Exploiting electron spectroscopies to probe the structure and organization of self-assembled monolayers: a review

Duwez, Anne‐Sophie

doi:10.1016/j.elspec.2003.10.005

Cited by 190 publications

(207 citation statements)

References 226 publications

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“…In chemical compounds and in molecular materials, Au(I)-thiolate species are well established (1)(2)(3)(4)(5). Bond polarizations can be both measured (27)(28)(29)(30)(31)(32)(33)(34)(35)(36) and calculated (19,29,31,32,(37)(38)(39)(40)(41)(42)(43), leading to the conclusion that the charge on S is of order −0.2 e (1-3). Although such quantities cannot be uniquely defined by either experimental measurement or computational evaluation, the broad range of methods that have been applied yield a recognizable consensus.…”

Section: Bond Polarization Data Indicates That Only Structures 1b Andmentioning

confidence: 98%

Gold surfaces and nanoparticles are protected by Au(0)–thiyl species and are destroyed when Au(I)–thiolates form

Reimers

Ford

Halder

et al. 2016

Proc. Natl. Acad. Sci. U.S.A.

124

163

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The synthetic chemistry and spectroscopy of sulfur-protected gold surfaces and nanoparticles is analyzed, indicating that the electronic structure of the interface is Au(0)-thiyl, with Au(I)-thiolates identified as high-energy excited surface states. Density-functional theory indicates that it is the noble character of gold and nanoparticle surfaces that destabilizes Au(I)-thiolates. Bonding results from large van der Waals forces, influenced by covalent bonding induced through s-d hybridization and charge polarization effects that perturbatively mix in some Au(I)-thiolate character. A simple method for quantifying these contributions is presented, revealing that a driving force for nanoparticle growth is nobleization, minimizing Au(I)-thiolate involvement. Predictions that Brust-Schiffrin reactions involve thiolate anion intermediates are verified spectroscopically, establishing a key feature needed to understand nanoparticle growth. Mixing of preprepared Au(I) and thiolate reactants always produces Au(I)-thiolate thin films or compounds rather than monolayers. Smooth links to O, Se, Te, C, and N linker chemistry are established.gold-sulfur bonding | synthesis | mechanism | electronic structure | nanoparticle G old self-assembled monolayers (SAMs) and monolayerprotected gold nanoparticles form important classes of systems relevant for modern nanotechnological and sensing applications (1-5). Understanding the chemical nature of these interfaces is critical to the design of new synthesis techniques, the design of new spectroscopic methods to investigate them, and to developing system properties or device applications. Over the last 10 y, great progress has been made in understanding the atomic structures of gold-sulfur interfaces (6). Most discussion (7) has focused on the identification of adatom-bound motifs of the form RS-Au-SR (where R is typically a linear alkyl chain or phenyl group) sitting above a regular Au(111) surface (8-10) or on top of a nanoparticle core of regular geometry (11), Other variant structures have also been either observed, such as polymeric chains such as the trimer RS-Au-SR-Au-SR) (10, 11), or proposed (8,12,13). By considering the four isomers of butanethiol (14), we have shown that alternative structures can also be produced in which RS groups bind directly to an Au(111) surface without gold adatoms. This occurs whenever steric interactions across the adatoms are too strong or steric intermolecular packing forces allow for very high surface coverages if both adatom and directly bound motifs coexist in the same regular SAM (15). The cross-adatom steric effect has also been demonstrated for gold nanoparticles (16), and we have shown that Coulombic interactions between charged tail groups can also inhibit adatom formation (17). SAMs involving adatoms have poor longrange order owing to the surface pitting that is required to deliver gold adatoms, while directly bound motifs lead to regular surfaces (18).There is clearly a delicate balance between the forces that direct these different in...

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Section: Bond Polarization Data Indicates That Only Structures 1b Andmentioning

confidence: 98%

Gold surfaces and nanoparticles are protected by Au(0)–thiyl species and are destroyed when Au(I)–thiolates form

Reimers

Ford

Halder

et al. 2016

Proc. Natl. Acad. Sci. U.S.A.

