Ultrafast Plasmon Thermalization in Epitaxial Graphene Probed by Time‐Resolved THz Spectroscopy

The control of carrier transport by electrical, chemical, or optical Fermi level tuning is central to graphene electronics. Here, an optical pump—terahertz (THz) probe spectroscopy—is applied to investigate ultrafast sheet conductivity dynamics in various epitaxially grown graphene layers representi...

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Bibliographic Details
Published in:Advanced functional materials Vol. 31; no. 45
Main Authors: Paingad, Vaisakh C., Kunc, Jan, Rejhon, Martin, Rychetský, Ivan, Mohelský, Ivan, Orlita, Milan, Kužel, Petr
Format: Journal Article
Language:English
Published: Hoboken Wiley Subscription Services, Inc 01.11.2021
Wiley
Subjects:
Allotropy
carrier cooling
Carrier mobility
Carrier transport
Chemical potential
Condensed Matter
Confinement
Cooling
epitaxial graphene
Epitaxial growth
Fermi level
Graphene
Graphical representations
localized plasmon
Materials Science
Physics
Plasmonics
sheet conductivity
Spectroscopy
Spectrum analysis
Substrates
terahertz
Thermalization (energy absorption)
ultrafast thermalization dynamics
localized plasmon
Fermi level
terahertz
epitaxial graphene
sheet conductivity
carrier cooling
ultrafast
ISSN:1616-301X, 1616-3028
Online Access:Get full text
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Summary:The control of carrier transport by electrical, chemical, or optical Fermi level tuning is central to graphene electronics. Here, an optical pump—terahertz (THz) probe spectroscopy—is applied to investigate ultrafast sheet conductivity dynamics in various epitaxially grown graphene layers representing a large variety of carbon allotropes, including H2 intercalated films. The graphene layers display a prominent plasmonic response connected with induced THz transparency spectra on ultrashort timescale. It is generally believed that the plasmonic excitations appear due to wrinkles, and substrate terraces that bring about natural confinement potentials. It is shown that these potentials act within micrometer‐sized domains with essentially isotropic character. The measured ultrafast dynamics are entirely controlled by the quasi‐Fermi level of laser‐excited carriers through their temperature. The photocarriers undergo a disorder‐enabled super‐collision cooling process with an initial picosecond transfer of the optically deposited heat to the lattice followed by a sub‐nanosecond relaxation governed by the lattice cooling. The transient spectra is described by a two‐temperature Drude‐Lorentz model revealing the ultrafast evolution of the carrier temperature and chemical potential and providing crucial material parameters such as Fermi energy, carrier mobility, carrier confinement length, and disorder mean free path. Graphene electronics rely on various routes towards Fermi level tuning. The plasmonic response of laser heated carriers on picosecond timescale in various allotropes of epitaxial graphene is assessed. This reveals ultrafast dynamics of the carriers’ Fermi level and temperature, and their relaxation is mediated by disorder‐assisted super collision cooling.
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ISSN:1616-301X
1616-3028
DOI:10.1002/adfm.202105763