Investigation of Transversal Conductance in Semiconductor CdTe Nanowires with and without a Coaxial Silica Shell

Semiconductor CdTe nanowires were coated with a coaxial layer of silica in aqueous solutions by the hydrolysis of tetraethyl orthosilicate. The structure and morphology of the nanowires before and after coating were studied by UV−vis spectroscopy, atomic force microscopy, and transmission electron microscopy. Interestingly, silica deposition on the nanowire ends was retarded. For sufficiently thin layers, this effect makes possible the preparation of coaxial insulated nanowires with electrical access to the semiconductor core. Insulating properties of the silica layer were tested by applying voltage to a conductive AFM tip placed directly on the sidewall surface of the nanowires. These experiments demonstrated that the silica layers had strong insulating properties for coatings as thin as 10 nm. Similar measurements done with naked nanowires showed that transversal conductance took place through the middle band-gap states.