From plasma to nanoparticles: optical and particle emission of a spark discharge generator

Abstract

The increased demand for high purity nanoparticles (NPs) of defined geometry necessitates the continuous development of generation routes. One of the most promising physical techniques for producing metal, semiconductor or alloy NPs in the gas phase is spark discharge NP generation. The technique has a great potential for up-scaling without altering the particles. Despite the simplicity of the setup, the formation of NPs in a spark discharge takes place via complex multi-scale processes, which greatly hinders the investigation via conventional NP measurement techniques. In the present work, time-resolved optical emission spectroscopy (OES) was used to provide information on the species present in the spark from as early as approximately 100 ns after the initiation of the discharge. We demonstrate that operando emission spectroscopy can deliver valuable insights into NP formation. The emission spectra of the spark are used to identify, among others, the main stages of material erosion and to calculate the quenching rate of the generated metal vapour. We demonstrate that the alteration of key control parameters, that are typically used to optimize NP generation, clearly affect the emission spectra. We report for Cu and Au NPs that the intensity of spectral lines emitted by metal atoms levels off when spark energy is increased above an energy threshold, suggesting that the maximum concentration of metal vapour produced in the generator is limited. This explains the size variation of the generated NPs. We report a strong correlation between the optical and particle emission of the spark discharge generator, which demonstrate the suitability of OES as a valuable characterization tool that will allow for the more deliberate optimization of spark-based NP generation.

Unconventional Alloys Confined in Nanoparticles: Building Blocks for New Matter

“…The electronic nature of the formed metallic bonding enables virtually unlimited mixing possibilities. Upon rapid quenching (10 7 -10 9 K s À1 ), 32,33 the conucleation of the multicomponents in the mixed vapor yields mixed nuclei clusters, which are kinetically trapped and subsequently grown into NPs according to the feeding composition (for details see sections S4 and S5 of Supplemental Information). Therefore, we coined the term ''sparking mashup'' to describe the mixing process for alloying any dissimilar metals into NPs.…”

Egy- és többkomponensű plazmonikus nanorészecskék szikra-plazma alapú előállítása és alkalmazásuk a felületerősített Raman spektroszkópiában

“…Az eljárást kísérletileg megvalósító, ún. szikrakisüléses nanorészecske generátort (az angol rövidítésből SDG) először 1988-ban alkalmazták [8], amely repetitív, nagy áramú és feszültségű, néhány mikroszekundum hosszúságú, oszcilláló szikrák létrehozásán alapul két elektromosan vezető elektród között [9,10]. A szikrázás hatására az elektródok anyaga erodálódik és egy gázáramba kerül, ahol nukleációt, kondenzációt és koagulációt követően NR-ek keletkeznek [11].…”

Hydrogen-assisted spark discharge generated metal nanoparticles to prevent oxide formation

“…From the presented results, we see that tin, cobalt, and bismuth nanoparticles generated in an inert nitrogen atmosphere will oxidize even for sub ppm levels of oxygen. As oxidation is more rapid at elevated temperatures, it is likely that this occurs during particle formation, when the vapor is quenched as it exits a very high temperature (Reinmann and Akram 1999;Kohut et al 2017) plasma. To heat a metal oxide under the presence of a reducing agent such as hydrogen is a general method to prevent formation of oxides.…”