Fantastic Nano-Voyage

Science and Art in Nanoworld

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Nanoflowers of silicon carbide, synthesized with widths less than a human hair. Banner image of nano-airplanes as novel self-assembled nanostructures (nanoairplanes, nanocombs, and tetrapod-like networks of zinc oxide) by a simple thermal evaporation technique in a single-stage furnace. Image Credit: IOP/Wei Ho (Flowers) and Airplanes (Liu)

Some of the most beautiful science images of the year so far are found in a collection of photomicrographs of tiny “flowers” and “trees” less than one thousandth the width of a human hair. The images are published in the Institute of Physics journal, Nanotechnology.

“Nano-” is Greek for dwarf. A nanometer is one billionth of a meter –approximately ten times the diameter of the hydrogen atom–and nanotechnology is the design and manufacture of artifacts in the range of 100 nanometers to 0.1 nanometers. In his visionary lecture delivered at Caltech in 1959, Nobel Laureate Richard Feynmann gave the idea of nanotechnology a quantitative look in his talk entitled: “There is Plenty of Room at the Bottom”. From the outset Feymann asked: “Why can’t we write the entire 24 volumes of the Encyclopedia Britannica on the head of a pin?” After four decades, his predictions have proven quite descriptive.

To showcase imaginative examples, new images were taken by Ghim Wei Ho, a PhD student studying nanotechnology at Cambridge University. She has named some of her best photographs nanobouquet, nanotrees, and nanoflower because of their curious similarity to familiar organic structures such as flower-heads and tiny growing trees.

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, nanometer 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 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.

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Silicon carbide nanoflowers and nanotrees.
Credit:IOP/Wei Ho

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”.

Dr Paul Danielsen, director of communications at the Institute of Physics, said: “Science can be beautiful. These images show cutting edge nanotechnology research but are strikingly images in their own right. Maybe science and art aren’t so different after all.”

Several techniques have already been developed for synthesizing silicon carbide (SiC) material in the form of nanospheres and nanowires/rods. The new report describes 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 centers around the combination of a simple growth process based on SiC nanowire formation, with a resultant structure having potentially complex mechanical and optical properties.

A second paper in the same issue of Nanotechnology describes a process of making networks of zinc oxide into shapes resembling airplanes and combs (see banner image). The typical scale of these tiny machine replicas is about one micron.

Classic 1966 film, Fantastic Voyage, based on book by science fiction writer Isaac Asimov.
Credit: IMdb

As highlighted in the (1966) film and book, Fantastic Voyage (by Isaac Asimov), the idea of nanomachines interacting with biological cells has captured the imagination of both researchers and speculative fiction writers. The Asimov classic details how a miniaturized surgical team gets inserted into a dying man and eventually explores the patient’s brain and circulatory systems.

To compare these recent images to the expectations of a typical biological cell’s size, 200 nanometers is probably the limit for any cell to contain the machinery of life like replicating DNA. “Generally,” said medical microbiologist Neva Ciftcioglu, at NASA’s Johnson Space Center in Houston, “we say that a microorganism should not be any smaller than 200 nanometers. So nanobacteria is within this range, however, there are some forms we detected that they are even 80 or 50 nanometers.” These smaller forms, she says however, may not be complete cells.

So on a relative scale, the smallest biological cell would tower over these nanoflowers and nanoairplanes– much like a 80-story skyscraper towers over a person looking up from ground level to the top floor. Or as Richard Feynmann titled his imaginative survey, “There is plenty of room at the bottom.”

 


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