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Self-Assembled Monolayer

Molecular self-assembled monolayers are films made up of long chain organic molecules, essentially alkanes, which spontaneously form on certain solid substrates by immersing the substrate in a solution of an active surfactant in an organic solvent. The organic monolayers formed through self-assembly are usually closely packed and, therefore, have a highly ordered structure [1].

The self-assembled monolayer in question in this module consists of sulfur-terminated n-alkanes, namely, CH3(CH2)nβˆ’1SHCH_3(CH_2)_{n-1}SH, where n = 15. The head group, viz., SH, is chemisorbed onto a gilded solid surface, the alkane chain consists of methylene, βˆ’CH2βˆ’-CH_2-, groups, while the free surface (tail group) consists of a methyl group, βˆ’CH3-CH_3.

The simplest CH3(CH2)nβˆ’1CH_3(CH_2)_{n-1} (n = 15)/gold(111) SAM consists of a commensurate (3Γ—3)R30∘(\sqrt{3}\times \sqrt{3})R30^{\circ} overlayer structure with one alkanethiol chain in the two-dimensional unit cell, according to electron diffraction results [2].

large circles: gold atoms; small circles: locations of SH groups

1.Ulman, A. (1996). β€œFormation and Structure of Self-Assembled Monolayers,” Chemical Reviews 96, 1533-1554. 1.Strong, L. and Whitesides, G.M. (1988), β€œStructures of Self-Assembled Monolayer Films of Organosulfur Compounds Adsorbed on Gold Single-Crystals-Electron-Diffraction Studies,” Langmuir 4, 546-558.