Growth mechanism and characterization of zinc oxide microcages

Abstract

We report the growth mechanism and structural properties of micrometer sized ZnO cages which were synthesized directly from Zn vapor deposition and oxidation. The ZnO microcages exhibit a hexagonal or spherical shape with partly or completely open surfaces and hollow interiors. The growth process of the microcages includes the deposition of Zn polyhedral particles, top face breaking of the Zn particles and Zn sublimation, and subsequent reaction to ZnO. By controlling the various growth stages, we obtained information on the growth mechanism of the ZnO cages, which appears to be different from a mechanism reported previously. The chemical composition and crystalline structure were studied using energy dispersive X-ray spectroscopy and transmission electron microscopy, respectively. The room-temperature photoluminescence spectrum indicates a large quantity of oxygen-vacancy related defects within the wall of the ZnO cages. q

Controlled Synthesis of Hollow Hemispheric ZnO Shells/Cages on Graphite Fiber

“…During the experiment, precipitation, oxidation, and sublimation are undergoing almost simultaneously and ceaselessly (i.e., in nonequilibrium level), hence more and more hemispheric ZnO shells/cages are stacked around the graphite fiber ( Figure 6(c)). It is necessary to note that a low oxygen partial pressure (2-5 × 10 −2 Torr in our experiment) is a crucial factor to obtain such hollow cage-like ZnO structures, which is consistent with Fan's report [17]. We have synthesized wirelike ZnO nanostructures around graphite fiber at higher pressure [22].…”

“…The structures of the hollow ZnO shells/cages exhibit with rough surface rather than polyhedral profile (as the reports [16][17][18]). Meanwhile, a detail discussion of the growth mechanism is presented based on a time-sequenced growth experiment.…”

“…However, up to now, synthesis of hollow cage-like ZnO structures is still a challenge. Recently, cagelike ZnO structures have also been achieved by different researchers [16][17][18]. However, the growth mechanism for the cage-like ZnO structures is still controversial and further investigation is necessary.…”

Zinc oxide nanostructures and their applications

“…A possible growth mechanism for the formation of the ZnO cages/spheres was proposed which involved the solidification of zinc liquid droplets in the form of singlecrystalline spherical and hexagonal-based rod zinc particles, surface oxidation which produce the textured ZnO nanocrystals on the zinc surfaces and finally the vaporization or sublimation of the zinc cores, which results the formation of ZnO cage/shell structures [46]. The detailed characterizations combined with the growth mechanism of zinc oxide microcages were reported by Fan et al [47], who synthesized these structures using the zinc powder and oxygen at 800 o C on the silicon substrates. They proposed a growth process that includes the deposition of the zinc polyhedral particles, breaking of top {0001} surfaces of the zinc polyhedral particles because of oxidation by the residual oxygen or water vapors.…”

Large-quantity synthesis of ZnO hollow objects by thermal evaporation: Growth mechanism, structural and optical properties

“…In this endeavor, recently scientists are inclined to pay much attention on the fabrication of materials with specific morphologies because of the expectation of novel properties. For the use of specific applications, so far a variety of ZnO nano-and microstructures are already fabricated and reported in the literature which include ZnO rods and wires [5][6][7][8][9][10][11][12][13][14], tubes [15,16], belts [17], propeller [18], stars [19], helixes, springs and rings [20], nanosheet networks and hexagonal disks [21], nanobridges and nails [22], columns [23], hierarchical structures [24], flower-shaped structures [25], nano and micro hollow shells, cages and spheres [26][27][28][29][30], and so on. Among these diverse morphologies of ZnO, the nano-and microspheres with hollow interiors/cages, because of their lower densities and higher surface areas, are presenting an appealing structural design as compared to their bulk materials.…”