Formation and superlattice of long-range and highly ordered alicyclic selenolate monolayers on Au(1 1 1) studied by scanning tunneling microscopy

The formation and surface structures of cyclohexanethiolate (CYH-S) and cyclohexaneselenolate (CYH-Se) self-assembled monolayers (SAMs) on Au(1 1 1) were probed to understand headgroup effects on the formation of SAMs with an alicyclic backbone using scanning tunneling microscopy (STM). CYH-S SAMs on Au(1 1 1) formed via solution deposition at room temperature (RT) were composed of small ordered domains with sizes ranging from 10 to 30 nm, whereas CYH-Se SAMs on Au(1 1 1) usually had a disordered phase. The molecular arrangements of CYH-S SAMs on Au(1 1 1) could be described as a (5 × 2√3)R30° structure. CYH-Se SAMs formed via vapor deposition at RT had a long-range ordered phase (greater than 100 nm) including missing rows and molecular defects. A highly ordered crystalline phase of CYH-Se SAMs on Au(1 1 1) with fewer structural defects was formed at 323 K for 12 h that was assigned to a (√3.5 × 2√10)R27° structure. STM observations revealed that the domain formation and surface structures of CYH-Se SAMs on Au(1 1 1) were completely different from those of CYH-S SAMs. Furthermore, we found that CYH-S and CYH-Se SAM can be utilized for bonding-induced work function modification of Au substrate through Kelvin probe force microscopy measurement.