Exploring unusual temperature-dependent optical properties of graphite single crystal by spectroscopic ellipsometry
Journal
Carbon
Journal Volume
197
Start Page
485
End Page
493
ISSN
00086223
Date Issued
2022
Author(s)
Abstract
This study investigated the optical properties of graphite single crystal as a function of temperature between 4.5 and 500 K and within the spectral range of 0.73–6.42 eV through spectroscopic ellipsometry. At room temperature, the complex dielectric function of graphite exhibited broad spectra in the ultraviolet energy region. The Breit–Wigner–Fano (BWF) line shape analysis of the optical absorption spectrum demonstrated that two BWF line shapes were fitted with central energies at 4.85 ± 0.01 eV and 6.21 ± 0.03 eV. These two features were attributed to interference between an excitonic transition at the saddle point (M) in the band structures and collective excitations of the surface plasmons. Analysis of the temperature-dependent asymmetric BWF line shape indicated that the peak position shifted to lower energies under increasing temperatures, with the linewidth becoming narrow and the intensity increasing; this can be explained by the asymmetric factor 1/qBWF, which decreased under increasing temperatures. The temperature dependence of optical absorption for graphite is opposite to that of the interband absorptions observed in silicon. First-principles calculations verified the presence of two resonant conditions in the ultraviolet energy region. The lifetime of surface plasmons was expected to decrease with increased temperatures, leading to a decrease of the 1/qBWF. These results offer insight into quasiparticle band structures and collective excitations of graphite and provide valuable information for the technological development of graphite-based ultraviolet optoelectronic and photonic devices at different temperatures.
Subjects
Absorption Spectroscopy
Calculations
Light Absorption
Optical Properties
Photonic Devices
Single Crystals
Spectroscopic Ellipsometry
Surface Plasmons
Temperature Distribution
Broad Spectrum
Collective Excitations
Complex Dielectric Functions
Energy Regions
Increasing Temperatures
Line Shape Analysis
Lines Shapes
Spectral Range
Surface-plasmon
Temperature Dependent
Graphite
SDGs
Publisher
Elsevier Ltd
Type
journal article