Chemical Vapor Deposition of Metal Borides, 4: The Application of Polyhedral Boron Clusters to the Chemical Vapor Deposition Formation of Gadolinium Boride Thin-film Materials

The chemical vapor deposition of high-quality polycrystalline thin films of gadolinium hexaboride, GdB6, was achieved through the vacuum copyrolysis of gas-phase boron hydride clusters, such as nido-pentaborane(9) [B5H9] and nido-decaborane(14) [B10H14], and gadolinium(III) chloride. These films typically displayed deep blue colors, were very hard and adhered very well to most deposition substrates. Depositions were carried out on a variety of substrates including quartz, copper, silicon, SiO2 and ceramic materials. X-ray diffraction and scanning electron microscopic data showed the formation of highly crystalline materials with a strongly preferred orientation in the (111) direction. Attempted depositions of gadolinium boride films on CaF2(111) resulted in the apparent formation of a ternary (Ca/Gd)B6 phase in which the calcium is presumably substituted for gadolinium atoms in the cubic GdB6 structure. The gadolinium boride thin films were investigated by scanning electron microscopy (SEM), X-ray emission spectroscopy (XES), X-ray diffraction (XRD), and glow-discharge mass spectrometry (GDMS). GDMS showed that the GdB6 films were relatively uniform in composition in the bulk material.