Anisotropic Growth of Nonlayered CdS on MoS₂ Monolayer for Functional Vertical Heterostructures

Abstract

wileyonlinelibrary.comconventional heterostructures is strongly dictated by lattice mismatch which determines the interface quality and thus, the heterostructure performance. Beyond the traditional group IV, III-V, or II-VI semiconductors, 2D layered crystals (e.g., graphene, [ 3 ] transition metal dichalcogenides, [ 4 ] hexagonal boron nitride ( h -BN), [ 5 ] phosphorene, [ 6 ] etc.) have emerged as promising candidates for next generation electronics and optoelectronics due to their unique properties. These 2D layered materials can be artifi cially combined to fabricate various van der Waals (vdW) heterostructures without the lattice match limitation. Novel physical properties of these vdW heterostructures have been investigated theoretically and experimentally, and devices based on those new heterostructures such as tunnel transistors and sensors have already been demonstrated. [7][8][9][10][11] This far, these vdW heterostructures have mainly been fabricated by a top-down process of manual transfer or a bottomup method of chemical vapor deposition (CVD) growth. The fi rst demonstration of vdW heterostructures were realized by vertically stacking different 2D materials (graphene/ h -BN, [ 8,12 ] MoS 2 /graphene, [ 10 ] graphene/WS 2 , [ 9 ] etc.) using conventional polymethyl-methacrylate-mediated transfer method. [ 7 ] The physical properties of these heterostructures are signifi cantly infl uenced by relative orientation of the layers and interfacial quality between them. However, the stacking style and crystal orientation cannot be easily controlled by mechanical transfer method. In addition, such strategies cannot ensure good interfacial quality. Compared to manual transfer, CVD epitaxial growth is a powerful approach for fabricating 2D vdW heterostructures with controlled stacking style, crystal orientation, and clean interface. Indeed, using this strategy, some vertical heterostructures have already been successfully grown, including graphene/ h -BN, [ 13 ] MoS 2 / h -BN, [ 14 ] MoSe 2 /graphene, [ 15 ] MoS 2 / graphene, [ 16 ] WS 2 /MoS 2 , [ 17 ] and MoS 2 /SnS 2 . [ 18 ] This far, the components of the reported 2D-vertical vdW heterostructures have been restricted to layered materials with planar crystal structures. However, many non-layered materials such as cadmium sulfi de (CdS) also exhibit attractive optoelectronic properties. [ 19 ] Combination of such non-layered functional semiconductors with layered materials (e.g., MoS 2 ) could create a new type of vdW heterostructure to provide novel

Single‐Crystal Hybrid Perovskite Platelets on Graphene: A Mixed‐Dimensional Van Der Waals Heterostructure with Strong Interface Coupling

“…Figure 1b shows the optical microscope (OM) images at different magnifications of some perovskite platelets grown on graphene/SiO 2 /Si substrates. It can be seen that MAPbBr 3 nucleates randomly on the graphene surface and grows fast laterally due to the small migration free energy barrier along the graphene surface 10,25,31. The lateral sizes of many MAPbBr 3 platelets can reach 5 µm as observed in a large‐scale OM image (Figure S1, Supporting Information), while the average thickness is usually less than 100 nm, confirming the highly anisotropic growth of perovskites.…”

“…Beyond 2D/2D stacks, mixed‐dimensional ( n D/2D or 2D/ n D, where n = 1 or 3) vdW heterostructures are more difficult to synthesize due to nonpassivated and subtle interfaces. Nevertheless, there have been some reports on mixed‐dimensional vdW heterostructures, such as PbS/graphene,8 PbS/MoS 2 ,9 CdS/MoS 2 ,10 MoS 2 /GaN,11 perovskite/WS 2 ,12 and MoS 2 /Si13,14 prepared by delicate high‐temperature physical/chemical vapor deposition (CVD) methods, which differ from stacking of 2D materials by mechanical methods. The contact areas of these heterojunctions are usually less than 1 × 1 µm 2 as a result of the nonpassivated interface of at least of one material 8–11.…”

“…Nevertheless, there have been some reports on mixed‐dimensional vdW heterostructures, such as PbS/graphene,8 PbS/MoS 2 ,9 CdS/MoS 2 ,10 MoS 2 /GaN,11 perovskite/WS 2 ,12 and MoS 2 /Si13,14 prepared by delicate high‐temperature physical/chemical vapor deposition (CVD) methods, which differ from stacking of 2D materials by mechanical methods. The contact areas of these heterojunctions are usually less than 1 × 1 µm 2 as a result of the nonpassivated interface of at least of one material 8–11. These mixed‐dimensional vdW heterostructures possess unique advantages such as faster charge transfer and tailored energy band alignments 1,2,7,15–17.…”

Enhanced photoelectrochemical and photocatalytic activities of CdS nanowires by surface modification with MoS2 nanosheets

“…However, the low activity and rapid photocorrosion make pure CdS photocatalyst unfavorable for hydrogen evolution reaction (HER) because photogenerated electron and hole pairs cannot be efficiently separated and transferred [14,15]. Loading cocatalysts on CdS to create hierarchical structures provides high activation potentials for HER and suppresses the photocorrosion of CdS [16][17][18]. For example, Pt as a cocatalyst could improve the photocatalytic HER efficiency of CdS [19].…”

Optical visualization of MoS2 grain boundaries by gold deposition

“…High quality, large-area and single-layer MoS 2 can be fabricated by chemical vapor deposition (CVD) [5][6], but the grain boundary (GB) is inevitable and difficult to be identified. GBs affect the electron transfer process, and degrade the electrical and mechanical performances of MoS 2 , which limit the application of MoS 2 [7][8][9][10]. In previous reports, GBs were studied using scanning tunneling microscopy (STM) [11], transmission electron microscopy (TEM) [12] and electron diffraction; hence several factors were inevitable, such as the requirement for complicated sample preparation, time delays, and a limited observation area.…”