High-Brightness Plasmon-Enhanced Nanostructured Gold Photoemitter

Plasmonic nanohole arrays are fabricated in gold thin films by focused ion beam (FIB) lithography. Subsequent heat treatment creates sub 100 nm nanometric structures including tips, rods and flakes, all localized in the nanohole array region. The combined nanohole array and nanostructured surface comprise an efficient photoemitter. High brightness photoemission is observed from this construct using photoemission electron microscopy (PEEM), following 780 nm femtosecond (fs) laser irradiation. By comparing our observables to results of finite difference time domain (FDTD) calculations, we demonstrate that photoemission from the sub-100 nm structures is enhanced in the region of propagating surface plasmons launched from the nanohole arrays. Additionally, by tuning hole diameter and separation in the nanohole array, the photoemission intensity of nanostructured photoemitters can be controlled. We observe a photoemission enhancement of over 108, relative to photoemission from the flat region of the gold substrate at laser intensities well below the ablation threshold.

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