Fabrication Of Heterostructures Research Articles

Enhanced Optoelectronic Performance of p-WSe2/Re0.12W0.42Mo0.46S2 Heterojunction.

Stacking of van der Waals (vdW) heterostructures and chemical element doping have emerged as crucial methods for enhancing the performance of semiconductors. This study proposes a novel strategy for modifying heterostructures by codoping MoS2 with two elements, Re and W, resulting in the construction of a RexWyMo1-x-yS2/WSe2 heterostructure for the preparation of photodetectors. This approach incorporates multiple strategies to enhance the performance, including hybrid stacking of materials, type-II band alignment, and regulation of element doping. As a result, the RexWyMo1-x-yS2/WSe2 devices demonstrate exceptional performance, including high photoresponsivity (1550.22 A/W), high detectivity (8.17 × 1013 Jones), and fast response speed (rise/fall time, 190 ms/1.42 s). Moreover, the ability to tune the band gap through element doping enables spectral response in the ultraviolet (UV), visible light, and near-infrared (NIR) regions. This heterostructure fabrication scheme highlights the high sensitivity and potential applications of vdW heterostructure (vdWH) in optoelectronic devices.

One-Pot Self-Assembly of Sequence-Controlled Mesoporous Heterostructures via Structure-Directing Agents.

Multimaterial heterostructures have led to characteristics surpassing the individual components. Nature controls the architecture and placement of multiple materials through biomineralization of nanoparticles (NPs); however, synthetic heterostructure formation remains limited and generally departs from the elegance of self-assembly. Here, a class of block polymer structure-directing agents (SDAs) are developed containing repeat units capable of persistent (covalent) NP interactions that enable the direct fabrication of nanoscale porous heterostructures, where a single material is localized at the pore surface as a continuous layer. This SDA binding motif (design rule 1) enables sequence-controlled heterostructures, where the composition profile and interfaces correspond to the synthetic addition order. This approach is generalized with 5 material sequences using an SDA with only persistent SDA-NP interactions ("P-NP1-NP2"; NPi = TiO2, Nb2O5, ZrO2). Expanding these polymer SDA design guidelines, it is shown that the combination of both persistent and dynamic (noncovalent) SDA-NP interactions ("PD-NP1-NP2") improves the production of uniform interconnected porosity (design rule 2). The resulting competitive binding between two segments of the SDA (P- vs D-) requires additional time for the first NP type (NP1) to reach and covalently attach to the SDA (design rule 3). The combination of these three design rules enables the direct self-assembly of heterostructures that localize a single material at the pore surface while preserving continuous porosity.

Continuous Manufacturing of Bioinspired Bone‐Periosteum Integrated Scaffold to Promote Bone Regeneration

AbstractThe scaffold that bioinspired natural bone‐periosteum is ideal for the repair of bone defects, while the achievement of a gradient scaffold with an integrated and stable interface remains challenging. Herein, a bioinspired bone‐periosteum integrated collagen‐based scaffold is developed, in which the top layer is electrospun collagen‐dense scaffold as bioinspired periosteum (BP) to prevent invasion of reticular fiber tissue and the bottom layer is in situ mineralized collagen scaffold (IMCS) to promote osteogenic differentiation. Owing to the proposed continuous manufacturing of successive 3D printing and electrospinning, the integrated scaffold (BP‐IMCS) comprised of BP and IMCS demonstrates excellent structural stability, ten times higher than that of direct‐combination scaffolds. Besides, in vivo implantation results confirmed that BP‐IMCS significantly improves new bone formation up to 32.47%, better than an individual layer, due to its co‐work of mineral ions and bioinspired structure. Therefore, this study offers a continuous manufacturing strategy to realize the integrated and interface‐stable bone‐periosteum structure, providing new solutions for heterostructure tissue fabrication.

