was counted to be 6.8 % at λ = 420 nm and 1.1 % at λ = 600 nm. Moreover, the photocatalytic property of g-C3N4/Au/Ni3(VO4)2 could remain unchanged almost with 50 h in 5 cycles. The improvement of photocatalytic H2 yield is attributed to the result of rapid separation of photogenic carriers in space and surface plasmon resonance effect of Au nanoparticles.

High energy storage efficiency and temperature stability realized in the Ba0.3Sr0.7Zr0.18Ti0.82O3/LaNiO3 heterostructure thin films directly deposited on the conductive Si substrate

A high-performance energy storage capacitor would not display high energy storage density (Ue) but high energy storage efficiency (η). However, during raising the electric field (E) or temperature (T), the η in dielectric thin films often shows an obvious degradation process. The degradation process is closely related to the change of the charge carrier transport mechanism as a function of E or T. Compared with the electric breakdown strength, the relationship between η and the charge carrier transport mechanisms in the dielectric thin films was less concerning. In this work, by increasing the trigger E and T of the space charge limited current mechanism, the beginning of the η degradation process was delayed into higher E and T. Consequently, a high Ue (∼56.6 J/cm3) and η (∼93.9%) were achieved simultaneously in Ba0.3Sr0.7Zr0.18Ti0.82O3/LaNiO3 heterostructure thin films directly deposited on low-cost conductive silicon wafers. Moreover, the temperature stability was greatly improved. This result would also offer a promising approach to improve the electrical properties of the dielectric oxide thin films in a harsh environment of high temperatures by redistributing oxygen vacancies through the heterostructure interface.

Enhanced optical emission at MoS2-WS2 heterostructure interface with n-N junction

Atomically thin transition metal dichalcogenide based heterostructures are of significant interest for the electronic and optoelectronic device applications. Growth of atomically thin heterostructures have gained remarkable importance due to the unusual electrical response and optical emission at the interface. Here, facile chemical vapour deposition growth of n-N type MoS2-WS2 heterostructure is demonstrated. Multifold enhancement in photoluminescence emission at the interface of MoS2-WS2 heterostructure with local excitonic amplifications arising at the interface is observed. The atomic level structure of interface has been investigated with the aid of aberration corrected scanning transmission electron microscopy. Electrical properties of MoS2-WS2 heterostructure with n-N semiconductor junction are systematically probed using micromanipulators interfaced with scanning electron microscope. Our microscopic and spectroscopic investigations along with electrical and optical responses at the interface contribute to the fundamental knowledge to empower the development of optical devices based on two dimensional heterostructures with enhanced emissions.

Low-Temperature Oxidation of Toluene over MnOx-CeO2 Nanorod Composites with High Sinter Resistance: Dual Effect of Synergistic Interaction on Hydrocarbon Adsorption and Oxygen Activation.

Synergistic interaction derived by a heterointerface structure on the surface of metal oxide catalysts has a crucial role in improving the catalytic activity. In this work, MnOx nanoparticles were dispersed on the surface of CeO2 nanorods to generate a MnOx-CeO2 heterointerface structure, and its effect on toluene adsorption and catalytic oxidation performance was investigated. The results show that MnOx is well dispersed on CeO2 nanorods, and the interaction of Mn-Ce significantly reduces the strength of the Ce-O bond and increases the conversion of Ce4+ to Ce3+, which further promotes the activation of oxygen. Compared to MnOx on SiO2 without synergistic interaction, the enhancement of toluene adsorption on this novel MnOx-CeO2 hetero-interface structure can also make a great contribution to the improvement of the catalytic reaction process. Among them, the synergistic effect of CeO2-MnOx could reduce the temperature of 90% toluene conversion to 210 °C (this value is 83 °C lower than that over pure CeO2 nanorods). In addition, the fresh MnOx-CeO2 catalyst not only shows excellent stability and moisture resistance but also retains highly low-temperature activity even after thermal aging at 750 °C for 100 h.

