Shape and composition control of Bi19S27(Br3−x,Ix) alloyed nanowires: the role of metal ions

Abstract

We present the first colloidal synthesis of highly uniform single-crystalline Bi₁₉S₂₇Br₃ nanowires (NWs) with a mean diameter of ∼9 nm and tunable lengths in the range of 0.15–2 μm in the presence of foreign metal ions (Al³⁺). The Al³⁺ ions not only control the growth of NWs, but also achieve species transformation, i.e., from Bi₂S₃ to Bi₁₉S₂₇Br₃, and are not present in the resulting NWs. This colloidal chemistry approach can be expanded to prepare a family of single-crystalline Bi₁₉S₂₇(Br_3−x,I_x) alloyed NWs with controlled compositions (0 ≤ x ≤ 3). Interestingly, these alloyed NWs show an unusual composition-independent band gap of ∼0.82 eV, and theoretical calculations indicate that this phenomenon comes from the very minor contributions of the halogens to the valence band maximum and conduction band minimum. The photodetectors made of Bi₁₉S₂₇(Br_3−x,I_x) alloyed NWs show a pronounced photoresponse with high stability and reproducibility, which makes the NWs potentially useful candidates in optoelectronic devices.