Structure-color-species correlation in photonic nanoarchitectures occurring in blue lycaenid butterfly scales.

The blue colored males of nine Polyommatine butterfly species were investigated under the aspect of color-structure-species correlation. A large number of individuals from museum collections (in total more than 100) were used to obtain average reflectance spectra to reduce the effect of individual variations as much as possible. Structural characteristics were investigated by scanning electron microscopy and transmission electron microscopy. The relevant structural data were extracted using the Biophot Analyzer software. It was found that the position of the main reflectance peak is decided primarily by the nearest neighbor distance of holes in the perforated layers constituting the pepper-pot type structure. However, very different value of the 2D filling factor may have a large enough effect on the spectral position and the width and asymmetry of the peak to overrule the classification on taking into account only the nearest neighbor distance. The comparison of the structural and spectral data may indicate that the species Polyommatus amandus may constitute an evolutionary link between different groups of species. The examined pepper-pot type nanoarchitectures show that with the alteration of the structural parameters (first neighbor distance, 2D filling factor) the tuning of the reflectance of such nanoarchitectures may be achieved. These type of nanoarchitectures may be attractive for practical applications as their large scale manufacturing may require less strict conditions as compared with fully regular nanoarchitectures.

Apparent diameter of carbon nanotubes in scanning tunnelling microscopy measurements.

Geometric effects influencing scanning tunnelling microscopy (STM) image formation of single wall carbon nanotubes (SWCNTs) were studied within the framework of a simple model potential. We focused on the geometrical effects which may influence the tunnelling probabilities and lead to discrepancies between the apparent height of the nanotubes measured by STM and their real geometrical diameter. We found that there are two main factors responsible for the underestimation of nanotubes diameter by measuring their height in STM images: (1) the curvature of the nanotube affects the cross sectional shape of the tunnelling channel; (2) the decay rate of tunnelling probabilities inside the tunnel gap increases with increasing curvature of the electrodes. For a nanotube with 1 nm diameter an apparent flattening of about 10%, due to these geometry-related effects, is predicted. Furthermore these effects are found to be dependent on the diameter of the tubes and tip-sample distances: an increasing flattening of the tubes is predicted for decreasing tube diameter and increasing tip-sample distance.

Role of photonic-crystal-type structures in the thermal regulation of a Lycaenid butterfly sister species pair.

One of the possible functions of the photonic-crystal structure found on the wing scales of some butterflies is investigated. The optical and electron microscopic investigation of two male butterflies-blue (colored) and brown (discolored)-representing a sister species pair and originating from different altitudes, revealed that the blue color can be attributed unambiguously to the fine, spongelike medium, called "pepper-pot structure," present between the ridges and the cross ribs in the scales of the colored butterfly. Only traces of this structure can be found on the scales of the discolored butterfly. Other physical measurements, mainly optical reflectivity, transmission, and thermal measurements, are correlated with structural data and simulation results. The thermal measurements reveal that under identical illumination conditions the high-altitude butterfly reaches a temperature 1.3-1.5 times the temperature reached by the low-altitude butterfly. This is attributed to the photonic-crystal-like behavior of the pepper-pot structure, which significantly reduces the penetration of light with wavelength in the blue region of the spectrum into the body of the scales. This sheds some light on the adaptation that enhances the survival chance of the butterfly in a cold environment rich in blue and UV radiation.

Bioinspired artificial photonic nanoarchitecture using the elytron of the beetle Trigonophorus rothschildi varians as a 'blueprint'.

An unusual, intercalated photonic nanoarchitecture was discovered in the elytra of Taiwanese Trigonophorus rothschildi varians beetles. It consists of a multilayer structure intercalated with a random distribution of cylindrical holes normal to the plane of the multilayer. The nanoarchitectures were characterized structurally by scanning electron microscopy and optically by normal incidence, integrated and goniometric reflectance measurements. They exhibit an unsaturated specular and saturated non-specular component of the reflected light. Bioinspired, artificial nanoarchitectures of similar structure and with similar properties were realized by drilling holes of submicron size in a multilayer structure, showing that such photonic nanoarchitectures of biological origin may constitute valuable blueprints for artificial photonic materials.