Initial stage of Si(001) surface oxidation from first-principles calculations

Area of Science:

• Surface science
• Materials science
• Computational chemistry

Background:

• The Si(001) surface is crucial for semiconductor devices.
• Understanding initial oxidation is key to controlling surface properties.
• Reconstruction of Si(001) influences reactivity.

Purpose of the Study:

• Investigate atomic structure, electronic properties, and optical response of Si(001) during early oxidation.
• Determine favored oxygen adsorption sites.
• Analyze the impact of oxidation on surface electronic states and disorder.

Main Methods:

• Comprehensive density-functional theory (DFT) calculations.
• Modeling of the (4 x 2)-reconstructed Si(001) surface.
• Analysis of adsorption energies, ionization energy, and energy gap.

Main Results:

• The most stable adsorption site for a single oxygen atom is the back-bond of a "down" Si dimer atom.
• Oxygen insertion into the Si-Si back-bond occurs without an energy barrier.
• Surface ionization energy peaks during the oxidation of the second silicon monolayer.
• Oxidation increases the energy gap between occupied and empty surface states.
• Calculated reflectance anisotropy spectroscopy (RAS) data indicate significant surface disorder after the first monolayer oxidation.

Conclusions:

• The initial oxidation of Si(001) is characterized by specific oxygen adsorption mechanisms.
• Oxidation fundamentally alters the electronic structure and optical properties of the Si(001) surface.
• Significant surface disorder is present even at the early stages of oxidation, impacting experimental observations.