Hot phonon decay in supported and suspended exfoliated graphene

TL;DR

This study investigates ultrafast charge carrier dynamics in graphene using pump-probe spectroscopy, revealing faster hot phonon decay in monolayer graphene compared to multilayer, independent of substrate coupling.

Contribution

It provides the first direct measurement of hot phonon decay rates in supported and suspended graphene, demonstrating intrinsic decay mechanisms.

Findings

Hot phonon decay occurs on 2 ps timescale.

Decay rate is faster in monolayer than multilayer graphene.

Enhanced decay is independent of substrate coupling.

Abstract

Near infrared pump-probe spectroscopy has been used to measure the ultrafast dynamics of photoexcited charge carriers in monolayer and multilayer graphene. We observe two decay processes occurring on 100 fs and 2 ps timescales. The first is attributed to the rapid electron-phonon thermalisation in the system. The second timescale is found to be due to the slow decay of hot phonons. Using a simple theoretical model we calculate the hot phonon decay rate and show that it is significantly faster in monolayer flakes than in multilayer ones. In contrast to recent claims, we show that this enhanced decay rate is not due to the coupling to substrate phonons, since we have also seen the same effect in suspended flakes. Possible intrinsic decay mechanisms that could cause such an effect are discussed.