Anisotropic plasmons due to carrier electrons in Cs-doped hexagonal WO3 studied by momentum transfer resolved electron energy-loss spectroscopy

Cs-doped hexagonal WO3 (CWO) is used as a solar heat-shielding material for windows, in which plasma oscillation due to carrier electrons (carrier plasmon) plays an important role for near infrared scattering. Despite the hexagonal crystal structure of CWO, the anisotropic properties of the carrier...

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Bibliographic Details
Published in:Journal of applied physics 2019-11, Vol.126 (18)
Main Authors: Sato, Yohei K., Terauchi, Masami, Adachi, Kenji
Format: Article
Language:English
Subjects:
Anisotropy
Applied physics
Crystal structure
Damping
Electron energy
Electron energy loss spectroscopy
Electron states
Excitation
Heat shielding
Momentum transfer
Oscillation modes
Plasma oscillations
Plasmons
Properties (attributes)
Relaxation time
Solar oscillations
Tungsten oxides
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Summary:Cs-doped hexagonal WO3 (CWO) is used as a solar heat-shielding material for windows, in which plasma oscillation due to carrier electrons (carrier plasmon) plays an important role for near infrared scattering. Despite the hexagonal crystal structure of CWO, the anisotropic properties of the carrier plasmons have not been investigated. This study reports the momentum transfer resolved electron energy-loss spectroscopic measurements of CWO to investigate the anisotropic properties of carrier plasmons. The experimental results clarified that the two plasma oscillation modes at 1.2 and 1.8 eV have different excitation properties in CWO. One plasma oscillation at 1.2 eV was excited for q along the ab plane with a large damping effect, which indicated that electron excitations occur for the q//ab plane. Another mode at 1.8 eV was an oscillation excited for q along the c-axis with a small damping effect, i.e., a long plasmon relaxation time. These two modes can be interpreted by the anisotropic energy dispersion of the electronic states around the Fermi level of CWO. Such anisotropic properties of the carrier plasmons led to an accurate understanding of the heat-shielding mechanism.
ISSN:0021-8979
1089-7550
DOI:10.1063/1.5115068