Two-probe study of hot carriers in reduced graphene oxide

TL;DR

This study investigates hot carrier energy relaxation in reduced graphene oxide using two-color pump-probe spectroscopy, revealing density-dependent phonon emission times and energy relaxation rates that challenge the phonon bottleneck model.

Contribution

It provides new insights into carrier relaxation dynamics in reduced graphene oxide, highlighting the density dependence of phonon emission times and energy relaxation rates.

Findings

Carrier density peaks at lower energy probe later than at higher energy

Lower energy peak shifts from 92 fs to 37 fs with increasing density

Energy relaxation rate increases from 4 to 10 meV/fs with density

Abstract

The energy relaxation of carriers in reduced graphene oxide thin films is studied using optical pump-probe spectroscopy with two probes of different colors. We measure the time difference between peaks of the carrier density at each probing energy by measuring a time-resolved differential transmission and find that the carrier density at the lower probing energy peaks later than that at the higher probing energy. Also, we find that the peak time for the lower probing energy shifts from about 92 to 37 fs after the higher probing energy peak as the carrier density is increased from 1.5E12 to 3E13 per square centimeter, while no noticeable shift is observed in that for the higher probing energy. Assuming the carriers rapidly thermalize after excitation, this indicates that the optical phonon emission time decreases from about 50 to about 20 fs and the energy relaxation rate increases from 4 to 10 meV/fs. The observed density dependence is inconsistent with the phonon bottleneck effect.