Single Crystalline Alkaline-Earth Metal Hexaboride One-Dimensional (1D) Nanostructures: Synthesis and Characterization

Catalytic material-assisted growth of alkaline-earth metal hexaboride (MB 6, M = Sr, Ba) 1D nanostructures was achieved by pyrolysis of diborane (B 2 H 6 ) over alkaline-earth metal oxide (MO) powders at elevated temperature (∼840−870 °C) and low pressure (∼165 mTorr). The as-synthesized MB 6 1D nanostructures were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), and Raman spectroscopy. Results show that the MB 6 nanostructures are single crystalline with the preferred growth direction along [001]. The SrB 6 nanowires are ∼20−100 nm in diameter and ∼2−5 μm in length. The BaB 6 nanostructures have a rectangular cross section (width ∼20−300 nm) and are ∼5−20 μm in length. The growth of these MB 6 nanostructures can be attributed to a nontraditional vapor−solid−liquid (VLS)-like growth mechanism. The as-synthesized MB 6 1D nanostructures are promising n -type low-dimensional thermoelectric materials.