Direct Synthesis of Selenium Nanowire Mesh on a Solid Substrate and Insights into Ultrafast Photocarrier Dynamics

Selenium (Se) nanowires have generated much interest both for the fundamental understanding of crystal formation and growth and for technological applications in optoelectronics, imaging, piezoelectricity, catalysis, and energy harvesting and storage. Several methods have been established to synthesize Se nanowires, but they require sophisticated fabrication steps, are energy intensive, and may involve complex chemical reactions. Moreover, despite an increasing interest, little is known regarding photocarrier dynamics of Se nanowires. Here, we investigate a solution-based approach for the facile synthesis of single-crystal Se nanowires over the large scale where nanowires are directly grown from an amorphous bulk in a solution at room temperature without any chemical reaction. We study the nanowire nucleation and growth mechanism via electron microscopy. We also investigate, for the first time, the charge carrier dynamics and mobility of Se nanowire meshes by means of ultrafast transient absorption spectroscopy, nanosecond flash photolysis, and time-resolved terahertz spectroscopy. These contact-free and noninvasive approaches reveal a lifetime on the picosecond scale for free carriers and on the microsecond scale for trapped carriers, both of which are limited by trap-assisted recombination and a free carrier mobility of similar to 3.0 cm(2) V-1 s(-1). Our work for the first time reveals the rationale behind the excellent properties of some Se NW-based optoelectronic devices. It also highlights the simplicity and robustness of the novel Se nanowire synthesis scheme and paves the way toward the simple fabrication of advanced nanowire-based electronic and optoelectronic nanodevices.