Jian Shang

Lattice-Directed Formation of Covalent and Organometallic Molecular Wires by Terminal Alkynes on Ag Surfaces

Surface reactions of 2,5-diethynyl-1,4-bis(phenylethynyl)benzene on Ag(111), Ag(110), and Ag(100) were systematically explored and scrutinized by scanning tunneling microscopy, molecular mechanics simulations, and density functional theory calculations. On Ag(111), Glaser coupling reaction became dominant, yielding one-dimensional molecular wires formed by covalent bonds. On Ag(110) and Ag(100), however, the terminal alkynes reacted with surface metal atoms, leading to one-dimensional organometallic nanostructures. Detailed experimental and theoretical analyses revealed that such a lattice dependence of the terminal alkyne reaction at surfaces originated from the matching degree between the periodicities of the produced molecular wires and the substrate lattice structures.

On-Surface Synthesis and Characterization of Honeycombene Oligophenylene Macrocycles

We report the on-surface formation and characterization of [30]-honeycombene, a cyclotriacontaphenylene, which consists of 30 phenyl rings (C180H120) and has a diameter of 4.0 nm. This shape-persistent, conjugated, and unsubstituted hexagonal hydrocarbon macrocycle was obtained by solvent-free synthesis on a silver (111) single-crystal surface, making solubility-enhancing alkyl side groups unnecessary. Side products include strained macrocycles with square, pentagonal, and heptagonal shape. The molecules were characterized by scanning tunneling microscopy and density functional theory (DFT) calculations. On the Ag(111) surface, the macrocycles act as molecular quantum corrals and lead to the confinement of surface-state electrons inside the central cavity. The energy of the confined surface state correlates with the size of the macrocycle and is well described by a particle-in-the-box model. Tunneling spectroscopy suggests conjugation within the planar rings and reveals influences of self-assembly on the electronic structure. While the adsorbed molecules appear to be approximately planar, the free molecules have nonplanar conformation, according to DFT.

Steering Surface Reaction Dynamics with Self-Assembly Strategy

Ullmann coupling of 4-bromobiphenyl thermally catalyzed on Ag(111), Cu(111), and Cu(100) surfaces was scrutinized by scanning tunneling microscopy as well as theoretical calculations. Detailed experimental evidence showed that initial formation of organometallic intermediates on the surface, as self-assembled structures or sparsely dispersed species, is determined by the subsequent reaction pathway. Specifically, the assembled organometallic intermediates at full coverage underwent a single-barrier process to directly convert into the final coupling products, while the sparsely dispersed intermediates at low coverage went through a double-barrier process via newly identified clover-shaped intermediates prior to formation of the final coupling products. These findings demonstrate that a self-assembly strategy can efficiently steer surface reaction pathways and dynamics.Ullmann coupling of 4-bromobiphenyl thermally catalyzed on Ag(111), Cu(111) and Cu(100) surfaces was scrutinized by scanning tunneling microscopy as well as theoretical calculations. Detailed experimental evidence showed that whether the initially formed organometallic intermediate self-assembled or sparsely dispersed at surfaces essentially determined its subsequent reaction pathways. In specific, the assembled organometallic intermediates at full coverage underwent a single-barrier process to directly convert into the final coupling products while the sparsely dispersed ones at low coverage went through a double-barrier process via newly identified clover-shaped intermediates prior to their formation of the final coupling products. This demonstrates that the self-assembly strategy can efficiently steer surface reaction pathways and dynamics.

Morphological Evolution of In 2 O 3 Crystallites by Metallothermal Reaction Growth: A Unified Elucidation

Metallothermal reaction growth of In2O3 nanocrystals via chemical vapor deposition technique gave rise to different morphologies, ranging from octahedron to triamond triangular frustum and their corresponding truncated variants. The formation of these polyhedral crystalline structures was triggered by high local temperature and supersaturation ratios generated by the intensive exothermic reactions at the source. There are several distinct co-playing forces at work: kinetic and thermodynamic effects in the gas phase and surface nucleation and growth on the Si(111) substrate. The experimentally observed shape evolution and size variation can be rationalized in terms of a unified mechanism.

Sacrificial-Template-Assisted Syntheses of Aluminate and Titanate Nanonets via Interfacial Reaction Growth

Crystalline FeAlO3/FeAl2O4 nanonets were synthesized by a modified template-assisted approach using anodic aluminum oxide (AAO) as a reactive and sacrificial template to direct and promote interfacial reaction growth (IRG). The as-prepared nanonets replicate the morphology of the porous AAO template and contain mixed FeAlO3 and FeAl2O4. To extend the applicability of the sacrificial-template-assisted IRG approach, porous anodic titanium oxide (ATO) was used as template in place of AAO, giving rise to Zn2TiO4 nanonet/nanotube and PbTiO3 nanonet/nanotube. These latter products are polycrystalline due to the polycrystalline nature of the ATO template. Growth mechanism for the formation of the Zn2TiO4 and PbTiO3 nanostructures is proposed. The present study shows that the IRG approach can be extended to fabricate patterned complex oxide nanomaterials that may find applications in a wide range of nanotechnologies such as electronics, photonics and spintronics.