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

Abstract

Articles you may be interested in X-ray photoelectron spectroscopy study of self-assembled monolayers of alkanethiols on (001) GaAs Modification of thiol-derived self-assembling monolayers by electron and x-ray irradiation: Scientific and lithographic aspects An unexpected packing of fluorinated nalkane thiols on Au (111): A combined atomic force microscopy and xray diffraction study Structural defects in selfassembled organic monolayers via combined atomic beam and xray diffraction J. Chem. Phys. 99, 744 (1993); 10.1063/1.465749 Surface structure and thermal motion of nalkane thiols selfassembled on Au(111) studied by low energy helium diffraction J. Chem. Phys. 94, 8493 (1991);We report on a new, more precise structural characterization of n-octadecane thiol monolayer self-assembled on the UHV-prepared Au͑001͒ 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 aϭ5.77Ϯ0.06 Å, bϭ4.81Ϯ0.02 Å, and ␣ϭ53.1Ϯ0.46°. The alkane chains are tilted 33.5Ϯ1.0°from the surface normal and the tilt direction is ϳ6.8Ϯ1.0°away from the elongated next-nearest-neighbor direction. The Au-thiol interface is found to have an unusual p͑1ϫ4͒ structure formed by an excess of Au atoms, which are believed to be produced in the dereconstruction process of the clean hexagonal Au͑001͒ 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 c͑2ϫ8͒ 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.

Writing self-assembled monolayers with Cs: Optimization of atomic nanolithography imaging using self-assembled monolayers on gold substrates

“…9 an estimate for the density of alkanethiol molecules on Au{111} is ≃ 4 molecules nm −2 . This value is in agreement with previous reports [37][38][39] and gives an estimate for the molecular occupational density of ≃ 4×10 14 cm −2 , assuming perfect hexagonal arrangement and no defects. Defects that appear as etch pits within the SAM monolayer can be ignored [26,31].…”

The growth of sulfur adlayers on Au(100)

“…[12][13][14][15] Kostelitz et al proposed a square-mesh model for the S/Au(100)-(2 × 2) reconstruction, in which there is one S atom in each (2 × 2) unit cell on the Au(100)-(1 × 1) surface. 20 The results in Figs.…”

“…Lifting this reconstruction causes an expulsion of the extra Au atoms from the surface layer, which typically results in a rough surface of Au islands and which has a great influence on the evolution of its surface morphology. [12][13][14][15] Previous studies have reported that the adsorption of S and thiols on the surfaces of noble metals may result in the significant redistribution of substrate atoms. For the growth of S on Cu(100) and Ag(100), the surfaces show the (2 × 2) and ( √ 17 × √ 17) R14 • reconstructions with a S coverage of 0.25 and 0.47 ML, respectively; the latter involves expelling substrate atoms from and forming vacancies in the surface layer.…”

The Application of Gold Surfaces and Particles in Nanotechnology

“…14 There is considerable experimental evidence to support this both from electrochemical 15,16 and adsorption studies. 12,17,18 Interpretation of the structural data from these experiments is complicated by the fact that a 25% excess of surface atoms are created in the hexagonal to 1x1 transition. LEED studies by Dubois et.…”