Chemical bonding in epitaxial ZrB2 studied by X-ray spectroscopy

THIN SOLID FILMS

卷:649

Article

Magnuson, Martin¹  Tengdelius, Lina¹  Greczynski, Grzegorz¹  Hultman, Lars¹  Hogberg, Hans¹ 

[1] Linkoping Univ, Dept Phys Chem & Biol IFM, Thin Film Phys Div, SE-58183 Linkoping, Sweden

关键词: Zirconium boride;    Thin films;    Bond distances;    Chemical bonding;    X-ray spectroscopy;    X-ray photoelectron spectroscopy;    X-ray diffraction;   

DOI  :  10.1016/j.tsf.2018.01.021

来源: Elsevier

【 摘 要 】

The chemical bonding in an epitaxial ZrB2 film is investigated by Zr K-edge (1s) X-ray absorption near-edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) spectroscopies and compared to the ZrB2 compound target from which the film was synthesized as well as a bulk alpha-Zr reference. Quantitative analysis of X-ray photoelectron spectroscopy spectra reveals at the surface: similar to 5% O in the epitaxial ZrB2 film, similar to 19% O in the ZrB2 compound target and similar to 22% O in the bulk a-Zr reference after completed sputter cleaning. For the ZrB2 compound target, X-ray diffraction (XRD) shows weak but visible 111, 111, and 220 peaks from monoclinic ZrO2 together with peaks from ZrB2 and where the intensity distribution for the ZrB2 peaks show a randomly oriented target material. For the bulk alpha-Zr reference no peaks from any crystalline oxide were visible in the diffractogram recorded from the metal with preferred 0001-orientation. The Zr K-edge absorption from the two ZrB2 samples demonstrate more pronounced oscillations for the epitaxial ZrB2 film than in the bulk ZrB2 attributed to the high atomic ordering within the columns of the film. The XANES exhibits no pre-peak due to lack of p-d hybridization in ZrB2, but with a chemical shift towards higher energy of 4 eV in the film and 6 eV for the bulk compared to alpha-Zr (17.993 keV) from the charge-transfer from Zr to B. The 2 eV larger shift in bulk ZrB2 material suggests higher oxygen content than in the epitaxial film, which is supported by XPS. In EXAFS, the modeled cell-edge in ZrB2 is slightly smaller for the film (a = 3.165 angstrom, c = 3.520 angstrom) when compared to the bulk target material (a = 3.175 angstrom, c = 3.540 degrees) and for the hexagonal closest-packed metal (alpha-phase, a = 3.254 angstrom, c = 5.147 angstrom). The modeled coordination numbers show that the EXAFS spectra of the epitaxial ZrB2 film is highly anisotropic with strong in-plane contribution, while the bulk target material is more isotropic. The Zr-B distance in the film of 2.539 angstrom is in agreement with the calculated value from XRD data of 2.542 angstrom. This is slightly shorter compared to that in the ZrB2 compound target 2.599 angstrom, supporting the XANES results of a higher atomic order within the columns of the film compared to bulk ZrB2.

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