Quasi-free-standing epitaxial graphene on 4H-SiC(0001) as a two-dimensional reference standard for Kelvin Probe Force Microscopy

Kelvin Probe Force Microscopy is a method to assess the contact potential difference between a sample and the probe tip. It remains a relative tool unless a reference standard with a known work function is applied, typically bulk gold or cleaved highly oriented pyrolytic graphite. In this report, we suggest a verifiable, two-dimensional standard in the form of a photolithographically patterned, wire-bonded structure manufactured in the technology of transfer-free p-type hydrogen-intercalated quasi-free-standing epitaxial Chemical Vapor Deposition graphene on semi-insulating high-purity nominally on-axis 4H-SiC(0001). The particular structure has its hole density pS= 1.61 × 1013 cm−2 measured through a classical Hall effect, its number of the graphene layers N= 1.74 extracted from the distribution of the ellipsometric angle Ψ, measured at the angle of incidence AOI = 50° and the wavelength λ= 490 nm, and its work function ϕGR= 4.79 eV postulated by a Density Functional Theory model for the specific pS and N. Following the algorithm, the contact potential difference between the structure and a silicon tip, verified at ΔVGR−Si=0.64V, ought to be associated with ϕGR= 4.79 eV and applied as a precise reference value to calculate the work function of an arbitrary material.