Disproportionation phenomena on free and strained Sn/Ge(111) and Sn/Si(111) surfaces

Area of Science:

• Surface Science
• Condensed Matter Physics
• Materials Science

Background:

• The sqrt[3]x sqrt[3] tin (Sn) on germanium (Ge)(111) and silicon (Si)(111) surfaces exhibit complex distortions.
• These distortions are related to the pseudocharge (Q) and surface band occupancy.
• Previous understanding of (3 x 3) distortions in Sn/Ge(111) was limited.

Purpose of the Study:

• To provide a novel understanding of the (3 x 3)-1U and (3 x 3)-2U distortions in Sn/Ge(111).
• To investigate the influence of strain on the surface pseudocharge and resulting distortions.
• To explore the phase diagram and potential fluctuating phases in Sn/Si(111).

Main Methods:

• Theoretical study of the phase diagram under varying strain conditions.
• Analysis of pseudocharge (Q) disproportionation and its relation to surface band occupancy.
• Modeling of different distortion states, including (3 x 3)-1U, (3 x 3)-2U, and (sqrt[3] x sqrt[3])-3U.

Main Results:

• Positive strain maintains the unstrained pseudocharge (Q=3) and suppresses distortions.
• Negative strain induces a (3 x 3)-2U distortion (Q=4) on both Sn/Ge(111) and Sn/Si(111) surfaces.
• Further negative strain leads to a (sqrt[3] x sqrt[3])-3U state (Q=6), characterized by 'all up' atoms.

Conclusions:

• Surface distortions are directly linked to the pseudocharge disproportionation influenced by strain.
• A detailed phase diagram reveals distinct distortion phases (Q=3, 4, 6) under different strain levels.
• The possibility of a fluctuating phase in unstrained Sn/Si(111) warrants further investigation.