Weidong Dou

Electronic structures of CuPc on a Ag(110) surface

Copper phthalocyanines (CuPc) on a Ag(110) surface have been studied by ultraviolet photoemission spectroscopy (UPS). On depositing CuPc organic films, the features from the substrate 3d valence fade and four new features corresponding to the adsorbed molecules emerge at 1.68, 4.45, 6.36 and 9.20 eV below the Fermi level. These features shift in binding energy with increasing thickness of the organic films. In the case of a monolayer, angle-resolved UPS measurements suggest that the molecular plane is nearly parallel to the substrate. Further theoretical calculation indicates that the adsorption of CuPc on a hollow site is the most favourable configuration, and the separation between the adsorbate and the substrate is about 2.7 A.

Study on the interaction between tetracene and Cu(110) surface

The electronic structure of tetracene on Cu (110) surface has been studied by using ultraviolet photoemission spectroscopy (UPS). The emission features from the organic molecule are located from 1 to 10 eV below the Fermi level, and they shift in binding energy with increasing the coverage of the organic material. For the surface with multilayer of tetracene, six well-resolved features were found at 1.90, 3.40, 4.70, 5.95, 6.95, and 9.15 eV below the Fermi level, respectively. On the surface with a lower coverage of tetracene, angle-resolved UPS measurements suggest that the molecular plane is parallel to the substrate. Density functional theory calculation confirms the flat-lying adsorption mode and shows that the tetracene molecule prefers to be adsorbed on the long bridge site with its long axis in the [110] azimuth.

Coverage dependence of the structure of tetracene on Ag(110)

The ordered adsorption structures of tetracene on Ag(110) have been studied by low energy electron diffraction (LEED), scanning tunneling microscopy (STM) and density functional theory (DFT) calculations. At a low coverage, as calibrated with LEED, both p(4 x 4) and c(8 x 4) ordered structures are simultaneously formed on an Ag(110) surface at room temperature. STM images suggest the molecular plane is parallel to the Ag surface with its long molecular axis aligned along the [001] azimuth. DFT optimization reveals a separation of 0.3 nm between the molecular plane and substrate surface while the center of the tetracene molecule is on the long bridge site. Increasing coverage slightly, a structure is formed while the adsorbed molecules maintain the flat-lying geometry with adjacent molecules alternating their height relative to the surface.

Interfacial electronic states of tetracene deposited on Si(111)

The interfacial electronic states of tetracene on Si(111) 7x7 substrate were studied by using ultraviolet photoelectron spectroscopy (UPS). After deposition of tetracene on the Si(111) 7x7 surface, the features originating from the tetracene molecule appear at 1.55, 3.36, 6.78, 9.24, and 10.76 eV below the Fermi level; they shift in binding energy with increasing organic film coverage. From the UPS measurements, the work function of the sample surface was found to decrease with increasing molecular coverage in the submonolayer range suggesting that an interfacial dipole is formed. A density functional theory calculation had also been carried out to determine the favorable adsorption structure. The molecule near the top of a center adatom with the longer molecular axis along the [110] azimuth is the most favorable.

The chemisorption of tetracene on Si(100)-2×1 surface

The adsorption of tetracene on Si(100)-2x1 substrate has been studied by ultraviolet photoemission spectroscopy (UPS). Six features deriving from the organic material are located at 1.22, 2.41, 3.63, 4.67, 7.11, and 8.77 eV below the Fermi level. These features shift in binding energy with increasing the thickness of the organic film. In the case of a monolayer, angle-resolved UPS measurements suggest that the molecular plane is parallel to the substrate. Further theoretical density functional theory calculation reveals the most stable structure of tetracene molecule on Si substrate in which six covalent Si-C chemical bonds are formed between carbon atoms of the tetracene molecule and the Si atoms on the substrate.

Valence electronic properties of n-channel organic materials based on fluorinated derivatives of perylene diimides.

The valence electronic states of three kinds of fluorinated derivatives of perylene diimides, D2MFPP, D3MFPP, and D4MFPP, on Cu(110) and SiO(2)Si surface were studied by photoemission and density functional calculations. When these organic molecules were deposited on the Cu(110) and thermally oxidized SiO(2) surfaces, five well-resolved photoemission features originating from the molecules were observed. On Cu(110) surface, two emission features with pi-like character increased their binding energy with increasing the coverage of organic molecule, indicating a strong interaction between the organic molecules and Cu substrate. The density functional calculations suggest flat-lying adsorption geometry for D3MFPP and D4MFPP on Cu(110) surface.

Study of the electronic structure at the interface between fluorene-1-carboxylic acid molecules and Cu(110)

The interface electronic properties of fluorene-1-carboxylic acid (FC-1) adsorbed on Cu(110) have been studied by ultraviolet photoemission spectroscopy (UPS) and first-principles calculations. Both the molecular orbitals and the Cu valence band are significantly modified upon adsorption. FC-1 is chemically bonded to Cu(110) through charge donation and back donation involving the lowest unoccupied molecular orbital (LUMO) and the highest occupied molecular orbital (HOMO) of the molecule. An observed reduction of the work function can be attributed to the adsorption induced charge redistribution, and the positive interface dipole.