Mixed-dimensional Van Der Waals Heterostructures Research Articles

Ligand Engineering for Improved All‐Inorganic Perovskite Quantum Dot‐MoS2 Monolayer Mixed Dimensional van der Waals Phototransistor

AbstractCombining intriguing physical properties of 2D crystals and intrinsically remarkable optical properties of halide perovskite quantum dots (QDs), the 0D–2D perovskite QD–based mixed dimensional van der Waals heterostructure (MvdWH) is considered as promising for optoelectronic applications. Even though the interfacial electronic structure of MvdWHs is sufficiently engineered to manipulate the charge carrier behavior, the issue of interfacial charge transfer efficiency originating from the residue ligands that are inevitably introduced by the QDs is still prominently remained. From this perspective, for the first time, a solution‐processed surface ligand density control strategy is demonstrated to balance the QD surface passivation and the interfacial charge carrier extraction and injection efficiency in the 0D–2D MvdWH system. The accurate adjustment of ligand density outside QDs enables the subsequent modulation on interfacial charge carrier transfer efficiency from the aspect of electronic and optoelectronic properties. Furthermore, such kind of ligand engineering toward MvdWH interface is substantially demonstrated in a photogating mechanism–based phototransistor with an improved photoresponsivity as high as 1.13 × 105 A W−1. These results may push forward the evolution of 0D–2D mixed dimensional van der Waals optoelectronics.

Electron transfer and cascade relaxation dynamics of graphene quantum dots/MoS2 monolayer mixed-dimensional van der Waals heterostructures

We realize the efficient modulation of relaxation channels in MoS 2 monolayers and interfacial electron transfer by forming mixed-dimensional VdW heterostructures with graphene quantum dots (GQDs) and find that the cascaded relaxation of hot electrons in GQDs that originate from the quantum confinement effect is the ultimate reason. With femtosecond pump–probe spectroscopy, the biphasic electron injection model and modified rate equations are employed to quantitatively solve the interfacial dynamics. Van der Waals (VdW) heterostructures have emerged as promising materials for atomically thin optoelectronic and photovoltaic applications, where the efficient charge separation after photo-excitation is significant to enhance device performances. However, modulating the interfacial charge transfer is still challenging due to the weak interlayer VdW interaction. Revealing electron transfer and relaxation processes in heterostructures lays foundation to tune the interfacial dynamics and optoelectronic properties. Here, we realize the efficient modulation of relaxation channels in MoS 2 monolayers and interfacial electron transfer by forming mixed-dimensional VdW heterostructures with graphene quantum dots (GQDs). With femtosecond pump–probe spectroscopy, the biphasic electron injection model and modified rate equations are employed to quantitatively solve interfacial transfer rates of mixed-dimensional VdW heterostructures. We find that the cascaded relaxation of hot electrons in GQDs that originates from the quantum confinement effect can intensively affect the interfacial dynamics. Our established model is instructive to optimize performances of future photon-harvesting devices based on mixed low-dimensional heterostructures.

Ultrahigh Vacuum Self-Assembly of Rotationally Commensurate C8-BTBT/MoS2/Graphene Mixed-Dimensional Heterostructures

Mixed-dimensional van der Waals heterostructures combine the advantages of nanomaterials with qualitatively distinct properties such as the extended bandstructures and high charge carrier mobilities of inorganic two-dimensional materials and the discrete orbital energy levels and strong optical absorption of zero-dimensional organic molecules. The synergistic interplay between nanomaterials of distinct dimensionality has enabled a variety of unique applications such as antiambipolar transistors, sensitized photodetectors, and gate-tunable photovoltaics. Because the performance of mixed-dimensional heterostructure devices depends sensitively on the buried interfacial structure, it is of great interest to identify materials and chemistries that naturally form highly ordered heterointerfaces. Toward this end, here we demonstrate ultrahigh vacuum self-assembly of 2,7-dioctyl[1]benzothieno[3,2-b][1]benzothiophene (C8-BTBT) monolayers onto epitaxial MoS2/graphene heterostructures. With molecular-resolution scan...

SbSI whisker/PbI2 flake mixed-dimensional van der Waals heterostructure for photodetection

Mixed-dimensional van der Waals heterostructure formed from an individual SbSI whisker and individual PbI2 flake for photodetection.

