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The ability to produce highly pure and crystalline nanoparticles with prescribed surface chemistry is of vital importance as these properties play crucial roles in enhancing the performance of nanoparticle-embedded opto- and nano-electronic devices. In this study, we sought to improve the purity, crystallinity, and surface passivation of silicon nanoparticles as they are produced via spark discharge generation by introducing a hydrogen atmosphere. When pure argon is used as the carrier gas, we find that some particles are oxidized (silicon oxide rather than silicon) due to the trace amounts of oxygen present in the system, and those that are not oxides are often amorphous, as the spark energy is insufficient to produce highly crystalline silicon nanoparticles. When hydrogen is introduced into the chamber, it creates a reducing environment within the spark discharge zone, which effectively reduces the formation of oxide particles. The portion of generated silicon oxide nanoparticles decreases as more hydrogen is introduced into the system. In addition, hydrogen plasma generated from the spark discharge process improved the crystallinity of the produced silicon nanoparticles, and aids passivation of the silicon nanoparticle surface by forming Si-H x bonds, enhancing their stability during handling in oxygen containing atmosphere. Thus, the presented technique can be used to produce hydrogen-passivated silicon nanoparticles with high purity and crystallinity, and it is expected that these particles can be utilized as quantum dots after size-selection or be incorporated into luminescence devices. [ABSTRACT FROM AUTHOR]

Scaling up the production capacity of spark discharge generated nanoparticles is crucial for their industrial application. Among various options, high-frequency spark discharge generation is a promising route as the mass production rate of nanoparticles should simply scale linearly with the spark frequency. However, reports of spark discharge generators operating above 1 kHz are scarce in the literature, as spark discharges at higher frequencies have been observed to be irregular, leading to premature spark discharges that result in a significantly lower mass production rate. In this study, we present a wire-to-plate electrode configuration that suppresses premature spark discharges during high-frequency operations above 1 kHz, and investigate the factors that contribute to the occurrence of premature spark discharges by comparing the performance of the wire-to-plate electrode configuration to those of rod-to-rod and wire-to-rod configurations. We identified that spark duration should be minimized to achieve stable spark discharge events as it correlates to the time required for the spark plasma to be completely removed from the spark zone, and found that increasing local electric field intensity and carrier gas velocity are both beneficial to achieving stable high frequency spark discharges. Lastly, using the wire-to-plate electrodes, we show that stable operation without premature spark discharges can be achieved up to 17.9 kHz and the copper nanoparticle production rate scales as expected (up to 7.6 mg/h) when premature spark discharges are eliminated during high frequency operations. Copyright © 2017 American Association for Aerosol Research [ABSTRACT FROM PUBLISHER]

The electrode configuration in a spark discharge generator plays a critical role in the characteristics of the process. For instance, the rod-to-rod configuration is unable to prevent nanoparticles from agglomerating due to slow local carrier gas velocity. On the other hand, the recently developed pin-to-plate configuration is able to produce unagglomerated nanoparticles; however, the geometric mean diameter and the number concentration of produced nanoparticles change over time as the pin gets eroded. In this work, we present a novel wire-in-hole-type spark discharge generator (WH-SDG) which is able to generate unagglomerated nanoparticles with a constant size distribution over a long time. The WH-SDG, which consists of a metal wire and a grounded plate with a hole in which the metal wire is located in the center, effectively suppressed changes in the electrode morphology and the gap distance, which cause the minimal variation of the spark discharge voltage and frequency in time. Therefore, the WH-SDG was able to maintain a constant size distribution of the generated nanoparticles for 12 h. In addition, it was found that the WH-SDG could control the diameter of nanoparticles by regulating the gas flow rate into generator, and could produce nanoparticles from various metals such as copper and palladium. Copyright 2015 American Association for Aerosol Research [ABSTRACT FROM PUBLISHER]