Tunning heterostructures interface of Cu2O@HKUST-1 for enhanced photocatalytic degradation of tetracycline hydrochloride

Cu2O is an attractive material for the architectural design of integrated nanomaterials in photocatalysis. Herein, a contrastive study was carried out to explore the influence of morphology/exposed Cu2O facets on the template growth process and the difference of fabricated composites in photocatalysis performance. A series of Cu2O@HKUST-1 with core–shell structure was developed via a self-confinement strategy, in which Cu2O nanocrystals with various shapes (cube, truncated octahedron and octahedron) act as self-confinement template to grow Cu-based metal–organic frameworks (HKUST-1) shell. It was revealed that the growth of HKUST-1 on Cu2O crystal depended on the original Cu2O crystal. The exposure of (111) facet in Cu2O was more favorable to the growth of HKUST-1 than (100) crystal plane. Optical and photoelectrochemical characterizations revealed that the cubic Cu2O@HKUST-1 exhibited the outstanding light response and most efficient interfacial charge transfer and separation among three types of composites. As a result, the degradation rates of tetracycline hydrochloride (TC-HCl) by cubic Cu2O@HKUST-1 under the visible light irradiation was 95.35% within 60 min, which was much higher than truncated octahedral Cu2O@HKUST-1 (78.81%) and octahedral Cu2O@HKUST-1 (66.58%). Mechanism explorations including radical capture experiments, electron paramagnetic resonance and band structure analysis showed that type II heterojunction was formed in cubic Cu2O@HKUST-1 and truncated octahedral Cu2O@HKUST-1, which was conducive to the separation and transfer of photo-generated carriers. However, type I heterojunction existed in octahedral Cu2O@HKUST-1 lead to the recombination of photocarriers. These findings revealed the interface-dependent photocatalytic performance in Cu2O@HKUST-1 and provided useful guidance for controllable construction of photocatalysts with heterojunction structure.

MoS2/SiNWs heterostructure based repeatable and highly responsive photodetector

This paper presents an efficient, highly responsive and highly repeatable MoS2/SiNWs heterostructure based photodetector. SiNWs samples were synthesized using metal assisted chemical etching and MoS2 nanoflakes were grown on SiNWs using wafer scalable processes. SiNWs, MoS2 and MoS2/SiNWs based devices were tested for photodetection performance in the visible region. The heterostructure interface between MoS2 and SiNWs helps to suppress dark current and enhance performance characteristics. The MoS2/SiNWs exhibits higher responsivity of 2.98 AW-1 at 450 nm illumination, which is 3 and 11 times higher than the SiNWs and MoS2 respectively. In addition, this heterojunction based device exhibits a higher detectivity of 2.7 × 1011 Jones and rise/fall time of 0.45/0.75 s. Moreover, the device fabrication method is simple and cost-effective. These results pave the way for the fabrication of scalable, highly repeatable and responsive miniaturized photodetectors based on MoS2/SiNWs for mass production.

Built-in electric field boosted ionic transport kinetics in the heterostructured ZnCo2O4/ZnO nanobelts for high-performance supercapacitor

Metal oxides are promising electrode candidates for supercapacitor due to their high theoretical capacitance, good reversibility, and low cost. However, they show inferior specific capacitance and power density because of their sluggish ion diffusion kinetics and intrinsically poor electrical conductivity within the solid phase. Herein, heterostructured ZnCo2O4/ZnO nanobelts are successfully prepared by using self-assembled Zn/Co-based nanosized coordination polymers as the precursors. The resulted nanobelts are composed of uniformly distributed ZnCo2O4 and ZnO nanocrystals, which spontaneously develop built–in electric fields in the nanobelts, and thus improve the conductivity and accelerate charge transport. The as-obtained ZnCo2O4/ZnO nanobelts display a high specific capacitance of 481.0 F g−1 at 1 A/g. The asymmetric supercapacitor, with a ZnCo2O4/ZnO positive electrode and an activated carbon negative electrode, deliver an energy of 23.77 Wh kg−1 at the power density of 399.98 W kg−1 and excellent prolonged cycle life. The excellent electrochemical performance benefits from both the special structure and built–in field at the heterostructure interface, which could significantly reduce the ion diffusion resistance and thus promote charge transport. This strategy may blaze a trail for engineering efficient electrode based on earth-abundant materials.

Adsorption and diffusion properties of calcium ions at the van der Waals interface of NbSe2-graphene 2D heterostructure for multivalent battery applications: density functional theory calculations

Multivalent-ion batteries such as calcium-ion batteries show promise as a high-density alternative to lithium-ion batteries which currently dominate the portable electronics market. In this work, the adsorption and diffusion properties of calcium ion at the van der Waals (vdW) interface of the 2D heterostructure formed by vertically stacking NbSe2 monolayer and graphene were investigated via density functional theory (DFT) calculations. Results showed that calcium can be effectively adsorbed on the vdW interface of the 2D heterostructure, with the binding energy of most stable site at −2.77 eV, much higher than most metal ions’ binding on pristine graphene. Thus, the NbSe2-graphene 2D heterostructure reinforced the binding of calcium ions at the interface. It is revealed that due to the random stacking nature of NbSe2 and graphene, a multi-path minimum energy pathways were identified at the van de Waals region, with relatively low diffusion barriers of around 0.20–0.50 eV. These indicate the capabilities of the 2D vdW heterostructure for fast multivalent ionic mobility and charge-discharge rate, while maintaining strong binding at the vdW interface. The results reveal NbSe2-graphene 2D vdW heterostructure’s potential as a promising anode material for multivalent battery applications.

