Oxide-metal based nanocomposite thin films have attracted great interests owing to their unique anisotropic structure and physical properties. A wide range of Au-based oxide-metal nanocomposites have been demonstrated, while other metal systems are scarce due to the challenges in the initial nucleation and growth as well as possible interdiffusions of the metallic nanopillars. In this work, a unique anodic aluminum oxide (AAO) template was used to grow a thin Co seed layer and the following self-assembled metal-oxide (Co-BaTiO₃) vertically aligned nanocomposite thin film layer. The AAO template allows the uniform growth of Co-seeds and successfully deposition of highly ordered Co pillars (with diameter < 5 nm and interval between pillars < 10 nm) inside the oxide matrix. Significant magnetic anisotropy and strong magneto-optical coupling properties have been observed. A thin Au-BaTiO₃ template was also later introduced for further enhanced nucleation and ordered growth of the Co-nanopillars. Taking the advantage of such a unique nanostructure, a large out-of-plane (OP) coercive field (H_c) of ~ 5000 Oe has been achieved, making the nanocomposite an ideal candidate for high density perpendicular magnetic tunneling junction (p-MTJ). A strong polar magneto-optical Kerr effect (MOKE) has also been observed which inspires a novel optical-based reading method of the MTJ states.

Multiferroics are an intriguing family of materials due to the simultaneous presence of two ferroic orderings, namely, ferroelectricity and ferromagnetism. They are scientifically and technologically important and have numerous potential applications, such as four-state logic memories and multiferroic tunneling junctions. However, the growth of epitaxial single-phase multiferroic thin films typically requires single crystalline oxide substrates, which hinders their future integration with Si-based devices. In this study, we report a generalized synthesis method that uses the polydimethylsiloxane (PDMS)-assisted wet-etching method with an Sr₃Al₂O₆ (SAO) sacrificial layer to transfer freestanding single-phase multiferroic Bi₂NiMnO₆ (BNMO) films from conventional SrTiO₃ (STO) substrates onto a Si wafer. The structures and properties of the films have been characterized before and after the transfer. These transferred films possess good multiferroic properties on Si wafers, indicating full compatibility with modern Si technology. This method can be generally applicable to other Bi-based multiferroic materials as well. Lastly, the original STO substrates after the transfer process have been recycled for preparing new batches of freestanding BNMO films, indicating a low-cost and sustainable method for manufacturing large-volume freestanding complex oxide thin films.

Two-dimensional (2D) layered oxides have recently attracted wide attention owing to the strong coupling among charges, spins, lattice, and strain, which allows great flexibility and opportunities in structure designs as well as multifunctionality exploration. In parallel, plasmonic hybrid nanostructures exhibit exotic localized surface plasmon resonance (LSPR) providing a broad range of applications in nanophotonic devices and sensors. A hybrid material platform combining the unique multifunctional 2D layered oxides and plasmonic nanostructures brings optical tuning into the new level. In this work, a novel self-assembled Bi₂MoO₆ (BMO) 2D layered oxide incorporated with plasmonic Au nanoinclusions has been demonstrated via one-step pulsed laser deposition (PLD) technique. Comprehensive microstructural characterizations, including scanning transmission electron microscopy (STEM), differential phase contrast imaging (DPC), and STEM tomography, have demonstrated the high epitaxial quality and particle-in-matrix morphology of the BMO-Au nanocomposite film. DPC-STEM imaging clarifies the magnetic domain structures of BMO matrix. Three different BMO structures including layered supercell (LSC) and superlattices have been revealed which is attributed to the variable strain states throughout the BMO-Au film. Owing to the combination of plasmonic Au and layered structure of BMO, the nanocomposite film exhibits a typical LSPR in visible wavelength region and strong anisotropy in terms of its optical and ferromagnetic properties. This study opens a new avenue for developing novel 2D layered complex oxides incorporated with plasmonic metal or semiconductor phases showing great potential for applications in multifunctional nanoelectronics devices.

A new vertically aligned nanocomposite (VAN) structure based on two-dimensional (2D) layered oxides has been designed and self-assembled on both LaAlO₃ (001) and SrTiO₃ (001) substrates. The new VAN structure consists of epitaxially grown Co₃O₄ nanopillars embedded in the Bi₂WO₆ matrix with a unique 2D layered structure, as evidenced by the microstructural analysis. Physical property measurements show that the new Bi₂WO₆-Co₃O₄ VAN structure exhibits strong ferromagnetic and piezoelectric response at room temperature as well as anisotropic permittivity response. This work demonstrates a new approach in processing multifunctional VANs structure based on the layered oxide systems towards future nonlinear optics, ferromagnets, and multiferroics.