Curriculum Vitae December 2006

Transcription

1 Appendix: (A brief description of some representative results) (1) Electronic states of Pb adatom and Pb adatom chains on Pb(111) have been investigated by spatially scanning tunneling spectroscopy (STS) at ~6 K. Isolated Pb adatoms were created in situ by controlled tip-sample contact. The di/dv images of Pb adatom and chains were obtained by lock-in technique. Single Pb adatom on Pb(111) terrace was imaged as spherically bright protrusion with an apparent height of 1.2±0.2 Å and a full width at half maximum (FWHM) of 10 Å. We observe a clear spatial inhomogeneity, i.e. a butterfly-like feature, for the spectral density of the Pb adatom in the di/dv image, as shown in Fig. 1. Figure 1 STM topography and simultaneously acquired di/dv images of single Pb adatom on Pb(111). (a) Topography image of an isolated Pb adatom; V = 100 mv, I = 2.0 na; (b) di/dv image of the same area, acquired simultaneously with the topography image in (a). Dark to light corresponds to increasing the conductance. By repeated and controlled lateral manipulations, individual Pb adatoms were placed at designated positions to build atomic chain, as shown in Fig. 2. An energy-dependent oscillating feature was observed in the corresponding di/dv images, as shown in Fig. 2. The emerging electronic density oscillations are evident in all these images along the chains in the plane parallel to the substrate surface. The phases of the oscillations change with the sample 1

2 bias changing, but the wavelength is constant. Figure 2 STM topography and simultaneously acquired di/dv images of single Pb adatom chain on Pb(111). Topography image (V = 1.50 V, I = 1.5 na) of a Pb adatom chain is shown in the first image. The rest are the di/dv images of the same area, acquired simultaneously at indicated sample bias. Dark to light corresponds to increasing the conductance. (2) Local adsorption, self-assembly and electronic structures of Iron(II) Phthalocyanine (FePc) molecules on Au(111) surface is studied with low-temperature scanning tunneling microscopy (LT-STM) at ~5 K. At low surface coverages, FePc molecules are clearly resolved to prefer to adsorb on terrace dispersedly as isolated adsorbates due to the weakness of lateral intermolecular interaction. At medium surface coverages, the FePc molecules assemble to form dimers, trimers and short chains, even peculiar porous hexamers. The results indicate that the adsorption behavior of FePc on Au(111) surface is governed by a coverage-dependent competition between molecule-substrate and the laterally intermolecular interactions. 2

3 Figure 3 STM images of FePc molecules on Au(111) surface. (a) ~0.1 ML (60 nm 60 nm, V = -1.5 V, I = 0.05 na); (b) ~0.3 ML (50 nm 50 nm, V = -2.0 V, I = 0.05 na); (c) ~0.6 ML (40 nm 40 nm, V = -1.5 V, I = 0.05 na); (d) ~0.6 ML (20 nm 20 nm, V = -1.5 V, I = 0.05 na). At saturated coverage, highly ordered FePc monolayer with quadratic commensurate superstructure are observed. When the FePc goes further to the second layer, the unit cell of the molecular superstructure just shifts compared with the unit cell of the first layer. The FePc molecules in the first layer are recognized as a four-lobed cross structure with a protrusion at the center, which is consistent with its chemical structure, indicating a flat-lying adsorption geometry on Au(111) surface. The FePc molecules in the second layer exhibit a triangle structure with only three lobes and a central protrusion, indicating a non-planar adsorption configuration. 3

4 Figure 4 STM images of FePc molecules on Au(111) surface. (a) 60 nm 60 nm, V = -0.4 V, I = 0.05 na; (b) 10 nm 10 nm, V = -0.4 V, I = 0.05 na; (c) 50 nm 50 nm, V = -2.2 V, I = 0.05 na; (d) 10 nm 10 nm, V = -2.2 V, I = 0.05 na. A large area of perfect first FePc layer on Au(111) is shown in (a), its unit cell and one molecule are marked in (b). A large area of perfect second FePc layer on Au(111) is shown in (c), its unit cell and one molecule are marked in (d). The STM spatial resolution can be enhanced by picking up a molecule with the STM tip. We functionalized the tip by transferring a molecule to the tip apex to sharpen the STM tip, then to see the molecules intramolecularly. The richer-featured STM images of FePc and ZnPc molecules than those with the bare tip are obtained, as shown in Fig. 5. 4

5 Figure 5 Close-up STM images of single FePc and ZnPc molecules on Au(111) obtained with bare metallic tip and functionalized tip. (a) 2 nm 2 nm, V = -0.4 V, I = 0.05 na; FePc, a bare metallic tip. (b) 2 nm 2 nm, V = -0.4 V, I = 0.05 na; FePc, a functionalized tip. (c) 2 nm 2 nm, V = -1.6 V, I = 0.1 na; ZnPc, a bare metallic tip. (d) 2 nm 2 nm, V = -1.6 V, I = 0.1 na; ZnPc, a functionalized tip. As to the molecules directly adsorbing on a metal surface, its electronic states are strongly influenced by a direct coupling to the electronic states of the substrate. So no intramolecular features are observed for the FePc molecules directly on Au(111) with bare STM tip. As to the molecules on the first layer, the FePc molecules can preserve their intrinsic electronic states due to the first layer as a buffer layer. The rich features were observed within the molecules on the first layer with a sharp bare metallic tip, which should be their intrinsic orbitals, as shown in Fig. 6. 5

6 Figure 6 The top part: STM images (3 nm 3 nm, I= 0.05 na) of single FePc molecule flatly adsorbing on the first FePc layer on Au(111), taken at indicated sample bias. The bottom part: the corresponding STM images (3 nm 3 nm, I= 0.05 na) of FePc molecules within the first layer directly adsorbing on Au(111). 6