Browsing by Author "Yang, Yi"

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    Converting ceria polyhedral nanoparticles into single-crystal nanospheres
    (2008-05-27T14:14:25Z) Feng, Xiangdong; Sayle, Dean C.; Wang, Zhong Lin ; Paras, M. Sharon; Santora, Brian; Sutorik, Anthony C.; Sayle, Thi X. T.; Yang, Yi; Ding, Yong; Wang, Xudong; Her, Yie-Shein
    Ceria (CeO2) nanoparticles are one of the key abrasive materials for chemical-mechanical planarization (CMP) of advanced integrated circuits. However, CeO2 nanoparticles synthesized by all existing techniques are faceted with irregular faceted-shapes, and they scratch the silicon wafers with increased defect concentrations. Here, we show for the first time an innovative approach for large-scale synthesis of spherical, single-crystal, CeO2 nanoparticles. Our synthetic strategy involves doping the CeO2 system with titanium, using flame temperatures that facilitate crystallization of the CeO2, yet retains the TiO2 in a molten state. In conjunction with Molecular Dynamics simulation, we show that under these conditions, the inner CeO2 core evolves in a single-crystal spherical-shape without faceting, because, throughout the crystallization, it is completely encapsulated by a molten 1-2 nm shell of TiO2, which, in liquid state, minimizes the surface energy. The single-crystal nanospheres reduce CMP defects by 80% and increase the silica removal rate by 50%, which will facilitate precise and reliable mass-manufacturing of chips for nanoelectronics at a precision of sub-nanometers. The principle demonstrated here could be applied to other oxide systems.
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    Fabrication of binder-free ultrafine WC-6CO composites by coupled multi-physical fields activation technology
    (Cranfield University Press, 2013-09-19) Huang, Kunlan; Qin, Yi; Yin, Deqiang; Yang, Yi; Yang, Gang
    A novel sintering method, named as coupled multi-physical fields activation technology, has been introduced for the forming of various material powder systems. Compared with the conventional ones, this technique presents more advantages: lower sintering temperature, shorter forming time, and remarkable inhibition of the grains coarsening. In the study, the cylinders of Φ4.0mm×4.0mm had been formed with ultrafine WC-6Co powders. The relative properties of sintered WC-6Co cemented carbides, such as hardness and the microstructures, had been obtained. The study has shown that a relative density, 97.80%, of the formed samples, could been achieved when the case of temperature 850℃, heating rate 50℃/s, pressure 75MPa and Electro-heating loop 6 times, were used. More importantly, the circumscription for the growth of grain size of WC, attributed to the effect of electrical field, renders coupled multi-physical fields activation technology applicable for getting WC-6Co cemented carbides with fine grain size and good properties.