Insight into STM image contrast of n-tetradecane and n-hexadecane molecules on highly oriented pyrolytic graphite |
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Authors: | Miao Zhao Peng Jiang Ke DengAi-Fang Yu Yan-Zhong HaoSi-Shen Xie Jie-Lin Sun |
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Institution: | a National Center for Nanoscience and Technology, China. Zhong-Guan-Cun, Beiyitiao, No. 11, Beijing 100190, PR China b Beijing Institute of Aeronautical Materials, Beijing 100095, PR China c Hebei University of Science & Technology, College of Science, Shijiazhuang 050018, PR China d School of Life Science and Biotechnology, Shanghai Jiao Tong University, Shanghai 200240, PR China e Institute of Physics, Beijing National Lab for Condensed Matter Physics, Chinese Academy of Sciences (CAS), Beijing 100190, PR China |
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Abstract: | Two-dimensional ordered patterns of n-tetradecane (n-C14H30) and n-hexadecane (n-C16H34) molecules at liquid/graphite interface have been directly imaged using scanning tunneling microscope (STM) under ambient conditions. STM images reveal that the two different kinds of molecules self-organize into ordered lamellar structures in which alkane chains of the molecules extend along one of three equivalent lattice axes of highly oriented pyrolytic graphite (HOPG) basal plane. For n-C14H30 molecules, the molecular axes are observed to tilt by 60° with respect to inter-lamellar trough lines and the carbon backbones of the alkane chains are perpendicular to the HOPG basal plane in an all-trans conformation. However, for n-C16H34 molecules, the molecular axes are perpendicular to lamellar borders (90°) and the planes of the all-trans carbon skeletons are parallel to the graphite basal plane. The results clearly indicate that outmost hydrogen atoms of the alkane chains dominate atom-scaled features of the STM images. That is, in the case of long-chain alkane molecules, topographic effects dominantly determine STM image contrast of the methylene regions of the alkane chains that are adsorbed on HOPG. |
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Keywords: | Scanning tunneling microscope Self-assembly Alkane |
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