Tailored Disorder in Photonics: Learning from Nature

Abstract

Through natural selection, optimally designed nano-and microstructures have arisen for tailored light-matter interactions, even despite a rather limited repertory of materials. [3] Hierarchy is a major reason for the multifunctionality of natural materials such as feathers, which keep the birds body warm and make it water repellant, create wings and tails for aerodynamic lift during flying, and furthermore, provide coloration for camouflage as well as for intraspecific sexual communication. [3][4][5][6][7][8] In comparison, mankind just very recently developed fabrication technologies, which can be separated into bottom-up and top-down approaches. In bottom-up approaches, small building blocks (e.g., nanoparticles or molecules) are organized using self-assembly strategies. Bottom-up approaches are scalable and, hence, are suitable for mass fabrication. However, self-assembly always faces the unavoidable risk of introducing unwanted defects (e.g., stacking faults, missing particles), as these processes are not fully controllable. Top-down processes on the other hand allow for full control (within the limits of the precision of the technique). Here, different techniques have been developed for 1D (e.g., atomic-layer deposition, chemical-vapor deposition, molecular beam epitaxy), 2D (e.g., photo-lithography or electron-beam lithography) as well as 3D (e.g., direct laser writing, direct inkjet printing, laser induced forward transfer) structures. With increasing number of dimension, suitability for mass fabrication reduces. However, top-down fabrication reaches the required precision of few tens of nanometers even for 3D approaches to address the length scales present in the intricate structures found in nature.Due to the growing worldwide interest in photonics, researchers study natural systems as many concepts are resilient against disorder or even utilize certain amounts of disorder to achieve the desired functionality. Coloration derived from the microstructure and the underlying photonic dispersion relations and transport processes play an important role, as these properties can be designed or tailored by controlling the microstructure. Combining the precision of top-down approaches with the flexibility of bottom-up strategies opens new avenues for structures with controlled amounts of disorder. Here, we want to review the mechanisms found in natural structures, briefly discuss the underlying theoretical principles before we provide a broader overview of materials and methods for fabrication. We will conclude with a detailed exposition of four illustrative examples that showcase different aspects of tailored disorder.

Evaporation-Induced Self-Assembly of Metal Oxide Inverse Opals: From Synthesis to Applications

“…Increased disorder results in less color-travel. 37 − 39 Meanwhile, the color purity of IOs can be enhanced by forming them on a substrate which absorbs visible light such as a silicon wafer or by including broadband or narrowband absorbers, such as carbon black or plasmonic particles, respectively, within the IO. 40 …”

Bottom-up synthesis of meta-atoms as building blocks in self-assembled metamaterials: recent advances and perspectives

“…Disorder and inaccuracy are inherent to bottom-up methods and are often viewed as a fundamental limitation of these approaches. However, recent trends in the literature have seen the inclusion of a controlled degree of disorder into such systems as potentially advantageous [22][23][24]. For instance, disordered surfaces can achieve perfect absorption, an application where 100% of the impinging light is resonantly absorbed [21].…”

Weak Localization Enhanced Ultrathin Scattering Media

“…[9][10][11][12][13][14][15][16] Furthermore, the fabrication of artificial structures capable to mimic the whiteness was shown using different techniques. [17][18][19][20][21] However, also in these artificial structures the light transport is treated as a diffusion process only approximating the real scattering behavior.…”

“…[9,10,15,16] This could hamper tailoring disordered photonic media since an unambiguously identified scattering mechanism is the basis for nanostructure design for optimized performance. Using ultrafast time-resolved spectromicroscopy [26,27] of scattered light outside the CBS cone, we here identify the coherent light scattering mechanisms for Cyphochilus scales and disordered Bragg stacks (DBS) [21,28] and show that weak localization in leaky photonic modes significantly contributes to the brilliant whiteness of these scatterers.…”