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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.

Background School is a multi-cultural setting where students need social, material, physical, and mental resources to attain school achievement. But they are often lacking, especially for immigrant students. In an early adolescence context, this study assessed risk for school difficulties among European and non-European immigrants and the roles of socioeconomic characteristics, physical health, psychological health, social relationships, living environment, and unhealthy behaviours. Methods This cross-sectional study included 1,559 middle-school adolescents from north-eastern France, who completed a self-administered questionnaire including socioeconomic characteristics (gender, age, family structure, father’s occupation, and family income), WHO-Quality of life (measuring the four dimensions physical health, psychological health, social relationships, and living environment), unhealthy behaviours (last-30-day uses of tobacco, alcohol, cannabis, and other illicit drugs and no regular sports/physical activities), grade repetition, low school performance ( Results Grade repetition affected 14.8% of students, low school performance 8.2%, and school dropout ideation 3.9%. European immigrants had a higher risk for grade repetition only with a gender-age-adjusted odds ratio (OR) of 2.44, vs. French students. This odds ratio decreased to 1.76 (contribution 47%) with further adjustment for all confounders (family structure, father’s occupation, family income, physical health, psychological health, social relationships, living environment, and unhealthy behaviours). Non-European immigrants had a statistically higher risk for all grade repetition, low school performance, and school dropout ideation with ORs of 3.29, 3.02, and 3.42, respectively vs. French students. These odds ratios decreased to 1.76, 1.54, and 1.54, respectively (contributions 66%, 73%, and 78%) with further adjustment for all confounders. Conclusions Compared with French students, European immigrant students were more affected only by grade repetition while non-European immigrant students by all grade repetition, low school performance, and school dropout ideation. The contribution of socioeconomic characteristics, physical health, psychological health, social relationships, living environment, and unhealthy behaviours was very high and much higher for non-European than for European immigrant students. Public policy should focus on these factors and services to reduce school difficulties.