ABSTRACT
Nanobowls, closely related to nanocups (see later), are known mainly for some elemental metals and oxides. As in the case of several other classic and less-common nanostructures, the indisputable leadership in their formation belongs to zinc oxide due to the great interest for photonic applications due to its wide band gap (3.37 eV), large exciton binding energy (60 meV), and its use as a promising material for light-emitting devices. ZnO in contact with noble metals may undergo charge transfer, a phenomenon essential to photocatalysis, photovoltaics, and next generation nanodevices.1 In this respect, the development of ZnO nanostructures (nanobowls and nanobagels) as well as core-shell ZnO structures with Au nanoshell (silica core-Au shell) core and ZnO epilayer coating with unique light emission properties, which may be useful in nanophotonics applications, has been extensively carried out by various techniques, frequently yielding doped or undoped different structures at the same time or depending on reaction conditions. Thus, ZnO and Cu2O were deposited by the electrochemical method via the colloidal crystal template.2 Not only 3D inverse opal structures and 2D nanobowls fabricated but also nanoparticles with a controlled shape were prepared. Mn-doped ZnO diluted magnetic semiconductor (DMS) nanostructures (nanorod, bowl, and cage, located at different deposition temperature zones) were synthesized by direct reaction of zinc metal and manganese chloride powder under oxygen environment using CVD method.3 It was revealed that the doped nanorods exhibited low-temperature ferromagnetism at 5 K with Curie temperature around 37 K, whereas the DMS nanocrystalline bowl/cage structures had room-temperature (r.t.) ferromagnetic behavior. Unusual bowl-, trough-, and ring-shaped structures resulted from the temperature-induced self-assembly of ZnO nanoparticles, leading to bowls and rings also serving as a template to make metal or metal oxide replicas.4 The tiny bowls were envisaged by authors not only to hold –uids of ultralow volume but also to grow nanoparticles, immobilize biomolecules, and screen submicrometer-sized particles.
