The Role of a Double Molecular Anchor on the Mobility and Self-Assembly of Thiols on Au(111): the Case of Mercaptobenzoic Acid (original) (raw)
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Surface structure and interface dynamics of alkanethiol self-assembled monolayers on Au(111)
The journal of physical chemistry. B, 2006
Scanning tunneling microscopy (STM) and high-resolution electron energy loss spectroscopy (HREELS) were used to examine the structural transitions and interface dynamics of octanethiol (OT) self-assembled monolayers (SAMs) caused by long-term storage or annealing at an elevated temperature. We found that the structural transitions of OT SAMs from the c(4 x 2) superlattice to the (6 x square root 3) superlattice resulting from long-term storage were caused by both the dynamic movement of the adsorbed sulfur atoms on several adsorption sites of the Au(111) surface and the change of molecular orientation in the ordered layer. Moreover, it was found that the chemical structure of the sulfur headgroups does not change from monomer to dimer by the temporal change of SAMs at room temperature. Contrary to the results of the long-term-stored SAMs, it was found that the annealing process did not modify either the interfacial or chemical structures of the sulfur headgroups or the two-dimension...
Mixed Methyl- and Propyl-Thiolate Monolayers on a Au(111) Surface
Langmuir, 2013
Mixed methyl-and propyl-thiolate self-assembled monolayers (SAMs) are prepared on a Au(111) surface by exposing the gold substrate to methyl-propyl-disulfide vapor at room temperature. Scanning tunneling microscopy imaging of such SAMs reveals a (3 × 4) phase consisting of CH 3-S-Au-S-CH 3 , CH 3-S-Au-S-(CH 2) 2 CH 3 , and CH 3-(CH 2) 2-S-Au-S-(CH 2) 2 CH 3. Partial desorption of methyl-thiolate occurs when samples are thermally annealed to 373 K, leading to the formation of a striped phase consisting of primarily CH 3-(CH 2) 2-S-Au-S-(CH 2) 2 CH 3 .
Self-assembled monolayers of alkanethiols on Au(111): surface structures, defects and dynamics
Physical Chemistry Chemical Physics, 2005
The surface structures, defects and dynamics of self-assembled monolayers (SAMs) on Au(111) are reviewed. In the case of the well-known c(4 Â 2) and O3 Â O3 R301 surface structures, the present discussion is centered on the determination of the adsorption sites. A more complex scenario emerges for the striped phases, where a variety of surface structures that depends on surface coverage are described. Recently reported surface structures at non-saturation coverage show the richness of the self-assembly process. The study of surface dynamics sheds light on the relative stability of some of these surface structures. Typical defects at the alkanethiol monolayer are shown and discussed in relation to SAMs applications.
The use of organic thin layers as active component in materials science and electronic devices is presently considered a potential alternative to conventional semiconductor based nano scale electronics since it directly provides precise well-defined nano-scale components for electronic devices which eventually allows for simple processing and device fabrication. In the area of interface and surface science covalently bound Self-Assembled Monolayers (SAMs) became of significant importance. In particular aromatic based materials became of paramount interest, since they exhibit strong intermolecular interactions, chemical stability and charge transport properties across metal-organic interface.
Thiol Adsorption on the Au(100)-hex and Au(100)-(1 × 1) Surfaces
The Journal of Physical Chemistry C, 2015
Alkanethiol adsorption on the Au(100) surfaces is studied by using scanning tunneling microscopy, X-ray photoelectron spectroscopy, and electrochemical techniques. Adsorption of hexanethiol (HT) on the Au(100)-hex surface results in the formation of elongated Au islands following the typical stripes of the reconstruction. Ordered molecular arrays forming hexagonally distorted square patterns cover the stripes with surface coverage ≈0.33. On the other hand, HT adsorption on the Au(100)-(1 × 1) surface shows the absence of the elongated island and the formation of square molecular patterns with a surface coverage ≈0.44. The core level shift of thiolates adsorbed on the Au(100)-(1 × 1) and Au(111) is only 0.15 eV, suggesting that chemistry rather than surface sites determines the binding energy of the S 2p core level. These results are also important to complete our knowledge of the chemistry and surface structure for small thiolated AuNPs where the Au(100) together with the Au(111) are the dominant faces.
