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  • 1
    Electronic Resource
    Electronic Resource
    In situ studies of thiol self-assembly on gold from solution using atomic force microscopy (1998)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 108 (1998), S. 5002-5012 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The kinetics and mechanism for the solution-phase adsorption of n-alkanethiols onto gold to form self-assembled monolayers (SAMs) have been monitored in situ using atomic force microscopy (AFM). Time-dependent AFM images reveal detailed structural information about the adsorbed layer during its growth. In 2-butanol, CH3(CH2)17SH molecules initially adsorb on gold with the molecular axis of their hydrocarbon chains oriented parallel to the surface. As the surface coverage increases to near saturation, a two-dimensional phase transition occurs and produces islands composed of molecules with their hydrocarbon axis oriented ∼30° from the surface normal. Continued exposure to the thiol solution results in a greater number of these islands and the growth of these nuclei until a SAM is formed with a commensurate ((square root of 3)×(square root of 3))R30° structure. The growth of the lying-down phase follows a first-order Langmuir adsorption isotherm, while the phase transition is best described by a second-order reaction. The kinetics of the self-assembly process also depends on the chain length of the alkanethiol and the cleanness of the gold surface. Longer-chained thiols, such as CH3(CH2)17O(CH2)19SH, formed complete SAMs more rapidly than did shorter-chained thiols, such as CH3(CH2)17SH. The physisorbed, lying-down phase for CH3(CH2)17O(CH2)19SH was less homogeneous and its two-dimensional phase transition was more complicated than for CH3(CH2)17SH and CH3(CH2)21SH, as the CH3(CH2)17O(CH2)19SH molecules adopt multiple conformations. Of these, the two dominant ones are an all-trans, and another where the hydrocarbon chain adopts an all-trans conformation except for a gauche bond on both sides of the ether unit. These conformers coexist on the surface during the initial adsorption and its transition to the standing-up phase, but change to the all-trans structure in the complete SAM. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.475908
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  • 2
    Electronic Resource
    Electronic Resource
    An unexpected packing of fluorinated n-alkane thiols on Au(111): A combined atomic force microscopy and x-ray diffraction study (1994)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 101 (1994), S. 4301-4306 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Atomic force microscopy (AFM) and grazing incidence x-ray diffraction (GIXD) have been used to study the structure of self-assembled monolayers of CF3(CF2)n(CH2)2SH (n=11, 7, and 5) on the Au(111) surface. Surprisingly, although the nearest-neighbor fluorinated alkane thiol distance is very close to the lattice constant of a commensurate p(2×2) structure, the close-packed rows of molecules are rotated ∼30° with respect to the underlying gold lattice. That packing is incommensurate or at most only close to the high-order commensurate c(7×7) structure. The relative orientation of the organic monolayer and the Au(111) substrate has been determined unambiguously both with GIXD, and by AFM, taking advantage of an earlier finding (Ref. ) that AFM tips can reversibly displace the thiol molecules under high loads. In addition, we demonstrate that the two techniques provide complementary information on the order and the domain structures of these monolayers.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.467479
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  • 3
    Electronic Resource
    Electronic Resource
    Preparation, Structure, and Mechanical Stability of Alkylsilane Monolayers on Mica (1995)
    s.l. : American Chemical Society
    Langmuir 11 (1995), S. 1600-1604 
    Details
    ISSN: 1520-5827
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/la00005a031
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  • 4
    Electronic Resource
    Electronic Resource
    Substrate dependence of the surface structure and chain packing of docosyl mercaptan self-assembled on the (111), (110), and (100) faces of single crystal gold (1993)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 98 (1993), S. 4234-4245 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Low-energy helium diffraction has been used to study the surface structure, chain packing, and thermal vibrations of docosyl mercaptan [CH3(CH2)21SH] self-assembled on single crystal Au(111), (110), and (100). The docosyl mercaptan molecules form monolayers with different periodicity on the different surfaces of gold. On Au(111) at low temperatures (≤100 K), the terminal methyl groups of the docosyl mercaptan molecules form domains of a hexagonal lattice with a unit mesh constant of 5.01±0.02 A(ring). The sulfur head groups are arranged in a commensurate ((square root of)3×(square root of)3)R30° structure and are believed to adsorb on the triple hollow sites of the Au(111) lattice. The unit mesh parameters for CH3(CH2)21S/Au(110) are a=b=4.99±0.08 A(ring) and α=109.5°, suggesting that the chemisorbed sulfur atoms remove the "missing row'' reconstruction of the Au(110) surface and form a commensurate c(2×2) lattice. The adsorption of docosyl mercaptan molecules on a Au(100) surface results in a complicated diffraction pattern. Analysis of the data reveals an oblique unit mesh with a=b=5.97±0.09 A(ring) and α=95°±5° with four kinds of equivalent domains present because of the fourfold symmetry of Au(100). The above results confirm that the sulfur–substrate interaction plays an important role in determining the periodicity and the packing density of the molecules within the monolayers. The estimated average domain size of the terminal methyl groups is 22.8, 38.6, and 23.4 A(ring) for CH3(CH2)21SH self-assembled on Au(111), (110), and (100) faces, respectively. The chain packing and orientation within the unit cell are also discussed in this paper in conjunction with the latest results obtained via other techniques such as reflection IR spectroscopy and low-energy electron diffraction.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.465030
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  • 5
    Electronic Resource
    Electronic Resource
