4, 156.0, 150.5, 150.0, 149.2, 139.3, 136.8, 130.1, 116.9, 123.8, 121.4, 118.8, 116.3, 69.9, 31.9, 29.7, 29.6, 29.4, 29.3, 26.1, 22.7, 14 4, 156.0, 150.3, 149.2, 136.8, 130.1, 128.5, 127.8, 127.2, 127.0, 123.8, 121.4, 118.8, 117.3, 71.8 4, 156.1, 151.9, 149.8, 149.2, 142.4, 140.4, 139.4, 137.2, 136.9, 127.7, 127.7, 126.1, 123.8, 121.5, 121.4, 120.2, 118.7, 55.4, 40.4, 31.8, 30.0, 29.2, 23.9, 22.6, 14.One-dimensional (1D) nanostructures, such as nanotubes, nanowires, nanorods, and nanobelts, have stimulated intensive interest owing to their unique applications in mesoscopic physics and the fabrication of nanoscale devices.[1±3] Many recent efforts have focused on the integration of 1D nanoscale building blocks into two-and three-dimensional (2D/3D) ordered superstructures or complex functional architectures, which is a crucial step toward realization of functional nanosystems.[4±7] For example, ordered nanorod arrays were obtained by the self-assembly of preformed uniform nanorods through hydrophobic interaction, [4] DNA hybridization, [8] and a Langmuir±Blodgett technique, [9] whereas multi-armed [5] and radially aligned [10] semiconductor nanorods were fabricated by solution-growth methods. Notably, the self-organized crystal growth of a variety of novel hierarchical nanostructures made of nanowires has been achieved recently; examples include the growth of ZnO nanobridges, nanosnails, and nanocombs by a vapor-transport and condensation technique, [11] and the polymer-directed synthesis of penniform BaWO 4 nanostructures in reverse micelles. [12] As a new family of 1D nanostructures, nanobelts have received much attention because of their unique properties and potential applications in building functional nanodevices; [13,14] however, there are few reports concerning the assembly of nanobelts into hierarchical nanostructures. [15] It remains a significant challenge to develop facile, mild, and effective methods for creating hierarchical architectures assembled from inorganic nanobelts. Reverse micelles and microemulsions have been widely used as soft colloidal templates for controlling the size and shape of inorganic nanocrystals.[16] Recently, reverse micelles formed by mixed surfactants have turned out to be promising nanostructured media for the controlled synthesis of 1D nanostructures. [17,18] Specifically, high-aspect-ratio, ultrathin BaWO 4 nanowires were produced using the so-called catanionic re-
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