  We have studied the evolution of the structural modulation in epitaxial,
c-axis oriented, Bi2Sr2-xLaxCuO6+d thin films when varying the La content x and
for a given x as a function of oxygen content. A series of thin films with
0<x<0.8 have been prepared in-situ by rf magnetron sputtering and characterized
by R(T) measurements and RBS, TEM and X-Ray diffraction techniques. The oxygen
content of each individual film was varied by thermal annealing across the
phase diagram. The evolution of the structural modulation has been thoroughly
studied by X-Ray diffraction in determining the variation of the amplitude of
satellite reflections in special 2 axes 2theta /theta-theta scans (reciprocal
space scans). It is shown that the amplitude of the modulation along the c-axis
decreases strongly when x increases from 0 to 0.2. It is demonstrated that this
variation is essentially governed by La content x and that changing the oxygen
content by thermal treatments has a much lower influence, even becoming
negligible for x>0.2. Such study is important to understand the electronical
properties of Bi2Sr2-xLaxCuO6+d thin films.
