FORMATION OF AN ORDERED SELF-ASSEMBLED MONOLAYER OF DOCOSANESELENOL ON GOLD(111) - STRUCTURE BY SURFACE X-RAY-DIFFRACTION

Docosaneselenol in solution spontaneously forms an ordered (self-assembled (SA)) monolayer on the gold(111) surface. The contact wetting angle of hexadecane (53-55-degrees) on the SA monolayer coated Au surface is consistent with a surface exposing methyl groups which are at the end of the C22 chains. The in-plane structure of this SA monolayer was probed by surface X-ray diffraction. The SA monolayer forms an incommensurate structure with an oblique unit cell with a = 5.204 angstrom, b = 4.897 angstrom, and gamma = 120-degrees. The (a over arrow pointing right + b over arrow pointing right) axis is along the Au [202BAR] direction. The correlation length obtained from the radial scan was approximately 60 angstrom. The tilt angle measured from the surface normal was 15-degrees with the chains tilted along the Au [202BAR] direction (i.e. R30-degrees). The oblique structure of the unit cell represents a distorted hexagonal close packed lattice.