Due to their small size, nanomaterials can easily enter into the body systems of living species through inhalation, injection and even skin contact. The figure on the right illustrates possible interactions between these nanomaterials and the surrounding cells and tissues. In many cases, depending on the concentration, size, shape, crystallinity, aggregation and surface chemistry, nanomaterials can disrupt cellular processes and result in cell death, chronic inflammation, and fibrosis.

Researchers at Prof. K Ostrikov's group at CSIRO Materials Science and Engineering and the University of Sydney, Australia, have described the advantages of using plasma-based processes for nanofabrication. Plasma is generally considered as the fourth state of matter along with gas, liquid and solid. It contains a diversity of energetic species including ions, electrons, atoms, excited molecules and charged particles, in contrast to the only neutral species in conventional thermal vapour processing. These energetic species could be deliberately controlled for many fabrication processes, as demonstrated in the emerging areas of nanoscale assembly and deterministic nanofabrication.

Promising technology

The top image illustrates why plasma processing is one of the most promising technologies for the safe fabrication of nanomaterials. Plasma-based technology mostly produces substrate-bound nanomaterials, which are fixed and the possibility of inadvertently exposing them to humans is low. Most of the plasma processes are performed in a confined chamber installed in a clean room or controlled environment. It is clean, in most cases under vacuum, and isolated from the external environment by the reactor chamber, so virtually no toxic gas or liquid chemicals can be exposed to humans. Humans are not exposed to nanomaterials during the synthesis, unless there is an unexpected leakage or failure of the system. Because of their energy efficiency, plasma processes often require a minimum concentration of chemical precursors to nucleate into nanoparticles and do not use organic solvents as many chemical methods do, therefore minimizing safety issues pertained to handling of dangerous gases or other chemicals. In addition, plasma is capable of reforming some very toxic gases and turning them into non-toxic ones, as exemplified by the fabrication of nanocrystalline silicon using silane. Due to the high-temperature processing, plasmas have also been implemented in waste treatment with effective gasification of hazardous wastes and generation of valuable by-products. For these reasons, dry plasma processes are widely considered "green" industrial processes.

Further details can be found in J. Phys. D: Appl. Phys.

•  For more perspectives in plasma nanoscience, check out the special issue homepage on IOPscience.