Chemical Approach to Functional Artificial Opals

Abstract

Artificial opals are self‐assembled colloidal crystals, which consist of a cubic dense packing (fcc) of hard (not film‐forming) colloids with diameters ranging from 200 to 900 nm. Because of their periodic nanostructure the assemblies are able to reflect light that matches their periodicity, i.e., UV‐ to IR‐radiation depending on the size of the colloids. Thus, they present a subgroup of ‘photonic crystals’. While, originally, the chemistry inside the colloids and the resulting opals was of minor significance, nowadays the chemical variation of opals is becoming more and more important for the preparation of functional and patterned opals. The search for functional opals is, therefore, especially focused on four topics: I) coloring agents, II) incorporation of fluorescent materials, III) replication, and IV) the controlled incorporation of defects.magnified image

Rear Side Diffractive Gratings for Silicon Wafer Solar Cells

“…Sophisticated instruments, which are often necessary in lithographic methods, are not needed. However, it is more difficult to control defects, which evolve during the self-assembly of the colloids, and to modify the structure of the colloidal crystal [77,78]. An example of an artificial opal prepared by self-assembly of monodisperse PMMA spheres is given in Figure 3.11.…”

Langmuir–Blodgett assembly of colloidal photonic crystals using silica particles prepared without the use of surfactant molecules

“…In general, for most of the assembly methods employed, the colloidal particles can consist of various polymers [7,26] or, in the case considered in this paper, of SiO 2 particles formed by the Stöber [9] method. It is usually believed that, in their asformed state, these particles are hydrophilic and thus to form stable films at the air/water interface as in the LB method, they must be functionalised by some compound which renders them hydrophobic.…”

“…In recent years there has been an enormous interest in the use of colloidal particle assemblies to create photonic crystal structures, which may find application in a wide range of both passive and active devices [1][2][3][4][5][6][7]. Of the various methods that have been employed for particle assembly, the Langmuir-Blodgett (LB) [3,8] has emerged as particularly attractive since it may be used to deposit a precisely defined number of monolayers [10,11,16,17,[19][20][21][22][23][24][25].…”

Artificial latex-based opals prepared by spin casting of monodispersed nano particles

“…Polymers are among the materials, which are used to fabricate of photonic crystals. The polymer photonic crystals (PPC) have been produced via different techniques such as melt compression [2][3][4][5][6], synthetic procedures [7][8][9][10][11][12][13], nanoimprint lithography [14], continuous coextrusion [15,16], layer-by-layer process [17][18][19][20], etc. These structures are first synthesized in a dispersion form, then, the crystalline structure of polymer particles would be obtained after drying the dispersion.…”