Inelastic electron scattering by intra- and interband plasmons in rhenium trioxide, tungsten trioxide, and some tungsten bronzes
Energy-loss spectra were measured by backscattering 500-eV electrons from films of WO/sub 3/ grown on single-crystal W(100), and from single crystals of Na/sub x/WO/sub 3/ (0.35 < x < 0.86) and ReO/sub 3/ which were cleaved in ultrahigh vacuum. The spectrum of a crystal with x = 0.61 was nearly identical to the surface loss function Im(-(epsilon + 1)/sup -/1) calculated from epsilon measured by optical reflectivity on a crystal with x = 0.65. For x = 0.61, two plasmons are observed, ..omega../sub -/ = 1.90 eV, and ..omega../sub +/ = 6.5 eV. ..omega../sub -/ scales approximately as x/sup 1/2/ and is assigned to the conduction-electron resonance. The plasmon lifetime tau/sub p/ = 1.9 x 10/sup -/15 sec determined from the observed linewidth agrees well with a value for the conduction-electron relaxation time tau/sub e/ = 2.1 x 10/sup -/15 sec we obtained from previously reported reflectivity data, but is shorter than a value tau/sub c/ = 6.7 x 10/sup -/15 sec we estimated from previously reported dc conductivity data. The higher-energy plasmon ..omega../sub +/ is assigned to a screened longitudinal resonance of an interband excitation near 5 eV. ..omega../sub +/ is essentially independent of x for 0 < or = x < 0.9. By fitting epsilon between 0 and 10 eV with a model dielectric function, we found a value for the mean effective conduction electron mass m* = 0.80m/sub e/, the interband contribution to the static dielectric constant epsilon/sub s/ = 4.35, and values for parameters characterizing the interband resonance. Taking these latter parameters to be independent of x, we calculated the bulk and surface loss functions for different x values. These calculations indicate that mode hybridization is unimportant for x < 1 in the bronzes. The effects of damping or joint density-of-states width, screening, and mode interference on the plasmon spectra are discussed. It is shown that ReO/sub 3/ and Ag metal have dielectric and energy-loss functions which are similar to the tungsten bronzes.
- Research Organization:
- Bell Laboratories, Murray Hill, New Jersey 07974
- OSTI ID:
- 6848091
- Journal Information:
- Phys. Rev., B; (United States), Vol. 17:10
- Country of Publication:
- United States
- Language:
- English
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RHENIUM OXIDES
ENERGY SPECTRA
OPTICAL PROPERTIES
TUNGSTEN OXIDES
COPPER ALLOYS
TIN ALLOYS
TUNGSTEN BASE ALLOYS
ELECTRONS
ENERGY LOSSES
INELASTIC SCATTERING
PLASMONS
ALLOYS
CHALCOGENIDES
ELEMENTARY PARTICLES
FERMIONS
LEPTONS
OXIDES
OXYGEN COMPOUNDS
PHYSICAL PROPERTIES
QUASI PARTICLES
RHENIUM COMPOUNDS
SCATTERING
SPECTRA
TRANSITION ELEMENT COMPOUNDS
TUNGSTEN ALLOYS
TUNGSTEN COMPOUNDS
360605* - Materials- Radiation Effects