Search for: All records

Dielectric mirrors based on Bragg reflection and photonic crystals have broad application in controlling light reflection with low optical losses. One key parameter in the design of these optical multilayers is the refractive index contrast, which controls the reflector performance. This work reports the demonstration of a high-reflectivity multilayer photonic reflector that consists of alternating layers of TiO₂films and nanolattices with low refractive index. The use of nanolattices enables high-index contrast between the high- and low-index layers, allowing high reflectivity with fewer layers. The broadband reflectance of the nanolattice reflectors with one to three layers has been characterized with peak reflectance of 91.9% at 527 nm and agrees well with theoretical optical models. The high-index contrast induced by the nanolattice layer enables a normalize reflectance band of Δλ/λ_oof 43.6%, the broadest demonstrated to date. The proposed nanolattice reflectors can find applications in nanophotonics, radiative cooling, and thermal insulation.

 

In this work, we present a binary assembly model that can predict the co-assembly structure and spatial frequency spectra of monodispersed nanoparticles with two different particle sizes. The approach relies on an iterative algorithm based on geometric constraints, which can simulate the assembly patterns of particles with two distinct diameters, size distributions, and at various mixture ratios on a planar surface. The two-dimensional spatial-frequency spectra of the modeled assembles can be analyzed using fast Fourier transform analysis to examine their frequency content. The simulated co-assembly structures and spectra are compared with assembled nanoparticles fabricated using transfer coating method are in qualitative agreement with the experimental results. The co-assembly model can also be used to predict the peak spatial frequency and the full-width at half-maximum bandwidth, which can lead to the design of the structure spectra by selection of different monodispersed particles. This work can find applications in fabrication of non-periodic nanostructures for functional surfaces, light extraction structures, and broadband nanophotonics.

 

Three-dimensional (3D) nanostructures play a crucial role in nanophotonics, lasers, and optical systems. This article reports on the fabrication of 3D nanostructures consisting of opal structures that are spatially aligned to an array of holes defined in the photoresist. The proposed method uses colloidal lithography to pattern a hexagonal array of holes, which are then used to direct the subsequent 3D assembly of colloidal particles. This approach allows the 3D opal structures to be aligned with the 2D array of holes, which can enhance spatial-phase coherence and reduce defects. The polymer patterns can be used as a sacrificial template for atomic layer deposition and create free-standing nanolattices. The final structure consists of a combination of nanolattice, upon which controlled deposition of opal structures is achieved. These structures result in nanostructured materials with high porosity, which is essential to create low-index materials for nanophotonics. A thick layer of titanium oxide with high refractive index is deposited over nanolattices to demonstrate the mechanical stability of underlying structures. These nanolattice structures with precisely controlled height can serve as a low-index layer and can find applications in Bragg reflectors, nanophotonics, and optical multilayers.

 

In this work, we investigate the anelastic deformation behavior of periodic three-dimensional (3D) nanolattices with extremely thin shell thicknesses using nanoindentation. The results show that the nanolattice continues to deform with time under a constant load. In the case of 30-nm-thick aluminum oxide nanolattices, the anelastic deformation accounts for up to 18.1% of the elastic deformation for a constant load of 500 μN. The nanolattices also exhibit up to 15.7% recovery after unloading. Finite element analysis (FEA) coupled with diffusion of point defects is conducted, which is in qualitative agreement with the experimental results. The anelastic behavior can be attributed to the diffusion of point defects in the presence of a stress gradient and is reversible when the deformation is removed. The FEA model quantifies the evolution of the stress gradient and defect concentration and demonstrates the important role of a wavy tube profile in the diffusion of point defects. The reported anelastic deformation behavior can shed light on time-dependent response of nanolattice materials with implication for energy dissipation applications. 

In this work, we introduce a roll-to-roll system that can continuously print three-dimensional (3D) periodic nanostructures over large areas. This approach is based on Langmuir-Blodgett assembly of colloidal nanospheres, which diffract normal incident light to create a complex intensity pattern for near-field nanolithography. The geometry of the 3D nanostructure is defined by the Talbot effect and can be precisely designed by tuning the ratio of the nanosphere diameter to the exposure wavelength. Using this system, we have demonstrated patterning of 3D photonic crystals with a 500 nm period on a 50 × 200 mm²flexible substrate, with a system throughput of 3 mm/s. The patterning yield is quantitatively analyzed by an automated electron beam inspection method, demonstrating long-term repeatability of an up to 88% yield over a 4-month period. The inspection method can also be employed to examine pattern uniformity, achieving an average yield of up to 78.6% over full substrate areas. The proposed patterning method is highly versatile and scalable as a nanomanufacturing platform and can find application in nanophotonics, nanoarchitected materials, and multifunctional nanostructures.

 

The fabrication of periodic 3D nanostructures with uniform material properties has been widely investigated and is important for applications in photonics, mechanics, and energy storage. However, creating nanostructures with spatially varying lattice geometry and material composition is still largely an unexplored challenge in nanofabrication. This work presents the fabrication of non‐uniform nanolattices by patterning multiple layers of 3D nanostructures using phase shift lithography and atomic layer deposition. By controlling the processing parameters, the lattice geometry and material composition of each individual nanolattice layer can be tailored to create arbitrary material property profiles. Using the proposed method, a five‐layer nanolattice with spatially varying porosity and oxide materials has been demonstrated. This process can be used to create gradient‐index antireflection nanostructures, and a fabricated four‐layer nanolattice structure consisting of TiO₂and Al₂O₃with gradually varying porosity reduces more than 90% of the specular reflectance from a silicon substrate. By enabling nanolattices with arbitrary profiles in physical properties, the demonstrated technique can find broad applications in nanophotonics, graded filters, energy storage systems, and nanoarchitected films.