The tremendous interest in nanoscale structures such as quantum dots (0-dimenion) and wires (quasi-one-dimension) stems from their size-dependent properties. One-dimensional (1D) semiconductor nanostructures are of particular interest because of their potential applications in nanoscale electronic and optoelectronic devices. In the physics of nanoscale structures, quantum effects play an increasingly prominent role. Quantum wires have demonstrated interesting electrical transport properties that are not seen in bulk materials. This is because, in quantum wires, electrons could be quantum-confined laterally and thus could occupy discrete energy levels that are different from the energy bands found in bulk materials.
• Our discovery of 0.4nm carbon nanotubes
The discovery of carbon nanotubes by direct high-resolution transmission electron microscopy imaging was one of the most important events in the history of electron microscopy. It was this observation plus the size-dependent unique properties of carbon nanotubes and their intriguing potentials for wide applications that have sparked an explosion of research.
Leading edge research on carbon nanotubes has become one of the fastest-growing and the most competitive area all over the world. Small and single-walled carbon nanotubes are more fundamental and have been the basis of a large body of theoretical predictions. One of the predictions for example was that carbon nanotubes can be either semi-conducting or metallic depending on their geometrical characteristics, i.e., the diameter. Carbon nanotube theory predicted that 0.4 nm single-walled carbon nanotubes might be the narrowest stably existing carbon nanotubes. Such small tubes may show exciting properties.
Using high-resolution transmission electron microscopy, Dr. N. Wang and colleagues directly detected the smallest carbon nanotubes (Nature 408 (2000) 50) with a diameter of about 0.4nm. This discovery has not only provided novel samples for forefront research on carbon nanotubes, but has also opened up new fields for applications. This research breakthrough has drawn worldwide attention (e.g, BBC News, CNN News, Science News, etc. have reported the breakthrough) and has been selected by mainland (Chinese Academy of Engineering and Chinese Academy of Sciences) and international (Chemical Engineering News, New York) academic bodies as among the "Top Ten International News of Scientific and Technological Progress in 2000” and “Chemistry Highlight 2000”.
Carbon nanotubes are long, thin cylinders of carbon. Carbon nanotubes do not exist in nature. They can only be formed under special circumstances. The carbon nanotubes that are produced by traditional techniques are usually larger in size, and contain a mixture of various kinds of carbon specimens structured in a disorderly manner. The challenge for scientists is to produce smaller-sized, mono-dispersed and regularly arrayed carbon nanotubes. Single-walled carbon nanotubes are formed by rolling single-atomic graphite layer into a cylinder. They are extremely small in size - a bundle of 1,000,000 carbon nanotubes equals the size of a hair. Using microporous zeolite single crystals as hosts, Dr Zikang Tang from the Physics Department succeeded in fabricating these ultrathin single-walled carbon nanotubes (SWNTs) that are periodically aligned in the crystal channels. The diameter of the single-walled carbon nanotube is only 0.4nm (nanometer).
The fabrication technology that was developed at HKUST is unique, and the nanotubes produced are unprecedented. They have made an important step towards the research of carbon nanotubes by pushing its size to its theoretical limit. The carbon nanotube that they fabricated is an ideal one-dimensional conductor, and its novel properties are yet to be explored. This discovery will provide new samples for further research on nanotubes.
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