The structure of Si(112): Ga-(Nx1) reconstructions

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.