State Key Laboratory of Polymer Physics and Chemistry, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, Changchun 130022, People's Republic of China.
J Phys Chem B. 2012 Feb 16;116(6):1812-8. doi: 10.1021/jp210535q. Epub 2012 Feb 6.
Weak epitaxy growth (WEG) is an effective method in the preparation of high-mobility thin films of disk-like organic semiconductors. The growth behavior and quality of the epitaxial thin film are closely related to the inducing layers. Here, a series of fluorinated molecules, 5,5"-bis(3'-fluoro-biphenyl-4-yl)-2,2':5',2"-terthiophene (m-F2BP3T), 5,5"-bis(3',5'-difluoro-biphenyl-4-yl)-2,2':5',2"-terthiophene (F4BP3T), and 5,5"-bis(4'-fluoro-biphenyl-4-yl)-2,2':5',2"-terthiophene (p-F2BP3T) as well as a referenced molecule 5,5"-bis(biphenyl-4-yl)-2,2':5',2"-terthiophene (BP3T), are introduced to serve as inducing layers for the epitaxy growth of phthalocyanine. Compared to the nonfluorinated inducing layer, the interactions between the fluorinated inducing layer and phthalocyanine might be relatively strong due to the potential existence of C-H···F weak hydrogen bonds. The growth behavior and mechanism of phthalocyanine on the fluorinated inducing layers are investigated by atomic force microscopy (AFM), grazing incidence X-ray diffraction (GIXD), selected area electron diffraction (SAED). According to the AFM and SAED, H(2)Pc presents a selective epitaxy growth depending on the position of fluorine: epitaxy growth on m-F2BP3T and F4BP4T, and nonepitaxy growth on p-F2BP3T. Comparison of CuPc with F(16)CuPc on monolayer p-F2BP3T further revealed that the uncommon nonepitaxy growth behavior of H(2)Pc (CuPc) on p-F2BP3T mainly originates from the enhanced interactions between the two types of molecules. As a consequence, the capability of molecules orienting themselves along the surface channel is decreased; meanwhile, the demand of the upper limit of the lattice mismatch is more rigorous for commensurate epitaxy. Finally, the oriented nucleation of H(2)Pc (CuPc) on monolayer p-F2BP3T is affected, and netlike crystals are formed. The sudden change of H(2)Pc (CuPc) from multiorientation on monolayer to just one orientation on double-layer p-F2BP3T suggests that there is a critical lattice mismatch value for commensurate epitaxy in WEG when the molecule-substrate interactions are enhanced.
弱外延生长（WEG）是制备高迁移率盘状有机半导体薄膜的有效方法。外延薄膜的生长行为和质量与诱导层密切相关。在这里，我们引入了一系列氟化分子，5,5'-双（3'-氟联苯-4-基）-2,2':5',2"-三联噻吩（m-F2BP3T）、5,5'-双（3',5'-二氟联苯-4-基）-2,2':5',2"-三联噻吩（F4BP3T）和 5,5'-双（4'-氟联苯-4-基）-2,2':5',2"-三联噻吩（p-F2BP3T）以及参考分子 5,5'-双（联苯-4-基）-2,2':5',2"-三联噻吩（BP3T）作为诱导层，用于外延生长酞菁。与非氟化诱导层相比，由于可能存在 C-H···F 弱氢键，氟化诱导层与酞菁之间的相互作用可能相对较强。通过原子力显微镜（AFM）、掠入射 X 射线衍射（GIXD）、选区电子衍射（SAED）研究了酞菁在氟化诱导层上的生长行为和机制。根据 AFM 和 SAED，H(2)Pc 呈现出依赖于氟位置的选择性外延生长：在 m-F2BP3T 和 F4BP4T 上外延生长，而在 p-F2BP3T 上无外延生长。在单层 p-F2BP3T 上比较 CuPc 和 F(16)CuPc 进一步表明，H(2)Pc（CuPc）在 p-F2BP3T 上的异常非外延生长行为主要源于两种分子之间相互作用的增强。因此，分子沿表面通道取向的能力降低；同时，对于共格外延，对上限晶格失配的要求更加严格。最后，影响 H(2)Pc（CuPc）在单层 p-F2BP3T 上的定向成核，形成网状晶体。H(2)Pc（CuPc）从单层上的多取向突然变为双层 p-F2BP3T 上的单一取向，表明在外延生长过程中，当分子-衬底相互作用增强时，存在一个共格外延的临界晶格失配值。
