Growth and characterization of magnetite-maghemite thin films by the dip coating method

Abstract

We present the process of growth and characterization of magnetite-maghemite thin films obtained by the dip coating method. The thin films were deposited on glass substrates, using a ferrofluid of nanostructured magnetite-maghemite particles as precursor solution. During the growth of the films the following parameters were controlled: number of dips of the substrates, dip velocity of the substrates and drying times. The films were characterized by Atomic Force Microscopy, Scanning Elelectron Microscopy, four-point method for resistance measurement, Room Temperature Mössbauer Spectroscopy and Hall effect. Mössbauer measurements showed the presence of a sextet attributed to maghemite (γ -Fe 2 O 3 ) and two doublets attributed to superparamagnetic magnetite (Fe 3 O 4 ), indicating a distribution of oxidation states of the iron as well as a particle size distribution of the magnetic phases in the films. Atomic force microscopy measurements showed that the films cover quasi uniformly the substrates, existing in them some pores with sub-micron size. Scanning Electron Microscopy measurements showed a uniform structure in the films, with spherical particles with size around 10 nm. Voltage versus current measurements showed an ohmic response of the films for currents between 0 and 100 nA. On the other hand, Hall effect measurements showed a nonlinear response of the Hall voltage with the magnetic flux density applied perpendicular to the plane of the films, however the response is fairly linear for magnetic flux densities between 0.15 and 0.35 T approximately. The results suggest that the films are promising for application as magnetic flux density sensors.

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“…Dip coating is the most utilized deposition method for both industrial and laboratory purposes. This is because of the technique's efficiency, low cost, and good coating quality [16]. The method involves the deposit of a liquid layer and the withdrawal of substrates from the coating medium [17].…”

“…After liquid film deposition, the required coating material must be dried to be obtained. While drying is typically carried out at room temp or temperatures as high as 250°C, this is not always the case [16]. To analyze the structure, interactions, as well as morphology of the planned bioactive coatings, analytical methods were applied.…”

“…The dip-coating is a humid method and has important advantages; among them are the simplicity and low cost of the implementation of the system for the growth of the sample. The thickness of the coating material may be regulated in this approach by choosing the appropriate number of dips of the substrate in the suitable solvent [16]. The IBAD (ion beam assisted deposition) technology was used to coat HA on the PEEK.…”