Scientists develop a simple way to organise nanoparticles on a surface without the need to first alter the surface.

Organising nanoparticles on surfaces is a desirable skill right now, with today’s current focus on nanofabrication and the drive to make circuits and devices ever smaller. There are many different approaches to arranging nanoparticles on surfaces; most of these involve modifying the surface itself in some way so that parts of it are more appealing to the nanoparticles than others. But surface modification can itself be tricky. A way to get around this is by use of a mask or stencil, which is used to protect the places on the surface where nanoparticles are not desired, and allows the user to deposit the particles everywhere else.

Now researchers based at Seoul National University (SNU) and Korea Institute of Science and Technology, both S. Korea, led by Professor M. Choi of SNU’s Center for Nanoparticle Control, have found a new way to produce nanoparticle arrays on a surface without the need to alter that surface. They use a mask that has a dielectric surface, that is, it can be polarised by use of an electric current, and they inject a cloud of charged particles and ions. When the current is switched on, the dielectric surface of the mask causes a so-called “electrostatic lens” to form in situ from the injected cloud, and this means that the scientists can very accurately focus their particles through this lens. Because the mask is used to focus the stream of particles being deposited, it is possible to make features on the surface very much smaller than the actual mask features.

The approach of Choi and his colleagues is better than simply using a mask because their mask does not clog unlike conventional ones – particles do not land actually on the mask but are directed through it by the electrostatic lens. This makes the new technique particularly advantageous if the particle you are patterning onto the surface is very precious or expensive, e.g. a protein, as the method minimizes waste.

Because any surface and many possible nanoparticles can be used, this is a very flexible technique. The team anticipate that it could be used to make a range of nanoparticle-based devices, including optical, electronic, biological, and magnetic devices. They have already demonstrated its success in making a simple gas sensor from zinc oxide nanoparticles which can detect both carbon monoxide and hydrogen gases.