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How can vapour condensation produce an amorphous thin film?

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Vapour condensation allows for the creation of amorphous thin films by bypassing the liquid phase entirely, enabling the construction of a solid in an atom-by-atom fashion.1

In this process, a vapour stream of the desired material is generated within a vacuum chamber—often through thermal evaporation, the use of an electron beam, or the plasma-induced decomposition of molecular species like silane. This vapour is directed toward a cold substrate, where the atoms condense upon impact.1

To successfully form an amorphous structure rather than a crystalline one, the process typically requires specific conditions, most notably a high rate of deposition combined with a low substrate temperature. By depositing atoms rapidly onto a cold surface, the material is effectively quenched, preventing the atoms from arranging into the ordered lattice characteristic of a crystal. This technique is essential for preparing amorphous forms of materials that cannot be easily produced via melt quenching, such as pure silicon, germanium, water, and certain elemental metallic glasses.12