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Detection of electron vortex beams: Using a scanning transmission electron microscope
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
2015 (English)Independent thesis Basic level (degree of Bachelor), 10 credits / 15 HE creditsStudent thesis
Abstract [en]

Electron vortex beams (EVBs) are electron beams with a doughnut-like intensity profile, carrying orbital angular momentum due to their helical phase shift distribution. When employed in an electron microscope, they are expected to be efficient for the detection of magnetic signals. In this report I have investigated high angle annular dark field (HAADF) images obtained using EVBs. This was done for 300 K and 5K. For 5 K,  I also compared HAADF images from an ordinary electron beam with HAADF images from an electron vortex beam.

What was found was that EVBs produced doughnuts around the atomic columns. However, when taking the size of the electron source into account, this phenomena could no longer  be observed. When comparing images from EVBs with images from ordinary electron beams, I found that the intensity of scattered electrons around atomic columns was broader for EVBs. This was persistent even after taking the source size into account.

Abstract [sv]

Elektronvirvelstrålar (EVS) är elektronstrålar med en munk-liknande intensitetsprofil. Dessa bär på rörelsemängdsmoment på grund av sin fasdistribution. När de används i ett elektronmikroskop förväntas de vara effektiva för detektering av magnetiska signaler. I denna uppsats har jag undersökt high angle annular dark field (HAADF) bilder som erhållits med hjälp av EVS. Detta gjordes för 300 K och 5K. För 5 K, jämförde jag även HAADF bilder från en vanlig elektronstråle med HAADF bilder från en elektronvirvelstråle.

Vad jag fann var att EVS producerade en munkformad intensitetsfördelning runt atomerna. Men när hänsyn till storleken på elektronkällan togs i beaktande kunde inte detta fenomen observeras längre. När bilder från EVS jämfördes med bilder från vanliga elektronstrålar, fann jag att intensiteten av spridda elektroner runt atomkolumnerna var bredare för EVS. Detta kunde observeras även efter att jag tagit hänsyn till elektronkällans storlek.

Place, publisher, year, edition, pages
2015. , 29 p.
Series
FYSAST, FYSKAND1033
Keyword [en]
microscopy, electron, vortex, beam, microscope, detection, detecting, doughnuts, microscopy, STEM, scanning, transsmision
Keyword [sv]
mikroskopi, elektronvirvelstråle, elektronvirvelstrålar, elektron, stråle, virvel, munk, munkar, elektrontransmissionsmikroskop, elektronmikroskop, transmissionsmikroskop, detektera, detektering
National Category
Condensed Matter Physics Other Natural Sciences
Identifiers
URN: urn:nbn:se:uu:diva-255330OAI: oai:DiVA.org:uu-255330DiVA: diva2:821838
Educational program
Bachelor Programme in Physics
Supervisors
Examiners
Available from: 2015-06-16 Created: 2015-06-15 Last updated: 2015-06-16Bibliographically approved

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André Löfgren(1527 kB)115 downloads
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