Exploring nanoscale thermal variations and photo-induced surface potential enhancement in plasmonic nanostructures

A significant consequence of resonant excitation is conversion of absorbed optical energy into heat, producing temperature gradients confined to the nanoscale. Despite this intrinsic nanoscale, most experimental thermal characterisations remain limited to micrometre resolution owing to diffraction limits, leaving the true spatial distribution of photothermal effects largely unresolved.<br>To resolve this limitation, a quantitative scanning-probe framework was implemented to map nanoscale temperature distributions in fabricated plasmonic arrays.

Scanning thermal microscopy (SThM) was used to image ordered gold (Au) and iron (Fe) nanodome arrays under two illumination geometries: top and bottom configurations. Comparative analysis shows that top illumination affords superior optical coupling and yields larger, highly localised temperature increases (ΔT ≈ 4.7 °C at 1.6 mW), whereas bottom illumination produces smaller but resolvable rises (ΔT ≈ 0.88 °C at 1.09 mW) for identical Au nanodomes.<br>The bottom-illumination geometry was adapted for photo-modulated Kelvin probe force microscopy (KPFM) to probe plasmo-electric effects and hot-carrier dynamics.