Ordered mono- and multilayer films of sexiphenyl on Al(111): a LEED investigation (original) (raw)
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Epitaxial Growth of Sexiphenyl on Al(111): From Monolayer to Crystalline Films
Langmuir, 2004
A combination of in situ surface sensitive-techniques, UV photoemission and low energy electron diffraction, with ex situ bulk sensitive X-ray diffraction reveals the formation of epitaxial thin films of sexiphenyl on Al(111) starting from the first monolayer. For room temperature growth, highly ordered films are formed with a unique alignment of the sexiphenyl molecules with the long axes of all molecules aligned parallel to both the surface and the 〈11 h0〉 azimuthal directions of Al(111). This is related to a densely packed highly commensurate first monolayer, which acts as a template for the unique (213 h) crystallite orientation observed.
Structure and morphology of sexiphenyl thin films grown on aluminium (1 1 1)
2004
The epitaxial growth of sexiphenyl (C 36 H 26 ) on an atomically clean aluminium (1 1 1) surface is studied on the basis of thin films grown at different substrate temperatures. Thin films with an average thickness of 350 A are investigated by X-ray diffraction techniques and atomic force microscopy. Grown at room temperature the films show epitaxial order. It is found that the aromatic planes of sexiphenyl are oriented parallel to Al(1 1 1) and the long axes of the sexiphenyl molecules are aligned along a AE1 )1 0ae azimuthal direction at the Al(1 1 1) surface. The films grow in islands with average lateral dimensions up to of 200 nm and to 50 nm in height, the areas between the islands are observed as rather flat. The films grown at 150°C show a completely different morphology: occasional large islands and irregularly distributed segmented needles with a relatively constant width of about 0.5 lm, lengths up to 100 lm and heights of about 600 nm.
The epitaxial sexiphenyl (001) monolayer on TiO2(110): A grazing incidence X-ray diffraction study
Surface Science, 2006
A para-sexiphenyl monolayer of near up-right standing molecules (nominal thickness of 30 Å ) is investigated in-situ by X-ray diffraction using synchrotron radiation and ex-situ by atomic force microscopy. A terrace like morphology is observed, the step height between the terraces is approximately one molecular length. The monolayer terraces, larger than 20 lm in size, are extended along the [0 0 1] direction of the TiO 2 (1 1 0) substrate i.e. along the Ti-O rows of the reconstructed substrate surface. The structure of the monolayer and its epitaxial relationship to the substrate is determined by grazing incidence X-ray diffraction. Extremely sharp diffraction peaks reveal high crystalline order within the monolayer, which was found to have the bulk structure of sexiphenyl. The monolayer terraces are epitaxially oriented with the (0 0 1) plane parallel to the substrate surface (out-of-plane order). Four epitaxial relationships are observed. This inplane alignment is determined by the arrangement of the terminal phenyl rings of the sexiphenyl molecules parallel to the oxygen rows of the substrate.
In-plane alignment of para-sexiphenyl films grown on KCl(0 0 1)
Applied Surface Science, 2002
The three-dimensional growth of para-sexiphenyl (p-6P) on KCl(0 0 1) is characterized by a large polymorphism. Using grazingincidence diffraction, we have found that two of the known ®ve orientational phases feature preferential in-plane alignments along the [1 1 0] in-plane direction of the substrate: p-6P(1 1 À1) k KCl(0 0 1) with [1 À1 0] k KCl[1 1 0] as well as p-6P(0 0 1) k KCl(0 0 1) with [1 À1 0] k KCl[1 1 0]. The latter structure is a peculiar low-symmetry con®guration, which can be understood by analysis of the molecular crystal lattice and the substrate symmetry. #
Molecular alignments in sexiphenyl thin films epitaxially grown on muscovite
Thin Solid Films, 2003
The epitaxial orientations of highly crystalline para-sexiphenyl (C H ) films on mica (001) surfaces are investigated by 36 26 selected area electron diffraction (SAED) and transmission electron microscopy (TEM). Films at the early growth stage (growth time 26 s) and at an advanced growth stage (growth time 10 min) are studied. Films at the early growth stage exhibit only threedimensional islands with an average size of 60=30=10 nm , whereas films at an advanced growth stage consist of long oriented 3 nano-fibres with a needle-like morphology. We identified three different types of epitaxial relations between the mica (001) substrate and the sexiphenyl crystallites, which are the same in both growth stages. Moreover, within a single island as well as within a single fibre crystalline domains with these three epitaxial orientations are observed. At the advanced growth stage, these domains are aligned antiparallel or perpendicular to the fibre axes; the typical size of the domains is 20 nm. ᮊ
The formation of crystalline para-sexiphenyl (6P) films on Cu(110) and Cu(110)-(2 Â 1)O (Cu-O) has been studied by low energy electron diffraction, X-ray absorption spectroscopy and both in situ and ex situ X-ray diffraction methods to elucidate the transition from the initial monolayers to crystalline thin films. It is found that, for Cu-O, a single and, for Cu(110), a double wetting layer is formed which then acts as a template for the subsequent 3D crystal growth. For both substrates the orientation of the long molecular axes of the 6P molecules in the first layers is conserved for the molecules in the bulk crystals growing on them. The main difference between both systems is that on Cu-O the first monolayer assembles in a form close to that of a 6P bulk plane which can be easily continued by crystallites grown upon them, while on the Cu(110) surface the 6P mono-and bi-layers differ substantially from the bulk structure. The bi-layer forms a complex periodically striped phase. Thin 6P films grow with the 6P(20 % 3) crystal plane parallel to the Cu-O substrate surface. For this orientation, the 6P molecules are stacked in layers and the molecules demonstrate only one tilt of the mean molecular plane with respect to the sample surface. On clean Cu(110), a more complex 6P( % 629) plane is parallel to the substrate surface and this orientation is likely a consequence of the super-molecular long-range periodicity of the second molecular layer striped phase.
Highly ordered anisotropic nano-needles in para-sexiphenyl films
Thin Solid Films, 2002
Atomic force microscopy (AFM) was used to investigate the early growth stage of highly ordered para-sexiphenyl thin films deposited by hot wall epitaxy on mica, in order to find the process controlling parameters. It was shown that the growth time and surface type are important parameters for controlling of the film morphology, in terms of the degree of anisotropy and long range order. X-Ray diffraction pole figure technique and transmission electron diffraction was also used to characterize the crystallographic structure of the thicker films. ᮊ
Revealing the buried interface: para-sexiphenyl thin films grown on TiO2(110)
Physical Chemistry Chemical Physics, 2010
The thickness dependent optical and electronic structure of para-sexiphenyl thin films grown on TiO 2 (110) at around 400 K reveals that the substrate is first wet by one monolayer of molecules lying with their long axis parallel to the [001] direction of the substrate, while the molecules in subsequent layers are almost standing upright. Whilst ultraviolet photoemission spectroscopy (UPS) is sensitive to the molecules in the outermost layer, reflection difference spectroscopy (RDS) shows that the molecules at the buried interface do not dewet and maintain the orientation of the original wetting monolayer.