Would You Like A Bouquet of Nanoflowers?

By Roland Piquepaille

Today, you're going to see the most beautiful scientific pictures of the year. And you'll ask yourself if science and art are far from each other. The winner of a photographic contest recently organized by the Department of Engineering of the University of Cambridge is Ghim Wei Ho, a PhD student in nanotechnology, for absolutely fabulous pictures of what she calls 'nanoflowers' or 'nanotrees.' In "Physicists reveal first 'nanoflowers'," the Institute of Physics says these nanostructures of silicon carbide are grown from droplets of gallium on a silicon surface. Not only these images are stunning, they also show cutting-edge nanotechnology research. And these nanoflowers will be used in new exciting applications, such as water repellant coatings or new types of solar cells.

Here is a link to the winning image.

Here are some technical details about these nanoflowers.

Ghim Wei's work involves making new types of materials based on nanotechnology and these flowers are an example of such a new material. Here, nanometre scale wires (about one thousandth the diameter of a human hair) of a silicon-carbon material (silicon carbide) are grown from tiny droplets of a liquid metal (Gallium) on a silicon surface, like the chips inside our home computers.

The wires grow as a gas containing methane flows over the surface. The gas reacts at the surface of the droplets and condenses to form the wires. By changing the temperature and pressure of the growth process the wires can be controllably fused together in a natural process to form a range of new structures including these flower-like materials.

As I said above, these nanostructures will open the way to new applications.

Professor Mark Welland, head of Cambridge's Nanoscale Science Laboratory and Ghim Wei's supervisor, said: "The unique structures shown in these images will have a range of exciting applications. Two that are currently being explored are their use as water repellant coatings and as a base for a new type of solar cell. We have already shown that as a coating water droplets roll off these surfaces when they are tilted at angles as small as 5 degrees. This behavior is a direct consequence of the ability of such nanostructured surfaces to strongly repel water."

All the photographs below have been taken and are copyrighted by Ghim Wei Ho. You can find many other photographs which were in competition in this photo gallery..

All these 3-dimensional Si composite nanostructures were shot with a scanning electron microscope and were color modified using the color balance function in Adobe Photoshop.

	Nano flower bouquet (Credit: Ghim Wei Ho)
	Nano bouquet (Credit: Ghim Wei Ho)
	Nano sunflower (Credit: Ghim Wei Ho)
	Nanoflower on flower (Credit: Ghim Wei Ho)
	Nano trees (Credit: Ghim Wei Ho)

For more information about this project, the Institute of Physics has published the research paper, "3D crystalline SiC nanowire flowers." Here is the abstract.

Several techniques have already been developed for synthesizing silicon carbide (SiC) material in the form of nanospheres and nanowires/rods. Here, we report the synthesis of a distinctly different kind of SiC nanostructure in the form of three-dimensional crystalline nanowire-based flower-like structures. Interest in such structures centres around the combination of a simple growth process based on SiC nanowire formation, with a resultant structure having potentially complex mechanical and optical properties, the latter a consequence of the wide band gap of bulk SiC. The synthesis of these SiC nanowire flowers is via a vapour-liquid-solid (VLS) process, on which a detailed study of both the chemical and structural composition has been carried out.

Here is a link to the full paper (PDF format, 4 pages, 239 KB). [Note: access to this paper is free, but you need an account at the Institute of Physics.]

Sources: Institute of Physics, June 21, 2004; University of Cambridge