Electron microscopy has been used to study the mesoscopic (nanometer-level)
and microscopic (micrometer-level) structural evolution of mesoscopic sili
ca 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, mesoscopic
ally ordered regions (hexagonally packed cylindrical channels) nucleate and
grow within the film. Scanning electron microscopy reveals microscopic str
uctural features such as ribbons, protrusions, domain boundaries, microinde
ntations, and pits. Our work shows that mesoscopic order develops within th
e film through a "disorder to order transition." Our observations also clar
ify the role of the air-water interface in confining film growth to two dim
ensions during the initial stages. We note that a two-dimensional (in-plane
) to three-dimensional (unconstrained) growth transition occurs when the fi
lm 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 microscopic features and consider the
possibility of a universal growth mechanism for films and particles.