Here only microspheres and microbubbles made in amorphous materials, namely in oxide or chalcogenide glasses and in amorphous polymers, will be considered. For the sake of completeness, however, it should be noted that many other materials, either natural or synthetic, can be used to fabricate Ms&Mb for different applications.
A few examples include stainless steel microspheres (for conductive spacers, shock absorption, and micromotor bearings); metallic nickel hollow glass microspheres (enhanced magnetic properties; Ni/Pt bimetallic microbubbles have potential applications in portable hydrogen generation systems, due to catalytic properties); single-crystal ferrite microspheres (for applications not only as magnetic materials but also in ferroflfluid technology and in biomedical fifields, e.g., biomolecular separations, cancer diagnosis and treatment, magnetic resonance imaging); single-crystal semiconductor microspheres (for active WGM resonators); ceramic ZrO2 hollow glass microspheres (for thermal applications).
Glass, polymer, ceramic, metal solid and hollow glass microspheres are commercially available; there is a wide choice of quality, sphericity (Sphericity was defifined in 1935 by the geologist H. Wadell, with reference to quartz particles (J. Geology 1935, 43, 250) as the ratio of the surface area of a sphere (with the same volume as the given particle) to the surface area of the particle), uniformity, particle size and particle size distribution, to allow the optimal choice for each unique application.
