A1 Refereed original research article in a scientific journal
Imaging empty states on the Ge(100) surface at 12 K
Authors: 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
Publication year: 2018
Journal: Physical Review B
Journal name in source: PHYSICAL REVIEW B
Journal acronym: PHYS REV B
Article number: ARTN 155322
Volume: 98
Issue: 15
Number of pages: 10
ISSN: 2469-9950
eISSN: 2469-9969
DOI: https://doi.org/10.1103/PhysRevB.98.155322
Self-archived copy’s web address: 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).
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