Figure 1

A vicinal $\mathrm{As}∕\mathrm{Si}\left(100\right)$ surface miscut $2°$ toward $\left(111\right)$, annealed under $42\mathrm{mtorr}$ ${\mathrm{AsH}}_3$ for $10\min$ at $725°\mathrm{C}$. The letters correspond to the 5-7-5 structures in Fig. 2. This $800\mathrm{\AA }\times 800\mathrm{\AA }$ STM image is artificially illuminated from the right. $V_{\mathrm{sample}}=-2.5\mathrm{V}$, $I_{\mathrm{tun}}=0.04\mathrm{nA}$.Reuse & Permissions

Figure 2

(a) Bulklike type-$A$ trench, (b) 5-7-5 type-$A$ trench, (c) 5-7-5 1-ML type-$A$ step, (d) 5-7-5 type-$B$ trench, (e) 5-7-5 type-$B$ step, and (f) 5-7-5 ridge. Elsewhere in this paper these are called structures “$a$”–“$f$”, and $e_h$ indicates a variation of structure $e$ in which the lower terrace height is adjusted to give a step height of $h$ ML. $\mathrm{As}\text{−}\mathrm{As}$ dimer bonds on the left-side terrace are either perpendicular (type $A$) or parallel (type $B$) to the line structure. All surface atoms are triply-bonded As (dark gray). All sub-surface atoms are quadruply-bonded $\mathrm{Si}$ (light gray). (g) STM image, artificially illuminated from the right. Continuity of a 5-7-5 core structure is seen where ${\mathrm{AsH}}_3$-etching of the upper terrace has converted part of a type-$B$ step into a ridge. To better show height differences, the ratio of height to width has been increased by 72%. $V_{\mathrm{sample}}=-2.5\mathrm{V}$, $I_{\mathrm{tun}}=0.04\mathrm{nA}$.Reuse & Permissions

Figure 3

(Main image) A $400\mathrm{\AA }\times 400\mathrm{\AA }$ STM image of $\mathrm{As}∕\mathrm{Si}\left(100\right)$ miscut $2°$ toward $\left(111\right)$ annealed under $42\mathrm{mtorr}$ ${\mathrm{AsH}}_3$ for $10\min$ at $805°\mathrm{C}$. The grayscale has been expanded to span only 3 monolayers (terraces 0, 1 and 2). $V_{\mathrm{sample}}=-2.5\mathrm{V}$, $I_{\mathrm{tun}}=0.07\mathrm{nA}$. (Inset) A $175\mathrm{\AA }\times 200\mathrm{\AA }$ STM image of $\mathrm{As}∕\mathrm{Si}\left(100\right)$. This surface was annealed under $42\mathrm{mtorr}$ ${\mathrm{AsH}}_3$ for $5\min$ at $725°\mathrm{C}$. $V_{\mathrm{sample}}=-3.0\mathrm{V}$, $I_{\mathrm{tun}}=0.07\mathrm{nA}$. In both images, the letters correspond to the 5-7-5 line structures of Fig. 2.Reuse & Permissions

Figure 4

Calculated average surface energy density (in $\mathrm{meV}∕{\mathrm{\AA }}^2$) as a function of spacing $n$ (in multiples of $d_0=3.84\mathrm{\AA }$) for an array of parallel type-$B$ 5-7-5 trenches (structure $d$ in Fig. 2). The surface energy is expressed with respect to that of a flat dimerized $\mathrm{As}∕\mathrm{Si}\left(100\right)$ surface $\left({\sigma }_0\right)$. Spacings less than two (shaded area) are unphysical, since a 5-7-5 structure has a finite width of $2d_0$.Reuse & Permissions