Surface Reconstruction of Germanium: Hydrogen Intercalation and Graphene Protection

Understanding the interfacial properties of functional nanomaterials on semiconductor surfaces is crucial for developing electronics, optoelectronics, and other devices. By using graphene on the germanium (110) surface as a model, we performed scanning tunneling microscopy (STM) and X-ray photoelectron spectroscopy (XPS) to examine the surface reconstructions of Ge (110) under graphene. Two reconstructions, the (1 × 1) phase (R2) which was previously proposed to survive only at high temperature and a [2251] superstructure (R1 phase), were determined based on atomically resolved STM images. The R2 phase will transform to R1 after annealing in UHV above 300 °C, while the R1 phase can reversibly change to the (1 × 1) phase after heating in hydrogen at 700 °C. Finally, we confirmed the presence of interfacial hydrogen that stabilized the (1 × 1) phase at the initial stage of graphene growth based on control experiments. The zigzag edge of graphene is perpendicular to the close-packed [1-10] direction of Ge(110) which ensures the unidirectional growth of graphene seeds for final merging into single crystal.