Plasmon-induced efficient hot carrier generation in graphene on gold ultrathin film with periodic array of holes: Ultrafast pump-probe spectroscopy

TL;DR

This study demonstrates that plasmonic resonances in a gold nanostructure with a hole array can efficiently generate hot carriers in adjacent graphene, with ultrafast dynamics and high spatial confinement, advancing hot carrier device potential.

Contribution

It reveals the mechanism of plasmon-induced hot carrier generation in graphene on holey gold films using ultrafast spectroscopy, highlighting the role of localized plasmonic fields and decay dynamics.

Findings

Efficient hot carrier generation at plasmonic resonances.

Hot carriers are highly confined near hole edges within 10-100 fs.

Decay dynamics include diffusion of hot carriers from edges.

Abstract

Using ultrafast pump-probe reflectivity with 3.1 eV pump and coherent white light probe (1.1 to 2.6 eV), we show that graphene on gold nanostructures exhibits a strong coupling to the plasmonic resonances of the ordered lattice hole array, thus injecting a high density of hot carriers in graphene through plasmons. The system being studied is single-layer graphene on ultrathin film of gold with periodic arrangements of holes showing anomalous transmission. A comparison is made with gold film with and without hole array. By selectively probing transient carrier dynamics in the spectral regions corresponding to plasmonic resonances, we show efficient plasmon-induced hot carrier generation in graphene. We also show that due to high electromagnetic field intensities at the edge of the sub-micron holes, fast decay time (10-100 fs) and short decay length (1 nm) of plasmons, a highly confined density of hot carriers (very close to edge of the holes) is generated by Landau damping of plasmons within the holey gold film. A contribution to transient decay dynamics due to diffusion of initial non-uniform distribution of hot carriers away from the hole edges is observed. Our results are important for future applications of novel hot carrier device concepts where hot carriers with tunable energy can be generated in different graphene regions connected seamlessly.