The substrate comprises a first silicon layer, a target layer made from silicon-germanium alloy-base material forming a three-dimensional pattern with first and second securing areas and at least one connecting area. The first silicon layer is tensile stressed and/or the target layer contains carbon atoms. The first silicon layer is eliminated in the connecting area. The target layer of the connecting area is thermally oxidized so as to form the nanowire. The lattice parameter of the first silicon layer is identical to the lattice parameter of the material constituting the suspended beam, after said first silicon layer has been eliminated.