Metallic and semiconducting single-wall carbon nanotubes are distinguished using a new imaging tool for rapidly screening the structures. The technology may hasten the use of nanotubes in creating a new class of computers and electronics that are faster and consume less power than those in use today.
Photo courtesy of Weldon School of Biomedical Engineering, Purdue University  


Researchers have demonstrated an imaging tool for rapidly screening single-wall carbon nanotubes, possibly hastening their use in creating a new class of computers and electronics that are faster and consume less power than today's devices.

The semiconducting nanostructures could be used to transform electronics by replacing conventional silicon components and circuits. However, one obstacle in their application is that metallic versions form unavoidably during the manufacturing process, contaminating the semiconducting nanotubes.

At Purdue University, West Lafayette, Ind., researchers have discovered that an advanced imaging technology could solve this problem, says Ji-Xin Cheng, an associate professor of biomedical engineering and chemistry at the university.

"The imaging system uses a pulsing laser to deposit energy into the nanotubes, pumping the nanotubes from a ground state to an excited state," he says. "Then, another laser called a probe senses the excited nanotubes and reveals the contrast between metallic and semiconductor tubes."

The technique, called transient absorption, measures the "metallicity" of the tubes. The detection method might be combined with another laser to zap the unwanted metallic nanotubes as they roll off of the manufacturing line, leaving only the semiconducting tubes.

Findings are detailed in a research paper appearing online in the journal Physical Review Letters.

The transient absorption imaging technique represents the only rapid method for telling the difference between the two types of nanotubes. The technique does not require that the nanotubes be marked with dyes, making it potentially practical for manufacturing, he said.

The researchers performed the technique with nanotubes placed on a glass surface. Future work will focus on performing the imaging when nanotubes are on a silicon surface to determine how well it would work in industrial applications.

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