The structure of [ital n]-octadecane thiol monolayers self-assembled on Au(001) studied by synchrotron x-ray and helium atom diffraction

Journal Article · Wed Mar 22 04:00:00 EST 1995 · Journal of Chemical Physics; (United States)

DOI:https://doi.org/10.1063/1.469551· OSTI ID:6767613

Li, J ^[1]; Liang, K S ^[2]; Camillone, N III; Leung, T Y.B.; Scoles, G ^[3]

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1. Exxon Corporate Research, Annandale, New Jersey 08801 (United States) Department of Chemistry, Princeton University, Princeton, New Jersey 08544 (United States)
2. Exxon Corporate Research, Annandale, New Jersey 08801 (United States)
3. Department of Chemistry, Princeton University, Princeton, New Jersey 08544 (United States)

We report on a new, more precise structural characterization of [ital n]-octadecane thiol monolayer self-assembled on the UHV-prepared Au(001) surface using a combination of helium atom diffraction, grazing incidence x-ray diffraction, and x-ray reflectivity measurements. Our results show that the equilibrated alkane chains form a two dimensional distorted hexagonal structure with lattice constants [ital a]=5.77[plus minus]0.06 A, [ital b]=4.81[plus minus]0.02 A, and [alpha]=53.1[plus minus]0.46[degree]. The alkane chains are tilted 33.5[plus minus]1.0[degree] from the surface normal and the tilt direction is [similar to]6.8[plus minus]1.0[degree] away from the elongated next-nearest-neighbor direction. The Au--thiol interface is found to have an unusual [ital p](1[times]4) structure formed by an excess of Au atoms, which are believed to be produced in the dereconstruction process of the clean hexagonal Au(001) surface during the chemisorption of thiols. We propose that this Au interfacial layer modulates the height of the alkane chains resulting in a highly corrugated top surface, which forms a [ital c](2[times]8) structure as observed by atom diffraction. These structural findings reveal a novel interplay between the head group/substrate interaction and the interchain van der Waals interaction which determines not only the alkane chain packing but also the structure of the interfacial layer of the substrate. Our studies also demonstrate that rich, complementary structural information can be obtained about the topmost surface, the chain packing, the interface arrangement, and the substrate of this and similar systems by the combination of atomic beam and synchrotron x-ray characterization techniques.

• DOE Contract Number: FG02-93ER45503
• OSTI ID: 6767613
• Journal Information: Journal of Chemical Physics; (United States), Journal Name: Journal of Chemical Physics; (United States) Vol. 102:12; ISSN JCPSA6; ISSN 0021-9606
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
360602* -- Other Materials-- Structure & Phase Studies
ALKANES
ATOM COLLISIONS
CHAINS
CHEMICAL REACTIONS
CHEMISORPTION
COHERENT SCATTERING
COLLISIONS
COUPLING
DECANE
DIFFRACTION
ELEMENTS
EQUILIBRIUM
FLUIDS
GASES
GOLD
HELIUM
HYDROCARBONS
INCIDENCE ANGLE
INTERFACES
METALS
NONMETALS
ORGANIC COMPOUNDS
ORGANIC SULFUR COMPOUNDS
RARE GASES
SCATTERING
SEPARATION PROCESSES
SORPTION
STRUCTURE FACTORS
THIOLS
TRANSITION ELEMENTS
ULTRAHIGH VACUUM
VAN DER WAALS FORCES
X-RAY DIFFRACTION