Synthesis of Icosahedral Boron Arsenide Nanowires for Betavoltaic Applications
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Synthesis of Icosahedral Boron Arsenide Nanowires for Betavoltaic Applications Clint D. Frye1, J.H. Edgar1, Yi Zhang1, Kevin Cooper1, Luke O. Nyakiti2, D.K. Gaskill2 1
Department of Chemical Engineering, Kansas State University, Manhattan, KS 66506,
2
U.S. Naval Research Laboratory, Washington DC, 20375
ABSTRACT With a wide band gap of greater than 3.0 eV and the ability to self-heal from radiation damage, icosahedral boron arsenide (B12As2) is an apt candidate for use in next-generation betavoltaics. By capturing and converting high energy electrons from radioisotopes into usable electricity, “nuclear batteries” made from B12As2 could potentially power devices for decades. Compared to bulk crystals or epitaxial films, B12As2 nanowires may have lower defect densities or may even be defect-free, leading to better electrical properties and device performance. In our study, B12As2 nanowires were synthesized via vapor-liquid-solid (VLS) growth using platinum powder and nickel powder on silicon carbide and 20 nm thick nickel film on silicon substrates from 700 °C to 1200 °C. Platinum yielded the highest quality nanowires from 900 °C to 950 °C, resulting in platinum particles densely covered with wires formed by straight segments connected by sharp angular kinks. At these growth temperatures, diameters ranged from less than 30 nm to about 300 nm as determined by scanning electron microscopy and transmission electron microscopy. Growth temperatures of 850 °C or less produced curled wires 200-1000 nm in diameter. Transmission electron microscopy and selected area electron diffraction revealed excellent crystallinity in wires grown above 850 °C, while wires grown at or below 850 °C were partially amorphous. Wires grown from the 20 nm nickel film displayed similar morphologies at temperatures up to 850 °C; from 900 °C to 950 °C, straight, isolated wires were grown with diameters of 200-400 nm. Nickel powder only produced wires larger than 1 μm in diameter. The comparative quality and growth of B12As2 nanowires will be discussed. INTRODUCTION Icosahedral boron arsenide, B12As2, has many useful properties, including its wide bandgap of greater than 3.0 eV[1], chemical inertness at high temperatures[2], and the ability for its crystal lattice to self-heal from intense bombardment of energetic electrons or ions[3, 4]. These properties make B12As2 particularly well suited in betavoltaic cells or “nuclear batteries,” potentially enabling low power batteries capable of producing power for years or even decades. Recent interest has been paid to the synthesis of boron nanowires via vapor-liquid-solid (VLS) mechanisms [5, 6], vapor-solid-solid (VSS) growth[6], laser ablation[7], and radio frequency magnetron sputtering[8, 9]; and boron carbide nanowires via catalytic annealing of boron carbide[10],annealing carbon nanotubes with boron powder [11], and vapor-solid reaction of carbon nanotubes with gaseous boron species[12]. However, growth of other boron compound nanowires such as B12As2 has not been investigated. Crystalline nanowi
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