Bending and shell formation of tellurium nanowires induced by thiols

Abstract

The reactivity of tellurium nanowires (Te NWs) with thiol-containing molecules was probed. Depending upon the presence or absence of the stabilizing surfactant in the solution, the product differs drastically. When excess surfactant was present, the reaction resulted in a core-shell-like structure. Through various spectroscopic and microscopic techniques, it was understood that there is a redox reaction between TeO₂, present on the NW surface, and thiols added into the solution that resulted in the reduction of TeO₂ to Te(0) with simultaneous oxidation of thiols to disulfides. Energy-dispersive analysis of X-rays (EDAX) confirmed that the shell has large sulfur and oxygen content. Raman spectra as well as the spectral image showed that the shell contains sulfur in the form of disulfides. Time-dependent Raman measurements established the redox nature of the conversion. The redox reaction was confirmed by X-ray photoelectron spectroscopy (XPS) also. When the excess surfactant was removed by repeated centrifugation, the addition of thiols resulted in the bending of NWs. The monodispersity as well as single crystallinity of the sample were affected. The bent NWs possessed many defects along the length as a consequence of the reaction. When excess surfactant was present in the solution, a combination of sodium dodecyl sulfate (SDS) and the formed disulfide were capable of capping the structures suitably, avoiding defects. But when excess surfactant is removed, the remaining SDS and disulfide were not enough to protect the surface well, creating more defect sites that resulted in the bending of the NWs. It appears that the enthalpy of the redox reaction at the surface contributes to the bending of the nanostructures.