Theoretical Study of Ethynylbenzene Adsorption on Au(111) and Implications for a New Class of Self-Assembled Monolayer

Ford, Michael J.; Hoft, R. C.; McDonagh, Andrew M.

doi:10.1021/jp053238o

Cited by 64 publications

(127 citation statements)

References 29 publications

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“…Moreover, using the linear relation obtained from our XPS data, we can extrapolate the thickness of the film for n = 0 to a value of 5.9 Å; this value corresponds to the length expected for a −CCCH 3 fragment. This extrapolation is also consistent with the ∼5.6 Å dimensions of an upright configuration of the −CCCH 3 molecule on Au(111), on the basis of the bonds lengths provided by previous DFT 24 calculations. Thus, the estimation of thickness using XPS is consistent with SAMs of HCC(CH 2 ) n CH 3 on Au(111) having the −CC− group perpendicular to the surface.…”

supporting

confidence: 89%

Formation of Highly Ordered Self-Assembled Monolayers of Alkynes on Au(111) Substrate

et al. 2014

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Self-assembled monolayers (SAMs), prepared by reaction of terminal n-alkynes (HC C(CH 2 ) n CH 3 , n = 5, 7, 9, and 11) with Au(111) at 60°Cwere characterized using scanning tunneling microscopy (STM), infrared reflection absorption spectroscopy (IRRAS), X-ray photoelectron spectroscopy (XPS), and contact angles of water. In contrast to previous spectroscopic studies of this type of SAMs, these combined microscopic and spectroscopic experiments confirm formation of highly ordered SAMs having packing densities and molecular chain orientations very similar to those of alkanethiolates on Au(111). Physical properties, hydrophobicity, high surface order, and packing density, also suggest that SAMs of alkynes are similar to SAMs of alkanethiols. The formation of high-quality SAMs from alkynes requires careful preparation and manipulation of reactants in an oxygen-free environment; trace quantities of O 2 lead to oxidized contaminants and disordered surface films. The oxidation process occurs during formation of the SAM by oxidation of the −CC− group (most likely catalyzed by the gold substrate in the presence of O 2 ).T hin organic films based on self-assembled monolayers (SAMs) 1 are ubiquitous in surface science. The reaction of organic thiols (RSH) with group Ib metals (Au and Ag) to generate SAMs with composition Au/AgSR is the reaction most commonly used to prepare SAMs, 1 although reactions that generate organosilanes on silicon 2 (SiR) and organic carboxylates on silver 3 (AgO 2 CR) have attractive properties, and a number of other precursors have been surveyed. There have also been scattered descriptions of SAMs formed on gold from solutions of alkynes 4 (HCC(CH 2 ) n CH 3 , n = 3, 5, 7, 9, 11, and 13), ethynylbenzene 5 (HCCC 6 H 5 ) or nalkylmercury(II) tosylates 6 (CH 3 (CH 2 ) n HgOTs, n = 4 and 18) on Au(111). Although the potential interest of SAMs having metal−CCR bonds is high, since they offer a new type of metal−organic bond, most of these studies have used preparations analogous to those employed with n-alkanethiols and have generated SAMs that do not seem to be highly ordered and, thus, are perhaps unsuitable for detailed studies of the physical chemistry of the surface. In particular, there are no procedures that describe the formation of SAMs that are highly ordered in two dimensionsa key requirement for high-quality surface science. The most recent analyses of n-alkyl-based SAMs on Au(111) indicate a "liquid-like" structure of the monolayer, 6 and XPS analyses of SAMs formed from alkynes 4,5 suggest that these SAMs are sensitive to oxidation at an undefined point in their formation; that is, oxidation occurs either during or after SAM formation (for example, by reaction of the AuCCR bond with O 2 ). Contact angle analyses of increasing lengths of alkynes (HCC(CH 2 ) n CH 3 , n = 5, 7, 9, and 11) also suggest 4 that the quality of these SAMs is lower than those based on n-alkanethiols.Although SAMs have enabled studies of wetting, 7,8 adhesion, 9,10 and charge transport 3,11−13 (...

