Reconfiguration of Amorphous Complex Oxides: A Route to a Broad Range of Assembly Phenomena, Hybrid Materials, and Novel Functionalities

Abstract

materials that are freestanding either at a stage in their fabrication, in their final state, or both. [1] NMs with thicknesses in the range of a few nanometers to a few hundred nanometers can be isolated from their substrates through synthesis and processing techniques that have become established in the last 20 years. [1][2][3][4][5] The lateral dimensions of NMs are at least two orders of magnitude larger than their thickness, making them a distinctive platform from 0D, 1D, and bulk materials. [6] NMs enable a vast range of possibilities, including i) the capability to subject materials to elastic strain fields with magnitudes or geometries that are not realizable in bulk materials or by direct growth; [7][8][9] ii) unique and rapid characterization of materials properties and kinetic processes; [10,11] iii) heterogeneous integration of materials via controlled transfer, including, into environments in which the NM materials would be otherwise inaccessible via synthesis; [12,13] iv) 3D structures that can be processed in parallel on large-area substrates and can find use in several applications. [14][15][16][17][18] The scope of applications and phenomena that benefit from NMs can be extended to a new spectrum of materials Reconfiguration of amorphous complex oxides provides a readily controllable source of stress that can be leveraged in nanoscale assembly to access a broad range of 3D geometries and hybrid materials. An amorphous SrTiO 3 layer on a Si:B/Si 1−x Ge x :B heterostructure is reconfigured at the atomic scale upon heating, exhibiting a change in volume of ≈2% and accompanying biaxial stress. The Si:B/Si 1−x Ge x :B bilayer is fabricated by molecular beam epitaxy, followed by sputter deposition of SrTiO 3 at room temperature. The processes yield a hybrid oxide/semiconductor nanomembrane. Upon release from the substrate, the nanomembrane rolls up and has a curvature determined by the stress in the epitaxially grown Si:B/Si 1−x Ge x :B heterostructure. Heating to 600 °C leads to a decrease of the radius of curvature consistent with the development of a large compressive biaxial stress during the reconfiguration of SrTiO 3 . The control of stresses via post-deposition processing provides a new route to the assembly of complex-oxide-based heterostructures in 3D geometry. The reconfiguration of metastable mechanical stressors enables i) synthesis of various types of strained superlattice structures that cannot be fabricated by direct growth and ii) technologies based on strain engineering of complex oxides via highly scalable lithographic processes and on large-area semiconductor substrates.The ORCID identification number(s) for the author(s) of this article can be found under https://doi.org/10.1002/smll.202105424.

Formation and Shape Changing of Conductive Helical Ribbons via Deposition of Highly Stressed Films on Mechanically Responsive Substrates

“…We have earlier shown that self-assembly [40] of ultra-thin films or nanomembranes into 3D structures [41] serves as a sensitive probe to measure film stress evolution [42,43] during the structural transformation of metastable films, such as amorphous complex oxides. [44] We use this approach to calculate the average stress in the electrodeposited Au films and stress/strain profile in the helix in x, y, and z directions.…”