Hibino Masahiro, Tsuchiya Hiroshi
J Nanosci Nanotechnol. 2014 Apr;14(4):2996-3000. doi: 10.1166/jnn.2014.8552.
Self-assembled monolayers of hexadecyl sulfide adsorbed on a graphite surface were studied using scanning tunneling microscopy (STM). STM images of the molecule indicate a bright spot and two relatively dim thin bands that correspond to the sulfur atom positioned at the center of the molecule and two alkyl chains that extend linearly from the sulfur atom, respectively. The contrast of the bands changes reversibly between the zigzag and aligned bright spots, which correspond to the zigzag methylene units of the alkyl chains; accordingly, the methylene units alternate between parallel and perpendicular orientations to the surface, respectively, on a time scale of minutes. The variation in contrast indicates cooperative rotation along the long axis of the molecules in the monolayer at the liquid-graphite interface. The reversibility of the contrast suggests that the solvent influences the difference in the free energies of the parallel and perpendicular configurations of the molecules with respect to the graphite surface.
利用扫描隧道显微镜（STM）研究了吸附在石墨表面的十六烷基硫自组装单分子层。该分子的STM图像显示一个亮点和两条相对较暗的细带，分别对应于位于分子中心的硫原子和从硫原子线性延伸的两条烷基链。这些带的对比度在锯齿形和对齐的亮点之间可逆变化，这对应于烷基链的锯齿形亚甲基单元；因此，亚甲基单元分别在与表面平行和垂直的方向之间以分钟为时间尺度交替变化。对比度的变化表明在液-石墨界面的单分子层中，分子沿长轴协同旋转。对比度的可逆性表明溶剂影响分子相对于石墨表面的平行和垂直构型的自由能差异。
