Neutron diffraction study of p-phenylene oligomer molecules adsorbed onto graphite

• Published in: Thin solid films Vol. 518; no. 14; pp. 3786 - 3791
• Main Authors: Kintzel, E.J., Herwig, K.W., Rols, S.
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier B.V 03.05.2010; Elsevier
• Subjects: Applied sciences; AROMATICS; Cross-disciplinary physics: materials science; rheology; DIFFRACTION; Electronics; Exact sciences and technology; Fullerenes and related materials; diamonds, graphite; GRAPHITE; LATTICE PARAMETERS; Materials science; MELTING; Monolayers; NEUTRON DIFFRACTION; Neutron scattering; NEUTRONS; Optoelectronic devices; p-Phenylene oligomers; Physics; PHYSICS OF ELEMENTARY PARTICLES AND FIELDS; SCATTERING; Semiconductor electronics. Microelectronics. Optoelectronics. Solid state devices; Specific materials; SUBSTRATES; THERMAL EXPANSION; Optoelectronic devices; p-Phenylene oligomers; Neutron scattering; Monolayers; Graphite; Molecular arrangement; Temperature dependence; Neutron diffraction; Two dimensional structure; Lattice parameters; Neutron diffusion; Thin films; Oligomers; Thermal expansion; Bilayers; Crystal structure
• ISSN: 0040-6090; 1879-2731
• DOI: 10.1016/j.tsf.2010.01.001

Neutron scattering experiments have been carried out on low-coverage films of the aromatic p-phenylene oligomer molecules ( p-nP, C 6 n H 10 + 4( n − 2), where n indicates the number of phenyl units per molecule) physisorbed onto the surface of graphite. The molecular arrangement within these films has been determined as a function of temperature, number of molecular layers, and molecular length. Analysis of the diffraction data reveals two-dimensional film structures consistent for molecules having their long-axis parallel to the underlying substrate. The experimental measurements provide evidence for a melting transition in a monolayer film and thermal expansion of a bilayer film of p-terphenyl ( p-3P). The planes of the phenyl rings are approximately parallel to the substrate in the monolayer structure but rotate out of this plane by 60 ± 20° in the bilayer film of p-3P. As the number of phenyl units is increased from n = 3 to n = 6, bilayer structures are observed having similar packing arrangements of the molecules but with lattice parameters that scale with molecular length.