Controllable Synthesis Of Low- Dimensional Organic Nanostructures On Metal Crystal With DMTP

In the information age, the integrated circuit is the basis of informatization and intelligentialize in every walk of modern society, and evolves toward miniaturization and micromation rapidly. However, the traditional microfabrication has gradually reached its limit in the processing of microelectronic devices. In recent decades, various functional molecules which can act as switching, capacitor, rectifier and other electron devices have been synthesized. The key challenge of application of molecular electronic devices is how to connect these functional molecules sequentially and controllably on surface. Therefore, it is crucial to realize the controllable on-surface synthesis of one-dimensional nanowires which is conductive and stable.In this thesis, DMTP (4,4"-dibromo-meta-terphenyl) was chosen as the precursor, Cu(110) and Au(111) as the substrates. With scanning tunneling microscopy (STM), X-ray photoelectron spectroscopy (XPS) and low energy electron diffraction (LEED), we synthesized zigzag molecular wires and other low-dimensional organic nanostructures successfully and controllably though molecular self-assembly and Ullman reaction on surface. In addition, we also studied the phenomena and low-dimensional organic products such as molecular self-assembly, on-surface Ullman reaction, substrate template effects, organometallic intermediates and molecular wires. With the researches above, we proved that the structure and selectivity of organometallic intermediates and covalent molecular wires are influenced greatly by the substrate. In addition, the longest zigzag polyphenylene chains by far was synthesized successfully on Au(111) surface, the longest chain observed by STM images was up to 85 nm. The main achievements in this thesis are summarized as the following two aspects:1. The formation and structure of one-dimensional organometallic and covalent oligomers on a Cu(110) surface were studied with scanning tunneling microscopy (STM), X-ray photoemission spectroscopy (XPS), and low energy electron diffraction (LEED) in ultrahigh vacuum (UHV). Vapor deposition of submonolayer DMTP onto Cu(110) at 300 K leads to scission of C-Br bonds and the formation of organometallic chains (cis/trans and all-trans) connected by C-Cu-C bonds. Larger islands(120×120nm2) of all-trans zigzag organometallic chains as sole products were obtained by deposition of DMTP onto Cu(110) held at 383 K. The domains are oriented along two directions with an angle of ±13° relative to the [001] direction due to the two-fold symmetry of the Cu(110) surface lattice. This study reveals at a sub-molecular level that the organometallic chains firstly lose copper atoms and then undergo C-C coupling into oligophenylene chains at a substrate temperature around 417 K. Annealing the large islands of organometallic chains to 458 K results in the formation of completely C-C covalent bonded zigzag oligophenylene chains. The zigzag angle of 125° slightly deviates from the ideal value of 120°. This is attributed to a stretching of the zigzag oligophenylene chains due to substrate template effects.2. With scanning tunneling microscopy (STM) and X-ray photoelectron spectroscopy (XPS), we studied the surface-assisted bottom-up stepwise synthesis of conjugated zigzag polyphenylene in long range order on Au(111). Vapor deposition of submonolayer DMTP onto Au(111) at 300 K lead to ordered molecular assembly. Subsequent annealing to 353 K transformed the ordered self-assembled structure to Au-DMTP coordination nanomesh. Large islands of dimers as the sole product was obtained when annealled to 383 K. Conjugated zigzag polyphenylene were formed when annealled to or directly deposit DMTP onto Au(111) held at 473 K, the length of the chains is 30nm on average and 85 nm at most, the longest well-defined zigzag conjugated polyphenylene chains that have ever been synthesized on surface. The behavior of Br adatoms in the stepwise synthesis was observed by submolecular resolution STM images and XP spectra. The Br adatoms between polyphenylene chains desorbed at 623 K, resulting in the reduction of the interchain distance from 13.6 A to 8.0 A. Annealling the zigzag polyphenylene chains on Au(111) to 653 K lead to certain zigzag armchair GNRs with double or triple of the original width through dehydrogenation coupling between neighbouring chains.