Extremely Monodispersed Micrometer-Scale Spherical Particle Synthesis of Ag Inside a Microdroplet Vaporizing in Plasma

Abstract

Spherical Ag particles have received considerable attention because of their unique properties as well as their applications in various fields. In the present study, the synthesis of micrometer-scale spherical Ag particles with an extremely narrow size distribution is demonstrated using a simple capacitively coupled atmospheric-pressure plasma reactor with an inkjet head. Droplets of a Ag nitrate aqueous solution are ejected from the inkjet head to synthesize Ag particles. The gaseous temperature in the reactor is adjusted such that Ag can be melted with a negligibly small vapor pressure. These particles exhibit a spherical shape with a smooth surface. The mean diameter of the particles is 0.91 ± 0.013 μm with a small coefficient of variation of 1.5%, the smallest value ever reported for Ag particles of less than 1 μm. The grain sizes of the particles are larger than 100 nm, as expected from the broadening of the X-ray diffraction peaks. The excellent monodispersity of the particles synthesized by this method may expand the applications with micrometer-scale spheres such as ball spacer, microsized ball bearing, and inks for printed electronics.

Synthesis of ZnO and ZnO/Ag fine particles by plasma-assisted inkjet processing

“…The applied power was adjusted to 50 W and the gas temperature (T g ), which was estimated using the spectral fitting technique of the optical emission spectra of N 2 (∼380 nm) or OH (∼310 nm) [35], was maintained in the range of 1100-1500 K, as listed in table 1. To suppress the excessive rise in gas temperature, the input power was pulsemodulated in Group B (duty ratio:50%, frequency:100 kHz) [30]. Since it is known that the rotational temperature of N 2 in plasma with Ar is sometimes slightly higher than the kinetic temperature [36], we admit that the temperatures for Group A may differ slightly from the kinetic temperature.…”

“…In this study, ZnO and ZnO/Ag composite particles have been synthesised from the solutions of various concentrations and compositions using plasma-assisted inkjet processing. Inkjet processing in combination with plasma has been performed mainly in the printing process [20][21][22][23][24][25][26][27] and a plasmaassisted inkjet particle synthesis process, in which inkjet droplets of dissolved raw materials are introduced directly into the plasma and reaction during their flight in the plasma has also been demonstrated [28][29][30]. This process is advantageous in terms of small variations in the initial inkjet droplet sizes and localised high-energy reaction fields provided by the atmospheric-pressure plasma.…”

“…Such a local high-temperature environment, coupled with highly energetic electrons (>∼1 eV), ions, and radicals, can rapidly evaporate the solvent [33,34] and decompose the raw materials to synthesise the desired materials within a few milliseconds to tens of milliseconds [28,29]. Although the synthesis of single metal or metal oxide particles with narrow size distributions has been demonstrated by this process [28][29][30], oxide-metal mixtures have not been synthesised to date. If a controlled solution composition is maintained in the synthesised composite particles with uniform densities, physical properties such as doping amount can be easily controlled.…”