Surface standing waves have been studied to investigate the scattering and transport properties on metal and semiconductor surfaces by scanning tunneling microscopy (STM) and spectroscopy (STS). We present a STS study of the standing waves confined in a single dimer row on the clean Si(001) surface. The Si(001) surface reconstructs by forming buckled dimers. The remaining dangling bonds (DB) on the dimers produce the filled and empty DB states near the Fermi level. Since the empty DB state is located within the bulk band gap and has dispersion along the dimer row, electron standing waves are observed near steps and dimer vacancies within the energy range corresponding to the empty DB state [1,2]. We fabricated one dimensional quantum wells (QW) on a single dimer row by depositing tungsten atoms from the STM tip [3]. The tungsten atoms were set on the two positions separated by 9.2 nm on a single dimer row. They acted as potential barriers to confine electron waves in the dimer row. STS confirmed that there were five bound states in the QW structure and the energy levels for the bound states were equally spaced by approximately 80 meV. Consequently, we attempted to fit the wave functions for the parabolic QW to the STS results. The fitting was successful and determined the effective mass of the empty DB state to be m*=0.55me (me is the free electron mass). This value is almost twice as large as that previously reported [4].
References:
[1] T. Yokoyama M. Okamoto, and Takayanagi, Phys. Rev. Lett. 81, 3423 (1998).
[2] K. Sagisaka and D. Fujita, Phys. Rev. B 72, 235327 (2005).
[3] K. Sagisaka and D. Fujita, Appl. Phys. Lett. 88, 203118 (2006).
[4] T. Yokoyama and Takayanagi, Phys. Rev. B 59, 12232 (1999).
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