Some 10 years ago scientific interest in dusty plasmas was motivated mostly by the needs of the microelectronics industry. In 1994, however, researchers at three laboratories almost simultaneously found that these low-pressure gas discharges can organize themselves into crystal-like structures. This opened the door to spectacular developments in controlled crystal growth, such as the synthesis of thin films for solar-cell applications.
A plasma is typically a gaseous discharge containing electrons and positively charged ions. However, in the surface-processing industry – in which plasmas are used to fabricate integrated circuits, for example – it has long been known that plasmas can contain larger particles too. The electric fields at the plasma boundaries, which are caused by electric sheaths around the discharge electrodes, can trap micron-sized “dust” particles in the plasma volume. These particles can support a high negative charge of up to several thousand electrons, and are therefore characterized by Coulomb electrostatic interactions.
However, our understanding of crystal growth in Earth-bound dusty plasmas has been hampered by the influence of gravity. Now astronauts on board the International Space Station have observed plasma crystals in microgravity for the first time.
These two results – which appear in a focus issue of New Journal of Physics on complex plasmas – represent only a taste of what is to come from further dusty-plasma experiments on board the International Space Station. Many teams in the world are joining this programme not only to gain fundamental insights into complex plasma science, but also with a view to developing applications such as particle coating and surface functionalization.
In the August issue of Physics World André Bouchoule and Laifa Boufendi from GREMI at Orléans University in France explain how the experiments have revealed crystal structures that have never been seen on Earth.