Exchange bias in heterostructures combining magnetic topological insulator MnBi2Te4 and metallic ferromagnet Fe3GeTe2

Introducing magnetism into topological insulators enables exotic phenomena such as quantum anomalous Hall effect. By fabricating van der Waals (vdW) heterostructures using layered magnetic materials, we can not only induce a gap in the non-magnetic topological surface states through magnetic proximity but also further manipulate the magnetic properties of magnetic topological insulators. However, the scarcity of 2D ferromagnetic insulator materials limits the fabrication of such heterostructures. Here, we demonstrate the vdW heterostructure devices comprising metal ferromagnetic Fe3GeTe2 nanoflakes and few-layer antiferromagnetic topological insulator MnBi2Te4 separated by an insulating hexagonal-boron nitride spacer. These devices exhibit significant exchange bias with the exchange bias field of over 100 mT under certain conditions. Our results prove that besides magnetic insulators, metallic magnets can also effectively adjust the magnetic properties of topological insulators, thereby inspiring diverse configurations of the heterostructures between topological insulators and magnetic materials.

Interface Modulation of 2D Superlattice Heterostructures with Oxygen-enriched Sites and Dissolution Restraint for Effective Rare-earth Elements Extraction

Effective recovery of rare earth elements from wastewater is crucial for the modern industry, as well as for protecting the human health and ecosystem. Nevertheless, it is still challenging to realize efficient and selective low-concentration rare earth extraction in systems containing high levels competing metal ions. Here, we report on the fabrication of two-dimensional superlattice heterostructures (VOGO-x) through the alternating restacking of VOPO4 nanosheets and GO-PDDA nanosheets via electrostatic self-assembly. The meticulously organized molecular scale of superlattice heterostructures enable the full exposure of accessible adsorption sites and facilitate the transport of rare earth ions, meanwhile the abundant oxygen-containing phosphate groups within the interlayer can realize selective rare earth ions extraction. Furthermore, the tunable interlayer interaction can promote structure stability to prevent dissolution. Consequently, VOGO-11 possesses excellent rare earth adsorption performance, with a saturated adsorption capacity (Nd(III) 631.52 mg/g, Dy(III) 689.48 mg/g, Lu(III) 716.06 mg/g), high utilization rate of adsorption sites and short adsorption equilibrium time of simply 10 min in the REE aqueous solution. Furthermore, VOGO-11 exhibits outstanding selective rare earth adsorption ability over a wide range of metal ions in the low-concentration simulated wastewater and actual leaching tailings. These results demonstrate the material’s promising potential in capturing rare earth ions and pave the way to the development of two-dimensional superlattice heterostructures through interface modulation for effective rare earth extraction.

Solar-blind UV detector with fast response speed and an ultrahigh detectivity based on SrTiO3 (111) substrate grown β-Ga2O3 thin film

Wide band gap semiconductor β-Ga2O3 thin film is widely used in photodetectors. Along the β-Ga2O3 [102] direction, the lattice mismatch between (2‾ 01) β-Ga2O3 and (111) SrTiO3 (STO) is approximately 2.4 %. STO can be used as a substrate for heterostructure fabrication. Here, taking advantage of the symmetry and interatomic super-cellular matching between β-Ga2O3 and the STO substrate, β-Ga2O3 epitaxial films were cultivated on STO (111) substrates via an LPCVD technique. Photoconductive solar blind ultraviolet (UV) detectors have been fabricated based on cultivated Ga2O3 thin films, and the intrinsic linkage of the detector performance with temperature variation has been analyzed in detail. The composition, surface morphology and electrical properties of the films were characterized. The optimized device showed a response rate of 66.64 A/W. The fast rise time (τr1/τr2) and decay time (τd1/τd2) at 20 V bias were 0.15 s/0.18 s and 0.20 s/0.25 s, respectively, with the detectivity of 4.1x1012 Jones.

Deterministic Fabrication and Quantum-Well Modulation of Phase-Pure 2D Perovskite Heterostructures for Encrypted Light Communication.

Deterministic integration of phase-pure Ruddlesden-Popper (RP) perovskites has great significance for realizing functional optoelectronic devices. However, precise fabrications of artificial perovskite heterostructures with pristine interfaces and rational design over electronic structure configurations remain a challenge. Here, the controllable synthesis of large-area ultrathin single-crystalline RP perovskite nanosheets and the deterministic fabrication of arbitrary 2D vertical perovskite heterostructures are reported. The 2D heterostructures exhibit intriguing dual-peak emission phenomenon and dual-band photoresponse characteristic. Importantly, the interlayer energy transfer behaviors from wide-bandgap component to narrow-bandgap component modulated by comprising quantum wells are thoroughly revealed. Functional nanoscale photodetectors are further constructed based on the 2D heterostructures. Moreover, by combining the modulated dual-band photoresponse characteristic with double-beam irradiation modes, and introducing an encryption algorithm mechanism, a light communication system with high security and reliability is achieved. This work can greatly promote the development of heterogeneous integration technologies of 2D perovskites, and could provide a competitive candidate for advanced integrated optoelectronics.

