Nanosphere lithography offers a rapid, low-cost approach for patterning of large-area two-dimensional periodic nanostructures. However, a complete understanding of the nanosphere self-assembly process is necessary to enable further development and scaling of this technology. The self-assembly of nanospheres into two-dimensional periodic arrays has previously been attributed solely to the Marangoni force; however, we demonstrate that the ζ potential of the nanosphere solution is critically important for successful self-assembly to occur. We discuss and demonstrate how this insight can be used to greatly increase self-assembled 2D periodic array areas while decreasing patterning time and cost. As a representative application, we fabricate antireflection nanostructures on a transparent flexible polymer substrate suitable for use as a large-area (270 cm2), broadband, omnidirectional antireflection film.

The incorporation of monovalent silver (Ag + ) cations into methylammonium lead bromide (CH 3 NH 3 PbBr 3 ) perovskite films leads to a strongly preferred (001) crystallographic orientation on a wide variety of substrates, ranging from glass to mesoporous TiO 2 . CH 3 NH 3 PbBr 3 films deposited without Ag + exhibit only a weakly preferred (011) orientation. Compositional maps and depth profiles from time-of-flight secondary ion mass spectrometry (TOF-SIMS) reveal Ag + segregated to grain boundaries and interfaces. In photovoltaic devices (PVs), addition of Ag + to MAPBr films resulted in poorer device performance, most likely because of the observed Ag + segregation in the films.

We demonstrate that arrays of hourglass-shaped nanopillars patterned into crystalline silicon substrates exhibit vibrant, highly controllable reflective structural coloration. Unlike structures with uniform sidewall profiles, the hourglass profile defines two separate regions on the pillar: a head and a body. The head acts as a suspended Mie resonator and is responsible for resonant reflectance, while the body acts to suppress broadband reflections from the surface. The combination of these effects gives rise to vibrant colors. The size of the nanopillars can be tuned to provide a variety of additive colors, including the RGB primaries. Experimental results are shown for nanopillar arrays fabricated using nanoimprint lithography and plasma etching. A finite difference time domain (FDTD) model is validated against these results and is used to elucidate the electromagnetic response of the nanopillars. Furthermore, a COMSOL model is used to investigate the angle dependence of the reflectance. In view of display applications, a genetic algorithm is used to optimize the nanopillar geometries for RGB color reflective pixels, showing that nearly all of the sRGB color space and most of the Adobe RGB color space can be covered with this technique.

We report tip-enhanced Raman spectroscopy and tip-enhanced photoluminescence studies of monolayer and bilayer MoS 2 in which we characterize photoluminescence and first and second order Raman spectra in monolayer, bilayer, and inhomogeneously strained MoS 2. From the transition of unstrained MoS 2 from monolayer to bilayer, we determine a spatial resolution of approximately 100 nm through the peak positions of the first order Raman modes. The strain dependence of the second order Raman modes, reported for the first time, reveals changes in the electronic band structure in strained MoS 2 that are directly observed through changes in the Raman peak positions and peak area ratios, which are corroborated through density functional theory calculations.

Low resistance and high transparency of TCEs are two essential prerequisites for a variety of applications, including the fabrication of smart windows. [8] Among various TCEs, highly transparent and conductive indium tin oxide (ITO) is most commonly employed; however, its highly brittle nature hinders its application in flexible electronics and the scarcity of indium results in high material cost. [9] The bending strain tolerance and mechanical flexibility of ITO/elastomeric substrates are inadequate because of the brittle nature of ITO, which renders flexible ITO substrates impractical for real-life stretchable, foldable, or bendable optoelectronics applications. [10] In addition, the relatively low thermal conductivity of ITO leads to longer response times for devices reliant on thermally activated transitions, such as thermochromic smart windows. Extensive research has therefore been devoted to ITO alternatives including carbon-based TCEs such as graphene, [11] carbon nanotubes, [12] or conducting polymers, [13] and metal-based TCEs such as metal nanowires [14] or metal meshes. [15] Among these ITO alternatives, metal meshes, which are composed of periodic micro-or nanostructured metal networks on a transparent substrate, have gained considerable attention as high performance TCEs offering several advantages, including excellent mechanical flexibility, high conductivity, tunable transmittance, and low fabrication cost. [16,17] The current fabrication methods for these metal mesh films often involve low throughput, smallscale fabrication techniques such as e-beam lithography, nanoimprint lithography, photolithography, and laser writing, which are generally time-consuming and require substantial capital investment. Therefore, the nanosphere lithography method which involves a scalable, high throughput fabrication process of metal mesh films was introduced. [18] Nanosphere lithography (NSL) enables rapid, low-cost fabrication of deep submicron metal nanomesh (NM) patterns via the self-assembled formation of a hexagonal close packed monolayer of spherical particles which serves as a patterning mask. It provides a scalable and high throughput lithography process which can be implemented for both rigid and flexible substrates. [19] Moreover, NSL enables precise control over the