Significance of Local Density of States in the Scanning Tunneling Microscopy Imaging of Alkanethiol Self-Assembled Monolayers

Riposan, A.; Liu, Gang-yu

doi:10.1021/jp063774w

Cited by 50 publications

(97 citation statements)

References 72 publications

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“…The surface structure of DT SAMs observed here is quite consistent with a number of previous STM studies for alkanethiol SAMs. 5,11,24,26,27 This result strongly supports the idea that DT SAMs are able to reach saturated monolayer coverage with these preparation conditions.…”

Section: Methodssupporting

confidence: 82%

“…It is generally believed that the c(4 × 2) structure is thermodynamically more stable than the hexagonally packed (√3 × √3)R30 o structure. 27 Lateral dimensions of ordered domains were in the range of 10 -20 nm. The VIs appeared as a result of chemisorption of thiols onto gold surfaces with a 0.25 nm depth, which corresponds to the monatomic step height of the Au(111) surface.…”

Section: Methodsmentioning

confidence: 99%

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Coexistence of Closely Packed c(4 × 2) and Striped Phases in Self-Assembled Monolayers of Decylthiocyanates on Au(111)

Choi¹,

Kang²,

Choi³

et al. 2010

Bulletin of the Korean Chemical Society

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Decylthiocyanate (DTC) self-assembled monolayers (SAMs) on Au(111) were prepared by solution and vapor phase deposition methods at 50 o C for 24 h. The formation and surface structure of DTC SAMs were examined using scanning tunneling microscopy (STM). STM imaging revealed that DTC SAMs formed in 1 mM ethanol solution at 50 o C were composed of small ordered domains with lateral dimensions of a few nanometers and disordered phases, whereas DTC SAMs formed in the vapor phase at 50 o C contained two ordered phases: a closely packed c(4 × 2) superlattice and a striped phase with an interstripe spacing of 2.6 -2.8 nm. It was also found that the ordered domain and vacancy island formation for DTC SAMs on Au(111) differs significantly from that of decanethiol SAMs, suggesting that adsorption mechanism is different from each other. From this study, it was confirmed that DTC SAMs with a high degree of structural order can be obtained by vapor phase deposition.

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Section: Methodssupporting

confidence: 82%

Section: Methodsmentioning

confidence: 99%

Coexistence of Closely Packed c(4 × 2) and Striped Phases in Self-Assembled Monolayers of Decylthiocyanates on Au(111)

Choi¹,

Kang²,

Choi³

et al. 2010

Bulletin of the Korean Chemical Society

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“…The row brightness may be due to differences in the adsorption sites of selenium headgroups or in the adsorption geometry of alkyl tail groups. 5,31 It is unlikely that the observed row structure is a striped phase, where the alkyl chain backbones are oriented parallel to the gold surface, because although the periodicity of the striped phase usually largely depends on the molecular length, 32 the distance between the molecular rows was about 10 ± 0.3 Å, which is smaller than the actual molecular length of octaneselenolates (14.3 Å). At present, it is unclear why octaneselenolate SAMs form such complicated row structures.…”

Section: 2225-27mentioning

confidence: 95%

Phase Transition of Octaneselenolate Self-assembled Monolayers on Au(111) Studied by Scanning Tunneling Microscopy

Choi¹,

Kang²,

Ito³

et al. 2011

Bulletin of the Korean Chemical Society

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We investigated the surface structure and wetting behavior of octaneselenolate self-assembled monolayers (SAMs) on Au(111) formed in a 50 µM ethanol solution according to immersion time, using scanning tunneling microscopy (STM) and an automatic contact angle (CA) goniometer. Closely-packed, well-ordered alkanethiol SAMs would form as the immersion time increased; unexpectedly, however, we observed the structural transition of octaneselenolate SAMs from a molecular row phase with a long-range order to a disordered phase with a high density of vacancy islands (VIs). Molecularly resolved STM imaging revealed that the missing-row ordered phase of the SAMs could be assigned as a (6 × √3)R30° superlattice containing three molecules in the rectangular unit cell. In addition, CA measurements showed that the structural order and defect density of VIs are closely related to the wetting behaviors of octaneselenolate SAMs on gold. In this study, we clearly demonstrate that interactions between the headgroups and gold surfaces play an important role in determining the physical properties and surface structure of SAMs.

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“…The formation process of a SAM and its structure on an Au(111) surface have been investigated with scanning tunneling microscopy (STM) [10][11][12][13][14][15], atomic force microscopy (AFM) [16,17], and X-ray diffraction [18]. Spectroscopic methods such as X-ray photoelectron spectroscopy [19], infrared absorption spectroscopy (IRAS) [20][21][22], high-resolution electron energy loss spectroscopy (HR-EELS) [23][24], Raman spectroscopy (RS) [25] and metastable atom electron spectroscopy [26] have also been employed to investigate the structure and electronic properties of SAMs.…”

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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Significance of Local Density of States in the Scanning Tunneling Microscopy Imaging of Alkanethiol Self-Assembled Monolayers

Cited by 50 publications

References 72 publications

Coexistence of Closely Packed c(4 × 2) and Striped Phases in Self-Assembled Monolayers of Decylthiocyanates on Au(111)

Coexistence of Closely Packed c(4 × 2) and Striped Phases in Self-Assembled Monolayers of Decylthiocyanates on Au(111)

Phase Transition of Octaneselenolate Self-assembled Monolayers on Au(111) Studied by Scanning Tunneling Microscopy

Inelastic electron tunneling process for alkanethiol self-assembled monolayers

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