Hard and elastic epitaxial ZrB2 thin films on Al2O3(0001) substrates deposited by magnetron sputtering from a ZrB2 compound target

Abstract

Hard and elastic epitaxial ZrB2 thin films on Al2O3(0001) substrates deposited by magnetron sputtering from a ZrB2 compound target

Chemical bonding in epitaxial ZrB2 studied by X-ray spectroscopy

“…As can be seen, the film demonstrates 000ℓ peaks (ℓ=1, 2, 3, and 4) of high intensities from the ZrB2 phase [32] and where the 0001 and 0002 peaks exhibit higher intensities than the 0006 and 00012 peaks from the Al2O3(0001) substrate and with no visible peaks from other phases such as an oxide. There is a weak ZrB2 1010 peak (not visible given the applied square root scale) showing a minority orientation in the film [4]. Furthermore from XRD pole figure measurements, the epitaxial relationships between the film and the substrate were determined to be in the out-of-plane direction ZrB2(0001) || Al2O3(0001) and with two in-plane relationships ZrB2[1010||Al2O3 [1010] and ZrB2[1120]||Al2O3[1010] [4].…”

“…There is a weak ZrB2 1010 peak (not visible given the applied square root scale) showing a minority orientation in the film [4]. Furthermore from XRD pole figure measurements, the epitaxial relationships between the film and the substrate were determined to be in the out-of-plane direction ZrB2(0001) || Al2O3(0001) and with two in-plane relationships ZrB2[1010||Al2O3 [1010] and ZrB2[1120]||Al2O3[1010] [4]. The diffraction pattern from the ZrB2 compound target displays all prominent ZrB2 peaks listed in the JCPDS card for the investigated 2θ region and where the intensity distribution among the ZrB2 peaks support a randomly oriented target material [32].…”

“…From the peak positions in the diffractograms in Figure 2, we determined the lattice parameters in the ZrB2 compound target and the α-Zr bulk reference to a=3.167 Å and c=3.531 Å and a=3.233 Å and c=5.149 Å, respectively (see Table III). The lattice parameters for the epitaxial ZrB2 film were determined from reciprocal space maps (RSM) to a=3.169 Å and c=3.528 Å, [4] and Table III. The measured values are close to the literature values with a=3.1687 Å and c=3.5300 Å for ZrB2 [32] and a=3.232 Å and c=5.147 Å for α-Zr [34] that are also listed in Table III.…”

“…Furthermore, due to the in-plane polarization of the X-rays, the epitaxial ZrB2 film has a significantly higher coordination number contribution in the basal-plane than along the c-axis in the EXAFS spectra. The strong polarization dependence is a consequence of the 0001orientation of the film to the Al2O3(0001) substrate [4]. It can be anticipated that future singlecrystal ZrB2 films will display even stronger polarization dependence.…”

Strategy for simultaneously increasing both hardness and toughness in ZrB2-rich Zr1−xTaxBy thin films

“…41 ZrB2, like other TM diborides, but contrary to TM nitrides which have very wide single-phase regions, 42,43 is a line-compound for which deviations from stoichiometry lead to the formation of second phases. 44 ZrB2 has a high melting point, 3245 °C, 45 and a relatively high hardness (reported values range from 19.3 to 45.0 GPa depending primarily upon microstructure, composition, and film stress) 44,[46][47][48][49][50][51] due to strong covalent bonding between Zr and B, as well as within the honeycomb B sheets. 46 We use dc magnetron sputtering (DCMS) from a ZrB2 target in pure Ar to grow ZrBy films on Al2O3(0001) and Si(001) substrates at 475 °C and vary the TM/B ratio by adding Ta via pulsed HiPIMS deposition from a Ta target.…”