Correlation between domain boundaries and surface steps: A scanning-tunneling-microscopy study on reconstructed Pt(100)

Rj, Behm; Hösler, W.; Ritter, Edmond F.; Binning, G.

doi:10.1103/physrevlett.56.228

Cited by 130 publications

(23 citation statements)

References 9 publications

(4 reference statements)

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“…These satellites originate in the buckling of the top and succeeding layers [7,10]. At 1600 K, the corrugation wave vector 8 ± makes an angle to the (1,1,0) axis of 3.8° and has a period of 13.84 A, consistent with the results of scanning tunneling microscopy measurements [11].…”

supporting

confidence: 60%

Orientational epitaxy of the hexagonally reconstructed Pt(001) surface

et al. 1991

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We describe x-ray-scattering studies of the orientational epitaxy displayed by the hexagonally reconstructed Pt(OOl) surface. At 1685 K, the reconstructed surface layer undergoes a continuous rotational transformation with respect to the underlying bulk and exhibits mean-field behavior. A second, discontinuous rotational transformation is observed at 1580 K. These results are inconsistent with the predictions of current theories and lead us to propose a mean-field description of rotational transformations.PACS numbers: 68.35.Rh, 64.70.Dv An important aspect of the growth of one crystal upon another involves their relative orientation: How are the high-symmetry directions of the ad-lattice and of the substrate lattice aligned? Our present understanding of this question has been guided by the calculations of Novaco and McTague [1], who explicitly considered incommensurate monolayers of rare gases adsorbed on a rigid, basal plane substrate of graphite. They showed that, even though there is no translational registry at the interface, there may exist a preferred orientation. This is called orientational epitaxy. Their calculations further revealed that the high-symmetry directions of an incommensurate overlayer may be rotated away from the high-symmetry directions of the substrate and that the rotation angle is determined by the incommensurability of the overlayer and by its phonon dispersion relations. In many instances, most notably for the rare gases on graphite [2] and for alkali metals on transition-metal surfaces [3], the predictions of Novaco and McTague describe the orientational epitaxy of an adsorbed layer. Other systems for which the rotational epitaxy has been characterized include layers of alkali metals intercalated into graphite [4], in situ deposited monolayers of Pb on Ag(lll) and Au(lll) electrodes [5], crystallites of Pb deposited on Si(l 11) and Ge(lll) substrates [6], and clean Au (001) surfaces held in vacuum [7] and under electrochemical conditions [8].In this paper, we describe the rotational behavior exhibited by the clean (001) surface of Pt between 300 and 1820 K. We have found that between 7 = 1685 and 1820 K, the surface reconstructs to form a buckled, hexagonal monolayer [9] on top of the bulk planes of square symmetry lying immediately beneath. The top layer is incommensurate in both directions within the surface plane, and the average area per atom is contracted by 8% relative to its value in a bulk (111) plane. In this phase, a hexagonal high-symmetry direction is aligned with the cubic (1,1,0) direction. However, as the temperature is reduced below T c = 1685 K, there is a structural transformation in which domains of the hexagonal overlayer rotate continuously to angles ±0.9° away from the bulk (1,1,0) direction. Remarkably, the rotational transformation exhibits mean-field behavior: That is, the dependence of the rotation angle on temperature follows a onehalf power law versus reduced temperature e = (T c -T)/ T c . At 1580 K, there is a second, discontinuous transformation, lea...

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confidence: 60%

Orientational epitaxy of the hexagonally reconstructed Pt(001) surface

et al. 1991

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“…We analyzed the surface resistance to deformation (elasticity) of syncytiotrophoblasts by microrheology with an atomic force microscope (AFM) [33]. For comparison, we measured the elastic modulus of mTSC.…”

Section: Resultsmentioning

confidence: 99%

Placental Syncytium Forms a Biophysical Barrier against Pathogen Invasion

et al. 2013

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Fetal syncytiotrophoblasts form a unique fused multinuclear surface that is bathed in maternal blood, and constitutes the main interface between fetus and mother. Syncytiotrophoblasts are exposed to pathogens circulating in maternal blood, and appear to have unique resistance mechanisms against microbial invasion. These are due in part to the lack of intercellular junctions and their receptors, the Achilles heel of polarized mononuclear epithelia. However, the syncytium is immune to receptor-independent invasion as well, suggesting additional general defense mechanisms against infection. The difficulty of maintaining and manipulating primary human syncytiotrophoblasts in culture makes it challenging to investigate the cellular and molecular basis of host defenses in this unique tissue. Here we present a novel system to study placental pathogenesis using murine trophoblast stem cells (mTSC) that can be differentiated into syncytiotrophoblasts and recapitulate human placental syncytium. Consistent with previous results in primary human organ cultures, murine syncytiotrophoblasts were found to be resistant to infection with Listeria monocytogenes via direct invasion and cell-to-cell spread. Atomic force microscopy of murine syncytiotrophoblasts demonstrated that these cells have a greater elastic modulus than mononuclear trophoblasts. Disruption of the unusually dense actin structure – a diffuse meshwork of microfilaments - with Cytochalasin D led to a decrease in its elastic modulus by 25%. This correlated with a small but significant increase in invasion of L. monocytogenes into murine and human syncytium. These results suggest that the syncytial actin cytoskeleton may form a general barrier against pathogen entry in humans and mice. Moreover, murine TSCs are a genetically tractable model system for the investigation of specific pathways in syncytial host defenses.

