Vibrational Modes of C_<60> Fullerene Adsorbed on Si(100)2×1 Surface Studied by High-Resolution Electron-Energy-Loss Spectroscopy

We have measured the inelastic electron-energy-loss spectra of C_ on the Si(100)2x1 surface in the infra-red energy range. If C_ is evaporated 5Å (approximately half a monolayer) on Si(100), a strong energy loss peak appears at 65 meV, and weak peaks and shoulders at 72, 144, and 175 meV. In the 12Å thick film, additional weak peaks at 96, 160, and 189 meV become more apparent. Intensities of these peaks are comparable to those of thick films measured by infra-red absorption and by Raman scattering spectroscopies. Moreover, we have measured the angle dependence of the inelastic electron intensity. These results suggest appreciable interactions between C_ and the dangling bonds of Si surface

Search for dark matter produced in association with bottom or top quarks in √s = 13 TeV pp collisions with the ATLAS detector

A search for weakly interacting massive particle dark matter produced in association with bottom or top quarks is presented. Final states containing third-generation quarks and miss- ing transverse momentum are considered. The analysis uses 36.1 fb−1 of proton–proton collision data recorded by the ATLAS experiment at √s = 13 TeV in 2015 and 2016. No significant excess of events above the estimated backgrounds is observed. The results are in- terpreted in the framework of simplified models of spin-0 dark-matter mediators. For colour- neutral spin-0 mediators produced in association with top quarks and decaying into a pair of dark-matter particles, mediator masses below 50 GeV are excluded assuming a dark-matter candidate mass of 1 GeV and unitary couplings. For scalar and pseudoscalar mediators produced in association with bottom quarks, the search sets limits on the production cross- section of 300 times the predicted rate for mediators with masses between 10 and 50 GeV and assuming a dark-matter mass of 1 GeV and unitary coupling. Constraints on colour- charged scalar simplified models are also presented. Assuming a dark-matter particle mass of 35 GeV, mediator particles with mass below 1.1 TeV are excluded for couplings yielding a dark-matter relic density consistent with measurements