Characterization and Growth Mechanism of Selenium MicrotubesSynthesized by a Vapor Phase Deposition Route

A simple and rapid vapor deposition route has been developed for the growth of trigonal phase selenium microtubes in a horizontal tubular furnace under argon flow gas. Selenium powder was evaporated by heating at 300 C, and the vapors were condensed on different quartz substrates located at 70-140 C. It was found that the morphologies of the products were strongly affected by small variations of the temperatures of the deposition zones. It was observed that the growth of microtubes was initiated by formation of nearly spherical microparticles with smooth surfaces; the smooth microspheres were first covered by a rough layer and then they slowly became empty. The additional selenium atoms transported from the heated part of the furnace or coming from the consumption of the inner core of the rough microparticles continued to adsorb on the empty microspheres, allowing two possible growth mechanisms. If the additional Se atoms preferentially went to the circumferential edges of the empty microspheres, crystalline microtubes with no defects were formed; however, Se atoms could also follow a spiral growth mechanism starting from the empty shells. This second growth mechanism led to the formation of semiclosed tubular structures with irregular surfaces, which developed into the relatively completed uniform microtubes with smooth surfaces. The morphology, microstructure, and chemical composition of the microtubes were characterized by various means (X-ray diffraction, energy-dispersive X-ray spectroscopy, Raman spectroscopy,UV-vis spectroscopy, scanning electron microscopy, and transmission electron microscopy). The as-grown Se microtubes may find application as rapid response photosensors and photocells.