A team of investigators at Indiana University in Bloomington has developed a technique for mapping the 3-D spatial distribution of radiation transmitted through nanoscale apertures in which the transmission is preserved as a polymer replica in a photoresist. The approach, presented in an online edition of Nano Letters on June 4, avoids the problems of methods that employ physical proximity probes, which affect the transmission pattern.

To demonstrate the mapping technique, the scientists fabricated aluminum-coated films with apertures from 110 to 770 nm in diameter by nano-sphere lithography. They coated the films with a 15-µm-thick layer of photoresist and exposed it through holes to 365-nm radiation from a high-pressure mercury lamp, varying the exposure time from 1 to 30 minutes. Postexposure baking and dissolution left free-standing pillars of polymer that replicated the transmission patterns, with pillar heights directly proportional to aperture diameter and exposure time.