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Dislocations are 1D topological defects with emergent electronic properties. Their low dimensionality and unique properties make them excellent candidates for innovative device concepts, ranging from dislocation-based neuromorphic memory to light emission from diodes. To date, dislocations are created in materials during synthesis via strain fields or flash sintering or retrospectively via deformation, for example, (nano)-indentation, limiting the technological possibilities. In this work, we demonstrate the creation of dislocations in the ferroelectric semiconductor Er(Mn,Ti)O3 with nanoscale spatial precision using electric fields. By combining high-resolution imaging techniques and density functional theory calculations, direct images of the dislocations are collected, and their impact on the local electric transport behavior is studied. Our approach enables local property control via dislocations without the need for external macroscopic strain fields, expanding the application opportunities into the realm of electric-field-driven phenomena., Nano Letters, 21 (8), ISSN:1530-6984, ISSN:1530-6992

Ferroelectric domain walls are quasi-2D systems that show great promise for the development of nonvolatile memory, memristor technology, and electronic components with ultrasmall feature size. Electric fields, for example, can change the domain wall orientation relative to the spontaneous polarization and switch between resistive and conductive states, controlling the electrical current. Being embedded in a 3D material, however, the domain walls are not perfectly flat and can form networks, which leads to complex physical structures. In this work, the importance of the nanoscale structure for the emergent transport properties is demonstrated, studying electronic conduction in the 3D network of neutral and charged domain walls in ErMnO3 . By combining tomographic microscopy techniques and finite element modeling, the contribution of domain walls within the bulk is clarified and the significance of curvature effects for the local conduction is shown down to the nanoscale. The findings provide insights into the propagation of electrical currents in domain wall networks, reveal additional degrees of freedom for their control, and provide quantitative guidelines for the design of domain-wall-based technology., The authors acknowledge NTNU for support through the Enabling Nanotechnologies: Nano program. The Research Council of Norway is acknowledged for the support to the Norwegian Micro- and Nano-Fabrication Facility, NorFab, project number 245963/F50. Z.Y. and E.B. were supported by the U.S. Department of Energy, Office of Science, Basic Energy Sciences, Materials Sciences, and Engineering Division under Contract No. DE-AC02-05-CH11231 within the Quantum Materials program-KC2202. D.M. acknowledges funding from the European Research Council (ERC) under the European Union's Horizon 2020 research and innovation program (Grant Agreement No. 863691) and further thanks NTNU for support through the Onsager Fellowship Program and NTNU Stjerneprogrammet. T.J.M. and B.D.H. are grateful for support from NSF DMR:MRI:1726862 to develop T-AFM. K.S. acknowledges the support of the European Research Council under the European Union's Horizon 2020 research and innovation program (Grant Agreement No. 724529) and Ministerio de Economia, Industria y Competitividad through Grant Nos. MAT2016-77100-C2-2-P and SEV-2015-0496., With funding from the Spanish government through the ‘Severo Ochoa Centre of Excellence’ accreditation (CEX2019-000917-S).

Focused ion beam (FIB) and scanning electron microscopy (SEM) are used to reversibly switch improper ferroelectric domains in the hexagonal manganite ErMnO3. Surface charging is achieved by local ion (positive charging) and electron (positive and negative charging) irradiation, which allows controlled polarization switching without the need for electrical contacts. Polarization cycling reveals that the domain walls tend to return to the equilibrium configuration obtained in the as-grown state. The response of sub-surface domains is studied by FIB cross-sectioning, enabling imaging in the direction perpendicular to the applied electric field. The results clarify how the polarization reversal in hexagonal manganites progresses at the level of domains, resolving both domain wall movements and the nucleation and growth of new domains. Our FIB-SEM based switching approach is applicable to all ferroelectrics where a sufficiently large electric field can be built up via surface charging, facilitating contact-free high-resolution studies of the domain and domain wall response to electric fields in 3D. All article content, except where otherwise noted, is licensed under a Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/).

