Thursday, December 11, 2014

Atomic Layer Lithography - Creation of nanogaps by ALD

A team led by Sang-Hyun Oh of the University of Minnesota is now saying that it has produced SEIRA (surface-enhanced infrared absorption) enhancements as high as 105 for nanogaps just 3 nm across arranged in a dense array of millimetre-long hotspots.

“In our scheme, we create the nanogaps by depositing thin layers of aluminium oxide on the sidewalls of metal patterns using a well known technique called atomic layer deposition,” Oh tells nanotechweb.org. “We can use this technique to control the thickness of the film, which then defines the gap width on the Angstrom scale. And since thin-film deposition is a fast batch process, we can also make dense arrays of nanogaps over an entire wafer in a quick and easy way.”

The researchers use standard photolithography to pattern gold films on a 4 inch silicon wafer. These patterns are conformally encapsulated with a thin alumina spacer using atomic layer deposition (ALD). Next, a silver film is deposited conformally on the pattern, and the whole structure is stripped off from the silicon substrate using UV cured epoxy and a glass slide. f) Cross-sectional schematic of a buried nanocavity. g) Contact mode AFM line scan across a 5 nm nanogap cavity showing a height difference between the gold and silver films due to the 5 nm thick Al<sub>2</sub>O<sub>3</sub> film. h) Photograph of a 4 inch wafer-containing metal stripes after lift-off. Each square is approximately 1.5 by 1.5 mm. i) SEM image of an array of buried nanogaps on a chip. Further zoomed-in images show a single cavity and a 5 nm nanogap on one side of the cavity. j and k) SEM of buried disks and wedges. Courtesy: <i>Nano Lett.</i>

The researchers use standard photolithography to pattern gold films on a 4 inch silicon wafer. These patterns are conformally encapsulated with a thin alumina spacer using atomic layer deposition (ALD). Next, a silver film is deposited conformally on the pattern, and the whole structure is stripped off from the silicon substrate using UV cured epoxy and a glass slide. f) Cross-sectional schematic of a buried nanocavity. g) Contact mode AFM line scan across a 5 nm nanogap cavity showing a height difference between the gold and silver films due to the 5 nm thick Al2O3 film. h) Photograph of a 4 inch wafer-containing metal stripes after lift-off. Each square is approximately 1.5 by 1.5 mm. i) SEM image of an array of buried nanogaps on a chip. Further zoomed-in images show a single cavity and a 5 nm nanogap on one side of the cavity. j and k) SEM of buried disks and wedges. Pictures from: Nano Lett.

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