Depolarization Field-Induced Photovoltaic Effect in Graphene/α-In2Se3/Graphene Heterostructures.

The ferroelectric photovoltaic effect (FPVE) enables alternate pathways for energy conversion that are not allowed in centrosymmetric materials. Understanding the dominant mechanism of the FPVE at the ultrathin limit is important for defining the ultimate efficiency. In contrast to the wide band gap conventional thin-film ferroelectrics, 2D α-In2Se3 has an ideal band gap of 1.3 eV and enables the fabrication of ultrathin and stable heterostructures, providing the perfect platform to explore FPVE in the nanoscale limit. Here, we study the ferroelectric layer thickness-dependent FPVE in vertical few-layer graphene/α-In2Se3/graphene heterostructures. We find that the short-circuit photocurrent is antiparallel to the ferroelectric polarization and increases exponentially with decreasing thickness. We show that the observed behavior is predicted by the depolarization field model, originating from the unscreened bound charges due to the finite density of states in semimetal few-layer graphene. As a result, the heterostructures show enhancement of the power conversion efficiency, reaching 2.56 × 10-3% under 100 W/cm2 in 18 nm thick α-In2Se3, approximately 275 times more than the 50 nm thick α-In2Se3. These results demonstrate the importance of the depolarization field at the nanoscale and define design principles for the potential of harnessing FPVE at reduced dimension.

Atomic-Scale Distribution and Evolution of Strain in Pt Nanoparticles Grown on MoS2 Nanosheet.

Interface strain significantly affects the band structure and electronic states of metal-nanocrystal-2D-semiconductor heterostructures, impacting system performance. While transmission electron microscopy (TEM) is a powerful tool for studying interface strain, its accuracy may be compromised by sample overlap in high-resolution images due to the unique nature of the metal-nanocrystals-2D-semiconductors heterostructure. Utilizing digital dark-field technology, the substrate influence on metal atomic column contrasts is eliminated, improving the accuracy of quantitative analysis in high-resolution TEM images. Applying this method to investigate Pt on MoS2 surfaces reveals that the heterostructure introduces a tensile strain of ≈3% in Pt nanocrystal. The x-directional linear strain in Pt nanocrystals has a periodic distribution that matches the semi-coherent interface between Pt nanocrystals and MoS2, while the remaining strain components localize mainly on edge atomic steps. These results demonstrate an accurate and efficient method for studying interface strain and provide a theoretical foundation for precise heterostructure fabrication.

Controlled epitaxy and patterned growth of one-dimensional crystals via surface treatment of two-dimensional templates

Mixed-dimensional van der Waals (vdW) heterostructures offer promising platforms for exploring interesting phenomena and functionalities. To exploit their full potential, precise epitaxial processes and well-defined heterointerfaces between different components are essential. Here, we control the growth of one-dimensional (1D) vdW microwires on hexagonal crystals via plasma treatment of the growth templates. AgCN serves as a model 1D system for examining the dependence of the nucleation and growth parameters on the surface treatment conditions and substrate types. The oxygen-plasma-treated transition metal dichalcogenides form step edges mediated by formation of surface metal oxides, leading to robust AgCN epitaxy with an enhanced nucleation density and low horizontal growth rates. Monte Carlo simulations reproduce the experimentally observed growth behaviors and unveil the crucial growth parameters, such as surface diffusivity. The plasma treatment results in distinct effects on graphite and hexagonal boron nitride templates, which undergo plasma-induced amorphization and deactivation of the AgCN vdW epitaxy. We achieve the selective growth of AgCN microwires on graphite using the deactivated vdW epitaxy. This study offers significant insights into the impact of surface treatment on 1D vdW epitaxy, opening avenues for controlled fabrication of mixed-dimensional vdW heterostructures.

