A New Synthetic Approach to Silicon Colloidal Photonic Crystals with a Novel Topology and an Omni‐Directional Photonic Bandgap: Micromolding in Inverse Silica Opal (MISO)

Abstract

The fabrication of photonic crystals based on colloidal crystal templating represents one of the most attractive approaches among those currently being considered to overcome the challenge of building up a 3D periodic modulation of refractive index at the micrometer length scale. [1,2] So far, important advances have been made by using micrometer-size silica or latex sphere colloidal crystals, i.e., artificial opals, as templates. Briefly, opal molds are built from a suspension of colloidal particles either by sedimentation on a flat substrate, [3] which gives rise to large size face-centered cubic (fcc) crystals, or by convection-force induced self-assembly, which results in planarized fcc crystals of controlled thickness. [4] By infiltrating the interstitial sites of these structures with high refractive index materials, such as silicon, [5,6] germanium, [7,8] or titanium oxide, [9,10] and later removal of the colloidal crystal scaffold, an inverted opal structure consisting of interconnected air cavities in a high dielectric constant medium is attained. This chemical approach to the fabrication of photonic crystals leads to optical-quality materials with the suitable geometry, topology, and dielectric contrast as to allow the opening of photonic bandgaps.[11]In this same context, it has also been demonstrated that it is possible to synthesize a new type of colloidal crystal made of a wide variety of dense and porous oxides and metals by means of a template approach that utilizes a mold consisting of a periodic distribution of interconnected spherical cavities in a latex background, which is obtained by replicating a silica colloidal crystal in latex and subsequently dissolving the silica template. [12,13] Infiltration of different precursors is used to coat the internal surfaces of the latex mold with different materials and gives rise to a novel kind of hybrid inverse colloidal crystal. The method has been referred to as micromolding in inverse polymer opals (MIPO), and while the approach is quite versatile, it cannot be easily applied to obtain compositions whose synthesis requires high temperatures or corrosive precursors.Here, we present a new type of silicon colloidal photonic colloidal crystal presenting a different topology than previously synthesized high refractive index contrast colloidal photonic crystals. It has been built using a new process of colloidal crystal templating based on micromolding in inverse silica opals (MISO), i.e., interconnected air cavities in a silica matrix. By chemical vapor deposition (CVD) of disilane within this lattice we form a continuous silicon layer of controlled thickness that coats the walls of the silica matrix. Later, by dissolution of the starting inverted silica opal it is possible to obtain fcc silicon colloidal photonic crystals with a topology never observed before, and which present a full photonic bandgap, as indicated by theoretical photonic band structure calculations.Samples employed in this study were prepared as follows. The silica micromold was first ...

Core-shell diamond-like silicon photonic crystals from 3D polymer templates created by holographic lithography

“…Recently several groups have investigated the fabrication of silicon photonic crystals through silicon chemical vapor deposition (CVD) of synthetic opals from silica [17][18][19], and polymers [20], or a double templating method using a sequential silica [21]/silicon [17][18][19] CVD process from polymeric wood-piles structures fabricated by direct-write assembly [22] and direct-laser writing [23], respectively. Core-shell morphology is often revealed during the CVD process when the deposited materials grow continuously on the 3D template surface to fill the interstitial pores.…”

Opals for Photonic Band-Gap Applications

“…3-D polymer templates obtained by direct laser writing [23] and by concentrated electrolyte inks [24] have recently been downscaled [25] and replicated with silicon [26], [27]. In PS artificial opals, a sol-gel process, with poor or no control on infiltration has been used to fill the opal voids with silica to later grow silicon in the inner surface of the silica inverse opals [28].…”

Preparation and Performance of Ordered Porous TiO2 Film Doped with Gd3+

“…Fabricating ordered porous TiO 2 films with high performance is a key factor to increasing the efficiency of DSSCs. Colloidal crystal templates provide an effective way to prepare ordered porous TiO 2 films ( Ref 11,12). However, there are limitations, such as the wide band gap and charge recombination between the TiO 2 electrode and the electrolyte.…”