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Item type:Publication, Access status: without files , Bottom-up Fabrication of Multilayer Stacks of 3D Photonic Crystals from Titanium Dioxide(2016-04-27); ; ; ; A strategy for stacking multiple ceramic 3D photonic crystals is developed. Periodically structured porous films are produced by vertical convective self-assembly of polystyrene (PS) microspheres. After infiltration of the opaline templates by atomic layer deposition (ALD) of titania and thermal decomposition of the polystyrene matrix, a ceramic 3D photonic crystal is formed. Further layers with different sizes of pores are deposited subsequently by repetition of the process. The influence of process parameters on morphology and photonic properties of double and triple stacks is systematically studied. Prolonged contact of amorphous titania films with warm water during self-assembly of the successive templates is found to result in exaggerated roughness of the surfaces re-exposed to ALD. Random scattering on rough internal surfaces disrupts ballistic transport of incident photons into deeper layers of the multistacks. Substantially smoother interfaces are obtained by calcination of the structure after each infiltration, which converts amorphous titania into the crystalline anatase before resuming the ALD infiltration. High quality triple stacks consisting of anatase inverse opals with different pore sizes are demonstrated for the first time. The elaborated fabrication method shows promise for various applications demanding broadband dielectric reflectors or titania photonic crystals with a long mean free path of photons.Publicationtype: Journal Article90 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Enhanced structural and phase stability of titania inverse opals(Elsevier, 2015-05-15); ; ; ; The applications and processing of nanostructured materials at high temperatures require stability of their morphology. However, in such environments (>1000. °C), these structures are prone to significant undesired microstructural changes that result in a loss of functional properties. The thermal stability of titania inverse opal films, prepared from self-assembled templates of monodisperse polystyrene spheres by infiltration utilizing atomic layer deposition and subsequent calcination, was assessed. Resistance to grain growth and a shift in the anatase-to-rutile transformation to higher temperatures was observed, with dramatic stability under vacuum. Vacuum annealed samples retained the anatase phase and exhibited minimal grain growth even after 3. h at 1300. °C. Photonic properties were retained until the transformation onset. The remarkable resistance was attributed to inhibition of surface diffusion and structure-substrate constraints. In addition to being technologically enabling, the results provide further insight into the titania system and its phase transformation mechanism.Publicationtype: Journal Article61 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Vertical convective coassembly of refractory ysz inverse opals from crystalline nanoparticles(American Chemical Society (ACS), 2013-12-09); ; ; ; A facile deposition method of 3D photonic crystals made of yttrium-stabilized zirconia (YSZ) was developed. YSZ nanoparticles with primary particle size below 10 nm and cubic crystalline phase were synthesized by hydrothermal treatment of solutions of zirconyl nitrate, yttrium nitrate and acetylacetone. Before coassembly with polystyrene (PS) microspheres, a dispersant Dolapix CE64 was added to the dialyzed sol of YSZ nanoparticles to render their surface negatively charged. Vertical convective coassembly resulted in 3D ordered YSZ/PS hybrid films, which were inverted at 500 C in air to produce inverse opals. The linear shrinkage of the coatings was in the range 15-20%, below previously reported values for YSZ. The obtained coatings demonstrated pronounced photonic properties and retained their ordered structure after annealing at 1000 C for 2 h. Increasing the filling fraction of crystalline nanoparticles in the templates should enable production of fully functional 3D photonic crystals for applications in high-temperature photonics.Publicationtype: Journal Article116 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Waveguide-based optical phased arrayA concept for a 3-D waveguide system, which can be used for optical phased arrays, is presented in this letter. We implemented static phased arrays with rod waveguides of different widths, which can be used for holographic applications. They are fabricated with direct laser writing, a technique based on two photon polymerization. As the element size of our phased array can be in the order of the visible wavelength, relatively large diffraction angles of up to 40° can be reached.Publicationtype: Journal Article79 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Gold-silicon metamaterial with hyperbolic transition in near infrared(American Institute of Physics (AIP), 2013-07-10); ; ; ; In this paper, we focus on the creation and characterization of a hyperbolic metamaterial for near infrared. To shift the hyperbolic transition there, a stack of alternating 7 nm gold and 42 nm silicon layers is chosen. Samples are manufactured using magnetron sputtering and different measurements confirm their structure. We fit the Drude model of gold to reproduce measured reflectivity and transmittance by simulations. The collision frequency of the thin film gold is increased by 9 times, which shifts the transition of our metamaterial to the hyperbolic regime to even larger wavelengths. The performance is comparable to other proposed metamaterials. © 2013 AIP Publishing LLC.Publicationtype: Journal Article173 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Photonic properties of titania inverse opal heterostructures(Optical Society of America (OSA), 2013); ; ; ; Titania inverse opal heterostructures demonstrating two distinctive photonic stopgaps were fabricated by repetitive vertical selfassembly and atomic layer deposition (ALD). Angle resolved reflectance measurements of the inverse opal heterostructure are reported for the first time. The comparison with the spectra of constituents show that the GL stopgaps of the heterostructure obey the superposition principle and the angular dispersion of their stopgaps is well-fitted with the modified Bragg's law at low incidence angles. Numerical simulations were used to predict the dominant features in the reflectance spectra. The total (specular and diffuse) transmission and reflectance measurements of the single inverse opals and the heterostructure reveal that the diffuse scattering could severely impair the photonic properties of the buried layers in the multi-stack photonic crystal (PhC) configurations. Ascending stacking is proposed as a means to improve the performance of the multi-layer coatings. © 2013 Optical Society of America.Publicationtype: Journal Article68 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Towards ceramic 3DOM-materials as novel high-temperature reflective coatings and filters for thermophotovoltaics(IOP Publishing, 2011-06-06); ; ; ; Studies on evaporation-induced vertical convective self-assembly as well as horizontal self-assembly are presented including inversion of the opals and deposition of heterostruc-tures. Opaline coatings were deposited on microscope slides from monodisperse particles of polystyrene and silicon dioxide with the particle sizes in the range from 400 to 1100 nm. Well defined photonic stopgaps were observed for both direct and inverted structures. We show that the horizontal deposition method facilitates self-assembly of large silica particles, so that the limitation of the conventional vertical convective self-assembly can be overcome. Successful stacking of the self-assembled polystyrene templates with unequal particle size is demonstrated.Publicationtype: Journal ArticleScopus© Citations 4 320 534