Nanoscopic Spotlight in a Spindle Semiconductor Nanowire.

Theoretically, no matter how thin a nanowire is, it can transport light in the form of an evanescent field. However, in practice, the low propagation efficiency induced by complex dissipation makes light transport difficult to realize when the nanowire is distinctly thinner than ∼ λ/2. Accordingly, nanowire photonics research at such a scale is limited. Herein, light propagation was achieved in a very thin spindle nanowire (diameter below 70 nm), in which a nanoscopic spotlight formed. The nanowire output a maximum emission in the transverse dimension as small as ∼53 nm. The finite-difference time-domain (FDTD) simulation implied that the increased dimension gradient near the tip induced a maximum leakage of the propagating light at a transverse feature, precisely determined by the intrinsic feature of the nanowire. Moreover, a spectrum splitter phenomenon was observed and demonstrated based on the wavelength-dependent light propagation behavior in such a nanowire. These results contribute to the rational design of nanoscopic near-field illuminant, optoelectric, and photobiological probes with improved resolution largely superior to the so-called subwavelength level.