Nanostructure and bonding of zirconium diboride thin films studied by X-ray spectroscopy

• Zr–B thin films of different compositions were grown at low substrate temperatures.
• EXAFS analysis indicates a ZrB2 crystal structure after vacuum annealing.
• The coexistence of crystalline and amorphous Zr–B phases is also observed.
• Films with excess Zr readily form t-ZrO2 during deposition, which coexists with ZrB2.
• Low temperature synthesis routes are important for technological applications.

Zirconium diboride (ZrB2) is an important ceramic due to its extremely high melting temperature of 3245 °C and metallic electrical conductivity, properties that make it an ideal candidate thin film electrode material for high temperature electronics. In this report, thin films of varying B:Zr ratio ranging from 3–0.67 have been grown by e-beam evaporation from elemental sources. X-ray absorption spectra at the Zr K-edge were measured before and after annealing in ultra-high vacuum for 9 h at 1000 °C. Films with compositions near ZrB2 stoichiometry show X-ray absorption fine structure that can be well modeled by crystalline ZrB2 with a small portion of a coexisting tetragonal zirconia (t-ZrO2) phase. Films far from stoichiometry show substantial disorder beyond the nearest-neighbor distances, and after vacuum annealing exhibit high levels of oxidation. Contributions to the X-ray absorption fine structure from a pure Zr phase are very small compared to ZrB2 and t-ZrO2 phases. The fact that nearly stoichiometric (3 < B:Zr < 1.6) as-deposited amorphous films form the same crystalline ZrB2 nanostructure after annealing is particularly encouraging for high temperature thin film electronics applications, because it would allow the production of highly stable electrodes with e-beam evaporation without the need of any high temperature heating during film growth.