Abstract
The controlled transformation of materials, both their structure and their physical properties, is key to many devices. Ionic liquid gating can induce the transformation of thin-film materials over long distances from the gated surface. Thus, the mechanism underlying this process is of considerable interest. Here we directly image, using in situ, real-time, high-resolution transmission electron microscopy, the reversible transformation between the oxygen vacancy ordered phase brownmillerite SrCoO2.5 and the oxygen ordered phase perovskite SrCoO3. We show that the phase transformation boundary moves at a velocity that is highly anisotropic, traveling at speeds ~30 times faster laterally than through the thickness of the film. Taking advantage of this anisotropy, we show that three-dimensional metallic structures such as cylinders and rings can be realized. Our results provide a roadmap to the construction of complex meso-structures from their exterior surfaces.
Highlights
The controlled transformation of materials, both their structure and their physical properties, is key to many devices
A single STO wafer was used to prepare samples for: in situ transmission electron microscopy (TEM) and STEM, ex situ STEM, and transport measurements, while samples on Nb-doped SrTiO3 (NSTO) were used for meso-structure fabrication and conductive atomic force microscope (CAFM) measurements
The channel of the field effect transistor (FET) is formed from a thin film of SrCoO2.5
Summary
The controlled transformation of materials, both their structure and their physical properties, is key to many devices. In situ high-resolution transmission electron microscopy (TEM) is an excellent technique for such studies, but a major challenge is that the IL strongly degrades the image quality due to scattering of the electron beam[13] We overcome this obstacle by positioning a droplet of the IL close to, but not within, the imaged region of the TEM lamellae by the use of an atomic force microscope. We find that the migration takes place over several minutes and that its time-scale is an order of magnitude faster parallel, as compared to perpendicular to the film surface Taking advantage of these findings we create a series of three-dimensional meso-structures in SrCoOx and several other oxide films
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