Large-Area Self-Assembly of Silica Microspheres/Nanospheres by Temperature-Assisted Dip-Coating

This work reports a temperature-assisted dip coating method for self-assembly of silica (SiO2) microspheres/nanospheres (SPs) as monolayers over large areas (similar to cm(2)). The area over which self-assembled monolayers (SAMs) are formed can be controlled by tuning the suspension temperature (T-s), which allows precise control over the meniscus shape. Furthermore, the formation of periodic stripes of SAMs, with excellent dimensional control (stripe width and stripe-to-stripe spacing), is demonstrated using a suitable set of dip-coating parameters. These findings establish the role of T-s, and other parameters such as withdrawal speed (V-w), withdrawal angle (theta(w)), and withdrawal step length (L-w). For T-s ranged between 25 and 80 degrees C, the morphological analysis of dip-coatings shows layered structures comprising of defective layers (25-60 degrees C), single layers (70 degrees C), and multilayers (>70 degrees C) owing to the variation of SP flux at the meniscus/substrate assembling interface. At Ts = 70 degrees C, there is an optimum V-w, approximately equal to the downshift speed of the meniscus (V-m = 1.3 mu m/s), which allows the SAM formation over areas (2.25 cm(2)) roughly 10 times larger than reported in the literature using nanospheres. Finally, the large-area SAM is used to demonstrate the enhanced performance of antireflective coatings for photovoltaic cells and to create metal nanomesh for Si nanowire synthesis.