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2-D and 3-D Nanosculptured Thin Film

In this Letter, glancing angle deposition is used to form an aluminum-jointed silicon dioxide octagon nanohelix array as a 3D nanostructured thin film. As a sculptured metal–dielectric composite, the film exhibits a complex refractive index of near unity with a small imaginary part. This structured film is demonstrated as an efficient light absorber to absorb light in a broad band and over a wide range of angles for both polarization states.

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Metals have been formed into nanostructures to absorb light with high efficiency through surface plasmon resonances. An ultra-thin plasmonic structure that exhibits strong absorption over wide ranges of wavelengths and angles of incidence is sought. In this work, a nearly perfect plasmonic nanostructure is fabricated using glancing angle deposition. The difference between the morphologies of obliquely deposited aluminum and silver nanohelices is exploited to form a novel three-dimensional structure,which is an aluminum-silver nanohelix array on a pattern-free substrate. With a thickness of only 70 nm, densely distributed nanohelices support rod-to-rod localized surface plasmons for broadband and polarization-independent light extinction. The extinctance remains high over wavelengths from 400 nm to 2000 nm and angles of incidence from 0° to 70°.

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Gold nanohelix arrays (NHAs) were fabricated on a smooth glass substrate using glancing angle deposition technique. At a deposition angle of 89°, gold NHAs were fabricated by introducing liquid nitrogen to flow under the backside of BK7 glass substrate holder to reduce the temperature of substrate to be around −140 °C under deposition. The spin rate was controlled with respect to the deposition rate to grow three different sized nanohelices. The morphology and optical properties were measured and compared for the three samples. In application, the surface-enhanced Raman scattering (SERS) from each three-dimensional NHA was measured and analyzed with near field simulation.

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