Observing the intrinsic linewidth of a quantum-cascade laser: beyond the Schawlow-Townes limit

A comprehensive investigation of the frequency-noise spectral density of a free-running mid-infrared quantum-cascade laser is presented for the first time. It provides direct evidence of the leveling of this noise down to a white noise plateau, corresponding to an intrinsic linewidth of a few hundred Hz. The experiment is in agreement with the most recent theory on the fundamental mechanism of line broadening in quantum-cascade lasers, which provides a new insight into the Schawlow-Townes formula and predicts a narrowing beyond the limit set by the radiative lifetime of the upper level.Comment: 4 pages, 4 figure

Towards the bisbenzothienocarbazole core: a route of sulfurated carbazole derivatives with assorted optoelectronic properties and applications

Ladder-type molecules, which possess an extended aromatic backbone, are particularly sought within the optoelectronic field. In view of the potential of the 14H-bis[1]benzothieno[3,2-b:2’,3’-h]carbazole core as a p-type semiconductor, herein we studied a set of two derivatives featuring a different alkylation patterning. The followed synthetic route, involving various sulfurated carbazole-based molecules, also resulted in a source of fluorophores with different emitting behaviors. Surprisingly, the sulfoxide-containing fluorophores substantially increased their blue fluorescence with respect to the nearly non-emitting sulfur counterparts. On this basis, we could shed light on the relationship between their chemical structure and their emission as an approach for future applications. Considering the performance in organic thin-film transistors, both bisbenzothienocarbazole derivatives displayed p-type characteristics, with hole mobility values up to 1.1 × 10-3 cm2 V-1 s-1 and considerable air stability. Moreover, the role of the structural design has been correlated with the device performance by means of X-ray analysis and the elucidation of the corresponding single crystal structures.This research was funded by the Ministerio de Economía, Indústria y Competitividad, grant number FUNMAT-PGC2018-095477-B-I00, and the Ministerio de Ciencia e Innovación, grant number PID2020-116719RB-C41.Peer ReviewedPostprint (published version

Potential signals of natural selection in the top risk loci for coronary artery disease: 9p21 and 10q11

Background: Coronary artery disease (CAD) is a complex disease and the leading cause of death in the world. Populations of different ancestry do not always share the same risk markers. Natural selective processes may be the cause of some of the population differences detected for specific risk mutations. Objective: In this study, 384 single nucleotide polymorphisms (SNPs) located in four genomic regions associated with CAD (1p13, 1q41, 9p21 and 10q11) are analysed in a set of 19 populations from Europe, Middle East and North Africa and also in Asian and African samples from the 1000 Genomes Project. The aim of this survey is to explore for the first time whether the genetic variability in these genomic regions is better explained by demography or by natural selection. Results: The results indicate significant differences in the structure of genetic variation and in the LD patterns among populations that probably explain the population disparities found in markers of susceptibility to CAD. Conclusions: The results are consistent with potential signature of positive selection in the 9p21 region and of balancing selection in the 9p21 and 10q11. Specifically, in Europe three CAD risk markers in the 9p21 region (rs9632884, rs1537371 and rs1333042) show consistent signals of positive selection. The results of this study are consistent with a potential selective role of CAD in the configuration of genetic diversity in current human populations

Self-trapping in B-doped amorphous Si: Intrinsic origin of low acceptor efficiency

We have used ab initio simulations to study the doping efficiency of amorphous semiconductors, in particular of B-doped amorphous Si. We have found that even in the optimum case of substitutional doping in dangling-bond free amorphous Si the holes provided by B atoms do not behave as free carriers. Instead, they are trapped into regions with locally distorted bond angles. Thus, the effective activation energy for hole conduction turns to be the hole binding energy to these traps. In the case of high B concentration, the trap states move deeper in the gap and the binding energy and spatial localization of holes increase. In addition, B atoms have lower energies for shorter bond lengths, configurations favored in the vicinity of these traps

New insights into the comprehension of the magnetic properties of dinuclear Mn(III) compounds with general formula [{MnL(NN)}2(μ-O)(μ-n-RC6H4COO)2]X2

Five new dinuclear Mn(III) compounds with benzoato derivative bridges [{Mn(bpy)L}2(μ-O)(μ-n-RC6H4COO)2]X2 (n-R = 3-MeO, 4-MeO and 4-tBu, X = NO3− and ClO4−) were synthesised and characterised. According to X-ray diffraction, the X anions tend to be coordinated to the Mn ions and may occupy the place of the monodentate ligand L. Two structural isomers that only differ in one of their monodentate ligands have been obtained with the 3-MeOC6H4COO− bridges. For all compounds, the Mn(III) ions display elongated octahedra with a pronounced rhombic distortion. To quantify these distortions separately, the elongation and rhombicity parameters Δ and ρ have been defined. The magnetic study shows a good relationship between the distortion of the coordination polyhedra and the zero field splitting parameters (DMn and EMn). From the magnetic data of a powder sample, it is possible to determine the sign and magnitude of DMn for ferromagnetic systems or weak antiferromagnetic systems with DMn < 0. For this kind of dinuclear compound, the R group at the meta position, the rhombic distortion of the octahedra, and large torsion angles between the Jahn-Teller axes lead to ferromagnetic interactions

