A LEED and neutron diffraction study of hexane adsorbed on graphite in the monolayer range: uniaxial commensurate-incommensurate transition

Krim, J.; Suzanne, J.; Shechter, H.; Wang, R.; Taub, H.

doi:10.1016/0039-6028(85)90933-1

Cited by 55 publications

(47 citation statements)

References 6 publications

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“…The backbone plane of 1-bromohexane molecules is always found to be oriented parallel to the surface plane (a flat configuration), in contrast to nonfunctionalized alkanes on graphite, where experimental data indicate a variable backbone orientation (4,5,7,(42)(43)(44). As discussed above, the orientation of the molecular backbone plane affects the nearestneighbor distance of the adsorbate layer (4, 7) and therefore influences the tradeoff between molecule-graphite and moleculemolecule dispersion interactions (47).…”

Section: Stm Image Contrast: Electronic and Spatial Factorsmentioning

confidence: 96%

“…Scanning tunneling microscopy (STM) (2-6, 8-10, 13, 14, 16-19, 24, 27, 28, 31-38, 40, 41) and diffraction-based probes (7,39,44,45) have been used to characterize the crystallographic monolayer parameters as well as the orientation and conformation of the constituent molecular species. For many alkane derivatives, STM images have revealed the formation of large, ordered adsorbate domains composed of parallel, close-packed molecules with their carbon skeleton in an extended all-trans conformation, oriented parallel to the surface plane.…”

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confidence: 99%

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Ultra-high vacuum scanning tunneling microscopy and theoretical studies of 1-halohexane monolayers on graphite

Müller

Werblowsky

Florio

et al. 2005

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

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A simple model system for the 2D self-assembly of functionalized organic molecules on surfaces was examined in a concerted experimental and theoretical effort. Monolayers of 1-halohexanes were formed through vapor deposition onto graphite surfaces in ultrahigh vacuum. Low-temperature scanning tunneling microscopy allowed the molecular conformation, orientation, and monolayer crystallographic parameters to be determined. Essentially identical noncommensurate monolayer structures were found for all 1-halohexanes, with differences in image contrast ascribed mainly to electronic factors. Energy minimizations and molecular dynamics simulations reproduced structural parameters of 1-bromohexane monolayers quantitatively. An analysis of interactions driving the self-assembly process revealed the crucial role played by small but anisotropic electrostatic forces associated with the halogen substituent. While alkyl chain dispersion interactions drive the formation of a close-packed adsorbate monolayer, electrostatic headgroup forces are found to compete successfully in the control of both the angle between lamella and backbone axes and the angle between surface and backbone planes. This competition is consistent with energetic tradeoffs apparent in adsorption energies measured in earlier temperature-programmed desorption studies. In accordance with the higher degree of disorder observed in scanning tunneling microscopy images of 1-fluorohexane, theoretical simulations show that electrostatic forces associated with the fluorine substituent are sufficiently strong to upset the delicate balance of interactions required for the formation of an ordered monolayer. The detailed dissection of the driving forces for selfassembly of these simple model systems is expected to aid in the understanding of the more complex self-assembly processes taking place in the presence of solvent.haloalkanes ͉ conformation ͉ simulations F uture advances in nanoscale science and engineering are expected to rely increasingly on the controlled bottom-up assembly of molecular arrays. The successful creation of targeted molecular device structures demands a fundamental understanding of the interactions governing 2D self-organization. Simple functionalized hydrocarbon molecules are known to form self-ordered structures at a variety of surfaces and interfaces (1-32) and can serve as ideal model systems to study the underlying forces driving the selfassembly process.Numerous experimental (1-10, 13, 14, 16-19, 21, 22, 24, 27, 28, 30-41) and theoretical (39, 42, 43) studies have investigated the self-assembled monolayers formed when a melt or solution containing alkanes or their derivatives is brought in contact with the basal plane of a graphite substrate. Scanning tunneling microscopy (STM) (2-6, 8-10, 13, 14, 16-19, 24, 27, 28, 31-38, 40, 41) and diffraction-based probes (7,39,44,45) have been used to characterize the crystallographic monolayer parameters as well as the orientation and conformation of the constituent molecular species. For many alkane...

