Xe 120

hBNs and 1L-WS₂ were mechanically exfoliated onto PDMS from bulk crystals^{47 (link)}: WS₂ bulk crystals were purchased from HQ graphene and hBN bulk crystals were provided by the National Institute for Materials Science, Japan. Exfoliated hBN flakes on PDMS generally come in various thicknesses and were identified by an optical microscope and subsequently pressed and peeled off onto ultra-flat Au substrates (Platypus Technologies) or a 300-nm-thick SiO₂ layer on a Si wafer at the substrate temperature of 100 °C⁴⁸ . Here, ultra-flat Au substrates were used to reduce the substrate roughness which may induce strain or incidental doping to 1L-WS₂. Our samples were then annealed at 150 °C in a vacuum oven for 12 h. The PL from the exfoliated 1L-WS₂ on PDMS was measured before the transfer. 1L-WS₂ samples were subsequently transferred onto the hBN/Au or hBN/SiO₂/Si substrates kept at 70 ^oC and then were annealed at 70 ^oC in the vacuum oven for 1-2 h. The thicknesses of hBN flakes were confirmed by atomic force microscope (XE-120, Park Systems).

All measurements were carried out using commercially available devices (PSIA XE100 and XE120, Park Systems, Korea) equipped with a “liquid cell” setup, in 10 mM PBS buffer. The surface topography of a fibronectin-coated mica surface was measured in contact mode over an area of 10 × 10 µm, with set point of 0.2 nN and scan rate of 0.8 Hz.

The atomic force microscope used for the elasticity measurements was an XE120 model (Park Systems, Suwon, Republic of Korea) working in a force spectroscopy mode. The AFM is equipped with a liquid cell sitting on an XY piezoscanner with a range of 100 × 100 μm². The approach and retraction of the AFM probe are realized using a separate piezoscanner with a Z-range of 25 μm. To estimate the elastic properties of the investigated samples, force curves were recorded in 36 different positions on a cell within a scan area of 10 μm × 10 μm. Triplicate measurements were carried out in liquid conditions for cells. The curves were acquired at an approach speed of 8 μm/s with the ORC8 cantilevers (a nominal spring constant of 0.1 N/m). The difference between force curves recorded on stiff glass and soft samples enables the determination of the force vs. indentation curves, which is the basis for the calculations of the elastic modulus. The elastic modulus (i.e., the Young’s modulus) was determined from the Hertz–Sneddon model, assuming that the indenting AFM probe had a conical shape [77 (link)].