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Laser-Aided Imaging May Speed Nanoelectronics Manufacturing

by Editor1 last modified December 13, 2010 - 17:31

Purdue University scientists have demonstrated a new laser-based imaging tool that could speed commercialization of semiconducting single-walled carbon nanotubes (SWNTs) for electronics and computers.

Laser-Aided Imaging May Speed Nanoelectronics Manufacturing

Metallic and semiconducting SWNTs are distinguished with a new imaging tool from Purdue researchers. Credit: Weldon School of Biomedical Engineering, Purdue University.

One big obstacle in mass producing SWNTs for semiconductors is the inability to remove metallic contaminants during the manufacturing process for semiconductor SWNTs. The Perdue team found their laser-aided advanced imaging technology could help solve this problem.

"The imaging system uses a pulsing laser to deposit energy into the nanotubes, pumping the nanotubes from a ground state to an excited state," said Purdue’s Ji-Xin Cheng, an associate professor of biomedical engineering and chemistry. "Then, another laser called a probe senses the excited nanotubes and reveals the contrast between metallic and semiconductor tubes."

Purdue researchers, working at its Weldon School of Biomedical Engineering, performed an imaging technique called “transient absorption” which, Cheng said, is the only rapid method for telling the difference between the two types of nanotubes. A key advantage to the technique, he added, is "label free," meaning it does not require that the nanotubes be marked with dyes, making it potentially practical for manufacturing.

Inside Laser-aided Advanced Imaging for SWNTs
The work focuses on performing transient absorption with nanotubes placed on a glass surface. "They can be seen with an atomic force microscope [AFM], but this only tells you the morphology and surface features, not the metallic state of the nanotube," Cheng said.

Cheng's research group, working with nanomaterials for biomedical studies, noticed the metallic nanoparticles and semiconducting nanowires transmitted and absorbed light differently after being exposed to the pulsing laser. The finding revealed that semiconductors conduct electricity under some conditions but not others, making them ideal for controlling electrical current in devices such as transistors and diodes.

Chen Yang, a fellow assistant professor at Purdue said the method might be used to screen the nanotubes for nanoelectronics. "When you make nanocircuits, you only want the semiconducting ones, so it's very important to have a method to identify the metallic nanotubes."

The detection method could even be combined with another laser to eliminate the unwanted metallic nanotubes as they roll off of the manufacturing line, leaving behind only the semiconducting tubes, Cheng added.

Findings are detailed in the journal Physical Review Letters. The research is funded by the National Science Foundation.

Authors of the paper include Cheng, Yang and Alexander E. Ribbe, manager of the Nanotechnology Group in Purdue's Department of Chemistry, Purdue physics doctoral student Yookyung Jung; biomedical engineering research scientist Mikhail N. Slipchenko; Chang-Hua Liu, an electrical engineering graduate student at the University of Michigan; Zhaohui Zhong, an assistant professor of electrical engineering and computer science at Michigan.

The team plans future work to focus on performing the imaging when nanotubes are on a silicon surface to determine how well it would work in industrial applications. SWNTs are formed by rolling up a one-atom-thick layer of graphite called graphene, a material which has the potential to rival silicon as a basis for computer chips.