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X-Ray Absorption Studies of Ge Layers Buried in Silicon Crystal

100%

Demchenko I., Ławniczak-Jabłońska K., Zhuravlev K., Piskorska E., Nikiforov A., Welter E.

Acta Physica Polonica A

2002

vol. 101

issue 5

709-717

Polarization-dependent X-ray absorption spectroscopy was used to study the local microstructure of Ge layers buried in silicon. The layers with thickness from 6 to 20 monolayers of Ge were grown by molecular beam epitaxy on Si substrate and were covered by Si (20 nm). To investigate the morphology of grown structures, X-ray absorption near edge structure and extended X-ray absorption fine structure analysis of the Ge K-edge was done. The performed qualitative analysis proves that X-ray absorption spectra are very sensitive to the local order in the formed structures and are sources of unique information about morphology of the buried Ge layers. Using these techniques we were able to observe the changes in atomic order around the Ge atoms in investigated buried layers and compare the formed atomic order with that in crystalline Ge. A substantial increase in intensity, broadening and chemical shift of the X-ray absorption near edge structure spectrum for 8 ML were observed. It can be related to the increase in density of electron states caused by increase in the localization of the states due to potential appearing at the Ge island boundaries and indicated the formation of quantum dots. The observed in-plane modulations of radial distribution and out-of-plane for different layers were discussed.

Investigation of Mixed Valence State of Sm_{1-x}B_{6} and Sm_{1-x}La_{x}B_{6} by XANES

100%

Gabáni S., Flachbart K., Bednarčík J., Welter E., Filipov V., Shitsevalova N.

Acta Physica Polonica A

2014

vol. 126

issue 1

338-339

We investigated the valence states of samarium ions in Sm deficient Sm_{1-x}B_{6} (x=0.03, 0.05, 0.08, 0.1 and 0.2) sintered samples, in single crystalline solid solutions Sm_{1-x}La_{x}B_{6} (x=0.16, 0.28, 0.4, 0.55 and 0.7) as well as in a SmB_{6} single crystal by X-ray absorption near edge structure (XANES) between 4.2 and 300 K. It was shown that the mixed valence state v_{Sm} of Sm-ions (v_{Sm} ≈ 2.51 for SmB_{6} at 4.2 K) in deficient samples is changed but maintained up to a concentration of 20% of vacancies and up to a concentration of 70% in samples doped with trivalent La-ions, and that in both cases it increases with temperature. On the other hand, the value of v_{Sm} increases with increasing vacancy level, whereas it decreases with increasing La^{3+} substitution. The obtained dependences of Sm-valence in SmB_{6} on vacancy as well as on La^{3+} ion concentration are in good agreement with susceptibility measurements and exact numerical calculation of the spinless Falicov-Kimball model in two dimensions.

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2 Acta Physica Polonica A

1 2014

1 2002

2 Welter E.

1 Bednarčík J.

1 Demchenko I.

1 Filipov V.

1 Flachbart K.

1 Gabáni S.

1 Nikiforov A.

1 Piskorska E.

1 Shitsevalova N.

1 Zhuravlev K.

1 Ławniczak-Jabłońska K.

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X-Ray Absorption Studies of Ge Layers Buried in Silicon Crystal

Investigation of Mixed Valence State of Sm_{1-x}B_{6} and Sm_{1-x}La_{x}B_{6} by XANES