In-liquid plasma processing using high-frequency or microwave irradiation

<jats:p>In-liquid plasma is generated by applying high-frequency (27 MHz) or microwave (2.45 GHz) radiation to hydrocarbon liquids or water. In-liquid plasma is expected to replace gas-phase plasma because the reaction rates for chemical deposition of in-liquid plasma are much higher than those for conventional vapor deposition. Moreover, the cooling effect of the liquid mitigates thermal damage to the substrate. In-plasma generation requires the existence of bubbles because this plasma occurs in bubbles in liquid. Two methods exist for generating bubbles. One is to generate vapor bubbles by heating the liquid. The other is to generate acoustic cavitaion bubbles. Sonoplasma is created when acoustic cavitation is used to generate in liquid plasma. This plasma is not arc-discharged plasma, but rather high-frequency or microwave plasma. Therefore, it is useful in many industrial applications. Using this technology as a chemical reactor, synthesis of diamondlike carbon, polycrystalline silicon carbide, and carbon nanotubes, decomposition of waste oils, and the production of hydrogen can be achieved easily in hydrocarbon liquids. Temperatures were measured from the ratio of emission intensities of Hα and Hβ. Plasma temperatures in hydrocarbon liquids are higher than those in water.</jats:p>