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Posted: September 5, 2007

Hetero-structured nano-ring

(Nanowerk News) Teaming up with co-workers at home and abroad, researchers from the Chinese Academy of Sciences (CAS) affiliated National Center for Nanoscience and Technology (NCNST) recently succeeded in fabricating a hetero-structured nano-ring in their laboratory. The work, which would be valuable for developing new optical or electronic nano-elements and related devices in the near future, was reported by Advanced Materials ("Mismatch Strain Induced Formation of ZnO/ZnS Heterostructured Rings").
Hetero-structured nano-rings
Wurtzite-structure materials, such as ZnO, ZnS, GaN, share a common feature: the existence of polar surfaces originated from cation- or anion-terminated surfaces. Such a unique crystalline structure gives rise to a variety of exceptional and bizarre nano-structures. Driven by minimizing energy, for example, the polar charge could induce the formation of novel nano-structures, such as nano-rings, nano-springs, nano-helices and nano-bows while during the crystalline growth, the self-catalysis on the cation-terminated surface could lead to the one-side toothed growth of nano-combs. So far, however, such maverick phenomena can only be observed in the single-constituent materials.
With the support of the National Natural Science Foundation of China and National Basic Research Program ("973" Program), a research team at NCNST present a new ring structure that is composed of hetero-structured ZnO/ZnS, with tooth decoration exclusively at the inner surface.
They have synthesized a novel heterostructured ZnO/ZnS ring. The formation process of the ring has been investigated, and is attributed due to the strain induced bending that arises mainly from the lattice mismatch between ZnO and ZnS. This growth model is in consistent to the electrostatic model proposed previously about the formation of nanorings, nanosprings and nanohelix, but it shows the dominant contribution from interface strain in the ring formation for such a special case. The ring structure of ZnO/ZnS provides an ideal candidate for investigate optoelectronics of ring structured II-VI semiconductors.
Employing the technology of vacuum sublimation, the scientists adopted ZnS as a source of evaporation and they first succeeded in developing a tooth-like hetero-structured ZnO/ZnS ring alternatively composed of ZnO and ZnS nano-belts. With the aid of field emission scanning electron microscopy and transmission electron microscopy, they carried out the characterization of the new structure. The formation process of the ring has been investigated, and is attributed due to the strain induced bending that arises mainly from the lattice mismatch between ZnO and ZnS. This growth model is in consistent to the electrostatic model proposed previously about the formation of nanorings, nanosprings and nanohelix, but it shows the dominant contribution from interface strain in the ring formation for such a special case. The ring structure of ZnO/ZnS provides an ideal candidate for investigate optoelectronics of ring structured II-VI semiconductors.
Source: Chinese Academy of Sciences
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