Scanning Tunneling Microscopy (STM) is a technique developed in the laboratories of IBM in Zurich by Gerd Binning and Heinrich Rohrer (Nobel Prize of Physics in 1986). This technique is based on a known physical phenomenon since the origins of quantum mechanics, the tunnel effect. A STM consists of two electrodes of reasonable conductivity of which one has the shape of a tipe and the other is the surface of the studied film. The tipe-sample distance is about a few angströms. If a biasing is applied between the tipe and surface, the electrons have a nonnull probability to pass from one electrode to the other and a tunnel current thus will be born. The principle of the experiment consists in moving the point above the film surface (using piezoelectric ceramics) by maintaining the tunnel current constant by a servo system. Thus the tipe-sample distance remains constant and the recording of vertical displacements of the tipe then reproduces accurately the topography of surface. If the tipe is sufficiently fine (few angströms), the relief observed can have the atomic resolution. The STM experiment can also work in spectroscopic (Scanning Tunneling Spectroscopy or STS) mode. In this case, the tipe is maintained fixed compared to the surface of the sample to a given position. The servo-control is opened and a V(t) voltage slope is applied between the tipe and the surface of the sample. For each applied voltage the tunnel current is measured and the study of the current-voltage characteristics give access the local electronic density of states on the surface.