Jun 22, 2010
Silver catalyst triggers growth of 2nm ultrathin single-crystal ZnO nanobelts
Scientists in Singapore have shown that 2 nm ultrathin ZnO nanobelts with high uniformity and crystalline quality can be reliably grown using a simple silver-catalysed vapour transport method.
The team from Nanyang Technological University surveyed many different metal catalysts for the purpose of growing ZnO nanomaterials, but found that only silver leads to the growth of ultrathin ZnO nanobelts with high crystal quality. This discovery may have a significant impact on related fields considering that ZnO is one of the most intensively pursued nanomaterials.
The fact that these ultrathin nanobelts can be grown on almost all conventional substrates including silicon, sapphire and glass suggests the critical role of silver catalyst in the deterministic synthesis. The nanobelts appear very uniform and transparent under electron microscope observation. They are several micrometers long and several hundred nanometers wide. Extensive transmission electron microscopy and atomic force microscopy studies reveal that the thickness of the ultrathin ZnO nanobelts is ~2 nm.
Microscopy and post-growth annealing studies suggest a "1D branching and 2D filling" growth process, simultaneously involving substantial precursor migration and effective mass redistribution. During the growth, silver in its melting state may serve as a soft template to assist vapour condensation and subsequent nanobelt growth. In addition, these ultrafine nanobelts exhibit stable field emission with an unprecedented high emission current density of 40.17 mA/cm2.
It is well known that the unique morphology of nanomaterials facilitates their applications. Compared with thin-film counterparts, the absence of film-substrate interaction in the free-standing nanobelts and their ultrathin nature may help to reveal novel quantum confinement effects and lead to unique electronic and optical properties.
In the future, the ultrathin ZnO nanobelts may serve as bottom-up building blocks and facilitate the construction of advanced devices, such as nanoscale resonant tunnelling devices, field-effect transistors and light-emitting devices.
The researchers presented their results in the journal Nanotechnology.
About the author
Xing Guozhong is a PhD student in Prof. Tom Wu's group in the Division of Physics and Applied Physics, School of Physical and Mathematical Sciences, Nanyang Technological University, Singapore. The group focuses on developing novel strategies to synthesize both thin films and nanomaterials of functional oxides and heterostructures. The team is also interested in understanding the collective behaviour of spin polarized electrons, their dynamics and interactions with phonons and photons, and exploring the fascinating emerging physics in a wide range of novel materials.