Utilizing quantum effects in complex oxides, such as magnetism, multiferroicity and superconductivity, requires atomic-level control of the material’s structure and composition. In contrast, the continuous conductivity changes that enable artificial oxide-based synapses and multiconfigurational devices are driven by redox reactions and domain reconfigurations, which entail long-range ionic migration and changes in stoichiometry or structure. Although both concepts hold great technological potential, combined applications seem difficult due to the mutually exclusive requirements. Here we demonstrate a route to overcome this limitation by controlling the conductivity in the functional oxide hexagonal Er(Mn,Ti)O3 by using conductive atomic force microscopy to generate electric-field induced anti-Frenkel defects, that is, charge-neutral interstitial–vacancy pairs. These defects are generated with nanoscale spatial precision to locally enhance the electronic hopping conductivity by orders of magnitude without disturbing the ferroelectric order. We explain the non-volatile effects using density functional theory and discuss its universality, suggesting an alternative dimension to functional oxides and the development of multifunctional devices for next-generation nanotechnology, We thank T. Grande for fruitful discussions. D.R.S. and S.M.S. were supported by the Research Council of Norway (project no. 231430/F20 and 275139) and acknowledge UNINETT Sigma2 (project no. NN9264K and ntnu243) for providing the computational resources. A.B.M. was supported by NTNU’s Enabling technologies: Nanotechnology. The Research Council of Norway is acknowledged for the support to the Norwegian Micro- and Nano-Fabrication Facility, NorFab, project no. 245963/F50 and Norwegian Centre for Transmission Electron Microscopy, NORTEM, Grant no. 197405. A.L.D. was funded by the Norwegian Research Council under project no. 274459 Translate. K.S. acknowledges the support of the European Research Council under the European Union’s Horizon 2020 research and innovation program (grant agreement no. 724529), Ministerio de Economia, Industria y Competitividad through grant nos. MAT2016-77100-C2-2-P and SEV-2015-0496, and the Generalitat de Catalunya (grant no. 2017SGR 1506). Z.Y. and E.B. were supported by the US Department of Energy, Office of Science, Basic Energy Sciences, Materials Sciences and Engineering Division under contract no. DE-AC02-05-CH11231 within the Quantum Materials program KC2202. J.A. was supported by the Academy of Finland under project no. 322832. D.M. thanks NTNU for support through the Onsager Fellowship Programme and NTNU Stjerneprogrammet.

Utilizing quantum effects in complex oxides, such as magnetism, multiferroicity and superconductivity, requires atomic-level control of the material's structure and composition. In contrast, the continuous conductivity changes that enable artificial oxide-based synapses and multiconfigurational devices are driven by redox reactions and domain reconfigurations, which entail long-range ionic migration and changes in stoichiometry or structure. Although both concepts hold great technological potential, combined applications seem difficult due to the mutually exclusive requirements. Here we demonstrate a route to overcome this limitation by controlling the conductivity in the functional oxide hexagonal Er(Mn,Ti)O

A focused ion beam (FIB) methodology is developed to lift out suitable specimens containing charged domain walls in improper ferroelectric ErMnO3. The FIB procedure allows for extracting domain wall sections with well-defined charge states, enabling accurate studies of their intrinsic physical properties. Conductive atomic force microscopy (cAFM) measurements on a 700 nm thick lamella demonstrate enhanced electronic transport at charged domain walls consistent with previous bulk measurements. A correlation is shown between domain wall currents in cAFM and applied ion beam polishing parameters, providing a guideline for further optimization. These results open the door for the study and functionalization of individual domain walls in hexagonal manganites, an important step toward the development of atomic scale domain-wall devices that can operate at low energy. This is the authors’ accepted and refereed manuscript to the article. This article may be downloaded for personal use only. Any other use requires prior permission of the author and AIP Publishing. The following article appeared in Applied Physics Letters and may be found at https://doi.org/10.1063/1.5115465

© 2018. This is the authors’ accepted and refereed manuscript to the article. Locked until 1.2.2019 due to copyright restrictions.

To efficiently evaluate the novel approach of focused ion beam (FIB) direct patterning of substrates for nanowire growth, a reference matrix of hole arrays has been used to study the effect of ion fluence and hole diameter on nanowire growth. Self-catalyzed GaAsSb nanowires were grown using molecular beam epitaxy and studied by scanning electron microscopy (SEM). To ensure an objective analysis, SEM images were analyzed with computer vision to automatically identify nanowires and characterize each array. It is shown that FIB milling parameters can be used to control the nanowire growth. Lower ion fluence and smaller diameter holes result in a higher yield (up to 83%) of single vertical nanowires, while higher fluence and hole diameter exhibit a regime of multiple nanowires. The catalyst size distribution and placement uniformity of vertical nanowires is best for low-value parameter combinations, indicating how to improve the FIB parameters for positioned-controlled nanowire growth.

GaAs nanowires (NWs) are seen as promising building blocks for future optoelectronic devices. To ensure reproducible properties, a high NW uniformity is required. Here, a substantial number of both position-controlled and randomly grown self-catalyzed GaAs/AlGaAs core-shell NWs are compared. Single NWs are characterized by correlated microphotoluminescence (µ-PL) spectroscopy and transmission electron microscopy (TEM). TEM is done in the 〈110〉- and 〈112〉-projections, and on the 〈111〉-cross-section of the NWs. The position-control grown NWs showed a higher degree of uniformity in morphology. All NWs on both samples had a predominantly stacking fault free zinc blende structure, with a main optical response around the GaAs free exciton energy. However, NW-to-NW structural variations in the tip region and radial compositional variations in the shell are present in both samples. These structural features could be the origin of variations in the optical response just below and above the free exciton energy. This correlated study demonstrates that the observed distinct, sharp PL peaks in the 1.6 - 1.8 eV energy range present in several NWs, are possibly related to radial compositional variations in the AlGaAs shell rather than the structural defects in the tip region.