Recent Advancement in Ferroic Freestanding Oxide Nanomembranes

Ferroic and multiferroic oxides have been of significant interest for the last four decades due to their tremendous potential for next-generation memory and computational technologies. Possessing multiple ferroic orders with strong coupling between them erects a new way toward fast and low voltage switching. The major challenge is the scarcity of multiferroic materials at room temperature operation with a high coupling strength and robust ferroic orderings. Integration of existing multiferroics, mostly complex oxides, into the silicon-based platform also poses a major challenge. The recent development of freestanding oxide membranes offers a versatile solution for new and novel strategies to develop new materials. In this mini-review, we summarize the significant developments that happened in very recent years with ferroic oxide nanomembranes. We outline different approaches that have been implemented in the freestanding membranes to modulate the ferroic orderings, magnetism, ferroelectricity, and ferroelasticity. Along with the well-developed methods, such as bending and stretching of the membranes, we also emphasize the strength of twisting as a promising way to design and tune novel multiferroic orderings.

Route to Enhancing Remote Epitaxy of Perovskite Complex Oxide Thin Films

Remote epitaxy is taking center stage in creating freestanding complex oxide thin films with high crystallinity that could serve as an ideal building block for stacking artificial heterostructures with distinctive functionalities. However, there exist technical challenges, particularly in the remote epitaxy of perovskite oxides associated with their harsh growth environments, making the graphene interlayer difficult to survive. Transferred graphene, typically used for creating a remote epitaxy template, poses limitations in ensuring the yield of perovskite films, especially when pulsed laser deposition (PLD) growth is carried out, since graphene degradation can be easily observed. Here, we employ spectroscopic ellipsometry to determine the critical factors that damage the integrity of graphene during PLD by tracking the change in optical properties of graphene in situ. To mitigate the issues observed in the PLD process, we propose an alternative growth strategy based on molecular beam epitaxy to produce single-crystalline perovskite membranes.

Freestanding complex-oxide membranes

Complex oxides show a vast range of functional responses, unparalleled within the inorganic solids realm, making them promising materials for applications as varied as next-generation field-effect transistors, spintronic devices, electro-optic modulators, pyroelectric detectors, or oxygen reduction catalysts. Their stability in ambient conditions, chemical versatility, and large susceptibility to minute structural and electronic modifications make them ideal subjects of study to discover emergent phenomena and to generate novel functionalities for next-generation devices. Recent advances in the synthesis of single-crystal, freestanding complex oxide membranes provide an unprecedented opportunity to study these materials in a nearly-ideal system (e.g. free of mechanical/thermal interaction with substrates) as well as expanding the range of tools for tweaking their order parameters (i.e. (anti-)ferromagnetic, (anti-)ferroelectric, ferroelastic), and increasing the possibility of achieving novel heterointegration approaches (including interfacing dissimilar materials) by avoiding the chemical, structural, or thermal constraints in synthesis processes. Here, we review the recent developments in the fabrication and characterization of complex-oxide membranes and discuss their potential for unraveling novel physicochemical phenomena at the nanoscale and for further exploiting their functionalities in technologically relevant devices.