Visualizing interface states in In_(2)Se_(3)–WSe_(2)monolayer lateral heterostructures

Recent findings of two-dimensional(2D)ferroelectric(FE)materials provide more possibilities for the development of 2D FE heterostructure electronic devices based on van der Waals materials and the application of FE devices under the limit of atomic layer thickness.In this paper,we report the in-situ fabrication and probing of electronic structures of In_(2)Se_(3)–WSe_(2) lateral heterostructures,compared with most vertical FE heterostructures at present.Through molecular beam epitaxy,we fabricated lateral heterostructures with monolayer WSe_2(three atomic layers)and monolayer In_(2)Se_(3)(five atomic layers).Type-Ⅱband alignment was found to exist in either the lateral heterostructure composed of anti-FEβ′-In_(2)Se_(3) and WSe_(2) or the lateral heterostructure composed of FEβ*-In_(2)Se_(3)and WSe_2,and the band offsets could be modulated by ferroelectric polarization.More interestingly,interface states in both lateral heterostructures acted as narrow gap quantum wires,and the band gap of the interface state in theβ*-In_(2)Se_(3)–WSe_(2)heterostructure was smaller than that in theβ′-In_(2)Se_(3)heterostructure.The fabrication of 2D FE heterostructure and the modulation of interface state provide a new platform for the development of FE devices.

Band alignment and interlayer hybridization in monolayer organic/WSe_(2) heterojunction

Semiconducting heterojunctions(HJs),comprised of atomically thin transition metal dichalcogenides(TMDs),have shown great potentials in electronic and optoelectronic applications.Organic/TMD hybrid bilayers hold enhanced pumping efficiency of interfacial excitons,tunable electronic structures and optical properties,and other superior advantages to these inorganic HJs.Here,we report a direct probe of the interfacial electronic structures of a crystalline monolayer(ML)perylene-3,4,9,10-tetracarboxylic-dianhydride(PTCDA)/ML-WSe_(2) HJ using scanning tunneling microscopy,photoluminescence,and first-principle calculations.Strong PTCDAAA/Se_(2) interfacial interactions lead to appreciable hybridization of the WSe_(2) conduction band with PTCDA unoccupied states,accompanying with a significant amount of PTCDA-to-WSe_(2) charge transfer(by 0.06 e/PTCDA).A type-ll band alignment was directly determined with a valence band offset of-1.69 eV,and an apparent conduction band offset of-1.57 eV.Moreover,we found that the local stacking geometry at the HJ interface differentiates the hybridized interfacial states.

Emergent quantum properties from low-dimensional building blocks and their superlattices

Low-dimensional materials,with highly tunable electronic structures depending on their sizes and shapes,can be exploited as fundamental building blocks to construct higher-order structures with tailored emergent properties.This is akin to molecules or crystals that are assembled by atoms with diverse symmetries and interactions.Prominent low-dimensional materials developed in recent decades include zero-dimensional(0D)quantum dots,one-dimensional(1D)carbon nanotubes,and two-dimensional(2D)van der Waals materials.These materials enclose a vast diversity of electronic structures ranging from metals and semimetals to semiconductors and insulators.Moreover,low-dimensional materials can be assembled into higher-order architectures known as superlattices,wherein collective electronic and optical behaviors emerge that are absent in the individual building blocks alone.Superlattices composed of interacting low-dimensional entities thus define an ultra-manipulatable materials platform for realizing artificial structures with customizable functionalities.Here,we review significant milestones and recent progress in the field of low-dimensional materials and their superlattices.We survey recently observed exotic emergent electronic and optical properties in these materials and delve into the underlying mechanisms driving these phenomena.Additionally,we hint the future opportunities and remaining challenges in advancing this exciting area of research.