One way to grow nanowires is to start by spreading a thin layer of plastic on a conducting substrate, such as copper. The plastic must have vertical pores in its structure stretching from the copper substrate to the surface. (It’s possible to make these pores by bombarding the plastic with high energy particles that rip holes through the layer.)
Next, place the substrate and plastic layer in an electroplating solution pass a current 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, switch off the current. Finally, dissolve the plastic leaving the metal nanowires.
What happens if you let the wires grow beyond the plastic surface? The answer is that they form nanoflowers, say Galina Strukova and buddies at the Institute of Solid State Physics in Chernogolovka, Russia.
These guys have created a variety of nanoflowers using silver and various alloys of lead, indium and palladium and nickel. (The above image shows flower bud-like structures made from lead and palladium nickel alloy.)
They’ve managed to make an extraordinary variety of shapes, some of which I’ve posted below. There are more in their paper.
The most striking thing about these pictures is the similarity many of these structures have with living organisms, such as ferns, coral, branches and leaves.
Strukova and co say this cannot be a coincidence. Instead, these nanoflowers and the organisms they are similar too must form using similar laws of growth.
They point out that many plants grow primarily from growing tips and a similar mechanism seems to operate for nanoflowers.
This goes some way to explain the similarities but Strukova and co will need to work harder to pin down the precise reasons for the different shapes they get.
In the meantime, there’s no disputing the beauty of the images they’ve obtained. Enjoy!