Dielectric function analysis of superstoichiometric samarium dihydride films

We have carried out an experimental study to reveal the dielectric function of SmH x ( x = 2.28 , 2.42 , 2.56 , 2.57 ) films based on room-temperature reflectivity for photon energies ranging from 0.05 to 6.5 eV. The derivation of the dielectric functions has been carried out using model dielectric...

Ausführliche Beschreibung

Gespeichert in:
Bibliographische Detailangaben
Veröffentlicht in:Journal of applied physics 2009-04, Vol.105 (8), p.083512-083512-11
Hauptverfasser: Sakai, M., Nanbo, T., Tanji, Y., Nakamura, O., Endo, M., Tajima, H.
Format: Artikel
Sprache:eng
Online-Zugang:Volltext
Tags: Tag hinzufügen
Keine Tags, Fügen Sie den ersten Tag hinzu!
Beschreibung
Zusammenfassung:We have carried out an experimental study to reveal the dielectric function of SmH x ( x = 2.28 , 2.42 , 2.56 , 2.57 ) films based on room-temperature reflectivity for photon energies ranging from 0.05 to 6.5 eV. The derivation of the dielectric functions has been carried out using model dielectric functions as well as Kramers-Kronig analysis. It is inferred from our analysis that when the H/Sm value is increased from 2.28 to 2.57, (i) the interband transition band located in the ultraviolet region shows a redshift of about 1 eV, (ii) the relatively weak transition band located in the near-infrared region shows a reduction in intensity, and (iii) the unperturbed plasma frequency of free carriers decreases slightly. The behaviors (i), (ii), and (iii) caused by the H/Sm value change are thoroughly approximately the same as those observed for YH x , suggesting that these trends are characteristic of H-M systems showing a metal-insulator transition. It was also confirmed from our structural analysis that these changes in the dielectric function are achieved without a change in the lattice constant. The origin of this constancy in the lattice constant in our samples with different H/Sm values is discussed by assessing the T - and O -site hydrogen concentrations. The hydrogen incorporation effect is also observed in the magnitude of the unperturbed plasma frequency, about 1.7 eV, which is unexpectedly small compared to conventional metals. This characteristic can possibly be attributed to mass enhancement of mobile carriers; we obtained an effective mass of about 10 m 0 (where m 0 is the free electron mass) when the carrier density estimated from the Hall coefficient value is used.
ISSN:0021-8979
1089-7550
DOI:10.1063/1.3088873