A specimen structure with a gradual variation in composition, an Sb doped region in Si, has been investigated by scanning electron microscopy, operating with backscattered electrons and secondary electrons. Numerical simulations and experimental observations have been carried out in order to highlight the influence of the boundary conditions on the capability to detect the implanted region. Moreover, it will be shown that a proper choice of the microscope operating conditions may achieve either enhanced compositional contrast or an analytical condition for dopant profiling.