Electric Conductivity and Gas-Sensing Properties of Nickel Ferrite Thin Films Formed by Ion-Beam Sputtering Deposition

Abstract

Ferrites with composition of NiMnxFe1-xO4, (with x = 0 ÷ 1.0) have been synthesized by self-propagating high-temperature synthesis (SHS). The particle size of the synthesized ferrite powder was about 10 nm. Additional heat treatment at 1270 K during 50 min allowed us to obtained product with the single phase composition NiFe2O4. We found out that the increasing of the manganese content (x) increased the lattice constant of the ferrites from 0.833896 nm (x = 0) up to 0.836369 nm (x = 1). The synthesized powder contains two types of ferrite particles that are varied in size and shape. The magnetic properties significantly depend on the microstructure and chemical composition of synthesized ferrites. It has been found that the coercive force Hc increased from 1.75 (x = 0.2) to 2.85 (x = 1). By using of IBSD technology thin film of NiFe2O4 was sputtered on the Si (100) substrate. All sputtered films were X-ray transparent. The structure of ferrite films consisted of agglomerate less than 35 nm. The thickness of the sputtered film was about 600 nm. Additional heat treatment at 770 K during 90 min resulted to homogeneity of the film microstructure. The temperature range 400-750 K corresponds to working temperature range of gas-sensing devices. The ferrite compounds were studied by TOF-SIMS (Time-of-Flight Secondary-Ion-Mass-Spectrometry) for all depth of film. The resistivity R of synthesized film was 39 kΩ. Measurement of gas-sensing sensitivity RCH4/Rair for gas (2%v. CH4) – air mixture showed increase of R up to 12% at the present of methane at 403 K. For further research we plan to replace iron to manganese ions in chemical compounds of ferrite.