The Metallic Garden of Nanowires

Nanowires are incredibly thin structures with diameter usually ranging from 30 to 60 nanometers or less. In contrast, human hair is usually between 60 and 120 micrometers wide – one micrometer being 1,000 nanometers. Because nanowires are extremely thin they cannot be manufactured by conventional methods; instead, they are grown chemically.

One way to grow nanowires is to start by spreading a thin layer of plastic on a conducting substrate, such as copper. The plastic is has several vertical pores in its structure stretching from the copper substrate to the surface. The pores are made by bombarding the plastic with high energy particles that rip holes through the layer. The substrate and plastic layer in then placed in an electroplating solution and a current is passed through it. The electroplating metal will be deposited in the pores, creating nanowires. When the wires have grown to the surface of the plastic layer, the current is switched off. Finally, the plastic is dissolved leaving the metal nanowires.

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But what happens if you let the wires grow beyond the plastic surface? Galina Strukova and her buddies at the Institute of Solid State Physics in Chernogolovka, Russia, have found the answer – nanoflowers.

The metals spontaneously built up fantastically complex forms that resemble ferns coral, branches and leaves. The team used alternating layers of lead and indium with those of palladium and nickel to create the amazing structures in the picture above.

Galina Strukova believes that the resemblance of the nanowires to more familiar, larger biological structures is because both are governed by simple geometric rules; real flowers and bones may be built up from single cells in the same way that these "forests" are grown from single atoms of metal.

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Alternate electroplating of lead and palladium-nickel alloys resulted in long, palm-like leaves, each ending in a "bud" like this one, just half a millionth of a metre across.

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