Self‐Assembly of Normal Alkanes on the Au (111) Surfaces

Abstract

The self-assembled monolayers (SAMs) of normal alkanes (n-C(n)H(2n+2)) with different carbon chain lengths (n=14-38) in the interfaces between alkane solutions (or liquids), and the reconstructed Au (111) surfaces have been systematically studied by means of scanning tunneling microscopy (STM). In contrast to previous studies, which concluded that some n-alkanes (n=18-26) can not form well-ordered structures on Au (111) surfaces, we observed SAM formations for all these n-alkanes without any exceptions. We find that gold reconstruction plays a critical role in the SAM formation. The alkane monolayers adopt a lamellar structure in which the alkane molecules are packed side-by-side, to form commensurate structures with respect to the reconstructed Au (111) surfaces. The carbon skeletons are found to lie flat on the surfaces, which is consistent with the infrared spectroscopic studies. Interestingly, we find that two-dimensional chiral lamellar structures form for alkanes with an even carbon number due to the specific packing of alkane molecules in a tilted lamella. Furthermore, we find that the orientation of alkane molecules deviates from the exact [011] direction, because of the intermolecular interactions among the terminal methyl groups of neighboring lamellae; this results in differences of molecular orientation between mirror structures of adjacent zigzag alkane lamellae. Structural models have been proposed, that shed new light on monolayer formation.

Nanoelectrical analysis of single molecules and atomic-scale materials at the solid/liquid interface

“…1b) recorded in 1-phenyloctane solvent (for spacer-layer-stability tests see Supplementary Section 1.2). The average length of an individual n-C 30 H 62 unit is (3.75 ± 0.05) nm, calculated from the in situ STM topographs and is in agreement with previous STM reports on identical systems 25,26 . The van der Waals binding energy between the alkyl-spacer and Au(111) calculated from molecular dynamics structures (Fig.…”

“…1c, for details see Supplementary Section 8.1) is (−2.6 ± 0.3) eV nm −2 , which corresponds to (−119 ± 14) kcal mol −1 , indicating a strong adsorption of the longchain alkanes on Au(111), in agreement with the highly ordered structures shown by in situ STM (ref. 25). The inset in Fig.…”

“…We further show that the organic spacer layer combined with in situ spectroscopy can sense energy-level shifts (energy resolution ∼50 meV) in chemically tailored molecules, which are rationalized using density functional theory (DFT) calculations. Importantly, the organic spacer serves as an intermediate cushioning layer that prevents metal-induced topological defects in single-layer graphene, thus opening a route towards engineering ultraflat two-dimensional nanostructures on metal supports.Organic spacer/gold interaction in liquids n-C 30 H 62 (solubilized in 1-phenyloctane) spray-deposited on Au(111) (Methods) at room temperature 24 forms close-packed two-dimensional lamellar structures 25,26 . The formation of ordered alkyl-organic layers and their lower dielectric constant (∼2) in comparison with inorganic spacers (NaCl, ε:∼6) make them…”

“…Organic spacer/gold interaction in liquids n-C 30 H 62 (solubilized in 1-phenyloctane) spray-deposited on Au(111) (Methods) at room temperature 24 forms close-packed two-dimensional lamellar structures 25,26 . The formation of ordered alkyl-organic layers and their lower dielectric constant (∼2) in comparison with inorganic spacers (NaCl, ε:∼6) make them…”

<i>n</i>-Alkane Monolayer on a Au(111) Template for Metal Growth<i></i>

“…1(a) [5][6][7][8][9]. Flat-lying alkyl chains are in contact with the substrate with the entire molecule.…”