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Disorder-Order Transition in Mesoscopic Silica Thin Nan Yao,, Anthony Y. Ku,,, Nobuyoshi Nakagawa,, Tu Lee,,

Summary: Disorder-Order Transition in Mesoscopic Silica Thin
Nan Yao,, Anthony Y. Ku,,, Nobuyoshi Nakagawa,, Tu Lee,,
Dudley A. Saville,, and Ilhan A. Aksay*,,
Department of Chemical Engineering and Princeton Materials Institute, Princeton University,
Princeton, New Jersey 08540
Received January 18, 2000
Electron microscopy has been used to study the mesoscopic (nanometer-level) and
microscopic (micrometer-level) structural evolution of mesoscopic silica thin films grown at
the air-water interface under dilute, acidic (pH < 2) conditions. Transmission electron
microscope observations reveal that the film begins with a disordered (amorphous) structure.
Over time, mesoscopically ordered regions (hexagonally packed cylindrical channels) nucleate
and grow within the film. Scanning electron microscopy reveals microscopic structural
features such as ribbons, protrusions, domain boundaries, microindentations, and pits. Our
work shows that mesoscopic order develops within the film through a "disorder to order
transition." Our observations also clarify the role of the air-water interface in confining
film growth to two dimensions during the initial stages. We note that a two-dimensional
(in-plane) to three-dimensional (unconstrained) growth transition occurs when the film
exceeds a critical thickness. We extend the current understanding of the structural evolution
of the film by providing a detailed mechanism for the development of mesoscopic order and


Source: Aksay, Ilhan A. - Department of Chemical Engineering, Princeton University


Collections: Materials Science