Deterministic Assembly of Arrays of Lithographically Defined WS2 and MoS2 Monolayer Features Directly From Multilayer Sources Into Van Der Waals Heterostructures

Abstract

One of the major challenges in the van der Waals (vdW) integration of two-dimensional (2D) materials is achieving high-yield and high-throughput assembly of predefined sequences of monolayers into heterostructure arrays. Mechanical exfoliation has recently been studied as a promising technique to transfer monolayers from a multilayer source synthesized by other techniques, allowing the deposition of a wide variety of 2D materials without exposing the target substrate to harsh synthesis conditions. Although a variety of processes have been developed to exfoliate the 2D materials mechanically from the source and place them deterministically onto a target substrate, they can typically transfer only either a wafer-scale blanket or one small flake at a time with uncontrolled size and shape. Here, we present a method to assemble arrays of lithographically defined monolayer WS2 and MoS2 features from multilayer sources and directly transfer them in a deterministic manner onto target substrates. This exfoliate–align–release process—without the need of an intermediate carrier substrate—is enabled by combining a patterned, gold-mediated exfoliation technique with a new optically transparent, heat-releasable adhesive. WS2/MoS2 vdW heterostructure arrays produced by this method show the expected interlayer exciton between the monolayers. Light-emitting devices using WS2 monolayers were also demonstrated, proving the functionality of the fabricated materials. Our work demonstrates a significant step toward developing mechanical exfoliation as a scalable dry transfer technique for the manufacturing of functional, atomically thin materials.

Actively variable-spectrum optoelectronics with black phosphorus

“…Moreover, the gold film evaporated on bP could have functioned as a clamping agent, adding/holding the biaxial compressive strain in bP. It is reported in our earlier work that metal evaporation on 2D materials results in the biaxial compressive strain due to the thermal expansion mismatch between the metal and material 56,57 . During photoconductor fabrication, except the 5s of g-line exposure, visible light exposure of bP was minimized to prevent photooxidation.…”

Strain and Charge Doping Fingerprints of the Strong Interaction between Monolayer MoS2 and Gold

“…Gold-mediated exfoliation has quickly attracted attention and has been utilized in the fabrication of flexible gas sensors, 4 lithography patterning for transistor applications, 5 and construction of large-area van der Waals (vdW) heterostructures. 6 , 7 …”

“… 8 It was suggested that the MoS 2 –Au interaction is of vdW rather than covalent nature, and that when the Au is removed, the optical and electronic properties of monolayer MoS 2 match those of the semiconducting 1H phase, exfoliated directly onto insulating substrates. 2 , 3 , 5 , 6 This signifies that the metallicity of MoS 2 endowed by the Au 3 , 9 can be reversed after its transfer onto another substrate, significantly increasing the scope of this method to optoelectronics, photovoltaics, and photocatalysis. Despite these efforts, little is known about the nature of the interaction between MoS 2 and Au, its dependence on the number of MoS 2 layers, and specific effects brought about in MoS 2 .…”

“…This is a major advancement for mechanical exfoliation, which produces the highest-quality crystals but has been challenging to scale up, unlike the readily scalable chemical vapor deposition (CVD) or liquid phase-exfoliation that produces lower-quality crystals. Gold-mediated exfoliation has quickly attracted attention and has been utilized in the fabrication of flexible gas sensors, lithography patterning for transistor applications, and construction of large-area van der Waals (vdW) heterostructures. , …”

Can Metals Other than Au be Used for Large Area Exfoliation of MoS2 Monolayers?

“…[11] Flakes produced via this method have already been used in multiple applications including gas sensing, [13] photodetection, [14,15] and heterostructure arrays. [16,17] It has been claimed that the stronger Au/2D TMD interfacial interaction or binding energy (BE) of the top layer overcomes the weaker interlayer van der Waals (VdW) forces between the top layers and subsequent layers in TMD materials, thereby leaving behind largearea ML flakes. [9,12,18] The origin of stronger Au/2D TMDs is due to the well-known affinity of Au towards chalcogen atoms and is well studied in self-assembling monolayers (SAM) formation.…”