49 research outputs found
Pixelated detectors and improved efficiency for magnetic imaging in STEM differential phase contrast
The application of differential phase contrast imaging to the study of polycrystalline magnetic thin films and nanostructures has been hampered by the strong diffraction contrast resulting from the granular structure of the materials. In this paper we demonstrate how a pixelated detector has been used to detect the bright field disk in aberration corrected scanning transmission electron microscopy (STEM) and subsequent processing of the acquired data allows efficient enhancement of the magnetic contrast in the resulting images. Initial results from a charged coupled device (CCD) camera demonstrate the highly efficient nature of this improvement over previous methods. Further hardware development with the use of a direct radiation detector, the Medipix3, also shows the possibilities where the reduction in collection time is more than an order of magnitude compared to the CCD. We show that this allows subpixel measurement of the beam deflection due to the magnetic induction. While the detection and processing is data intensive we have demonstrated highly efficient DPC imaging whereby pixel by pixel interpretation of the induction variation is realised with great potential for nanomagnetic imaging
Sub-100 nanosecond temporally resolved imaging with the Medipix3 direct electron detector
Detector developments are currently enabling new capabilities in the field of
transmission electron microscopy (TEM). We have investigated the limits of a
hybrid pixel detector, Medipix3, to record dynamic, time varying, electron
signals. Operating with an energy of 60keV, we have utilised electrostatic
deflection to oscillate electron beam position on the detector. Adopting a
pump-probe imaging strategy we have demonstrated that temporal resolutions
three orders of magnitude smaller than are available for typically used TEM
imaging detectors are possible. Our experiments have shown that energy
deposition of the primary electrons in the hybrid pixel detector limits the
overall temporal resolution. Through adjustment of user specifiable thresholds
or the use of charge summing mode, we have obtained images composed from
summing 10,000s frames containing single electron events to achieve temporal
resolution less than 100ns. We propose that this capability can be directly
applied to studying repeatable material dynamic processes but also to implement
low-dose imaging schemes in scanning transmission electron microscopy.Comment: 11 pages, 6 figures; improve ref formatting + revise tex
Magnetic microscopy of topologically protected homochiral domain walls in an ultrathin perpendicularly magnetized Co film
Next-generation concepts for solid-state memory devices are based on
current-driven domain wall propagation, where the wall velocity governs the
device performance. It has been shown that the domain wall velocity and the
direction of travel is controlled by the nature of the wall and its chirality.
This chirality is attributed to effects emerging from the lack of inversion
symmetry at the interface between a ferromagnet and a heavy metal, leading to
an interfacial Dzyaloshinskii-Moriya interaction that can control the shape and
chirality of the magnetic domain wall. Here we present direct imaging of domain
walls in Pt/Co/AlO films using Lorentz transmission electron microscopy,
demonstrating the presence of homochiral, and thus topologically protected,
N\'{e}el walls. Such domain walls are good candidates for dense data storage,
bringing the bit size down close to the limit of the domain wall width
Indentation-Induced Damage Mechanisms in Germanium
The response of crystalline Ge to indentation has been studied over a range of maximum loads. At a certain load, an unusual 'giant pop-in' event occurs, in which a discontinuous extension of >1 μm is observed in the force-displacement curve. In such cas
Focused Electron-Beam Induced Deposition, In Situ TEM And Off-Axis Electron Holography Investigation of Bi-Magnetic Core-Shell Nanostructures
No abstract available
Ultrafast Imaging of Plasmons in a Transmission Electron Microscope
Miniaturized plasmonic and photonic integrated circuits are generally considered as the core of future generations of optoelectronic devices, due to their potential to bridge the size-compatibility gap between photonics and electronics. However, as the nanoscale is approached in increasingly small plasmonic and photonic systems, experimentally observing their behavior involves ever more stringent requirements in terms of both temporal and spatial resolution. This talk focuses on the use of time-resolved Photon-Induced Near-Field Electron Microscopy (PINEM) to study the excitation, propagation, (self-)interference and dynamics of surface plasmon polaritons (SPPs) in various plasmonic nanostructures with both nanometer and ultrafast resolution in a transmission electron microscope. Using this field-ofview technique, we directly show how photo-excited plasmonic interference patterns are controlled through the combination of excitation polarization and nanostructure geometry. Moreover, we capture the propagation of the photoinduced self-interfering plasmonic wave, clearly demonstrating the effects of axial confinement in nanostructured plasmonic thin film stacks
Differential Phase Contrast Imaging of the Magnetostructural Transition and Phase Boundary Motion in Uniform and Gradient-doped FeRh-based Thin Films
No abstract available
Quantitative Differential Phase Contrast Imaging of the Magnetostructural Transition and Current-driven Motion of Domain Walls in FeRh Thin Films
No abstract available
Effect of annealing on the magnetic states of FEBID-grown cobalt nanopatterns examined by off-axis electron holography
The growth of cobalt nanopatterns (NPs) using focused electron‐beam induced deposition (FEBID) for localised magnetic studies is presented. The initial FEBID products are shown to be polycrystalline and form hetero‐structured core‐shell NPs through surface oxidation. Off‐axis electron holography is performed to reconstruct their morphology, thickness profile and image their individual magnetic vortex domain states. In situ annealing to 400°C promoted migration of the Co‐overspray to grow the Co NPs and improved their crystallinity through coarsening, as well as induced diffusion of embedded carbon out of their surface. It is found that the change in their morphology and chemical instability under heating restricts their suitability for examining thermally induced magnetic variations
Quantifying the Performance of a Hybrid Pixel Detector with GaAs:Cr Sensor for Transmission Electron Microscopy
Hybrid pixel detectors (HPDs) have been shown to be highly effective for
diffraction-based and time-resolved studies in transmission electron
microscopy, but their performance is limited by the fact that high-energy
electrons scatter over long distances in their thick Si sensors. An advantage
of HPDs compared to monolithic active pixel sensors (MAPS) is that their sensor
does not need to be fabricated from Si. We have compared the performance of the
Medipix3 HPD with a Si sensor and with a GaAs:Cr sensor using primary electrons
in the energy range of 60 - 300keV. We describe the measurement and calculation
of the detectors' modulation transfer function (MTF) and detective quantum
efficiency (DQE), which show that the performance of the GaAs:Cr device is
markedly superior to that of the Si device for high-energy electrons.Comment: 15 pages + references, 13 figure