Extremely non-equilibrium oxygen plasma for direct synthesis of metal oxide nanowires on metallic substrates

Miran Mozetic (1)

1 Department of Surface Engineering and Optoelectronics

A promising method for synthesis of metal oxide nanowires is based on application of extremely non-equilibrium gaseous environment found in oxygen plasma created by some types of discharges. The kinetic temperature of neutral gas is kept close to the room temperature, the electron temperature is few eV, the ionization fraction below 10 -6 and the dissociation fraction close to 100%. Plasma with such characteristics is obtained using electrode-less high frequency discharges driven by radiofrequency or microwave generators. Plasma parameters such as the electron density and energy distribution function, the Debye length, the dissociation and ionization fractions, the density of negatively charged molecules, the ratio between the positively charged molecules and atoms, the distribution of atoms and molecules over excited states, etc. depend on discharge parameters. The most important discharge parameters are the generator power, frequency and coupling, the purity and pressure of working gas and the gas flow, the dimensions of the discharge chamber, the materials facing plasma, the residual atmosphere, and, usually very important though often neglected, the properties of the samples mounted into a discharge chamber. Proper construction of the experimental system for synthesis of metal oxide nanowires allows for almost 100% dissociation fraction and thus extremely rapid growing of nanowires. The particularities of oxygen plasma as well as real - time monitoring of the dissociation fraction are elaborated in this contribution. The lack of reliable experimental results on characterization of extremely non-equilibrium oxygen plasma is stressed. 1. Charged particles in cold weakly ionized plasma Gaseous plasma is partially ionized gas. Since there are always some charged particles presented in any gas, an additional requirement to this simple definition was stated: the gas is properly called plasma if the density of charged particles is large enough to screen any DC electrical potential at a length much smaller than the typical linear dimension of plasma. For the case of non-equilibrium low pressure plasma where the electrons in unperturbed plasma have much higher kinetic energy than positive ions, the requirement is often checked by comparison of the plasma dimension with the Debye length: ionized

Mots clés: Physical Sciences

Miran Mozetic. Extremely non-equilibrium oxygen plasma for direct synthesis of metal oxide nanowires on metallic substrates. Journal of Physics D: Applied Physics, 2011, 44 (17), pp.174028. ⟨10.1088/0022-3727/44/17/174028⟩. ⟨hal-00613282⟩