Robust Phonon-Plasmon Coupling in Quasifreestanding Graphene on Silicon Carbide.

Using inelastic electron scattering in combination with dielectric theory simulations on differently prepared graphene layers on silicon carbide, we demonstrate that the coupling between the 2D plasmon of graphene and the surface optical phonon of the substrate cannot be quenched by modification of the interface via intercalation. The intercalation rather provides additional modes like, e.g., the silicon-hydrogen stretch mode in the case of hydrogen intercalation or the silicon-oxygen vibrations for water intercalation that couple to the 2D plasmons of graphene. Furthermore, in the case of bilayer graphene with broken inversion symmetry due to charge imbalance between the layers, we observe a similar coupling of the 2D plasmon to an internal infrared-active mode, the LO phonon mode. The coupling of graphene plasmons to vibrational modes of the substrate surface and internal infrared active modes is envisioned to provide an excellent tool for tailoring the plasmon band structure of monolayer and bilayer graphene for plasmonic devices such as plasmon filters or plasmonic waveguides. The rigidity of the effect furthermore suggests that it may be of importance for other 2D materials as well.

Neurotoxicity evaluation of rats after subchronic inhalation exposure to isobutanol.

The subchronic neurotoxic effects of isobutanol were studied by exposing Sprague-Dawley rats to isobutanol vapor concentrations of 0, 250, 1000, and 2500 ppm for 6 hrs/day, 5 days/wk, for 3 months. A comprehensive set of neurotoxicity tests (functional observational battery, motor activity, perfusion fixation neuropathology, and schedule-controlled operant behavior) including an assessment of complex behavior dependent on learning and memory was conducted. In addition, full histopathology and blood chemistry evaluations were conducted in order to assess any potential functional/behavioral effects in the context of other possible systemic toxicities. There were no morphological or behavioral effects indicative of a specific, persistent or progressive effect of isobutanol on the nervous system at exposure concentrations up to 2500 ppm. A slight decrease in response to external stimuli was observed during exposures at all concentrations. These effects are likely transient effects of acute exposure to isobutanol.