Direct Fabrication of Atomically Defined Pores in MXenes Using Feedback-Driven STEM.

Controlled fabrication of nanopores in 2D materials offer the means to create robust membranes needed for ion transport and nanofiltration. Techniques for creating nanopores have relied upon either plasma etching or direct irradiation; however, aberration-corrected scanning transmission electron microscopy (STEM) offers the advantage of combining a sub-Å sized electron beam for atomic manipulation along with atomic resolution imaging. Here, a method for automated nanopore fabrication is utilized with real-time atomic visualization to enhance the mechanistic understanding of beam-induced transformations.

Stress and Curvature Effects in Layered 2D Ferroelectric CuInPS.

Nanoscale ferroelectric 2D materials offer the opportunity to investigate curvature and strain effects on materials functionalities. Among these, CuInPS (CIPS) has attracted tremendous research interest in recent years due to combination of room temperature ferroelectricity, scalability to a few layers thickness, and ferrielectric properties due to coexistence of 2 polar sublattices. Here, we explore the local curvature and strain effect on polarization in CIPS via piezoresponse force microscopy and spectroscopy.

Design of high polarization low switching barrier hybrid improper ferroelectric perovskite oxide superlattices.

Hybrid improper ferroelectricity is a useful tool to design ABO/A'BO polar superlattices from non polar building blocks. In this study, we have designed high polarization-low switching barrier hybrid improper ferroelectric superlattices with efficient polarization, and polarization-magnetization switching properties above room temperature, using density functional theory and molecular dynamics simulations. Superlattices with a chemical formula of (AAlO)/(A'AlO), where / = 1/1, 1/3, 3/1, 1/5 and 5/1, A, A' = Lanthanide and Y cations are considered to outline the design principles behind polarization switching and (LaFeO)/(CeFeO) is investigated for polarization-magnetization switching.

Probing Electron Beam Induced Transformations on a Single-Defect Level via Automated Scanning Transmission Electron Microscopy.

A robust approach for real-time analysis of the scanning transmission electron microscopy (STEM) data streams, based on ensemble learning and iterative training (ELIT) of deep convolutional neural networks, is implemented on an operational microscope, enabling the exploration of the dynamics of specific atomic configurations under electron beam irradiation via an automated experiment in STEM. Combined with beam control, this approach allows studying beam effects on selected atomic groups and chemical bonds in a fully automated mode. Here, we demonstrate atomically precise engineering of single vacancy lines in transition metal dichalcogenides and the creation and identification of topological defects in graphene.

Exploring electron beam induced atomic assembly via reinforcement learning in a molecular dynamics environment.

Atom-by-atom assembly of functional materials and devices is perceived as one of the ultimate targets of nanotechnology. Recently it has been shown that the beam of a scanning transmission electron microscope can be used for targeted manipulation of individual atoms. However, the process is highly dynamic in nature rendering control difficult.

Automated and Autonomous Experiments in Electron and Scanning Probe Microscopy.

Machine learning and artificial intelligence (ML/AI) are rapidly becoming an indispensable part of physics research, with domain applications ranging from theory and materials prediction to high-throughput data analysis. In parallel, the recent successes in applying ML/AI methods for autonomous systems from robotics to self-driving cars to organic and inorganic synthesis are generating enthusiasm for the potential of these techniques to enable automated and autonomous experiments (AE) in imaging. Here, we aim to analyze the major pathways toward AE in imaging methods with sequential image formation mechanisms, focusing on scanning probe microscopy (SPM) and (scanning) transmission electron microscopy ((S)TEM).

Surface structure and energetics of low index facets of bismuth ferrite.

Bismuth ferrite (BiFeO3) is a multiferroic material that has received significant interest due to its functional properties which could lead to potential novel applications in microelectronics, spintronics, and controlled catalytic reactions. Here, we provide the results of an extensive theoretical study to understand the surface structure and describe the energetics of differently terminated BiFeO3 surfaces. We specifically evaluate low index crystal facets and surface level atomic terminations via density functional theory and ab initio thermodynamics techniques.

Electronic and Magnetic Properties of Lanthanum and Strontium Doped Bismuth Ferrite: A First-Principles Study.

While bismuth ferrite BiFeO (BFO) is a well studied multiferroic material, its electronic and magnetic properties in the presence of A-site dopants have not been explored widely. Here we report the results of a systematic study of the local electronic structure, spontaneous polarization, and magnetic properties of lanthanum (La) and strontium (Sr) doped rhombohedral bismuth ferrite within density functional theory. An enhanced ferroelectric polarization of 122.

First-principles studies of spontaneous polarization in mixed poly(vinylidene fluoride)/2,3,3,3-tetrafluoropropene polymer crystals.

Spontaneous polarization P of mixed polymer crystals based on β poly(vinylidene fluoride) (PVDF, -CH2-CF2-) and 2,3,3,3-tetrafluoropropene (TFP, -CH2-CF(CF3)-) was evaluated for β-PVDF/iso-PTFP, β-PVDF/P(VDF-alt-iso-TFP) and β-PVDF/syndio-PTFP. A plane-wave-based density-functional theory (DFT) approach, combined with the Modern Theory of Polarization formalism utilizing maximally-localized Wannier functions for calculating P, indicates that all systems exhibit similarly high or even slightly larger polarization than that of perfectly crystalline β-PVDF (0.18 C m-2).