The Experts below are selected from a list of 360 Experts worldwide ranked by ideXlab platform
David A Muller - One of the best experts on this subject based on the ideXlab platform.
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structure and bonding at the atomic scale by scanning transmission Electron microscopy
Nature Materials, 2009Co-Authors: David A MullerAbstract:A new generation of Electron microscopes is able to explore the microscopic properties of materials and devices as diverse as transistors, turbine blades and interfacial superconductors. All of these systems are made up of dissimilar materials that, where they join at the atomic scale, display very different behaviour from what might be expected of the bulk materials. Advances in Electron Optics have enabled the imaging and spectroscopy of these buried interface states and other nanostructures with atomic resolution. Here I review the capabilities, prospects and ultimate limits for the measurement of physical and Electronic properties of nanoscale structures with these new microscopes.
Ondrej L Krivanek - One of the best experts on this subject based on the ideXlab platform.
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brief history of the cambridge stem aberration correction project and its progeny
Ultramicroscopy, 2015Co-Authors: Michael L Brown, P E Batson, N Dellby, Ondrej L KrivanekAbstract:Abstract We provide a brief history of the project to correct the spherical aberration of the scanning transmission Electron microscope (STEM) that started in Cambridge (UK) and continued in Kirkland (WA, USA), Yorktown Heights (NY, USA), and other places. We describe the project in the full context of other aberration correction research and related work, partly in response to the incomplete context presented in the paper “In quest of perfection in Electron Optics: A biographical sketch of Harald Rose on the occasion of his 80th birthday”, recently published in Ultramicroscopy.
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sub angstrom resolution using aberration corrected Electron Optics
Nature, 2002Co-Authors: P E Batson, N Dellby, Ondrej L KrivanekAbstract:Following the invention of Electron Optics during the 1930s, lens aberrations have limited the achievable spatial resolution to about 50 times the wavelength of the imaging Electrons. This situation is similar to that faced by Leeuwenhoek in the seventeenth century, whose work to improve the quality of glass lenses led directly to his discovery of the ubiquitous "animalcules" in canal water, the first hints of the cellular basis of life. The Electron optical aberration problem was well understood from the start, but more than 60 years elapsed before a practical correction scheme for Electron microscopy was demonstrated, and even then the remaining chromatic aberrations still limited the resolution. We report here the implementation of a computer-controlled aberration correction system in a scanning transmission Electron microscope, which is less sensitive to chromatic aberration. Using this approach, we achieve an Electron probe smaller than 1 A. This performance, about 20 times the Electron wavelength at 120 keV energy, allows dynamic imaging of single atoms, clusters of a few atoms, and single atomic layer 'rafts' of atoms coexisting with Au islands on a carbon substrate. This technique should also allow atomic column imaging of semiconductors, for detection of single dopant atoms, using an Electron beam with energy below the damage threshold for silicon.
Stephen R Power - One of the best experts on this subject based on the ideXlab platform.
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valley hall effect and nonlocal resistance in locally gapped graphene
Physical Review B, 2021Co-Authors: Thomas Aktor, Jose H Garcia, Stephan Roche, Anttipekka Jauho, Stephen R PowerAbstract:We report on the emergence of bulk, valley-polarized currents in graphene-based devices, driven by spatially varying regions of broken sublattice symmetry, and revealed by nonlocal resistance (${R}_{\mathrm{NL}}$) fingerprints. By using a combination of quantum transport formalisms, giving access to bulk properties as well as multiterminal device responses, the presence of a nonuniform local band gap is shown to give rise to valley-dependent scattering and a finite Fermi-surface contribution to the valley Hall conductivity, related to characteristics of ${R}_{\mathrm{NL}}$. These features are robust against disorder and provide a plausible interpretation of controversial experiments in graphene/hexagonal boron nitride superlattices. Our findings suggest both an alternative mechanism for the generation of valley Hall effect in graphene and a route towards valley-dependent Electron Optics, by materials and device engineering.
Stephan Roche - One of the best experts on this subject based on the ideXlab platform.
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valley hall effect and nonlocal resistance in locally gapped graphene
Physical Review B, 2021Co-Authors: Thomas Aktor, Jose H Garcia, Stephan Roche, Anttipekka Jauho, Stephen R PowerAbstract:We report on the emergence of bulk, valley-polarized currents in graphene-based devices, driven by spatially varying regions of broken sublattice symmetry, and revealed by nonlocal resistance (${R}_{\mathrm{NL}}$) fingerprints. By using a combination of quantum transport formalisms, giving access to bulk properties as well as multiterminal device responses, the presence of a nonuniform local band gap is shown to give rise to valley-dependent scattering and a finite Fermi-surface contribution to the valley Hall conductivity, related to characteristics of ${R}_{\mathrm{NL}}$. These features are robust against disorder and provide a plausible interpretation of controversial experiments in graphene/hexagonal boron nitride superlattices. Our findings suggest both an alternative mechanism for the generation of valley Hall effect in graphene and a route towards valley-dependent Electron Optics, by materials and device engineering.
Avik W Ghosh - One of the best experts on this subject based on the ideXlab platform.
