Nanografting versus Solution Self-Assembly of α,ω-Alkanedithiols on Au(111) Investigated by AFM

Abstract

The solution self-assembly of alpha,omega-alkanedithiols onto Au(111) was investigated using atomic force microscopy (AFM). A heterogeneous surface morphology is apparent for 1,8-octanedithiol and for 1,9-nonanedithiol self-assembled monolayers (SAMs) prepared by solution immersion as compared to methyl-terminated n-alkanethiols. Local views from AFM images reveal a layer of mixed molecular orientations for alpha,omega-alkanedithiols, which evidence surface structures with heights corresponding to both lying-down and standing-up orientations. For dithiol SAMs prepared by solution self-assembly, the majority of alpha,omega-alkanedithiol molecules chemisorb with both thiol end groups bound to the Au(111) surface with the backbone of the alkane chain aligned parallel to the surface. However, AFM images disclose that there are also islands of standing molecules scattered throughout the surface. To measure the thickness of alpha,omega-alkanedithiol SAMs with angstrom sensitivity, methyl-terminated n-alkanethiols with known dimensions were used as molecular rulers. Under conditions of spatially constrained self-assembly, nanopatterns of alpha,omega-alkanedithiols written by nanografting formed monolayers with heights corresponding to an upright configuration.

First-principles study of 1,4-butanedithiol molecules and radicals adsorbed on unreconstructed Au(111) and Au(100)

“…2,15 In recent years intense experimental research effort is devoted to the adsorption of different dithiol molecules on the Au͑111͒ surface under ultra high vacuum ͑UHV͒, ambient as well as electrochemical ͑EC͒ conditions. 19,[31][32][33][34][35][36][37][38][39][40][41] However, the details of metastable adsorption phases and equilibrium structures remains controversial. The existence of two thiol groups within the molecule raises the question whether dithiol molecules bind via one ͑upright configuration͒ or two ͑lying-down configuration͒ Au-S bonds to the surface.…”

“…In case of the most common deposition methods either from the gas phase or from solution both upright ͑Refs. 19,32,36,37, and 42͒ and lying-down configurations ͑Refs. 19, 32-37, and 43͒ were observed.…”

Mapping mechanical properties of organic thin films by force-modulation microscopy in aqueous media

“…The sample was backfilled with thiol molecules at high concentration for different lengths of time. An EG 3 -thiol SAM is about 2.4 nm thick when thiols are in a close-packed configuration, while the thickness is only about 0.4 nm when the thiol chains lie flat on the surface [63]. …”

Diffusion of 1,4-butanedithiol onAu(100)−(1×1): A DFT-based master-equation approach

“…2,[26][27][28][29][30][31][32][33][34][35][36][37][38][39][40][41][42][43] Intense experimental research effort is devoted to further the understanding of different dithiol molecules adsorbed on the Au͑111͒ surface under ultrahigh vacuum, ambient, as well as electrochemical ͑EC͒ conditions. [44][45][46][47][48][49][50][51][52][53][54] The existence of two thiol groups within the molecule raises the question whether dithiol molecules bind via one ͑upright configuration͒ or two ͑lying-down configuration͒ Au-S bonds to the surface. In case of the most common deposition methods either from the gas phase or from solution both upright configurations at saturation coverage ͑Refs.…”

“…In case of the most common deposition methods either from the gas phase or from solution both upright configurations at saturation coverage ͑Refs. 45,49,50, and 55͒ as well as submonolayer lying-down configurations ͑Refs. 45-50 and 56͒ were observed.…”