also very important for their potential uses as electronic Cubic ferric oxide ( a-Fe 2 O 3 ) single crystals (several tens of materials, which require the particles to be assembled in two nanometers) of narrow size distribution were prepared by forced dimensions in an orderly manner. The Langmuir-Blodgett hydrolysis of acidified FeCl 3 aqueous solutions in open vessels. (LB) technique proved to be an effective assembly method The X-ray diffraction (XRD) and electron diffraction patterns of in that it produced ordered monolayer or multilayer structhe single crystals were produced. The formation of the single tures of alternating ferric oxide-organic LB films (3, 4). crystals was studied using time resolved TEM and XRD. Two In order to obtain more ordered structures, nanostructured stages were considered to exist in the formation process. During particles of cubic morphology should be used since they the nucleation stage, only amorphous iron oxide particles of 3easily form ordered structures in two or three dimensions if 5 nm can be found in the solution; in the growth stage, phase transformations occurred from amorphous iron oxide to b-FeOOH they possess similar size. Therefore, it is of interest to preand from b-FeOOH to a-Fe 2 O 3 . The three phases coexist in the pare monodispersed cubic single crystals of a-Fe 2 O 3 . solution during the formation process. The middle phase, b-
In addition to its morphology, the size of the particle is FeOOH, possesses two changing tendencies: to aggregate or to also a determining factor for the assembly. Our work has break up. The former tendency leads to the formation of the temshown that small ferric oxide particles are easier to assemble plates on which cubes form; the latter results in the transformation using the LB method. A number of reports have shown that from b-FeOOH to amorphous iron oxide. A fast nucleation method ferric oxide possesses special magnetic (5-8) and photocatwas introduced in this work, through which the nucleation process alytic (9-11) characteristics as particle size decreases, so it takes only several seconds, and the cubes so prepared are slightly is necessary to decrease the particle size. larger than those prepared by the ordinarily used method (nucle-Since the first report, a series of studies on the preparation ation lasting several minutes). Hydrolysis at lower temperature and formation mechanism of monodispersed cubic a-Fe 2 O 3 produced quasi-cubes which are not single crystals.