√7  ×  √3 surface with a double layer of In on Si(1 1 1) exhibiting both hexagonal and rectangular features

Area of Science:

• Surface Science
• Materials Science
• Nanotechnology

Background:

• The Si(111) surface is a well-studied substrate for thin film growth.
• Indium (In) deposition on Si(111) can form various surface reconstructions.
• Previously, √7×√7 and √7×√7 phases were thought to represent different In coverages.

Purpose of the Study:

• To investigate the structural relationship between the In-induced √7×√7-hex and √7×√7-rect phases on Si(111).
• To determine the actual In coverage and structure responsible for these observed surface phases.
• To clarify the prevailing understanding of In/Si(111) surface reconstructions.

Main Methods:

• Scanning Tunneling Microscopy (STM) was employed to image the surface structures.
• Bias-dependent STM imaging was used to analyze the electronic properties of the domains.
• In-situ observations of island formation on different phases provided thickness information.

Main Results:

• Both √7×√7-hex and √7×√7-rect features were observed within the same domain using bias-dependent STM.
• The formation of a √7×√7-hex island on a √7×√7-'striped' (single-layer In) phase suggests a double-layer In structure for the √7×√7 phases.
• A long-range Moiré-like superstructure was observed, attributed to lattice mismatch between In and Si(111).

Conclusions:

• The In-induced √7×√7-hex and √7×√7-rect phases on Si(111) originate from the same double-layer In structure.
• This finding contradicts the existing notion of two distinct √7×√7 surfaces with different In coverages.
• The observed Moiré superstructure is a consequence of the epitaxial relationship between the In double layer and the Si(111) substrate.