Self‐Organization of Heteroepitaxial CeO₂ Nanodots Grown from Chemical Solutions

Abstract

The appearance of new functionalities and devices arising from size-and shape-dependent properties has triggered the interest in creating well-defined structures at the nanometricscale. While conventional lithography is used to fabricate structures in the range of hundreds of nanometers, self-organizing and self-assembling processes following a bottom-up approach can easily decrease this size limit and also cover cost-effectively much larger surfaces. [1,2] Semiconductors, metals, oxides and molecular materials are different areas where such principles are intensively pursued to generate nanostructures. [1] In particular, self-assembling based on the stress associated to heteroepitaxial growth is an attractive fabrication route in which the generation of semiconductor nanostructures has been extensively investigated [1,3] and, recently, it has spread to other emerging fields such as oxide-based nanotechnology. Complex oxides attract a great interest for a wealth of different physical and chemical properties and applications such as ferromagnetism, ferroelectricity, colossal magnetoresistance, high dielectric constants, catalysis, optical properties, high temperature superconductivity, solar cells, etc.[4] Based on these properties, many device concepts are under investigation requiring lateral confinement at the nanometric scale, [5][6][7] therefore, it constitutes a real scientific challenge to understand the formation mechanisms of nanometric structures. So far the mechanisms that drive self-organized nanodot growth have been studied in certain detail in epitaxial materials prepared from vapor deposition techniques, including oxides [1,[5][6][7] , and either Stranski-Krastanov or Volmer-Weber mechanisms were found to apply. On the other hand, vicinal substrates have been widely considered as templates for growing low dimensional nanostructures. [8,9] The role of lattice steps on the growth mechanism of oxide films has been analyzed by several authors, though the formation of self-organized nanostructures using the terraces as templates has been very scarce. [5,6] Much less attention has been devoted to investigate the capabilities of Chemical Solution Deposition (CSD), [10,11] a preparation methodology bearing a high interest for many functionalities and practical applications requiring the use of large areas or long lengths.[12] Particularly, CeO 2 is a key material which is being extensively investigated because of its very high intrinsic interest in many areas such as catalysis, ionic conductivity, optical and dielectric properties, [13] buffer layer for oxide superconductors, [14,15] or nanotemplates to manipulate the vortex properties in superconducting materials. [16] In the last case, the use of self-organized templates in combination with superconducting films could lead to a wealth of new superconducting phenomena.[17] It appears then as highly demanding, scientifically and technologically, the study of the mechanisms generating nanostructured networks of CeO 2 . Very thin films grown by CSD have b...

Nanoscale magnetic structure and properties of solution-derived self-assembled La0.7Sr0.3MnO3 islands

“…8 In this context, the bottom-up self-assembly approach based on the chemical solution deposition (CSD) route used in this work offers an effective route to overcome the shortcomings of lithography-based techniques, while uniformly covering large areas (in the $cm 2 range) without vacuum environment requirements. [13][14][15] Inherent to heteroepitaxial growth, lattice strain may lead to relevant variations of the Curie temperature, electrical resistivity and magnetoresistance in nm thick films of mixedvalence manganite grown on bulk single crystals. 16 Its effect is further evidenced on the magnetic anisotropy and microscopic magnetic domain configuration of, e.g., LSMO films and nanostructures.…”

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

“…Straight step edges will preferentially form on substrates with an azimuthal miscut angle along a low-index direction whereas "zigzag" steps will form when the azimuthal angle is off-low-index directions [34]. Since surface steps give rise to ES barriers for atomic diffusion, preferential alignment along the steps of epitaxial nanodots of ∼50 nm in diameter and less than 10 nm in height has been grown by preferential diffusion along the steps [44]. Also, as the surface atomic steps have an energetic cost (lower coordination sites), they will preferentially assemble together when the atomic surface diffusion will be larger than the mean terrace width, to form well-defined stable higher steps and wider terraces of lower energy (like surface facets of low Miller indexes).…”

Interface structure governed by plastic and structural dissimilarity in perovskite La0.7Sr0.3MnO3 nanodots on rock-salt MgO substrates

“…Among deposition techniques, chemical solution deposition (CSD) is emerging as a high-throughput growth technique that has already been proved efficient for the preparation of nanostructures of a variety of complex oxide materials. 4,5 Here, we present a structural analysis of the perovskite/rock-salt interface between La 0.7 Sr 0.3 MnO 3 (LSMO) and the MgO substrate, in order to get insights into the role of plastic and structural dissimilarity on the development of interfacial structures.…”

“…8 Close inspection of the fine structure of the {101}-LSMO-poles (see inset in Fig. 2(a)) reveals that each pole is associated to four satellites lying along the [110] and [1][2][3][4][5][6][7][8][9][10] directions, indicating the occurrence of four additional orientation domains related to the precise cube-on-cube orientation by 2 to 5 tilts about the [110] and [1][2][3][4][5][6][7][8][9][10] axes. In order to determine the average in-plane strain state of the nanodots ensemble, we conducted XRD / -2h/x space mapping (/ is the azimuthal orientation) at a grazing incidence angle of 0.…”

“…3(a) . We, therefore, assign (101), (1)(2)(3)(4)(5)(6)(7)(8)(9)(10)(11), and (111) to the lateral facets and (001) to the top one. The location and character of interfacial dislocations labeled 1 to 7 is indicated.…”