It is demonstrated, using reflectance difference spectroscopy, scanning tunneling microscopy, and low-energy electron diffraction, combined with deliberate straining of the surface, that the presence of atomic steps dramatically changes the optical anisotropy of the Si(001) surface. The step-induced reflectance difference signal originates predominately from rebonded steps and is comparable in magnitude to that of the terrace signal. [S0031-9007(98)08282-9]

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Using Fourier transform infrared-attenuated total reflectance spectroscopy in conjunction with hydrogen adsorption to probe surface layer composition, we observe a reversible place exchange between Ge and Si on Ge-covered Si(001) when the surface is dosed with atomic H at elevated temperatures. First-principles calculations confirm a thermodynamic driving force for this place exchange. To explain the intriguing kinetics of the place exchange, which shows no time dependence, we propose a dimervacancy diffusion-assisted mechanism limited by vacancy interactions. [S0031-9007(98)

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