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1.4 Influence of the reduced dimension on the physical properties more oxygen and less oxygen vacancies which increases bandwidth anch charge carrier number and therefore conductivity. The R-T measurements were done in vacuum and grazing incidence X-ray diifraction (GIXRD) after confirmed that there was a phase change from LNO to LNO(2.5) due to oxygen loss. Polycrys- talline film on Si were losing oxygen much faster than the epitaxial films. And films on STO were losing oxygen slower than on LAO probably due to extra vertical pressure from tensile strain which forbid a quick escape of oxygen (55). SNO/LAO films deposited by RF magnetron sputtering and on the same sub- strate not only experience about 15 % compressive strain but also exhibit different out-of plane unit cell parameters (50). The parameters increase with decreasing deposition pressure which is said to be an effect of varying stoichiometry. The lower pressure results in reduction of oxygen content and lower oxidation state of nickel ions which instead of 3+ are rather closer to 2+ and therefore having larger ionic radius and bigger unit cell. The higher pressure should therefore be necessary to stabilize Ni3+ state. The 250 mTorr film grow ”cube-on-cube”, with (113) pseudocubic reflection of SNO aligned with LAO(111) reflection as seen on the φ scans. The film is also very smooth, with a low RMS roughness of about 5 ̊A. 1.4.2 Electrical resistivity For SNO films annealed in different temperatures and pressures it was found that the higher the oxygen pressure the higher the conductivity (61). High temperature and low pressure inhibit appearance of metal-insulator transition. For 770 K and air-annealed films are strongly resistive, 770 K and 10 bar O2 are semiconducting while 770 K and 100 bar O2 have a reversible transition with TMI = 400K like in bulk. The authors indicated that such a temperature for a film is characteristic to unstrained and polycrystalline films. The stoichiometry-deviated films undergo a non-reversible MI transition which the authors attributed to unstable phases and loss of oxygen during cycling. Low temperature and high pressure result in a hysteretic MI transition which is not repeatable in subsequent cycles. It has been shown that the deposition pres- sure influences greatly the electrical behaviour of SNO films (50). The insulating state is favoured with the low- and high-pressure deposited films, while metallic was seen for moderate pressures. The low pressure sample exhibits a transition in R(T) curve with a shift/increase in resistivity unrecoverable when returning to lower temperature, presumably due to permanent oxygen loss. The metallic phase 27PDF Image | Investigation of metal-insulator transition in magnetron sputtered samarium nickelate thin films
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