Origin of Different Growth Modes for Epitaxial Manganite Films

Abstract

The microstructures of the Bi0.4Ca0.6MnO3 (BCMO) and La0.67Ca0.33MnO3 (LCMO) epitaxial films are investigated by transmission electron microscopy in detail. BCMO epitaxial films (~ 10 and ~ 40 nm) exhibit an island growth mode whereas the LCMO films (~ 6 and ~ 30 nm) follow a layer by layer growth mode. Combined with the critical thickness models for the expected onset of the misfit dislocations in epitaxial films, an atomic collapse model is introduced to explain their mechanism of formation in manganite films. At the beginning of deposition, the strain caused by the lattice mismatch between the epitaxial film and substrate can be accommodated by elastic deformation. With the increase of film thickness, the strain becomes larger and larger. When the film thickness reaches the critical thickness, the strain can only be relaxed by the formation of misfit dislocations. Meanwhile, the atomic configuration of the epitaxial film will reorganize and some atoms begin to collapse, thus an island morphology will be formed. Once the collapse morphology is formed, maintenance of this wave‐like morphology depends on atomic diffusion length of the deposited atoms. If the diffusion length of the deposited atoms is long, the island morphology will not be maintained. If the diffusion length of the deposited atoms is short, the island morphology will keep until the epitaxial film is thick enough. The results could shed light on the growth modes for other perovskite epitaxial films.

Exchange-bias field induced by surface inhomogeneities in ferromagnetic/charge-ordered bilayer structure

“…Moreover, we can see the presence of large particulates (near top right-hand corner) in Fig. 2(a), suggesting an atomic collapse model [14]. Such surface deformities (large particulates) are typically related with non-stoichiometric deposition of island growth thin film [15,16].…”

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“…4 It has been widely accepted that compressive stress on bulk perovskite manganite materials can increase magnetization, Curie temperature (T c ), peak resistivity temperature (T p ), and decrease resistivity by reducing Jahn-Teller distortion, namely decreasing Mn-O bond length and increasing Mn-O-Mn bond angle. [5][6][7][8] The stress-induced effect on the properties of LSMO films deposited on crystal substrate LaAlO 3 , 9,10 SrTiO 3 , 11,12 (1Àx)Pb(Mg 1/3 Nb 2/3 )O 3 -xPbTiO 3 , 13 etc., has also been widely studied, because the stress state can be relatively precisely confirmed by lattice mismatch. However, few studies about stress-induced effect has been conducted on polycrystalline LSMO film deposited on Si substrate prepared by sol-gel method, because it is difficult to tailor stress state.…”

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“…For preparing a magneto‐optical film with high quality, the deposit method and the substrate are all important. At present, several film growth techniques such as pulsed laser deposition technology, liquid phase epitaxy (LPE) method, sol–gel method, metal‐organic chemical vapor deposition (MOCVD) method, and the radio‐frequency (RF) magnetron sputtering technique have been applied. Among these methods, frequently used pulsed laser deposition technology cannot be applied for mass production because the thin film deposition area is small, the equipment is relatively expensive, and the high‐energy laser is unsafe for the user.…”