We have studied the structure of Si(112):Ga-(N x 1) reconstructions using a
tomic-resolution scanning tunneling microscopy and first-principles calcula
tions. The nanofaceted clean Si(112) surface becomes planar following the a
dsorption of Ga, which forms long chains on the surface interrupted by isol
ated quasi-periodic defects. The defects create a mixture of (N x 1) struct
ures (N approximate to 4-7) with 5 x 1 and 6 x 1 unit cells most common. We
demonstrate that this structure consists of a chain of Ga atoms adsorbed a
t the (111)-like step edge within the (112) unit cell, and that the defects
are Ga vacancies where the exposed step edge Si atoms form a dimer bond. C
alculations performed as a function of vacancy period confirm that the surf
ace energy is minimized at N = 5-6, when compressive strain associated with
the Si-Ga bonds is effectively minimized. (C) 1999 Elsevier Science B.V. A
ll rights reserved.