Aluminum Borate Nanowires from the Pyrolysis of Polyaminoborane Precursors

Polyaminoboranes [N(R)H-BH₂]_n (1: R = H, 2: R = Me) were pyrolyzed on a range of substrates: silicon, metal foils (stainless steel, nickel, and rhodium), and sapphire wafers, as well as on Al₂O₃ and AlN powders. The pyrolysis of 2 on a Si-wafer resulted in porous nanostructures containing hexagonal-boron nitride (h-BN). In the case of 1 or H₃N·BH₃ as precursor, using rhodium foil as substrate afforded amorphous B and N-containing nanostructures, and polydisperse spherical nanoparticles, respectively. Switching the substrate to sapphire wafers, as well as to Al₂O₃ or AlN powders, resulted in formation of crystalline Al₅BO₉ nanostructures (nanowires, nanotubes, and nanoribbons).  For sapphire wafers, the size of the resulting nanowires was influenced by modifying the surface defect density.