1,6-hexanedithiol monolayers on Au(111): A multitechnique structural study
Monolayers of 1,6-hexanedithiol [HS(CH{sub 2}){sub 6}SH] deposited on Au(111) from the gas phase were characterized by scanning tunneling microscopy (STM), grazing incidence X-ray diffraction (GIXD), and low-energy atom diffraction (LEAD). Molecular resolution STM images suggest that the molecules lie prone in a striped arrangement with an inter-row spacing of 5 {angstrom}. For the films prepared at an elevated temperature, two uniaxial incommensurate phases were found by GIXD. With respect to the surface substrate net, the diffraction patterns of both phases can be described by rectangular (p x {radical}3) nets, where p is 4.24 {+-} 0.01 and 4.30 {+-} 0.01. These values of p correspond to spacings of 12.23 {+-} 0.04 and 12.40 {+-} 0.02 {angstrom} along the nearest-neighbor (NN) direction of the substrate, whereas the spacing along the next-nearest-neighbor direction is 5 {angstrom} in both cases. The LEAD patterns can be described by a 3 x 1 superlattice with respect to the mesh observed by GIXD. Lattice nonuniformity and angular broadening along the NN direction were observed by GIXD. The structure of the striped phases is consistent with the molecules being fully extended and flat on the surface with their molecular C-C-C plane parallel to the surface. Using different growth protocols, including liquid-phase deposition, the order of the striped phases was observed to change considerably; however, no evidence of nucleation of other ordered phases was found. Even if denser phases exist, the striped phases may act as effective kinetic traps preventing the transition to other denser phases. The results of both varied growth conditions and performed annealing experiments can be explained by the strong molecule/substrate interaction in the striped phases, which is a consequence of the strong, but not site-specific, interaction of both sulfur atoms with the gold surface.
- Research Organization:
- Princeton Univ., NJ (US)
- Sponsoring Organization:
- USDOE
- DOE Contract Number:
- FG02-93ER45503; AC02-76CH00016
- OSTI ID:
- 20015184
- Journal Information:
- Langmuir, Vol. 16, Issue 2; Other Information: PBD: 25 Jan 2000; ISSN 0743-7463
- Country of Publication:
- United States
- Language:
- English
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