Germanium (Ge) is of high interest to the semiconductor industry due to its high charge carrier mobility, which is a key figure of merit for electronic device applications. However, the nature of the native Ge oxide, GeO2, which is water soluble and forms a defect-rich interface with high interface state density, inhibits Ge from broader use in device applications. Efforts to passivate Ge have therefore been made, such as H/Cl/S terminations and organic passivation layers, but remained unsuccessful due to their limited stability. Recently, graphene (gr) arises as a potential candidate for long-term Ge passivation. Certain studies demonstrated that gr grown by chemical vapor deposition (CVD) on Ge suppresses substrate oxidation in ambient environments for several weeks up to months yet this behaviour has been subject to debate. Despite the encouraging results, graphene defects (pinholes, point defects, grain boundaries etc.) have been suspected to undermine passivation since they are prone to oxidants..
In this thesis, we provide evidence that the gr/Ge(110) system is ambient stable against Ge oxidation for 12 weeks and clarified the roles of different graphene defects using low energy electron diffraction (LEED) and microscopy (LEEM). Interfacial hydrogen present following CVD growth is also proven indispensable for Ge passivation in comparison to the strong oxidation of gr/Ge(110) that is observed in ambient after hydrogen is purged by thermal desorption through graphene. LEED results of the sample with interfacial hydrogen intact indicated a well-defined graphene LEED pattern after 12 weeks of ambient exposure, which is a strong indication that substrate oxidation is suppressed. Nevertheless, some sample modifications are observed after exposure in LEEM that have a strong affinity for graphene wrinkles, folds and pinholes. LEEM intensity-voltage (I-V) measurements and their annealing behaviours strongly exclude the possibility of substrate oxidation. Rather, these results suggest that the localized oxidation of graphene occurs at these defects.. These observations are significant because the roles of wrinkles/folds and interfacial hydrogen had not been considered before. Ultimately, this work solidifies the understanding to the oxidation mechanism in a gr/Ge system and contributes to the development of Ge-based devices.