  We demonstrate that it is possible to distinguish two conductance switching
mechanisms in silver sulfide devices at room temperature. Experiments were
performed using a Ag$_2$S thin film deposited on a wide Ag bottom electrode,
which was contacted by the Pt tip of a scanning tunneling microscope. By
applying a positive voltage on the silver electrode the conductance is seen to
switch to a state having three orders of magnitude higher conductance, which is
related to the formation of a conductive path inside the Ag$_2$S thin film. We
argue this to be composed of a metallic silver nanowire accompanied by a
modification of the surrounding lattice structure. Metallic silver nanowires
decaying after applying a negative voltage allow observing conductance steps in
the breaking traces characteristic for atomic-scale contacts, while the lattice
structure deformation is revealed by gradual and continuously decreasing
conductance traces.
