In-Situ Exfoliation Method of Large-Area 2D Materials

2D materials offer an exciting platform for exploring new physical phenomena driven by the quantum confinement of charge carriers. Many of these phenomena are studied using surface sensitive techniques like photoemission spectroscopy, which require ultra-high vacuum (UHV) conditions. However, achieving high-quality, large-area, adsorbate-free samples is essential for successful experimental studies. Mechanical exfoliation from bulk-grown samples produces the best quality 2D materials, but transferring these samples into UHV often necessitates surface cleaning, which can degrade the quality of the samples. Here, we present a straightforward method for in-situ exfoliation within UHV, producing large-area, single-layer films. We demonstrate this technique with various metallic and semiconducting transition metal dichalcogenides exfoliated onto Au, Ag, and Ge. The resulting sub-millimeter flakes exhibit excellent crystallinity and purity, as confirmed by angle-resolved photoemission spectroscopy, atomic force microscopy, and low-energy electron diffraction. This method is particularly suitable for air-sensitive 2D materials, allowing the study of new electronic properties.