A novel approach for fabrication of bismuth-silicon dioxide core-shell structures by atomic layer deposition

Bismuth (Bi) nanowires were grown electrochemically into the pores of anodic aluminium oxide (AAO) templates. The diameter of the pores in the AAO membranes has been precisely tuned down to 30 nm by atomic layer deposition (ALD) of silicon dioxide onto the pore walls. Bi nanowires with diameters of 30, 50, and 200 nm were subsequently deposited by potentiostatic electrochemical deposition. The fabricated Bi nanowires showed a highly preferential growth orientation along the (110) direction. High resolution transmission electron microscopy (HRTEM) and selected area electron diffraction (SAED) investigations further confirmed the existence of a preferred growth orientation and polycrystalline nature of the nanowires. Using Fourier transform infrared (FT-IR) spectroscopy, optical absorption of nanowires was investigated as a function of wire diameter. The absorption edge energy, similar to 87 meV, of narrower 30 nm diameter semiconducting nanowires decreased with increasing the wire diameter and led ultimately to the observation of semimetallic behavior in the 200 nm thick wires. In the electrical measurements, a metallic contact to an array of 50 nm diameter nanowires was made and the resistance of the array was measured in the temperature range 130-300 K. The semiconducting bandgap energy, similar to 67 meV, was obtained by comparison of the experimental data to a simple theoretical model.