We study the effect of fluid flow on three-dimensional (3D) dendrite growth using a phase-field model on an adaptive finite-element grid. In order to simulate 3D fluid flow, we use an averaging method for the flow problem coupled to the phase-field method and the semi-implicit approximated projection method (SIAPM). We describe a parallel implementation for the algorithm, using the CHARM++ FEM framework, and demonstrate its efficiency. We introduce an improved method for extracting dendrite tip position and tip radius, facilitating accurate comparison to theory. We benchmark our results for 2D dendrite growth with solvability theory and previous results, finding them to be in good agreement. The physics of dendritic growth with fluid flow in three dimensions is very different from that in two dimensions, and we discuss the origin of this behavior.

Silver nanowire (Ag NW) based transparent electrodes are inherently unstable to moist and chemically reactive environment. A remarkable stability improvement of the Ag NW network film against oxidizing and sulfurizing environment by local electrodeposition of Ni along Ag NWs is reported. The optical transmittance and electrical resistance of the Ni deposited Ag NW network film can be easily controlled by adjusting the morphology and thickness of the Ni shell layer. The electrical conductivity of the Ag NW network film is increased by the Ni coating via welding between Ag NWs as well as additional conductive area for the electron transport by electrodeposited Ni layer. Moreover, the chemical resistance of Ag NWs against oxidation and sulfurization can be dramatically enhanced by the Ni shell layer electrodeposited along the Ag NWs, which provides the physical barrier against chemical reaction and diffusion as well as the cathodic protection from galvanic corrosion.

We study the growth of a single dendrite from a small initial seed in an undercooled melt in the presence of a forced flow. Three-dimensional models are constructed in which the solidification is computed using an adaptive finite-element mesh and a phase-field method. We compare our calculations with available theories and experiments and conclude that there are significant open questions remaining about the evolution of microstructure when flow is present.

Metal halide perovskite light-emitting diodes (PeLEDs) have gained significant interest for next-generation optoelectronic devices, since PeLEDs exhibit narrow emission bandwidth that allows for vivid and clear images based on their high color purity. [1][2][3][4][5][6] The emission color of PeLEDs is tunable in the visible and near-infrared (NIR) spectral regions and they offer low operating and turn-on voltages, along with promising efficiency values. [3,4,[7][8][9] In addition, thin films have shown nearunity photoluminescence quantum yield (PLQY) and population inversion at room temperature, [10][11][12][13][14] potentially allowing for electrically pumped lasers with various emission colors.There has recently been rapid growth in the external quantum efficiency (EQE) of PeLEDs, to values of over 20%, [9,[15][16][17][18][19][20][21][22][23][24][25][26][27] since early reports of PeLEDs in 2014 with efficiency below 0.25%. [28] Numerous strategies to improve the EQE of PeLEDs are being actively pursued in order to bring their performance in line with other, more established, LED technologies. [8] However, a disparity of refractive index (n) between organic transport layers (typically in the range of 1.6-1.8) and the perovskite emissive layer (≈2.3 near the emission wavelength) holds back performance. [29][30][31][32] Due to the high n of the perovskite layer, the maximum EQE of PeLEDs is limited by outcoupling efficiency and restricted to ≈20%, with the remainder of light being trapped within the thin film and substrate materials, as well as parasitic absorption. [31,32] Therefore, it is necessary to investigate alternative device architectures that are able to enhance outcoupling efficiency and realize direct benefits to EQE.In this study, we demonstrate EQE of 14.6% in methylammonium lead iodide (MAPbI 3 ) based red/NIR LEDs using a randomly distributed nanohole array (NHA) embedded in a SiN layer between the indium tin oxide (ITO) anode and glass substrate. The SiN layer with a high n of 2.02 at the peak emission wavelength possesses a high-index contrast with the voids of the NHA with n of 1.0. This layer effectively compensates for the high n of the perovskite emissive layer and aids outcoupling of waveguided and substrate modes. As a result, PeLEDs with NHAs show 1.64 times higher light extraction than PeLEDs without NHAs. Figure 1a displays the device structure of PeLEDs with and without NHAs, as well as the molecular structures of transport Organic-inorganic hybrid perovskite light-emitting diodes (PeLEDs) are promising for next-generation optoelectronic devices due to their potential to achieve high color purity, efficiency, and brightness. Although the external quantum efficiency (EQE) of PeLEDs has recently surpassed 20%, various strategies are being pursued to increase EQE further and reduce the EQE gap compared to other LED technologies. A key point to further boost EQE of PeLEDs is linked to the high refractive index of the perovskite emissive layer, leading to optical losses of more than 70% of ...

Many high-resolution patterning techniques have been developed to realize nano- and microscale applications of electric devices, sensors, and transistors. However, conventional patterning methods based on photo or e-beam lithography are not employed to fabricate optical elements of high aspect ratio and a sub-100 nm scale due to the limit of resolution, high costs and low throughput. In this study, covalent bonding-assisted nanotransfer lithography (CBNL) was proposed to fabricate various structures of high resolution and high aspect ratio at low cost by a robust and fast chemical reaction. The proposed process is based on the formation of covalent bonds between silicon of adhesive layers on a substrate and oxygen of the deposited material on the polymer stamp. The covalent bond is strong enough to detach multiple layers from the stamp for a large area without defects. The obtained nanostructures can be used for direct application or as a hard mask for etching. Two nano-optical applications were demonstrated in this study, i.e., a meta-surface and a wire-grid polarizer. A perfect absorption meta-surface was generated by transferring subwavelength hole arrays onto a substrate without any post-processing procedures. In addition, a wire-grid polarizer with high aspect ratio (1 : 3) and 50 nm line width was prepared by the nano-transfer of materials, which were used as a hard mask for etching. Therefore, CBNL provides a means of achieving large-area nano-optical elements with a simple roll-to-plate process at low cost.