124

163

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“…Thus, fabricated nanodevices that use an alkanethiol SAM as a tunneling barrier retain stable electron transport properties for a relatively long period of time (more than several months) [2]. Because of these advantages, the formation processes, structures, and electron transport properties of SAMs have been intensively investigated [3][4][5][6]. The wealth of available experimental data on alkanethiol SAMs makes them benchmark materials to evaluate the validity of various theoretical approaches, including density functional theory (DFT) and nonequilibrium Green's function (NEGF) calculations [7][8][9].…”

Section: Alkanethiol Self-assembled Monolayermentioning

confidence: 99%

Inelastic electron tunneling process for alkanethiol self-assembled monolayers

Okabayashi

Paulsson

Komeda

2013

Progress in Surface Science

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Recent investigations of inelastic electron tunneling spectroscopy (IETS) for alkanethiol self-assembled monolayers (SAMs) are reviewed. Alkanethiol SAMs are usually prepared by immersing a gold substrate into a solution of alkanethiol molecules, and they are very stable, even under ambient conditions. Thus, alkanethiol SAMs have been used as typical molecules for research into molecular electronics. Infrared spectroscopy and electron energy loss spectroscopy (EELS) have frequently been employed to characterize SAMs on the macroscopic scale. For characterization of alkanethiol SAMs on the nanometer scale region, or for single alkanethiol molecules through which electrons actually tunnel, IETS has proven to be an effective method. However, IETS experiments for alkanethiol SAMs employing different methods have shown large differences, i.e., there is a lack of standard data for alkanethiol SAMs with which to understand the IET process or to satisfactorily compare with theoretical investigations.An effective means of acquiring standard data is the formation of a tunneling junction with scanning tunneling microscopy (STM). After explanation of the STM experimental techniques, standard IETS data are presented whereby a contact condition between the tip and SAM is tuned. We have found that many vibrational modes are detected by STM-IETS, as is also the case for EELS. These results are compared with IET spectra measured with different tunneling junctions. In order to precisely investigate which vibrational modes are active in IETS, isotope labeling of alkanethiols with specifically synthesized isotopically substituted molecule has been examined. This method provides unambiguous assignments of IET spectra peaks and site selectivity for alkanethiol SAMs such that all parts of the alkanethiol molecules almost equally contribute to the IET process. The IET process is also discussed based on density functional theory and nonequilibrium Green's function calculations. These results quantitatively reproduce many the experimentally observed features, whereas Fermi's golden rule for IETS qualitatively explains the propensity rule and site selectivity observed in the experiments. However, comparison between experiment and theory reveals a large difference in IETS intensity for the C-H stretching mode that originates from the side chains of the alkanethiol molecules. In order to explain this difference, we discuss the importance of an intermolecular tunneling process in the SAM. Application of STM-IETS to identify a hydrogenated alkanethiol molecule inserted into a deuterated alkanethiol SAM matrix is also demonstrated.

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“…Functionalized alkanethiol self-assembled monolayers (SAM) on gold as a model system for organic functional groups at the surface of biomolecules [4,5,6,7,8,9], and supported lipid 3 bilaysers (SLB) of phospholipid molecules as a biological model membrane [10,11] (figure 1).…”

Section: Introductionmentioning

confidence: 99%

In situphotoelectron spectroscopy study of water adsorption on model biomaterial surfaces

Ketteler

Ashby

Mun

et al. 2008

J. Phys.: Condens. Matter

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Abstract. Using in situ photoelectron spectroscopy at near ambient conditions, we compare the interaction of water with four different model biomaterial surfaces: self-assembled thiol monolayers on Au(111) that are functionalized with methyl, hydroxyl, and carboxyl groups, and phosphatidylcholine (POPC) lipid films on Silicon. We show that the interaction of water with biomaterial surfaces is mediated by polar functional groups that interact strongly with water molecules through hydrogen bonding, resulting in adsorption of 0.2-0.3 ML water on the polar thiol films in 700 mTorr water pressure and resulting in characteristic N1s and P2p shifts for the POPC films. Provided that beam damage is carefully controlled, in situ electron spectroscopy can give valuable information about water adsorption which is not accessible under ultra-high vacuum conditions.

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Exploiting electron spectroscopies to probe the structure and organization of self-assembled monolayers: a review

Cited by 190 publications

References 226 publications

Gold surfaces and nanoparticles are protected by Au(0)–thiyl species and are destroyed when Au(I)–thiolates form

Gold surfaces and nanoparticles are protected by Au(0)–thiyl species and are destroyed when Au(I)–thiolates form

Inelastic electron tunneling process for alkanethiol self-assembled monolayers

In situphotoelectron spectroscopy study of water adsorption on model biomaterial surfaces

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