# Formation, Structure, and Thermal Annealing Effects of Ordered Self-Assembled Monolayers of 4-Fluorobenzeneselenol on Au(111)

## TL;DR

This study explores how 4-fluorobenzeneselenol molecules form and change structure on gold surfaces, revealing new insights into their organization and thermal behavior.

## Contribution

The paper reports a novel transformation of ordered SAMs into short molecular rows after thermal annealing, not previously observed in similar systems.

## Key findings

- Ordered (4 × 2√3) phase of 4-FBSe SAMs forms within 30 seconds to 3 minutes of deposition.
- Thermal annealing at 373 K transforms ordered SAMs into randomly distributed short molecular rows.
- The average areal molecular density was calculated as 29.0 Ų/molecule, indicating dense packing.

## Abstract

The formation, surface structure, and thermal annealing effects of self-assembled monolayers (SAMs) via vapor deposition of 4-fluorobenzeneselenol (4-FBSeH) on Au(111) at room temperature were investigated using scanning tunneling microscopy (STM). The most prominent structural feature is that 4-fluorobenzeneselenolate (4-FBSe) SAMs on Au(111) are composed of numerous SAM-covered Au adatom islands, regardless of the deposition time. High-resolution STM observations revealed that the ordered phase of 4-FBSe SAMs was formed after very short deposition times of 30 s and 3 min, whereas the disordered phase was formed after long deposition times of 1 h and 24 h. The ordered phase can be described as a (4 × 2√3) structure, and the average areal molecular density of the SAMs was calculated to be 29.0 Å2/molecule, suggesting the formation of densely packed monolayers with a standing-up adsorption structure. Interestingly, after thermal annealing at 373 K for 30 min, the (4 × 2√3) ordered phase of the SAMs was transformed to randomly distributed, short, single-molecular rows ranging from several nanometers to approximately ten nanometers in length, which has not been observed previously in organic thiolate SAMs. The high-resolution STM results of this study can provide very meaningful information for understanding the formation, surface structure, and thermal annealing effects of 4-FBSe SAMs on Au(111).