Large-Area Deterministic Stamping of 2D Materials on Arbitrarily Patterned Surfaces

Abstract

2D materials and their monolayers have attracted widespread interest by virtue of their unique electronic and optical properties. In addition to their remarkable physical characteristics, their atomically thin nature enables their integration in ultra-compact photonic and electronic devices, with potential for dynamic tunability via strain, charge carrier modulation or heterostructure engineering. While early research relied on micrometer-scale mechanically exfoliated flakes, recent advances, particularly gold-assisted exfoliation of transition metal dichalcogenides (TMDCs), have enabled the preparation of high-quality, large-area monolayers, opening new opportunities for scalable device integration. For the field of nanophotonics in particular, the ability to transfer large-area 2D materials onto both flat and patterned substrates is essential for the development of functional devices. However, existing transfer techniques are often limited in scalability, and compatibility with structured surfaces. Here, we present a versatile and reliable transfer method of large-area monolayers and hBN/monolayer heterostructures onto both flat and nanostructured substrates. Our approach, based on the physical properties of low-density polyethylene, preserves the intrinsic optical quality of the materials and is compatible with a variety of device architectures. We demonstrate its applicability by fabricating devices that modulate the photoluminescence of TMDC monolayers through the manipulation of the photonic environment, strain or electrical gating. We further demonstrate the fabrication of van der Waals heterostructures using the same method. By enabling clean transfer of a wide range of monolayers and heterostructures, this technique offers a practical pathway for the development of next-generation optoelectronic platforms with improved functionality, scalability, and tunability.

Figures (13)

• Figure 1: Transfer method for large-area monolayers using the LDPE-based stamp. (a) Procedure for monolayer pickup. (b) Bright field image of the WS$_2$ monolayer after GAE, before pickup. The cracks in the monolayer originate from the exfoliated bulk crystal. (c) Normal and in-plane force measurements during the pickup procedure. (d) Procedure for monolayer transfer. (e) Monolayer and LDPE residue after transfer to the target substrate. (f) Normal and in-plane force measurements during the transfer of the monolayer. (g) Procedure for LDPE residue removal. Bright field (h) and wide field PL (i) image of the transferred WS$_2$ monolayer. The grid-like structure with darker regions are stitching artifacts resulting from the merger of multiple high resolution microscope images into a large-area overview. (j) Bright field image of the initial substrate after transfer, highlighting the original transferred area.
• Figure 2: Characterization of the monolayer before and after transfer. (a) Raman and (b) PL spectra of the monolayer before and after transfer, as well as after LDPE residue removal. (c) AFM map and (d) averaged line scan of the monolayer, showing the thickness after transfer. The white dashed line in (c) highlights the central location where the line scan in (d) is taken.
• Figure 3: Transfer of a WS$_2$ monolayer on a SiO$_2$/Si substrate with hyperuniform patterned nanoholes. (a) Bright field and (b) wide field PL images of the transferred WS$_2$ monolayer. Top view (c) and tilted (d) SEM images of the monolayer conforming to the substrate, where monolayer draping over the holes is clearly visible. AFM map (e) and cross section (f) of the monolayer on the patterned substrate. Inset: zoomed traces of several monolayer covered nanoholes showing a typical height variation of $\sim15$ nm above the holes. (g) Back focal plane (BFP) microscope image of the PL emission of the sample, showing a ring with emission enhancement at $k_{x}/k_{0}=1.016$ due to light scattering by the hyperuniform pattern.
• Figure 4: Transfer of hBN/monolayer heterostructures. (a) Procedure for hBN pickup. (b) Bright field image of the hBN flake before transfer. (c) Normal and in-plane force measurements during the pickup of an hBN flake. (d) Procedure for monolayer pickup with hBN and release on a target substrate. (e) Bright field microscope image of the flake after deposition, covered in LDPE residue. (f) Normal and in-plane force measurements during the pickup of the monolayer with hBN (left) and release of the structure on the final substrate (right). (g) Procedure for LDPE removal by air plasma treatment. (h) Bright field and wide field PL (i) images of the hBN flake after LDPE residue removal. (j) PL spectra before, after transfer, and after LDPE residue removal.
• Figure 5: Transfer of a hBN/WS$_2$ heterostructure onto a dome-patterned sapphire substrate.(a) Dark field and (b) WFPL microscope images of the heterostructure on the domes after the transfer and plasma cleaning. (d,e) Tilted SEM images of the heterostructure on top of the sapphire domes. (f) PL map of the heterostructure, where each pixel represents the integrated PL intensity. The points of contact are highlighted with white dashed circles. (g) PL spectra of the structure on tip and in between the domes. (h) AFM measurement of the heterostructure on top of the domes. Inset: small-area measurement of top of the flake.