FeO Ultrathin Layers And The Adsorbed TiOPc: An STM Study

In recent decades, ultrathin oxide films have stimulated great research enthusiasm because of their novel physical and chemical properties, which differ from those of their bulk counterparts, and play a pivotal role in high dielectric materials, solar cells, organic light-emitting diodes, heterogeneous catalysts as well as in the molecular based bottom-up nanotechnology. The periodic change in stacking between atoms in epitaxial oxide films and substrate is responsible for a spatial modulation of the surface properties:surface potential, dipole strength and work function. These properties vary periodically across the surface forming a suitable template for tuning molecular or clusters’adsorption and electronic states. In this thesis, the growth, structure and electronic properties of Pt(111) supported double-layer FeO and the adsorption of TiOPc molecules with tunable site and orientation were presented. The results indicate a template effect of FeO on TiOPc molecules. We also studied the area-selectviely assembly of TiOPc on monolayer FeO films. The molecules prefer to adsorb on FCC domains forming a regular rotors of dislocations. STM results reveal two kinds of molecular rotors, whose mechnism is explained by DFT calculations in detail.(1) We studied the growth of double-layer FeO on Pt(111) and found that the second FeO bilayer extends on the bottom terrace from the edge of the adjacent upper terrace. According to the atom positions deduced from the atomic-resolution STM image of the second FeO bilayer, we clarify and propose the lattice superstructure as. The second FeO bilayer is non-stoichiometric iron/oxygen ratios. The modulation of the epitaxial relation between both FeO bilayers induces the periodic variation of the total dipole moment. The resulted periodic distribution of dipole interaction between the polar TiOPc molecule and FeO layer effectively governs the molecular adsorption process. Tuning adsorption of the polar molecules with the nanostructured double-layer FeO provides a reliable method to govern area-selectively assemble polar molecules, not only the adsorption sites but also the molecular orientations, to explore their potential applications in future functional molecular devices. (2) Our field emission resonance experimental data demonstrates that the growth of FeO insulating layers leads a continuous reduction of the work function of the clean Pt(111) surface. By taking into account the atomic electronegativity and the detail stacking structures, we explain the mechanisms for the work function reduction. The significant morphology difference between the double-layer FeO STM images at the positive and negative bias indicates that the carrier barriers obviously change with the WF decrease. The current-voltage curves and the dI/dV spectra show remarkable rectifying effect. The substantial lowering of the WF decreases the electron injection barrier and increases hole-injection barrier. We made a qualitative analysis and discussion for the changes of the carrier injection barriers with schematic tunnel-junction energy diagram.(3) Our Low-temperature scanning tunneling microscopy results demonstrated that TiOPc molecules are sensitive to the regional differences and prefer to adsorb on FCC-region of FeO monolayer forming a regular rotors array of dislocations. The molecular configurations of non-planar TiOPc on surface could be O atom pointing to the substrate and the vacuum, which have significant influence on the interface properties, rotational rates and barriers. Experimental data combined with DFT calculations studied the detailed absorbed structures of the two kinds of molecular rotors and identified the correlation between STM apparent features and the actual adsorbed structures. At last, we explained mechanisms of the rotations with the adsorption details that reflect information of interaction.