Manufacturing Bits: Sept. 13

Direct-write liquid litho; fishy DSA nanowires.


Direct-write liquid litho
The Department of Energy’s Oak Ridge National Laboratory has developed what could be called direct-write liquid lithography.

In the lab, researchers have modified a scanning transmission electron microscope (STEM). Then, using the STEM as an e-beam tool, researchers have devised a technology that enables the direct write of tiny features in “microfabricated liquid cells.”

The modified STEM makes use of an external e-beam control system and aberration-corrected technology. In the flow, researchers used grayscale images to create tiny templates. Then, using the STEM, electron beams were shot into specific locations in a sealed liquid cell. The liquid cell consist of a solution of palladium chloride.

The resolution of this system is 40nm, although researchers hope to push the technology down to 10nm. The technology enables new ways to fabricate nanostructures using direct-write lithography and liquid-phase precursors.

“We can now deposit high-purity metals at specific sites to build structures, with tailored material properties for a specific application,” said Raymond Unocic of the Center for Nanophase Materials Sciences (CNMS), a DOE Office of the Science User Facility at Oak Ridge. “We can customize architectures and chemistries. We’re only limited by systems that are dissolvable in the liquid and can undergo chemical reactions.”

Fishy DSA nanowires
Directed self-assembly (DSA) was until recently a rising star in the next-generation lithography (NGL) landscape, but the technology has recently lost some of its luster, if not its momentum.

DSA is taking longer than expected to develop and is still not in mass production in semiconductor fabs.

Still, the technology is promising in other fields. Using DSA, Hokkaido University has developed a method to pattern biomolecular nanowires.

To develop such structures, researchers have developed a self-assembly technology called structure-controllable amyloid peptides (SCAPs). The amyloid peptides are the building blocks that form the tiny nanowires.

Amyloid is a general term for protein fragments. A peptide is a compound, which consists of two or more amino acids linked in a chain. Interestingly, amyloid peptides are believed to be the causative molecules for Alzheimer’s disease, according to researchers.

To create a single or tandem nanowire structure, the SCAP process starts with a tiny template. The template is made using amyloid fibrils. A nanofibril is a material obtained from chitin, which comes from a crustacean and fishery waste.

The SCAP process allows the amyloid peptide to self-assemble and extend from the starting fibrils. Then, in another demonstration, the fibrils are attached to gold nanoparticles. The SCAP process allows these fibrils to self-assemble and extend from the template.

(Left) Growth of tandem fluorescent fibrils. (Right) Fibrils extended from gold nanoparticles placed on the surface of a substrate. (Source: Hokkaido University)

(Left) Growth of tandem fluorescent fibrils. (Right) Fibrils extended from gold nanoparticles placed on the surface of a substrate. (Source: Hokkaido University)

This method is applicable to the self-assembly of nanowires for nanoelectrodes. “It could also be used to prepare a wide variety of fibril patterns and hence open up new avenues for the development of novel self-assembled nanodevices,” said Kazuyasu Sakaguchi, a professor of the Department of Chemistry at Hokkaido University.