A Three Component Self‐Assembled Epitaxial Nanocomposite Thin Film

Abstract

3091wileyonlinelibrary.com magnetic, ferroelectric, piezoelectric, and multiferroic behaviors. [1][2][3][4][5] Nanocomposite oxides, with heterogeneous structures, can enable combinations of useful properties in one fi lm, and such fi lms can be formed by codeposition of two dissimilar phases. A notable example is the vertical nanocomposites formed from a spinel and a perovskite phase, such as BiFeO 3 -CoFe 2 O 4 grown on (001) SrTiO 3 which consist of columnar crystals of the spinel within a perovskite matrix, both epitaxial with the substrate. These have shown magnetism, ferroelectricity, and magnetoelectric coupling, [5][6][7][8] and, moreover, the locations of the spinel pillars on the substrate can be guided using a template. [12][13][14] The selfassembled fi lms are conveniently grown using pulsed laser deposition (PLD) from a single target or by alternating deposition from two different targets. Nanocomposite fi lms have also been produced consisting of metallic nanostructures in an oxide matrix, including Co x Ni 1-x alloy nanowires, Co nanocrystals, nanofi bers, or Fe nanorods embedded in a CeO 2 , TiO 2 , perovskite or other oxide matrix. [15][16][17][18][19] For example, metallic Cu nanopillars or nanoparticles in an oxide matrix have been reported for plasmon resonance studies and for battery electrodes. [20][21][22] The vertical nanocomposite fi lms reported to date comprise two different phases, but additional functionalities and crosscoupling of properties may be possible in nanocomposites with more than two phases. Three-phase oxide nanocomposites consisting of La 2 O 3 , SrO, and Co 2 O 3 were reported previously [ 23,24 ] but there has been no report on three-phase nanocomposites showing a vertically oriented epitaxial growth analogous to that seen in two-phase nanocomposites. Other examples of selfassembled oxide nanostructures include SrO x and (La,Sr)O x nanodots at the interface of Sr(Ti,Fe)O 3 and La 0.7 Sr 0.3 MnO 3 thin fi lms, which formed as a consequence of strain relaxation and electrostatic and elastic interactions, [ 25,26 ] and compositional heterogeneities which were found to develop in perovskite fi lms due to cation size and charge effects. [ 27 ] In this article, we describe the growth of a three-phase self-assembled epitaxial nanocomposite thin fi lm, denoted nc-STCu (nanocomposite-STCu), consisting of metallic Cu nanorods surrounded by a rocksalt-structured SrO oxide shell within a matrix of a Sr(Ti,Cu)O 3-δ perovskite phase. We then discuss the formation of a nanoporous oxide fi lm by

Metal Oxide Nanocomposites: A Perspective from Strain, Defect, and Interface

“…The strain energy can be reduced by the formation of TiO x /MgO core–shell structure, producing a similar effect as by reducing the MgO nanopillar feature size. The formation of a three‐phase VAN with Cu nanopillars in cubic SrO shell embedded in a matrix of Sr(Ti, Cu)O 3− δ films could be driven by the same mechanism (Figure a) . The formation of cubic SrO nanopillars ( d = ≈9 nm) indicates the large elastic strain energy between the SrO and the Sr(Ti, Cu)O 3− δ .…”

“…Different from nucleation and growth, phase separation driven by decomposition often forms nanocomposites with thermodynamically and/or kinetically more stable phases. Ross and co‐workers reported the growth of an interesting three‐phase VAN with Cu nanopillars ( d = 3 nm) in cubic SrO shell embedded in a matrix of Sr(Ti, Cu)O 3− δ films . Chemical etching using ammonium hydroxide removed 3 nm diameter Cu nanopillars leaving porous SrO pillars in film matrix, as shown in Figure a.…”

“…Inset shows the pores in the SrO rods after removing Cu. Reproduced with permission . Copyright 2015, Wiley.…”

Coexisting multiple order parameters in single-layerLuMnO3films

“…Future applications of multiferroic materials will heavily rely on thin films, as is the case for other advanced materials used in applications [8][9][10][11][12][13][14]. Switching the magnetization with an applied electric field using multiferroic materials is attempted by preparing heterostructures of, e.g., multiferroic and FM thin films, as shown for CoFe/BiFeO 3 bilayers [15].…”

Oxide Single-Crystal Surfaces: A Playground for Self-assembled Oxide Nanostructures

“…For instance, crystallization annealing of lattice mismatched oxides deposited by chemical solution (CSD) can lead to the formation of epitaxial nanoislands by solid state dewetting where the size, shape, and spatial ordering can be controlled through self-patterning [7,12,[16][17][18]. It is also worth noting that some oxide nanocomposites of different structures can be formed by self-assembly through spinodal decomposition mechanisms, as the artificial multiferroic nanocomposites composed of a ferromagnetic spinel and ferroelectric perovskite [19][20][21][22][23]. Stencil masks or nanoporous polymeric layers can also be used as templates for the realization of periodic arrays of functional oxide nanodots or nanowires [3,[24][25][26].…”