Fig. 2: Electron redistribution at A and B sublattice of monolayer BP-Bi.
From: Two-dimensional ferroelectricity in a single-element bismuth monolayer
a, AFM image of a monolayer BP-Bi. Red and blue dotted circles highlight two atoms in the two sublattices. Scale bar, 4.0 Å. b, Constant-height dI/dV spectra obtained along the red dashed arrow in a. c,d, Constant-height dI/dV mapping of the occupied states (c) and empty states (d) in the same area as a. e, Typical frequency shift (Δf) curve as a function of sample bias is measured above the Bi atoms at the constant-height mode (black circles). Red parabolic fitting (red solid line) yields the V* at the maximum to represent the LCPD. The inset shows the uniform fitted residual. f, AFM image of the normal BP-Bi contains four topmost A atoms and one B atom in the middle. g, LCPD grid map (30 × 30) measured at the area of f illustrates the localized potential difference between the A and B sublattices. h, Simulated electrostatic potential above the same structure at a distance of 3 Å from the top Bi plane. Dotted circles in g and h mark the position of A and B atoms. Tip heights z = −260 pm (a), −100 pm (b), −150 pm (c,d), −230 pm (f) and −100 pm (e,g), relative to the height determined by the setpoint V = 100 mV, I = 10 pA above the BP-Bi surface.
