Oxidation mode on charge transfer mechanism in formation of Mn-Co-Ni-O spinel films by RF sputtering

摘要

Series of negative temperature coefficient Mn-Co-Ni-O spinel oxide thin films were successfully prepared on thermally oxidized SiO_2/Si (100) substrates by RF sputtering a Mn-Co-Ni metal alloy target with the sputtering gas of different Ar:O_2 partial pressure ratios. The crystallinity of the spinel films was improved as O_2 contents increased. The film conductivity was reduced. The minute variation in an optical absorption peak at around 1.7 eV by spectroscopic ellipsometry may be ascribed to the different charge transfer mechanism between Co~(2+) in tetragonal and Co~(3+) in octahedral or between O~(2−) and Mn~(4+) in octahedral sites. Raman and XPS results provided further evidences.