Each micromotor is shaped like pollen and measures only 12 microns wide - about a tenth the width of a human hair. These particles are manufactured from zinc oxide and are coated with an ultra-thin layer of gold. The gold layer is essential, as it absorbs heat from directed near infrared light.
When the light beam is targeted at the micromotors, the gold rapidly heats, warming the surrounding air. This temperature differential generates subtle convection currents under and around the particles, causing them to lift off surfaces and move through the air. Researchers can steer the micromotors by simply adjusting the angle and location of the light beam, offering fine control over direction and motion without the need for onboard power, fuel, or wires.
Previously, the movement of micromotors depended on fluids such as water because buoyancy would support the tiny structures and enable propulsion. Moving in air, where gravity dominates and there is no surrounding fluid, posed a far more complex engineering challenge. The Concordia team's successful demonstration means similar light-driven mechanisms could be adapted for use in open air environments.
Potential future applications include dispersing microscopic sensors for real-time pollution monitoring, deploying airborne cleaning agents to mitigate particle contaminants, or developing swarms of light-controlled micro-vehicles for research in challenging or hard-to-access environments.
The study was led by John Capobianco, now professor emeritus and Honorary Chair in Nanoscience at Concordia University. The research was backed by the Natural Sciences and Engineering Research Council of Canada (NSERC) and received additional support from the FABrIC project, funded through CMC Microsystems and the Government of Canada.
Research Report:Light-Activated Micromotors in Air Propelled by Thermal Convection
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