Two-probe study of hot carriers in reduced graphene oxide

Journal of Applied Physics (Impact Factor: 2.18). 03/2011; 109(8). DOI: 10.1063/1.3573674
Source: arXiv


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.

Download full-text


Available from: Hui Zhao, May 12, 2015
  • Source
    • "A large body of experimental work on ultrafast spectroscopy of graphene is available [1] [2] [3] [4] .However, so far, most studies have been performed with a time resolution which is too low to observe e-e scattering dynamics and thus have probed an equilibrated hot electron/hole distribution, established within the pump pulse duration (~100- 150 fs). These studies have revealed the dynamics of carrier cooling through interaction with the lattice. "
    [Show abstract] [Hide abstract]
    ABSTRACT: We study the ultrafast dynamics of non-thermal electron relaxation in graphene upon impulsive excitation. The 10-fs resolution two color pump-probe allows us to unveil the non-equilibrium electron gas decay at early times.
    The European Physical Journal Conferences 05/2012; DOI:10.1051/epjconf/20134104025
  • [Show abstract] [Hide abstract]
    ABSTRACT: Ultra-fast optical measurements of few-layer suspended graphene films grown by chemical vapor deposition were performed with femtosecond pump–probe spectroscopy. The relaxation processes were monitored in transient differential transmission (ΔT/T) after excitation at two different wavelengths of 350 and 680 nm. Intraband electron–electron scattering, electron–phonon scattering, interband Auger recombination and impact ionization were considered to contribute to ΔT/T. All these processes may play important roles in spreading the quasiparticle distribution in time scales up to 100 fs. Optical phonon emission and absorption by highly excited non-equilibrium electrons were identified from ΔT/T peaks in the wide spectral range. When the probe energy region was far from the pump energy, the energy dependence of the quasiparticle decay rate was found to be linear. Longer lifetimes were observed when the quasiparticle population was localized due to optical phonon emission or absorption.
    Applied Physics B 04/2012; 107(1). DOI:10.1007/s00340-011-4853-0 · 1.86 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Carrier dynamics in single-layer graphene grown by chemical vapor deposition (CVD) is studied using spatially and temporally resolved pump-probe spectroscopy by measuring both differential transmission and differential reflection. By studying the expansion of a Gaussian spatial profile of carriers excited by a 1500-nm pump pulse with a 1761-nm probe pulse, we observe a diffusion of hot carriers of 5500 square centimeter per second. We also observe that the expansion of the carrier density profile decreases to a slow rate within 1 ps, which is unexpected. Furthermore, by using an 810-nm probe pulse we observe that both the differential transmission and reflection change signs, but also that this sign change can be permanently removed by exposure of the graphene to femtosecond laser pulses of relatively high fluence. This indicates that the differential transmission and reflection at later times may not be directly caused by carriers, but may be from some residue material from the sample fabrication or transfer process.
    Optical Materials Express 04/2012; 2(6). DOI:10.1364/OME.2.000708 · 2.84 Impact Factor
Show more