Anchoring structure of smectic liquid-crystal layers on MoS2 observed by scanning tunnelling microscopy

Hara, Masahiko; Iwakabe, Yasushi; Tochigi, Kenji; Sasabe, Hiroyuki; Garito, A. F.; Yamada, Akira

doi:10.1038/344228a0

Cited by 176 publications

(64 citation statements)

References 10 publications

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“…[5][6][7][8][9][10][11] The STM images reveal a highly ordered arrangement of molecules on the surface as might be expected for a liquid crystal. High-resolution images of individual molecules show sufficient detail to resolve the aromatic and aliphatic parts of the molecules and even the cyano group, as well as to obtain details of molecular packing and orientation on the surface.…”

Section: Stm Studies Of the Liquid-solid Interfacementioning

confidence: 89%

STM Investigations of Organic Molecules Physisorbed at the Liquid−Solid Interface

1996

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Investigations of long-chain hydrocarbon and substituted hydrocarbon materials physisorbed at the liquid-solid interface have provided a particularly fruitful area of investigation for the scanning tunneling microscope (STM). Studies of this kind provide considerable information concerning surface-adsorbate interactions, the nature of the STM contrast mechanism for molecules adsorbed on surfaces, the effect of the chemical nature of the liquid solvent on the rearrangement and bonding of adsorbates, and the role played by the underlying structure of the surface itself (defects, domains, etc.) in determining the molecular arrangement of these adsorbates. All of these studies are aimed at the elucidation and control of surface and adsorbate structures and their relationship to the electronic and chemical properties of materials. The successful imaging of numerous physisorbed organic films at the solution-solid interface has demonstrated that the STM is sensitive enough to differentiate chemical functional groups within these films, but participation of molecular states in the tunneling process for many organic thin-film insulators remains a topic of vigorous discussion. Simulations of the self-assembly of long-chain molecules at the liquidsolid interface provide a microscopic, molecular scale view of the dynamic processes that lead to the kinds of structures observed in STM studies of interfaces. These model molecular dynamics simulations offer useful clues to the physical and chemical driving forces that control molecular assembly. This paper reviews the progress and interconnections among the areas of interfacial adsorbate images, imaging mechanisms, and dynamical processes at the liquid-solid interface.

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Section: Stm Studies Of the Liquid-solid Interfacementioning

confidence: 89%

STM Investigations of Organic Molecules Physisorbed at the Liquid−Solid Interface

1996

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“…No signs of mobility were observed during investigations, which lasted up to 1 h in a single region. That such an array can form is probably due to the intermolecular hydrogen bonding capability of the DNA bases (4).Ordered molecular layers of organic molecules, such as benzene (5), alkanes (6), or liquid crystals (7,8), are the most prominent examples to have been imaged recently by STM at atomic resolution. STM results of adenine, one of the four DNA bases, have recently been obtained on graphite by Allen et al (9).…”

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confidence: 99%

Two-dimensional ordering of the DNA base guanine observed by scanning tunneling microscopy.

Heckl

Smith

Binnig

et al. 1991

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

142

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Guanine, one ofthe four DNA bases, has been observed by tunneling microscopy to form a two-dimensional ordered structure on two crystalline substrates, graphite and MoS2. The two-dimensional lattice formed by guanine is nearly identical on the two surfaces, and heteroepitaxy appears to be the growth mechanism in both cases. Although the resolution of molecular details is superior for the graphite substrate, the simpler results on MoS2 are not only easier to interpret but also facilitate the understanding of the more complex images on graphite. We propose that the interfacial structure is composed of linear chains of hydrogen-bonded molecules aligned into a closely packed two-dimensional array.Several recent studies have examined the possibility of imaging DNA by scanning tunneling microscopy (STM) (1-3). However, the ultimate goal-to read the code contained in the strands-has not yet been achieved. To do so it must be possible to recognize clearly and distinguish between the four bases of the genetic code. One essential requirement for imaging small organic molecules by STM is to find experimental preparation conditions whereby the molecules stick firmly to the substrate and form a highly stable layer. This is necessary to withstand the forces of the STM tip during imaging. Compared to the binding of complete DNA strands to the basal planes of MoS2 or graphite, the adsorption of "naked" nucleotide bases is favored by their greater hydrophobicity and, as is shown in this report, by their ability to register with the substrate, thus forming a stable twodimensional ordered array. No signs of mobility were observed during investigations, which lasted up to 1 h in a single region. That such an array can form is probably due to the intermolecular hydrogen bonding capability of the DNA bases (4).Ordered molecular layers of organic molecules, such as benzene (5), alkanes (6), or liquid crystals (7,8), are the most prominent examples to have been imaged recently by STM at atomic resolution. STM results of adenine, one of the four DNA bases, have recently been obtained on graphite by Allen et al. (9). Using a sample preparation technique similar to theirs (9), we prepared samples of guanine on the surfaces of natural MoS2 crystals and highly oriented pyrolytic graphite. We often observed steps from the bare substrate to monolayers of guanine. The results presented in this paper were obtained on such monolayer islands. The character of the steplines provides additional information since the orientation of the molecular lattice with respect to the substrate can be measured there. In the STM images the bases look quite different depending on whether they are deposited on MoS2 (Fig. 1) or on graphite (see Fig. 3). The main differences are that on MoS2 the bases appear as distinct well-isolated nearly structureless blobs; on graphite more details become visible, although it is still not possible to determine the 8003The publication costs of this article were defrayed in part by page charge payment. This article must ...

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“…Although LC molecules adsorbed on HOPG and Au(1 1 1) have been examined by STM since the early 1990's [4][5][6], the effect of potential on the structure of LC molecules has not been reported. Because LC display always operates under electric field, the study of LC molecules adsorbed on a conducting substrate under potential control can be important to the understanding of molecular anchoring on metal surface.…”

Section: Discussionmentioning

confidence: 99%

“…Earlier STM studies performed in the 1990s reveal details of 4-nalkoxycyanobiphenyl (n = 8 or 12) adsorbed on graphite, MoS 2 , and Au(1 1 1). The arrangement of LC molecules on a solid support can differ greatly from that of the bulk, because of the influence of the substrate [4][5][6]. The use of STM in studying adsorption of organic molecules has grown exponentially in the past decade [7][8][9][10][11].…”

Section: Introductionmentioning

confidence: 99%

In situ scanning tunneling microscopy of 5-(Dodecyloxy)-2-(5-(4-(pentyloxy)phenyl)-1H-pyrazol-3-yl)phenol adsorbed on Au(111) electrode

Chen

Huang

Yau

et al. 2012

Journal of Electroanalytical Chemistry

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Anchoring structure of smectic liquid-crystal layers on MoS2 observed by scanning tunnelling microscopy

Cited by 176 publications

References 10 publications

STM Investigations of Organic Molecules Physisorbed at the Liquid−Solid Interface

STM Investigations of Organic Molecules Physisorbed at the Liquid−Solid Interface

Two-dimensional ordering of the DNA base guanine observed by scanning tunneling microscopy.

In situ scanning tunneling microscopy of 5-(Dodecyloxy)-2-(5-(4-(pentyloxy)phenyl)-1H-pyrazol-3-yl)phenol adsorbed on Au(111) electrode

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