Direct access to the graphene-metal interface using Raman spectroscopy to study the origin of contact resistance in operational devices.

We present and validate a reliable approach for investigating the graphene-metal interface in the top metallic contacts of operational devices using Raman spectroscopy. A transparent substrate was optimized for graphene visualization and processing by adjusting the thickness of aluminum and amorphous silicon nitride on a glass substrate. After graphene photolithography and Cr/Au contact fabrication, the device was flipped upside down to directly expose the graphene-metal interface for Raman analysis using 457 nm excitation. Electrical characterization was performed on the same devices: the sheet resistance was measured using the van der Pauw method, and the contact resistance was determined using the transfer length method. This approach enables direct correlation between Raman features-an increased D peak and a reduced 2D peak at the graphene-metal interface-and electrical parameters of the contact. In particular, the higher sheet resistance of graphene beneath the metal corresponds to the reduced p-doping obtained using Raman spectroscopy.