High-Performance Photoinduced Memory with Ultrafast Charge Transfer Based on MoS2 /SWCNTs Network Van Der Waals Heterostructure.

Photoinduced memory devices with fast program/erase operations are crucial for modern communication technology, especially for high-throughput data storage and transfer. Although some photoinduced memories based on 2D materials have already demonstrated desirable performance, the program/erase speed is still limited to hundreds of micro-seconds. A high-speed photoinduced memory based on MoS2 /single-walled carbon nanotubes (SWCNTs) network mixed-dimensional van der Waals heterostructure is demonstrated here. An intrinsic ultrafast charge transfer occurs at the heterostructure interface between MoS2 and SWCNTs (below 50fs), therefore enabling a record program/erase speed of ≈32/0.4ms, which is faster than that of the previous reports. Furthermore, benefiting from the unique device structure and material properties, while achieving high-speed program/erase operation, the device can simultaneously obtain high program/erase ratio (≈106 ), appropriate storage time (≈103 s), record-breaking detectivity (≈1016 Jones) and multibit storage capacity with a simple program/erase operation. It even has a potential application as a flexible optoelectronic device. Therefore, the designed concept here opens an avenue for high-throughput fast data communications.

Consecutive Junction-Induced Efficient Charge Separation Mechanisms for High-Performance MoS2/Quantum Dot Phototransistors.

Phototransistors that are based on a hybrid vertical heterojunction structure of two-dimensional (2D)/quantum dots (QDs) have recently attracted attention as a promising device architecture for enhancing the quantum efficiency of photodetectors. However, to optimize the device structure to allow for more efficient charge separation and transfer to the electrodes, a better understanding of the photophysical mechanisms that take place in these architectures is required. Here, we employ a novel concept involving the modulation of the built-in potential within the QD layers for creating a new hybrid MoS2/PbS QDs phototransistor with consecutive type II junctions. The effects of the built-in potential across the depletion region near the type II junction interface in the QD layers are found to improve the photoresponse as well as decrease the response times to 950 μs, which is the faster response time (by orders of magnitude) than that recorded for previously reported 2D/QD phototransistors. Also, by implementing an electric-field modulation of the MoS2 channel, our experimental results reveal that the detectivity can be as large as 1 × 1011 jones. This work demonstrates an important pathway toward designing hybrid phototransistors and mixed-dimensional van der Waals heterostructures.

Anisotropic Magneto-Coulomb Properties of 2D-0D Heterostructure Single Electron Device.

Fabrication and spintronics properties of 2D-0D heterostructures are reported. Devices based on graphene ("Gr")-aluminium nanoclusters heterostructures show robust and reproducible single-electron transport features, in addition to spin-dependent functionality when using a top magnetic electrode. The magnetic orientation of this single ferromagnetic electrode enables the modulation of the environmental charge experienced by the aluminium nanoclusters. This anisotropic magneto-Coulomb effect, originating from spin-orbit coupling within the ferromagnetic electrode, provides tunable spin valve-like magnetoresistance signatures without the requirement of spin coherent charge tunneling. These results extend the capability of Gr to act both as electrode and as a platform for the growth of 2D-0D mixed-dimensional van der Waals heterostructures, providing magnetic functionalities in the Coulomb blockade regime on scalable spintronic devices. These heterostructures pave the way towards novel device architectures at the crossroads of 2D material physics and spin electronics.

SnS nanoribbon/graphene mixed-dimensional heterostructures: Group VII passivation and quantum size effects

The mixed-dimensional van der Waals heterostructures (vdWHs) are attracting extensive attention in the electronic and optoelectronic device, while the related physics mechanisms are still unclear. Here, we study theoretically the stability and electronic properties of the SnS nanoribbon (SnSNR)/graphene mixed-dimensional vdWHs. The results show that these considered mixed-dimensional vdWHs are energetically stable, and Dirac-cone of graphene is close to the top of valence band of SnSNR and thus p-type Schottky contact is formed. Interestingly, group VII passivation can induce transformation from p-type to n-type Schottky contact. Particularly for the F-passivated case, the Fermi level is closer to the CBM of SnSNR. Also, quantum size of SnSNR slightly decreases the p-type Schottky barrier height (SBH). Therefore, this work understands the physics mechanism and related experiments of graphene-based mixed-dimensional vdWHs.

