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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.

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Surface potential maps for two focus values.(a) 1308 mA (b) 1321 mA.
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f6: Surface potential maps for two focus values.(a) 1308 mA (b) 1321 mA.

Mentions: Although the focus value changes the intensity contrast between domains, it does not influence the MEM-LEEM transition. This can be checked by recording image series as a function of SV in both under-focusing and over-focusing conditions. The value of the surface potential for each pixel is then determined by a fit of a complementary error function to the MEM-LEEM curve. The maps of the surface potential over the full field of view are shown in Fig. 6. The surface potential is always lower in Pup domains with respect to Pdown by ~100 mV, irrespective of the focus value, although the absolute surface potential may shift. This makes the measurement of the surface potential difference between Pup and Pdown robust against slight (here about 1%) defocusing.


Low energy electron imaging of domains and domain walls in magnesium-doped lithium niobate
Surface potential maps for two focus values.(a) 1308 mA (b) 1321 mA.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

f6: Surface potential maps for two focus values.(a) 1308 mA (b) 1321 mA.
Mentions: Although the focus value changes the intensity contrast between domains, it does not influence the MEM-LEEM transition. This can be checked by recording image series as a function of SV in both under-focusing and over-focusing conditions. The value of the surface potential for each pixel is then determined by a fit of a complementary error function to the MEM-LEEM curve. The maps of the surface potential over the full field of view are shown in Fig. 6. The surface potential is always lower in Pup domains with respect to Pdown by ~100 mV, irrespective of the focus value, although the absolute surface potential may shift. This makes the measurement of the surface potential difference between Pup and Pdown robust against slight (here about 1%) defocusing.

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.


Related in: MedlinePlus