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

• Main Authors: Hokuto Fuse, Naoto Koshizaki, Yoshie Ishikawa, Zaneta Swiatkowska-Warkocka
• Format: Article
• Language: English
• Published: MDPI AG 2019-02-01
• Series: Nanomaterials
• Subjects: laser melting in liquid; Au-Fe alloy; submicrometre spherical particles; phase separation; reaction control; core-shell particles; laser wavelength; zeta potential
• Online Access: https://www.mdpi.com/2079-4991/9/2/198

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.