Novel “203” type of heterostructured MoS2-Fe3O4-C ternary nanohybrid: Synthesis, and enhanced microwave absorption properties

It is widely recognized that constructing multiple interface structures to enhance interface polarization is very good for the attenuation of electromagnetic (EM) wave. Here, a novel “203” type of heterostructured nanohybrid consisting of two-dimensional (2D) MoS2 nanosheets, zero-dimensional (0D) Fe3O4 nanoparticles and three-dimensional (3D) carbon layers was elaborately designed and successfully synthesized by a two-step method: Fe3O4 nanoparticles were deposited onto the surface of few-layer MoS2 nanosheets by a hydrothermal method, followed by the carbonation process by a chemical vapor deposition method. Compared to that of “20” type MoS2-Fe3O4, the as-prepared heterostructured “203” type MoS2-Fe3O4-C ternary nanohybrid exhibited remarkably enhanced EM and microwave absorption properties. And the minimum reflection loss (RL) value of the obtained MoS2-Fe3O4-C ternary nanohybrid could reach −53.03 dB at 14.4 GHz with a matching thickness of 7.86 mm. Moreover, the excellent EM wave absorption property of the as-prepared ternary nanohybrid was proved to be attributed to the quarter-wavelength matching model. Therefore, a simple and effective route was proposed to produce MoS2-based mixed-dimensional van der Waals heterostructure, which provided a new platform for the designing and production of high performance microwave absorption materials.

MoS2-Based Mixed-Dimensional van der Waals Heterostructures: A New Platform for Excellent and Controllable Microwave-Absorption Performance.

It is widely recognized that constructing multiple interface structures for enhanced interface polarization is beneficial to microwave absorption. Here, we report our work of achieving excellent microwave-absorption performance and controlling better-defined interfaces in vertically stacked two-dimensional (2D) MoS2 with other dimensional building blocks. The optimal reflection loss and effective absorbing bandwidth (reflection loss <-10 dB) of several mixed-dimensional van der Waals heterostructures are as follows: (i) for 2-0 type (2D MoS2/zero-dimensional Ni nanoparticles), -19.7 dB and 2.92 GHz; (ii) for 2-1 type (2D MoS2/one-dimensional carbon nanotubes), -47.9 dB and 5.60 GHz; and (iii) for 2-3 type (2D MoS2/three-dimensional carbon layers), -69.2 dB and 4.88 GHz. As a result, by selected synthesis of different types of microstructures, we can regulate and control microwave-absorption properties in MoS2 mixed-dimensional van der Waals heterostructures. In addition, attributing to the better-defined interfaces generated in mixed-dimensional van der Waals heterostructures, we found an alternative strategy to improve microwave attenuation properties of 2-0, 2-1, and 2-3 samples by controlling interfacial contacts. The results indicate that mixed-dimensional van der Waals heterostructures provide a new stage for the next generation of microwave-absorbing materials.

Ultrafast Exciton Dissociation and Long-Lived Charge Separation in a Photovoltaic Pentacene–MoS2 van der Waals Heterojunction

van der Waals heterojunctions between two-dimensional (2D) layered materials and nanomaterials of different dimensions present unique opportunities for gate-tunable optoelectronic devices. Mixed-dimensional p-n heterojunction diodes, such as p-type pentacene (0D) and n-type monolayer MoS2 (2D), are especially interesting for photovoltaic applications where the absorption cross-section and charge transfer processes can be tailored by rational selection from the vast library of organic molecules and 2D materials. Here, we study the kinetics of excited carriers in pentacene-MoS2 p-n type-II heterojunctions by transient absorption spectroscopy. These measurements show that the dissociation of MoS2 excitons occurs by hole transfer to pentacene on the time scale of 6.7 ps. In addition, the charge-separated state lives for 5.1 ns, up to an order of magnitude longer than the recombination lifetimes from previously reported 2D material heterojunctions. By studying the fractional amplitudes of the MoS2 decay processes, the hole transfer yield from MoS2 to pentacene is found to be ∼50%, with the remaining holes undergoing trapping due to surface defects. Overall, the ultrafast charge transfer and long-lived charge-separated state in pentacene-MoS2 p-n heterojunctions suggest significant promise for mixed-dimensional van der Waals heterostructures in photovoltaics, photodetectors, and related optoelectronic technologies.