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“…Carbon monoxide is not resolved within this structure, as in previous STM work. 2 We analyze the structure of the overlayer at step edges and domain boundaries and find evidence for diffusion of benzene molecules. Our observations are an important step towards real-space imaging of surface-molecule interac-tions.…”

mentioning

confidence: 99%

Scanning Tunneling Microscopy Observations of Benzene Molecules on the Rh(111)-(3 × 3) (C6H6
Ohtani
¹
,
Wilson
²
,
Chiang
³

et al. 1988
Phys. Rev. Lett.
361
9
134
0
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Scanning tunneling microscopy (STM) images of the (3x3) superlattice of benzene and carbon monoxide coadsorbed on the Rh(l 11) surface reveal a well-ordered array of ringlike features associated with individual benzene molecules, while CO is not resolved. Images further show translational domain boundaries, step-edge structures, and evidence for surface diffusion. The origin of the STM image contrast of these molecules and implications for STM imaging of other molecular adsorbates are briefly discussed.PACS numbers: 68.35.Bs, 61.16.Di Scanning tunneling microscopy (STM) has been proven to be a very powerful tool for atomic resolution imaging of surfaces. This technique has been successfully applied to semiconductor and metal surfaces, both with and without atomic adsorbates. l Early results for molecular adsorbates on metal surfaces have been somewhat less encouraging. For example, chemisorbed carbon monoxide molecules have not been resolved on Pt(lOO) surfaces, even though the CO-induced restructuring of the metal surface was observed. 2 Images of Cu phthalocyanine on Ag surfaces 3 showed low symmetry and resolution, which was interpreted in terms of molecular motion induced by the electric field gradients near the tip. The difficulties in imaging of molecular adsorbates have been thought to be due either to rapid surface diffusion, possibly augmented by electric fields, or to the absence of molecular orbitals near the Fermi level (£>), which are accessible by STM.In this Letter, we report the first real-space images of an ordered array of coadsorbed molecules on a clean metal surface. This allows us to study, for the first time, the source of STM image contrast for different molecules under the same experimental conditions. The system studied is the ordered (3x3) superlattice of coadsorbed benzene (C6H6) and CO on a Rh(lll) surface, which has been well characterized by other surface techniques. 4-6 The detailed geometry of this 3x3 overlayer, as determined with a dynamical LEED analysis, 6 is shown in Fig. 1. The unit cell contains one flat-lying benzene molecule and two upright CO molecules, all chemisorbed over hep-type threefold hollow sites which, as opposed to fec-type hollow sites, are directly above second-layer Rh atoms. STM images of this structure reveal individual benzene molecules as threefold ringlike features. Carbon monoxide is not resolved within this structure, as in previous STM work. 2 We analyze the structure of the overlayer at step edges and domain boundaries and find evidence for diffusion of benzene molecules. Our observations are an important step towards real-space imaging of surface-molecule interac-tions.The sample was prepared and analyzed in a surface preparation and analysis chamber connected to the STM chamber by internal transfer mechanisms, which is described elsewhere. 7 The Rh(l 11) sample was cleaned by repeated cycles of 1-keV ion bombardment and heating at 1000°C in the presence of 4xl0" 5 Torr Ar and 8xl0~1 0 Torr O2. The sample was then annealed at 800 °C for 10 min. Azi...

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Correlation between domain boundaries and surface steps: A scanning-tunneling-microscopy study on reconstructed Pt(100)

Cited by 130 publications

References 9 publications

Orientational epitaxy of the hexagonally reconstructed Pt(001) surface

Orientational epitaxy of the hexagonally reconstructed Pt(001) surface

Placental Syncytium Forms a Biophysical Barrier against Pathogen Invasion

Scanning Tunneling Microscopy Observations of Benzene Molecules on the Rh(111)-(3 × 3) (C6H6
Ohtani
¹
,
Wilson
²
,
Chiang
³

et al. 1988
Phys. Rev. Lett.
361
9
134
0
View full text Add to dashboard Cite

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Correlation between domain boundaries and surface steps: A scanning-tunneling-microscopy study on reconstructed Pt(100)

Cited by 130 publications

References 9 publications

Orientational epitaxy of the hexagonally reconstructed Pt(001) surface

Orientational epitaxy of the hexagonally reconstructed Pt(001) surface

Placental Syncytium Forms a Biophysical Barrier against Pathogen Invasion

Scanning Tunneling Microscopy Observations of Benzene Molecules on the Rh(111)-(3 × 3) (C6H6Ohtani1, Wilson2, Chiang3 et al. 1988Phys. Rev. Lett.36191340View full textAdd to dashboardCite

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Scanning Tunneling Microscopy Observations of Benzene Molecules on the Rh(111)-(3 × 3) (C6H6
Ohtani
¹
,
Wilson
²
,
Chiang
³

et al. 1988
Phys. Rev. Lett.
361
9
134
0
View full text Add to dashboard Cite