Carbon nanotubes grown on Cu substrates

Magnetic nanowires grown on carbon nanotubes

Carbon nanowalls

Schematic illustration of carbon nanowalls

Carbon nanowalls filled by 20nm Fe particles

Carbon nanowalls

Assoc Prof YH Wu has succeeded in growing and observing the first two- dimensional carbon nanostructures - dubbed carbon nanowalls. We believe this is a world first.

The nanowalls which are aligned almost vertically on the substrates exhibit a lateral dimension of 0.1 to several microns and a thickness of several nanometers. In the nanoworld, both the dimension and dimensionality play important roles in determining the properties of the materials. The lowest dimensionality for a material is called zero-dimensional, or simply 0D, which refers to the situation that the movement of both electrons and atoms are confined by a "sensible" boundary from every directions.

The existence of boundaries will not be "felt" by the electrons or atoms, however, when the dimension of the material is large. This is just like the situation that the water inside the sea far away from the coast can hardly sense the existence of the coast, but the water everywhere inside a small basket can feel the existence of the latter. That explains why both the dimensionality and dimension are important. The most typical carbon in the 0D form is the buckminsterfullerene, in which the carbon atoms are arranged into a shape of soccer ball. After the discovery of buckminsterfullerene by Kroto and Smalley, Iijima discovered the one-dimensional carbon nanostructures - carbon nanotubes. The successful growth of carbon nanowalls makes it possible for the first time to grow carbon nanostructures in all three dimensionalities, i.e., from 0D to 2D.

The work has been started as a small project at the Data Storage Institute to explore the possibility of using carbon nanotubes in probe recording and nano-memories. The nanowall was found accidentally during the process of refining the nanotube structures. After the first finding, a detailed study of the growth mechanism has been carried out, and we are now able to grow both the nanotubes and nanowalls in a well-controlled fashion. In addition to the bare carbon nanowalls, a class of nanostructured materials using carbon nanowalls as the templates has also been fabricated and their potential applications in several strategic areas are being explored. Following are some scanning electron microscopy images of carbon nanotubes, nanowalls and the associated nanostructures.

Publications: Y.H. Wu and T.C. Chong, paper presented at the MRS 2001 Spring Meeting, abstract No. W8.3, San Francisco, USA, April 16-20, 2001. Y.H. Wu, P.W. Qiao, T.C. Chong, Z.X. Shen, Adv.Mater.14, 64 (2002). Y.H. Wu, P.W. Qiao, J.J. Qiu, T. C. Chong, and T. S. Low, Nano Letters 2, 161 (2002). Y.H. Wu and B.J. Yang, Nanoletters, Articles ASAP, released on January 24, 2002. Y.H. Wu, B. J. Yang, G.C. Han, B.Y. Zong, H.Q. Ni, P. Luo, T. C. Chong, T.S. Low, Z. X. Shen, Accepted by Advanced Functional Materials.

Electrical field controlled growth of carbon nanowalls

Selective growth of different
types of nano walls

Nano structured zinc
oxides on carbon
nano walls

Selective growth of nano

Ultrathin coating of carbon nano walls with zinc oxide

Electroplated Ni nano-particle
on carbon nano walls

Au nano-particles on
carbon nano walls