Determining the Composite Structure of Au-Fe-Based Submicrometre Spherical Particles Fabricated by Pulsed-Laser Melting in Liquid.

Hokuto Fuse,Yoshie Ishikawa,Zaneta Swiatkowska-Warkocka,Naoto Koshizaki

doi:10.3390/nano9020198

Abstract

Submicrometre spherical particles made of Au and Fe can be fabricated by pulsed-laser melting in liquid (PLML) using a mixture of Au and iron oxide nanoparticles as the raw particles dispersed in ethanol, although the detailed formation mechanism has not yet been clarified. Using a 355 nm pulsed laser to avoid extreme temperature difference between two different raw particles during laser irradiation and an Fe2O3 raw nanoparticle colloidal solution as an iron source to promote the aggregation of Au and Fe2O3 nanoparticles, we performed intensive characterization of the products and clarified the formation mechanism of Au-Fe composite submicrometre spherical particles. Because of the above two measures (Fe2O3 raw nanoparticle and 355 nm pulsed laser), the products—whether the particles are phase-separated or homogeneous alloys—basically follow the phase diagram. In Fe-rich range, the phase-separated Au-core/Fe-shell particles were formed, because quenching induces an earlier solidification of the Fe-rich component as a result of cooling from the surrounding ethanol. If the particle size is small, the quenching rate becomes very rapid and particles were less phase-separated. For high Au contents exceeding 70% in weight, crystalline Au-rich alloys were formed without phase separation. Thus, this aggregation control is required to selectively form homogeneous or phase-separated larger submicrometre-sized particles by PLML.

Highlights

Pulsed-laser melting in liquid (PLML) is a technique derived from pulsed-laser ablation in liquid (PLAL) for nanoparticle fabrication [1,2]
Submicrometre spherical particles were formed in all concentration ranges, from Au10 to Au90
From Au10 to Au60, compositional inhomogeneity, mainly in a core (Au-rich)/shell (Fe-rich) structure, was observed. This structure is totally opposite to the core (Fe-rich)/shell (Au-rich)-structured nanoparticles obtained by PLAL [36], which will be discussed later

Summary

Introduction

Pulsed-laser melting in liquid (PLML) is a technique derived from pulsed-laser ablation in liquid (PLAL) for nanoparticle fabrication [1,2]. In PLML, raw nanoparticles dispersed in liquid are irradiated by a pulsed-laser with a moderate fluence of about 50–200 mJ pulse−1 cm−2 (lower fluence than PLAL), resulting in melting and fusion of irradiated particles and subsequently the formation of submicrometre-sized spherical particles via cooling [3,4,5,6]. Given the unique features of submicrometre spherical particles—including their dispersibility, stability, crystallinity and sphericity—applications utilizing optical [5,12], medical [13], mechanical [14,15] and magnetic [16] functionality have been examined. Reactive fabrication of submicrometre spherical particles with a different composition than the raw particles has been reported for B4C from B [3,4], Cu from CuO [8] and Fe and

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Results

Conclusion