Atomic-scale patterning in two-dimensional van der waals superlattices

Abstract

Two-dimensional (2D) van der Waals superlattices comprised of two stacked monolayer materials have attracted significant interest as platforms for novel optoelectronic and structural behavior. Although studies are focused on superlattice fabrication, less effort has been given to the nanoscale patterning and structural modification of these systems. In this report, we demonstrate the localized layer-by-layer thinning and formation of nanopores/defects in 2D superlattices, such as stacked MoS2-WS2 van der Waals heterostructures and chemical vapor deposited bilayer WSe2, using aberration-corrected scanning transmission electron microscopy (STEM). Controlled electron beam irradiation is used to locally thin superlattices by removing the bottom layer of atoms, followed by defect formation through ablation of the second layer of atoms. The resulting defects exhibit atomically-sharp pore edges with tunable diameters down to 0.6 nm. Structural periodicities and focused STEM irradiation are also utilized to form close-packed nanopore arrays in superlattices with varying twist angles and commensurability. Applying these methods and mechanisms provides a forward approach in the atomic-scale patterning of stacked 2D nanodevices.

Aligned Stacking of Nanopatterned 2D materials -- Towards 3D printing at atomic resolution

“…Structuring within each layer can be performed with nearly atomic precision, as evidenced in Fig 3d, and also in prior works [49][50][51][52][53][54][55][56]. We also note that the lattice structure of the WS 2 is practically unaffected outside of the holes that were defined by the focused electron beam.…”

“…2D materials can be structured by conventional lithographic techniques, after they are deposited on a substrate [47,48]. However, much higher resolution can be achieved if 2D materials are available as free-standing membranes: In particular, the direct cutting of graphene [49][50][51][52], other 2D materials [53,54], or complete vdW heterostructures [55,56] by the focused electron beam in a transmission electron microscope (TEM) or scanning transmission electron microscope (STEM) makes it possible to define feature sizes in the nanometer range. Similarly, electron-beam induced etching (EBIE) [57,58] or cutting of 2D materials by ion beams [59,60] is preferentially done with free-standing membranes.…”

Ions and Water Dancing through Atom-Scale Holes: A Perspective toward “Size Zero”

“…(b) Molecular dynamics model of water and K + and Cl – ion flow through sub-nanometer diameter 2D MoS 2 pores used for modeling ion-irradiated membranes with many atomic-scale holes, as in the TEM image shown in (c). (c) AC-TEM image of 2D WS 2 membrane after Ga ion irradiation using the Ga irradiation doses from previous works. , (d) Schematic of a pore drilled in two 2D material layers, monolayer MoS 2 on top of monolayer WS 2 . (e,f) Inspired by Geim and Grigorieva, this exquisite level of structural control is reminiscent of atomic-scale LEGO.…”

“…Three-dimensional, “size zero” atomic pores in 2D bilayers have been formed by stacking and patterning 2D materials and removing atoms from individual layers, also illustrated here by LEGO blocks. The removal of atoms can proceed selectively, one layer at a time, by selective beam irradiation . Image credits: (a) Dr. William Parkin for making and imaging the 2D MoS 2 pore by electron irradiation in AC-TEM, (b) Prof. Adrien Nicolai for the molecular dynamics model, (c) Paul Masih Das and Jothi Priyanka Thiruraman for making and imaging the ion-irradiated 2D WS 2 membrane in AC-TEM, (d) Milivoj Segan for making the illustration based on our TEM image, (e,f) Gabriela Buvac-Drndic for LEGO pores.…”

Stochastic Ionic Transport in Single Atomic Zero-Dimensional Pores

“…Recent advancements in electron microscopy also open possibilities for precise nanopore device engineering in 2D materials: to controllably make single and few atom-sized pores and to atomically engineer the pore edges. Defect and pore creation in 2D materials has been studied in vacuum inside the TEM, − where 2D flakes typically hang off the supporting substrate or TEM grid and the chip is not designed for ex situ nanofluidics. Correlating advanced microscopy (AC-TEM) insights with transport properties from the same 2D devices measured ex situ has been challenging due to device requirements, such as having a single nanopore within an otherwise continuous membrane that does not leak and a nanopore that is sufficiently stable in liquid or gas environments.…”