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Coatings

Spin coating makes epitaxial films

Simple, low-cost method provides alternative to specialized procedures for growing orderly films of electronic materials

by Mitch Jacoby
April 20, 2019 | APPEARED IN VOLUME 97, ISSUE 16

 

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Credit: Science (top); Jay Switzer/MUST (bottom)
These crystalline films (top, cesium lead bromide on strontium titanate, and lead iodide on gold) were grown via spin-coating.

An inexpensive liquid-phase deposition method can form molecularly ordered films of various materials, a feat usually carried out commercially via costly vapor deposition techniques (Science 2019, DOI: 10.1126/science.aaw6184). To make sophisticated electronic devices composed of multiple thin layers of semiconductors, manufacturers generally rely on techniques such as molecular beam epitaxy. That method ensures that the lattices of the substrate and deposited film align in an orderly fashion, a key to controlling electronic, optoelectronic, and other properties. Epitaxial deposition, however, usually requires specialized vacuum equipment and high temperatures. Now, Meagan V. Kelso, Jay A. Switzer, and coworkers at Missouri University of Science and Technology have shown that ordered films of cesium lead bromide, lead iodide, and other electronic-device materials can be formed by spin coating solutions of precursors onto crystalline substrates. Spin coating is a fast, low-cost method commonly used to “paint” surfaces with amorphous layers, such as polymer masks in lithography and perovskite solar-cell films. The team explains that by controlling the viscosity of the solution, the rotation rate, and other parameters, the deposited liquid can be coaxed into forming a micrometer-thin supersaturated layer at the substrate interface. As spinning continues, the solvent evaporates, causing crystals to nucleate in that layer and grow into ordered films.

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