Intrinsic supercurrent diode effect in NbSe2 nanobridge

The significance of the superconducting diode effect (SDE) lies in its potential application as a fundamental component in the development of next-generation superconducting circuit technology. The stringent operating conditions at low temperatures have posed challenges for the conventional semiconductor diode, primarily due to its exceptionally high resistivity. In response to this limitation, various approaches have emerged to achieve the SDE, primarily involving the disruption of inversion symmetry in a two-dimensional superconductor through heterostructure fabrication. In this study, we present a direct observation of the supercurrent diode effect in a NbSe2 nanobridge with a length of approximately 15 nm, created using focused helium ion beam fabrication. Nonreciprocal supercurrents were identified, reaching a peak value of approximately 380 μA for each bias polarity at B zmax = ± 0.2 mT. Notably, the nonreciprocal supercurrent can be toggled by altering the bias polarity. This discovery of the SDE introduces a novel avenue and mechanism through nanofabrication on a superconducting flake, offering fresh perspectives for the development of superconducting devices and potential circuits.

Printable Block Molecular Assemblies with Controlled Exciton Dynamics.

Creating hierarchical molecular block heterostructures, with the control over size, shape, optical, and electronic properties of each nanostructured building block can help develop functional applications, such as information storage, nanowire spectrometry, and photonic computing. However, achieving precise control over the position of molecular assemblies, and the dynamics of excitons in each block, remains a challenge. In the present work, the first fabrication of molecular heterostructures with the control of exciton dynamics in each block, is demonstrated. Additionally, these heterostructures are printable and can be precisely positioned using Direct Ink Writing-based (DIW) 3D printing technique, resulting in programable patterns. Singlet excitons with emission lifetimes on nanosecond or microsecond timescales and triplet excitons with emission lifetimes on millisecond timescales appear simultaneously in different building blocks, with an efficient energy transfer process in the heterojunction. These organic materials also exhibit stimuli-responsive emission by changing the power or wavelength of the excitation laser. Potential applications of these organic heterostructures in integrated photonics, where the versatility of fluorescence, phosphorescence, efficient energy transfer, printability, and stimulus sensitivity co-exist in a single nanowire, are foreseen.

Fabrication of nickel-cobalt sulfide heterostructures with stable thermodynamic interfaces and enhanced electrochemical performance

Transition metal sulfides (TMS) with multicomponent heterostructure have been widely used as electrodes in electrochemical energy storage devices due to their abundant electroactive sites and fast charge transfer across the interfaces. Different kinds of heterostructures with specific TMS are fabricated by various routes to date, but it is still poorly understood how specific thermodynamic interfaces can be designed and easily coupled. Herein, the spinel and cobalt-pentlandite crystal phases of nickel–cobalt sulfides were chosen as models to demonstrate the formation of epitaxial heterointerface. The density functional theory calculations revealed the easy combination and high compatibility of these two crystal phases at the (111) plane. Along this guideline, a novel NiCo2S4/[Ni, Co]9S8 heterostructure was synthesized by a facile one-step hydrothermal strategy, with nanosheet-like shapes and well-defined heterointerfaces along the [111] crystal direction. The formation mechanism of the epitaxial heterointerface was proposed through the combination of solid and liquid phase reaction fields. As a proof-of-concept application, the obtained NiCo2S4/[Ni, Co]9S8 heterostructure as redox electrode for supercapacitor exhibits an enhanced specific capacitance of 1780F g−1 at 1 A/g and high capacitance retention of 70 % at 20 A/g. Moreover, the assembled aqueous hybrid supercapacitor of NiCo2S4/[Ni, Co]9S8//activated carbon delivers a high energy density of 62.8 Wh kg−1 at 0.4 kW kg−1 and excellent electrochemical stability after 3000 cycles. This work provides a new perspective on the epitaxial design of nickel–cobalt sulfide heterostructure with good lattice match as a promising electrode in energy storage devices.

