Insulators Intercalation And Physical Properties Of Epitaxial Single-layer Graphene On Single-crystal Metal Substrates

Since graphene,with the sp~2 hybridized honeycomb lattice,was successfully exfoliated for the first time in 2004,it attracts extensive attention.The superior electrical,mechanical,and optical properties of graphene make it promising in many applications.To realize the applications in electronics,it is crucial to fabricate large-area,high-quality graphene on insulating substrates.With the development of research,people found that epitaxial growth on single-crystal transition metal surfaces is an effective way to fabricate high-quality,large-area graphene.However,the strong interaction between graphene and transition metal substrates,which arises from the hybridization of graphene's?bands with the d orbitals of metal atoms,destroys its unique electronic structure.Moreover,the conductivity of the metal substrates is also an obstacle for the application of graphene.To overcome this problem,intercalation is proposed.Intercalation method can decouple the interaction of epitaxial high-quality graphene and the transition metal substrates.However,the complete insulation between graphene and the metal substrate has not been achieved.This thesis concentrates on insulators intercalation and physical properties of epitaxial single-layer graphene on single-crystal metal substrates,including graphene/silicon oxide/Ru(0001),graphene/magnesium oxide/Ru(0001)and graphene/germanium oxide/Ir(111).Following innovative results are obtained.1.The intercalation and physical properties of crystalline and amorphous silicon oxide between the epitaxial graphene and Ru(0001)surface were studied.The graphene/crystalline silicon oxide and graphene/amorphous silicon oxide heterostructures were successfully constructed by the stepwise intercalation method.The thickness of intercalated crystalline silicon oxide is 1.1 nm and the thickness of amorphous silicon oxide is 1.8 nm.The insulating properties of the crystalline and amorphous silicon oxide are verified by transport measurements.The quality of graphene after intercalation is confirmed by the measurements on Hall bar devices.Furthermore,the thickness of the oxide layer achieved by the oxidation of Ru Si intercalated samples can reach 11 nm.The oxide layer is not a pure silicon oxide,but a mixture of Ru-Si-O.2.The intercalation and structure of magnesium oxide between epitaxial graphene and Ru(0001)surface was explored.The intercalation process is also stepwise.The graphene/crystalline magnesium oxide and graphene/amorphous magnesium oxide heterostructures were successfully constructed.After Mg intercalation,a 2×2superstructure emerged.After oxidation,the crystalline Mg O with a rock salt structure was obtained.Crystalline Mg O has multiple domains.The thickness of the intercalation layer of crystalline Mg O is not very uniform,and the thickest Mg O layer is about 2.3nm.Moreover,the inserted Mg O layer can be decomposed at high temperature,and the entire intercalation process is reversible.3.The intercalation and physical properties of amorphous germanium oxide between the epitaxial graphene and Ir(111)surface was investigated.The intercalation of this material,similar to that of silicon oxide,is realized with stepwise method.After germanium intercalation,a new set of diffraction spots with 2×2 periodicity appear in LEED pattern.The intercalated Ge is difficult to be completely oxidized in the MBE chamber.The fully oxidation of intercalated Ge is realized in a tube furnace with a higher oxygen pressure and lower temperature.The thickness of Ge O_x layer is about1.5 nm.XPS characterizations confirm that Ge and Ge O_x intercalation induce p-type doping of graphene.Electrical transport measurements on Gr/Ge O_x/Ir(111)heterostructure show the intercalated Ge O_x layer can act as an effective tunneling barrier.It has been demonstrated that high-quality and large-area graphene on insulating layers has been achieved by stepwise intercalation.This provides new ideas for the applications of graphene and its heterostructure in future electronic devices.