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 (∼cm²). 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 cm²) 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.