Page 25 - Synthesis of Functional Nanoparticles Using an Atmospheric Pressure Microplasma Process - LiangLiang Lin

Introduction - Plasma and Microplasma-assisted Nanofabrication
Figure 1.6 The schematic setup and the photograph of the direct contact plasma-liquid system for the synthesis of Sn nanoparticles. Reprinted with permission from [106,127], copyright 2014 Elsevier, 2013 Materials Research Society
Compared to other microplasma-assisted nanofabrication techniques, the microplasma-liquid systems are rather new and attractive. It’s well-known that the liquid has a larger density than the gas. The generation of plasmas in the liquid will have additional confinements, which may offer potential routes to prepare nanomaterials.82 Furthermore, in liquids the heat can be dissipated immediately, ensuring a rather low temperature in the system. Therefore, the particles nucleation and growth rate are limited, resulting smaller sizes as well as narrower size distributions. In terms of choosing precursor, numerous salts or consumable materials can be the choices in the microplasma-liquid systems, rendering it possible to produce a series of nanomaterials. On the other hand, limitations also exist in this plasma type. Since reactions take place in the liquid, and in some cases, surfactants are involved in the process, it is unavoidable to use post-treatment like washing, filtering or centrifuge to get high purity products. Due to the evaporation of liquids during the plasma treatment, the electrodes distance is also altered, which may limit the continuous synthesis of nanomaterials. Additionally, the microplasma-liquid system is very complex, for the existence of various species such as gaseous/solution ions, electrons or neutral radicals. Nowadays, it is still unclear how charged species, neutrals and metastable radicals are transferred from the plasma to the liquid and vice versa.86 Extensive studies are required to fully understand the plasma- liquid charge transfer processes and reaction kinetics.
We have shown representative examples of existing microplasma systems for nanomaterials synthesis above. To give a better overview of the state-of-art of this technique, Table 1.2 provides a summary of reported configurations that have been used for nanofabrication, together with the relevant power sources and target products. These systems not only illustrate the versatility of microplasma sources, but also reflect the high degree of flexibility in processing parameters.
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