The interaction of Sb 4 molecular beams with Si(100) surfaces: Modulated-beam mass spectrometry and thermally stimulated desorption studies

Modulated-beam mass spectrometry and thermally-stimulated desorption measurements were used to show that Sb ₄ is dissociatively chemisorbed on clean Si(100) at all temperatures investigated, from 100 to 1025°C. For Si substrate temperatures T_s less than 600°C, desorption was only observed from precursor states corresponding to Sb ₄ molecules adsorbed on top of a dissociatively chemisorbed Sb layer. The Sb ₄ sticking probability s was nearly unity and independent of θ_Sb for θ_Sb ≲ 0.7 monolayers (ML) but decreased rapidly with increasing θ_Sb above 0.7 ML to reach s = 0 at a saturation coverage of θ_Sb = 1.0 ML (referenced to the surface site density of unreconstructed Si(100), 6.8 × 10 ¹⁴ cm ^-2). Above 600°C, the desorbing Sb ₄ flux decreased rapidly as the saturation coverage decreased and an increasing fraction of the impinging Sb ₄ flux was desorbed from dissociatively chemisorbed states as Sb monomers. Sb ₁ was the only desorbing species detected at T_s ≳ 800°C. The activation energy for Sb ₁ desorption was 2.40 ± 0.1 eV for θ_Sb ≲ 0.5 ML and 2.33 ± 0.1 eV for θ_Sb ≳ 0.5 ML as determined by thermally stimulated desorption, surface lifetime, and saturation coverage measurements. A simple model for Sb ₄/Si(100) interactions involving a mobile Sb ₄ precursor state and repulsive lateral interactions between chemisorbed Sb adatoms was used to calculate desorption rate kinetics and found to provide excellent agreement with the measured data.