Chemical Vapor Deposition of Metal Borides

The chemical vapor deposition (CVD) of high quality polycrystalline thin films of lanthanum hexaboride, LaB6, was achieved through the vacuum copyrolysis of the boron hydride clusters, nido-pentaborane(9) [B5H9] and nido-decaborane(14) [B10H14], with lanthanum(III) chloride at 800–900°C. The reddish purple films adhered well to the deposition substrates explored (copper, quartz, Pyrex and ceramic materials). Deposition rates of approximately 1–2 μm/h were typically observed. The films were analyzed by scanning electron microscopy (SEM), X-ray emission spectroscopy (XES), X-ray diffraction (XRD), wavelength dispersive X-ray emission spectrometry (WDXES), and glow discharge mass spectrometry (GDMS). WDXES and GDMS data showed that the LaB6 films were relatively uniform in composition in the bulk material. SEM data showed that the as-deposited materials were very highly crystalline. Films which consisted either partly or entirely of square rods of LaB6 with either square or finely tapered tips could also be grown. Reflection high energy electron diffraction (RHEED) experiments confirmed the identity of the square rods as crystalline cubic LaB6.