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- Creator:
- Huan, Qing, Cheng, Zhihai, Gao, Li, Zhang, Lizhi, Jiang, Nan, Liu, Qi, Guo, Haiming, Lin, Xiao, Du, Shi-Xuan, Deng, Zhitao, He, Xiao-Bo, and Gao, Hong-jun
- Description:
- Adsorption behavior of iron-phthalocyanine (FePc) at low submonolayer coverage on a reconstructed Au(111) single crystalline surface was investigated by a combination of low temperature scanning tunneling microscopy (STM) and density functional theory (DFT) calculations. A site- and orientation-selective adsorption was found at different temperatures and molecular coverages by means of STM. Further DFT calculations demonstrate that the energy difference between different adsorption configurations leads to the selectivity, and thus the formation of one-dimensional molecular chains on the monatomic step edges in the fcc surface reconstruction domains. The exact adsorption site and configuration of the FePc molecule as well as the simulated STM images are obtained on the basis of DFT calculations, which is in good agreement with experimental observations.
- Resource Type:
- Article
- Identifier:
- 1932-7447
- Campus Tesim:
- Northridge
- Creator:
- Cheng, Zhihai, Gao, Li, Shi, Dong-Xia, Jiang, Nan, Liu, Qi, Guo, Haiming, Du, Shi-Xuan, Gao, Hong-jun, and Deng, Zhitao
- Description:
- Adsorption behavior of iron(II) phthalocyanine (FePc) on Au(111) surface at submonolayer coverage has been investigated using low-temperature scanning tunneling microscopy (STM) and density functional theory (DFT) calculations. At the initial adsorption stage, FePc molecules prefer to adsorb on terrace dispersedly as isolated adsorbates because of the stronger molecule?substrate interaction than the lateral intermolecular interaction. Two different configurations of FePc on Au(111) surface are resolved on the basis of STM image analysis and are further identified by DFT calculations. When increasing molecule coverage, the intermolecular interaction becomes more important. The FePc molecules assemble to dimers, trimers, and short chains and even peculiar porous hexamers with two configurations. At a saturated coverage, highly ordered FePc monolayer with only one configuration of FePc is observed. The results indicate that the adsorption behavior of FePc on Au(111) is governed by a coverage-dependent competition between molecule?substrate and intermolecular interactions.
- Resource Type:
- Article
- Identifier:
- 1932-7447
- Campus Tesim:
- Northridge
- Creator:
- Cheng, Zhihai, Du, Shi-Xuan, He, Xiao-Bo, Deng, Zhitao, Hu, H., Gao, Hong-jun, Gao, Li, Sun, J.T., Lin, Xiao, and Liu, Feng
- Description:
- Two surface reconstruction patterns, strikingly different from the Au(111) intrinsic herringbone reconstruction, have been observed at the interfaces between Au(111) and the self-assembled monolayer of perylene or iron phthalocyanine by scanning tunneling microscopy (STM). These interfacial structures, elucidated by using the two-dimensional Frenkel-Kontorova model and density-functional theory (DFT) calculations, are attributed to the anisotropic surface stress induced by interfacial charge transfer. The length scales of the induced reconstruction periodicities are theoretically estimated, in quantitative agreement with experiments. Our findings afford the possibility of tailoring the contact structure of molecular electronic devices by molecular and surface engineering.
- Resource Type:
- Article
- Identifier:
- 2469-9950
- Campus Tesim:
- Northridge
- Creator:
- Shi, Dong-Xia, Wang, Kang L., Goel, Niti, Hicks, Robert F., Deng, Zhitao, Woo, Robyn L., Kodambaka, Suneel, Gao, Li, Cheng, Zhihai, Guo, Haiming, Hudait, Mantu K., Guo, Wei, and Gao, Hong-jun
- Description:
- The self-assembly behavior of the mixture of tetra-tert-butyl zinc(II) phthalocyanine (TB-ZnPc) isomers on a Au(111) surface has been investigated by means of scanning tunneling microscopy (STM). Four tert-butyl groups are added to four peripheral benzene rings of zinc(II) phthalocyanine, which gives the planar molecules a three-dimensional structure. Two possible substituting locations for each tert-butyl group result in a mixture of structural isomers, which are easily identified by STM. Two different structures have been distinguished in the monolayer regime depending on the preparation procedure. One is a quasi-ordered structure whereby the molecules are arranged in the closest-packed way, and the second is an ordered structure in which the molecules are arranged side by side. The more ordered molecular network in the latter is considered to be a consequence of unification of TB-ZnPc isomers.
- Resource Type:
- Article
- Identifier:
- 1932-7447
- Campus Tesim:
- Northridge
- Creator:
- Cheng, Zhihai, Tang, Hao, Jiang, Nan, Guo, Haiming, Guo, Wei, Gao, Li, Du, Shi-Xuan, Deng, Zhitao, and Gao, Hong-jun
- Description:
- High-resolution scanning tunneling microscope images of iron phthalocyanine and zinc phthalocyanine molecules on Au(111) have been obtained using a functionalized tip of a scanning tunneling microscope (STM), and show rich intramolecular features that are not observed using clean tips. Ab initio density functional theory calculations and extended Hückel theory calculations revealed that the imaging of detailed electronic states is due specifically to the decoration of the STM tip with O2. The detailed structures are differentiated only when interacting with the highly directional orbitals of the oxygen molecules adsorbed on a truncated, [111]-oriented tungsten tip. Our results indicate a method for increasing the resolution in generic scans and thus, have potential applications in fundamental research based on high-resolution electronic states of molecules on metals, concerning, for example, chemical reactions, and catalysis mechanisms.
