Transistors can be built more precisely by using ice as a mask, according to researchers at Harvard University. Daniel Branton and colleagues placed single-walled carbon nanotubes onto a silicon wafer, cooled it to about -163 Celsius, and sprayed it with water, which formed an 80-nanometer-thick layer of ice. The team used an electron beam to carve away two squares of ice, exposing the tops of some nanotubes, and deposited a layer of palladium on top of the ice mask. The researchers dipped the structure in alcohol to melt the ice. The palladium layer above it fell off, except in the two squares where the metal had stuck directly to the nanotubes. The resulting cluster of nanotubes, fused to two palladium electrodes, acted as a transistor.
The process, dubbed ice lithography, resembles how computer chips are made, but using ice is cleaner, cheaper, and gentler on the nanotubes. Also, the use of ice, which is a clear solid, allows researchers to see where to remove sections of the mask so that electrodes end up precisely aligned with the nanotubes below. "It could potentially fabricate devices which might be very difficult to fabricate using standard lithographic procedures," Branton says.
From New Scientist
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