• Guerette, Michael

Abstract

<jats:title>ABSTRACT</jats:title><jats:p>The recently discovered orthorhombic allotrope of silicon, Si<jats:sub>24</jats:sub>, is an exciting prospective material for the future of solar energy due to a quasi-direct bandgap near 1.3 eV, coupled with the abundance and environmental stability of silicon. Synthesized via precursor Na<jats:sub>4</jats:sub>Si<jats:sub>24</jats:sub> at high temperature and pressure (∼850 °C, 9 GPa), typical synthesis results have yielded polycrystalline samples with crystallites on the order of 20 μm. Several approaches to increase the crystal size have yielded success, including in-situ thermal spikes and refined selection of the starting materials. Microstructural analysis suggests that coherency exists between diamond silicon (d-Si) and Na<jats:sub>4</jats:sub>Si<jats:sub>24</jats:sub>. This hypothesis has led to the successful attempts at single crystal synthesis by selecting large crystals of d-Si along with metallic Na as the precursors rather than powdered and mixed precursor material. The new synthesis approach has yielded single crystals of Na<jats:sub>4</jats:sub>Si<jats:sub>24</jats:sub> greater than 100 μm. These results represent a breakthrough in synthesis that enables further characterization and utility. The promise of Si<jats:sub>24</jats:sub> for the future of solar energy generation and efficient electronics is strengthened through these advances in synthesis.</jats:p>

Topics

• impedance spectroscopy
• single crystal
• Silicon