Figure 3: Bound states of single and paired DBs.
From: Quantum engineering at the silicon surface using dangling bonds
(a,f) Ball and stick models (perspective view) of a single DB, and two next-nearest neighbour DBs. (b–d) STM images of a single DB, recorded at +2 V, 5 pA; +2 V, 100 pA; and −2 V, 50 pA, respectively. (g–i) STM images of next-nearest neighbour DBs under similar imaging parameters to the corresponding single-DB images (+2 V, 5 pA; +2 V, 95 pA; and −2 V, 95 pA, respectively). All STM images 3 × 2 nm2. Length measurements have associated uncertainties of ±0.05 nm. (e,j) Probability distributions of the bound states of the single- and double-DB wells, and the potential wells used to generate them. The energy levels for each of the bound states (single DB: −0.95 and −0.02 eV; double DB: −1.07, −0.88 and −0.07 eV) are indicated by horizontal lines on the potential well. A Pöschl–Teller (PT) potential 
is used for the single DB, and the double DB is modelled by the addition of two such PT wells separated by 0.77 nm. The single well fits within the surface Coulomb (C) potential (−e2/4πεr); a lower bound to the true potential. Parameters: α=0.24 nm, λ=2.2 and ε=ε0(εb+1)/2, where ε0 and εb are the permitivity of free space and dielectric constant of Si, respectively. Note that the calculations indicate that the STM images in panels g and h correspond to the situations represented, respectively, by the solid and dashed lines in Fig. 2d.
