Incommensurate Crystalline phase of n-Alkane Monolayers on Graphite (0001)

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• 作者：Osamu Endo ; Toko Horikoshi ; Nobuyuki Katsumata ; Keita Otani ; Takumi Fujishima ; Hiromichi Goto ; Kazuhiro Minami ; Kouki Akaike ; Hiroyuki Ozaki ; Ryouhei Sumii ; Kenta Amemiya ; Masashi Nakamura ; Nobuhiro Kosugi
• 刊名：Journal of Physical Chemistry C
• 出版年：2011
• 出版时间：April 7, 2011
• 年：2011
• 卷：115
• 期：13
• 页码：5720-5725
• 全文大小：977K
• 年卷期：v.115,no.13(April 7, 2011)
• ISSN：1932-7455

文摘

An incommensurate crystalline phase of the (sub)monolayer of n-C₃₆H₇₄ lying on graphite (0001) is observed on cooling the smectic phase using normal incidence near edge X-ray absorption fine structure spectroscopy at the carbon K-edge (NI C K-NEXAFS) and scanning tunneling microscopy (STM). The orientation of the CCC plane of the all-trans alkyl chain with respect to the substrate is confirmed by the 1s 鈫?蟽_CH^*/R resonance detected by the NI C K-NEXAFS spectra at the absorption edge. Almost all molecules take the parallel (flat-on) orientation in the smectic phase, and at least half of them change to the perpendicular (edge-on) orientation in the incommensurate crystalline phase. A lamellar structure with a width corresponding to the chain length and no internal structure is observed by STM in the smectic phase, whereas that in the incommensurate crystalline phase exhibits a ladder-like structure with a periodicity of ca. 2 nm transverse to the chain direction. The periodicity is incommensurate with the substrate lattice. The molecular orientation in the ladder-like structure is related to the molecular width varying from 0.43 to 0.63 nm in the magnified STM image.