Determination of ZFS parameters from the EPR spectra of mono-, di- and trinuclear MnII complexes: impact of magnetic coupling

A family of new MnII compounds, consisting of seven dinuclear, three mononuclear, and four trinuclear ones, were synthesised using benzoic acid derivatives n-RC6H4COOH, where n-R = 2-MeO, 3-MeO, 4-MeO, or 4-tBu, and 2,2′-bipyridine (bpy) or 1,10-phenantroline (phen) as blocking ligands. The crystal structures of nine of these compounds and the magnetic studies of all of them are reported here. Each type of compound was formed depending on the presence or absence of ClO4− ions, the solvent used, and/or the presence of a small amount of water in the reaction medium. The use of the tert-buthylbenzoate ligand gave unexpected results, very likely due to the steric hindrance caused by the voluminous tBu groups. The EPR spectra of each type of compound give some peculiar features that allow its identification. Attempts to fit these spectra have been made in order to determine the ZFS parameters, D and E, of the MnII ion (for mononuclear and dinuclear systems) or of the ground state (for trinuclear systems). For trinuclear systems, the single-ion ZFS parameters estimated from those of the ground state provided a good simulation of the EPR spectra of these compounds. The EPR signals observed in each case have been rationalised according to the energy level distribution and the plausible population in the excited states. In some particular situations, the sign of DMn could be determined from the fit of the EPR spectra of the antiferromagnetic dinuclear compounds, the source of the difference between the spectra lying in the second excited state

Biomimetic Mn-catalases based on dimeric manganese complexes in mesoporous silica for potential antioxidant agent

Two new structural and functional models of the Mn-catalase with formula [{MnIII(bpy)(H2O)}(μ-2-MeOC6H4CO2)2(μ-O){MnIII(bpy)(X)}]X, where X = NO3 (1) and ClO4 (2) and bpy = 2,2′-bipyridine, were synthesized and characterized by X-ray diffraction. In both cases, a water molecule and an X ion occupy the monodentate positions. The magnetic properties of these compounds reveal a weak antiferromagnetic behavior (2J = −2.2 cm 1 for 1 and −0.7 cm 1 for 2, using the spin Hamiltonian H = −2J S1·S2) and negative zero-field splitting parameter DMn (−4.6 cm 1 and −3.0 cm 1 for 1 and 2, respectively). This fact, together with the nearly orthogonal orientation of the Jahn Teller axes of the MnIII ions explain the unusual shape of χMT versus T plot at low temperature. Compound 1 presents a better catalase activity than 2 in CH3CN H2O media, probably due to a beneficial interaction of the NO3− ion with the Mn complex in solution. These compounds were successfully inserted inside two-dimensional hexagonal mesoporous silica (MCM-41 type) leading to the same hybrid material ([Mn2O]@SiO2), without the X group. The manganese complex occupies approximately half of the available pore volume, keeping the silica's hexagonal array intact. Magnetic measurements of [Mn2O]@SiO2 suggest that most of the dinuclear unit is preserved, as a non-negligible interaction between Mn ions is still observed. The X-ray photoelectron spectroscopy analysis of the Mn 3s peak confirms that Mn remains as MnIII inside the silica. The catalase activity study of material [Mn2O]@SiO2 reveals that the complex is more active inside the porous silica, probably due to the surface silanolate groups of the pore wall. Moreover, the new material shows catalase activity in water media, while the coordination compounds are not active

Singlet ground state in compounds with [MnIII4O2]8+ core due to broken degeneration

Two new tetranuclear compounds with a formula [MnIII4(μ-O)2(μ-4-RC6H4COO)7−m(L)2m(phen)2](ClO4)1+m, where R = MeO or tBu and m = 0 or 1, were synthesised and studied structurally and magnetically. The core of these compounds comprises a central Mn2O2 rhombus to which two terminal ions are attached - one to each oxo bridge. There are two types of bridges that alternately bind the central and terminal ions, those having a triple (μ-O)(μ-RCOO)2 or a double (μ-O)(μ-RCOO) bridge. The fit of the magnetic data of analogous compounds has so far been performed considering two different magnetic interactions, that between central ions (J1) and those between terminal and central ions (Jct), leading to ground states with ST = 2 or 3, or to five energetically degenerate ground states with ST = 0-4, depending on the J1/Jct ratio. In contrast, the compounds presented herein show an isolated ST = 0 ground state, and it was necessary to distinguish the two types of magnetic interactions between central and terminal ions (J2 and J3) to achieve a good fit of the experimental data. The differentiation of these interactions causes a spin state redistribution: the degeneration of ST = 0-4 breaks and the states with ST ≠ 0 become unstable as J2 and J3 become more different. Nevertheless, the assignment of these states to a particular spin configuration was unachievable because the composition of these states changes upon decreasing the J3/J2 ratio. The importance of considering the relative orientation of Jahn-Teller axes is also highlighted