M. Egen

Structuring of self-assembled three-dimensional photonic crystals by direct electron-beam lithography

An electron-beam lithography technique is described capable of structuring three-dimensional self-assembled photonic crystals. It is shown that the control of the writing depth can be achieved by varying the electron acceleration voltage. Microscopic structures with a depth from 0.4 up to 2 μm are fabricated with a typical lateral resolution of 0.4 μm. The relevance of this technique for the fabrication of deterministic defects sites in opal photonic crystals is discussed and its extension towards buried structures is suggested.

Micromoulding of three-dimensional photonic crystals on silicon substrates

The growth of three-dimensional photonic crystals (PhCs) on patterned silicon substrates is reported. It is shown that deep trenches can be uniformly filled by a self-assembly of polymer microspheres, in a close-packed face-centred cubic lattice. The crystalline quality is compared for different channel widths. These observations are confirmed by optical reflectance measurements in the visible range, showing a bandwidth of enhanced reflection. The possibility to detach the PhC, i.e. to use the substrate as a mould, is also demonstrated. The potential of this approach for building PhC-based complex architectures is discussed.

Self-assembly of three-dimensional photonic crystals on structured silicon wafers

The growth of an opal-like polymer photonic crystal (PhC) on deeply etched silicon wafers is reported. It is shown that 10 μm deep trenches, as narrow as 10 μm can be uniformly filled by self-assembly of microspheres, in a close-packed face-centered-cubic lattice. These observations are confirmed by optical reflectance measurements in the visible range, in agreement with theoretical calculations of the photonic band gap. A slight fluctuation of the lattice parameter is noticed in the case of the narrowest channels. The possibility to detach the PhC from the substrate is also demonstrated. The potential of this approach for building complex PhC-based complex architectures is discussed.

Exploring integration prospects of opal-based photonic crystals

Different methods of functionalisation of thin opal films are discussed, including synthesis of opals on pre-patterned substrates, post-synthesis electron beam lithography, preparation of opals with heterogeneous photonic band gap structure and integrating opals with light sources. These approaches have been tested experimentally and key technological problems have been identified.

Photonic Crystals Based on Two-Layer Opaline Heterostructures

Optical properties of several heterostructures representing two-layer opaline photonic crystals have been examined. Two separate stop-bands have been observed both in transmission and emission spectra. The effect of the interface disorder on the optical spectra was not observed, probably, due to the insufficient degree of order of the opaline layers.

Light transport in hetero-opal photonic crystals

The effect of photonic bandgap interface upon the light scattering was studied in hetero-opals consisting of two opal thin films with different lattice constant. It is shown that the weak scattering regime is preserved in thin hetero-opal films. By comparing scattering spectra of single and hetero-opal films recorded under reversing angles of light incidence and detection it was demonstrated that the interface scatters stronger the light at oblique incident angles. Squeezing of the scattering diagram of hetero-opals compared to single opal films is also assigned to the interface scattering.