Sulfate radicals induced from peroxymonosulfate on electrochemically synthesized TiO2-MoO3 heterostructure with Ti-O-Mo bond charge transfer pathway for potential organic pollutant removal under solar light irradiation.

Here, a novel method for synthesis of heterostructured TiO2-MoO3 (MT) nanosheets photocatalyst by utilizing a facile electrochemical method and examined it's photocatalytic activity by the degradation of tetracycline hydrochloride (TCH), a model of organic pollutants, in the presence of peroxymonosulfate (PMS) under solar light irradiation (SL) was reported for the first time. The influence of several factors on the degradation efficiency including the initial concentration of TCH, solution pH, catalyst dosage, PMS concentration, and the existence of inorganic anions was explored. The MT-15/PMS system displayed a promising photocatalytic performance and up to 97% of TCH was degraded in 90min the rate of the degradation reaction of MT-15/PMS was the highest (0.05299 min-1) compared to 0.00251, 0.00337, 0.00546, 0.00735, 0.01337min-1of TiO2-P25, TiO2-P25/PMS, MoO3, MoO3/PMS, and MT-15 respectively. The enhancement can be attributed to several reasons. First, the 2D morphology of the optimized heterostructure photocatalyst plays a significant role in providing much more active sites on its surface. Next, the boosted light absorption efficiency and higher photoproduced electron-hole pair separation ability, induced by the unique direct transformation of photogenerated electrons from the valance band of TiO2 to the conduction band of MoO3 via the Ti-O-Mo bond formed at the interface of MT heterostructure. Finally, the appropriate accessible reactive sites for the activation of PMS together with the synergistic effect between activation of PMS and photocatalytic processes eased the production of active species for the degradation of pollutants. Based on the scavenger experiments and EPR analysis, hydroxide and sulfate radicals were found to be the dominant free radical active species in the degradation process. Furthermore, the synergistic degradation reaction mechanism was proposed.

Sandwich-like GaN/MoSe2/GaN heterostructure nanosheet: A First-principle study of the structure, electronic, optical, and thermodynamical properties

Due to the wide range of applications of two-dimensional heterostructures in photocatalysis, electronics, and optoelectronics, research on these materials has received considerable interest. This paper provides a systematic understanding of the sandwich-like GaN/MoSe2/GaN heterostructure nanosheet to explore geometrical structures and electronic, optical, and thermodynamical properties using a density functional theory. As per the band structure analysis, the heterostructure is a type-II semiconductor with a direct band-gap of 1.36 eV. The optical properties of the nanosheet in different polarization directions were studied. The work function of the heterostructure shows 5.10 eV, which is smaller than the constituent nanosheets. The phonon dispersion curves do not show a negative acoustic band that shows the stability of the studied nanosheets. The alignment of the band structures, charge difference and generated electric field at the vdW heterostructure interface advantage constrain photogenerated electron-hole recombination, enabling improved optical characteristics in the ultraviolet-visible and near-infrared spectroscopy regions, indicating the studied heterostructure can be employed in photovoltaic, photocatalytic, and optical devices.

Electric fields and strains effect on the electronic and optical properties of Zr2CO2/MoSSe van der Waals heterostructure

For emerging two-dimension materials, transition-metal dichalcogenides and MXenes have arrested massive attractiveness of investigators. They are diffusely applied in photocatalytic water splitting, photodetector and capacitor on account of their attractive electronic and physical properties. To explore characteristics of MXene/Janus MXY heterostructures, Zr2CO2/MoSSe heterostructures are systematically investigated which employed the first-principles calculations. The results of band structure, density of states and band edge diagram illustrate that the Zr2CO2/MoSSe (Se atoms in the interface) heterostructure is an indirect band gap semiconductor (0.85 eV) and exhibits type II band arrangement which can separate carriers effectively. Comparison with individual Zr2CO2 and MoSSe, the formation of heterostructure can procure higher-intensity and wider-range optical absorption. In addition, the formation of Zr2CO2/MoSSe heterostructure implements high electron and hole mobilities along zigzag direction up to 2526.86 cm2V−1s−1 and 1462.51 cm2V−1s−1, respectively, which is remarkably profitable for upgrading its photocatalytic efficiency. To further comprehensively acquaint Zr2CO2/MoSSe heterostructure, various strains and electric fields are applied to modify its electrical and optical performance. Biaxial strains demand to maintain within − 6–2%, while electric fields require to sustain under positive electric fields. In consequence, the Zr2CO2/MoSSe van der Waals heterostructures conceive prosperous potential to be adopted in high-performance photocatalysts.

