Electrostatic Control over Optically Pumped Hot Electrons in Optical Gap Antennas

Abstract

We investigate the influence of a static electric field on the incoherent nonlinear response of an unloaded electrically contacted nanoscale optical gap antenna. Upon excitation by a tightly focused near-infrared femtosecond laser beam, a transient elevated temperature of the electronic distribution results in a broadband emission of nonlinear photoluminescence (N-PL). We demonstrate a modulation of the yield at which driving photons are frequency up-converted by means of an external control of the electronic surface charge density. We show that the electron temperature and consequently the N-PL intensity can be enhanced or reduced depending on the command polarity and the strength of the control static field. A modulation depth larger than 100% is observed for activation voltages of a few volts.

Wave-vector analysis of plasmon-assisted distributed nonlinear photoluminescence along Au nanowires

“…5,6 An estimation of the temperature of the electronic distribution is inferred from a fit of the spectrum (Figure S2, supporting information) using Planck's law. 4,33,34 We find the electron temperature at the bias-controlled end to be T e = 1250 K. This is a temperature somewhat cooler than previously reported values obtained from spectra measured directly under the laser focus. 4,33 This is expected because the N-PL at the bias-controlled end of the nanowire is remotely generated from the laser focus through the mediation of a lossy surface plasmon.…”

“…4,33,34 We find the electron temperature at the bias-controlled end to be T e = 1250 K. This is a temperature somewhat cooler than previously reported values obtained from spectra measured directly under the laser focus. 4,33 This is expected because the N-PL at the bias-controlled end of the nanowire is remotely generated from the laser focus through the mediation of a lossy surface plasmon. When a positive electrostatic bias (V = +20 V, Figure 1(c)) is applied to the AuNW with respect to the ground electrode, a ∼ 100% enhancement of the N-PL signal is observed at the bias-controlled end.…”

“…In an earlier report, we have shown that N-PL intensity increases with the local electron gas temperature (T e ). 33 Dwelving on the fact that T e varies as the inverse square root of the surface electron density, N e , a capacitive accumulation of positive charges at the surface of the nanowire explains the signal enhancement upon application of positive bias pulses. 33 However, Figure 2(c) features an intriguing behavior when the voltage polarity of the pulses is reversed at t = 3390 s.…”

“…Indeed, keeping the capacitive scenario in mind, this polarity should lead to a periodic quenching of the signal because of the higher electron density generated at the surface of the nanowire. 33 At t = 3445 s, +16 V voltage pulses are again applied to the system.…”

Distinguishing Thermal from Nonthermal (“Hot”) Carriers in Illuminated Molecular Junctions

“…We suggest further experiments that can be analyzed within our theory, and the necessary improvements to state-of-the-art theories for the electron nonequilibrium distribution and current through a MJ, thus providing a direct route to solving one of the outstanding questions in plasmonic systems, namely, the form of the electron distribution under continuous illumination. Finally, the methodology presented here can be used for as a starting point for a theoretical treatment of other experiments where nanoscale transport is coupled to plasmonic effects. ,,− …”