Nanowriting a big step in electronics

U. ILLINOIS (US) — A method for direct writing of metal lines less than five nanometers wide is expected to have a big impact in creating contacts to and interconnects between nanoscale device structures.

Recent research has demonstrated methods for depositing graphene on semiconducting substrates and creating semiconducting carbon nanotubes that make these carbon-based materials practical candidates for integration into electronics and other devices that now rely on silicon and certain metals to operate.

In the new research, published in ACS Nano, scientists report on a technique for the patterning of metallic nanostructures on surfaces toward future fabrication of nanoelectronics and quantum devices.

Joe Lyding, professor of electrical and computer engineering, Gregory Girolami, professor of chemistry, and Angus Rockett, professor of materials science and engineering, all at the University of Illinois, say that current top-down fabrication technologies used in industry involve conventional lithographic processes, which are approaching their fundamental size limits.

Responding to the current challenges involving fabrication at scales smaller than 10 nm, the researchers demonstrated the ability to write metal lines that are less than 5nm wide.

“To do this we use the electrons from our STM tip to ‘crack’ molecules that are introduced in the gas phase to the STM tip-sample junction. The procedure of using STM electrons to break apart molecules and yield a metallic deposit is not new, however previous attempts have been plagued by high levels of carbon impurities in the deposits and metallic behavior had not been demonstrated.

“To circumvent this issue we used a novel molecular precursor for the metallic ceramic hafnium diboride that was developed by Gregory Girolami for low temperature chemical vapor deposition (CVD) applications,” the study says.

Girolami’s CVD precursor contains no carbon; only hafnium, boron and hydrogen. Electron beam induced deposition (EBID) by the STM cleanly drives out the hydrogen leaving a metallic HfB2 deposit, as confirmed by STM spectroscopy.

In conclusion, the researchers write that “To our knowledge this is the first demonstration of sub-5 nm metallic nanostructures in an STM-EBID experiment, and it opens new opportunities for making deterministic molecular scale metallic contacts.”

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