Topological properties of CsCl type superconducting materials

By using the first-principles electronic structure calculation, we have studied electronic band structures and topological properties of CsCl type binary superconductors RuTi and OsTi. Due to the protection of higher crystal symmetry, there are three-dimensional nodal rings around high symmetry points X, Y and Z without spin-orbital coupling (SOC). When SOC is considered, we find the topological phase transition from strong topological insulator phase in RuTi to Dirac semimetal in OsTi. The corresponding surface states are consistent with these nontrivial topologies. We also find strong topological insulator phases near Fermi level in isostructure material MgRh. Based on the topological surface states, the interface of heterostructure of superconductor RuTi (OsTi) and doped topological material MgRh could realize observable topological superconductivity. The nontrivial topological properties in binary superconductors RuTi and OsTi provide us new desirable avenues to study Majorana bound states in vortex cores of topological superconductor.

Pomegranate-inspired porous SnSe/ZnSe@C anode: A stress-buffer nanostructure for fast and ultrastable sodium-ion storage

Tin selenide (SnSe) is considered as a potential anode for sodium-ion batteries (SIBs) owing to its high theoretical specific capacity. Unfortunately, it suffers from drastic volume expansion/contraction during sodium ions insertion/extraction, resulting in poor cycling stability. Herein, a pomegranate-inspired porous carbon shell wrapped heterogeneous SnSe/ZnSe composite (SnSe/ZnSe@C) is exquisitely designed and fabricated through electrostatic spraying followed by high-temperature selenization. The polyacrylonitrile-derived carbon shell acts as an adhesive to link the porous cubic SnSe/ZnSe and form highly interconnected microcircuits to improve the electron/ion transfer efficiency and inhibit the bulk volume change of internal metallic selenide nanoparticles and polyselenides dissolution during repeated cycling. Moreover, the abundant heterostructure interface of SnSe/ZnSe further significantly accelerates the electrons/ions transport. As a result, the as-prepared SnSe/ZnSe@C electrode exhibits a high specific capacity (508.3 mAh g−1 at 0.05 A g−1), excellent rate performance (177.8 mAh g−1 at 10.0 A g−1), and remarkable cycling stability (195.9 mAh g−1 after 10,000 cycles at 5.0 A g−1). Furthermore, in-situ X-ray diffraction (XRD)/Raman, ex-situ transmission electron microscopy, and kinetic analysis clearly reveal a four-step electrochemical reaction process and battery-capacitor dual-mode sodium storage mechanism. This work provides a new perspective for developing commercial SIBs anode materials with high capacity and long lifespan.

Surface Reconstruction of Co4N Coupled with CeO2 toward Enhanced Alkaline Oxygen Evolution Reaction.

Constructing the active interface in a heterojunction electrocatalyst is critical for the electron transfer and intermediate adsorption (O*, OH*, and HOO*) in alkaline oxygen evolution reaction (OER) but still remains challenging. Herein, a CeO2/Co4N heterostructure is rationally synthesized through the direct calcination of Ce[Co(CN)6], followed by thermal nitridation. The in situ electrochemically generated CoOOH on the surface of Co4N serves as the active site for the OER, and the coupled CeO2 with oxygen vacancy can optimize the energy barrier of intermediate reactions of the OER, which simultaneously boosts the OER performance. Besides, electrochemical measurement results demonstrate that oxygen vacancies in CeO2 and optimized absorption free energy originating from the electron transfer between CeO2 and CoOOH contribute to enhanced OER kinetics. This work provides new insight into regulating the interface heterostructure to rationally design efficient OER electrocatalysts under alkaline conditions.

