Influence of molecular structure on phase transitions:: A study of self-assembled monolayers of 2-(aryl)-ethane thiols
Influence of molecular structure on phase transitions:: A study of self-assembled monolayers of 2-(aryl)-ethane thiols
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DOI：
10.1021/jp073979k
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发表时间：
2007-11-15
影响因子：
3.7
通讯作者：
Woell, Christof
中科院分区：
文献类型：
--
作者：
Cyganik, Piotr;Buck, Manfred;Woell, Christof
从欧米伽-溶液在Au（111）基底上制备的自组装单层（SAMs）（4 '-甲基联苯-4-基）乙硫醇（CH 3（C6 H4）（2）（CH 2）（n）SH，n = 2，BP 2），并随后在高达423 K的温度下退火，使用扫描隧道显微镜，低能电子衍射，高分辨X射线光电子能谱，和近边X射线吸收精细结构光谱。在退火时，发生相变，从低温（5根3 × 3）的结构共同的所有自组装膜制备的系列BPn同系物与n =甚至研究到目前为止，一个新的结构，这是显着不同的高温相的更高的BPn同系物。虽然其基本结构可以近似为（2根3 × 2）单位晶胞，但仅沿沿着11（2）方向运行的线缺陷的规律性出现是该新相的最典型特征。无论这些缺陷的相变显着提高了稳定性的BP 2单层交换实验所证明的。与BP 2相反，由密切相关的2-苯基乙烷硫醇（C6 H5（CH 2）（2）SH，P2）制成的SAM不显示任何相变。BP 2、其高级同系物和P2之间的差异突出了决定SAM结构的不同因素之间相互作用的微妙之处。
Self-assembled monolayers (SAMs) prepared on Au(111) substrates from solutions of omega-(4'-methylbiphenyl-4-yl)ethane thiol (CH3(C6H4)(2)(CH2)(n)SH, n = 2, BP2), at room temperature and subsequently annealed at temperatures of up to 423 K were studied using scanning tunneling microscopy, low-energy electron diffraction, high-resolution X-ray photoelectron spectroscopy, and near-edge X-ray absorption fine structure spectroscopy. Upon annealing a phase transition occurs from the low-temperature (5 root 3 x 3) structure common to all SAMs prepared from the series of BPn homologues with n = even studied so far, to a new structure which is markedly different from the high-temperature phases of the higher BPn homologues. Although its basic structure can be approximated by a (2 root 3 x 2) unit cell, the regular occurrence of line defects running exclusively along the 11 (2) over bar direction is the most characteristic feature of this new phase. Irrespective of these defects the phase transition dramatically improves the stability of the BP2 monolayer as demonstrated by exchange experiments. In contrast to BP2, SAMs made from the closely related 2-phenylethane thiol (C6H5(CH2)(2)SH, P2) do not show any phase transition. The differences between BP2, its higher homologues, and P2 highlight the subtleties of the interplay of different factors determining the structure of a SAM.