Theoretical and Experimental Investigation of 2D Hematite

Abstract

Novel two-dimensional non-van der Waals materials have been reported, boosting efforts to probe their properties and identify key applications. In this work, we report the synthesis, by means of a novel route via sonication of synthetic hematite, and characterization by transmission electron and atomic force microscopy of samples composed of two-dimensional hematite ([001]-cut layered α-Fe2O3). Microscopy images show a layered material with a handful of possible crystalline orientations, of which the [001] is the most abundant, presenting thickness of up to approximately 100 nm. Next, we employed first-principles calculations to study their structural stability and evaluate their thickness distribution. The stability of single, double, and triple layered structures is confirmed by phonon spectra and the formation energy is obtained, pointing out to the possibility of few layers, freestanding, stable samples. Further statistical modeling suggests that even though such thin samples are stable, their abundance is very small in comparison to thicker layers. We show that the antiferromagnetic ordering of the bulk phase is preserved in the nanostructured material, from the double-layered sample onward; however, a nonzero magnetization arises due to distinct localized moments in surface Fe atoms. Finally, our calculated band structures present narrower gaps in the layered structures in comparison to the bulk, and a charge-trapping acceptor level is identified at the surface Fe atoms.

Exfoliation of hematite: Morphological, structural and magnetic investigations

“…The overall yield of lamellae in the exfoliation process is roughly estimated from our data to lie in the range of one part in 10 3 to one part in 10 4 , and the yield of scarce hematene lamellae with a thicknesses of less than a nanometer may be a factor of 10 less, in agreement with recent modelling [18].…”

Multiferroic Decorated Fe2O3 Monolayer Predicted from First Principles

“…S1 (f) [20], which is consistent with recent experiments [14]. The ferrimagnetic ground state also has been confirmed by recent theoretical and experimental works [21]. Pure Fe 2 O 3 monolayer possesses the C 2h structural symmetry, which renders same electron distributions on Fe atoms at the upper and lower surfaces (Fe2 and Fe4), and the whole system thus has zero out-of-plane electric polarization.…”

Hematite at its thinnest limit

“…They also attempted to support the experimental results by a DFT study, however, they considered only on a monolayer structure, which was not present in experiment at all. In the meantime, 2D α-Fe 2 O 3 (named hematene) was reported in experimental and in DFT-based study as a stable anti-ferromagnetic semiconductor, 47,48 same as bulk, which further clouds the conclusions regarding thickness dependence of the magnetic properties of hematite in its thinnest limit.…”

“…6(a), which agrees with the earlier results in literature. 47,48 Basically, magnetization of Fe atoms in the hexagonal buckled sublayers are parallel. The sublayers have antiparallel magnetization with respect to each other.…”