desublimate

Desublimate, or desublimation, is the phase transition in which a substance changes from a gas directly to a solid, bypassing the liquid phase. The term is often used interchangeably with deposition, especially in meteorology and materials science, where gas-to-solid growth is observed on surfaces.

Mechanism and conditions. Desublimation occurs when environmental conditions—primarily temperature and pressure—favor the formation of a solid from vapor rather than condensation into a liquid. In practice, this typically happens when a vapor is cooled below the substance’s freezing point (or when the equilibrium vapor pressure over the solid at that temperature is reached) so that molecules deposit as a solid onto surfaces or within a supersaturated gas. The rate depends on temperature, the presence of nucleation sites, surface properties, and the ambient gas pressure.

Natural occurrences. Frost forming on windows and vegetation is a common example, where water vapor desublimates as ice on cold surfaces. Deposition also explains the appearance of hoarfrost and other frost patterns in cold, humid environments. In planetary science, solids such as carbon dioxide or water ice can deposit from vapor onto surfaces in extremely cold conditions.

Industrial and scientific contexts. Desublimation is relevant in vacuum and cryogenic technologies, where control of deposition affects system cleanliness and film formation. In materials science and semiconductor processing, gas-to-solid deposition can contribute to thin-film growth and crystal formation under appropriate temperature and pressure conditions.

Distinctions. Desublimation is the direct gas-to-solid transition, distinct from condensation (gas to liquid) and sublimation (solid to gas). In many contexts, the term deposition is used as a synonym for desublimation.