摘要/Abstract

利用超高真空低温扫描隧道显微镜系统研究了meso-四对甲氧基苯基卟啉钴分子在Au（111）、Ag（111）和Cu（111）表面的吸附与自组装.该分子在金属表面可以形成两种组装结构A和B.在结构A中，分子间的相互作用主要为π-π堆叠，仅在Au（111）和Ag（111）表面被实验观察到；在结构B中，分子间的相互作用为氢键，仅在Ag（111）和Cu（111）表面被实验观察到.分子-衬底相互作用的差异所引起的分子吸附构象变化被认为是导致不同衬底上的分子形成不同组装结构的原因.研究发现在不同衬底上，分子形成自组装结构的行为存在明显差异.在相近覆盖度下，未参与组装的分子的比例在Cu（111）表面最高，Au（111）次之，Ag（111）最低.表面上参与形成两种组装结构的分子与未参与组装的分子的比例还可通过覆盖度和退火来进行调控.
关键词: 钴卟啉, 分子自组装, 吸附构型, 结构调控, 扫描隧道显微镜
The adsorption and self-assembly of meso-tetra(p-methoxyphenyl)porphyrinatocobalt(Ⅱ)[Co(TAP)] on Au(111), Ag(111) and Cu(111) have been systematically studied by ultrahigh vacuum low-temperature scanning tunneling microscopy (STM). The atomically flat metal substrate surfaces are prepared by cycled ion sputtering and subsequent annealing at 750 K. Co(TAP) molecules are deposited onto the substrate surfaces via thermal evaporation from a home-made tantalum boat. The as-prepared samples are then annealed to achieve energetically stable self-assembly structures and transferred to the STM chamber for further analyses. All STM measurements are carried out at about 4.4 K. On these metal surfaces, Co(TAP) molecules mainly form two types of two-dimensional molecular assembly structures A and B. Structure A only exists on Au(111) and Ag(111), while Structure B merely appears on Ag(111) and Cu(111). The intermolecular interactions in Structures A and B are due to π-π stacking and hydrogen bonding, respectively. The difference in strength of the molecule-substrate interaction, which induces conformational changes of peripheral p-methoxyphenyl substituent in Co(TAP) on difference substrate, is attributed to govern the formation of different self-assembly structures on the aforementioned surfaces. The substrate surface also has an effect on the formation of the self-assembly structures. At similar coverage, the percentage of dispersed Co(TAP) molecules follow the sequence:Cu(111) > Au(111) > Ag(111). With the coverage increase, the percentage of dispersed Co(TAP) molecules decreases on all metal surfaces employed in this study. Specifically, on Au(111) and Ag(111), the dispersed Co(TAP) molecules disappear at coverages of about 1 ML and 0.1 ML, respectively, while on Cu(111) they survive even at the coverage of about 0.85 ML. In addition, Structure A gradually dominates on Au(111). On Cu(111), Structure B only occupies half of the surface structures even at nearly saturated coverage. The ratio of Structures A to B almost retains over the whole coverage range on Ag(111). Thermal annealing of the molecule-covered Ag(111) substrate helps the transformation from Structure B to A, and the elimination of the structural domain boundaries as well.
Key words: Co-porphyrin, molecular self-assembly, adsorption conformation, structural mediation, scanning tunneling microscopy


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