Lattice disorder and impurity induced variation of electrical transport properties of the Heavy Fermion systems CeCu2Si2 and CeCu6

X-ray diffraction experiments have been performed on mono- and submonolayers of CF₃Cl physisorbed on the (001) surfaces of exfoliated graphite. Five quasi-twodimensional solid phases including the commensurate 2×2 phase, an electrically ordered phase and a disordered incommensurate phase have been observed. A phase diagram is proposed and the various phase transitions are discussed.