Nanoscale Lenses Beat Diffraction Limit

Imaging nanometer-scale objects with visible light is difficult for lens-based systems because the diffraction limit of the lens material restricts the instrument's resolution. Kwang S. Kim of South Korea's Pohang University of Science & Technology, Philip Kim of Columbia University, and coworkers report one way to beat the diffraction limit via nanoscale spherical lenses made by the self-assembly of calix[4]hydroquinone (Nature 2009, 460, 498). The researchers fabricated the lenses by slowly evaporating a water-acetone solution of the hydroquinone to form nanotube crystals. When these crystals are heated, they release calix[4]hydroquinone molecules that reassemble into nanospheres on the crystal surface. The lenses, which are convex on one side and flat on the other, have shorter focal lengths and correspondingly higher magnification than expected for conventional geometric optics. And the lens size can be controlled by adjusting the time and temperature of the self-assembly process. The researchers used the lenses with 472-nm light to resolve metallic stripe arrays spaced 220 or 250 nm apart, which is narrower than the lenses' diffraction limit. Such lenses could be used in arrays with atomic force microscopes or as auxiliary components to enhance the resolution of scanning probe microscopes, the researchers write.