A low-cost and easy-of-developing system that allows to cover large-areas by highly crystalline monolayers consisting in nano- and micro-metric spheres.
In this work published in December 2017 in ACS Applied Materials and Interfaces, we present a home-made dip-coating system (see 3D schematic illustration above) allowing the self-assembly of micro- and nano-spheres over large areas (from few mm2 up to tens of cm2). The main novelty presented in this work is related to the investigation of the role of the spheres solution temperature on the assembling mechanism.
The synchronization of the solvent evaporation ratio and the withdrawal speed of the receiver substrate, was demonstrated to be crucial for the formation of self-assembled monolayers consisting of micro- and nano-spheres over large areas.
We have observed that the reduction of the spheres size makes the self-assembly mechanism more difficult mainly due to the formation of defects and multi-layers. The control over the system operational parameters (solution temperature, withdrawal speed, withdrawal angle, inmersion time, etc.) has allowed us to cover tens of cm2 with silica spheres with diameters down to 100 nm. This interesting achievement can have an important impact in a wide range of applications.
In this work, we have used the large-area coatings of silica spheres for two applications, including anti-reflective coatings for solar cells, and micro-/nano-mask for synthesis of semiconductor nanowires through top-down approaches.
This work shows the successful dip-coating of a solar cell surface by silica spheres, forming an anti-reflective coating, and exhibiting a relevant improvement of the photovoltaic performance. The excellent properties of silica as anti-reflecting material have been taken as an advantage, coating the surface of an amorphous-Si solar cell by a self-assembled monolayer of silica spheres, observing an important improvement of the solar cell efficiency.
Moreover, the dip-coating method was demonstrated to be useful for depositing nanoporous metallic layers that have been used to synthesize Si nanowires through a metal-assisted chemical etching (MACE) method.