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

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.


(a) PFM-phase image of the sample where −200 V was applied. (b) PFM-phase profile extracted along the blue line on the PFM-phase image. (c) PFM-amplitude image of the same area. (d) PFM-amplitude profile extracted along the blue line. The position of the domain walls are indicated by dotted lines.
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f2: (a) PFM-phase image of the sample where −200 V was applied. (b) PFM-phase profile extracted along the blue line on the PFM-phase image. (c) PFM-amplitude image of the same area. (d) PFM-amplitude profile extracted along the blue line. The position of the domain walls are indicated by dotted lines.

Mentions: In order to confirm the assignment of up/down polarization, we applied −200 V to the PFM tip to locally reverse the polarization of the surface. Figure 2(a) shows the PFM-phase image after poling. The dark domain does not change, whereas poling reverses part of the initially bright domain. Hence, in Fig. 2(a) the bright areas correspond to Pdown and the darker areas to Pup. Figure 2(b) plots the phase profile along Pdown – Pup – Pdown, showing the characteristic PFM-phase of each domain. Figure 2(c) shows the out of plane component of the PFM-amplitude signal, proportional to the piezo-response. It can be seen that at each domain wall the amplitude is minimum, as expected for a 180° domain wall separating Pup and Pdown domains.


Low energy electron imaging of domains and domain walls in magnesium-doped lithium niobate
(a) PFM-phase image of the sample where −200 V was applied. (b) PFM-phase profile extracted along the blue line on the PFM-phase image. (c) PFM-amplitude image of the same area. (d) PFM-amplitude profile extracted along the blue line. The position of the domain walls are indicated by dotted lines.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

f2: (a) PFM-phase image of the sample where −200 V was applied. (b) PFM-phase profile extracted along the blue line on the PFM-phase image. (c) PFM-amplitude image of the same area. (d) PFM-amplitude profile extracted along the blue line. The position of the domain walls are indicated by dotted lines.
Mentions: In order to confirm the assignment of up/down polarization, we applied −200 V to the PFM tip to locally reverse the polarization of the surface. Figure 2(a) shows the PFM-phase image after poling. The dark domain does not change, whereas poling reverses part of the initially bright domain. Hence, in Fig. 2(a) the bright areas correspond to Pdown and the darker areas to Pup. Figure 2(b) plots the phase profile along Pdown – Pup – Pdown, showing the characteristic PFM-phase of each domain. Figure 2(c) shows the out of plane component of the PFM-amplitude signal, proportional to the piezo-response. It can be seen that at each domain wall the amplitude is minimum, as expected for a 180° domain wall separating Pup and Pdown domains.

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.