Chemical bonding in epitaxial ZrB2 studied by X-ray spectroscopy

Abstract

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 α-Zr reference. Quantitative analysis of X-ray Photoelectron Spectroscopy spectra reveals at the surface: ~5% O in the epitaxial ZrB2 film, ~19% O in the ZrB2 compound target and ~22% O in the bulk α-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 α-Zr reference no peaks from any crystalline oxide were visible in the diffractogram recorded from the 0001-oriented metal. 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 α-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 modelled cell-edge in ZrB2 is slightly smaller in the thin film (a=3.165 Å, c=3.520 Å) in comparison to the bulk target material (a=3.175 Å, c=3.540 Å) while in hexagonal closest-packed metal (α-phase, a=3.254 Å, c=5.147 Å). The modelled 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 Å is in agreement with the calculated value from XRD data of 2.542 Å. This is slightly shorter compared to that in the ZrB2 compound target 2.599 Å, supporting the XANES results of a higher atomic order within the columns of the film compared to bulk ZrB2.

The Effects of Annealing Temperature on the Structural Properties of ZrB2 Films Deposited via Pulsed DC Magnetron Sputtering

“…The estimated that of O atom adsorbed on the ZrB 2 surface forming a (2 × 2) super-structure but smaller than that of fully oxidized state Zr oxides [23]. The B1s peak appears at 187.9 eV, which agrees with the reported B1s energy in ZrB 2 [24]. These binding energies are in agreement with those determined for epitaxial ZrB 2 films deposited on 4H-SiC(0001) in Reference [25], with values of 179.0, 181.3, and 188.0 eV, respectively.…”

Atom Probe Tomography of Hard Nitride and Boride Thin Films

“…XPS calibrated using ISO standards was used in Paper V to acquire the bonding characteristics of ZrTaB2. The same ZrB2 films investigated in Paper IV have also been characterized by XPS in a separate Paper [67].…”

Titangruppe: Elemente der vierten Nebengruppe

“…Die Abscheidung aus der Gasphase durch Reaktion von Zirconium-IVchlorid mit Bortrichlorid unter Verwendung von Wasserstoff als Trägergas bei Temperaturen um 800 C ist ein gutes Beispiel (Randich 1979). Kürzlich gelang die Abscheidung sehr dünner Filme epitaktischer Ausrichtung aus der Gasphase (Magnuson et al 2018) .…”