It is not a counter myth. It is a scientific fact that pure silver films will not readily form silver oxide (Ag2O) under ambient conditions. I studied the surface chemistry and electronic structure of silver films extensively using a variety of surface sensitive spectroscopies. These experiments were all done in an ultra high vacuum system on pure clean silver films with controlled exposure to a variety of gases. The silver films were vacuum deposited and alternately argon-ion etched followed with high temperature annealing until a 100% pure silver surface was obtained. The silver films were then exposed to controlled amounts of O2 gas (pure O2 and O2 + water vapor) at room temperature and analyzed with Photoelectron Spectroscopy. No evidence of Ag2O formation was observed even after hours of exposure. However, low concentrations of physisorbed O2 were observed. For dissociative chemisorption to occur, it required heating the silver film to several hundred degrees C, in which case the formation of Ag2O was observed. In comparison, similarly prepared metal films of Cu, Al, and Ni all formed an oxide layer within seconds of exposure to O2 gas at room temperature. Exposure of the silver films to controlled amounts of hydrogen sulfide (H2S) gas (pure H2S and H2S + water vapor) resulted in a Ag2S layer within minutes of exposure at room temperature. The presence of water vapor increases the reaction rate considerably.
I would like to clarify that silver in it bulk form is not readily reactive with O2 but in its atomic form it is very reactive. For example in silver nanoparticles, a large portion of the silver atoms at the surface of the nanoparticle are not fully coordinated (they have atomic-like properties) and are very reactive. This is the reason that silver nanoparticles are widely used as catalysts. It is possible that a poor silver film with a lot of defects at the surface could have silver atoms that are not fully coordinated and could react with O2 at these defect sites.
The statement regarding Ag2S being a semiconductor is only to dispel the myth that the surface remains conductive after the formation of the Ag2S layer. This is obvious when analyzing the silver surface after exposure to H2S gas and observing the formation of a layer of Ag2S on the silver surface. Analysis of the Ag2S layer with Photoelectron Spectroscopy and Low Energy Inverse Photoemission Spectroscopy, illustrates that the surface electronic properties change from a conductor to a semiconductor and the surface becomes less conductive.
