Controlling strain in new functional materials with tunable and enhanced properties

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Designing novel materials with multifunctional properties for potential applications is a long-term goal in materials science. Strain is a novel approach to manipulating functionalities in correlated complex oxides. Significant epitaxial strain has only been achieved in ultrathin layers, which limits their potential applications. A team of Laboratory researchers and users of the Center for Integrated Nanotechnologies (CINT) tuned lattice strain, microstructure, and defect and interface coupling to develop a new approach to produce nanocomposite films with controlled functionality. The journal Science Advances reported the results.

Epitaxial strain is only effective in a conventional strain engineering framework below the critical thickness, which is usually less than a few tens of nanometers. Tuning electron transport by epitaxial strain has only been achieved in ultrathin layers due to the relaxation of epitaxial strains in relatively thick films. Therefore, the challenges of tuning the magnetic and electron transport properties by strain in thick films is challenging and limits their potential applications.

Vertical nanocomposites with two integrated functional components could exhibit multifunctionalities that do not exist in the single components. The team designed a framework-design-synthesis approach in a vertical lattice strain method. The approach creates a large vertical lattice strain in the matrix by selecting two phases with a large lattice mismatch and a large elastic modulus mismatch. Different from substrate-induced strain, which only exists within a critical thickness (usually very thin), film thickness does not limit the vertical strain induced by the vertical interface. Phase-field simulations predicted strain distribution in thick nanoscaffolding films and determined that the vertical interfacial area and interfacial dislocation density between the scaffold network and film matrix would control the ultimate strain status.

The team’s experimental results confirmed theoretical conclusions and proved that the vertical strain plays a critical role in manipulating magnetism, magnetic anisotropy, and low-field magnetotransport in thick nanoscaffolding films. The researchers showed that the direct lattice matching framework approach could achieve large and uniform vertical strain up to 2%. This increase could significantly modify the magnetic anisotropy, magnetism, and magnetotransport properties in heteroepitaxial nanoscaffold films that are more than a few hundred nanometers in thickness. This is the first demonstration of significantly enhanced low field magnetoresistance in very thick epitaxial manganite nanocomposite films. The novel approach provides a new route to design functional materials for high density data storage and beyond.

The research uncovers the interplays among vertical interfaces, strain and functionality, which could allow the design of a variety of functional nanocomposites with enhanced/new properties.

The research findings provide guidance to design large strain in nanoscaffolding films and to use large vertical strain to tune functional properties beyond magnetism and magnetotransport. The insight could lead to new opportunities in fundamental discoveries in physics, chemistry, and materials science. Incorporating these high-density nanowires in thin films could be generalized for a variety of material systems to achieve tunable multifunctional properties for potentially useful applications.

Reference: “Role of Scaffold Network in Controlling Strain and Functionalities of Nanocomposite Films,” Science Advances 2, e1600245 (2016); doi: 10.1126/sciadv.1600245.

Researchers: Aiping Chen, Dmitry Yarotski, Quanxi Jia, Erik Enriquez, and Marcus Weigand (Center for Integrated Nanotechnologies, MPA-CINT); Jia-Mian Hu, Tiannan Yang, and Long-Qing Chen (Pennsylvania State University); Ping Lu (Sandia National Laboratories); Wenrui Zhang, Leigang Li, Qing Su, and Haiyan Wang (Texas A&M University); Jian-Xin Zhu and Towfiq Ahmed (Physics of Condensed Matter and Complex Systems, T-4); and Judith L. MacManus-Driscoll (University of Cambridge).

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The high resolution scanning transmission electron microscope image, shows a top view of a nanocomposite thin film with magnesium oxide nanowires (approximately 4 nm in diameter, dark contrast) embedded in a perovskite oxide thin film matrix (white contrast).