Imaging empty states on the Ge(100) surface at 12 K

: M. Kuzmin, J. Mäkelä, J.-P. Lehtiö, M. Yasir, M. Tuominen, Z.S. Jahanshah Rad, A. Lahti, M.P.J. Punkkinen, P. Laukkanen, K. Kokko

Publisher: AMER PHYSICAL SOC

: 2018

: Physical Review B

: PHYSICAL REVIEW B

: PHYS REV B

: ARTN 155322

: 98

: 15

: 10

: 2469-9950

: 2469-9969

DOI: https://doi.org/10.1103/PhysRevB.98.155322

: https://research.utu.fi/converis/portal/detail/Publication/36584667

Our understanding of bias-dependent scanning-tunneling-microscopy (STM) images is complicated not only by the multiplicity of the surface electronic structure, but also the manifold tunneling effects in probing semiconductor surfaces having directional dangling- and covalent-bond orbitals. Here we present a refined interpretation of empty-state STM images from the model semiconductor surface, Ge(100), on the basis of measurements at low temperature (12 K) combined with density-functional-theory calculations. In the lower-bias regime (<= 1.6 V), the electron tunneling is found to occur predominantly in antibonding dangling-bond or/and dimer-bond states (pi*(1)pi*(2) and sigma*) of Ge(100) at the surface-parallel wave vector k(parallel to) = 0, leading to the tunneling current maxima located directly on the dimer rows. At higher biases (e.g., at 2 V), the current maxima are shifted to the position in the troughs between the dimer rows, because the tunneling occurs efficiently in the pi*(2) states at k(parallel to )not equal 0 associated with the dimer-up atoms of two adjacent dimer rows, i.e., because of increased sideways tunneling. Thus, the empty-state STM images of Ge(100), albeit strongly bias-dependent, reflect the dimer arrangement rather than the backbonds and surface resonances at all experimental conditions used. The results are also discussed in comparison with the counterpart system of Si(100).

2018 BU13978.pdf