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supporting

confidence: 89%

Formation of Highly Ordered Self-Assembled Monolayers of Alkynes on Au(111) Substrate

et al. 2014

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“…Here we use a value of 5 mRy, which represents a good choice between well-converged total energies and computational effort. 43 The numerical basis sets, in all cases, are equivalent to double-zeta plus were also performed using VASP using slabs 4-layers thick of the 6 ×√3 Au(111) unit cell with a 2 × 6 surface k grid; the lowest layer of each slab was frozen at the optimized structure of bulk gold. …”

Section: Methodsmentioning

confidence: 99%

Chemical Analysis of the Superatom Model for Sulfur-Stabilized Gold Nanoparticles

et al. 2010

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Abstract:The superatom model for nanoparticle structure is shown inadequate for the prediction of the thermodynamic stability of gold nanoparticles. The observed large HOMO-LUMO gaps for stable nanoparticles predicted by this model are, for sulfur-stabilized gold nanoparticles, attributed to covalent interactions of the metal with thiyl adsorbate radicals rather than ionic interactions with thiolate adsorbate ions, as is commonly presumed. In particular, gold adatoms in the stabilizing layer are shown to be of Au(0) nature, subtle but significantly different from the atoms of the gold core owing to the variations in the proportion of gold-gold and gold-sulfur links that form. These interactions explain the success of the superatom model in describing the electronic structure of both known and informatory nanoparticle compositions. Nanoparticle reaction energies are, however, found not to correlate with the completion of superatom shells. Instead, local structural effects are found to dominate the chemistry and in particular the significanctly different chemical properties of gold nanoparticle and bulk surfaces.

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“…22,31 Characterization of SAMs of C≡CPh n on gold indicates that the acetylene group binds in an upright configuration on gold. [32][33][34] A recent report from Zaba and coworkers demonstrates that it is possible to form highly-ordered SAMs of n-alkyl acetylenes on gold in non-oxidizing environments; 35 Table S7) than saturated n-alkanes where the HOMO-LUMO gap is much larger (~7 eV). 21 Moreover, the energy level of the HOMO of conjugated molecules aligns more favorably with the Fermi level of the metal, than does that for aliphatic molecules, and results in lower tunneling barriers.…”

Section: Introductionmentioning

confidence: 99%

Tunneling across SAMs Containing Oligophenyl Groups

et al. 2016

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This paper describes rates of charge tunneling across self-assembled monolayers (SAMs) of compounds containing oligophenyl groups, supported on gold and silver, using Ga 2 O 3 /EGaIn as the top electrode. It compares the injection current, J 0 , and the attenuation constant, β, of the simplified Simmons equation, across oligophenyl groups (R = Ph n ; n = 1, 2, 3), with three different anchoring groups (thiol, HSR; methanethiol, HSCH 2 R; and acetylene, HC≡CR) that attach R to the template-stripped gold and silver substrates. The results demonstrate that the structure of the molecules between the anchoring group (-S-or -C≡C-) and the oligophenyl moiety significantly influences charge transport. SAMs of SPh n , and C≡CPh n on gold show similar values of β and log|J 0 | (β = 0.28 ± 0.03 Å -1 and log|J 0 | = 2.7 ± 0.1 for Au/SPh n ; β = 0.30 ± 0.02 Å -1 and log|J 0 | = 3.0 ± 0.1 for Au/C≡CPh n ). The introduction of a single intervening methylene (CH 2 ) group, between the anchoring sulfur atom and the aromatic units to generate SAMs of SCH 2 Ph n , increases β to ~0.6 Å -1 on both gold and silver substrates. (For nalkanethiolates on gold the corresponding values are β = 0.76 Å -1 and log|J 0 | = 4.2). As a generalization, based on this and other work, it seems that increasing the height of the tunneling barrier in the region of the interfaces increases β, and may decrease J 0 ; by contrast, it appears that lowering the height of the barrier at these interfaces has little influence on β or J 0 .

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Theoretical Study of Ethynylbenzene Adsorption on Au(111) and Implications for a New Class of Self-Assembled Monolayer

Cited by 64 publications

References 29 publications

Formation of Highly Ordered Self-Assembled Monolayers of Alkynes on Au(111) Substrate

Formation of Highly Ordered Self-Assembled Monolayers of Alkynes on Au(111) Substrate

Chemical Analysis of the Superatom Model for Sulfur-Stabilized Gold Nanoparticles

Tunneling across SAMs Containing Oligophenyl Groups

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