Torsional force microscopy of van der Waals moirés and atomic lattices

In a stack of atomically thin van der Waals layers, introducing interlayer twist creates a moiré superlattice whose period is a function of twist angle. Changes in that twist angle of even hundredths of a degree can dramatically transform the system's electronic properties. Setting a precise and uniform twist angle for a stack remains difficult; hence, determining that twist angle and mapping its spatial variation is very important. Techniques have emerged to do this by imaging the moiré, but most of these require sophisticated infrastructure, time-consuming sample preparation beyond stack synthesis, or both. In this work, we show that torsional force microscopy (TFM), a scanning probe technique sensitive to dynamic friction, can reveal surface and shallow subsurface structure of van der Waals stacks on multiple length scales: the moirés formed between bi-layers of graphene and between graphene and hexagonal boron nitride (hBN) and also the atomic crystal lattices of graphene and hBN. In TFM, torsional motion of an Atomic Force Microscope (AFM) cantilever is monitored as it is actively driven at a torsional resonance while a feedback loop maintains contact at a set force with the sample surface. TFM works at room temperature in air, with no need for an electrical bias between the tip and the sample, making it applicable to a wide array of samples. It should enable determination of precise structural information including twist angles and strain in moiré superlattices and crystallographic orientation of van der Waals flakes to support predictable moiré heterostructure fabrication.

Evidence of Temperature-Dependent Interplay between Spin and Orbital Moment in van der Waals Ferromagnet VI3.

van der Waals materials provide a versatile toolbox for the emergence of new quantum phenomena and fabrication of functional heterostructures. Among them, the trihalide VI3 stands out for its unique magnetic and structural landscape. Here we investigate the spin and orbital magnetic degrees of freedom in the layered ferromagnet VI3 by means of temperature-dependent X-ray absorption spectroscopy and X-ray magnetic circular and linear dichroism. We detect localized electronic states and reduced magnetic dimensionality, due to electronic correlations. We furthermore provide experimental evidence of (a) an unquenched orbital magnetic moment (up to 0.66(7) μB/V atom) in the ferromagnetic state and (b) an instability of the orbital moment in the proximity of the spin reorientation transition. Our results support a coherent picture where electronic correlations give rise to a strong magnetic anisotropy and a large orbital moment and establish VI3 as a prime candidate for the study of orbital quantum effects.

Lateral Heterometal Junction Rectifier Fabricated by Sequential Transmetallation of Coordination Nanosheet.

Heterostructures of two-dimensional materials realise novel and enhanced physical phenomena, making them attractive research targets. Compared to inorganic materials, coordination nanosheets have virtually infinite combinations, leading to tunability of physical properties and are promising candidates for heterostructure fabrication. Although stacking of coordination materials into vertical heterostructures is widely reported, reports of lateral coordination material heterostructures are few. Here we show the successful fabrication of a seamless lateral heterojunction showing diode behaviour, by sequential and spatially limited immersion of a new metalladithiolene coordination nanosheet, Zn3 BHT, into aqueous Cu(II) and Fe(II) solutions. Upon immersion, the Zn centres in insulating Zn3 BHT are replaced by Cu or Fe ions, resulting in conductivity. The transmetallation is spatially confined, occurring only within the immersed area. We anticipate that our results will be a starting point towards exploring transmetallation of various two-dimensional materials to produce lateral heterojunctions, by providing a new and facile synthetic route.

Lateral Heterometal Junction Rectifier Fabricated by Sequential Transmetallation of Coordination Nanosheet**

AbstractHeterostructures of two‐dimensional materials realise novel and enhanced physical phenomena, making them attractive research targets. Compared to inorganic materials, coordination nanosheets have virtually infinite combinations, leading to tunability of physical properties and are promising candidates for heterostructure fabrication. Although stacking of coordination materials into vertical heterostructures is widely reported, reports of lateral coordination material heterostructures are few. Here we show the successful fabrication of a seamless lateral heterojunction showing diode behaviour, by sequential and spatially limited immersion of a new metalladithiolene coordination nanosheet, Zn3BHT, into aqueous Cu(II) and Fe(II) solutions. Upon immersion, the Zn centres in insulating Zn3BHT are replaced by Cu or Fe ions, resulting in conductivity. The transmetallation is spatially confined, occurring only within the immersed area. We anticipate that our results will be a starting point towards exploring transmetallation of various two‐dimensional materials to produce lateral heterojunctions, by providing a new and facile synthetic route.

Circumventing the Uncertainties of the Liquid Phase in the Compositional Control of VLS III-V Ternary Nanowires Based on Group V Intermix.

