Dynamics of Solid Microbubble Formation

Hollow particles are usually synthesized by a templating approach in which a sacrificial core is coated with a suitable material and the core is then removed to produce a hollow particle. We report a novel technique that produces hollow particles that may be described as solid microbubbles, namely, hollow solid spheres, about 1 micron in size, surrounded by an ultra-thin solid layer. These microbubbles are formed under irradiation by an electron beam of precursor particles synthesized in a low-pressure plasma and their formation can be observed under TEM.

Toluene is introduced to a low-pressure plasma reactor that is capacitively coupled by a radio frequency generator (13.56 MHz). After formation of plasma particles they are taken to a transmission electron microscope (TEM) that works at 120 kV. Spherical plasma particles with diameter of 500±50 nm start to evolve, first grow and then shrink, over 8 to 12 seconds. Final size of the spherical particles are 1.6±0.6 microns in diameter and the average thickness of the hollow particle shells are 90 nm. We have introduced these particles to a field emission scanning electron microscope (FESEM) that works with lower accelerating voltage, 5 kV, and particles showed the same behavior and formed bubbles. These smart particles are even sensitive to other sources of energy such as argon laser that works at 120 mW.