Yapu Zhao

Chinese Academy of Sciences, Peping, Beijing, China

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Publications (5)10.13 Total impact

  • Source
    Journal of Materials Science 02/2005; 40(6):1501-1504. · 2.31 Impact Factor
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    Sili Ren, Shengrong Yang, Yapu Zhao
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    ABSTRACT: A novel self-assembled C60 film was prepared by chemical adsorption of C60 molecules onto an amino-group-containing polyethyleneimine-coated silicon substrate surface. The contact angle of distilled water on the C60 film was measured, the thickness was determined by means of ellipsometric analysis, and the morphology was observed with an atomic force microscope. The tribological properties of the films were investigated as well. It was found that the C60 thin film had a contact angle of about 72 degrees and thickness of 1.8 nm and exhibited a surface domain microstructure composed of fullerene clusters. Due to the hydrophobicity and low surface energy, the C60 film possessed good adhesive resistance and had an adhesive force of about 7.1 nN, which was about an order of magnitude lower than that of the silicon substrate surface. Moreover, the C60 film showed good friction reduction, load-carrying capacity, and antiwear ability, which were attributed to the higher mechanical stiffness and elastic modulus of C60 molecules. Besides, the friction coefficient decreased with increasing sliding velocity and normal loads, due to the rolling effect of the physisorbed C60 molecules.
    Langmuir 05/2004; 20(9):3601-5. · 4.38 Impact Factor
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    Sili Ren, Shengrong Yang, Yapu Zhao
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    ABSTRACT: A novel self-assembled dual-layer film as a potential excellent lubricant for micromachines was successfully prepared on single-crystal silicon substrate by chemical adsorption of stearic acid (STA) molecules on self-assembled monolayer of 3-aminopropyltriethoxysilane (APS) with terminal amino group. The structure and morphology of the film were characterized by means of contact-angle measurement, ellipsometric thickness measurement, Fourier transformation infrared spectrometric analysis, and atomic force microscopic analysis. The micro-and macro-tribological properties of the dual-layer film were investigated as well. As the results, the dual-layer STA-APS film was hydrophobic with the contact angle for water to be about 98° and the overall thickness about 2.2 nm. Atomic force microscopic images showed that the APS surface was characterized by defects such as small grains and holes; it became relatively smooth and homogeneous after the self-assembly of the STA film. The STA-APS film possessed good adhesive resistance and could greatly reduce the micro-and macrofriction force. Moreover, it registered better load-carrying capacity and antiwear ability than the self-assembled monolayer of octadecyltrichlorosilane (OTS) in sliding against the ceramic counterface. Thus, the dual-layer self-assembled film might find promising application in the lubrication of micro-electromechanical systems (MEMS).
    Langmuir. 01/2003; 19(7).
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    ABSTRACT: A novel ultrahydrophobic ultrathin film was prepared by stearic acid (STA) chemically adsorbed onto the polyethyleneimine (PEI) coated aluminum wafer. The formation and the structure of the films have been characterized by means of water contact angle measurement, ellipsometry, Fourier transformation infrared spectroscopy, and X-ray photoelectron spectroscopy. The static contact angle for water on the surface of this ultrathin organic film was measured to be as high as 166°. Apart from the hydrophobic STA monolayer, the needle-like surface nanostructures with enough roughness was found to be essential for the generation of ultrahydrophobicity. We suggest that a composite interface formed by the needle-like surface nanostructures, water droplet, and air trapped in the crevices is responsible for the superior water-repellent property.
    Surface Science 01/2003; · 1.84 Impact Factor
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    ABSTRACT: A self-assembled monolayer of octadecyltrichlorosilane (OTS) was prepared on a single-crystal silicon wafer (111) and its tribological properties were examined with a one-way reciprocating tribometer. The worn surfaces and transfer film on the counterface were analyzed by means of scanning electron microscopy and X-ray photoelectron spectroscopy. The results show that, due to the wear of the OTS monolayer and the formation of the transfer film on the counterpart ball, the friction coefficient gradually increases from 0.06 to 0.13 with increasing sliding cycles and then keeps stable at a normal load of 0.5N. The transfer film is characterized by deposition, accumulation, and spalling at extended test duration. Though low friction coefficients of the monolayer in sliding against steel or ceramic counterfaces are recorded, poor load-carrying capacity and antiwear ability are also shown. Moreover, the monolayer itself or the corresponding transfer film on the counterface fails to lubricate even at a normal load of 1.0N. Thus, the self-assembled monolayer of octadecyltrichlorosilane can be a potential boundary lubricant only at very low loads.
    Tribology Letters 01/2002; 13(4):233-239. · 1.74 Impact Factor

Publication Stats

150 Citations
10.13 Total Impact Points

Institutions

  • 2002–2005
    • Chinese Academy of Sciences
      • • State Key Laboratory of Nonlinear Mechanics
      • • State Key Laboratory of Solid Lubrication
      Peping, Beijing, China
  • 2003
    • Northeast Institute of Geography and Agroecology
      • State Key Laboratory of Nonlinear Mechanics
      Peping, Beijing, China