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 (SiO 2 ) microspheres/nanospheres (SPs) as monolayers over large areas (∼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 (θ w ), and withdrawal step length ( L w ). For T s ranged between 25 and 80 °C, the morphological analysis of dip-coatings shows layered structures comprising of defective layers (25–60 °C), single layers (70 °C), and multilayers (>70 °C) owing to the variation of SP flux at the meniscus/substrate assembling interface. At T s = 70 °C, there is an optimum V w, approximately equal to the downshift speed of the meniscus ( V m = 1.3 μm/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.