Two-dimensional self-assemblies of silica nanoparticles formed using the "bubble deposition technique"

Solvent-controlled spin-coating method for large-scale area deposition of two-dimensional silica nanosphere assembled layers

In this article, we show that introducing a N,N-dimethyl-formamide (DMF) solvent for silica nanosphere (SNS) monolayer spin-coating can offer a low-cost and simple spin-coating approach for SNS monolayer deposition even on large-area silicon surfaces. From our method, more than 95% monolayer coverage for a 2 in round Si surface was achieved, which is one of the highest reported coverage by a spin-coating method. We prove that DMF offers highly enhanced wettability and slow solvent evaporation rate compared to a conventional solvent, water, in addition to excellent SNS dispersibility in solution preventing SNS cluster deposition on the surface and consequently produces a close-packed SNS monolayer with good uniformity over the surface. In addition, the benefits of DMF are retained as the deposition area increases indicating its high tolerance to spin-coating area. Better than 90% SNS monolayer coverage on a 4 in Si substrate was achieved with the DMF spin-coating method. Moreover, DMF has the advantage that SNS spin-coating can be done under common ambient laboratory conditions with 100% pure DMF unlike previous approaches which require humidity and temperature controls or additional surfactant additions to the solution.

Role of substrate wettability in the "bubble deposition method" applied to the CeVO4 nanowire films

Homogeneous two-dimensional structures of CeVO(4) nanowires (NWs) deposited on silicon substrates are obtained by means of the bubble deposition method (BDM). Surface wettability (i.e., surface energy) and film ripening (i.e., film thickness) are two major parameters in nanoparticle confinement and deposition. As the presence of surfactant could be detrimental to applications, a washing treatment is developed without CeVO(4) chemical changes or NW film modifications. Careful investigations of the film topography are carried out by atomic force microscopy (AFM), and X-ray photoelectron spectroscopy (XPS) is used to check the chemical composition of the film at different stages. Finally, samples made by BDM are compared to those made by dip-coating method, demonstrating the higher efficiency of the BDM in providing large areas of well-organized and dense CeVO(4) monolayer.