Figure 3.
STM constant-height conductance maps (10.3 nm × 2.0 nm; It = 0.03 nA; modulation voltage Vrms = 12 mV) (a) within the band gap at −50 mV, (b) near the valence band onset at −150 mV, (c) at −250 mV, (d) at −350 mV, (e) at −550 mV, and (f) at −650 mV, exhibiting confined standing waves along the ribbon. (g) Constant current STM image of the same ribbon, showing the path (red dashed line) followed by the equidistant dI/dV spectra. (h) Color-coded conductance signal obtained from equidistant dI/dV point spectra (open-feedback parameters: Vs = 1.50 V; It = 0.8 nA; Vrms= 12 mV) on the ribbon and along the red dashed line displayed in panel g. (i) Line-by-line Fourier transform from the stacked spectra in panel h, showing the two-parameter parabolic fit (gray dashed line) used for extracting the effective mass. The additional parabola centered around the Brillouin zone edge is displayed with a green dashed line. Gray horizontal lines corresponding to the voltage biases of maps in panels a–f are superimposed in panels h and i as a guide to the eye.