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5. CONCLUSIONS chemical composition and crystalline structure. Large lattice mismatch of the film-substrate system forced strain on deposited films. As X-ray diffraction ex- periments have shown, depending on the thickness of the film the level of strain is different but smaller for thicker films or for films deposited in pure argon plasma atmosphere. The atmospheric condition in deposition chamber may have also in- fluenced the surface of silicon substrate which is covered with a layer of oxidized silicon whose structure was not detectable in the course of investigation. The annealing procedure after deposition was necessary to stabilize the per- ovskite structure. Without that step, films did not present long-range crystal order in diffraction experiments as well as no critical temperature in Raman spec- troscopy experiments. Presence of oxygen as the second component of plasma in the sputtering deposition chamber (AO films) resulted in formation of highly tex- tured films. The texture was not formed in films deposited in pure argon plasma. Even though further high temperature and high-pressure oxygen annealing were applied, the later films did not form any crystalline texture. The films sputtered by argon plasma (A films) have been found to have almost twice the thickness as respective AO films despite the same deposition time. What is more the calcu- lated pseudocubic parameter is larger, the lattice mismatch lower and the atomic ratio of Sm:Ni atoms present in the films is much lower for A films than for AO films. Experimental results have confirmed that for magnetron sputtered SNO films deposited on silicon substrate annealing is the necessary step to obtain the proper crystalline structure which exhibits metal-insulator transition. The as-deposited films do not present the signature of the perovskite structure neither in X-ray diffraction patterns nor in Raman spectra. It is however interesting that X-ray photoelectron spectra of not annealed film do exhibit temperature dependence. The most visible change occurs between 103 K and room temperature - the sep- aration of 2p3/2 constituent lines decreases and there is a shift of spectral weight from lower to higher binding energy. However, for the as-deposited film, the energy difference decreases for only about 0.2 eV. Whereas for films that underwent the annealing procedure the change was as large as about 1.5 eV for S-12AOw thin film or 0.7 eV for much thicker S-36AOw film. The annealing operation was done in order to stabilize the perovskite struc- ture and nickel ion in 3+ chemical state. High oxygen pressure and temperature were necessary to ’pump’ oxygen atoms deep into the film’s structure. Extensive annealing time favoured film crystallization and formation of long-range order. 118PDF Image | Investigation of metal-insulator transition in magnetron sputtered samarium nickelate thin films
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