Researchers from NIST have been using combined optical techniques (internal photoemission or IPE and spectroscopic ellipsometry, or SE) to determine graphene's work function and the band alignment of a graphene-insulator-semiconductor structure.

IPE is used to measure the energy of electrons emitted from materials in order to determine binding energies, while in SE, broadband light sources are shone upon a material, and optical properties are ascertained from the reflectivity.

The researchers studied a structure that consisted of a graphene film grown by chemical vapor deposition (CVD), a degenerately doped p-type silicon substrate, and a 10 nm thick thermal SiO2 layer. The IPE revealed the offset between bands and how they aligned with respect to each other, but only on one side of the device. SE measurements allowed the calculation of the band gaps, which led to the determination of the entire band structure.