Uwe Erb
Department of Materials Science and Engineering, University of Toronto, Canada
Title: Crystallography of the Corneal Nanonipple Structure on Butterfly Eyes
Biography
Biography: Uwe Erb
Abstract
One specific type of corneal nano-nipple arrays found on many insect compound eyes are hexagonally arranged protrusions in the shape of inverted paraboloids. Prior studies have focused on the anti-reflection properties of the eyes due to the nano-nipple structure [e.g. 1], which depends mainly on the shape of individual nipples. However, in the past little attention was given to the details of the arrangement of nano-nipples, which was qualitatively described as consisting of multiple domains. In the current study, remarkable defect structures were found through structural analysis using crystallographic principles.
The investigated species is the Mourning Cloak butterfly (Nymphalis antiopa), which is common in North America as well as Europe and Asia. On its corneas, nano-nipples are predominantly in 2-D hexagonal arrangement with an average diameter of 170 nm and an average lattice parameter of 205 nm [2]. An eye with 2 mm in diameter has approximately 10,000 ommatidia and 140 million nipples. However, within the hexagonal structure, there are nipples that deviate from the regular arrangement by having different numbers of nearest neighbours (NN); instead of 6 NN required by hexagonal symmetry, about 10% of nano-nipples have 5 or 7 NN and are described as 5- and 7-fold coordination defects (disclinations), respectively. Since the 5- and 7-fold disclinations usually occur adjacent to each other, they are collectively referred to as 5-7 defects.