He Pi-Mo

The ordered thin-film growth of organic semiconductor on Ag(110).

Growth of ordered perylene thin films on the Ag(110) surface has been investigated with scanning tunneling microscope. By saturating the surface with a monolayer of perylene molecules, two kinds of ordered structures are simultaneously formed with flat-lying perylene molecules on the Ag(110) surface, in which one is commensurate relative to the Ag substrate with a periodicity of while the other is commensurate with a periodicity of (-2724). There is one molecule within the former unit cell with a surface coverage of 0.1 molecule per Ag atom, while there are two molecules within the latter unit cell, which gives a slightly lower surface coverage of 0.091 molecule per Ag atom. Ab initio calculations have been carried out to identify the adsorption geometry and bonding sites.

The growth of perylene on Ru(0001)

The structure of perylene adsorbed on Ru(0001) surface has been studied by ultraviolet photoemission spectroscopy (UPS) and low-energy electron diffraction. An ordered p(4x4) structure is observed from a monolayer (about 4 A thickness) of the perylene on Ru(0001) surface. UPS measurements show the molecular features, from the perylene multiplayer, between 2 and 10 eV below the Fermi level. Angle-resolved ultraviolet photoemission spectroscopy measurements suggest that the perylene molecular plane is parallel to the substrate. Temperature dependent UPS measurements show that the perylene multilayer is stable on Ru(0001) surface up to 125 degrees C. The desorption of the multilayer and the decomposition of the monolayer are observed above 125 degrees C.

Adsorption behavior of iron phthalocyanine on a Ag(110) surface

An investigation on the growth behavior of FePc on a Ag (110) surface is carried out by using scanning tunneling microscopy (STM). At an FePc coverage of 3.5 ML, an ordered superstructure (densely packed) with a lateral shift is observed. The densely packed superstructure can be attributed to the substrate commensuration and the intermolecular van der Waals attractive interaction. The in-plane lateral shift in the superphase is specifically along the direction of [10] azimuth. The results provide a new perspective to understanding the intermolecular and the molecule—substrate interactions.

Pits and adatoms at the interface of 1-ML C84/Ag (111)

We prepare a well-defined C84 monolayer on the surface of Ag (111) and study the geometric structure by scanning tunneling microscopy (STM). The C84 molecules form a nearly close-packed incommensurate R30° lattice. The lattice is long-distance ordered with numerous local disorders. The monolayer exhibits complex bright/dim contrast; the largest height difference between the molecules can be greater than 0.4 nm. Annealing the monolayer at 380 °C can desorb part of the molecules, but more than sixty percent molecules stay on the Ag (111) surface even after the sample has been annealed at 650 °C. Our analyses reveal that the 7-atom pits form beneath many molecules. Some other molecules sit at the 1-atom pits. Ag adatoms (those removed substrate atoms, accompanying the pit formation) play a very important role in this system. The adatoms can either stabilize or destabilize the monolayer, depending on the distribution manner of the adatoms at the interface. The distribution manner is determined by the co-play of the following factors: the dimension of the interstitial regions of the C84 overlayer, the number of the adatoms, and the long-distance migration of part adatoms.

Geometric and Electronic Structures at the Interface between Iron Phthalocyanine and Si (110)

The geometric and electronic structures at the interface between iron phthalocyanine (FePc) and Si(110) surface are studied by ultraviolet photoelectron spectroscopy and density functional theory (DFT) calculation. After FePc is deposited on Si(110), the emission features are located at 2.56, 4.90, 7.90, 10.88 eV below the Fermi level for monolayer and 2.73, 4.90, 7.74, 10.52 eV below the Fermi level for multilayer. At the coverage of 1 ML, FePc molecules are adsorbed on the bridge site in a flat-lying geometry with a 2.17 A separation between the molecule and the substrate. The molecular plane is bent due to the interaction between the adsorbate and the substrate.

Mn overlayers on PbTe (111): Substitutional adsorption and interface formation

The formation of the Mn/PbTe (111) interface is investigated by photoemission spectrum. The core level behavior of Mn 2p is consistent with Mn substitutional adsorption during the initial Mn deposition, forming a (√3 × √3)R30°-Pb0.67Mn0.33Te phase of the second layer. Further deposition of Mn can cause metallic Mn islands to cover the substitutional substrate. Ultraviolet photoemission measurements show that the Fermi level is shifted into the conduction band, indicating Ohmic contact formation at the Mn/PbTe (111) interface. The valence band maximum associated with the Pb0.67Mn0.33Te layer is located at 1.27 eV below the Fermi level, and a schematic electronic structure of the Mn/PbTe (111) interface is given. The work function of the substituted substrate with Pb-covered Mn islands is determined to be 4.16 eV, in comparison with 4.35 eV for the Pb-covered substituted substrate and 3.95 eV for the pristine PbTe (111) surface.

A shortcut for determining growth mode

Thin and thick films of iron phthalocyanine (FePc) molecules are deposited on a Ag (110) surface. The nature of the FePc growth and the interaction with the substrate have been studied by X-ray photoelectron spectroscopy (XPS). All of the core level spectra exhibit rigid shifts towards lower binding energies following the deposition of the organic films, each by a different magnitude. A greater change and a larger shift in the Fe2p level as compared to C1s core level reveals that the adsorbate interacts with the substrate mainly via the Fe atom, located at the center of the molecule. An increase/decrease in the intensity of C1s/Ag3d level is found to be exponentially linked to the overlayer molecular coverage. Finally, the so-called growth/decay curve indicates that FePc thin films initially develop following the FM growth mode and then transform to SK mode, resulting in 3D island aggregation.