Band alignment of monolayer MoS2/4H-SiC heterojunction via first-principles calculations and x-ray photoelectron spectroscopy

2D/3D heterostructures have received extensive attention due to their unique structures and outstanding properties. In this work, the structural and electronic properties of monolayer MoS2/4H-SiC(Si-face) heterojunctions are systematically investigated through density functional theory calculation and experimental analysis. The calculated results show that the monolayer MoS2/4H-SiC heterostructure is a van der Waals heterojunction because of low formation energy and shows a type-II band alignment with a valence band offset of 1.43 eV. Then the type-II band alignment of the MoS2/4H-SiC heterostructure is verified by x-ray photoelectron spectroscopy. However, there is a deviation of 0.44 eV in the valence band offset between the calculated results and the experimental data, which may be caused by the underestimation of the bandgap by the Perdew–Burke–Ernzerhof method and the introduction of impurities at the interface. Our experimental results reveal the type of band alignment and the combination of the MoS2/4H-SiC heterostructure interface, which is an effective way to understand and design photocatalysts and electronic devices.

Determining Atomic Structure of Grain Boundaries and Heterostructure Interfaces at Solid-State Electrode/Electrolyte Heterostructures in Lithium Based Oxides

Determining Atomic Structure of Grain Boundaries and Heterostructure Interfaces at Solid-State Electrode/Electrolyte Heterostructures in Lithium Based Oxides

A Tungsten Chloride Free, One‐Step Hydrothermal Method to Synthesize P25/Blue WO3‐x Heterostructures

AbstractLow‐cost and high efficiency P25 (nanoparticles TiO2)/blue anoxic tungsten oxide (WO3‐x) heterostructure was successfully constructed by one‐step low‐temperature hydrothermal method. Moreover, sodium tungstate dihydrate (Na2WO4 ⋅ 2H2O) instead of tungsten hexachloride (WCl6) further lowers cost and facilitates preparation. P25/blue WO3‐x heterostructure, rich in oxygen vacancies with typical blue color, exhibits improved performances in both electrocatalysis and photocatalysis. Compared with the pure P25 and blue WO3‐x, the exchange current density of P25/blue WO3‐x was increased by 6 times and 22 times, respectively. P25/blue WO3‐x showed the lowest over potential and relatively small Tafel slope. Also, the degradation efficiency of P25/blue WO3‐x was much higher than other samples. The mechanism of photocatalysis was investigated. The trapping experiments confirmed h+ and ⋅OH were the main active species in photocatalytic reaction. The matched energy levels and built‐in electric field of heterostructure interface can inhibit the recombination of photogenerated electron‐hole pairs to enhance the photodegrading efficiency. The simple low‐cost method is a beneficial attempt to prepare excellent bi‐functional materials with electrocatalytic and photocatalytic properties for practical application prospect in energy shortage and environmental pollution.

Improving photodetection performance of ReS2@Ti3C2 composite by efficient charge transportation

Metal doping is a proven strategy to improve the performance of two dimensional (2D) optoelectronic devices in recent studies. Due to the high price and scarcity of the noble metal, low-cost and high-efficiency noble-metal-alternative as Ti3C2 MXene is greatly anticipated. Herein, the ReS2@Ti3C2 based photodetector is fabricated by liquid-phase exfoliation technique combined with electrophoretic deposited method. The ReS2@Ti3C2 photodetector exhibits a high photocurrent density approximately 5.98 μA/cm2, wide detection ability in UV–vis region, and outstanding flexibility and folding resistance. The main reasons for the improved photodetection performance in ReS2@Ti3C2 composites are the superior electron conductivity and the metallic properties of Ti3C2 and strong charge transportation at the heterostructure interface. This work offers an effective way to improve the performance of 2D flexible optoelectronic devices by doping non-noble metallic conductors.

Nanoscale p–n junction integration via the synergetic hybridization of facet-controlled Cu2O and defect-modulated g-C3N4-x atomic layers for enhanced photocatalytic water splitting

Tailoring multidimensional heterostructure interface in nanoscale with robust electronic configuration and regulated charge steering is of great significance for photocatalysis. In this contribution, an effective p–n heterojunction nanocomposites were formulated by hybridizing N-deficient g-C3N4 atomic layers (g-C3N4-x) and rhombic dodecahedral Cu2O with controlled facets. The concomitant outcomes from the p–n junction induce a built-in electric field that propel the atomic-level directional charge transfer and accommodate electrons and holes at separated locations of n-type g-C3N4-x and p-type Cu2O, respectively. This substantially enhances the electron–hole pairs separation and prolongs the lifetime of charge carriers. As a result, the best performing 3 wt% Cu2O/g-C3N4-x sample demonstrated an exceptional photocatalytic H2 evolution rate of 420.3 μmol/g/h under visible light irradiation, which is 1.8-fold augmentation in contrast to the individual counterpart (g-C3N4-x). In brief, this work presents a powerful strategy to modulate the interaction of heterointerface in achieving highly efficient photocatalytic application.