Single-particle detection of a semiconductor-to-metal transition by scanning dielectric microscopy

Abstract

Hybrid nanostructures that combine semiconducting and metallic components offer great potential for photothermal therapy, optoelectronics, and sensing, by integrating tunable optical properties with enhanced light absorption and charge transport. Boosting the integrated performance of these hybrid systems demands techniques capable of probing local variations of the physical properties inaccessible to bulk analysis. Here, we report the single-particle dielectric characterization of hybrid, semiconducting bismuth sulfide (Bi$_2$S$_3$) nanorods (NR) decorated with metallic Au nanoparticles (NP), employing scanning dielectric microscopy, which uses electrostatic force microscopy in combination with finite-element numerical simulations. We reveal a pronounced enhancement in the local dielectric response of Bi$_2$S$_3$ upon Au decoration, attributed to interfacial polarization and electron transfer from Au to the Bi$_2$S$_3$ matrix, thus suggesting a semiconductor-to-metal-like transition at the single-particle level. Numerical simulations show that the response is dominated by the vertical component of the permittivity and that the decorating metallic Au NP produce only moderate shielding of the semiconductor Bi$_2$S$_3$ NR core, indicating that the large increase in the dielectric response originates primarily from intrinsic modifications within the NR. Overall, these findings provide direct insight into structure--property relationships at the single-particle level, supporting the rational design of advanced hybrid nanostructures with tailored electronic functionalities.