Template‐Directed Solidification of Eutectic Optical Materials

Abstract

polarizers, some waveguides, and many lasers. [1][2][3] Materials with powerful optical functionalities, including negative-index of refraction and optical chirality, can be realized by appropriate placement of materials with suitable properties in 2D or 3D space. [4][5][6] Light in the visible spectrum can be manipulated, although the tolerance for defects is exceedingly low at visible frequencies, and the number of materials with the appropriate properties is limited. [7,8] Most photonic crystals are fabricated by high-resolution top-down 2D patterning methods such as electron-beam lithography, interference lithography, and focused ion beam milling. [9] However, it is challenging to fabricate large-area bulk materials with these techniques, especially with intricate internal structures. [8] Additionally, many materials with promising optical properties are not compatible with these top-down patterning methods. [4,10] As work on colloidal crystals has shown, controlled self-assembly is an effective route to organizing materials into 3D architectures, which interact strongly with light. [9][10][11][12][13] Colloidal self-assembly, however, only offers a limited set of symmetries (generally those of close packed arrangements), and a spherical basis. [12] For many applications, considerably more complex structures are of interest. Particularly promising approaches for forming materials with complex internal microstructures include eutectic solidification and block copolymer self-assembly, [14][15][16][17] and materials with interesting optical properties have been reported using both approaches. These methods are advantageous due to the wide range of microstructures they form. Here, we focus on the structures formed by eutectic solidification since materials with a broader range of optical properties are available compared to that provided by block copolymers, and because the characteristic lengths of structures accessible through eutectic solidification better match the wavelengths of visible and IR light. Further, forming materials with sufficiently large characteristic dimensions for interaction with visible light by block copolymer assembly is synthetically challenging as it requires high molecular weight polymers. [18] Similarly, self-assembly of other building blocks, e.g., nanoparticles, [19,20] molecules, [21,22] and DNA, [23,24] tend to produce structures with characteristic dimensions too small to provide strong light-matter interactions (via diffractive phenomena), [2,3,25] and are thus not the emphasis of this review.Mesostructured materials can exhibit enhanced light-matter interactions, which can become particularly strong when the characteristic dimensions of the structure are similar to or smaller than the wavelength of light. For controlling visible to near-infrared wavelengths, the small characteristic dimensions of the required structures usually demand fabrication by sophisticated lithographic techniques. However, these fabrication methods are restricted to producing 2D and a limited range of 3D...

Multi‐Step Crystallization of Self‐Organized Spiral Eutectics

“…Thus, an understanding of crystallization phenomena is the key to lock into place materials with morphologies and/or functionalities not present in equilibrium states . Particularly appealing are spiral eutectics, mixtures of two or more solid phases that grow simultaneously from a parent liquid phase and which arrange into intricate spiraling patterns, in some cases akin to a DNA helix. The intrinsic chirality of spiral eutectics offers a new strategy for rapid, bottom‐up manufacturing of large‐area photonic materials in the visible/infrared spectrum, owing to the fact that conventional top‐down techniques—whose speed and complexity scale up with the number of helices—sets a bottleneck for large‐scale production …”

Chemical modification of degenerate eutectics: A review of recent advances and current issues

“…80 Hecht et al have reviewed the advances in phase field modeling of multiphase solidification. 81 Other reviews 82,83 and research articles, 84,85 as well as references therein, provide additional examples of how PF modeling and other theoretical methods can be used to understand the physical mechanisms controlling the microstructural development. However, in a phase field simulation, the interface is diffuse and thus the incorporation of interfacial energy anisotropy requires careful consideration.…”

Mechanism behind columnar pattern formation during directional quenching-induced phase separation

“…But there is a universality behind pattern formation during homogeneous phase separation (the so-called model B [12]); thus, other quenching methods are required to control and diversify the patterns which are formed. One such method is inducing phase separation in templated quenching systems [13][14][15][16][17][18][19][20], where phase separation is affected by the boundaries of a volume due to wetting effects. Investigations which apply asymmetric affinity to walls [13][14][15][16], Janus particles [17][18][19], and templated colloids [20] have also been carried out.…”