In such reactor for low-pressure plasmas, microwaves with a frequency of 2.45 GHz are radiated via a transmission line and a horn antenna into a vacuum chamber. Underneath the bottom of the vessel, a magnet array consisting of 48 cobalt-samarium permanent magnets creates a magnetic field, whose intensity corresponds to an electron cyclotron resonance frequency of 2.45 GHz. In this way, the energy transfer between the incoming microwaves and the electrons of the gaseous molecules is very efficient, allowing a stable plasma to be produced and sustained. Homogeneous treatments on large areas (up to 0.5 m2) can be achieved by a horizontal movement of the magnet array.
Homogeneous treatments on large areas (up to 0.5 m2) can be achieved by a horizontal movement of the magnet array.
By such principle, furthermore, it is also possible to ignite a plasma directly inside a hollow body with a complex geometry, for example a bottle. In this case, a magnet is inserted into the bottle and the plasma is then generated inside the magnetic field, i.e. only in the internal bottle volume.
The low temperature of such a plasma allows the treatment of very sensitive substrates like paper, tissue, thin plastic foils and electric devices, without risk of thermally damaging them.
By carefully choosing and mixing the plasma feeding gases, it is possible to deposit thin films with different chemical compositions (among others, oxygen barrier films or to treat surfaces in order to increase their adhesion or tune their wettability.