Synthesis and characterization of coaxial SnO2–SiOx core–shell nanorods

Free-standing coaxial SnO2–SiOx core–shell nanorods were synthesized in a kinetically controlled manner by the chemical vapor transport method. The free-standing SnO2–SiOx core–shell nanorods appear with uniform morphology exhibiting smooth surface, diameters of 100–200 nm, and length of 1 μm. The low oxygen partial pressure and high reaction temperature are advantageous to form the (101) surface, which decreases the (101) crystal surface energy. The [101] growth direction in our process also satisfies the lowest energy principle in thermodynamics due to change of (101) surface energy. A heterogeneous nucleation site was provided by the SiOx dismutation reaction, and the formation of core–shell (SnO2–SiOx) structure should result from the phase separation energy. The free-standing coaxial SnO2–SiOx heterostructured nanorods grow by modification of the mass transfer coefficient. As-grown depositions show shrimp-like, flower-like, and worm-like morphologies under a higher mass transfer coefficient. Formation of the free-standing core–shell structure depends on the vertical growth mechanism.