Sliding Disassembly of van der Waals Heterostructures

TL;DR

This work introduces a non-destructive, reversible sliding disassembly technique for van der Waals heterostructures using a microstructured PDMS stamp to deterministically remove or reconfigure layers. By modulating the dielectric environment and enabling access to subsurface layers, the method enables in situ Raman environment probing, atomic-resolution STM/STS on air-sensitive 2D materials, and gate-tunable measurements within a single device. The approach is demonstrated across graphene-based, TMD, and moiré systems, including the creation of moiré patterns via a lamination process, and shows potential to broaden device geometries, improve assembly yields, and unlock dynamic studies of 2D electron systems. Overall, sliding disassembly reframes vdW heterostructures as controllable, reconfigurable objects for exploring proximity effects, dielectric engineering, and moiré physics.

Abstract

Many recent advances in our understanding of two-dimensional (2D) electron systems stem from van der Waals (vdW) heterostructures. The assembly process relies on the weak bonding across interfaces between layered vdW compounds, making it possible to construct exceptionally clean heterostructures from chemically and structurally distinct materials - a challenging task for traditional thin-film growth techniques. Here we demonstrate an additional, dynamic degree of freedom afforded by vdW interfaces, wherein we use microstructured polymer stamps to disassemble and reconfigure vdW heterostructures by sliding. We apply this technique to alter the dielectric environment of monolayer graphene, perform scanning tunneling microscopy on semiconducting and air-sensitive monolayers, and manipulate strain-sensitive moiré materials. Together these demonstrations suggest a new paradigm for assembling and dynamically modifying van der Waals heterostructures, with the potential to reveal new insights into 2D electron systems.

Figures (9)

• Figure 1: Sliding disassembly of van der Waals heterostructures.(A) Schematic illustration of the sliding disassembly technique. First, a heterostructure is assembled using the conventional dry-assembly technique, followed by a short plasma treatment to clean the surface. To manipulate the layers, we use a PDMS stamp designed to limit the contact area to the target layer for sliding. By contacting the top layer with the sample and sliding laterally, for example, it can be removed from the heterostructure to reveal the layer underneath. (B) Optical image of an encapsulated monolayer graphene (mlg) before sliding the top hBN. (C) Optical image of the device in (B) after sliding the top BN to partially reveal the monolayer graphene. (D) AFM topograph of the exposed graphene edge (white box in (C)), revealing a clean, flat monolayer graphene surface.
• Figure 1: Process for preparing manipulation slides.(A) An aperture wafer used as a mold is filled with PDMS and cured. After curing, excess PDMS outside the mold is removed. (B) On a new slide, a thin layer of PDMS is spread to adhere to the molded PDMS. The mold and PDMS structure is flipped onto this slide and cured. Finally, the mold is removed. (C) A PC film is tented over the slide to prevent bending the PDMS pillar. By heating at 100-180 $^\circ$C for 2 min, the film conforms to the PDMS. (D) Profile optical image of a representative PDMS dome and micropillar.
• Figure 2: Reconfigurable van der Waals heterostructures.(A) Schematic reconfiguration of a vdW heterostructure by replacing the top encapsulating material. (B) Optical images shown at multiple stages of the reconfiguration. After standard dry-transfer assembly, the top hBN is shifted to partially reveal the underlying monolayer graphene, then shifted back to cover it. Next the top hBN is completely removed, exfoliated 2$H$-WSe$_2$ is placed over top, and then shifted to partially expose the graphene. (C) The spatial variation of the graphene 2D Raman peak $\omega_\mathrm{2D}$ for each stage pictured in (B). (D) Scatter plot of the graphene Raman G ($\omega_\mathrm{G}$) and 2D ($\omega_\mathrm{2D})$ peaks of fully hBN-encapsulated graphene as assembled and after sliding manipulation, showing minimal variation. (E) Scatter plot of $\omega_\mathrm{G}$ and $\omega_\mathrm{2D}$ in the partially exposed stages, illustrating the systematic shift in $\omega_{2D}$ due to differences in the dielectric environment surrounding the graphene sheet. (F) Median values of (left) $\omega_\mathrm{G}$ and (right) $\omega_\mathrm{2D}$ histograms, with one standard deviation error bars, as a function of the effective dielectric constant $\kappa_\mathrm{eff}$.
• Figure 2: Manipulation of top and bottom layers.(A) Stack of few layer graphite (flg) encapsulated in hBN on Si/SiO2. (B) An image after partially sliding the top hBN to the left, (C),(D) after sliding the bottom hBN down in two steps, and (E), (F) and after sliding the top hBN to fully expose the flg in two steps.
• Figure 3: Scanning tunneling microscopy of disassembled devices.(A) Schematic cartoon of the assembled monolayer $H$-WSe2 heterostructure with charge-transfer contacts, channel gate, and contact gate. The top hBN layer is etched into a removable region using an etch procedure designed to stop on the $\alpha$-RuCl$_3$ layer over the contacts. After etching, this region is slid to expose the device channel for (C) STM measurements. False color image of the device (B) before and (D) after the sliding release step. (E) Scanning atomic resolution topography of a gate-tuned region of the sample. (inset) Overlaid $H$-WSe2 crystal structure with tungsten (blue) and selenium (gray) atoms. (F)$dI/dV$ spectroscopy of the sample showing a 2.11 $\pm$ 0.08 eV band gap and Fermi level offset due to tip induced band bending. (inset) Two-terminal conductance of the sample as a function of contact gate measured at low temperature prior to removing the top hBN. (G) Schematic illustration of the sample consisting of a sacrificial top hBN, monolayer 1$T'$-WTe2, bottom hBN, with a graphite contact and back gate. (H) False colored optical micrograph of the heterostructure as assembled. (I) Schematic of the final device heterostructure. (J) False color image of device after removing the top hBN layer inside a glovebox. (K) STM topograph of monolayer 1$T'$-WTe2. (inset) Overlaid 1$T'$-WTe2 crystal structure with tungsten (blue) and tellurium (yellow) atoms. (L)$dI/dV$ spectrum measured at two different values of $V_\mathrm{g}$ averaged within $V_\mathrm{g}$ = 0.04 V windows. (inset) $dI/dV$ spectroscopy map versus $V_\mathrm{g}$.