Rapid Chemical Vapor Transport Growth of Inorganic Double Helix Tin Iodide Phosphide Crystals with Increased Yield and Their Liquid-Phase Exfoliation

Abstract

Tin iodide phosphide (SnIP), the first atomic-scale one-dimensional (1D) double-helical inorganic semiconductor, has triggered growing interest due to its high structural flexibility, excellent electron mobility, and remarkable optical properties. Chemical vapor transport reaction has been the sole approach to growing SnIP crystals, though it suffers from time-consumption (∼2–3 weeks) and low yield. Inspired by its unique structure and properties, advancing rapid growth of SnIP crystals with a high yield is crucial. Herein, a systematic series of experiments have been designed to search the suitable synthesis conditions, viz., temperature gradient and temperature variations as well as precursors amount and ampule lengths to achieve the optimal conditions for the synthesis of SnIP crystals. Three transport agents, namely, SnI₂, SnI₄, and I₂, were analyzed and compared, and SnI₂ was deemed the most suitable agent for SnIP crystal growth. The optimal synthetic route enables high-yield (up to 84%) and high-quality SnIP crystals at a maximum temperature of 600 °C within only 10 days. Additionally, a comprehensive exploration of liquid-phase exfoliation of SnIP crystals is investigated to screen the optimal solvent in terms of the total surface tensions and polar/dispersive component ratios. It is demonstrated that cyclohexane can effectively isolate as-grown SnIP crystals into SnIP nanowires (NWs), boasting a high aspect ratio exceeding 950. The exfoliated NWs show smooth surfaces and clear signatures of the 1D SnIP helix. These findings shed light on the future applications of double-helical SnIP crystals in flexible electronics, mechanical sensors, and semiconductor devices.