Method for forming a porous thin film

On a substrate, forming a metal portion of a first metallic component, the composite thin film and the metal compound portion made of a compound of different second metal component is mixed dispersed each other with the first metal component, then the removing the metal components of the composite thin film, or on a substrate, a first metal part made of a first metal component, a second comprising a second metal different components from the first metal component metal parts and are mixed and dispersed with each other composite thin film was formed comprising, then a method for forming a porous thin film and removing only the first or the second one of the metal parts of the composite thin film provide.