Hierarchical Nanoparticle Bragg Mirrors: Tandem and Gradient Architectures

Abstract

To manipulate electrons in semiconductor electronic and optical devices, the usual approach is through materials composition, electronic bandgap, doping, and interface engineering. More advanced strategies for handling electrons in semiconductor devices include composition-controlled heterostructures and gradient structures. By analogy to the manipulation of electrons in semiconductor crystals by electronic bandgaps, photons in photonic crystals can be managed using photonic bandgaps. In this context, the simplest photonic crystal is the Bragg mirror, a periodic dielectric construct whose photonic bandgap is engineered through variations of the optical thickness of its constituent layers. Traditionally the materials comprising these periodic dielectric layers are nonporous, and they have mainly been used in the field of optical and photonic devices. More recently these Bragg mirrors have been made porous by building the layers from nanoparticles with functionality and utility that exploit their internal voids. These structures are emerging in the area of photonic color-coded chemical sensing and controlled chemical release. Herein, a strategy for enhancing the functionality and potential utility of nanoparticle Bragg mirrors by making the constituent dielectric layers aperiodic and porous is described. It is exemplified by prototypical tandem and gradient structures that are fully characterized with regards to their structure, porosity, and optical and photonic properties.

Electrochromic Bragg Mirror: ECBM

“…[16][17][18][19][20][21] To electrically tune the optical properties of the ECBM, a cell has been constructed containing the electrolyte and FTO as a transparent counter-electrode. Applying a bias voltage of + 2.5 V switches the WO 3 4 to be the ideal electrolyte-system.…”

Lithium Tin Sulfide—a High‐Refractive‐Index 2D Material for Humidity‐Responsive Photonic Crystals

“…Although a high RI contrast and good optical device quality were achieved, the sensitivity toward vapors is severely reduced due to the limited textural porosity of the titania layer. Another approach to increase the RI contrast is to identify new porous materials with a similar or even higher RI compared to TiO 2 , although current alternatives such as WO 3 sol ( n = 2.03), ZrO 2 nanoparticles ( n = 1.70), Ta 2 O 5 nanoparticles ( n = 1.80), undoped or antimony‐doped SnO 2 films ( n (undoped) = 1.83, n (3% Sb‐doped) = 2.34) all feature lower RIs compared to dense titania or suffer from low transparency in the visible range. Thus, the highest RI contrast BSs reported so far combine highly porous silica layers stacked with dense titania layers, exhibiting an RI contrast of Δ n = 0.83, Δ n = 0.84, and Δ n = 0.89 .…”

Ethanolamine-assisted low-temperature crystallization of hydroxide nanoparticle ink into transparent and conductive ITO layers

“…Besides the effect of ink concentration on the quality of coated layers, it was found out that the coating atmosphere also plays an important role, especially in avoiding the generation of surface defects such as 'streaks' and 'comets'. As reported by Redel 27 and Puzzo, 28 streaks and comets are frequent defects in spin-coated nanoparticle layers because of particle agglomeration, dust particles in air, inappropriate setting of spin-coating parameters, etc. Our coating practice indicates that such defects can be avoided by generating a suitable atmosphere within the spin-coater chamber.…”