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Hot carriers are energetic photoexcited carriers driving a large range of chemicophysical mechanisms. At the nanoscale, an efficient generation of these carriers is facilitated by illuminating plasmonic antennas. However, the ultrafast relaxation rate severally impedes their deployment in future hot-carrier based devices.
In this paper, we report on the picosecond relaxation dynamics of hot carriers in plasmonic monocrystalline gold nanoantennas. The ultrafast dynamics of the hot carriers is experimentally investigated by interrogating the nonlinear photoluminescence response of the antenna [1]. From this investigation, we reveal some leverages to control the dynamics of such hot carriers within nano antenna. In particular, an increase by a factor up to five of this dynamics (from 0.5 ps to 2.5 ps) is observed for resonant nanoantenna compared to off-resonance antenna and when excitation power increases. By a two temperature model we model quantitatively the dynamics of hot carriers and we demonstrate the nonlinear generation of these carriers. The control over the carrier dynamics should allow to employ their energy more effieciently within physico-chemical processes.
In a second part, we investigate the hot carrier dynamics with a spectrally resolved two-pulse correlation configuration, and demonstrate that the relaxation of the photoexcited carriers depends of their energies relative to the Fermi level. We find a 60% variation in the relaxation rate for electron−hole pair energies ranging from ca. 0.2 to 1.8 eV. The quantitative relationship between hot-carrier energy and relaxation dynamics is an important finding for optimizing hot-carrier-assisted processes and shed new light on the intricacy of nonlinear photoluminescence in plasmonic [2].
[1] O. Demichel et al, ACS Photonics 3, 791 (2016)
[2] R. Méjard et al, ACS Photonics 3, 1482 (2016)
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