Growth of Atomically Smooth Epitaxial Nickel Ferrite Films by Direct Liquid Injection CVD

Abstract

Magnetoelectric heterostructures are being actively investigated for utilization in next generation microwave devices such as tunable filters and phase shifters. For efficient microwave absorption and magnetoelectric coupling, relatively thick (>1 mm) epitaxial spinel ferrite films with smooth topographies are required for the magnetic/ferroelectric heterostructures. Towards this goal, direct liquid injection (DLI)-CVD has been utilized for epitaxial growth of nickel ferrite (NiFe 2 O 4 ) films on MgAl 2 O 4 (100) and MgO (100) substrates with high deposition rates. Anhydrous Ni(acac) 2 and Fe(acac) 3 (acac ¼ acetylacetonate) are used as precursor sources dissolved in N,N-dimethyl formamide for the DLI vaporizer system. The influence of deposition temperature on the film properties has been investigated using optimized process conditions for flow of the injected precursors and oxygen. Epitaxial nickel ferrite films of stoichiometric composition are obtained in the temperature range 500-800 8C on both substrates with growth rates in the range 0.6-1.1 mm h À1. Because of changes in the surface diffusion behavior, the film morphology is found to be dependent on the deposition temperature with atomically smooth films being obtained for deposition in the temperature range 600-700 8C. Magnetic measurements reveal an increase in the saturation magnetization for the films with increasing growth temperature, which correlates well with the trend for improved epitaxial growth as indicated by X-ray and Raman spectroscopy measurements. Nickel ferrite films deposited on MgAl 2 O 4 (100) at 800 8C exhibit saturation magnetization very close to the bulk value of 300 emu cm À3.

Electrostatic tuning of ferromagnetic resonance and magnetoelectric interactions in ferrite-piezoelectric heterostructures grown by chemical vapor deposition

“…Unlike NFO films grown on MgAl 2 O 4 and MgO substrates that are atomically smooth (rms < 0.5 nm) even for thickness >1 lm, 16 the roughness increases with increasing film thickness on PZN-PT and PMN-PT substrates, with roughness in the range of 20-30 nm for the films studied. HRTEM study confirmed epitaxial growth of the films on both substrates, but also indicated the presence of dislocations and anti-phase boundaries in the films, which may contribute to increased FMR line-width.…”

“…Anhydrous Ni(acac) 2 and Fe(acac) 3 (acac ¼ acetylacetonate) in the molar ratio of 1:2 were used as precursor sources dissolved in N,N-dimethylformamide for the DLI vaporizer system using argon as the carrier gas. 16 The vaporized mixture was combined with a flow of preheated oxygen gas prior to introduction into the CVD reactor. Films were deposited at substrate temperatures of 600 and 700 C with thicknesses in the range of 1.5-2.0 lm.…”

Structural features of epitaxial NiFe2O4 thin films grown on different substrates by direct liquid injection chemical vapor deposition

“…The NFO thin films are grown by the DLI-CVD process [12]. The precursor solution is prepared by mixing anhydrous Ni(acac) 2 and Fe(acac) 3 (acac is an abbreviation for acetylacetonate) in molar ratio of 1:2 and dissolving them in N,N-dimethylformamide (DMF).…”

“…The major problems are limited volatility, thermal stability and uniform delivery of metal precursors during CVD growth [9][10][11]. Recently, we have developed a direct liquid injection chemical vapor deposition (DLI-CVD) process to grow NFO thin films where efficient delivery of metal acetylacetonate at relatively low temperatures allows excellent control over stoichiometry and surface morphology [12].…”

Probing optical band gaps at the nanoscale in NiFe2O4 and CoFe2O4 epitaxial films by high resolution electron energy loss spectroscopy

“…Innovation in large area epitaxial thin film growth technology, particularly using direct liquid injection chemical vapor deposition (DLI-CVD), has made it possible to grow such materials with stoichiometric composition and physical properties close to the bulk crystals. 13 The stable structure is inverse spinel (space group 216, F-43 m), and because of the large open structure, the cations have freedom to arrange themselves in different configurations under various growth conditions. Antiphase domain boundaries (APBs) are commonly observed in this system, where A site cation occupancy alternating from one region to another with a translation vector of 1 = 4 h110i.…”