Experimental Realization of Atomic Monolayer Si₉ C₁₅

Monolayer Si_x C_y constitutes an important family of 2D materials that is predicted to feature a honeycomb structure and appreciable bandgaps. However, due to its binary chemical nature and the lack of bulk polymorphs with a layered structure, the fabrication of such materials has so far been challenging. Here, the synthesis of atomic monolayer Si₉ C₁₅ on Ru (0001) and Rh(111) substrates is reported. A combination of scanning tunneling microscopy (STM), X-ray photoelectron spectroscopy (XPS), scanning transmission electron microscopy (STEM), and density functional theory (DFT) calculations is used to infer that the 2D lattice of Si₉ C₁₅ is a buckled honeycomb structure. Monolayer Si₉ C₁₅ shows semiconducting behavior with a bandgap of ≈1.9 eV. Remarkably, the Si₉ C₁₅ lattice remains intact after exposure to ambient conditions, indicating good air stability. The present work expands the 2D-materials library and provides a promising platform for future studies in nanoelectronics and nanophotonics.