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Epitaxial films by spin coating
A simple way to apply a uniform film to a surface is to apply a spin coating. The substrate rotates at high speed and a droplet of solution containing the coating is added in the center, spreads and evaporates. This method is used to make polycrystalline inorganic coatings and amorphous films, such as polymers used in lithography. Kelso et al. performed a spin coating with monocrystalline substrates, carefully controlling the thickness of the spreading solution according to its viscosity and rotational speed. In this way, they obtained epitaxial growth – in which the crystallites are oriented by the substrate – for perovskites, zinc oxide and sodium chloride.
Science, this number p. 166
Abstract
Spin-coated films, such as photoresist resins for lithography or perovskite films for solar cells, are either amorphous or polycrystalline. We show that epitaxial films of inorganic materials such as lead bromide and cesium (CsPbBr3), lead iodide (II) (PbI2), zinc oxide (ZnO) and sodium chloride (NaCl) can be deposited on a variety of monocrystalline or monocrystalline substrates by simply spin coating solutions of the material or precursors. The off-plane and in-plane orientations of rotor coated films are determined by the substrate. The thin stagnant layer of supersaturated solution produced during spin coating promotes heterogeneous nucleation of the material on the monocrystalline substrate relative to homogeneous nucleation in the bulk solution, and superimposed layers of anions can reduce activation energy for nucleation at the surface. The method can be used to produce functional materials such as inorganic semiconductors or to deposit water-soluble materials such as NaCl that can serve as growth matrices.
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