Control over the composition of III-V ternary nanowires grown by the vapor-liquid-solid (VLS) method is essential for bandgap engineering in such nanomaterials and for the fabrication of functional nanowire heterostructures for a variety of applications. From the fundamental viewpoint, III-V ternary nanowires based on group V intermix (InSbxAs1-x, InPxAs1-x, GaPxAs1-x and many others) present the most difficult case, because the concentrations of highly volatile group V atoms in a catalyst droplet are beyond the detection limit of any characterization technique and therefore principally unknown. Here, we present a model for the vapor-solid distribution of such nanowires, which fully circumvents the uncertainties that remained in the theory so far, and we link the nanowire composition to the well-controlled parameters of vapor. The unknown concentrations of group V atoms in the droplet do not enter the distribution, despite the fact that a growing solid is surrounded by the liquid phase. The model fits satisfactorily the available data on the vapor-solid distributions of VLS InSbxAs1-x, InPxAs1-x and GaPxAs1-x nanowires grown using different catalysts. Even more importantly, it provides a basis for the compositional control of III-V ternary nanowires based on group V intermix, and it can be extended over other material systems where two highly volatile elements enter a ternary solid alloy through a liquid phase.

Pillar‐Layered Metal‐Organic Framework decorated onto TiO2: An Efficient Photocatalyst for Mineralization of Nonsteroidal Anti‐Inflammatory Drugs (NSAIDs)

AbstractHeterostructures of metal‐organic frameworks (MOFs) and metal oxide nanostructured are extensively explored as promising photocatalysts owing to their combined advantages of the highly porous and molecular sieving characteristics of MOFs and the effectual features of encapsulated metal oxide nanostructures. Herein, we reported for the first time two novice hybrid materials abbreviated as PMOF‐55@TiO2 and PMOF‐56@TiO2 constructed by incorporation of Zn4(TRZ)4(2,6‐NDC)2.2DMFand Zn4(TRZ)4(2,4‐BDC)2. 2DMF (TRZ=1,2,4‐triazole, 2,6‐NDC=2,6‐naphthalene dicarboxylic acids, and BDC=terephthalic acid) into the TiO2 nanostructure. The resultant heterostructures were explore for the photodegradation of three Nonsteroidal Anti‐Inflammatory Drugs (ibuprofen, salicylic acid, and aspirin). The successful fabrication of heterostructures was authenticated by various spectroscopic and microscopic techniques. The surface morphological studies revealed the highly dense coating of MOFs nanoparticles on the surface of TiO2. The maximum % degradation i. e. (87.5 %, 88 %) IBU, (81.3 %, 86.5 %) SAL, (80 %, 85.5 %) ASP was achieved using PMOF‐55@TiO2 and PMOF‐56@TiO2 heterostructures with (catalyst dose‐0.6 g/L, and drug concentration‐5 mg/L) under UV light irradiation within 105 min. PMOF‐56@TiO2 is superior photocatalyst compare to PMOF‐55@TiO2 as confirmed by high rate constant (k) and lower half‐life time (t1/2) values of PMOF‐56@TiO2. Moreover, they also maintain a good recyclability performance.

Direct Characterization of Buried Interfaces in 2D/3D Heterostructures Enabled by GeO2 Release Layer.

Inconsistent interface control in devices based on two-dimensional materials (2DMs) has limited technological maturation. Astounding variability of 2D/three-dimensional (2D/3D) interface properties has been reported, which has been exacerbated by the lack of direct investigations of buried interfaces commonly found in devices. Herein, we demonstrate a new process that enables the assembly and isolation of device-relevant heterostructures for buried interface characterization. This is achieved by implementing a water-soluble substrate (GeO2), which enables deposition of many materials onto the 2DM and subsequent heterostructure release by dissolving the GeO2 substrate. Here, we utilize this novel approach to compare how the chemistry, doping, and strain in monolayer MoS2 heterostructures fabricated by direct deposition vary from those fabricated by transfer techniques to show how interface properties differ with the heterostructure fabrication method. Direct deposition of thick Ni and Ti films is found to react with the monolayer MoS2. These interface reactions convert 50% of MoS2 into intermetallic species, which greatly exceeds the 10% conversion reported previously and 0% observed in transfer-fabricated heterostructures. We also measure notable differences in MoS2 carrier concentration depending on the heterostructure fabrication method. Direct deposition of thick Au, Ni, and Al2O3 films onto MoS2 increases the hole concentration by >1012 cm-2 compared to heterostructures fabricated by transferring MoS2 onto these materials. Thus, we demonstrate a universal method to fabricate 2D/3D heterostructures and expose buried interfaces for direct characterization.