Epitaxial Fe3O4 Films Grown on R-Plane Sapphire by Pulsed Laser Deposition

Abstract

We have studied the influence of growth temperature and molecular oxygen pressure on the properties of thin (≤180 nm) epitaxial magnetite (Fe 3 O 4 ) (001) films grown by pulsed laser deposition on R-plane single-crystal sapphire (Al 2 O 3 ( 012)) with and without MgO seed layer. The electrical, morphological, and structural characteristics of the films have been investigated as functions of growth conditions. Fe 3 O 4 has been shown to have a stable growth plateau at pressures in the range (4-9) × 10 -5 Torr. The properties of the epitaxial Fe 3 O 4 films grown on a MgO seed layer (5 nm thick) approach those of magnetite films grown on single-crystal MgO substrates and are superior to those of films grown on pure R-plane sapphire. The best electrical characteristic of the films and the corresponding crystal structure can be obtained at elevated growth temperatures, whereas reduced growth temperatures minimize the roughness of their surface and maximize its homogeneity. These conditions can be reconciled by high-temperature high-vacuum annealing of magnetite films grown at reduced temperatures.

Room-Temperature Epitaxial Growth of Zn-Doped Iron Oxide Films on c-, a-, and r-Cut Sapphire Substrates

“…The tilt can be important; for example, the (100) MgO may epitaxially grow on (102) Al 2 O 3 with a tilt up to 5° or 6°, depending upon the growth temperature . From such results, it was concluded that the surface state of r-plane sapphire is an important factor leading to the tilted growth of the epilayer. − In our present case, it is not surprising that the epitaxial growth of ZFO on the r-plane Al 2 O 3 occurs at RT with a tilt of about 4.7°.…”

“…It must be noticed that in the case of the epitaxial growth of various oxide films on the r-cut sapphire substrate, the surface plane of the oxide film was tilted with respect to the (102) plane of sapphire. This phenomenon was observed for instance in the epitaxial growth of ZnO, CeO 2 , MgO, , or Fe 3 O 4 . The tilt can be important; for example, the (100) MgO may epitaxially grow on (102) Al 2 O 3 with a tilt up to 5° or 6°, depending upon the growth temperature .…”

“…This phenomenon was observed for instance in the epitaxial growth of ZnO, 61 CeO 2 , 62 MgO, 63,64 or Fe 3 O 4 . 65 The tilt can be important; for example, the (100) MgO may epitaxially grow on (102) Al 2 O 3 with a tilt up to 5°or 6°, depending upon the growth temperature. 66 From such results, it was concluded that the surface state of r-plane sapphire is an important factor leading to the tilted growth of the epilayer.…”