Potential-Induced Structural Change in a Self-Assembled Monolayer of 4-Methylbenzenethiol on Au(111)
Journal of Physical Chemistry C, 2007
Potential-induced structural change in a self-assembled monolayer (SAM) of 4-methylbenzenethiol (4-MBT) on Au(111) is investigated by in situ scanning tunneling microscopy (STM). STM images in 0.1 M HClO 4 indicate that a 4-MBT SAM on Au(111) consists of multiple phases in electrochemical environments. These phases include ordered domains (R-phase), aggregated molecular patches ( -phase), and potential dependent structures ( ′-phase and γ-phase). At a potential positive of 0.3 V SCE , comparable to the potential of zero charge (pzc) of Au , Ostwald ripening of R-phase domains is observed. Aggregated molecular patches are annealed, by the applied potential, to form a structured ′-phase. At a potential negative of 0.3 V SCE , the structure of 4-MBT SAMs transforms to a new phase (γ-phase), 2.0 ( 0.5 Å higher than the surrounding R-phase surface. This is shown to be an STM tip-enhanced structural change, and is a consequence of the weak binding of thiol to gold at a potential negative of the pzc. Stepping the substrate potential back from 0.2 to 0.4 V SCE transforms the γ-phase to the R-phase.
Theoretical study of thiol-induced reconstructions on the Au(111) surface
Chemical Physics Letters, 2002
A new suggestion for the structure of the Au substrate underlying self-assembled monolayers (SAM) made of thiols is presented on the basis of density functional theory results for methylthiolate (-SCH 3 Þ adsorption on Au(1 1 1). It is found that by introducing vacancy defects on the substrate, the adsorption of SCH 3 is stabilized by about 0.8 eV with respect to the perfect Au(1 1 1) surface. As this overcomes the vacancy formation energy (%0.6 eV), a net driving force exists leading to an adsorbate-induced reconstruction, that enhances adsorption at defected Au(1 1 1). A comparison of results at high and low SCH 3 coverage provides further insight into which specific gold vacancy sites enhance the adsorption energy of the SCH 3 molecule. Ó
Journal of Theoretical Chemistry, 2013
Using sound physical principles we modify the DFT-D atom pairwise semiempirical dispersion correction to density functional theory to work for metallic systems and in particular self-assembled monolayers of thiols on gold surfaces. We test our approximation for two functionals PBE-D and revPBE-D for lattice parameters and cohesive energies for Ni, Pd, Pt, Cu, Ag, and Au, adsorption energies of CO on ( ) surfaces of Pd, Pt, Cu, Ag, and Au, and adsorption energy of benzene on Ag( ) and Au( ). Agreement with experimental data is substantially improved. We apply the method to self-assembled monolayers of alkanethiols on Au( ) and nd reasonable agreement for PBE-D and revPBE-D for both physisorption of n-alkanethiols as well as dissociative chemisorption of dimethyl disul de as an Au-adatom-dithiolate complex. By modifying the C 6 coe cient for Au, we obtain quantitative agreement for physisorption and chemisorption for both PBE-D and revPBE-D using the same set of parameters. Our results con rm that inclusion of dispersion forces is crucial for any quantitative analysis of the thiol and thiolate bonds to the gold surface using quantum chemical calculations.
Langmuir, 2004
A comparative study of charge-transfer processes from/to methyl-terminated and carboxylate-terminated thiolate-covered Au(111) surfaces to/from immobilized methylene blue (MB) molecules is presented. Scanning tunneling microscopy images with molecular resolution reveal the presence of molecular-sized defects, missing rows, and crystalline domains with different tilts that turn the thickness of the alkanethiolate SAM (the spacer) uncertain. The degree of surface heterogeneity at the SAMs increases as the number of C units (n) in the hydrocarbon chain decreases from n) 6. Defective regions act as preferred paths for MB incorporation into the methyl-terminated SAMs, driven by hydrophobic forces. The presence of negativecharged terminal groups at the SAMs reduces the number of molecules that can be incorporated, immobilizing them at the outer plane of the monolayer. Only MB molecules incorporated into the SAMs close to the Au(111) surface (at a distance < 0.5 nm) are electrochemically active. MB molecules trapped in different defects explain the broad shape and humps observed in the voltammogram of the redox couple. The heterogeneous charge-transfer rate constants for MB immobilized into methyl-terminated thiolate SAMs are higher than those estimated for carboxylate-terminated SAMs, suggesting a different orientation of the immobilized molecule in the thiolate environment.