Figure 1: Principle of LEEM-based band structure measurements.
From: Nanoscale measurements of unoccupied band dispersion in few-layer graphene
(a) LEEM image (acquired at a landing energy of E0=4.7 eV) of monolayer (bright), bilayer (darker) and trilayer (darkest) graphene grown on SiC. (b) IV-curves, that is, reflected electron intensity as a function of landing energy E0=E−Evac, for monolayer (red), bilayer (blue) and trilayer (black) areas. The curves are shifted in intensity for clarity. The data are collected from single pixels indicated in a. (c) Schematic side view of SiC covered with monolayer and bilayer graphene (silicon atoms are shown in yellow, carbon atoms in grey). An electrically insulating buffer layer resides between SiC and the bottommost graphene layer. One interlayer state is formed for the monolayer graphene case between buffer layer and graphene (sketched schematically in red). For bilayer graphene, two of these interlayer states are found. They give rise to the minima in b (refs 24, 25). (d) Sketch of our experiment: In contrast to conventional LEEM (left), we introduce an in-plane momentum 
of the electrons by tilting the electron beam (right). The kinetic electron energy (Ekin) is related to 
and the out-of-plane momentum 
via the vacuum dispersion relation. It determines the angle of incidence, which is equal to the angle of reflection, as well as the parabolic electron trajectories. (e) LEED analysis allows us to quantify 
. Here, the untilted case of 
is shown where the specular spot resides at the Γ-point in the center of the Brillouin zone (red hexagon). The dotted line indicates where the aperture is placed to detect only specularly reflected electrons (bright-field LEEM). (f,g) For the tilted cases, the central (0,0) spot is tilted towards the M-point and to the K-point, respectively. Scale bars in e–g correspond to 1 Å−1.
