Ice Lithography on the Nanoscale Moves Up a Notch in Complexity

Researchers at Harvard University are moving beyond patterning simple nanowires with ice lithography to creating more complex nanodevices.

The Harvard researchers, who are part of the Harvard Nanopore Group, including Daniel Branton and Anpan Han, published research back in 2005 that demonstrated that they could successfully execute nanometer-scale patterning with ice.

Now the researchers have reported in the November 1, 2010 online edition of Nano Letters that they can use ice lithography to produce nanodevices made from single-walled carbon nanotubes.

According to interviews for both Branton and Han in a Nanowerk article, the research provides a method for scaling up the applications for CNT-based nanodevices.

One of the ways in which the ice method provides scaling potential is by replacing atomic force microscopes (AFM) with scanning electron microscopes (SEM) in the mapping of the carbon nanotubes.

“Although not generally spelled out in publications, it is well known among the cognoscenti that nanotubes are contaminated or damaged by mapping their location in an electron microscope" Han is quoted as saying in the Nanowerk article. "To avoid contaminating or damaging, CNTs are often mapped by atomic force microscopes (AFM). But AFM is extremely slow. SEM mapping through ice is much faster and could be automated."

Ice lithography also eliminates a problem when using polymer-based resists, the resist residue affectionately known in the semiconductor industry as ‘scum’. While the scum is often less than one or two nanometers thick, that’s enough to obscure partially a carbon nanotube or to bosure completely a single layer for graphene. The process of getting rid of the scum (oxygen plasma) also manages to remove any carbon-based nanocomponents, according to Han. 

The ice lithography technique doesn’t leave any residue, which will likely improve the quality of the resulting nanodevices.

Now that the researchers have moved their research from patterning of simple nanowires to nanodevices, they see the next steps to be in the direction of making 3D nano- and graphene-based devices with this ice lithography technique. But the fundamental research into understanding the mechanisms behind ice lithography remains incomplete.

“Finally, we need to achieve a deeper understanding of the mechanisms behind ice lithography, about which we still know very little," says Branton.

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Nanoclast

IEEE Spectrum’s nanotechnology blog, featuring news and analysis about the development, applications, and future of science and technology at the nanoscale.

 
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