Simple colloidal synthesis of single-crystal Sb-Se-S nanotubes with composition dependent band-gap energy in the near-infrared

We report the first synthesis of high-quality binary and ternary Sb(2)Se(3-x)S(x) nanotubes across the entire compositional range from x = 0 to 3 via a simple, low-cost, colloidal synthetic method of injection of Sb(III)-complex solution into a hot paraffin liquid containing Se, S, or a mixture thereof. In contrast to the classic rolling mechanism, the modular formation of the reported nanotubes follows a four-stage self-seeding process: (i) amorphous nanospheres, (ii) short crystalline nanotubes growing out of relatively large amorphous nanospheres, (iii) long crystalline nanotubes attached to small amorphous nanospheres, and (iv) single-crystal nanotubes. The obtained single-crystal nanotubes have tunable composition, orthorhombic phase, well-defined rectangular cross sections, and growth direction along [001], as revealed by X-ray diffraction, scanning electron microscopy, energy-dispersive X-ray spectroscopy, transmission electron microscopy, and selected area electron diffraction studies. UV-vis-NIR absorption spectroscopy reveals that the optical bandgap energy of the Sb(2)Se(3-x)S(x) (0 < or = x < or = 3) nanotubes increases quadratically with the sulfur concentration x with these bandgap energies falling in the range from 1.18 to 1.63 eV at the red edge of the solar spectrum. The present study opens a new avenue to low-cost, large-scale synthesis of high quality semiconductor nanotubes with technological applications in solar energy conversion and also for a wide range of optical nanodevices operating in the near-infrared.