Formation of gold nanoparticles in a free-standing ionic liquid triggered by heat and electron irradiation. (February 2019)

• Record Type: Journal Article
• Authors: Keller, Debora; Henninen, Trond R.; Erni, Rolf
• Is Part Of: Micron. Volume 117(2019)
• Page Start: 16
• Page End: 21
• Publication Date: 2019-02
• Subjects: Ionic liquid -- In situ -- TEM -- Heat -- Gold -- Nanoparticle growth; Microscopy -- Periodicals; Electron Probe Microanalysis -- Periodicals; Microscopy -- Periodicals; Microscopie -- Périodiques; Microscopy; Periodicals; 502.82
• DOI: 10.1016/j.micron.2018.10.008
• Languages: English
• ISSNs: 0968-4328

Abstract

Graphical abstract: Highlights: Au particle formation is studied by in situ transmission electron microscopy in an ionic liquid. The nanoparticle growth process is triggered by in situ heating and electron irradiation. Small (<10 nm), spherical nanoparticles are created during the initial, isotropic growth phase. Growth by monomer attachment, Ostwald ripening and coalescence are observed. The second growth phase shows anisotropic growth of large (>10 nm), faceted particles. Abstract: Ionic liquids (ILs) feature negligibly low vapor pressures and can thus be freely introduced into the high vacuum of a transmission electron microscope. With this extraordinary property, the ILs offer a powerful tool for in situ transmission electron microscopy (TEM) in window-free liquid media at very high resolution. In this work, we use the IL 1-butyl-3-methylimidazolium chloride in order to study nucleation and growth of gold nanoparticles (NPs) in free-standing liquid droplets by scanning TEM (STEM). The results confirm that the used IL allows for generating Au NPs in situ, triggered by electron irradiation and heat. Firstly, the isotropic growth of small, spherical Au NPs was initiated and monitored, whereas different growth mechanisms were observed, i.e. growth by monomer attachment, growth through particle coalescence and possible Ostwald ripening events. After the initial growth phase, a second, anisotropic growth process was induced by a moderate temperature increase and continued electron irradiation. As a result, larger, faceted crystals, such as tetrahedra, octahedra or decahedra, were formed. As all these polymorphs are terminated by {111}-facets, the IL might not only act as liquid medium but in addition as a surfactant which preferentially attaches on the {100}-facets.