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Thermal annealing is a controlled heat treatment in which a material is held at an elevated temperature, normally below its melting point, for a defined time and then cooled, so that its microstructure relaxes towards a state of lower free energy. In cold-worked metals and welded joints it relieves residual stress and homogenises segregation, and further heating drives recovery, recrystallisation and grain growth ^[1]. In thin films and semiconductors the same step lowers defect densities and restores crystalline order, with rapid thermal annealing chosen when a short high-temperature excursion is needed to limit unwanted diffusion ^[2]. Annealing is also applied to solution-deposited oxides and halides, where it converts an as-deposited amorphous or poorly ordered layer into the crystalline phase that carries the target property ^[3], and to polymers, where it raises chain orientation and the degree of crystallinity ^[4]. Typical conditions span roughly 100-1500 °C for seconds to several hours, in air, inert or reducing gas, or vacuum; the outcome depends on temperature, time and heating rate, and also on the earlier thermal and mechanical treatment of the sample ^[5]. Because grain growth is thermally activated and largely irreversible, excessive annealing coarsens the microstructure and lowers strength, so the temperature-time window is usually chosen as a compromise between defect removal and grain coarsening ^[1].