Synthesis and super-resolution imaging performance of a refractive-index-controllable microsphere superlensElectronic supplementary information (ESI) available. See DOI: 10.1039/c5tc02310f

Microspheres can function as optical superlenses for nanoscale super-resolution imaging. The imaging performance is mainly affected by the size and refractive index of the microsphere. Precise control of these parameters is a challenging task but of fundamental importance to the further development of the technique. In this study, we demonstrate for the first time a nanoparticle-hybrid suspension polymerization approach to chemically synthesize high-quality microspheres (ZrO 2 /polystyrene) with optical properties that are highly controllable. Microspheres of different sizes ( d : 2-20 μm) and refractive indexes ( n p : 1.590-1.685) were synthesized and their super-resolution imaging performances were evaluated and compared. Our results show that continuously increasing the refractive index of microspheres can enhance the imaging resolution and quality. A 60 nm resolution has been obtained in the wide-field imaging mode and a 50 nm resolution has been obtained in the confocal mode imaging of semiconductor chip samples. The obtained 50-60 nm resolutions have significantly gone beyond the conventional 200 nm resolution limit for visible light optical microscopes; the super-resolution mechanism has been discussed. The synthesized microsphere superlenses may find applications in many other areas as well, including nanolithography, nano-sensing, nano-diagnosis, nano-spectroscopy and ultra-high density optical data storage. Refractive-index-controllable and optically transparent PS/ZrO 2 microspheres as superlens for super-resolution imaging of semiconductor chips with 75 nm and 50 nm gaps.