Self-assembly of defect-free nanostripe arrays on B-doped Si(001)

We have developed a method to grow large, self-assembled, defect-free arrays of vacancy or adatom stripes on atomically flat, boron-doped Si(001)-(2×1). The subnanometer-high stripes form between ∼870 and 990 °C, with a spacing that depends on temperature. Si deposition is used to prevent sublimation-induced defect formation and to allow time for ordering via surface diffusion. Ordering mechanisms, observed in real time by low-energy electron microscopy, include island nucleation and growth, longitudinal splitting, and coarsening. At formation temperatures, the arrays are only stable when the area fractions of vacancy (${\theta }_{\mathrm{v}}$) or adatom stripes (${\theta }_{\mathrm{a}}$) are ∼½, consistent with stress domain theory predictions. At room temperature, arrays are preserved indefinitely and are a potential template for nanowire growth.

Figure 1

Low-energy electron microscopy (LEEM) image sequence of initial stripe array formation. (a) Onset of vacancy stripe formation on an atomically flat surface. The atomically smooth pit bottom is dark, and the newly formed vacancy stripe is white. (b) Stripe growth and defect formation. (c) Stripe array with several types of defects: forked stripe (enlarged inset); (i) incomplete stripes; (ii) adatom protrusions; (iii) adatom stripes. (d) A partially ordered stripe array showing many incomplete stripes and a small next layer vacancy stripe (enlarged square inset).

Figure 2

LEEM image of a defect-free stripe array formed after 2 min at 875 °C. Stripes are 6.5 μm long, ∼60 nm wide, and 0.14 nm deep.

Figure 3

LEEM images of stripe arrays formed at several temperatures in the same pit (a)–(d). Corresponding stripe spacing dependence on temperature (e). Below ∼850 °C stripes do not form, and the spacing becomes undefined.

Figure 4

LEEM images of stripe spacing decrease via longitudinal stripe splitting (a),(b), and new stripe nucleation (c),(d), at 905 °C.

Figure 5

LEEM image sequence of stripe spacing increase via stripe shrinking in the middle of an array (arrows), and at the periphery (circle) at 958 °C.

Figure 6

LEEM image sequence of stripe coarsening.

Figure 7

LEEM images of a stripe array under two limiting conditions: (a) Si deposition leads to adatom stripe nucleation; (b) sublimation leads to next-layer vacancy stripe nucleation.