Page 19 - Synthesis of Functional Nanoparticles Using an Atmospheric Pressure Microplasma Process - LiangLiang Lin

Introduction - Plasma and Microplasma-assisted Nanofabrication
1.3.2 Existing Microplasma Systems for Nanomaterials Synthesis
So far a broad range of microplasma systems have been developed for nanofabrication. The classification is diverse, based on the aspects such as plasma power source (excitation frequency), electrode geometry, power coupling method, precursor injection way, target products and so on. According to the general configurations of microplasma systems for nanomaterial synthesis, they can be divided into four main categories: hollow-electrode microdischarges, microplasma jets with external electrodes, microplasma jets with consumable electrodes and plasma-liquid systems. Generally for the first three plasma systems, nanomaterials are generated in the gas phase, while in the fourth plasma system products are obtained in the liquid phase. It should be noted that the classification is not rigid, and mixed cases can be developed.
1) Hollow-electrode microdischarges
Among microplasma systems hollow-electrode microdischarges are relatively simple and easily to operate. They mostly use DC powers coupling to sustain the plasmas, which is considerably less expensive and easier to implement compared to pulsed plasmas. Generally a hollow capillary functions as one electrode as well as the gas guiding tube, in which precursors are diluted and transported by a flow of inert gas such as argon or helium. Meanwhile, another capillary or mesh is used as the counter electrode, with an interelectrode distance of 1~2 mm. Both electrodes are connected to a DC power supply, and the plasma is formed between the electrodes.143 An electrostatic precipitator or a filter is installed downstream of the aerosol to collect the obtained products.
One representative example demonstrated by PA Lin et al. is shown in Figure 1.2. Two SS capillary tubes (O.D.=1.6 mm, I.D.=180 μm) were used as the cathode and the anode. Organometallic compounds were used as the precursors and being carried into the plasma zone by separate gas lines in continuous argon flows. In all experiments the total gas flow was kept constant at 100 sccm, and the gas flow rates in different precursors lines were individually controlled by mass flow controllers. In this manner metallic alloys of tunable compositions were produced by varying the relative gas flow rate in precursor and dilution gas lines.
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