Room-Temperature Seeded Growth of Tetraphenylphosphonium Bromide Single-Crystalline Fibers

Growth of single-crystalline fibers (SCFs) has so far mainly depended on melt growth techniques, which have limitations and are not suitable for growth of thermally unstable or polymorphic SCFs. Here, a solution growth method for high-quality SCFs is reported. By seeded growth in solution at room temperature, tetraphenylphosphonium bromide (TppBr) SCFs with width of 1 to 10 μm and length of a few centimeters are produced successfully. The defect-free TppBr SCF seed grows rapidly along 1D, while its prismatic growth is completely suppressed. The steady 1D growth can be initiated in solution at 13.4% supersaturation and kept until the supersaturation rises up to 62.6%. AFM reveals that TppBr SCF obtained has a highly anisotropic surface micromorphology. We propose an enhanced anisotropic 2D nucleation mechanism to interpret the 1D growth of TppBr fiber seeds. The solution-seeded growth technique of SCFs will greatly expand the types of fiber crystals that can be grown for advanced device applications.