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Contact interface properties are important in determining the performances of devices that are based on atomically thin two-dimensional (2D) materials, especially for those with short channels. Understanding the contact interface is therefore important to design better devices. Herein, we use scanning transmission electron microscopy, electron energy loss spectroscopy, and first-principles calculations to reveal the electronic structures within the metallic (1T′)-semiconducting (2H) MoTe2 coplanar phase boundary across a wide spectral range and correlate its properties to atomic structures. We find that the 2H-MoTe2 excitonic peaks cross the phase boundary into the 1T′ phase within a range of approximately 150 nm. The 1T′-MoTe2 crystal field can penetrate the boundary and extend into the 2H phase by approximately two unit-cells. The plasmonic oscillations exhibit strong angle dependence, that is a red-shift of π+σ (approximately 0.3–1.2 eV) occurs within 4 nm at 1T′/2H-MoTe2 boundaries with large tilt angles, but there is no shift at zero-tilted boundaries. These atomic-scale measurements reveal the structure–property relationships of the 1T′/2H-MoTe2 boundary, providing useful information for phase boundary engineering and device development based on 2D materials. [ABSTRACT FROM AUTHOR]

Ferroelectric vortices formed through complex lattice–charge interactions have great potential in applications for future nanoelectronics such as memories. For practical applications, it is crucial to manipulate these topological states under external stimuli. Here, we apply mechanical loads to locally manipulate the vortices in a PbTiO3/SrTiO3 superlattice via atomically resolved in-situ scanning transmission electron microscopy. The vortices undergo a transition to the a-domain with in-plane polarization under external compressive stress and spontaneously recover after removal of the stress. We reveal the detailed transition process at the atomic scale and reproduce this numerically using phase-field simulations. These findings provide new pathways to control the exotic topological ferroelectric structures for future nanoelectronics and also valuable insights into understanding of lattice-charge interactions at nanoscale. Controlling topological polar vortices promises to open up new applications for ferroelectric materials. Here, the authors proposed a method to mechanically manipulate polar vortices and monitored the transition between vortex and ferroelectric phase by in-situ scanning transmission electron microscopy. [ABSTRACT FROM AUTHOR]

Defects exist ubiquitously in crystal materials, and usually exhibit a very different nature from the bulk matrix. Hence, their presence can have significant impacts on the properties of devices. Although it is well accepted that the properties of defects are determined by their unique atomic environments, the precise knowledge of such relationships is far from clear for most oxides because of the complexity of defects and difficulties in characterization. Here, we fabricate a 36.8° SrRuO3 grain boundary of which the transport measurements show a spin-valve magnetoresistance. We identify its atomic arrangement, including oxygen, using scanning transmission electron microscopy and spectroscopy. Based on the as-obtained atomic structure, the density functional theory calculations suggest that the spin-valve magnetoresistance occurs because of dramatically reduced magnetic moments at the boundary. The ability to manipulate magnetic properties at the nanometer scale via defect control allows new strategies to design magnetic/electronic devices with low-dimensional magnetic order. [ABSTRACT FROM AUTHOR]

Domain walls are of increasing interest in ferroelectrics because of their unique properties and potential applications in future nanoelectronics. However, the thickness of ferroelastic domain walls remains elusive due to the challenges in experimental characterization. Here, we determine the atomic structure of ferroelastic domain walls and precisely measure the polarization and domain wall thickness at picometer scale using annular bright field imaging from an aberration-corrected scanning transmission electron microscope. We find that the domain wall thickness in PbZr 0.2 Ti 0.8 O 3 and PbTiO 3 thin films is typically about one unit cell, across which the oxygen octahedron distortion behavior is in excellent agreement with previous first-principles calculations. Remarkably, wider domain walls about two unit cells in thickness are also observed for those domains walls are coupled with dislocations and underwent a compressive strain. These results suggest that the thickness of ferroelastic domain walls highly depends on their atomic environments. This study can help us to understand the past debatable experimental results and provide further insights into control of domain wall thickness via strain engineering for their possible applications in nanoelectronics. Image, graphical abstract [ABSTRACT FROM AUTHOR]