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Section: Stm Image Contrast: Electronic and Spatial Factorsmentioning

confidence: 96%

mentioning

confidence: 99%

Ultra-high vacuum scanning tunneling microscopy and theoretical studies of 1-halohexane monolayers on graphite

Müller

Werblowsky

Florio

et al. 2005

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

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“…Hexane on graphite has been studied experimentally [3][4][5][6] and computationally, [6][7][8][9][10][11][12] and details of its behavior may be found in the appropriate references. In essence, experimentally, uniaxially incommensurate ͑UI͒ or commensurate herringbone ͑HB͒ phases are seen at low temperatures ͑depending on coverage͒, which transition into a rectangular solid/liquid coexistence region, melting finally at temperatures ca.…”

Section: 2mentioning

confidence: 99%

“…In particular, the adsorption of alkanes has been of interest because of the many applications that these simple hydrocarbons have to commercial lubricants and adhesives. Specifically, hexane ͑C 6 H 14 , or CH 3 -͑CH 2 ͒ 4 -CH 3 ͒ is a member of the family of straight-chained n-alkanes whose members differ only in their length ͑C n H 2n+2 , or CH 3 -͑CH 2 ͒ n−2 -CH 3 ͒. This family is simple in structure compared to other organic molecules, yet they still exhibit many internal degrees of freedom, thus, representing an interesting challenge to study.…”

Section: Introductionmentioning

confidence: 99%

Behavior of hexane on graphite at near-monolayer densities: Molecular dynamics study

2006

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We present the results of molecular-dynamics studies of hexane physisorbed onto graphite for eight coverages in the range 0.875ഛ ഛ 1.05 ͑in units of monolayers͒. At low temperatures, the adsorbate molecules form a uniaxially incommensurate herringbone solid. At high coverages, the solid consists of adsorbate molecules that are primarily rolled on their side perpendicular to the surface of the substrate. As the coverage is decreased, the amount of molecular rolling diminishes until = 0.933, where it disappears ͑molecules become primarily parallel to the surface͒. If the density is decreased enough, vacancies appear. As the temperature is increased, we observe a three-phase regime for Ͼ 0.933 ͑with an orientationally ordered nematic mesophase͒; for lower coverages, the system melts directly to the disordered ͑and isotropic͒ liquid phase. The solid-nematic transition temperature is very sensitive to coverage, whereas the melting temperature is quite insensitive to it, except for at low coverages where increased in-plane space and, ultimately, vacancies soften the solid phase and lower the melting temperature. Our results signal the importance of molecular rolling and tilting ͑which result from the competition between molecule-molecule and molecule-substrate interactions͒ for the formation of the intermediate phase, while the insensitivity of the system's melting temperature to changing density is understood in terms of in-plane space occupation through rolling. Comparisons to experimental results are discussed.

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“…Its behavior on a graphite substrate has been extensively studied both experimentally [1][2][3][4][5] and computationally [4][5][6][7][8][9][10][11][12][13]. Neutron scattering and X-ray diffraction reveal that, at near monolayer coverage, the system transits from a herringbone solid into a rectangular solid/liquid coexistence region as the temperature is raised, finally melting at temperatures ~ 170 K [1][2][3][4][5].…”

Section: Introductionmentioning

confidence: 99%

Melting of Hexane Monolayers Adsorbed on Graphite: The Role of Domains and Defect Formation

Wexler¹,

Firlej²,

Kuchta³

et al. 2009

Langmuir

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We present the first large-scale molecular dynamics simulations of hexane on graphite that completely reproduces all experimental features of the melting transition. The canonical ensemble simulations required and used the most realistic model of the system: (i) fully atomistic representation of hexane; (ii) explicit site-by-site interaction with carbon atoms in graphite; (iii) CHARMM force field with carefully chosen adjustable parameters of non-bonded interaction; (iv) numerous ! 100 ns runs, requiring a total computation time of ca. 10 CPU-years. This has allowed us to determine correctly the mechanism of the transition: molecular reorientation within lamellae without perturbation of the overall adsorbed film structure. We observe that the melted phase has a dynamically reorienting domain-type structure whose orientations reflect that of graphite.

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A LEED and neutron diffraction study of hexane adsorbed on graphite in the monolayer range: uniaxial commensurate-incommensurate transition

Cited by 55 publications

References 6 publications

Ultra-high vacuum scanning tunneling microscopy and theoretical studies of 1-halohexane monolayers on graphite

Ultra-high vacuum scanning tunneling microscopy and theoretical studies of 1-halohexane monolayers on graphite

Behavior of hexane on graphite at near-monolayer densities: Molecular dynamics study

Melting of Hexane Monolayers Adsorbed on Graphite: The Role of Domains and Defect Formation

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