Jeremy W. Galusha

Diamond-structured titania photonic-bandgap crystals from biological templates.

Adv. Mater. 2010, 22, 107–11

Study of natural photonic crystals in beetle scales and their conversion into inorganic structures via a sol–gel bio-templating route

The origin of the structural colors from several different examples of the weevil and longhorn families (Curculionidae and Cerambycidae, respectively) was investigated by structural and optical characterization techniques. A range of interesting three-dimensional photonic crystal structures operating at visible wavelengths was discovered, including both disordered and ordered non-close-packed lattices of cuticular spheres and bicontinuous diamond-based architectures. The discovered photonic structures display a large variation in lattice constants and dielectric filling fractions and thereby create optical reflectance colors spanning the entire visible range. To transform these bio-polymeric photonic crystals into heat and photo-stable inorganic structures, a low-temperature bio-templating method was developed. Using organic–inorganic hybrid silica sol–gel infiltration–templation chemistry combined with acid-etching template removal, stable inverse photonic structures were fabricated. The inverse structures display good structural quality and vivid reflection properties.

Toward Subdiffraction Transmission Microscopy of Diffuse Materials with Silver Nanoparticle White-Light Beacons

We demonstrate high resolution transmission microscopy in a conventional two-photon wide-field fluorescence microscope by exploiting nonlinear white light generation from clusters of silver nanoparticles placed beneath the specimen. Surface-enhanced two-photon luminescence occurs at nanoparticle hot spots in the form of spectrally broad, spatially confined light which can be exploited to determine the transmission properties of a sample placed on the silver nanoparticles. We demonstrate the versatility of the technique by revealing individual crystalline domains formed in the diffuse biological photonic crystals of the scales of a beetle. We can identify submicron changes between photonic crystal facets as well as the occurrence of stacked domains invisible to surface-sensitive methods. Control over wavelength, polarization, and pulse shape promises selective addressing of hot spots in nanoparticle assemblies for motionless spatial scanning of the transmission properties with subdiffraction resolution.

High resolution three-dimensional reconstruction of photonic crystal structure found in beetle scales

In this paper we demonstrate how sequential FIB milling combined with scanning electron microscopy imaging can be used to achieve a previously unprecedented high-resolution 3D reconstruction of the photonic crystal structure found in beetle scales.