"He and his colleagues noted that electroadhesion, the process of adhering materials via an applied voltage, has been used in some industrial settings to pick and place large objects, such as fabrics, textiles, and whole silicon wafers. But this same electroadhesion had never been applied to objects at the microscopic level, because a new material design for controlling electroadhesion at smaller scales was needed.
Hart's group has previously worked with carbon nanotubes (CNTs)—atoms of carbon linked in a lattice pattern and rolled into microscopic tubes. CNTs are known for their exceptional mechanical, electrical, and chemical properties, and they have been widely studied as dry adhesives.
"Previous work on CNT-based dry adhesives focused on maximizing the contact area of the nanotubes to essentially create a dry Scotch tape," Hart says. "We took the opposite approach, and said, 'let's design a nanotube surface to minimize the contact area, but use electrostatics to turn on adhesion when we need it.'"
The team found that if they coated CNTs with a thin dielectric material such as aluminum oxide, when they applied a voltage to the nanotubes, the ceramic layer became polarized, meaning its positive and negative charges became temporarily separated. For instance, the positive charges of the tips of the nanotubes induced an opposite polarization in any nearby conducting material, such as a microscopic electronic element.
As a result, the nanotube-based stamp adhered to the element, picking it up like tiny, electrostatic fingers. When the researchers turned the voltage off, the nanotubes and the element depolarized, and the "stickiness" went away, allowing the stamp to detach and place the object onto a given surface. 'Electroadhesive' stamp picks up and puts down microscopic structures
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