Worawut Khunsin

Ordered 2D Colloidal Photonic Crystals on Gold Substrates by Surfactant‐Assisted Fast‐Rate Dip Coating

EA and MO acknowledge the support of the Irish Research Council under awards RS/2010/2920 and RS/2010/2170. WK and CMST acknowledge support from the Spanish National I+D Plan projects TAPHOR (MAT-2012–31392) and CONSOLIDER nanoTHERM (CSD2010–00044). COD acknowledges support from Science Foundation Ireland under award no. 07/SK/B1232a-STTF11, the UCC Strategic Research Fund, and from the Irish Research Council New Foundations Award.

Optical transmission in triple-film hetero-opals

Angle-resolved transmission of s-polarized light in triple-film hetero-opals has been investigated in the spectral range including high-order photonic band gaps, and compared to the transmission of its constituent single-film opals. The interfaces do not destroy the predominantly ballistic light propagation over the studied frequency and angular ranges, but heterostructuring leads to a smoothed angular distribution of intensity of the transmitted light and to the reconstruction of the transmission minima dispersion. The interface transmission function has been extracted by comparing the transmission of the hetero-opal and its components in order to demonstrate the difference. This deviation from the superposition principle was provisionally assigned to light refraction and reflection at the photonic crystal interfaces and to the mismatch between mode group velocities in hetero-opal components.

Defect analysis and alignment quantification of line arrays prepared by directed self-assembly of a block copolymer

Different linear patterns obtained from the directed self-assembly of the block copolymer (BCP) polystyrene-b-polyethylene oxide (PS-b-PEO) were analysed and compared. The hexagonal phase PS-b-PEO in a thin film exhibits linear pattern morphology, by conventional solvent annealing in an atmosphere saturated in chloroform. The surface energy of the silicon substrates was varied using surface functionalization of a self-assembly monolayer (SAM) and a polymer brush, chosen to investigate the influence of the surface energy on the self-assembly of the BCP. The linear patterns formed were analyzed with innovative image analysis software specifically developed in our laboratory to identify elements and defects of line arrays from block copolymer self-assembly. The technique starts by performing dimensional metrology to calculate the pitch size and estimate the linewidth of the lines. Secondly, the methodology allows identification and quantification of typical defects observable in BCP systems, such as turning points, disclination or branching points, break or lone points and end points. The defect density and the quantification of the alignment were estimated using our technique. The methodology presented here represents a step forward in dimensional metrology and defect analysis of BCP DSA systems and can be readily used to analyze other lithographic or non-lithographic patterns.

Stochastic resonance in photonic crystal growth

We study the role of noise during the growth process of opal-based photonic crystals, and demonstrate that noise significantly improves their structural properties. We observe a stochastic resonance-like behaviour, where the ordering of the resulting structure improves up to a certain optimal noise level and then deteriorates for larger noise volumes. This demonstrates that noise can have a nontrivial effect when applied during a non-equilibrium pattern forming process.

Bleaching-induced evolution of directional emission from dye-loaded opals

The evolution of angular-dependent photoluminescence from thin-film colloidal photonic crystals assembled from silica spheres encapsulating Rhodamine 6G dye has been investigated as a function of the time of their exposure to the incident laser irradiation. Resulting diagrams showing this angular dependence in emission reveal 3 types of behaviour which can be explained in terms of the spatial configuration of the light sourced inside the colloidal crystal due to inhomogeneous bleaching of dye emission, the ballistic propagation of photons in well-ordered crystals, and self-absorption of the emission by non-excited dye molecules.

2D Photonic Defect Layers in 3D Inverted Opals on Si Platforms

Dielectric spheres synthesised for the fabrication of self-organized photonic crystals such as opals offer large opportunities for the design of novel nanophotonic devices. In this paper, we show a hexagonal superlattice monolayer of dielectric spheres inscribed on a 3D colloidal photonic crystal by e-beam lithography. The crystal is produced by a variation of the vertical drawing deposition method assisted by an acoustic field. The structures were chosen after simulations showed that a hexagonal super-lattice monolayer in air exhibits an even photonic band gap below the light cone if the refractive index of the spheres is higher than 1.93