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Low energy electron imaging of domains and domain walls in magnesium-doped lithium niobate

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ABSTRACT

The understanding of domain structures, specifically domain walls, currently attracts a significant attention in the field of (multi)-ferroic materials. In this article, we analyze contrast formation in full field electron microscopy applied to domains and domain walls in the uniaxial ferroelectric lithium niobate, which presents a large 3.8 eV band gap and for which conductive domain walls have been reported. We show that the transition from Mirror Electron Microscopy (MEM – electrons reflected) to Low Energy Electron Microscopy (LEEM – electrons backscattered) gives rise to a robust contrast between domains with upwards (Pup) and downwards (Pdown) polarization, and provides a measure of the difference in surface potential between the domains. We demonstrate that out-of-focus conditions of imaging produce contrast inversion, due to image distortion induced by charged surfaces, and also carry information on the polarization direction in the domains. Finally, we show that the intensity profile at domain walls provides experimental evidence for a local stray, lateral electric field.

No MeSH data available.


(a) Intensity profile in MEM (SV = 1.15 V) and LEEM (SV = 1.90 V). (b) Surface potential profile across a domain wall determined from the MEM-LEEM curves for over- and under-focus values.
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f7: (a) Intensity profile in MEM (SV = 1.15 V) and LEEM (SV = 1.90 V). (b) Surface potential profile across a domain wall determined from the MEM-LEEM curves for over- and under-focus values.

Mentions: In MEM, domain walls appear as successive bright and dark lines extending over 2 μm, two orders of magnitude higher than the spatial resolution. This clearly indicates that local field effects dominate in the electron image of the wall. The intensity profiles extracted across a domain wall within the blue rectangles on Fig. 3(a,c) are shown in Fig. 7(a). The maxima of the intensity correspond to the bright lines in the image while the minima correspond to the dark lines. The latter are on the Pdown side of the domain wall while the bright lines are on the Pup side. In LEEM (Fig. 3(c)), the dark/bright order across the domain wall is the same as in MEM whereas the domain contrast inverts with SV.


Low energy electron imaging of domains and domain walls in magnesium-doped lithium niobate
(a) Intensity profile in MEM (SV = 1.15 V) and LEEM (SV = 1.90 V). (b) Surface potential profile across a domain wall determined from the MEM-LEEM curves for over- and under-focus values.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC5016809&req=5

f7: (a) Intensity profile in MEM (SV = 1.15 V) and LEEM (SV = 1.90 V). (b) Surface potential profile across a domain wall determined from the MEM-LEEM curves for over- and under-focus values.
Mentions: In MEM, domain walls appear as successive bright and dark lines extending over 2 μm, two orders of magnitude higher than the spatial resolution. This clearly indicates that local field effects dominate in the electron image of the wall. The intensity profiles extracted across a domain wall within the blue rectangles on Fig. 3(a,c) are shown in Fig. 7(a). The maxima of the intensity correspond to the bright lines in the image while the minima correspond to the dark lines. The latter are on the Pdown side of the domain wall while the bright lines are on the Pup side. In LEEM (Fig. 3(c)), the dark/bright order across the domain wall is the same as in MEM whereas the domain contrast inverts with SV.

View Article: PubMed Central - PubMed

ABSTRACT

The understanding of domain structures, specifically domain walls, currently attracts a significant attention in the field of (multi)-ferroic materials. In this article, we analyze contrast formation in full field electron microscopy applied to domains and domain walls in the uniaxial ferroelectric lithium niobate, which presents a large 3.8 eV band gap and for which conductive domain walls have been reported. We show that the transition from Mirror Electron Microscopy (MEM – electrons reflected) to Low Energy Electron Microscopy (LEEM – electrons backscattered) gives rise to a robust contrast between domains with upwards (Pup) and downwards (Pdown) polarization, and provides a measure of the difference in surface potential between the domains. We demonstrate that out-of-focus conditions of imaging produce contrast inversion, due to image distortion induced by charged surfaces, and also carry information on the polarization direction in the domains. Finally, we show that the intensity profile at domain walls provides experimental evidence for a local stray, lateral electric field.

No MeSH data available.