Properties of ZrB$_{2}$ Thin Films Grown by E-Beam Evaporation

Zirconium diboride (ZrB$_{2}$) is a candidate material for many high temperature applications because it has a high melting point, high hardness, thermal shock resistance, and metallic conductivity. However, very little work has been reported concerning growth of ZrB$_{2}$ thin films and high temperature oxidation behavior. In this study, ZrB$_{2}$ films with nominal thickness of 200 nm have been deposited using electron-beam evaporation of either ZrB$_{2}$ pellets or elemental B and Zr sources. The ZrB$_{2}$ source yields a film that has a 1:1 Zr:B average composition as measured by X-ray photoelectron spectroscopy, consisting of ZrB$_{2}$ precipitates within an amorphous Zr matrix as determined by X-ray diffraction. Use of elemental B and Zr sources allows precise control of film growth over a range of stoichiometries and yields ZrB$_{2}$ films with much lower oxygen contamination. After annealing ZrB$_{2}$ films to 1200$^{\circ}$C in air, oxidation leads to a loss of B and formation of a textured monoclinic ZrO$_{2}$ phase. Several strategies, including deposition of a thin Al$_{2}$O$_{3}$ capping layer over the ZrB$_{2}$ film are being pursued in an attempt to stabilize the electrically conductive ZrB$_{2}$ phase at high temperature, where it can be used for high temperature electronic devices in harsh environments.