Convective deposition of a monolayer of microspheres by drawing a meniscus of a suspension across a substrate is used to fabricate microlens arrays to enhance the photon extraction efficiency of light emitting diodes (LEDs). The self-assembly of a colloidal crystal within the blade-drawn thin film is dominated by capillary forces and the thickness of this crystal depends on many parameters, including the deposition rate and particle size. This study investigates these and other parameters such as angle and hydrophobicity of the deposition blade that have not previously been considered. Using a confocal laser scanning microscope, the local and long-range order of the deposited particles are evaluated by the radial distribution function, and the fraction of the number of nearest neighbors and local bond order, demonstrating the dependence of the microstructure on the deposition parameters. Our results suggest previous descriptions of the critical deposition parameters are inadequate for understanding how various processing conditions influence deposition. For instance, increasing the deposition blade angle from 20 degrees up to 90 degrees requires an increase in deposition rate to achieve a monolayer deposition. The microlens arrays were fabricated on LEDs where polystyrene and silica are coated in consecutive depositions. Heat is used to sacrifice the polystyrene layers to result in an ordered array of partially buried silica microspheres that act as lenses to scatter light from the device. Enhancement in light extraction efficiency of 2.66 times was demonstrated for InGaN-based light emitting diodes employing micron scale microlens arrays with 1 um diameter silica microspheres.

TiO2 with arbitrarily tunable facets is directly grown onto the conductive substrate. H+ promotes the growth of the high energy {001} facet rather than F−.

Improvement of light extraction efficiency of InGaN quantum wells light emitting diodes ͑LEDs͒ using SiO 2 /polystyrene microspheres was demonstrated experimentally. The utilization of SiO 2 /polystyrene microlens arrays on InGaN quantum wells LEDs, deposited via rapid convective deposition, allows the increase of the effective photon escape cone and reduction in the Fresnel reflection. Improvement of output power by 219% for InGaN quantum wells LEDs emitting at peak wavelength of 480 nm with SiO 2 /polystyrene microspheres microlens arrays was demonstrated.

All-inorganic halide perovskites without volatile components have great potential for long term thermal stability. However, the phase stability of all-inorganic perovskites is sensitive to moisture and has been seldom studied. In this work, the phase stability of α-CsPbI2Br was studied in different relative humidity conditions. The moisture resistance of α-CsPbI2Br can be significantly enhanced by using a polymer or organic molecule capping layer including Spiro-MeOTAD. Although an all-inorganic CsPbI2Br perovskite based device using the typical Li salt doped Spiro-MeOTAD layer could offer an efficiency up to 12.6%, it exhibited even worse moisture resistance than a bare perovskite film under the same ambient conditions. This unusual phenomenon is ascribed to the hygroscopic properties of Li-TFSI inducing moisture sensitive phase degradation. Therefore, it is desirable to decrease the amount of, or avoid the Li salt, as a dopant for stable all-inorganic perovskite solar cells with balanced stability and high performance.

Improvement of light extraction efficiency of InGaN light emitting diodes (LEDs) using polydimethylsiloxane (PDMS) concave microstructures arrays was demonstrated. The size effect of the concave microstructures on the light extraction efficiency of III-Nitride LEDs was studied. Depending on the size of the concave microstructures, ray tracing simulations show that the use of PDMS concave microstructures arrays can lead to increase in light extraction efficiency of InGaN LEDs by 1.5 to 2.0 times. Experiments utilizing 2.0 micron thick PDMS with 1.0 micron diameter of the PDMS concave microstructures arrays demonstrated 1.70 times improvement in light extraction efficiency, which is consistent with improvement of 1.77 times predicted from simulation. The enhancement in light extraction efficiency is attributed to increase in effective photon escape cone due to PDMS concave microstructures arrays.

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We investigate the coupling between the suspension properties and the deposition process during convective deposition of aqueous binary suspensions of 1 microm silica microspheres and 100 nm polystyrene (PS) nanoparticles. The structures formed from this rapid and scalable process have use in a variety of optical, chemical, and biochemical sensing applications. At conditions that produce a well-ordered microsphere monolayer at a silica volume fraction of 20% in the absence of nanoparticles, we examine the effect of varying the concentration of nanoparticles from 0% to 16% on the quality of the microsphere deposition and the exposure of the microspheres within the PS layer. At low concentrations of nanoparticles, the deposition results in an instability that forms stripes parallel to the receding contact line. Optimum deposition occurs between 6% and 8% PS and forms a monolayer having the same high degree of uniformity as the monodisperse suspension is fabricated. For higher concentrations, the deposition is increasingly less uniform as a result of nanoparticle depletion destabilizing the microspheres. The degree to which each microsphere is buried by the nanoparticles in the deposited thin film increases with nanoparticle concentration. This variation in coverage also suggests interplay between deposition and nanoparticle engineered properties of the suspension that influence the deposited morphology.

Immunoaffinity microfluidic devices have recently become a popular choice to isolate specific cells for many applications. To increase cell capture efficiency, several groups have employed capture beds with nanotopography. However, no systematic study has been performed to quantitatively correlate surface nanopatterns with immunoaffinity cell immobilization. In this work, we controlled substrate topography by depositing close-packed arrays of silica nanobeads with uniform diameters ranging from 100 to 1150 nm onto flat glass. These surfaces were functionalized with a specific antibody and assembled as the base in microfluidic channels, which were then used to capture CD4+ T cells under continuous flow. It is observed that capture efficiency generally increases with nanoparticle size under low flow rate. At higher flow rates, cell capture efficiency becomes increasingly complex; it initially increases with the bead size then gradually decreases. Surprisingly, capture yield plummets atop depositions of some particle diameters. These dips likely stem from dynamic interactions between nanostructures on the substrate and cell membrane as indicated by roughness-insensitive cell capture after glutaraldehyde fixing. This systematic study of surface nanotopography and cell capture efficiency will help optimize the physical properties of microfluidic capture beds for cell isolation from biological fluids.