Researchers at Harvard University, US have developed a new, clean and simple ice lithography technique, to fabricate nanodevices. In this method a thin film of water ice is used as a resist for electron-beam lithography. This procedure does not contaminate or degrade samples, unlike other conventional nanofabrication methods. The fabrication can be made in one cluster tool, a modified scanning electron microscope (SEM).
Here, the sample made of carbon nanotubes is loaded into their SEM. cooled to 110 K and water vapour is leaked into the SEM vacuum to condense as a layer of amorphous ice on the cold sample. Using the SEM's electron beam, patterns are drawn on the sample when ice in those areas is removed to add electrical leads, thus forming a mask for metal electrodes contacting the nanotubes. Because ice is transparent, the researchers were able to see through it and make sure that the electrodes were precisely aligned with the nanotubes. The ice layer also protects the nanotubes and the sample with its nanopatterned ice resists. It is then transferred to another chamber, where it is sputtered with palladium (Pd). The sample is removed and quickly dunked into a room-temperature alcohol solution to remove the ice and Pd film from on top of the ice, leaving behind just the electrical leads connected to the nanotubes. Interconnections between the Pd and nanotubes exist at the points where ice had originally been removed by the electron beam and the resulting structure acts as a transistor.