Fig. 3: Triangular indium monolayer on SiC(0001).

a STM topography image (constant current mode with V_set = 1.5 V and I_set = 50 pA) of indenene next to the structural model illustrating the triangular atom lattice forming on the SiC(0001) substrate. Also shown is the (1 × 1) unit cell with its inequivalent A and B halves. At the chosen bias voltage STM probes essentially the out-of-plane In p_z orbitals such that the bright spots directly reflect the positions of the In atoms. b Film edge between an indenene monolayer and uncovered SiC. Both lattices appear structurally identical but are distinguishable by their electronic spectra in e. Imaging parameters for SiC and indenene are (V_set = 1.65 V, I_set = 80 pA) and (V_set = 0.45 V, I_set = 100 pA), respectively. c Side view of the structural model highlighting the bond length d between the indenene layer and the Si-terminated 4H-SiC substrate. The accompanying graph schematically illustrates the evolution of the energy gap E_gap as a function of d in the vicinity of the topological phase transition at d^crit (see text for further details). d STM height profiles of indenene along the red and orange paths in a showing the lattice constant and the asymmetry between the A and B voids of the unit cell, respectively. The gray height profile taken on the uncovered SiC(0001) substrate in b proves the identical lattice constants. e dI/dV spectra measured on an indenene film and SiC substrate. In contrast to the metallic states in the close vicinity of the Fermi level in indenene, SiC exhibits a wide tunneling gap of ~3.2 eV¹⁶. The black arrow indicates conductance minimum attributed to the Dirac point of indenene.