Copper(I) selenideCopper selenide is an inorganic binary compound between copper and selenium, with the chemical formula Cu2Se.PropertiesStoichiometric copper selenide is a zero-bandgap material with metal-like behavior. Copper-deficient Cu2−xSe is an intrinsic p-type semiconductor with direct and indirect bandgap energies in the range of 2.1–2.3 eV and 1.2–1.4 eV respectively. It is frequently grown as nanoparticles or other nanostructures.UsesCopper selenide is produced in situ to form a protective black coating on iron or steel parts in some cold-bluing processes. Bluing solutions that operate in this manner will typically be labeled as containing selenous acid or selenium dioxide. It has also been investigated for use in the treatment of colon cancer.Natural occurrencesCopper selenides are the most common selenium minerals. Cu2Se occurs as two polymorphs: berzelianite and bellidoite. There are more natural Cu selenides to date, including umangite, Cu3Se2 and athabascaite, Cu5Se4.