- Resource Type:
- Article
- Identifier:
- 1998-0124
- Campus Tesim:
- Northridge
- Creator:
- Cheng, Zhihai, Lin, Xiao, Ji, Wei, Xie, X.C., Hofer, Werner A., Deng, Zhitao, Guo, Wei, Gao, Li, Liu, Qi, Hu, Y.B., Jiang, Nan, Du, Shi-Xuan, and Gao, Hong-jun
- Description:
- Kondo resonances are a very precise measure of spin-polarized transport through magnetic impurities. However, the Kondo temperature, indicating the thermal range of stability of the magnetic properties, is very low. By contrast, we find for iron phthalocyanine a Kondo temperature in spectroscopic measurements which is well above room temperature. It is also shown that the signal of the resonance depends strongly on the adsorption site of the molecule on a gold surface. Experimental data are verified by extensive numerical simulations, which establish that the coupling between iron states and states of the substrate depends strongly on the adsorption configuration.
- Resource Type:
- Article
- Identifier:
- 0031-9007
- Campus Tesim:
- Northridge
- Creator:
- Cheng, Zhihai, Du, Shi-Xuan, He, Xiao-Bo, Gao, Hung-Jun, Deng, Zhitao, Gao, Li, Liu, Qi, and Lin, Xiao
- Description:
- Growth behavior of iron(II) phthalocyanine (FePc) molecules on Au(111) surface at the initial stage is studied with low-temperature scanning tunneling microscopy. The FePc molecules are separately adsorbed on the face-centered cubic and the hexagonal close-packed regions at the submonolayer regime, indicating that the molecular adsorption is greatly affected by the molecule?substrate interaction. At the monolayer regime, the molecules can form a close-packed ordered structure. When the FePc goes further to the second layer, the unit cell of the formed molecular superstructure shifts compared with the unit cell of the first layer. Comparison of the growth behavior between the FePc and the CoPc also is made to understand the growth difference within the family of the phthalocyanine (Pc) molecules. And it is found that the central metal atom of the metal Pc makes a main contribution to the shift. Our results are helpful for understanding the growth of the Pc molecule family and controlling the related physical properties.
- Resource Type:
- Article
- Identifier:
- 1932-7447
- Campus Tesim:
- Northridge
- Creator:
- Cheng, Zhihai, Lin, Xiao, He, Xiao-Bo, Deng, Zhitao, Lu, Jun-Ling, Gao, Hong-jun, Gao, Li, Shi, Dong-Xia, and Huan, Qing
- Description:
- The electrical transport properties of nanosystems, including a few kinds of nanowires, have attracted much attention because of their potential application in nanoelectronics. However, the contact effect or impurities between the nanosystems and electrodes made it difficult to study the intrinsic I-Vproperties in previous measurements. Here, we present a manipulation and four-terminal method electrical transport measurement of low-dimensional systems using a new instrument consisting of a specially designed tunneling microscope with four tips that can be positioned independently in three dimensions. The electrical conductivities of zinc oxide (ZnO), perylene, gallium sesquioxide (Ga2O3), and cuprum-7,7?,8,8?-tetracyanoquinodimethane (Cu-TCNQ) nanowires were obtained. Our results have shown that this technique is a powerful tool for studying the intrinsic transport properties of nanosystems.
- Resource Type:
- Article
- Identifier:
- 0142-2421
- Campus Tesim:
- Northridge
- Creator:
- Cheng, Zhihai, Lin, Xiao, He, Xiao-Bo, Hofer, Werner A., Deng, Zhitao, Lu, Jun-Ling, Gao, Hong-jun, Gao, Li, and Shi, Dong-Xia
- Description:
- Selective analysis of molecular states in scanning tunneling microscopy (STM) has so far been achieved in a few cases by tuning the bias range of the STM in high-resolution measurements. Correspondingly, perylene adsorbed in a close-packed monolayer on Ag(110) is imaged mainly through the ? states of the molecule. By contrast, functionalizing the STM tip with a perylene molecule leads to a mismatch between the energy levels of the STM tip and the molecule adsorbates and, instead, images only the metal states of the underlying silver surface. The observation opens a route for better energy selectivity in electron transport measurements through organic interfaces.
- Resource Type:
- Article
- Identifier:
- 0031-9007
- Campus Tesim:
- Northridge
- Creator:
- Cheng, Zhihai, Du, Shi-Xuan, He, Xiao-Bo, Deng, Zhitao, Huan, Qing, Gao, Hong-jun, Gao, Li, Sun, J.T., Shi, Dong-Xia, Lin, Xiao, and Lu, Jun-Ling
- Description:
- We report on the structural evolution at the initial growth stage of perylene thin films on Au(1 1 1) surface. Scanning tunneling microscopy and spectroscopy have been employed to investigate the structural and electronic properties at 78 K. Rapid molecular diffusion was observed at low submonolayer coverage. Molecules form an ordered structure at monolayer coverage. For the second layer, impinging molecules nucleate into molecular islands with an ordered intermediate structure.
- Resource Type:
- Article
- Identifier:
- http://www.sciencedirect.com/science/article/pii/S0039602807005900, 0039-6028
- Campus Tesim:
- Northridge