A5005262381- Advanced Electron Microscopy Techniques and Applications
- Electron and X-Ray Spectroscopy Techniques
- Integrated Circuits and Semiconductor Failure Analysis
- Magnetic properties of thin films
- Magnetic Properties of Alloys
- Physics of Superconductivity and Magnetism
- Surface and Thin Film Phenomena
- Quantum and electron transport phenomena
- Semiconductor materials and devices
- Magnetic and transport properties of perovskites and related materials
- Characterization and Applications of Magnetic Nanoparticles
- Semiconductor materials and interfaces
- Machine Learning in Materials Science
- Geomagnetism and Paleomagnetism Studies
- Advanced Condensed Matter Physics
- Metallurgical Processes and Thermodynamics
- 2D Materials and Applications
- Iron-based superconductors research
- Chalcogenide Semiconductor Thin Films
- Advanced Thermoelectric Materials and Devices
- Phase-change materials and chalcogenides
- Geological and Geochemical Analysis
- Perovskite Materials and Applications
- Ion-surface interactions and analysis
- Copper-based nanomaterials and applications
University of Cambridge
2007-2025
Imperial College London
2008-2014
Technical University of Denmark
2009
Magnetic skyrmions are topologically nontrivial particles with a potential application as information elements in future spintronic device architectures. While they commonly portrayed two dimensional objects, reality magnetic thought to exist elongated, tube-like objects extending through the thickness of sample. Study this skyrmion tube (SkT) state is highly relevant for investigating metastability and implementation recently proposed magnonic computing. However, direct experimental imaging...
The intense research effort investigating magnetic skyrmions and their applications for spintronics has yielded reports of more exotic objects including the biskyrmion, which consists a bound pair counter-rotating vortices magnetization. Biskyrmions have been identified only from transmission electron microscopy images not observed by other techniques, nor seen in simulations carried out under realistic conditions. Here, quantitative Lorentz microscopy, X-ray holography, micromagnetic are...
Semiconductor device structures are becoming increasingly three-dimensional at the nanometer scale. A key issue that must be addressed to enable future development is mapping of dopant distributions, ideally under "working conditions". Here we demonstrate how a combination electron holography and tomography can used determine quantitatively electrostatic potential in an electrically biased semiconductor with spatial resolution.
2D hybrid organic-inorganic perovskites (2D HOIPs) are of interest for optoelectronic and phase-change applications. Using ultra-fast (flash) differential scanning calorimetry (FDSC), this study shows the HOIPs (S-Cl-MBA)2PbI4 (R-Cl-MBA)2PbBr4 (Cl-MBA referring to 4-chloro-α-methylbenzylamine) form a glass on cooling. Both show evidence liquid-to-glass transition during quenching from liquid state; reheating, glass-to-liquid is followed by crystallization melting. continuous heating in FDSC,...
We compare the magnetism of single crystals intercalated transition metal dichalcogenides ${\mathrm{Cr}}_{1/3}\mathrm{Nb}{\mathrm{S}}_{2}$ and ${\mathrm{Mn}}_{1/3}\mathrm{Nb}{\mathrm{S}}_{2}$ using techniques such as dc ac susceptibility Lorentz transmission electron microscopy (LTEM). present a detailed structural investigation these materials single-crystal x-ray diffraction measurements to show how substitutional disorder stacking faults can manifest in...
Summary Focused Ion beam (FIB) prepared GaAs p‐n junctions have been examined using off‐axis electron holography. Initial analysis of the holograms reveals an experimentally determined built‐in potential in that is significantly smaller than predicted from theory. In this paper we show through combinations situ annealing and biasing specimens, by varying intensity incident beam, modifying FIB operating parameters, can develop improved understanding phenomena such as electrically ‘inactive’...
Electron beam irradiation is shown to significantly influence phase images recorded from focused ion milled GaAs p-n junction specimens examined using off-axis electron holography in the transmission microscope. Our results show that use of improved electrical connections specimen overcomes this problem, and may allow correct built potential across be recovered.
We report small angle X-ray scattering (SAXS) measurements of the skyrmion lattice in two 200~nm thick Cu$_2$OSeO$_3$ lamellae aligned with applied magnetic field parallel to out plane [110] or [100] crystallographic directions. Our show that equilibrium phase both samples is expanded significantly compared bulk crystals, existing between approximately 30 and 50~K over a wide region field. This state elliptically distorted at low fields for sample, symmetric possibly due crystalline...
Skyrmion-based devices have been proposed as a promising solution for low-energy data storage. These include racetrack or logic structures and require skyrmions to be confined in regions with dimensions comparable the size of single skyrmion. Here we examine FeGe device shapes using Lorentz transmission electron microscopy reveal consequences skyrmion confinement device-like structure. Dumbbell-shaped elements were created by focused ion beam milling provide where are adjacent areas...
Abstract The need to determine the electrical properties of semiconductor junctions with high spatial resolution is as pressing now ever. One technique that offers possibility quantitative high‐resolution mapping two‐ and three‐dimensional electrostatic potential distributions off‐axis electron holography. In this study, we review some issues associated interpreting phase shifts measured using holography, describe how a determination dopant‐related can be achieved for device structures....
We report the results of muon-spin relaxation and magnetometry investigations bulk ${\mathrm{Mn}}_{1.4}{\mathrm{Pt}}_{0.9}{\mathrm{Pd}}_{0.1}\mathrm{Sn}$ MnNiGa, two materials that have been proposed to host topological magnetic states in thin lamellae (antiskyrmions for biskyrmions MnNiGa), show spin reorientation transitions bulk. Our measurements reveal dynamic fluctuations surrounding phase each material. In particular, we demonstrate behavior approaching higher-temperature reflects a...
Abstract After the publication of “Direct formation hard‐magnetic tetrataenite in bulk alloy castings” Ivanov et al., Advanced Science 10 (2022) 2204315, authors identified a potential misinterpretation experimental data. Further work confirms that original conclusions cannot be supported, and accordingly paper is retracted. X‐ray diffraction shows presence (Fe,Ni) 3 P, giving additional Bragg peaks were previously attributed to tetrataenite. Extra reflections observed transmission electron...
Off‐axis electron holography has been used to characterise the dopant potential in GaAs p‐n junctions. We show that measured across junctions is affected by both FIB specimen preparation and charging TEM suggest methods can be minimise these problems.
We report scanning transmission X-ray microscopy of mixed helical and skyrmion magnetic states in thin FeGe lamellae. This imaging the out-of-plane magnetism allows clear identification different states, reveals details about coexistence states. In particular, our data show that finite length helices are continuously deformable down to size individual skyrmions hence topologically equivalent skyrmions. Furthermore, we observe transition between across thickness lamella evidence for frozen...