    Superlattice structure at the surface of a monolayer of octadecanethiol self-assembled on Au(111) (1993)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 98 (1993), S. 3503-3511 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We report direct evidence of a unit mesh containing more than one hydrocarbon chain at the surface of a self-assembled monolayer of long-chain n-alkanethiols. Our helium diffraction measurements for a monolayer of n-octadecanethiol on Au(111) are consistent with a rectangular primitive unit mesh of dimensions 8.68×10.02 A(ring) containing four crystallographically distinct hydrocarbon chains. This packing arrangement can also be described as a c(4×2) superlattice with respect to the fundamental simple hexagonal [((square root of)3×(square root of)3)R30°] array of lattice parameter 5.01 A(ring) previously observed for monolayers of other n-alkanethiols on gold. No temperature-dependent phase behavior is observed in the temperature range where surface diffraction is measurable (30–100 K) and cycling up to temperatures as high as 50 °C caused no observable change in the diffraction. It is proposed that this larger unit mesh is the result of a patterned arrangement of rotations of the hydrocarbon chains about their molecular axes. This patterned arrangement must be different than the herringbone structure expected by simple analogy to bulk n-alkanes.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.464071
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  • 6
    Electronic Resource
    Electronic Resource
    Low energy helium diffraction studies of CH3Br overlayers physisorbed on C(0001), NaCl(001), and LiF(001) surfaces (1992)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 96 (1992), S. 9212-9220 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Low energy helium diffraction has been used to determine the unit mesh parameters of overlayers of CH3Br physisorbed on C(0001), NaCl(001), and LiF(001) at ≈35 K. CH3Br forms a uniaxially commensurate overlayer on C(0001) with unit mesh parameters 4.26 A(ring)×6.75 A(ring). On NaCl(001), CH3Br forms a high coverage and a low coverage phase. The high coverage phase is incommensurate and has unit mesh parameters 4.54 A(ring)×6.73 A(ring), whereas the low coverage phase is commensurate with a ((2)1/2×3(2)1/2)R45° unit mesh. The structure of CH3Br/LiF(001) is essentially the same as that of the high coverage phase of CH3Br/NaCl(001) with unit mesh parameters 4.52 A(ring)×6.71 A(ring). The unit mesh parameters (with the exception of low coverage CH3Br/NaCl ) are very similar to the lattice parameters of the a-b [or (001)] plane of bulk crystalline CH3Br at ≈153 K. By analogy with the bulk crystal, it is likely that there are two molecules per unit mesh and that the CH3Br dipoles are nearly perpendicular to the surface and antiferroelectrically ordered. Our results suggest that the unit mesh for the low coverage phase of CH3Br/NaCl contains four molecules and that the molecular axes are parallel to the substrate surface. The implications of these results for photodissociation studies of physisorbed CH3Br are briefly discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.462231
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  • 7
    Electronic Resource
    Electronic Resource
    Surface structure and thermal motion of n-alkane thiols self-assembled on Au(111) studied by low energy helium diffraction (1991)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 94 (1991), S. 8493-8502 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Low energy helium diffraction has been used to study the packing and thermal motion of the terminal CH3 groups of monolayers of n-alkane thiols self-assembled on Au(111)/mica films and a Au(111) single crystal surface. At low temperatures (〈100 K), the terminal CH3 groups are arranged in domains containing a hexagonal lattice with a lattice constant of 5.01 A(ring). As the length of the carbon chain is shortened, an abrupt decrease in the diffraction peak intensities is observed for CH3(CH2)9SH/Au(111)/mica, and no diffraction is observed for CH3(CH2)5SH/Au(111)/mica. This is indicative of a sudden decrease in surface order at around ten carbon atoms per chain. A semi-quantitative estimation of the average domain size of each monolayer surface shows a maximum of 46 A(ring) at intermediate chain length [CH3(CH2)13SH/Au(111)/mica], decreasing to 26 A(ring) at longer [CH3(CH2)21SH/Au(111)/mica] and 41 A(ring) at shorter [CH3(CH2)9SH/Au(111)/mica] chain lengths. No phase transitions could be detected at the surfaces of these monolayers from 35 K to 100 K, but as expected for a soft material, the thermal motion of the n-alkane thiol molecules increases with increasing surface temperature and reduces the diffraction intensities to zero at around 100 K. The relative mean square displacements of the surface CH3 groups along the directions perpendicular and parallel to the surface have been calculated from the temperature dependence of the diffraction peak intensities using the standard Debye–Waller formalism. The measured values are in good agreement with the results from a recent molecular dynamics simulation. [J. Hautman and M. Klein, J. Chem. Phys. 93, 7483 (1990).]
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.460082
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  • 8
    Electronic Resource
    Electronic Resource
    Molecular order at the surface of an organic monolayer studied by low energy helium diffraction (1989)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 91 (1989), S. 4421-4423 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We demonstrate that the surface structure of organic monolayers can be determined by low energy helium diffraction at low surface temperatures. This uniquely surface-sensitive and nondestructive technique shows that the CH3-terminated surface of a monolayer of docosane thiol (CH3(CH2)21SH) on Au(111) is composed of small, ordered domains (lattice constant 5.01±0.02 A(ring)), a large fraction of which share a common orientation. The helium diffraction intensities decrease monotonically with increasing temperature and vanish around 100 K, due to thermal motion of the CH3 groups. Surface order is observed for chains as short as ten carbons (CH3(CH2)9SH) but a shorter chain, (CH3(CH2)5SH), gave no diffraction.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.456776
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  • 9
    Electronic Resource
    Electronic Resource
    Hemoglobin quaternary structure change monitored directly by transient UV resonance Raman spectroscopy (1989)
    s.l. : American Chemical Society
    Journal of the American Chemical Society 111 (1989), S. 3457-3459 
    Details
    ISSN: 1520-5126
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/ja00191a068
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  • 10
    Electronic Resource
    Electronic Resource
    Erratum: "In situ studies of thiol self-assembly on gold from solution using atomic force microscopy" [J. Chem. Phys. 108, 5002 (1998)] (2000)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 113 (2000), S. 9357-9357 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1320001
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