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impact of geometry and non idealities on Electron Optics based graphene p n junction devices
Applied Physics Letters, 2019Co-Authors: Mirza M Elahi, K Masum M Habib, Ke Wang, Gilho Lee, Philip Kim, Avik W GhoshAbstract:We articulate the challenges and opportunities of unconventional devices using the photon like flow of Electrons in graphene, such as Graphene Klein Tunnel (GKT) transistors. The underlying physics is the employment of momentum rather than energy filtering to engineer a gate tunable transport gap in a 2D Dirac cone bandstructure. In the ballistic limit, we get a clean tunable gap that implies subthermal switching voltages below the Boltzmann limit, while maintaining a high saturating current in the output characteristic. In realistic structures, detailed numerical simulations and experiments show that momentum scattering, especially from the edges, bleeds leakage paths into the transport gap and turns it into a pseudogap. We quantify the importance of reducing edge roughness and overall geometry on the low-bias transfer characteristics of GKT transistors and benchmark against experimental data. We find that geometry plays a critical role in determining the performance of Electron Optics based devices that utilize angular resolution of Electrons.We articulate the challenges and opportunities of unconventional devices using the photon like flow of Electrons in graphene, such as Graphene Klein Tunnel (GKT) transistors. The underlying physics is the employment of momentum rather than energy filtering to engineer a gate tunable transport gap in a 2D Dirac cone bandstructure. In the ballistic limit, we get a clean tunable gap that implies subthermal switching voltages below the Boltzmann limit, while maintaining a high saturating current in the output characteristic. In realistic structures, detailed numerical simulations and experiments show that momentum scattering, especially from the edges, bleeds leakage paths into the transport gap and turns it into a pseudogap. We quantify the importance of reducing edge roughness and overall geometry on the low-bias transfer characteristics of GKT transistors and benchmark against experimental data. We find that geometry plays a critical role in determining the performance of Electron Optics based devices that...
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impact of geometry and non idealities on Electron Optics based graphene p n junction devices
arXiv: Mesoscale and Nanoscale Physics, 2018Co-Authors: Mirza M Elahi, K Masum M Habib, Ke Wang, Gilho Lee, Philip Kim, Avik W GhoshAbstract:We articulate the challenges and opportunities of unconventional devices using the photon like flow of Electrons in graphene, such as Graphene Klein Tunnel (GKT) transistors. The underlying physics is the employment of momentum rather than energy filtering to engineer a gate tunable transport gap in a 2D Dirac cone bandstructure. In the ballistic limit, we get a clean tunable gap that implies subthermal switching voltages below the Boltzmann limit, while maintaining a high saturating current in the output characteristic. In realistic structures, detailed numerical simulations and experiments show that momentum scattering, especially from the edges, bleeds leakage paths into the transport gap and turns it into a pseudogap. We quantify the importance of reducing edge roughness and overall geometry on the low-bias transfer characteristics of GKT transistors and benchmark against experimental data. We find that geometry plays a critical role in determining the performance of Electron Optics based devices that utilize angular resolution of Electrons.
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high efficiency switching using graphene based Electron Optics
Applied Physics Letters, 2011Co-Authors: Redwan N Sajjad, Avik W GhoshAbstract:We demonstrate a way to open a gate-tunable transmission gap across graphene p-n junction by introducing an additional barrier in the middle that replaces Klein tunneling with regular tunneling, allowing us to modulate current by several orders of magnitude. The gap arises by angularly sorting Electrons by their longitudinal energy and filtering out the hottest, normally incident Electrons with the tunnel barrier, and the rest through total internal reflection. Using analytical and atomistic numerical studies, we show that the barrier causes graphene p-n junction act as a metamaterial with metal-insulator transition and overcome the KTln10/decade limit for subthreshold conduction.
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high efficiency switching using graphene based Electron Optics
arXiv: Mesoscale and Nanoscale Physics, 2011Co-Authors: Redwan N Sajjad, Avik W GhoshAbstract:The absence of a band-gap in graphene limits the gate modulation of its Electron conductivity, both in regular graphene as well as in PN junctions, where electrostatic barriers prove transparent to Klein tunneling. We demonstrate a novel way to directly open a gate-tunable transmission gap across graphene PN junctions (GPNJ) by introducing an additional barrier in the middle that replaces Klein tunneling with regular tunneling, allowing us to electrostatically modulate the current by several orders of magnitude. The gap arises by angularly sorting Electrons by their longitudinal energy and filtering out the hottest, normally incident Electrons with the tunnel barrier, and the rest through total internal reflection. Using analytical and atomistic numerical studies of quantum transport, we show that the complete filtering of all incident Electrons causes the GPNJ to act as a novel metamaterial with a unique gate-tunable transmission-gap that generates a sharp non-thermal switching of Electrons. In fact, the transmission gap gradually diminishes to zero as we electrostatically reduce the voltage gradient across the junction towards the homogeneous doping limit. The resulting gate tunable metal-insulator transition enables the Electrons to overcome the classic room temperature switching limit of kTln10/q = 60mV/decade for subthreshold conduction.