Sub-50 nm optical imaging in ambient air with 10x objective lens enabled by hyper-hemi-microsphere

Optical microsphere nanoscope has great potential in the inspection of integrated circuit chips for semiconductor industry and morphological characterization in biology due to its superior resolving power and label-free characteristics. However, its resolution in ambient air is restricted by the magnification and numerical aperture (NA) of microsphere. High magnification objective lens is required to be coupled with microsphere for nano-imaging beyond the diffraction limit. To overcome these challenges, in this work, high refractive index hyper-hemi-microspheres with tunable magnification up to 10x are proposed and realized by accurately tailoring their thickness with focused ion beam (FIB) milling. The effective refractive index is put forward to guide the design of hyper-hemi-microspheres. Experiments demonstrate that the imaging resolution and contrast of a hyper-hemi-microsphere with a higher magnification and larger NA excel those of a microsphere in air. Besides, the hyper-hemi-microsphere could resolve similar to 50 nm feature with higher image fidelity and contrast compared with liquid immersed high refractive index microspheres. With a hyper-hemi-microsphere composed microscale compound lens configuration, sub-50 nm optical imaging in ambient air is realized by only coupling with a 10x objective lens (NA = 0.3), which enhances a conventional microscope imaging power about an order of magnitude.

Automated summary

The optical microsphere nanoscope has the potential to be used in inspecting integrated circuit chips and characterizing morphology in biology. However, its resolution in ambient air is limited by the magnification and numerical aperture of the microsphere. To overcome this, high refractive index hyper-hemi-microspheres with tunable magnification were proposed and realized. Experimental results show that these hyper-hemi-microspheres have better imaging resolution and contrast compared to microspheres in air.