Layer-Dependent Mechanical Properties and Enhanced Plasticity in the Van der Waals Chromium Trihalide Magnets.

The mechanical properties of magnetic materials are instrumental for the development of magnetoelastic theories and the optimization of strain-modulated magnetic devices. In particular, two-dimensional (2D) magnets hold promise to enlarge these concepts into the realm of low-dimensional physics and ultrathin devices. However, no experimental study on the intrinsic mechanical properties of the archetypal 2D magnet family of the chromium trihalides has thus far been performed. Here, we report the room temperature layer-dependent mechanical properties of atomically thin CrCl3 and CrI3, finding that the bilayers have Young's moduli of 62.1 and 43.4 GPa, highest sustained strains of 6.49% and 6.09% and breaking strengths of 3.6 and 2.2 GPa, respectively. This portrays the outstanding plasticity of these materials that is qualitatively demonstrated in the bulk crystals. The current study will contribute to the applications of the 2D magnets in magnetostrictive and flexible devices.

Ionic Species in a Naphthalene Plasma: Understanding Fragmentation Patterns and Growth of PAHs.

The role of polycyclic aromatic hydrocarbons (PAHs) in the interstellar medium (ISM) is a key question in astrophysics. Moreover, our limited understanding of the plasma-driven processes of PAHs in the ISM motivates the present study on naphthalene as a model compound. In this work, a mass spectrometric characterization of the positive and negative ionic species in a naphthalene plasma was carried out. According to our findings, the main naphthalene dissociation channels upon electronic excitation proceed through hydrogen or acetylene loss. In addition, we report experimental evidence of the hydrogen abstraction-acetylene addition mechanism taking place under plasma conditions, which contributes to our understanding of the growth of PAHs. Regarding negative ions, species belonging to the astrochemically relevant family of polyynyl anions were detected, i.e., C4H- and C6H-. We postulate that the latter could be formed in a "top-down" chemistry as fragments of PAHs. Finally, our results show that negative ions add to neutral naphthalene molecules yielding larger anions, which suggests that negatively charged species may also play a role in the growth of PAHs.