Manipulation of Electronic Transport in the Bi(111) Surface State

We demonstrate the controlled manipulation of the 2D-electronic transport in the surface state of Bi(111) through the deposition of small amounts of Bi to generate adatoms and 2D islands as additional scatterers. The corresponding increase in resistance is recorded in situ and in real time. Model calculations based on mean-field nucleation theory reveal a constant scattering efficiency of adatoms and of small 2D Bi islands, independent of their size. This finding is supported by a detailed scanning tunneling microscopy and spectroscopy study at 5 K which shows a highly anisotropic scattering pattern surrounding each surface protrusion.

Figure 1

Measured relative change of surface resistance (green dotted line) during deposition of Bi on a 9 nm Bi(111) base film at 80 K. The data are fitted with the total density of scatterers (adatoms $n_a$: purple line, islands $n_i$: blue line, total ($n_a+n_i$): red line) and scaled by characteristic scattering efficiency $b$. The inset shows a closeup of the low-coverage regime with the dashed yellow line indicating the linear onset.

Figure 2

(a) Constant current STM image of a Bi(111) surface (tunneling parameters: $U_{\mathrm{bias}}=-0.16\mathrm{V}$, $I=0.5\mathrm{nA}$, field of view 25 nm) shows atomically resolved Bi(111) terraces separated by bilayer steps. The inset shows weak starlike height corrugations surrounding each adatom or 2D island. (b) A $dI/dV$ map ($U_{\mathrm{bias}}=0.16\mathrm{V}$) of the same region. A distinct standing wave pattern caused by interference of scattered electrons at a step edge is visible. Each adatom and island shows an anisotropic threefold symmetric scattering pattern. Bright areas correspond to higher topography and larger LDOS, respectively. (c) Closeup of the anisotropic scattering pattern of the pointlike structure shown in (b). (d) Profiles of the $dI/dV$ map taken across the step edge. From the periodicity of the standing wave pattern, a Fermi wavelength of 2.4 nm is estimated. (e) STM apparent height profiles measured across two different scattering centers (small protrusions) marked in the topographic image, (a). (f) Profiles across the scattering patterns in the $dI/dV$ map, (b), averaged from the three profiles indicated by purple lines (solid and dotted).