Structure of Normal Alkane Evaporated Films: Molecular Orientation
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The molecular orientations of $n$-alkane ($n$-C23H48, $n$-C24H50, $n$-C25H52, $n$-C26H54, and $n$-C27H56) evaporated films prepared by considering various deposition conditions, including the type of substrate, substrate temperature, and evaporation rate, have been systematically investigated by X-ray diffraction analysis and scanning probe microscopy. Two typical molecular orientation states, namely, the "perpendicular orientation state", in which the molecular chain axes are perpendicular to the substrate surface, and the "parallel orientation state", in which the molecular chain axes are parallel to the substrate surface, are observed. At a high substrate temperature and a low evaporation rate, a "perpendicular (P) film", which consists of only the perpendicular orientation state, is obtained. At a low substrate temperature and a high evaporation rate, a "coexistent (C) film", which consists of both the perpendicular and parallel orientation states, is obtained. It is concluded, from the experimental results, that the most thermodynamically stable is the perpendicular orientation state. Furthermore, it is found that the molecular orientation behavior depends on the type of substrate and deposition time. These molecular orientation dependences are considered to be mainly due to a kinetic mechanism rather than the thermodynamic stability in the case of the evaporated film in this study.
- Jpn J Appl Phys
Jpn J Appl Phys 46(2), 761-769, 2007-02-15
INSTITUTE OF PURE AND APPLIED PHYSICS