A sensitivity speck is a place in silver halide crystal where
latent image
{{citations needed, date=November 2015
A latent image is an invisible image produced by the exposure to light of a photosensitive material such as photographic film. When photographic film is developed, the area that was exposed darkens and for ...
is preferentially formed. This is very often the site of shallow electron traps, such as crystalline defect (particularly edge
dislocation
In materials science, a dislocation or Taylor's dislocation is a linear crystallographic defect or irregularity within a crystal structure that contains an abrupt change in the arrangement of atoms. The movement of dislocations allow atoms to s ...
) and
silver sulfide
Silver sulfide is an inorganic compound with the formula . A dense black solid, it is the only sulfide of silver. It is useful as a photosensitizer in photography. It constitutes the tarnish that forms over time on silverware and other silver o ...
specks created by sulfur sensitization process.
When a photon is absorbed by a silver halide crystal, a free-carrier (electron in the conduction band) is generated. This free-carrier can migrate through the
crystal lattice
In geometry and crystallography, a Bravais lattice, named after , is an infinite array of discrete points generated by a set of discrete translation operations described in three dimensional space by
: \mathbf = n_1 \mathbf_1 + n_2 \mathbf_2 + n ...
of
silver halide
A silver halide (or silver salt) is one of the chemical compounds that can form between the Chemical element, element silver (Ag) and one of the halogens. In particular, bromine (Br), chlorine (Cl), iodine (I) and fluorine (F) may each combine wi ...
, until captured by the shallow electron trap, where the electron is likely to reduce an interstitial silver ion to form an atomic silver. Subsequent exposure can grow the size of silver cluster through the same mechanism. This forms the
latent image
{{citations needed, date=November 2015
A latent image is an invisible image produced by the exposure to light of a photosensitive material such as photographic film. When photographic film is developed, the area that was exposed darkens and for ...
where the silver cluster becomes large enough to render the entire crystal developable in developer solution.
Science of photography
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