Synthesis and structure of Ag-Si nanoparticles obtained by the electron-beam evaporation/condensation method

Abstract

Metal-semiconductor composite Ag-Si nanostructures, including Ag/Si core-shell nanoparti cles, have been synthesized for the first time by a high efficiency evaporation/condensation method using rel ativistic electron beam. In the Ag/Si core-shell nanoparticles, the core is crystalline, while the shell consists of amorphous silicon. It is found that the synthesis of these particles requires taking into account the differ ence in the saturated vapor pressures of evaporated components. The dependences of the particle size on the electron beam power at the evaporation stage and the pressure of argon at the condensation stage have been studied. It is established that (i) the main process of Ag/Si nanoparticle formation is coagulation and (ii) the Si shell formation decreases the size of particles.

Structure and mechanism of the formation of core–shell nanoparticles obtained through a one-step gas-phase synthesis by electron beam evaporation

“…For these established techniques, the mechanisms of formation have been investigated and the various parameters which affect the particle formation are known [ 1 , 6 ]. Recently, the authors have synthesized core–shell Ag–Si and Cu–Si type particles in a new way using electron beam evaporation [ 7 – 8 ]. In this method, the core–shell particles are synthesized in one-step directly from the gas phase without substrates.…”

Formation of metal/semiconductor Cu–Si composite nanostructures

“…This is indicative of the possibility of producing composite nanoparticles with various properties, which could be useful in various applications. The strong nonequilibrium processes make it possible to obtain composite nanoparticles from elements immiscible under standard conditions [5][6][7][8]. The basic parameters, as was shown here, are the ratio of the initial materials and the vapour cooling rate, which also determine the zone of particle forma-tion and their size.…”

“…Then, in the second stage, the beam current rises up to 20 mA, and the mix begins to evaporate from the surface. The transport gas comes through the nozzle (5), enters into the evaporation chamber (2), and cools the vapours of two substances and transfers them into the intermediate chamber (7) through a nozzle (6) for cooling the vapours and partial precipitation of the powder. The composite nanoparticle vapour, passing into the chamber (9) through the pipe (8), is deposited on the filter (10).…”

“…The shell can be oxides, noble metals, phosphates or polymers [3,4]. Compositions of materials that are immiscible in the bulk state, such as Mo-Cu [5], Ag-Si [6], Ag-Cu [7], Au-Ni [8], are of special interest. Shells can have both a smooth spherical or a polyhedral shape, can have mesopores [9] or dendrites [10], or can even consist of three layers [11,12].…”

“…The structure of these nanoparticles is primarily determined by the methods and conditions of synthesis, which should allow us to combine the two materials even if they are immiscible in the bulk state. In addition to chemical techniques [9][10][11][12], physical methods such as gas-phase methods [5,6,15], laser ablation [7,8,16], and magnetron-sputter gas-phase condensation [17] have been developed. When these methods are combined with the possibility of rapid heating and evaporation of both materials and the possibility of rapid controlled cooling of the resulting vapour mixture, the formation of nanoparticles with a complex structure is possible.…”