13 research outputs found
Isoreticular two-dimensional magnetic coordination polymers prepared through pre-synthetic ligand functionalization
Chemical functionalization is a powerful approach to tailor the physical and chemical properties of two-dimensional materials, increase their processability and stability, tune their functionalities and, even, create new 2D materials. This is typically achieved through post-synthetic functionalization by anchoring molecules on the surface of an exfoliated 2D crystal, but it inevitably alters the long-range structural order of the material. Here we present a pre-synthetic approach that allows the isolation of crystalline, robust, and magnetic functionalized monolayers of coordination polymers. A series of five isoreticular layered magnetic coordination polymers based on Fe(II) centres and different benzimidazole derivatives (bearing a Cl, H, CH3, Br or NH2 side group) were first prepared. On mechanical exfoliation, 2D materials are obtained that retain their long-range structural order and exhibit good mechanical and magnetic properties. This combination, together with the possibility to functionalize their surface at will, makes them good candidates to explore magnetism in the 2D limit and to fabricate mechanical resonators for selective gas sensing
Measurement of the ttÂŻ production cross-section using eÎŒ events with b-tagged jets in pp collisions at âs=7 and 8 TeV with the ATLAS detector
The inclusive top quark pair (ttÂŻttÂŻ) production cross-section ÏttÂŻÏttÂŻ has been measured in protonâproton collisions at sâ=7 TeVs=7 TeV and sâ=8 TeVs=8 TeV with the ATLAS experiment at the LHC, using ttÂŻttÂŻ events with an opposite-charge eÎŒeÎŒ pair in the final state. The measurement was performed with the 2011 7 TeV dataset corresponding to an integrated luminosity of 4.6 fbâ1fbâ1 and the 2012 8 TeV dataset of 20.3 fbâ1fbâ1. The numbers of events with exactly one and exactly two bb-tagged jets were counted and used to simultaneously determine ÏttÂŻÏttÂŻ and the efficiency to reconstruct and bb-tag a jet from a top quark decay, thereby minimising the associated systematic uncertainties. The cross-section was measured to be:
ÏttÂŻÏttÂŻ=182.9±3.1±4.2±3.6±3.3 pb (sâ=7 TeV)and=242.4±1.7±5.5±7.5±4.2 pb (sâ=8 TeV),
ÏttÂŻ=182.9±3.1±4.2±3.6±3.3 pb (s=7 TeV)andÏttÂŻ=242.4±1.7±5.5±7.5±4.2 pb (s=8 TeV),
where the four uncertainties arise from data statistics, experimental and theoretical systematic effects, knowledge of the integrated luminosity and of the LHC beam energy. The results are consistent with recent theoretical QCD calculations at next-to-next-to-leading order. Fiducial measurements corresponding to the experimental acceptance of the leptons are also reported, together with the ratio of cross-sections measured at the two centre-of-mass energies. The inclusive cross-section results were used to determine the top quark pole mass via the dependence of the theoretically predicted cross-section on mpoletmtpole giving a result of mpoletmtpole=172.9+2.5â2.6=172.9â2.6+2.5 GeV. By looking for an excess of ttÂŻttÂŻ production with respect to the QCD prediction, the results were also used to place limits on the pair-production of supersymmetric top squarks t~1t~1 with masses close to the top quark mass, decaying via t~1âtÏ~01t~1âtÏ~10 to predominantly right-handed top quarks and a light neutralino Ï~01Ï~10, the lightest supersymmetric particle. Top squarks with masses between the top quark mass and 177 GeV are excluded at the 95 % confidence level
Optical Controlled Terahertz Modulator Based on Tungsten Disulfide Nanosheet
© 2017 The Author(s). The terahertz (THz) modulator, which will be applied in next-generation wireless communication, is a key device in a THz communication system. Current THz modulators based on traditional semiconductors and metamaterials have limited modulation depth or modulation range. Therefore, a THz modulator based on annealed tungsten disulfide (WS2, p-type) and high-resistivity silicon (n-type) is demonstrated. Pumped by a laser, the modulator presents a laser power-dependent modulation effect. Ranging from 0.25 to 2 THz, the modulation depth reaches 99% when the pumping laser is 2.59 W/cm2. The modulator works because the p-n heterojunction can separate and limit carriers to change the conductivity of the device, which results in a modulation of the THz wave. The wide band gap of WS2 can promote the separation and limitation of carriers to obtain a larger modulation depth, which provides a new direction for choosing new materials and new structures to fabricate a better THz modulator