Electronic Band Structure Changes across the Antiferromagnetic Phase Transition of Exfoliated MnPS3 Flakes Probed by μ-ARPES

Exfoliated magnetic 2D materials enable versatile tuning of magnetization, e.g., by gating or providing proximity-induced exchange interaction. However, their electronic band structure after exfoliation has not been probed, presumably due to their photochemical sensitivity. Here, we provide micrometer-scale angle-resolved photoelectron spectroscopy of the exfoliated intralayer antiferromagnet MnPS3 above and below the Néel temperature down to one monolayer. Favorable comparison with density functional theory calculations enables identifying the orbital character of the observed bands. Consistently, we find pronounced changes across the Néel temperature for bands consisting of Mn 3d and 3p levels of adjacent S atoms. The deduced orbital mixture indicates that the superexchange is relevant for the magnetic interaction. There are only minor changes between monolayer and thicker films, demonstrating the predominant 2D character of MnPS3. The novel access is transferable to other MPX3 materials (M: transition metal, P: phosphorus, X: chalcogenide), providing several antiferromagnetic arrangements

Raman imaging of twist angle variations in twisted bilayer graphene at intermediate angles

Van der Waals layered materials with well-defined twist angles between the crystal lattices of individual layers have attracted increasing attention due to the emergence of unexpected material properties. As many properties critically depend on the exact twist angle and its spatial homogeneity, there is a need for a fast and non-invasive characterization technique of the local twist angle, to be applied preferably right after stacking. We demonstrate that confocal Raman spectroscopy can be utilized to spatially map the twist angle in stacked bilayer graphene for angles between 6.5 and 8 degree when using a green excitation laser. The twist angles can directly be extracted from the moiré superlattice-activated Raman scattering process of the transverse acoustic (TA) phonon mode. Furthermore, we show that the width of the TA Raman peak contains valuable information on spatial twist angle variations on length scales below the laser spot size of ∼500 nm

Voluntary carbon offsetting schemes for aviation : efficiency and dredibility

International audienc

Voluntary carbon offsetting schemes for aviation: efficiency, credibility and sustainable tourism

Tourism is becoming increasingly dependent on air transport. Recent scientific work has pointed out the significant and growing contribution of air transport to greenhouse gas (GHG) emissions. Obligations to reduce GHG emissions under the Kyoto Protocol and post-Kyoto instruments might make transport more expensive or even restricted in the future. This paper examines these questions and the issues raised by the increasing number of organisations offering voluntary carbon offsetting schemes as a means of compensating for emissions of GHGs, mostly from transport, which could help to stabilise or reduce emissions. There are substantial differences between the approaches chosen by these organisations in terms of their calculation of emissions, compensation measures, price levels, company structures and evaluation processes. The paper discusses these differences and their consequences for the efficiency and credibility of voluntary carbon offsetting schemes. Within this increasingly contested area, there is general agreement that increased clarity and regulation is required