The Stanford researchers put down a thin layer of gold with each stamp. Once the gold and nanotubes are in place, the researchers etch away areas of gold where they want to place each transistor’s electrical contacts. They then fill these holes with a metal contact material such titanium and palladium. Finally, they etch away the rest of the gold. This entire structure is built up on top of a silicon dioxide wafer patterned with back gates for the transistors. This work is described online this week in the journal Nano Letters.
Mitra says it should be possible to perform several transfers for for a density of 100 to 200 nanotubes per micrometer. The transfer technique is also compatible with techniques the group has developed in the past to deal with stray metallic nanotubes and the occasional misplaced nanotube.
“Nanotubes are messy to work with today,” says Franklin. But “there is no fundamental bottleneck that says this can’t be done.”