Laser ablation in the growth of thin films of complex materials such as MxMo6S8 cluster compounds: The case of CuxMo6S8

We present here some new developments about deposition of complex materials thin films by pulsed laser deposition. The chosen example is a Chevrel pha se. of composition CuxMo6S8 (2 less than or equal to x less than or equal t o 4). The CuxMo6S8 has been in situ deposited, i.e. without any post-anneal ing: using an excimer laser (XeCl), under vacuum or under a low pressure of argon. For the highest deposition temperatures (typically above 820 degree s C) the films synthesized under secondary vacuum (P similar to 10(-6) mbar ) present an epitaxial growth on single crystal substrates : their crystall ine axes are aligned with those of the substrates in the plane of the sampl e as well as along the growth direction. as evidenced by x-ray diffraction experiments performed in theta-2 theta and phi-scan modes. On R-plane sapph ire the films are (100) oriented whereas on cubic substrates such as (100)M gO or (100) Y : ZrO2 they present a (120) orientation. Pulsed laser deposition which has been widely developed in the case of epit axial growth of oxides has allowed to control for the first time the epitax ial growth of CuxMo6S8 films whereas only textured films of this type of co mpound had been obtained by the other deposition methods, like sputtering o r evaporation, used in previous studies. The various microstructures available via the control of the orientation in fluence the behaviour of the critical current densities under applied magne tic field but the critical temperature and width of the superconducting tra nsition recorded on the different films depend only on the copper content, in agreement with measurements performed on bulk materials, but are indepen dent of the orientation characteristics of the films.